No, that LABhorn was a well built horn, I'm pretty sure. It's the one that was at the Michigan shootout, and was the darling of that event.
Originally Posted by weltersys
Let’s qualify your statement:
"The LABhorn makes as much distortion at 40 watts as the 12Pi basshorn does at full power."
A little more information would provide context:
A LABHorn of unknown build quality, tested at a vague power level under unspecified conditions, had high distortion below Fc, where any reasonable person would HP the sub, since it is producing little acoustic power .
The links to the 2002(?)Michigan sub shootout seem to be all gone, making it impossible to get a real handle on the test methods, or see what other subs did under the same test conditions.
That said, in the picture you use, citing a 10 to 12 volt input, the LABhorn distortion levels above 38 Hz are only about .3%, that is, less than 1/3 % distortion.
12 volts into a LABhorn is about 48 watts at the minimum impedance of 3 ohms.
48 watts is about 3 dB less power than 100 watts
Above 38 Hz, at 100 watts the 12Pi reads about -32 dB , about 2% distortion.
Your oft quoted distortion figure for the LABhorn only relates to it well below cutoff frequencies, a comparison with no meaning for pro sound use, where HP filters are always used.
The comparison is made even more useless since the method you chose to measure your speaker with can not differentiate between background noise and actual distortion at the frequencies and SPL level where you claim the PP has a vast improvement.
PP may make your 12Pi horn distortion lower below cutoff, but it seems to do little in the pass band compared to other similar sized horns loaded with good speakers.
Art Welter
Let’s qualify your statement:
"The LABhorn makes as much distortion at 40 watts as the 12Pi basshorn does at full power."
A little more information would provide context:
A LABHorn of unknown build quality, tested at a vague power level under unspecified conditions, had high distortion below Fc, where any reasonable person would HP the sub, since it is producing little acoustic power .
Wayne,
The links to the 2002(?)Michigan sub shootout seem to be all gone, making it impossible to get a real handle on the test methods, or see what other subs did under the same test conditions.
That said, in the picture you use, citing a 10 to 12 volt input, the LABhorn distortion levels above 38 Hz are only about .3%, that is, less than 1/3 % distortion.
12 volts into a LABhorn is about 48 watts at the minimum impedance of 3 ohms.
48 watts is about 3 dB less power than 100 watts
Above 38 Hz, at 100 watts the 12Pi reads about -32 dB , about 2% distortion.
Your oft quoted distortion figure for the LABhorn only relates to it well below cutoff frequencies, a comparison with no meaning for pro sound use, where HP filters are always used.
The comparison is made even more useless since the method you chose to measure your speaker with can not differentiate between background noise and actual distortion at the frequencies and SPL level where you claim the PP has a vast improvement.
PP may make your 12Pi horn distortion lower below cutoff, but it seems to do little in the pass band compared to other similar sized horns loaded with good speakers.
Art Welter
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That's a misinterpretation, Art, and you know it. At 100 watts, the only thing shown in the 12Pi distortion chart is the noise floor. The distortion lies somewhere below that, probably well under 1%.
As I've said before, the 12Pi distortion below cutoff being vastly lower is prima facie evidence that push-pull is effective. There is reduction of distortion at higher frequencies too, but it is most obvious at low frequencies, making it a "smoking gun", so to speak.
You, yourself, in an effort to disprove this claim, measured push-pull drive reducing the second-harmonic by 30dB. That's a pretty obvious smoking gun too.
These things are pretty convincing evidence that push-pull drive works to reduce even harmonics. I would go so far as to say it's more than convincing evidence - it's proof.
You can continue to quote figures that tend to obfuscate the truth if you want to. You can talk about fractional percentages and whatever else, in an effort to minimize the benefits of push-pull. But your own measurements showed that it reduced the second harmonic by 30dB. In terms of power, that's a 1000-fold improvement. Now when you combine that with a bandpass system, like a horn, that reduces the higher harmonics, you can really get rock-bottom distortion levels. The 12Pi basshorn is a system that does exactly that.
Oh, now that's BS, Art. We chose the 10M distance because it works best for high-power hornsub testing. It tends to reduce path-length error, since most basshorns are at least a couple meters long, internally. And the noise floor is still low enough to provide accurate measurement down to ~2% distortion, which is more than adequate for balls-out testing. Most of the things we'd want to see would be levels much higher than that.
The fact that response falls at cutoff (effectively lowering signal-to-noise) is of little consequence for what we were testing, And even at the lower frequencies with reduced signal-to-noise, you can still see the distortion rise at cutoff to the level of the fundamental or even higher in most subwoofers. That's visible, and it's obvious.
I think this is worth repeating, just in case it has been missed in the last few pages:
The second harmonic is what is usually strongest in a traditional basshorn, so using push-pull drive to remove it is very useful. After all, by 50Hz, the third harmonic is above the passband and being attenuated by the front chamber and the horn folds. So about all that's left is the third harmonic below 50Hz, in the lower half of the passband. Second harmonics are cancelled by push-pull drive, third harmonics are reduced by the front chamber and horn folds and fourth is reduced by both the push-pull drive and the front chamber.
So in the case of the 12Pi hornsub, we're really not talking about what happens when we lose even orders and keep odd orders. We're talking about what happens when we lose the one harmonic that is really powerful in a hornsub - the second. The higher harmonics are already largely attenuated by the bandpass nature of the horn.
As for the LMS measurements, maybe some clarification is in order. See the 800 watt chart for the 12Pi hornsub:
Notice that from 40Hz to 50Hz, THD is about 33dB below the fundamental, which is 2% to 3%. Distortion rises as frequency falls towards cutoff, to a peak level of 15% to 18% at 32Hz. Below that, the distortion chart and the SPL chart track together, having the same slope. That means the percentage stays the same too, since it's a ratio of the two levels.
The percentage value, being a ratio of the amplitude response (blue line) and the distortion (violet line), reaches 100% when the two lines cross, provided they cross above the noise floor. In the chart above, we see the two lines cross around 15Hz - over an octave below cutoff. But this is also below the noise floor so we cannot really know what the distortion is below about 20Hz. Both amplitude and distortion are just falling too fast, as the horn just gets quiet.
I could see distortion might rise above 20% this far below cutoff. In fact, I'd be surprised if it didn't. But that's one of the amazing things about the 12Pi hornsub, it just doesn't distort much - not even above 20% - before the horn is so far into the stop band that the whole thing is just "off".
One of the things in the test plan at the Prosound Shootouts was to measure the noise floor for the amplitude response sweeps. What we did was to setup like we were going to do an amplitide response chart for a speaker, but then disconnect the amplifier so all we recorded was ambient noise. That chart is shown below:
The thing is, I neglected to record the noise floor for the distortion sweeps, an oversight on my part. It has the same spectral balance, but is about 8dB higher. The reason is simple, the configuration is different. LMS uses a sharp bandpass filter that tracks the fundamental during response sweeps. This is great for noise immunity, since the only sound that is recorded is the fundamental. So, in this configuration, when the noise floor sweep is run, the only part of the ambient sound that recorded is the tiny part that is the same frequency as the sweep. When the distortion sweeps are run, the exact opposite is done. A sharp band-stop filter is used to block the fundamental, but allow everything else to pass. The goal is to get THD+N, which is basically everything except what was sent to the speaker. Naturally, this also allows a much higher part of the ambient noise to be recorded, resulting in about an ~8dB higher noise floor for the distortion sweeps.
There is one way you can see the noise floor for the distortion sweeps. When looking at a low-distortion speaker run at a low power level, if the distortion is below the noise floor, then all you'll see is the noise floor. You can tell when you're looking at it, because it has that same "spectral signature" as the noise floor recorded above. It's just a diagonal line, rather than peaks and dips that track the amplitude response. For example, look at the 100 watt chart of the 12Pi hornsub, where the distortion is below the noise floor through the entire sweep:
In some of the better subwoofers, the distortion is below the noise floor at 100 watts, and is not visible until power levels are increased. Only when the violet (distortion) curve rises above what you see in the 100 watt chart above is there measurable distortion; Our noise floor limit was about 1-2% for speakers that could reach 110dB or more.
If we wanted to measure low-power distortion levels, we could have moved the microphone closer to increase signal-to-noise. Then our noise floor could have been reduced into the fractional percentage range. But our whole purpose what to see what distortion was at the business end, at high power levels. These were all prosound subs, intended to be used for extended periods at high levels.
The second harmonic is what is usually strongest in a traditional basshorn, so using push-pull drive to remove it is very useful. After all, by 50Hz, the third harmonic is above the passband and being attenuated by the front chamber and the horn folds. So about all that's left is the third harmonic below 50Hz, in the lower half of the passband. Second harmonics are cancelled by push-pull drive, third harmonics are reduced by the front chamber and horn folds and fourth is reduced by both the push-pull drive and the front chamber.
So in the case of the 12Pi hornsub, we're really not talking about what happens when we lose even orders and keep odd orders. We're talking about what happens when we lose the one harmonic that is really powerful in a hornsub - the second. The higher harmonics are already largely attenuated by the bandpass nature of the horn.
As for the LMS measurements, maybe some clarification is in order. See the 800 watt chart for the 12Pi hornsub:
Notice that from 40Hz to 50Hz, THD is about 33dB below the fundamental, which is 2% to 3%. Distortion rises as frequency falls towards cutoff, to a peak level of 15% to 18% at 32Hz. Below that, the distortion chart and the SPL chart track together, having the same slope. That means the percentage stays the same too, since it's a ratio of the two levels.
The percentage value, being a ratio of the amplitude response (blue line) and the distortion (violet line), reaches 100% when the two lines cross, provided they cross above the noise floor. In the chart above, we see the two lines cross around 15Hz - over an octave below cutoff. But this is also below the noise floor so we cannot really know what the distortion is below about 20Hz. Both amplitude and distortion are just falling too fast, as the horn just gets quiet.
I could see distortion might rise above 20% this far below cutoff. In fact, I'd be surprised if it didn't. But that's one of the amazing things about the 12Pi hornsub, it just doesn't distort much - not even above 20% - before the horn is so far into the stop band that the whole thing is just "off".
One of the things in the test plan at the Prosound Shootouts was to measure the noise floor for the amplitude response sweeps. What we did was to setup like we were going to do an amplitide response chart for a speaker, but then disconnect the amplifier so all we recorded was ambient noise. That chart is shown below:
The thing is, I neglected to record the noise floor for the distortion sweeps, an oversight on my part. It has the same spectral balance, but is about 8dB higher. The reason is simple, the configuration is different. LMS uses a sharp bandpass filter that tracks the fundamental during response sweeps. This is great for noise immunity, since the only sound that is recorded is the fundamental. So, in this configuration, when the noise floor sweep is run, the only part of the ambient sound that recorded is the tiny part that is the same frequency as the sweep. When the distortion sweeps are run, the exact opposite is done. A sharp band-stop filter is used to block the fundamental, but allow everything else to pass. The goal is to get THD+N, which is basically everything except what was sent to the speaker. Naturally, this also allows a much higher part of the ambient noise to be recorded, resulting in about an ~8dB higher noise floor for the distortion sweeps.
There is one way you can see the noise floor for the distortion sweeps. When looking at a low-distortion speaker run at a low power level, if the distortion is below the noise floor, then all you'll see is the noise floor. You can tell when you're looking at it, because it has that same "spectral signature" as the noise floor recorded above. It's just a diagonal line, rather than peaks and dips that track the amplitude response. For example, look at the 100 watt chart of the 12Pi hornsub, where the distortion is below the noise floor through the entire sweep:
In some of the better subwoofers, the distortion is below the noise floor at 100 watts, and is not visible until power levels are increased. Only when the violet (distortion) curve rises above what you see in the 100 watt chart above is there measurable distortion; Our noise floor limit was about 1-2% for speakers that could reach 110dB or more.
If we wanted to measure low-power distortion levels, we could have moved the microphone closer to increase signal-to-noise. Then our noise floor could have been reduced into the fractional percentage range. But our whole purpose what to see what distortion was at the business end, at high power levels. These were all prosound subs, intended to be used for extended periods at high levels.
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Wayne,
So the 12Pi may be 1% instead of 2% at 100 watts, but we can’t tell because the noise floor is too high.
And since background noise is random, and distortion does not track the fundamental evenly, we can’t really be sure of distortion levels where the speaker under test response falls below about 70, or perhaps 78 dB, or whatever SPL the random noise happened to reach during your LMS tests.
The only LABhorn test you have shown shows it around 1/3% distortion in the pass band at about 12v (about 48 watts), yet you say I’m misrepresenting your data when I say it is similar in level to the 12Pi in the passband.
I made no effort to disprove your claim that PP reduced second harmonic distortion.
I did measure the difference between normal loading compared to PP in the same enclosure with a method that shows the relationship of the different harmonic distortion levels, something you never did.
Way back when you were developing the 12Pi, you wrote you would, but you didn’t.
You have for years claimed “prima facie evidence” comparing different cabinets under different test conditions as your only proof, total hogwash.
The results of my PP to normal tests were interesting:
http://www.diyaudio.com/forums/subwoofers/191833-push-pull-vs-normal-distortion-compared.html
If you bothered to read them you might learn something, that although the second harmonic was reduced at some frequencies, at others it was not, and since the third harmonic sometimes rose higher with PP, overall distortion was not always reduced.
Also, at high power, low frequency, where excursion is the largest contributing factor to distortion, the overall distortion was barely reduced at all in the front loaded Lab 12.
The horn 12Pi may react completely differently, but until you measure distortion of the 12Pi run normal compared to PP, don’t expect me to accept your BS “prima facie evidence” comparing different cabinets under different test conditions, with your tests not able to distinguish speaker distortion from background noise.
Readers can draw their own conclusions from the data you and I have already presented.
I have expended far too much time here with you, I’ll stop responding to your trolling and simply let the thread die before moderators lock it, as they have in the past when you have endlessly repeated the same unfounded arguments.
Art Welter
That's right. All we can see from that chart is it is under the noise floor. I would expect at 100 watts, 12Pi hornsub distortion is probably in the range of 0.2% to 0.5%. This is not a terribly important metric to me, since the 12Pi hornsub (or any other prosound hornsub) will almost always be used at much higher power levels.
Yes, I was glad when you did that. I had been telling you over and over that push-pull reduced even harmonics by an order of a magnitude. But you always dismissed it, and your constant arguments were getting old. Then finally decided to see for yourself:
When you saw the results of those tests - second harmonic reduced 30dB - I thought you finally got it. But I guess not.
You know, the push-pull woofer configuration is well understood. The mechanism for reducing even order harmonics is nothing new. The amount of reduction and the frequencies where it is achieved is largely dependant on the distance between sound sources and the symmetry of their acoustic load.
My 12Pi hornsub design simply takes some well understood ideas - horn loading and push-pull drive - and uses them together. The horn is a bandpass system, which attenuates upper harmonics. And the push-pull drive reduces the second harmonic. They're a natural fit for a hornsub.
Still, even when you simply turned the woofers around, you achieved significant even harmonic distortion. That should have been enlightening for you. Then add to what you've seen, the fact that the basshorn is a bandpass system, one that reduces higher harmonics and you have a really low-distortion system.
It surprises me a little nobody is responding on Wayne's post # 140. Especially those who use high power and extended LF drivers of the latest generation.
Please, correct me if my interpretation is wrong wayne, but what you are actually saying is that nonlinearities caused by the suspension will lead to odd harmonics. Maybe that is true in case of the Lab12 but in general nonlinearities caused by the suspension can lead to odd and/or even harmonics since it depends largely on the type of suspension (suspension character) that is used and the way it is built up (its symmetry).
You are also saying that LF woofers with shorting ring(s) will tend to have higher odd harmonics compared to even harmonics. By openly wondering whether this application is an improvement for specialised LF drivers it suggests it is not an improvement. In line with my previous comment, research from companies like RCF, 18Sound, B&C among a few others brands has proven that engineering techniques like the tuning of the ‘suspension character’ can balance specific harmonics that shorting rings can produce.
One other reason you seem to be using for questioning the use of shorting rings in LF drivers is that they tend to work best at mid and high frequencies. I agree that the influence of shorting rings to compensate flux modulation is less effective as frequency drops, but still there are measurable benefits. Of course some manufacturers are better in implying this technique then others.
What you didn’t describe is the other benefits of shorting rings. These benefits may have become actually more important then their original functions. Shorting rings can play an important role in extracting heat from the voice coil. Multiple rings on different locations can extract heat from other elements in the motor although you can question if their name ‘shorting rings’ is still legitimate in this function.
The third advantage of the use of shorting ring is it can act as a physical break. Positioned at the end(s) of the voice coil it can prevent physical damage to the voice coil or bobbin (piston) in case it hits the back plate (or even to prevent exceeding the gap completely in some drivers). It definitely has saved drivers that were wrong loaded or lacked efficient low-cut filtering.
Therefore I see these shorting rings almost as a must for specialised extended LF drivers that are capable handling several kilowatts and endure extreme excursions. In other words, the benefits of shorting rings are bigger then just Flux control and the negative side effects of odd harmonics can be suppressed with techniques like tuning the ‘suspension character’ as mentioned earlier.
More generally speaking, I miss a very important element in the whole discussion about harmonics while it is the main source, the cone. Besides that the cone suffers from its own resonances (and the resulting partial movements) that are much higher and play an important role even before Xmax is reached. It also has damping qualities that can deal with harmonics from suspension or other elements in its structure. Using ripple technique in the cone surface is one of the oldest. The use of exotic cone materials like magnesium particles or complete Carbon fibre based cones makes it possible to suppress harmonics even more effective.
Nevertheless we all shouldn’t forget that harmonics produced by a system or often more related to the type of loading and makes the side effects of specific driver related harmonics of minor importance.
Please, correct me if my interpretation is wrong wayne, but what you are actually saying is that nonlinearities caused by the suspension will lead to odd harmonics. Maybe that is true in case of the Lab12 but in general nonlinearities caused by the suspension can lead to odd and/or even harmonics since it depends largely on the type of suspension (suspension character) that is used and the way it is built up (its symmetry).
You are also saying that LF woofers with shorting ring(s) will tend to have higher odd harmonics compared to even harmonics. By openly wondering whether this application is an improvement for specialised LF drivers it suggests it is not an improvement. In line with my previous comment, research from companies like RCF, 18Sound, B&C among a few others brands has proven that engineering techniques like the tuning of the ‘suspension character’ can balance specific harmonics that shorting rings can produce.
One other reason you seem to be using for questioning the use of shorting rings in LF drivers is that they tend to work best at mid and high frequencies. I agree that the influence of shorting rings to compensate flux modulation is less effective as frequency drops, but still there are measurable benefits. Of course some manufacturers are better in implying this technique then others.
What you didn’t describe is the other benefits of shorting rings. These benefits may have become actually more important then their original functions. Shorting rings can play an important role in extracting heat from the voice coil. Multiple rings on different locations can extract heat from other elements in the motor although you can question if their name ‘shorting rings’ is still legitimate in this function.
The third advantage of the use of shorting ring is it can act as a physical break. Positioned at the end(s) of the voice coil it can prevent physical damage to the voice coil or bobbin (piston) in case it hits the back plate (or even to prevent exceeding the gap completely in some drivers). It definitely has saved drivers that were wrong loaded or lacked efficient low-cut filtering.
Therefore I see these shorting rings almost as a must for specialised extended LF drivers that are capable handling several kilowatts and endure extreme excursions. In other words, the benefits of shorting rings are bigger then just Flux control and the negative side effects of odd harmonics can be suppressed with techniques like tuning the ‘suspension character’ as mentioned earlier.
More generally speaking, I miss a very important element in the whole discussion about harmonics while it is the main source, the cone. Besides that the cone suffers from its own resonances (and the resulting partial movements) that are much higher and play an important role even before Xmax is reached. It also has damping qualities that can deal with harmonics from suspension or other elements in its structure. Using ripple technique in the cone surface is one of the oldest. The use of exotic cone materials like magnesium particles or complete Carbon fibre based cones makes it possible to suppress harmonics even more effective.
Nevertheless we all shouldn’t forget that harmonics produced by a system or often more related to the type of loading and makes the side effects of specific driver related harmonics of minor importance.
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No, what I was doing in post 140 was to explain how symmetrical nonlinearities cause odd harmonics and nonsymmetrical nonlinearities cause even harmonics, with a few examples of potential causes of each. I also said that exceeding xmax can result in both even and odd harmonics, depending on the gap geometry and the suspension. I went in to just a little detail into some of the things that can cause either type of nonlinearity.
I agree with that statement. It is well known in the industry that shorting rings reduce even harmonics. I find this to be an improvement, much the same way push-pull is an improvement. But just as you and others have said, if the third harmonic isn't also reduced, then the distortion character may be less favorable. I tend to not get into discussions about subjective "perception" but I do think that third harmonics are at least as objectionable as second harmonics, perhaps more. One should strive to reduce both odd and even harmonics, not just focus on one and disregard the other.
But the third harmonic is a different beast than the second harmonic. The things you do to reduce one are not effective on the other. Both have to be dealt with separately, using different techniques. The symmetrical nonlinearities (odd-harmonics) are largely improved by doing things that keep the flux equally strong throughout the voice coil travel. The asymmetrical nonlinarities (even-harmonics) are improved by reducing flux modulation and making the flux symmetrical around the coil.
That's true. I definitely like drivers with shorting rings for midwoofers and midrange, and have been very vocal about using them and suggesting them to others. But I do find them to be less effective at the lowest frequencies. You're right that some manufacturers have had more success at others, but I still think most have trouble getting them to do much below 50Hz, and many can't get them to work well below 100Hz. As a result, I think push-pull drive is probably better at subwoofer frequencies than a shorting ring is.
I agree with you 100% there, absolutely. I'd call these kinds of devices "cooling plugs".
For a hornsub, I think the cone has to be strong to handle the pressure. But as long as you can keep it from folding up, I think it probably is not too much trouble to keep it pistonic through the (<150Hz) passband. It just has to be strong for a hornsub.
On the other hand, I find the cone to be very important in more traditional woofers, those that will be used into the midrange (i.e. above 100Hz to 200Hz or so). The cone shape and material is extremely important in midwoofers and midranges. Down low, where the cone remains pistonic, I don't know that it does anything that causes distortion. But up high, I think the cone is a huge part of the picture, preventing or at least damping breakup. For midwoofer and midranges, I prefer drivers that have a well-damped curvilinear cone, always with the flex control ridges you speak of. Material and shape makes all the difference at midrange and higher frequencies.
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I think we've established that the 12Pi hornsub produces high SPL output with extremely low distortion levels. Push-pull hornsubs combine the attenuation of third and higher harmonics from the natural bandpass nature of a horn, it's front chamber and folds with the reduction of the second harmonic from the push-pull drive. It's a very potent combination, capable of ultra-low distortion levels even at very high SPL.
But one thing we really haven't discussed in detail is what this does for you. What is the benefit of having 2% THD at subwoofer frequencies versus say 5-7% THD? I mean, we all agree that distortion below 100Hz is less audible than it is at midrange frequencies. In fact, some would say a little distortion down low even sounds better to them. So what do we gain by reducing subwoofer distortion?
What is the audibility of distortion at subwoofer frequencies? What other effects might it have? I know one respected professional that claims blind testing showed bass distortion to be inaudible below a certain level. Others have said a little bit of bass distortion is actually preferred to lower distortion levels. If this is true, then that would seem to indicate that bass distortion is audible. You can't "prefer" something that isn't audible.
One thing that is lacking in that kind of study is the effects of long-term exposure. In all the blind tests I'm aware of done to test distortion audibility and/or preference, the listeners were only exposed for a few minutes. I am not aware of a study that tests the effects of various distortion levels over extended periods of time, or at high SPL levels.
I say this because I find one of the effects of distortion is listener fatigue. It becomes irritating, and even causes temporary tinnitus. It seems to be a function of SPL/time, in that high sound levels cause irritation fairly soon, but the same irritation can be felt at low sound levels if experienced over a longer period of time. These are my own personal observations but I have also heard comments from many other people that make me believe they experience the same things.
This is what I perceive where distortion is concerned:
1. In main speakers, lower distortion speakers tend to sound clearer to me, all other things being equal. However, the audibility is a function of SPL, and below a certain level, I cannot detect the distortion.
2. At high power level, a speaker with a little more distortion will be more fatiguing, making me want to "turn it down" much sooner than a less distorted speaker.
3. At low power levels, a speaker with a little more distortion will be more fatiguing over a long period of time. At low power levels, I cannot tell that it is going to fatigue me at first, even for a few hours, but after a few days at a trade show, for example, the higher distortion speaker will fatigue me, where the lower distortion speaker does not.
4. In subwoofers, distortion is much less noticeable, but higher distortion tends to sound louder and fatter. (Sorry for the subjective terms, just trying to describe what I hear)
5. Just like the mains, a high distortion woofer will be fatiguing, even if it cannot be easily detected.
I gained these opinions after many years of using my own speakers which often come in a stock or upgraded version. The upgraded version usually has a midwoofer with a shorting ring, creating less distortion. Their response curves are very similar between the stock and upgraded versions, but the upgraded model has lower distortion.
My personal opinion is it is worthwhile to reduce distortion where I can. This is especially true in a hornsub, where the synergy between push-pull drive and a folded horn is compelling. It is not much more difficult to build the cabinet with push-pull drive, especially if two woofers would be used anyway. The high SPL requirement of a prosound hornsub makes low distortion even more attractive, in my opinion.
But one thing we really haven't discussed in detail is what this does for you. What is the benefit of having 2% THD at subwoofer frequencies versus say 5-7% THD? I mean, we all agree that distortion below 100Hz is less audible than it is at midrange frequencies. In fact, some would say a little distortion down low even sounds better to them. So what do we gain by reducing subwoofer distortion?
What is the audibility of distortion at subwoofer frequencies? What other effects might it have? I know one respected professional that claims blind testing showed bass distortion to be inaudible below a certain level. Others have said a little bit of bass distortion is actually preferred to lower distortion levels. If this is true, then that would seem to indicate that bass distortion is audible. You can't "prefer" something that isn't audible.
One thing that is lacking in that kind of study is the effects of long-term exposure. In all the blind tests I'm aware of done to test distortion audibility and/or preference, the listeners were only exposed for a few minutes. I am not aware of a study that tests the effects of various distortion levels over extended periods of time, or at high SPL levels.
I say this because I find one of the effects of distortion is listener fatigue. It becomes irritating, and even causes temporary tinnitus. It seems to be a function of SPL/time, in that high sound levels cause irritation fairly soon, but the same irritation can be felt at low sound levels if experienced over a longer period of time. These are my own personal observations but I have also heard comments from many other people that make me believe they experience the same things.
This is what I perceive where distortion is concerned:
1. In main speakers, lower distortion speakers tend to sound clearer to me, all other things being equal. However, the audibility is a function of SPL, and below a certain level, I cannot detect the distortion.
2. At high power level, a speaker with a little more distortion will be more fatiguing, making me want to "turn it down" much sooner than a less distorted speaker.
3. At low power levels, a speaker with a little more distortion will be more fatiguing over a long period of time. At low power levels, I cannot tell that it is going to fatigue me at first, even for a few hours, but after a few days at a trade show, for example, the higher distortion speaker will fatigue me, where the lower distortion speaker does not.
4. In subwoofers, distortion is much less noticeable, but higher distortion tends to sound louder and fatter. (Sorry for the subjective terms, just trying to describe what I hear)
5. Just like the mains, a high distortion woofer will be fatiguing, even if it cannot be easily detected.
I gained these opinions after many years of using my own speakers which often come in a stock or upgraded version. The upgraded version usually has a midwoofer with a shorting ring, creating less distortion. Their response curves are very similar between the stock and upgraded versions, but the upgraded model has lower distortion.
My personal opinion is it is worthwhile to reduce distortion where I can. This is especially true in a hornsub, where the synergy between push-pull drive and a folded horn is compelling. It is not much more difficult to build the cabinet with push-pull drive, especially if two woofers would be used anyway. The high SPL requirement of a prosound hornsub makes low distortion even more attractive, in my opinion.
In respond to Wayne's post # 148:
I don’t think we disagree that a shorting ring still can have an effect in the band pass of PA subwoofer range. What I would like to add is that almost all PA drivers specialised for extended LF use have a shorting ring. Also you seem to know the use for ‘flex control ridges’ in mid drivers to damp harmonics in the cone (partial movement is part of that). Again almost all PA drivers specialised for extended LF and paper based cones have these ‘flex control ridges'.
At RCF they started research on partial movement/resonances in ‘exotic’ materials like Carbon fibre in early nineties. The RCF L8S800 (8”) was the Brand’s first PA driver (along a few RCF car speakers) with Carbon cone. They wanted to implement this technology for bigger diameters but fabrication costs at the time were too high. The same technicians continued their research under the 18Sound flag. After big investments in research, specialised equipment and machinery (most was developed under their own roof) they are now able to produce woven carbon fibre strips cones as large as 21”. The advantages over their traditional paper based cones are low weight, much stronger cones and meanwhile much higher internal damping values. In your words: “well-damped curvilinear cones”.
They also use triple spider (of which two functions in a PP principle), quad coils to lower heat development in the coil (low pwr compr figures) and has a ‘split-wire’ concept. They have achieved much lower THD figures and internal resonances compared to the same structure with paper cones. But what you may find more interesting is how they implied their way of a ‘cooling-plug’ that is built in the motor structure.
I don’t think we disagree that a shorting ring still can have an effect in the band pass of PA subwoofer range. What I would like to add is that almost all PA drivers specialised for extended LF use have a shorting ring. Also you seem to know the use for ‘flex control ridges’ in mid drivers to damp harmonics in the cone (partial movement is part of that). Again almost all PA drivers specialised for extended LF and paper based cones have these ‘flex control ridges'.
At RCF they started research on partial movement/resonances in ‘exotic’ materials like Carbon fibre in early nineties. The RCF L8S800 (8”) was the Brand’s first PA driver (along a few RCF car speakers) with Carbon cone. They wanted to implement this technology for bigger diameters but fabrication costs at the time were too high. The same technicians continued their research under the 18Sound flag. After big investments in research, specialised equipment and machinery (most was developed under their own roof) they are now able to produce woven carbon fibre strips cones as large as 21”. The advantages over their traditional paper based cones are low weight, much stronger cones and meanwhile much higher internal damping values. In your words: “well-damped curvilinear cones”.
They also use triple spider (of which two functions in a PP principle), quad coils to lower heat development in the coil (low pwr compr figures) and has a ‘split-wire’ concept. They have achieved much lower THD figures and internal resonances compared to the same structure with paper cones. But what you may find more interesting is how they implied their way of a ‘cooling-plug’ that is built in the motor structure.
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That looks like one heck of a woofer there!
Have you seen the Acoustics Elegance woofers? I'm impressed with their build quality. I always liked the JBL Professional Series woofers too.
I wonder how far down the shorting ring concept can be used. The only experiences I have had with shorting rings in subs were not particularly optimistic, but then again, the company I was working with at the time did not have the R&D budget to do the kinds of optimizations it takes to get the best results, in my opinion. Their engineers were not able to get significant reduction of the second-harmonic at frequencies below about 150Hz. I know other companies have been able to get useful second-harmonic reduction an octave below that, those with greater resources and more dedication to advanced technology.
I have played around with magnetics FEA software (Vector Fields) enough to see it as being very helpful when optimizing motor structures, but also enough to realize some things are counter-intuitive, sort of like fluid dynamics. I think to optimize the magnetic circuit takes a lot of R&D, and most loudspeaker companies, frankly, lack the resources to obtain tools like that. So I think most loudspeaker driver manufacturers sort of stick to what they know.
As for the cooling plug concept, I'm completely sold on that. In my opinion, forced air cooling is very important, but does little to cool the motor core, which is also very important. Without cooling of the motor core, the local ambient temperature can become hot enough to bake the adhesive holding the voice coil to the former. So the best thing to do, in my opinion, is to have both mechanisms. Any woofer that lacks a cooling plug is inferior to one that has a cooling plug, because the plug wicks heat out of the core. This thermal transfer mechanism is very important for driver longevity, especially when it is used for extended periods at high power levels.
Have you seen the Acoustics Elegance woofers? I'm impressed with their build quality. I always liked the JBL Professional Series woofers too.
I wonder how far down the shorting ring concept can be used. The only experiences I have had with shorting rings in subs were not particularly optimistic, but then again, the company I was working with at the time did not have the R&D budget to do the kinds of optimizations it takes to get the best results, in my opinion. Their engineers were not able to get significant reduction of the second-harmonic at frequencies below about 150Hz. I know other companies have been able to get useful second-harmonic reduction an octave below that, those with greater resources and more dedication to advanced technology.
I have played around with magnetics FEA software (Vector Fields) enough to see it as being very helpful when optimizing motor structures, but also enough to realize some things are counter-intuitive, sort of like fluid dynamics. I think to optimize the magnetic circuit takes a lot of R&D, and most loudspeaker companies, frankly, lack the resources to obtain tools like that. So I think most loudspeaker driver manufacturers sort of stick to what they know.
As for the cooling plug concept, I'm completely sold on that. In my opinion, forced air cooling is very important, but does little to cool the motor core, which is also very important. Without cooling of the motor core, the local ambient temperature can become hot enough to bake the adhesive holding the voice coil to the former. So the best thing to do, in my opinion, is to have both mechanisms. Any woofer that lacks a cooling plug is inferior to one that has a cooling plug, because the plug wicks heat out of the core. This thermal transfer mechanism is very important for driver longevity, especially when it is used for extended periods at high power levels.
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Yep, it’s a nice driver and a nice facility where they assemble these drivers. I have never heard/seen Acoustic Elegance drivers on this side of the ocean so it is difficult to judge. Like you said, building quality is very important especially if tight tolerances between different drivers are wanted. To me that is important because the driver with the biggest tolerances often is the one that burns out first.
About the rings, the more massive they become the lower in frequency the effect goes. The reason why only one shorting ring is used for extended LF drivers is probably because more rings often make the intermodulation rise rapidly down low. With FEA software like Opera or MagNet you can see how all parameters are connected, including those of demodulating rings.
Your enthusiasm for the ‘cooling-plug’ is clear to us. Your measurements show the effectiveness of the plug and together with the PP setting your 12Pi is quiet an achievement!That brings me to your post # 149 and you question about THD. From a practical PA point of view, I think Art had a point in post # 5 by questioning if all the effort and costs are worth the benefits of achieving extreme low THD in subs.
Although I agree with your statement about “the effects of distortion is listener fatigue”, I think that is more a matter for studio’s where an engineer needs to perform all day long and looses his reference if his monitoring is producing to much THD. Trying to build an almost studio reference low THD PA sub at cost of size, weight and SPL is more a personal goal and a admirable achievement, I think.
An extra 3dB from the same size would be received as an improvement for the sector. Lowering peaks in group delay without offering size or SPL will be received as an improvement. Lowering weight is also an improvement since most companies care more and more about employee and transport costs. Only in those rare and very specific occasions, for example fixed installations, I can imagine a sound reinforcement designer wants that extra bit of high performance, because he can justify it within the budget limits. But that’s just my view based on a different designing philosophy.
About the rings, the more massive they become the lower in frequency the effect goes. The reason why only one shorting ring is used for extended LF drivers is probably because more rings often make the intermodulation rise rapidly down low. With FEA software like Opera or MagNet you can see how all parameters are connected, including those of demodulating rings.
Your enthusiasm for the ‘cooling-plug’ is clear to us. Your measurements show the effectiveness of the plug and together with the PP setting your 12Pi is quiet an achievement!That brings me to your post # 149 and you question about THD. From a practical PA point of view, I think Art had a point in post # 5 by questioning if all the effort and costs are worth the benefits of achieving extreme low THD in subs.
Although I agree with your statement about “the effects of distortion is listener fatigue”, I think that is more a matter for studio’s where an engineer needs to perform all day long and looses his reference if his monitoring is producing to much THD. Trying to build an almost studio reference low THD PA sub at cost of size, weight and SPL is more a personal goal and a admirable achievement, I think.
An extra 3dB from the same size would be received as an improvement for the sector. Lowering peaks in group delay without offering size or SPL will be received as an improvement. Lowering weight is also an improvement since most companies care more and more about employee and transport costs. Only in those rare and very specific occasions, for example fixed installations, I can imagine a sound reinforcement designer wants that extra bit of high performance, because he can justify it within the budget limits. But that’s just my view based on a different designing philosophy.
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The problem of the shorting ring size is what started me thinking maybe they weren't the way to go for subs. When I started development of the 12Pi hornsub, it was in conjunction with development of a high-end hifi home subwoofer that was going to use a shorting ring for flux stabilization. I was planning to use the same woofer in both designs, leveraging reusability where I could. I was also working on an intercooler approach for the cooling vent, to get the heat from the vented air out of the rear chamber.
But two things conspired to send me on a different path. Both of those approaches proved to be dead-ends, making the early intercooler and the low-distortion (flux stabilized) subwoofer non-starters. The shorting rings provided reduction of distortion in the midbass, but not into the subwoofer region. And the vent air was not particularly hot, so the intercooler idea was a bust. That's what prompted me to look at cooling plugs to wick the heat from the core, which was very hot, and to use push-pull drive to reduce distortion instead of shorting rings.
Now I know larger shorting rings can be made that are effective down to lower frequencies, but they definitely lose effectiveness as frequency drops. The deeper you want them to work, the more "meat" you have to put in the rings, displacing the amount of magnet you have. This, in turn, reduces the strength of the flux in the gap. Neodymium can be used, which helps, of course. But I think no matter what you do, the bottom line is electro-magnetic coupling is better at higher frequencies, and not as good down low.
Push-pull drive has the opposite characteristic. It tends to couple best at low frequencies. So from that, I think push-pull concept seems a natural fit for a subwoofer. I like to combine the approaches in the bands where they make the most sense, with push-pull drive on the subs and shorting rings on the mains. And of course, the push-pull drive works best when combined with a bandpass system to reduce higher harmonics. I think a hornsub is a natural fit, since they often use two woofers anyway. The folded horn decreases excursion, and has acoustic low-pass because of the front chamber and horn folds.
It was sort of a "light bulb" moment for me, after trying to get woofers with shorting rings to reduce distortion in the lowest frequencies. They just weren't working down low. Push-pull drive knocks out the second harmonic at (under 50Hz) subwoofer frequencies very well, often reducing the second harmonic by 100x to 1000x, even when no particular attention is paid to acoustic symmetry. It stood to reason that fighting to get electro-magnetic coupling to work below 50Hz was not necessary, since push-pull drive is best suited for this frequency range. Especially after seeing the idea of the "slot-loaded" push-pull idea, which uses the mild low-pass filter of the slot to reduce the upper harmonics - I thought how much better a hornsub would work with this approach, because the passband is fairly narrow and the upper rolloff is pretty steep. The push-pull drive would remove the second harmonic, and the low-pass filter formed by mass-rolloff, the front chamber and folds would reduce the third and higher harmonics. The 12Pi hornsub embodies this design approach and I think it achieves the low-distortion goals very well.
On the matter of size, one can always look at different metrics. The goals are different between the guy that will carry everything himself in a van than the crew that will load in a semi-truck using ramps. The small operator really needs something light and portable. The larger crew needs wheels and handles, and can handle bigger boxes because they're loading on a ramp. In their case, having a relatively small number of large boxes is a lot easier than a huge number of smaller boxes. And especially when the larger boxes need less amplification, the full size high-efficiency hornsub really makes sense for large venues and outdoor events.
No matter how you slice it, the bulk-efficiency of groups of hornsubs is better than any other subwoofer configuration. Direct radiating "front-loaded" boxes consume lots of power and tend to run out of steam after just a few cabinets. You can pack a dozen of them together, perhaps, but their reduced efficiency starts becoming more and more apparent in large groups, when compared to a similar volume of basshorns. That's why groups of hornsubs have proven to be the installation of choice for high-SPL applications.
As to whether or not the reduced distortion is worth it, I guess some might not care but as for me, I think it is kind of a no-brainer. I mean, if you have two drivers, why not take advantage of this arrangement? Hornsubs are typically a little more complex than front-loaded cabinets anyway, so I don't think there is any real added complexity using push-pull drive. One should pay attention to detail that the front and rear chambers are sized properly and symmetrical, but I think attention to detail is always a worthy goal. It isn't any different than anything else, if you are a little sloppy in the build, the device will still work, but might have a little more ripple or whatever than a more carefully built box.
In post 149, I questioned the audibility of distortion at subwoofer frequencies. That's a matter of debate for some, whether subwoofer distortion is audible, and if so, whether or not it objectionable. I think most agree that distortion below 100Hz is less audible than it is at midrange frequencies. But at what level does it become audible? At what level does it cause listener fatigue? I think probably it is a function of SPL, frequency and time. I think distortion at lower frequencies can be fatiguing after a while, and that longer exposures to a given SPL level can be similar to high SPL levels for shorter durations.
My personal opinion is it is worthwhile to reduce distortion where I can. This is especially true in a hornsub, where the synergy between push-pull drive and a folded horn is compelling. It is not much more difficult to build the cabinet with push-pull drive, especially if two woofers would be used anyway. The high SPL requirement of a prosound hornsub makes low distortion even more attractive, in my opinion.
But two things conspired to send me on a different path. Both of those approaches proved to be dead-ends, making the early intercooler and the low-distortion (flux stabilized) subwoofer non-starters. The shorting rings provided reduction of distortion in the midbass, but not into the subwoofer region. And the vent air was not particularly hot, so the intercooler idea was a bust. That's what prompted me to look at cooling plugs to wick the heat from the core, which was very hot, and to use push-pull drive to reduce distortion instead of shorting rings.
Now I know larger shorting rings can be made that are effective down to lower frequencies, but they definitely lose effectiveness as frequency drops. The deeper you want them to work, the more "meat" you have to put in the rings, displacing the amount of magnet you have. This, in turn, reduces the strength of the flux in the gap. Neodymium can be used, which helps, of course. But I think no matter what you do, the bottom line is electro-magnetic coupling is better at higher frequencies, and not as good down low.
Push-pull drive has the opposite characteristic. It tends to couple best at low frequencies. So from that, I think push-pull concept seems a natural fit for a subwoofer. I like to combine the approaches in the bands where they make the most sense, with push-pull drive on the subs and shorting rings on the mains. And of course, the push-pull drive works best when combined with a bandpass system to reduce higher harmonics. I think a hornsub is a natural fit, since they often use two woofers anyway. The folded horn decreases excursion, and has acoustic low-pass because of the front chamber and horn folds.
It was sort of a "light bulb" moment for me, after trying to get woofers with shorting rings to reduce distortion in the lowest frequencies. They just weren't working down low. Push-pull drive knocks out the second harmonic at (under 50Hz) subwoofer frequencies very well, often reducing the second harmonic by 100x to 1000x, even when no particular attention is paid to acoustic symmetry. It stood to reason that fighting to get electro-magnetic coupling to work below 50Hz was not necessary, since push-pull drive is best suited for this frequency range. Especially after seeing the idea of the "slot-loaded" push-pull idea, which uses the mild low-pass filter of the slot to reduce the upper harmonics - I thought how much better a hornsub would work with this approach, because the passband is fairly narrow and the upper rolloff is pretty steep. The push-pull drive would remove the second harmonic, and the low-pass filter formed by mass-rolloff, the front chamber and folds would reduce the third and higher harmonics. The 12Pi hornsub embodies this design approach and I think it achieves the low-distortion goals very well.
On the matter of size, one can always look at different metrics. The goals are different between the guy that will carry everything himself in a van than the crew that will load in a semi-truck using ramps. The small operator really needs something light and portable. The larger crew needs wheels and handles, and can handle bigger boxes because they're loading on a ramp. In their case, having a relatively small number of large boxes is a lot easier than a huge number of smaller boxes. And especially when the larger boxes need less amplification, the full size high-efficiency hornsub really makes sense for large venues and outdoor events.
No matter how you slice it, the bulk-efficiency of groups of hornsubs is better than any other subwoofer configuration. Direct radiating "front-loaded" boxes consume lots of power and tend to run out of steam after just a few cabinets. You can pack a dozen of them together, perhaps, but their reduced efficiency starts becoming more and more apparent in large groups, when compared to a similar volume of basshorns. That's why groups of hornsubs have proven to be the installation of choice for high-SPL applications.
As to whether or not the reduced distortion is worth it, I guess some might not care but as for me, I think it is kind of a no-brainer. I mean, if you have two drivers, why not take advantage of this arrangement? Hornsubs are typically a little more complex than front-loaded cabinets anyway, so I don't think there is any real added complexity using push-pull drive. One should pay attention to detail that the front and rear chambers are sized properly and symmetrical, but I think attention to detail is always a worthy goal. It isn't any different than anything else, if you are a little sloppy in the build, the device will still work, but might have a little more ripple or whatever than a more carefully built box.
In post 149, I questioned the audibility of distortion at subwoofer frequencies. That's a matter of debate for some, whether subwoofer distortion is audible, and if so, whether or not it objectionable. I think most agree that distortion below 100Hz is less audible than it is at midrange frequencies. But at what level does it become audible? At what level does it cause listener fatigue? I think probably it is a function of SPL, frequency and time. I think distortion at lower frequencies can be fatiguing after a while, and that longer exposures to a given SPL level can be similar to high SPL levels for shorter durations.
My personal opinion is it is worthwhile to reduce distortion where I can. This is especially true in a hornsub, where the synergy between push-pull drive and a folded horn is compelling. It is not much more difficult to build the cabinet with push-pull drive, especially if two woofers would be used anyway. The high SPL requirement of a prosound hornsub makes low distortion even more attractive, in my opinion.
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Wayne,
if we assume that your 12pi is everything you set out to achieve.
In what ways is it better (and by how much) then the other 2 x 12 or 1 x 15 subwoofer designs available?
in simple language.
1.it has ??/% lower distortion from ??hz to ??hz
2. it gets ?? db louder at ?? hz
3.??
if we assume that your 12pi is everything you set out to achieve.
In what ways is it better (and by how much) then the other 2 x 12 or 1 x 15 subwoofer designs available?
in simple language.
1.it has ??/% lower distortion from ??hz to ??hz
2. it gets ?? db louder at ?? hz
3.??
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This trick can work all the way up the midrange too. As a rule of thumb, I would want to keep the two woofers within one quarter wavelength of the highest frequency. In the pic above, I have a back loaded horn using 2" Peerless drivers. Based on the formula, you could probably run the horn up to 1688hz.
Another trick you can do is to run one woofer full-range, and one woofer with a low pass. This has a couple advantages. By running just one driver full range, it eliminates comb filtering at high frequencies. Second, it provides ample cone area at low frequencies, where we need displacement. This is particularly effective in back loaded horns, where the woofer isn't "buried" inside the horn.
Push-pull makes a lot of cheap woofers very attractive. For instance, I don't know that I could live with the distortion and power handling of a ten dollar two inch woofer. But a pair of them in push-pull has double the power handling, and more importantly, sound as clean as a much larger woofer.
I've used some very unconventional woofers in horns, like the 2" Tang Bands, to good effect. Horn size is tied to the size of the cone, so if you want a small horn you need to use small woofers.
Anyways, good post, and I've found the harmonic distortion reduction is audible and measurable.
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That little bitty horn is just too cool, Patrick. Good application of push-pull drive, in my opinion. The horn reduces distortion by way of reducing excursion, and the push-pull configuration helps reduce distortion even further.
Is it a full range rear-loaded horn, like a transmission line? Or is there a rear chamber that's just not showing?
I agree with you on the spacing between drivers. Once you get too far apart, the summing isn't good. It's not just a matter of lobing, but also a matter of acoustic loading and symmetry. I think this may make some systems work better than others, because they can achieve better acoustic symmetry between the two drivers.
Your idea about using a 2.5-way approach, running the helper woofer and midwoofer in push-pull is interesting. Sounds like a good idea to me, provided the drivers have real low odd-harmonics. I always liked the 2.5-way configuration, and use a similar approach that I call "flankning subs". It's related to the multisub configuration, but is used to smooth the higher end of the modal region, and the notches from the nearest boundaries. Then I use more distant subs for the lower-frequency modes.
Is it a full range rear-loaded horn, like a transmission line? Or is there a rear chamber that's just not showing?
I agree with you on the spacing between drivers. Once you get too far apart, the summing isn't good. It's not just a matter of lobing, but also a matter of acoustic loading and symmetry. I think this may make some systems work better than others, because they can achieve better acoustic symmetry between the two drivers.
Your idea about using a 2.5-way approach, running the helper woofer and midwoofer in push-pull is interesting. Sounds like a good idea to me, provided the drivers have real low odd-harmonics. I always liked the 2.5-way configuration, and use a similar approach that I call "flankning subs". It's related to the multisub configuration, but is used to smooth the higher end of the modal region, and the notches from the nearest boundaries. Then I use more distant subs for the lower-frequency modes.
Wayne, you are completely correct in everything in your statement. But maybe it would be more appropriate if you give an example that is based on similar design principles. I'll make you a more realistic example of 3 cabs: Cab A and B have same dimension. All three cabs have similar response. Also the costs in drivers are from all cabs are similar:
Horn A: 18” driver, 1800W (136dB) continue, 3600W (139dB) program, 10Kw peak. Best SPL figures, since it uses the latest generation driver technology. Should be used in groups of at least 2 to give a flat response
Horn B: 2x 12”, 800 watt continue (133dB), 1600W program (136dB), 3200W peak.Best THD figures, since it uses Push-Pull. Should be used in groups of at least 4 to give a flat response.
Tapped Horn C: 18” driver, 1800W (136dB) continue, 3600W (139dB) program, 10Kw peak. Lowest Volume and lowest weight since it is 30% smaller then cab A and B and uses the same driver as Horn A. Of all three cabs this cab is worst in THD. Has the most flat response and can be used in singles without a problem.
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Thanks!
I actually started out with much larger woofers, but shrunk the size by 75% when I realized that you could get fairly amazing output from the smallest drivers. The original experiments used a 4" TangBand woofers, then I switched to 2" Peerless woofers:
In a conventional front-loaded horn, there's a sealed chamber which does a few things. First, the chamber raises the resonance of the woofer. For instance, if the woofer starts with an FS of 29hz, the sealed chamber might raise the Fb to 60hz. And then the horn is tuned to that Fb.
The problem with very small drivers is that the QTS is way too high. For instance, if I build a front-loaded horn with a prosound driver, the Fb of the system might be something like 60hz with a system 'Q' of .8 or 1.0. But these tiny TangBand and Peerless woofers have a QTS of 0.8 or 1.0 already! So if you put them in a front-loaded horn the system Q gets insanely high, like 2.0 or even 2.5.
So a simple solution is to simply ditch the sealed chamber. That transforms the enclosure, changing it from a front-loaded horn to a back-loaded horn. (In other words, we're getting output from both sides of the cone.)
But I'm not using a back-loaded horn for the typical reason, which is to get full-range output and deep bass. The reason that I'm going with a back-loaded horn in this design is that these tiny little woofers just won't work in a front-loaded horn, because the QTS is way too high.
I think it's hard to make too many comparisons, since we're talking generalities. But I think some generalizations can be made.
Comparing two traditional horns, if both are well optimized, then the size really affects the smoothness of response. I wouldn't expect two horns that are the same size and operated over the same passband to have different characteristics with respect to the number of horns needed for smooth response. This is largely a function of mouth area, or more specifically, of the flare rate, i.e. the area expansion increase.
A traditional horn is an impedance transformer, and it needs this area increase to work properly. So I wouldn't expect to need more of your "Horn B" models than "Horn A" models to get smooth response, unless "Horn A" was larger. That is assuming both are well optimized. This then makes the comparison between A and B largely a comparison of the driver(s) chosen, one having a higher thermal limit than the other. Naturally, the driver capable of handling more power will have higher output, all other things being equal.
Tapped horns can definitely be made smaller than full-size traditional horns. But that's because they are like transmission lines, not having the same area expansion as a horn nor its corresponding impedance transformation. As a result, they aren't as efficient. So while I would expect smaller size, I would also expect lower SPL output. Tapped horns and lines trade smaller size for reduced output and higher distortion. They give smoother response down low, but rougher response up high.
So I think probably the "Tapped Horn C" should not be expected to have as high SPL as the full-size "Horn A". I'm not sure how the bulk efficiency works out, but I have always read that tapped horns do not gain the same advantage in groups that full-size horns do, and that they are best used in smaller venues where large installations aren't appropriate.
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