Guys, I thought I was sure about this, but no longer so, and I REALLY need to know for sure:
This isn’t a question of sealed vs ported vs TH vs FH.
And this DEFINITELY is not a questionn about SPL. - I have found countless threads about that.
For this thread, I’m concerned only with LF “throw." My definition being: The ability for a sub system to maintain as even an SPL level as possible over distance. For this discussion, let's say from around 10 feet to 100 feet. (I do small gigs.) I have always been of the opinion that total cone / port / horn mouth area is what matters. (More speakers at lower volume each.) Other people seem to think that cone excursion & total dispersion are all that matters. Or maybe it’s displacement, but it's the same result in that case: Less speakers with more power to them / more excursion.
(Again, this is not a discussion of ported vs horn loaded, etc.)
Here’s the simple setup / question: (I know this is fairly obvious, but I want to be sure we are discussing exactly the same thing.)
——————————————————————————————
Take three of any subwoofer you like, and set them up with a pair of decent tops. Tops that should carry well over the same 10 - 100 feet test range. For this test, put the tops right next to each other, and not too high.
Run your amp into sub “A” by itself, and get its output balanced with the tops.
Also test with a meter.
Now listen at 100 feet and note how much apparent loss there is.
Also test with a meter.
Now repeat this test, except with both sub B and sub C running, (No sub A) but with the subs amp turned down, so the tops are still balanced.
Also test with a meter. At ten feet, I would assume the subs’ spl level will be very close to the first test.
OK, so at 100’, is there any difference in balance / in subwoofer spl?
Based on my own (limited) experience, and just using my ears, there will be. Test #2 will give noticeably more LF at distance.
- But some pretty intelligent guys disagree with this, so it’s driving me nuts. Especially since this is driving the design theory behind my new subs system build.
What say you? And why?
My theory, assuming that my ears are not fooling me, or that it has something to do with small room nodes and compression, is thus:
If you can excite more air molecules at the source (the subwoofer) but use less energy per molecule, then the less loss there will be as the waves travel through the air.
That just makes sense.
The guys that disagree say that more cone excursion creates just as much dispersion, thus just as many air molecules moving.
My counter to THAT is, even if it’s true (I don’t know) there is more energu behind those molecules, thus higher resistance through the air, yada yada yada….
Am I wrong?
I’m planning on building four smallish subs, and running them at “medium” power, instead of two equal subs pushed really hard. This gives the advantage of using lower-powered and hence more sensitive drivers. This also may have a small advantage is sound quality, due to less excursion. - But that doesn’t matter for this discussion. I just want opinions on the issue of “throw.”
thx.
This isn’t a question of sealed vs ported vs TH vs FH.
And this DEFINITELY is not a questionn about SPL. - I have found countless threads about that.
For this thread, I’m concerned only with LF “throw." My definition being: The ability for a sub system to maintain as even an SPL level as possible over distance. For this discussion, let's say from around 10 feet to 100 feet. (I do small gigs.) I have always been of the opinion that total cone / port / horn mouth area is what matters. (More speakers at lower volume each.) Other people seem to think that cone excursion & total dispersion are all that matters. Or maybe it’s displacement, but it's the same result in that case: Less speakers with more power to them / more excursion.
(Again, this is not a discussion of ported vs horn loaded, etc.)
Here’s the simple setup / question: (I know this is fairly obvious, but I want to be sure we are discussing exactly the same thing.)
——————————————————————————————
Take three of any subwoofer you like, and set them up with a pair of decent tops. Tops that should carry well over the same 10 - 100 feet test range. For this test, put the tops right next to each other, and not too high.
Run your amp into sub “A” by itself, and get its output balanced with the tops.
Also test with a meter.
Now listen at 100 feet and note how much apparent loss there is.
Also test with a meter.
Now repeat this test, except with both sub B and sub C running, (No sub A) but with the subs amp turned down, so the tops are still balanced.
Also test with a meter. At ten feet, I would assume the subs’ spl level will be very close to the first test.
OK, so at 100’, is there any difference in balance / in subwoofer spl?
Based on my own (limited) experience, and just using my ears, there will be. Test #2 will give noticeably more LF at distance.
- But some pretty intelligent guys disagree with this, so it’s driving me nuts. Especially since this is driving the design theory behind my new subs system build.
What say you? And why?
My theory, assuming that my ears are not fooling me, or that it has something to do with small room nodes and compression, is thus:
If you can excite more air molecules at the source (the subwoofer) but use less energy per molecule, then the less loss there will be as the waves travel through the air.
That just makes sense.
The guys that disagree say that more cone excursion creates just as much dispersion, thus just as many air molecules moving.
My counter to THAT is, even if it’s true (I don’t know) there is more energu behind those molecules, thus higher resistance through the air, yada yada yada….
Am I wrong?
I’m planning on building four smallish subs, and running them at “medium” power, instead of two equal subs pushed really hard. This gives the advantage of using lower-powered and hence more sensitive drivers. This also may have a small advantage is sound quality, due to less excursion. - But that doesn’t matter for this discussion. I just want opinions on the issue of “throw.”
thx.
More cone excursion creates more volume displacement, doubling displacement results in a 6dB increase in SPL, but no change in the dispersion angle. Dispersion angle vs frequency is determined by size of the cone/baffle or array orientation.
The inverse distance effect (inverse square law) holds true for any type of subwoofer measured at a distance beyond the near field, "throw" is a matter of physics.
The SPL of any loudspeaker drops at 6dB per doubling of distance once outside the near field.
Pat Brown, (a guru of measurement) wrote :
"It is often thought that a remote measurement position is necessary for low frequencies since their wavelengths are long. Actually the opposite is true. It is more difficult to get into the far-field of a device at high frequencies, since the shorter wavelengths make the criteria in Item 4 more difficult to satisfy."
Item 4:
"4. The distance from the source where the path length difference for wave arrivals from points on the device on the surface plane perpendicular to the point of observation are within one-quarter wavelength at the highest frequency of interest ."
This is an important distinction between high frequency and low frequency measurement, criteria #4 can be satisfied at 95 Hz and below for a subwoofer of one square meter mouth area measured at one meter.
Large arrays of subwoofers change radiation patterns and the near/field far field transition point, but the inverse distance effect is still rules.
https://www.freespeakerplans.com/downloads/rog-mogale-a-practical-guide-to-bass-arrays/viewdocument
You can measure those effects yourself (as I have) or review any number of simulation programs (Meyers MAPP, DanleyDirect, etc.) or see the difference between two meters and ten meter results in Josh Ricci's tests of many completely different sub designs.
Data-Bass: Subwoofer Measurements
Of interest, the only sub on that site not following the inverse distance law between 1, 2 and 10 meters was the dual 21" side firing home stereo sub, which happens to not fit Pat Brown's criteria #4.
As Josh put it, that sub required "Dual Opposed Distance Compensation" since the distance to the side driver radiation point was longer than the distance from the front of the cabinet, where exits normally are placed ;^)
Art
The inverse distance effect (inverse square law) holds true for any type of subwoofer measured at a distance beyond the near field, "throw" is a matter of physics.
The SPL of any loudspeaker drops at 6dB per doubling of distance once outside the near field.
Pat Brown, (a guru of measurement) wrote :
"It is often thought that a remote measurement position is necessary for low frequencies since their wavelengths are long. Actually the opposite is true. It is more difficult to get into the far-field of a device at high frequencies, since the shorter wavelengths make the criteria in Item 4 more difficult to satisfy."
Item 4:
"4. The distance from the source where the path length difference for wave arrivals from points on the device on the surface plane perpendicular to the point of observation are within one-quarter wavelength at the highest frequency of interest ."
This is an important distinction between high frequency and low frequency measurement, criteria #4 can be satisfied at 95 Hz and below for a subwoofer of one square meter mouth area measured at one meter.
Large arrays of subwoofers change radiation patterns and the near/field far field transition point, but the inverse distance effect is still rules.
https://www.freespeakerplans.com/downloads/rog-mogale-a-practical-guide-to-bass-arrays/viewdocument
You can measure those effects yourself (as I have) or review any number of simulation programs (Meyers MAPP, DanleyDirect, etc.) or see the difference between two meters and ten meter results in Josh Ricci's tests of many completely different sub designs.
Data-Bass: Subwoofer Measurements
Of interest, the only sub on that site not following the inverse distance law between 1, 2 and 10 meters was the dual 21" side firing home stereo sub, which happens to not fit Pat Brown's criteria #4.
As Josh put it, that sub required "Dual Opposed Distance Compensation" since the distance to the side driver radiation point was longer than the distance from the front of the cabinet, where exits normally are placed ;^)
Art
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Thanks, Art.
Call me stubborn, but I'm still not 100% convinced.
Is the inverse square law the same for all amplitudes?
Everything else in nature has more loss with higher source “power” - electricity through wire, water through pipes, an accellerating car through air. - So why wouldn’t sound be similar?
Hmm, I do realize that sound is not actually “traveling through” the air, but rather consecutive molecules being excited, so perhaps that's the difference, but it still seems logical that higher energy will dissipate sooner.
Call me stubborn, but I'm still not 100% convinced.
Is the inverse square law the same for all amplitudes?
Everything else in nature has more loss with higher source “power” - electricity through wire, water through pipes, an accellerating car through air. - So why wouldn’t sound be similar?
Hmm, I do realize that sound is not actually “traveling through” the air, but rather consecutive molecules being excited, so perhaps that's the difference, but it still seems logical that higher energy will dissipate sooner.
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Let's look at it another way:
Take a typical modern outdoor concert. The main FOH system has to reach to the people near the first delay towers. From what I've read, those towers are typically at a minimum of 50 meters from the stage. So let's use that for now.
Now assume the soundman hates his audience, and cranks the mains up to 105 dB. According to the inverse square law, that gives less than 87 dB at the delay towers.
So ears in the front row are getting destroyed, while people in the 40th row can have a nice relaxed conversation. That can't be.
Isn't the answer that there's a huge amount of cone & horn area at the source? - Or are they simply sending differing amounts of SPL to each vertical section of the array?
Take a typical modern outdoor concert. The main FOH system has to reach to the people near the first delay towers. From what I've read, those towers are typically at a minimum of 50 meters from the stage. So let's use that for now.
Now assume the soundman hates his audience, and cranks the mains up to 105 dB. According to the inverse square law, that gives less than 87 dB at the delay towers.
So ears in the front row are getting destroyed, while people in the 40th row can have a nice relaxed conversation. That can't be.
Isn't the answer that there's a huge amount of cone & horn area at the source? - Or are they simply sending differing amounts of SPL to each vertical section of the array?
The inverse square law holds true for a point source in the 'free field'; in fact the free field is actually defined by the space in which the inverse square power law holds true. How small the source needs to be to behave like a point source is relative to the both wavelength in question, and the distance from the source.
For a larger source area, the 'near field' extends further from the source, and in the near field the SPL does not follow the inverse square power law.
As the 'array' of subwoofers becomes larger the 'free field' where a 6dB per drop in SPL per doubling of distance holds begins further away from the source.
If the source array is infinitely large in two dimensions, the free field would theoretically be pushed out to infinity. That would mean there is no drop in SPL with distance.
For an infinitely long line array source, the free field is also pushed out to infinity, however in this case the drop in SPL would be 3dB per doubling of distance.
For a larger source area, the 'near field' extends further from the source, and in the near field the SPL does not follow the inverse square power law.
As the 'array' of subwoofers becomes larger the 'free field' where a 6dB per drop in SPL per doubling of distance holds begins further away from the source.
If the source array is infinitely large in two dimensions, the free field would theoretically be pushed out to infinity. That would mean there is no drop in SPL with distance.
For an infinitely long line array source, the free field is also pushed out to infinity, however in this case the drop in SPL would be 3dB per doubling of distance.
Cableaddict,
Don't understand your first "question" in post #4, but regarding the second, yes, there generally is amplitude shading as well as elevation and angle adjustment to achieve reasonably uniform HF coverage from front to back.
If a single subwoofer were only 105 dB SPL at 1 meter, the level at 50 meters would be only 71 dB. If the level was 105 dB at 50 meters, the level at 1 meter must be 139 dB. That would require one or two "high power" subwoofers.
The four 2x12" Eminence Kappalite 3012LF subs in small boxes you are considering building could do over 134 dB at one meter, they could do over 105 dB at 25 meters.
Audio calculations in English acoustics calculator convert audio formulas sound dB audio system microphone electro engineering electronics formula sound recording studio useful stuff free audio calculator recording studio acoustic audio engineering s
How does the sound decrease with distance? sound pressure distance wave drop decrease increase fall off damping sound source noise pressure intensity Level acoustic inverse distance law 1/r for sound pressure Inverse square law 1/r2 for acoustic inte
At high frequencies, there is also air absorption in addition to the inverse distance losses.
Calculation method of absorption of sound by atmosphere air damping dissipation absorbtion high frequencies attenuation sound during propagation outdoors outdoor - sengpielaudio Sengpiel Berlin
Don't understand your first "question" in post #4, but regarding the second, yes, there generally is amplitude shading as well as elevation and angle adjustment to achieve reasonably uniform HF coverage from front to back.
If a single subwoofer were only 105 dB SPL at 1 meter, the level at 50 meters would be only 71 dB. If the level was 105 dB at 50 meters, the level at 1 meter must be 139 dB. That would require one or two "high power" subwoofers.
The four 2x12" Eminence Kappalite 3012LF subs in small boxes you are considering building could do over 134 dB at one meter, they could do over 105 dB at 25 meters.
Audio calculations in English acoustics calculator convert audio formulas sound dB audio system microphone electro engineering electronics formula sound recording studio useful stuff free audio calculator recording studio acoustic audio engineering s
How does the sound decrease with distance? sound pressure distance wave drop decrease increase fall off damping sound source noise pressure intensity Level acoustic inverse distance law 1/r for sound pressure Inverse square law 1/r2 for acoustic inte
At high frequencies, there is also air absorption in addition to the inverse distance losses.
Calculation method of absorption of sound by atmosphere air damping dissipation absorbtion high frequencies attenuation sound during propagation outdoors outdoor - sengpielaudio Sengpiel Berlin
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Thanks, John.
"For a larger source area, the 'near field' extends further from the source, and in the near field the SPL does not follow the inverse square power law."
So doesn't that basically support my theory? "More cones / or more cabinets" means the inverse-square losses start further out, hence a longer throw.
Am I missing something?
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I thought of something else that's probably related:
Regardless of whether my basic idea is correct, there is simply no question that a small "subs plus tops" rig, which is well balanced at near distance, will sound bass shy at farther distance. I suddenly realized (My "DUH" moment ) that "most of" the tops are going through a 60 or 90 degree horn, yet the subs are omnidirectional.
I've seen Art's idea for adding "Barn Doors" to his (or any) Keystone subs. It's theoretically not possible to add directionality to LF, and yet these evidently work.
I (Once again) have always assumed that they work because they are extending the mouth of the horn, effectively exciting a larger amount of air molecules at the source, at a lower energy per molecule, and there I go again. 🙂
- But if in fact these are actually acting as a wave guide, then can't we do the same thing with ported subs?
And if so, why doesn't everybody do it already?
"For a larger source area, the 'near field' extends further from the source, and in the near field the SPL does not follow the inverse square power law."
So doesn't that basically support my theory? "More cones / or more cabinets" means the inverse-square losses start further out, hence a longer throw.
Am I missing something?
--------------------------------------
I thought of something else that's probably related:
Regardless of whether my basic idea is correct, there is simply no question that a small "subs plus tops" rig, which is well balanced at near distance, will sound bass shy at farther distance. I suddenly realized (My "DUH" moment ) that "most of" the tops are going through a 60 or 90 degree horn, yet the subs are omnidirectional.
I've seen Art's idea for adding "Barn Doors" to his (or any) Keystone subs. It's theoretically not possible to add directionality to LF, and yet these evidently work.
I (Once again) have always assumed that they work because they are extending the mouth of the horn, effectively exciting a larger amount of air molecules at the source, at a lower energy per molecule, and there I go again. 🙂
- But if in fact these are actually acting as a wave guide, then can't we do the same thing with ported subs?
And if so, why doesn't everybody do it already?
1) No support to your theory, just means you can't expect a large source to behave in the near field as it does in the far field.
2) Wasn't my idea, was used in the bass section of theater woofers 100 years ago, when power was expensive, and excursion very limited.
The 3dB bass gain from large barn doors simply is due to the increased boundary area, reducing the rear spill from 360 to 180 degrees. No magic, just less sound behind, more in front. Same "theory" as going from full to half to 1/4 space forward gain increases.
Everybody doesn't do it because it requires hauling around big sheets of plywood and longer set up times.
For 3dB gain, I seldom used them other than on multiple day set-ups, and even then, it would be rare anybody else would have noticed, even if they were mixing. Did make the system look bigger...
In a large system, the boundary area of a sub array is already huge, doubling it wouldn't be possible with out messing up sight lines.
Doubling set up labor costs, reducing sight lines for 3dB more bass does not fit tour budgets.
For DIY, if you got the time, go for it.
Art
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Yes, quite clearly there an acoustics based reason for the effect you perceive.
In my days of yore engineering outdoor PA rigs for audiences >>10,000s (pre-line array technology) a line of subs under the lip of the stage from extreme left to extreme right, say 24 dual 18 cabinets, would create a line source to overcome inverse square law power loss of the subs, without upsetting sight lines. It was also useful for mitigating noise complaints from the sides of the venue.
That is the line I was waiting for.
Indoors, the room totally dominates low frequency reproduction so yeah.. it has everything to do with room nodes. The nodal pattern is so complex the heavest bass could very well be at the back of the room but that is only because of all the cancellation going on elsewhere in the room. This is NOT throw.. a term that really does not describe any aspect of sound propagation through air. If your only experience is inside structures then what you think you have figured out is actually just a misinterpretation of what's really going on. And yes 3 subs subs lined up side by side is enough of a positioning difference to change the nodal pattern they produce.
Multiple subs vs a single.
To do this comparison correctly the multiple combo must have the same displacement capability as the single, otherwise it's not a fair fight because a larger sub is always a more effective transducer.. converting more of the electrical energy into acoustic energy.
Propagation Loss of Low Frequency Horn Loudspeakers:
Is “throw” a real phenomenon?
AES E-Library >> Propagation Loss of Low Frequency Horn Loudspeakers:Is "throw" a real phenomenon?
Is “throw” a real phenomenon?
AES E-Library >> Propagation Loss of Low Frequency Horn Loudspeakers:Is "throw" a real phenomenon?
I was surprised to see that this paper has just been published this year. There actually was quite a lot of research by companies such as JBL and Electro-Voice in the 1970s and earlier, and Meyer and others from the 1980s, but this isn't usually published in the Journal of the AES and over time these resources tend to disappear into the ether, especially as the internet has taken over as the prime source of information (and mis-information unfortunately).
Reassuringly the AES paper is entirely consistent with my previous posts, which means physics isn't broken and still works like it used to.
A good read, thanks, but it doesn't address my question. I'm well aware that horns don't have more throw than an "equivalent" ported box.
What I'm asking about has very rarely been discussed. - As far as I can see. It always ends up about either horn vs ported, or maximum SPL.
Thanks, John.
But again, you are agreeing with my basic premise, correct?
Or if not, then how does this negate it?
Maybe the line of subs acted sort of as a waveguide, more like Art's barn door concept? Everything I'v ever read says you can't easily direct sound waves below 100 Hz, but I'm trying to stay open to that possibility. (Maybe the side subs or a barn door simply absorb some energy, so the front SPL stays the same, but there's less molecular energy past the obstructions?) Well, concrete barriers might work, I guess, so maybe that line of subs was dense enough to cause LF energy re-direction instead of absorption?
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The answer is this: the speakers aren't on the ground. Once you fly the cabinets, the difference in distance from the front to the back decreases, meaning more even SPL vs distance.
Chris
Directional sound is possible at any frequency, the problem at low frequencies is those very long wavelengths require very large solutions. A large horizontal cluster of subs produces direction bass the same way a vertical line array does for the rest of the spectrum, the output from all those drivers adds to produce more output directly in front while cancelling output off axis.
quote: "the problem at low frequencies is those very long wavelengths require very large solutions."
Ah, that makes sense. Those wide sub clusters might ALSO be working due to the "extended nearfield" effect, but this is probably the main factor.
This is more complicated than I expected. 😱
Ah, that makes sense. Those wide sub clusters might ALSO be working due to the "extended nearfield" effect, but this is probably the main factor.
This is more complicated than I expected. 😱
Constructive and destructive interference in the output of an array of drivers determines the overall shape and intensity of the response pattern, and both the c-c distance between drivers and the frequency in question affect the results. Even over a fairly narrow range of frequencies such as the typical subwoofers range the response pattern can be complex and vary significantly.
Check out this video it has some great visualizations. Subwoofer Arrays - YouTube
Check out this video it has some great visualizations. Subwoofer Arrays - YouTube
Yes it is.
You really should try reading "A Practical Guide To Bass Arrays" by Rog Mogale that was linked in post #2, as well as using the Sengpielaudio calculators, after you read my reply to your e-mails...
The picture below gives you an idea of what happens outdoors in "simple" terms at just one frequency- put the subs indoors and the picture would look more like a Rorschach test 😉
Art
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Sure, but this was not supposed to be a discussion of directionality. I kind oif took it there myself, when I brought up the "barn door" thing, but that was a bit of a red herring.
A large horizontal cluster of subs blocks some sound going to the sides or rear, ok I get that, but does not affect the ration of SPL in front, from near to far.
So far the only concrete thing mentioned seems to be that concept of the "nearfield" response extending further out, before the inverse-square law takes over. And that, again, seems to support my theory.