Touched on this a while back in this thread where I show some measurements for my 0.6 Q sealed tempests in room. Pretty much concluded that an EBS type alignment would have negated the need for EQ.
Can't see why it would need a new acronym unless for marketing a product.
Rob.
Can't see why it would need a new acronym unless for marketing a product.
Rob.
I suggest you review the articles by Roy Allison on "The Influence of Room Boundaries on Loudspeaker Power Output" from the 70's. Here is a link to where you can download them:
Roy Allison article
Also, later Roy was involved with RDL Acoustics. At the link below, toward the bottom of the page, there is a link to download a software called BestPlace.exe that simulates the boundary gain accordin to driver placement in regards to the front and sidewalls and floor. It is based on Roy Allisons theories.
Look for Bestplace Speaker Placement program by RDL inc.
Roy Allison article
Also, later Roy was involved with RDL Acoustics. At the link below, toward the bottom of the page, there is a link to download a software called BestPlace.exe that simulates the boundary gain accordin to driver placement in regards to the front and sidewalls and floor. It is based on Roy Allisons theories.
Look for Bestplace Speaker Placement program by RDL inc.
Rob,
part of my point was that RGC tuning is different from EBS tuning. For one thing RGC calls for either a smaller box or lower tuning than EBS, as the bass shelf that characterizes EBS would be an undesirable feature... if indeed the real world works as I have postulated.
For another, the term "Room Gain Complementary" is really more of a concept than a specific alignment, as the tuning that does the job in one situation may well be different from the tuning that does the job on another.
Earl,
I got more details on those measurements from my customer:
"The measurements I took were without any correction -- I didn't do any and there was none built in to the test CD. The reference level was 70 dB.
"It was minus 5 dB starting at 23 Hz, was minus 3 dB at 27 Hz, but then had a 8 dB peak at about 40 Hz. It then it headed straight down to about minus 20 dB at about 60 Hz. There was another 18 dB valley at about 90 Hz and another at about 115 Hz. There were a couple of sharp (narrow) 13-15 dB peaks at about 140 and 160 Hz and another valley 12 dB valley at about 290 Hz."
I suspect his "too much bass" is from the peak at 40 Hz.
Here is a link to a page about corrections for readings taken with the Radio Shack SPL meter:
http://www.svsound.com/questions-faqs-rscomp.cfm
The recommended correction at 25 Hz is +5 dB, so the customer's reading of -5 dB at 23 Hz is pretty close to "flat".
The speaker system uses the Pioneer TAD TL-1102 [Fs = 31 Hz, Qts = .30, Qes = .32, Vas = 121 liters, Re = 7.1 ohms] in a 4.4 cubic foot vented box tuned to 26 Hz, and the amp's output impedance is .5 ohms. The series resistance of the crossover inductors adds another .69 ohms. I'm not asking you to crunch any numbers - just giving you the data.
Duke
part of my point was that RGC tuning is different from EBS tuning. For one thing RGC calls for either a smaller box or lower tuning than EBS, as the bass shelf that characterizes EBS would be an undesirable feature... if indeed the real world works as I have postulated.
For another, the term "Room Gain Complementary" is really more of a concept than a specific alignment, as the tuning that does the job in one situation may well be different from the tuning that does the job on another.
Earl,
I got more details on those measurements from my customer:
"The measurements I took were without any correction -- I didn't do any and there was none built in to the test CD. The reference level was 70 dB.
"It was minus 5 dB starting at 23 Hz, was minus 3 dB at 27 Hz, but then had a 8 dB peak at about 40 Hz. It then it headed straight down to about minus 20 dB at about 60 Hz. There was another 18 dB valley at about 90 Hz and another at about 115 Hz. There were a couple of sharp (narrow) 13-15 dB peaks at about 140 and 160 Hz and another valley 12 dB valley at about 290 Hz."
I suspect his "too much bass" is from the peak at 40 Hz.
Here is a link to a page about corrections for readings taken with the Radio Shack SPL meter:
http://www.svsound.com/questions-faqs-rscomp.cfm
The recommended correction at 25 Hz is +5 dB, so the customer's reading of -5 dB at 23 Hz is pretty close to "flat".
The speaker system uses the Pioneer TAD TL-1102 [Fs = 31 Hz, Qts = .30, Qes = .32, Vas = 121 liters, Re = 7.1 ohms] in a 4.4 cubic foot vented box tuned to 26 Hz, and the amp's output impedance is .5 ohms. The series resistance of the crossover inductors adds another .69 ohms. I'm not asking you to crunch any numbers - just giving you the data.
Duke
Earl,
Ah yes... my bad. Ambiguous wording.
A claim of "flat" - as in no significant peaks or dips - to the lower 20's would have set off my BS detectors, too!
On another subject - does the bass in your downstairs room change audibly between door-open and door-closed? If so, would that be an effect of room pressurization, or increased damping with the door open (perhaps acting as bass trap), or what?
In that big room in New Orleans, there was an audible change in the bass between multipe doors open and all the doors closed.
Duke
Ah yes... my bad. Ambiguous wording.
A claim of "flat" - as in no significant peaks or dips - to the lower 20's would have set off my BS detectors, too!
On another subject - does the bass in your downstairs room change audibly between door-open and door-closed? If so, would that be an effect of room pressurization, or increased damping with the door open (perhaps acting as bass trap), or what?
In that big room in New Orleans, there was an audible change in the bass between multipe doors open and all the doors closed.
Duke
Earl, at one time you penned some outside-the-box thinking (surprise, surprise) on the psychophysics of low-frequency reverberation:
"In a small room, we all know that the modal density is low. This yields large peaks and dips in the response, which with multiple sources gets smoother, but the limiting factor is still the room configuration. The only way to smooth this limiting room response is to use a large amount of LF damping. This is the solution that I recommend. But, and here is the downside, as a result, the reverberation at these lower frequencies goes way down. There is essentially no LF reverberation field at all in this kind room.
"Some might say that this is a good thing, and I would probably have said that some years back, except for a recent experiment that I did that convinced me otherwise. Now at HF, there is no doubt that a strong reverberant field is a good thing, given the right kind of sources, etc. (see my white paper, same web site).
"I had a second pair of Summas that I needed to store, so I put them in my living room - may as well set them up! Now this room is pretty big, (> 15 foot ceiling, very open space, etc.) and VERY live (wooden floor stone fireplace, leather furniture). The thing that struck me was the impressive perception of the bass. The highs sounded about the same as the theater, as would be expected since the room is less of a dominate factor at these frequencies, especially with Summas, but the bass was dramtically better.
"I specifically used the word "perception" since the actual measured response in this room was not notably different than in my theater. THIS intrigued me immensly, especially since I had been studying this problem for decades.
"Now, I had always known that bass sounded very good in an auditorium. Some years back, my brother, a bass player, and I once talked about this at a concert. He asked me why the bass always sounded so good in a big room. I have hought about this a lot over the years. I could explain the physics of the problem well enough, but the psychophysics of the perception was not at all clear to me.
"This question and my recent experinces have led me to the conclusion that it is the large reverberant field in a large room that yields that full bass sound without it being overly oppressive. This makes eminent sense since our perception of loudness and pitch is strongly influenced by the duration of a signal. A very short bass note is very difficult to sense the pitch and it's actual loudness seems negligable. We can raise the volume to overcome the loudness problem (ala Fletcher Munson), but this still leaves the pitch difficult to *****. This is basic psychoacoustics.
"In a big room with a lot of LF reverberation the bass is clean and clear with no need for increased output to give a perception of loudness. This then is the difference between the large room and the small room - the reverberation at LF. You see it's the modes that carry the energy in the reverberant field and the lack of modes creates an inevitable lack of reverberant energy.
"So why not make the small room reverberant? First, this can only be done to a limited extent for the modal reason given above, and second a small reverberant room will have a large spatial and frequency variation in the sound field that cannot be removed with EQ or any other technique that I know of except adding damping. But then the damping kills the reverberant field and we are left with that muddy (non-clear or pitch-perception-difficult) bass that we are trying to avoid.
"So you see, IMO, there is no real solution to this problem. We will have to take the tradeoffs one way or the other, but, for a small room, we will always have to live with poor bass of one kind or another.
"I am working on a concept of making the subs reverberant with the hope of creating a simulated reverberant field in the small room. But this is an elaborate and difficult to impliment solution to this critical problem. Only time will tell. I'll let you know if I manage to solve this problem." - Speaker Asylum post, October 30, 2005
Has there been any significant change in your thinking on the subject?
Thanks,
Duke
"In a small room, we all know that the modal density is low. This yields large peaks and dips in the response, which with multiple sources gets smoother, but the limiting factor is still the room configuration. The only way to smooth this limiting room response is to use a large amount of LF damping. This is the solution that I recommend. But, and here is the downside, as a result, the reverberation at these lower frequencies goes way down. There is essentially no LF reverberation field at all in this kind room.
"Some might say that this is a good thing, and I would probably have said that some years back, except for a recent experiment that I did that convinced me otherwise. Now at HF, there is no doubt that a strong reverberant field is a good thing, given the right kind of sources, etc. (see my white paper, same web site).
"I had a second pair of Summas that I needed to store, so I put them in my living room - may as well set them up! Now this room is pretty big, (> 15 foot ceiling, very open space, etc.) and VERY live (wooden floor stone fireplace, leather furniture). The thing that struck me was the impressive perception of the bass. The highs sounded about the same as the theater, as would be expected since the room is less of a dominate factor at these frequencies, especially with Summas, but the bass was dramtically better.
"I specifically used the word "perception" since the actual measured response in this room was not notably different than in my theater. THIS intrigued me immensly, especially since I had been studying this problem for decades.
"Now, I had always known that bass sounded very good in an auditorium. Some years back, my brother, a bass player, and I once talked about this at a concert. He asked me why the bass always sounded so good in a big room. I have hought about this a lot over the years. I could explain the physics of the problem well enough, but the psychophysics of the perception was not at all clear to me.
"This question and my recent experinces have led me to the conclusion that it is the large reverberant field in a large room that yields that full bass sound without it being overly oppressive. This makes eminent sense since our perception of loudness and pitch is strongly influenced by the duration of a signal. A very short bass note is very difficult to sense the pitch and it's actual loudness seems negligable. We can raise the volume to overcome the loudness problem (ala Fletcher Munson), but this still leaves the pitch difficult to *****. This is basic psychoacoustics.
"In a big room with a lot of LF reverberation the bass is clean and clear with no need for increased output to give a perception of loudness. This then is the difference between the large room and the small room - the reverberation at LF. You see it's the modes that carry the energy in the reverberant field and the lack of modes creates an inevitable lack of reverberant energy.
"So why not make the small room reverberant? First, this can only be done to a limited extent for the modal reason given above, and second a small reverberant room will have a large spatial and frequency variation in the sound field that cannot be removed with EQ or any other technique that I know of except adding damping. But then the damping kills the reverberant field and we are left with that muddy (non-clear or pitch-perception-difficult) bass that we are trying to avoid.
"So you see, IMO, there is no real solution to this problem. We will have to take the tradeoffs one way or the other, but, for a small room, we will always have to live with poor bass of one kind or another.
"I am working on a concept of making the subs reverberant with the hope of creating a simulated reverberant field in the small room. But this is an elaborate and difficult to impliment solution to this critical problem. Only time will tell. I'll let you know if I manage to solve this problem." - Speaker Asylum post, October 30, 2005
Has there been any significant change in your thinking on the subject?
Thanks,
Duke
gedlee said:
Thank you for your elaborate reply.
Could you seal your HVAC with a solid oak external double trap and take some LF measurements for fun ?
I'd really like to see some pressure vessel gain... 
You say the physics says that there isn't any gain. Why all this talk about pressure vessel gain when wavelength is too long for a room ? I was thinking that was basic objective audio theory supported by physics... Is there a formula or something, or it's 100% pure myth, 100% pure subjective ******** ? We should call Mythbusters on this ! I've been fooled !
Thanks again !
No its not 100% myth, there is a pressure vessel effect, but its strongly dependent on factors which are very hard to quantify and hence its very hard to scale or calibate the effect. It's like the skin effect in wire - sure it occurs at audio frequencies, but the effect is insignificant (true but irrelavent). I have always LOOKED for this effect, especially since finding it and identifying it back in 1983 in several papers on car acoustics. But I have yet to find it in a room in a home.
If you sealed a small room airtight, you would certainly see the effect, but thats simply not possible, and the leakage is what determines the scale of the effect. The leakage relative to the room volume is very high in a room larger than a car (think of the effect to go as 1 / (room volume * leakage), it takes very low leakage to get this effect in a large room). Thus the effect is there, its simply miniscule. Cars show this effect, vans don't, unless they are sealed by ellaborate means. They do this in the SPL races.
But in a home listening room - don't count on it.
Once again, don't count on much of anything at LFs in a room, thats the point I keep trying to make. You have to have an approach that works in any room and that approach is multiple subs (as best as I can tell). Everyone is or has come to this conclusion. But you do need to do some custom tailoring to get this right. I'm thinking about some PC software that will do this as its not that hard to do, but you have to have some way to measure the results. Otherwise its just a shot in the dark.
If you sealed a small room airtight, you would certainly see the effect, but thats simply not possible, and the leakage is what determines the scale of the effect. The leakage relative to the room volume is very high in a room larger than a car (think of the effect to go as 1 / (room volume * leakage), it takes very low leakage to get this effect in a large room). Thus the effect is there, its simply miniscule. Cars show this effect, vans don't, unless they are sealed by ellaborate means. They do this in the SPL races.
But in a home listening room - don't count on it.
Once again, don't count on much of anything at LFs in a room, thats the point I keep trying to make. You have to have an approach that works in any room and that approach is multiple subs (as best as I can tell). Everyone is or has come to this conclusion. But you do need to do some custom tailoring to get this right. I'm thinking about some PC software that will do this as its not that hard to do, but you have to have some way to measure the results. Otherwise its just a shot in the dark.
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