Then quit justifying your own preference here and leave the people focused on performance to focus on performance! You're in the wrong place for someone who doesn't care about getting the last few percent.
And for Art I have another example that I think is connected to the same principles. Although, I never heard any Danley TH you seem to have experiences with the TH118. A while ago I did some reading about the difference between the TH118 loaded with an 18Sound or the B&C. If I’m correctly informed the SPL levels were both very similar but the B&C was described as ‘more obvious kick’. Also the 18Sound got ‘blown’ more easily as some stated. But I wondered why nobody was talking or comparing THD figures…
(Wayne, as mastering engineer you learn these kind of tricks to separate 'psycho' acoustic effects from reality
or in other words separate the ears from the eyes)
(Wayne, as mastering engineer you learn these kind of tricks to separate 'psycho' acoustic effects from reality
or in other words separate the ears from the eyes)
Last edited:
I do want to remind everyone reading, before we get too far into psychoacoustics, the audibility of distortion, and the euphoncs of odd verses even harmonics. Remember that there are a few mechanisms in play in the 12Pi hornsub, each complementing the other. The main thing is push-pull drive reduces the second harmonic, and the bandpass nature of the horn reduces about half the third harmonics and almost all of the higher harmonics. As I said a post or two back, once you solve the problem of the second harmonic in a hornsub, you pretty much have distortion licked.
Art measured 30dB reduction of the second harmonic. He wasn't sure if push-pull drive did anything, and now he knows.
The 30dB reduction of the second harmonic is huge - It's the the harmonic that is strongest in a traditional horn, 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.
Art measured 30dB reduction of the second harmonic. He wasn't sure if push-pull drive did anything, and now he knows.
The 30dB reduction of the second harmonic is huge - It's the the harmonic that is strongest in a traditional horn, 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.
Last edited:
...Then half of them (those who have more theoretical knowledge) 'suddenly' had changed their minds and stated the lower THD sounded better...
For Jbell, that was the flute theory that seems missing in PPTH
amazing... simply amazing.
I think it's interesting how much insight flutes and clarinets can offer.
but Low-A bari-sax playing Basie is MUCH more fun....
The distortion levels in TH are nothing to brag about compared to BR, and regular horns can have far less at similar output level. No manufacturer wants to talk about their product's warts, however small.And for Art I have another example that I think is connected to the same principles. Although, I never heard any Danley TH you seem to have experiences with the TH118. A while ago I did some reading about the difference between the TH118 loaded with an 18Sound or the B&C. If I’m correctly informed the SPL levels were both very similar but the B&C was described as ‘more obvious kick’. Also the 18Sound got ‘blown’ more easily as some stated. But I wondered why nobody was talking or comparing THD figures…
(Wayne, as mastering engineer you learn these kind of tricks to separate 'psycho' acoustic effects from reality
This was obvious in discussion of distortion figures of the TH-115 at the NYC sub shootout, background noise was mentioned as the culprit.
Funny, there was a front end loader working across the arroyo from me yesterday, and my SN was still in the 60 dB range, somehow I doubt people talking in a room would affect the background noise below 100 Hz much at all.
Since few bother to measure distortion, and perception of LF distortion is so subjective, no surprise that it gets little mention.
Wayne,
I never doubted that push pull did something, my unanswered curiosity was how much, and at what frequencies.
The measured reduction in the first harmonic was actually 32.4%, dropping from 27% to .5% in the PP, but the sealed PP Lab 12s actually increased in distortion at the 3rd harmonic, compared to the “normal” cabinet, rendering the THD for 49 v (800 watts) 20 Hz 96.25%, which appears to be about the same as the 12 Pi at that frequency, and less than 1% better than the standard configuration.
I am in complete agreement with all your points regarding distortion in post 119, so I think you would agree that anything approaching 100% distortion sounds like garbage, exactly why we filter that junk out with a properly set HP .
I’ll be posting distortion pictures and percentages with tones up to 100 Hz in another thread , but from what I am observing of my data thus far, the reduction in distortion from PP in the ported and sealed cabinet seems much more prevalent in the upper sub range, not down below where we HP the subs .
Back to the test results, about 14 hours work so far, at least I’m over half way ...
Art Welter
Not sure what you're doing with the numbers, but a 30dB reduction is a scale of 1/1000. The second harmonic was reduced by 1000.
I think this is worth repeating, just in case it has been missed:
The 30dB reduction of the second harmonic is huge (1000x) - It's the the harmonic that is strongest in a traditional horn, 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.
I don't get where you came up with that number either. I'm not seeing 100% anywhere. The violet (distortion) line crosses the amplitude response (blue) line around 15Hz, and that's where the ratios are the same, i.e. 100%. But that's where the amplitude of the distortion products have fallen below the noise floor. What you're actually seeing is the amplitude response chart matching the noise floor, not the distortion.
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:
You can see this same kind of chart in some of the better hornsubs when run at low power levels. The distortion is below the noise floor 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% for speakers that could reach 110dB or more.
Last edited:
Posted by djk ( M ) on May 16, 2003 at 17:26:18
In Reply to: Subwoofer configurations posted by Wayne Parham on May 16, 2003 at 02:49:27:
The reductions in 2nd harmonic distortion from PP mounting on a flat baffle are well known, the non-linearities are equal and opposite and thus the 2nd harmonic is canceled. Because of the driver spacing it only happens in the bottom octaves. The cheaper the driver, the bigger the improvement. I have measured as much as a 20dB change.
By mounting in a plenum several things change. The spacing becomes much tighter so the cancellation will work at higher frequencies, and a cavity is formed.
The cavity does several things, in no particular order:
The size, especially the depth, acts like a low pass filter. This can reduce 3rd harmonic distortion products near the top end of the passband, the effect is small, but audible. The cavity sizes I use have to be crossed in the 150hz~250hz region. It gives a slope of roughly 12dB/oct that must be taken into consideration in the design of the crossover. There is a small peak about two octaves above this point, ~800hz on many that I have done. By varying the Q of the 12dB/oct lowpass filter I can get a LR4 transfer function. This filter also reduces the out-of-band peak to -30dB or better. There is also a big reduction in FMD, on the order of 6dB. The air mass at the exit of the plenum seems to act like a point source with no doppler, the cones are moving back-and-forth sideways rather than towards-and-away from you. At first glance this would seem to eliminate the FMD, in practice the reduction is on the order of 4dB~10dB depending on the frequencies.
I mounted a pair of drivers in another cabinet in a face-to-face, push-push mode. The box became very 'thick' sounding and had a broad peak centered at 160hz, just like the EV MTL4. In room the response of the push-pull was 6dB smoother in the 100hz~200hz octave.
Being compared side-by-side with the Klipschorn and Cornwall was interesting. At first the push-pull sounded 'funny'. Couldn't put my finger on it. Went back to the push-push cabinet. The push-push cabinet had that 'hi-fi' sound, similar to the Cornwall, but a bit 'thicker'. Klipschorn, much cleaner sounding. Back to the push-pull.
The reason the push-pull sounded 'funny' was the total lack of distortion. Much less than the Klipschorn.
I have not built a basshorn since.
I still use horns, but only above 150hz.
There are some drivers that are not suitable for home hi-fi, mainly those with small magnet vents that can make 'chuffing' sounds when up close.
In Reply to: Subwoofer configurations posted by Wayne Parham on May 16, 2003 at 02:49:27:
The reductions in 2nd harmonic distortion from PP mounting on a flat baffle are well known, the non-linearities are equal and opposite and thus the 2nd harmonic is canceled. Because of the driver spacing it only happens in the bottom octaves. The cheaper the driver, the bigger the improvement. I have measured as much as a 20dB change.
By mounting in a plenum several things change. The spacing becomes much tighter so the cancellation will work at higher frequencies, and a cavity is formed.
The cavity does several things, in no particular order:
The size, especially the depth, acts like a low pass filter. This can reduce 3rd harmonic distortion products near the top end of the passband, the effect is small, but audible. The cavity sizes I use have to be crossed in the 150hz~250hz region. It gives a slope of roughly 12dB/oct that must be taken into consideration in the design of the crossover. There is a small peak about two octaves above this point, ~800hz on many that I have done. By varying the Q of the 12dB/oct lowpass filter I can get a LR4 transfer function. This filter also reduces the out-of-band peak to -30dB or better. There is also a big reduction in FMD, on the order of 6dB. The air mass at the exit of the plenum seems to act like a point source with no doppler, the cones are moving back-and-forth sideways rather than towards-and-away from you. At first glance this would seem to eliminate the FMD, in practice the reduction is on the order of 4dB~10dB depending on the frequencies.
I mounted a pair of drivers in another cabinet in a face-to-face, push-push mode. The box became very 'thick' sounding and had a broad peak centered at 160hz, just like the EV MTL4. In room the response of the push-pull was 6dB smoother in the 100hz~200hz octave.
Being compared side-by-side with the Klipschorn and Cornwall was interesting. At first the push-pull sounded 'funny'. Couldn't put my finger on it. Went back to the push-push cabinet. The push-push cabinet had that 'hi-fi' sound, similar to the Cornwall, but a bit 'thicker'. Klipschorn, much cleaner sounding. Back to the push-pull.
The reason the push-pull sounded 'funny' was the total lack of distortion. Much less than the Klipschorn.
I have not built a basshorn since.
I still use horns, but only above 150hz.
There are some drivers that are not suitable for home hi-fi, mainly those with small magnet vents that can make 'chuffing' sounds when up close.
Last edited:
Absolutely, Dennis, I couldn't agree more. I used this approach in the 12Pi basshorn because it only made sense. A basshorn is a bandpass system, and when driven with push-pull drive, a lot of things come together to make very impressive performance. I think this is lost on some, but once you see it (measure it, hear it), you definitely get it.
If the speaker produced an abnormally high content of odd harmonics, as the front-loaded push-pull experiment Art did creates, then the speaker might sound objectionable. But a bandpass system such as a basshorn already greatly attenuates third harmonics and up. So in a basshorn, the distortion produced is predominantly the even harmonic.
A 30dB reduction of the second harmonic is huge - It's the the harmonic that is strongest in a traditional horn, 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.
Basically, when you solve the problem of second harmonics in a basshorn, you have distortion pretty much licked. I realized this might be overlooked by some, so I've restated it a few times. It is a very important concept.
I think another place where there may have been some misunderstanding is the terms, math and values used. There seems to have been some confusion between even and odd harmonics, and differences in scale too.
Even harmonics are even multiples of the fundamental, i.e. 2x, 4x, etc. They are caused by asymmetrical nonlinearity, which is what is reduced by push-pull drive. Odd harmonics are odd multiples of the fundamental, i.e. 3x, 5x, etc. They are caused by symmetrical nonlinearity, usually the suspension. They cannot be reduced by push-pull drive.
The ratio between the fundamental and harmonics are often expressed as a percentage of pressures. That's the common way to do it, so the numbers expressed are pressure ratios. But other than that, I tend to think in terms of power ratios, because we're often discussing things in terms of what they do at a specific power level, i.e. W/M. I also like to describe things in terms of decibels gained or lost, i.e. -25dB.
This is a key distinction, because the scale of pressure ratios is 20 log, and the scale of power ratios is 10 log. There's a huge difference in scale.
To me, when I see a 20dB difference, I immediately think 100x power. It would take 100x power to increase 20dB, and likewise, 1/100th the power to drop 20dB. So that's a huge difference to me, very significant. But when you look at this same value in terms of pressure, it's only 10x scale. Same thing, stated a different way.
When you start playing around with percentages, you can even make the values seem smaller than that. For example, if the distortion of one speaker is -35dB, and another is -55dB, when you compare percentages, the higher distortion speaker is 2% (-35dB) and the lower distortion speaker is 0.2% (-55dB). One person might shrug this off saying, it's nothing, less than 2% difference. That's technically true but competely fails to convey the huge difference there actually is between the two, which is 20dB, equivalent to 100x power.
Now that I understand that what looked like distortion in the low end response of the 12Pi was mostly just background noise, the lack of distortion is even more interesting after doing my PP to normal distortion tests.
http://www.diyaudio.com/forums/subwoofers/191833-push-pull-vs-normal-distortion-compared.html
The interesting thing about the front loaded PP measurements is they show it reduces even order harmonic distortion at some frequencies by large amounts, other frequencies by little.
At some frequencies PP added anharmonic components (not related to the fundamental), and others it increased the level of the third harmonic over what the second was.
The net result was though the speaker averaged lower distortion with PP, in this case it did not sound cleaner when pushed hard.
It may be that the relationship of the port location (a phase inversion device), to the PP may partially cancel each other out at some frequencies.
We only listened to the ported versions, I regret not having done an A/B listening test between the sealed PP compared to normal, as it “looks” better as a PP than the ported cabinet.
PP seems to works exceptionally well in the 12Pi due to the synergetic interplay of the various attributes of the design.
The same seems true of Dennis’ (djk) ported PP designs using a plenum .
From my tests, it is apparent with the Lab 12 that PP needs to be combined with other design features and some careful attention to detail to get a net improvement in sound quality.
In other words, flipping a speaker and reversing it’s polarity won’t necessarily have a net positive effect .
So, my advice for low distortion fans looking for big and loud: buy a 12Pi, or prepare to do a lot of design and testing, PP by itself is no automatic guarantee of good sound.
Art Welter
The Push-Pull system is only able to equalise (constant) nonlinearities in the magnetic field between the two drivers.
The Push-Pull is not able to equalise (variable) nonlinearities in the cone movement and cone structure that happen when the drivers reach their Xmax and/or certain thermal values/limits (or in other words when the drivers get pushed hard).
Last edited:
Originally Posted by weltersys
The net result was though the speaker averaged lower distortion with PP, in this case it did not sound cleaner when pushed hard.
What you say seems to correspond to the tests I did, though my testing did not heat the voice coils up enough to show any power compression, only excursion related distortion.
If what you say is correct, it seems the Labhorn should have similar distortion below FC to the 12Pi, according to Wayne’s Hornresp charts the 12Pi has slightly more excursion below Fc than the Lab, and both exceed Xmax by a good margin at only 45 volts.
It would be interesting to see the results of a well built LABsub tested under the same conditions as the 12Pi.
Art Welter
The net result was though the speaker averaged lower distortion with PP, in this case it did not sound cleaner when pushed hard.
Djim,
What you say seems to correspond to the tests I did, though my testing did not heat the voice coils up enough to show any power compression, only excursion related distortion.
If what you say is correct, it seems the Labhorn should have similar distortion below FC to the 12Pi, according to Wayne’s Hornresp charts the 12Pi has slightly more excursion below Fc than the Lab, and both exceed Xmax by a good margin at only 45 volts.
It would be interesting to see the results of a well built LABsub tested under the same conditions as the 12Pi.
Art Welter
Attachments
Hi Art,
What I tried to explain is that the working principles of the Push-Pull concept are linked to the (constant) nonlinearities of the magnetic field and not linked to excursion or thermal effects. Your comparison between ‘if I’m correct’ and your test suggestion is based on the excursion-PP relation. So, you can't link my earlier statement to your test suggestion.
In other words you assume two different loadings to have similar THD figures because both are using Push-Pull. However you can expect similar THD figures because both loadings are very similar, not because both use PP.. In case of the 12Pi and the Labhorn I believe both are quiet different in volume, horn path/compression ratios and the Pi12 has the cooling plug. That are many differences...
Last edited:
Remember what I said:
"When you solve the problem of second harmonics in a basshorn, you have distortion pretty much licked. I realized this might be overlooked by some, so I've restated it a few times. It is a very important concept."
The second harmonic is strongest in a traditional horn, 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.
This is made even more true when using a woofer with relatively high excursion limits, because the symmetrical nonlinearity is less than those with lower xmax and xmech. This kind of woofer tends to have reduced odd-harmonics, even at higher power levels.
So the lesson for the day is, use a woofer with reduced third-harmonics at low frequency, and put it in a basshorn with push-pull drive.
Both the 12Pi basshorn and the LABhorn maintain good loading through the passband, so excursion is low. But it skyrockets at cutoff, around 30Hz. Naturally, distortion does too. But the woofer doesn't generate many third harmonics (compared to even harmonics), indicating its motion tends to become asymmetrical. This is what push-pull drive helps most with.
What we have, when comparing the LABhorn and the 12Pi horn, is that even at cutoff and below, the second harmonc dominates. The third harmonic is about the same in both, but that doesn't rise too much at full power. It's the second harmonic that is very high in the LABhorn, and that's what's eliminated in the 12Pi horn. That's why you see such low distortion in the 12Pi even at full power. The LABhorn makes as much distortion at 40 watts as the 12Pi basshorn does at full power.
Remember, when you're talking basshorns:
When you solve the problem of second harmonics, you have distortion pretty much licked.
"When you solve the problem of second harmonics in a basshorn, you have distortion pretty much licked. I realized this might be overlooked by some, so I've restated it a few times. It is a very important concept."
The second harmonic is strongest in a traditional horn, 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.
This is made even more true when using a woofer with relatively high excursion limits, because the symmetrical nonlinearity is less than those with lower xmax and xmech. This kind of woofer tends to have reduced odd-harmonics, even at higher power levels.
So the lesson for the day is, use a woofer with reduced third-harmonics at low frequency, and put it in a basshorn with push-pull drive.
Both the 12Pi basshorn and the LABhorn maintain good loading through the passband, so excursion is low. But it skyrockets at cutoff, around 30Hz. Naturally, distortion does too. But the woofer doesn't generate many third harmonics (compared to even harmonics), indicating its motion tends to become asymmetrical. This is what push-pull drive helps most with.
What we have, when comparing the LABhorn and the 12Pi horn, is that even at cutoff and below, the second harmonc dominates. The third harmonic is about the same in both, but that doesn't rise too much at full power. It's the second harmonic that is very high in the LABhorn, and that's what's eliminated in the 12Pi horn. That's why you see such low distortion in the 12Pi even at full power. The LABhorn makes as much distortion at 40 watts as the 12Pi basshorn does at full power.
Remember, when you're talking basshorns:
When you solve the problem of second harmonics, you have distortion pretty much licked.
1.can you name a few drivers that have reduced third-harmonics at low freq?
2.nice
Below are examples of the Lab 12, relatively low in 3rd harmonic distortion, and an EVX-150A, showing higher 3rd harmonic distortion.1.can you name a few drivers that have reduced third-harmonics at low freq?
2.nice
The Lab 12 driven with 49 V at 35 Hz, about 400 watt per speaker, shows the 2nd harmonic is 30.5 dB down from the fundamental, about 3% distortion, the 3rd harmonic 31.5 dB down from the fundamental, less than 3% distortion.
The EVX-150A driven with 25V, about 78 watts, shows the 2nd harmonic is 13.2 dB down from the fundamental, about 22% distortion, the 3rd harmonic 10.1 dB down from the fundamental, 32% distortion.
Cabinets obviously have a big influence on distortion, but the Lab 12 is a very clean speaker when not driven past Xmax.
In the case above, the Lab 12 has an order of magnitude less 3rd harmonic distortion than the EVX-150A.
Unfortunately, harmonic distortion figures, even when they are given, are often at such low power as to be near useless for anyone using the speaker near rated power.
Unlike frequency response, which remains pretty constant at different drive levels, distortion changes in harmonic content radically at different drive levels.
You may want to search for Klippel data if you are interested in distortion , here is a quote from his website:
“The linear model assumes that all parameters are independent of displacement and time - and thus is valid only for small excursions. At notable displacement levels, the voice coil moves out of the gap and the force factor decays, the suspension gets (usually) stiffer with displacement, and the inductance changes. Thermal heating limits the output power, and the suspension gets softer at the rest position. Unfortunately, these mechanisms interact strongly, and so we end up with a nonlinear feedback system: adding new frequency and a DC component, compressing the output, and with "history" - behavior is dependent not only on the instantaneous signal, but also on the signal from the time before.”
Art Welter
Attachments
Wayne,
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 .
Of course, one could argue that “reasonable persons” would not use a single horn sub designed for PA use in multiples for home use, but that is another discussion
.There are a lot of badly built LABhorns that suffer from air leaks, rattling parts, some have even purposely omitted the chamber covers, which actually fills in the dip you have noted in the LABhorn, but obviously would make excursion go wild below Fc, or actually what would be a combination Fc/Fb.
Although it could be argued that any improvement in distortion is beneficial, most people actually having tested and listened for LF distortion agree that LF distortion within the passband less than 10% or so is difficult to detect at high volume in the presence of normal level HF content.
Most also would agree that for high power use, it is best to cut frequencies below Fc, since power below FC is mostly wasted in excess excursion and heat, best to use available power where the speaker produces decent output.
The 12Pi, averaging less than 2% distortion from 35 Hz to 100 Hz with 1600 watt input certainly qualifies as low distortion.
The 12Pi has more output below 70 Hz, but below 35 Hz, in single units, both the 12Pi and the BassMaxx both fall off at about the same rate. The 12Pi from a distortion standpoint could stand a lower HP than the BassMaxx, but both would benefit from a BW24 around 30 Hz.
The BassMaxx at 1600 watts averages less than 3% distortion from 35 Hz to 100 Hz, also very low distortion.
The BassMaxx does not use PP, but also seems to have solved the problem of second harmonics, and have distortion pretty much licked.
Art Welter
Attachments
You'll just have to scan the measurement charts of various woofer products to find woofers with those characteristics. What you'll see is some woofers have pretty much a diagonal line of decending harmonics, others have a little more even-harmonics and other have a little more odd-harmonics. Then at the lowest frequencies, the distortion rises at a higher rate (as the increased excursion starts making the voice coil leave the gap.) Sometimes the high-excursion balance between harmonics stays the same, but sometimes not.1.can you name a few drivers that have reduced third-harmonics at low freq?
2.nice
A little bit more examination reveals what is happening, and what causes the distribution of distortion components in various designs.
Anything that causes the speaker cone to fail to track the input signal precisely causes distortion. The cause of even harmonics is asymmetrical nonlinearity and the cause of odd harmonics is symmetrical nonlinearity. There are also nonharmonically related distortions, like from cabinets buzzing, vents chuffing and even from irratic motion that arises out of complex acoustic or mechanical loading. Harmonic distortion will be seen as evenly spaced peaks in amplitude response as a result of a fixed sine wave input. Nonharmonic distortion can be found anywhere, and can be seen as added noise (above the noise floor) in a THD+N measurement.
The idealized perfect loudspeaker would move one unit forward with one unit of positive voltage and one unit backward with one unit of negative voltage. Things that make a speaker symmetrically nonlinear create odd harmonics (third, fifth, etc.) and things that make it asymmetrically nonlinear create even harmonics (second, fourth, etc). So distortion measurements can help identify the cause.
An example of asymmetrical nonlinearity is flux modulation, which causes the cone to move slightly further in one direction than the other with the same amplitude of drive voltage in both directions. As an example, consider a speaker that moves, say 1.1 units in the forward direction and 0.9 units in the backward direction, with one unit positive and negative voltage, respectively. This is asymmetrical nonlinearity, and it is identified by increased even harmonics. Some of this is due to suspension nonlinearities, other is because of electro-magnetic nonlinearities. Some can even come from abnormal acoustic loading. But the most common cause of even harmonics is asymmetrical flux, from an asymmetrical gap geometry and/or flux modulation.
Symmetrical nonlinearity is usually caused by the suspension (exceeding xmax), and it makes the speaker move slightly more or less at different excursions. So for example, if the speaker moves 1 unit of distance with 1 unit of voltage, but then 2 units of voltage only moves the cone 1.9 units of distance, if this movement is the same both forward and backward, then the nonlinearity is symmetrical. This kind of nonlinearity creates odd harmonics. This kind of distortion can also be caused by suspension nonlinearities (progressive suspensions), electro-magnetic nonlinearities or abnormal acoustic loading. But the most common cause of excessive odd harmonics is when the voice coil moves partially beyond the gap, losing flux.
At low power levels - low excursion - the driver is in its most linear region. Most drivers that are loaded in an appropriate enclosure are pretty linear at low to moderate power levels through their passbands. Excursion rises as frequency drops, so nonlinearity (distortion) will tend to increase as frequency drops. If the box unloads down low, like a ported box or a horn, then distortion will rise rapidly under cutoff. It can easily exceed xmax, even at low power levels, so the distortion curve goes straight up. So that's where the xmax ~10% figure makes most sense - it's when the power levels are so low that through the passband, the distortion is very low. Unloaded, even at low power levels, xmax can be reached at low frequencies, so as it shoots up, when it rises from basically zero to 10%, that's a good indicator that the driver is out of its linear range. That excurison value becomes a useful figure. But again, above the unloaded frequency where xmax is reached, within the passband, at low to moderate power levels, the speaker is typically pretty linear and distortion is low.
Exceeding xmax means the voice coil is moving beyond the gap. The flux is most concentrated at the gap, and so as the excurison rises to the point where the voice coil leaves the gap, it is going to start becoming nonlinear. The force isn't linear, so acceleration won't be linear either, Cone movement will stop being linear. However, the flux in the gap isn't necessarily symmetrical either. So while extreme excursion levels will almost always cause odd harmonics to rise (as the coil isn't being "pushed" or "pulled" very well), in some drivers, the first thing to happen is one half cycle loses strength before the other does, i,e. cone movement becomes asymmetrically nonlinear, before becoming symmetrically nonlinear. So sometimes, as the cone begins to exceed xmax, the "push" fades before the "pull". In this kind of woofer, even harmonics will rise dramatically when xmax is exceeded, sometimes before the onset of odd harmonics becoming excessive at still higher excursion levels.
High quality woofers usually have gap geometries that are symmetrical. If the manufacturer takes care to machine a motor structure that provides symmetrical flux, then it will enjoy reduced distortion at all power levels. This is even more true if the magnet is electrically conductive (or uses shorting rings) to counter flux modulation. However, a woofer made like this will tend to have higher odd harmonics compared to even harmonics, especially when pushed past xmax. So I'm not sure that's a big plus in a subwoofer, especially one used in a push-pull hornsub. These would definitely be my choice for midwoofers in mains speakers though, because we want flux symmetry, and reduced flux modulation. Flux modulation control rings tend to work best at mid to high frequencies too.
Last edited:
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.