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Seperate drivers for LF and ULF or one driver? - Page 3

post #61 of 354
Is it really that complex to high pass a ported enclosure say the 25hz tuned jbl then hand off to an IB or multiple sealed to get to single digits? Getting down to 25hz-easy. Down to single digits = displacement and potentially eq and POWER depending on application. just seems that getting a 3 way speaker to play nice would be much harder. I'm probably under estimating the task just typing out loud.
post #62 of 354
Quote:
Originally Posted by gpmbc View Post

Is it really that complex to high pass a ported enclosure say the 25hz tuned jbl then hand off to an IB or multiple sealed to get to single digits? Getting down to 25hz-easy. Down to single digits = displacement and potentially eq and POWER depending on application. just seems that getting a 3 way speaker to play nice would be much harder. I'm probably under estimating the task just typing out loud.

Plenty of things to take into consideration. Placement of the speakers, which in turn creates phase and delay/ cancellation issues. Get these fixed and EQ, then you are all set. Notice around 50hz how hairy it gets, this is exactly where my crossover is set. Obviously takes some work to fix these issues, and Ive already eq'd that out somewhat...

post #63 of 354
Quote:
Originally Posted by bossobass View Post

"You no longer have waves reflecting around the room". Sound waves that don't reflect? OK, where do the waves go if they don't reflect around the room? If you can't grasp this part of it, you'll never understand the phenomenon at all, much less explain it.
"the more openings that you have in the room, the less the pressure builds and the less gain that you get".
Window shut vs window open. If what you were saying is true, the low end would immediately revert back to anechoic response. Instead, the opposite occurs. This is what we call evidence. It calls into question the myth that says the more a room is sealed, the more low end boost it will exhibit at the LP.
FRnopostEQwindowshutopen.jpg
The whole room is not being compressed and decompressed. It behaves nothing like a hyperbaric chamber, wherein the pressure is changed from introduction of additional atmosphere from an external source. I don't see how you can confuse the difference.
Why does Josh measure out in a field? Why does he then lay the microphone on the ground? Why does he place the microphone at 2M instead of 1M? How does his microphone record the sound? Does atmospheric pressure change while he's measuring?
Unless you show me some evidence from a credible source that supports your claims, I have to move on from this train wreck. I hope the OP goes with something like the UXL or LMS and shows the results of his experiments.

several people have explained the concept serveral times. we will just have to agree to disagree.

as for how you can get more bass with a window open vs. a window closed. one possiblity is that you are turning your entire room into a helmholtz resonator...essentially a giant ported sub, with the port being the window. that could provide an increase in the bass vs. a sealed room.

josh's measurements outdoors present the sound to the microphone in the way that you understand sound to operate. from low frequencies to high frequencies, it will all be the same. a zone of high pressure followed by low pressure moves from the source toward and across the microphone and there is no 12db/oct gain in any of his measurements.

---

as for the op, i think scott was planning to use his 2226's up to about 350hz(?) or so, so he will need something in between his large sealed low end and his midhorn.

it might also be worth taking note that there is a low inductance 18" on the way from ist (the guys who make the uxl) called the lle-18.

dayton has the rss390hf and the rss390ho. the former is described as a "sound quality" sub. it has 1/2 the coil windings and 1/2 the normalized inductance.

alpine has three versions of essentially the same 12" sub. the primary difference between the three is the greater use of copper for the purpose of inductance control.

while all three may just be marketing ploys, inductance and its related effects have been implicated in "sound quality" from john j. to jbl.

so inductance might be one place to look for transient response or what bosso calls signal tracking.

another area to look for sound differences is energy storage. a well damped driver will sound subjectively different from a poorly damped one, even eq'd similarly.

somebody tested a jbl 2241 vs the 2242 same room same cab. the 2242 has lower inductance, more linear inductance, and better damping. it was described as subjectively better.

another guy tested the jbl 2268 vs the 2242 same room same cab. the 2242 has better damping. again subjectively better.

i suspect that most of what we hear is frequency response and compression distortion, but these other effects may be partial contributors to what people subjectively describe as "fast or slow bass"--even though we all know 60hz is 60hz--particularly energy storage.

these effects don't show up in frequency response and they don't show up in harmonic distortion, so there is something else at work.

cheers,
post #64 of 354
John. Nope, the JBL's are what's in between the midhorn and subs. The sub system will extend the response of the mains speakers just like everyone else system's do. You'll see. wink.gif

Beast. Plug. Those. Ports. Try again. tongue.gif
post #65 of 354
Quote:
Originally Posted by Scott Simonian View Post

John. Nope, the JBL's are what's in between the midhorn and subs. The sub system will extend the response of the mains speakers just like everyone else system's do. You'll see. wink.gif
Beast. Plug. Those. Ports. Try again. tongue.gif

Duly noted, I am certainly planning on it, just waiting on the other cab to get here now. I should have it next weekend, so then im back in the game!!!!
post #66 of 354
Quote:
Originally Posted by Bunga99 View Post

That’s interesting and impressive!! Just curious as I dont have the answer but does the doors swing open in the room or out of the room - meaning if you are in the room, do you pull the doors to open or push them to open or both Push/pull?

I push the doors open when inside.
post #67 of 354
"John. Nope, the JBL's are what's in between the midhorn and subs."

that is what i said. you will need something between your ulf sealed subs and your midhorn...the 2226's are playing that role.

...

i think that with this idea that the room is a helmholtz resonator, we might be onto something.

just doing some quick calculations, a 2400 cubic foot room with a 24"x24"x4" open window will tune the room to 5hz.

all the air leaks in a room might be behaving like a port.

so with a window open or the doors open, bosso and mk are running "sealed subs in a ported room". :-)
post #68 of 354
Thread Starter 
Quote:
Originally Posted by beastaudio View Post

Plenty of things to take into consideration. Placement of the speakers, which in turn creates phase and delay/ cancellation issues. Get these fixed and EQ, then you are all set. Notice around 50hz how hairy it gets, this is exactly where my crossover is set. Obviously takes some work to fix these issues, and Ive already eq'd that out somewhat...

But these Are the same things which happens When using multiple subs and by crossing mains to subs at 80hz...? Why is it more complex than a new component crossed at 30hz?
post #69 of 354
Quote:
Originally Posted by JonasHansen View Post

But these Are the same things which happens When using multiple subs and by crossing mains to subs at 80hz...? Why is it more complex than a new component crossed at 30hz?

Couple reasons, that are easily doable. In most cases people use audyssey or the like to automatically get the handoff right between mains and subs. Adding a third speaker to cover more of the range requires some type of unit like the miniDSP or dcx to make an all new handshake between the components. so just right there you are incorporating another component into the chain. Im sure some could get lucky without having to do this, but I am certainly not one of them thus far. After all that, understanding phase and delay and how to adjust everything to play nicely together, takes a little bit of time. Im still learning the ins and outs for sure. Bottom line though is, more of the same sub in multiples, is a much easier way to possibly achieve something similar to two different types of subs could ALSO do.

I went on this adventure to try and get some more midbass back that I have been missing since my f-20's and I parted company and to handle some of the efficiency issues the XXX18's have further up in their passband. I couldve gone for two more RE's and fixed it all, but this route cost about half as much as that, so i figured I would try it first. when i go for some more RE's, ill repurpose the jbl drivers for some SEOS mains or something. biggrin.gif
post #70 of 354
Quote:
Originally Posted by noah katz View Post

You seem to be engaging in black-or-white thinking and over-defined a pressure change as only being such if static.
What is your response to LTD's point about room gain?
If the pressure is not increasing, there can be no increase in SPL, where the P stands for pressure.
As freq decreases the pressure moves from local toward ambient.
In a perfectly sealed room, it would be a static increase in barometric pressure.
The fact that no room is perfectly sealed in no way nullifies the concept, but merely reduces its effect.

Regarding room gain, there are 2 schools. Back in '95, Nousaine was smart enough to briefly mention the 2 camps, but just presented measurements of the phenomenon in car cabins and in his living room and avoided joining either camp, much less including any of his own data to support or refute either theory.

I'm obviously of the school who believes the phenomenon results strictly from boundary gain. Below the magic distance-to-wavelength number, you simply eliminate the destructive influences of standing waves and destructive to unity reflections, which leaves constructive reflections vs transmission losses.

I base everything I do in low frequency reproduction on the weight of the evidence, not far-fetched thought experiments or personal preference, especially personal preferences that are solely the result of liking what someone said and not backed by data. That's why I get positive results from my efforts.

The idea that a drivers cone increases and decreases a rooms atmosphere during its production of a sound pressure wave is just silly to me. The movement/size of the cone has such a negligible effect on the atmospheric volume of a leaky room as to be immeasurably small. Anyone here please feel free to produce measurements that will change my position.

Yes, the 'P' is for pressure, but the 'S' is for sound, not atmospheric or barometric. SPL is a measurement of sound pressure in air, not barometric pressure that fluctuates in a room, which invented phenomenon is impossible to affect with a drivers cone and would not produced sound if it was. This is based on the complete absence of any data anywhere to support such a notion. Anyone here please feel free to produce data that will change my position.

OTOH, boundary gain across the entire frequency spectrum is easily measured and has been documented and is equally easily harmonic with the phenomena of standing waves, destructive, constructive and unity reflections, the law of reflection, boundary construction transmission losses, boundary-induced pressure zones, sympathetic boundary resonances and transmission losses proportional to wavelength.

MKT's experiences and measurements are in harmony with my understanding of the phenomenon, as are my own experiences and data even though his room is far better sealed and of masonry construction vs my 2nd floor frame and far more air lossy room.

I would also like to chuckle out loud regarding the window open vs shut measurement I posted being explained away as turning the room into a ported sub. W-O-W. Yeah, I can see the drivers excursion drop to nothing at 7 Hz as I sit on the wrong side of the port inside of what would actually be a bandpass sub, not a ported sub. And, what happened to the barometric pressure baloney in this explanation? I thought dipoles and ported subs need not apply? Like the whole pressure pot theory, there's no evidence and the invented explanations get crazier and crazier.
post #71 of 354
Quote:
Originally Posted by beastaudio View Post

Duly noted, I am certainly planning on it, just waiting on the other cab to get here now. I should have it next weekend, so then im back in the game!!!!

Nice! I am very much awaiting your results. I'm pretty sure you'll get positive results with a little work. smile.gif

Quote:
Originally Posted by LTD02 View Post

"John. Nope, the JBL's are what's in between the midhorn and subs."
that is what i said. you will need something between your ulf sealed subs and your midhorn...the 2226's are playing that role.
...
:-)

Oh, lol. Silly me. redface.gif I thought you meant something to go between the JBL's and the RLp's. tongue.gif
post #72 of 354
"I would also like to chuckle out loud regarding the window open vs shut measurement I posted being explained away as turning the room into a ported sub. W-O-W. Yeah, I can see the drivers excursion drop to nothing at 7 Hz as I sit on the wrong side of the port inside of what would actually be a bandpass sub, not a ported sub. And, what happened to the barometric pressure baloney in this explanation? I thought dipoles and ported subs need not apply? Like the whole pressure pot theory, there's no evidence and the invented explanations get crazier and crazier."

laughter is healthy, but that is what you have done. you are correct that it would be a 4th order bandpass and not a ported. thanks for the correction. a 4 cubic foot rear chamber (the sealed sub) placed in a 2400 cubic foot front chamber (the room) with a 24"x24"x4" port (the window) tunes the system to 5.2hz. that is consistent with your own data!

in such a bandpass, the drivers' excursion would not drop to a minimum like a ported sub. have a look. it would continue to increase in excursion as frequency response falls.

the pressure baloney is alive and well, just as it is above tuning in the front chamber of a bandpass sub. if the pressure did not increase and decrease in the front chamber of a bandpass sub, then all the air would simply blow in and out the port and bandpass subs would produce no gain. that is your argument and it is just plain wrong.

look at it this way, if all the air just blew out of every opening without respect to frequency, a ported sub would not work. the driver would move and the air would just be pushed out of the sub. that is not how it works.

to your last point, that is not what i said. i said ported subs *below tuning* don't pressurize a room and that is born out in the data. above tuning, ported subs absolutely can pressure a room in the pressure vessel gain region.

the evidence is overwhleming.
post #73 of 354
Quote:
Originally Posted by tuxedocivic View Post

I'm extending what's being said and asking, do high frequencies act as atmospheric pressures also? No they don't. Very low frequencies are no different, they just behave with the room differently than very high frequencies.

Yes, they do, or would, if they were in a room with the same dimensions and loss properties relative to their wavelength as low freq.
Quote:
Originally Posted by bossobass View Post


1. Below the magic distance-to-wavelength number, you simply eliminate the destructive influences of standing waves and destructive to unity reflections, which leaves constructive reflections vs transmission losses.

I'll offer an analogy to explain what I meant by it being peculiar to talk about wavelengths many times longer than the room reflecting.

Take a bathtub half full of water.

The height of the water at any point on the surface is analogous to pressure.

There's a block of wood partly submerged that can be driven up and down.

If the time between cycles is short compared to how long it takes waves to propagate to the walls of the tub, i.e. the freq is high, visible waves on the surface will propagate and reflect from the tub walls; there will be standing waves (modes), same as in a room

However at very low freq the overall water level will rise and fall more or less uniformly throughout the tub and there will be no discernible waves.

The water level/pressure changes, but I would submit that there is no wave, so how can they reflect and constructively/destructively interfere?

2. The idea that a drivers cone increases and decreases a rooms atmosphere during its production of a sound pressure wave is just silly to me.

3. Yes, the 'P' is for pressure, but the 'S' is for sound, not atmospheric or barometric. SPL is a measurement of sound pressure in air, not barometric pressure that fluctuates in a room, which invented phenomenon is impossible to affect with a drivers cone and would not produced sound if it was.

Once again, pressure is pressure, whether it be SPL or barometric; if that's too "silly" for you to comprehend, so be it.

A pressure transducer will as easily measure SPL or barometric pressure, and again, you're inventing false distinctions between them, I guess do to the very differnt ways they subjectively manifest.

You demand evidence; here is some:

Our UV solar telescopes use thin film filters (1500 A of aluminum) to block visible light but allow UV to get through.

They're subject to damage by excessive SPL from the rocket motors at launch.

When we couldn't find microphones small to fit inside to measure the SPL, we instead used tiny pressure sensors and converted the pressure to SPL.

Edited by noah katz - 8/2/12 at 11:09pm
post #74 of 354
"Oh, lol. Silly me."

nah, my post was a little unclear; it's cool. i don't see much that is wrong with your plan other than it is extreme overkill, and i refuse to put that in the category of doing anything wrong. :-)
post #75 of 354
"I'm obviously of the school who believes the phenomenon results strictly from boundary gain. Below the magic distance-to-wavelength number, you simply eliminate the destructive influences of standing waves and destructive to unity reflections, which leaves constructive reflections vs transmission losses."

that is not how it works at all. boundary gain (moving from 1/2 to 1/4 to 1/8 space gives you a non frequency dependant increase of 6db spl assuming a theoretical boundary loaded point source per halving of space) has nothing to do with pressure vessel gain (the pressure that builds and in turn the spl that builds at 12db/oct below what you call the "magic frequency"--what others would call about 1/2 wavelength vs. the long dimension of the "room").

the two are entirely different topics, though both have application in home bass spl.

pressure vessel gain is based on the volume of the room and the wavelength being produced.

you can call it a "magic distance" all day long, but you can't change physics.
post #76 of 354
Thread Starter 
Quote:
Originally Posted by beastaudio View Post

Couple reasons, that are easily doable. In most cases people use audyssey or the like to automatically get the handoff right between mains and subs. Adding a third speaker to cover more of the range requires some type of unit like the miniDSP or dcx to make an all new handshake between the components. so just right there you are incorporating another component into the chain. Im sure some could get lucky without having to do this, but I am certainly not one of them thus far. After all that, understanding phase and delay and how to adjust everything to play nicely together, takes a little bit of time. Im still learning the ins and outs for sure. Bottom line though is, more of the same sub in multiples, is a much easier way to possibly achieve something similar to two different types of subs could ALSO do.
I went on this adventure to try and get some more midbass back that I have been missing since my f-20's and I parted company and to handle some of the efficiency issues the XXX18's have further up in their passband. I couldve gone for two more RE's and fixed it all, but this route cost about half as much as that, so i figured I would try it first. when i go for some more RE's, ill repurpose the jbl drivers for some SEOS mains or something. biggrin.gif
You Are right... If one is a audyssey black box type of guy, it will never be good. But with the right knowledge and equipment, it will be just the same as integrating mains to subs.

But I would prefer a subwoofer solution for both lf and ulf. Have you heard about Earthquake diverse? They have some modified versions of their car drivers which are optimized for home use. BL of 50 and 4" xmax... Seems interesting!
post #77 of 354
Quote:
Originally Posted by JonasHansen View Post

You Are right... If one is a audyssey black box type of guy, it will never be good. But with the right knowledge and equipment, it will be just the same as integrating mains to subs.
But I would prefer a subwoofer solution for both lf and ulf. Have you heard about Earthquake diverse? They have some modified versions of their car drivers which are optimized for home use. BL of 50 and 4" xmax... Seems interesting!

Ill look into that, 4 inches peak to peak is fun though smile.gif (the RE's can do that too)

In most cases folks are for the most part "plug and play" I know around this forum that we all go much further than the typical home theater person could even fathom. My local installer thinks I am insane... As you said, with a little extra work, it is easily doable to accomplish much more than the typical high-end system, and put your own little personal touch on your setup. Most people to care or even see the need to go that extra step, but that is what separates their systems from the big ones... and I will never go back to that.
post #78 of 354
http://www.earthquakesound.com/holees.htm

i don't see any specs, just a bunch of marketing hoopla. 4" xmax i suspect is a fraud.

msrp $2499.
post #79 of 354
Quote:
Originally Posted by LTD02 View Post

http://www.earthquakesound.com/holees.htm
i don't see any specs, just a bunch of marketing hoopla. 4" xmax i suspect is a fraud.
msrp $2499.


MODEL: HoLeeS-15"

•15,000 Watts MAX
•Xmax: 4" Peak to Peak So Xmax is 2-inch
•Dual (2x1ohms) 4" x 8" High Temp military grade flat wire voice coil.
•(4)Quad Nomax / Romax spiders
•8 gauge speaker connections
•112lbs.
•Patented PSP terminal
•MSRP: $2,499.00
post #80 of 354
Thread Starter 
post #81 of 354
ah, so they just tried to copy the lms ultra response in a 15" with more throw.

they both have pretty much the same 1w1m frequency response in a 4 cubic footer tuned to 23hz and roughly the same max spl if the earthquake specs are accurate...why would anybody doubt the earthquake xmax spec? :-)

bottom line, the lms is there for less than half the price.
post #82 of 354
Quote:
Originally Posted by noah katz View Post


The height of the water at any point on the surface is analogous to pressure.

However at very low freq the overall water level will rise and fall more or less uniformly throughout the tub and there will be no discernible waves.

The water level/pressure changes, but I would submit that there is no wave, so how can they reflect and constructively/destructively interfere?

Once again, pressure is pressure, whether it be SPL or barometric; if that's too "silly" for you to comprehend, so be it.

Water waves are irrelevant to the conversation. Your illustration is one of displacing the water with a solid object and your premise is that just because you plunge the solid object into, then pull it out of the water more slowly that you aren't creating reflections at the tubs walls. Failing to mention that the water is in a water tight container is convenient as well. What happens to your analogy when you unstop the bathtub drain? Just as with the "pressure is pressure" generalization (my masseuse applies pressure but that doesn't mean it relates to the discussion), these generalizations do nothing to prove the premise.

Bathtubs, spaceships and syringes, everything but a subwoofer in a room.

Here is what evokes the 'silliness' comment, and maybe you can address it directly without taking me out to sea or into outer space:

I wanted to look more realistically at the syringe illustration that's "a little out of scale" and bring it a little more into scale. I took the volume, boundary area and air loss area of my room and drew it as a syringe, roughly to scale. The 'plunger' is the equivalent Sd to a 4 X 15 sub, which is what I used to create the window open/shut graph and the opening, far from being even close to the hole in a needle in the syringe example, is equivalent to the openings in my room:

Syringe-1.jpg

Of course, I've worked at a drawing table for some 35 years as part of my job description and hobbies, so I didn't need to draw it for my own benefit. I was able to picture the actual scale quite like the drawing shows, thus my 'silly' comments.

The theory that the cone causes an ambient atmospheric change simply by reducing the frequency of of it's motion is... well, silly and as far as 'ignoring the calculations' goes, feel free to use the scaled drawing to make new ones that might actually be relevant. I don't need calculations for this one. It's a no-brainer.

In a perfectly air tight chamber, cone motion would cause a fluctuation in ambient atmospheric pressure at all frequencies. That does not mean that there would not be reflections or at some 'magic frequency' between 3-120 Hz reflections cease to exist. Do sound waves behave differently in an airtight enclosure? Dunno, I'll leave that to you because, although it might be interesting, it is irrelevant information.

Sound waves move through the air at the speed of sound through air. There is a point source where the sound wave begins and ends. There will be reflections. Those reflections will be either constructive, destructive or unity and everything in between. They will set up standing waves between parallel surfaces if the wavelength is twice the distance between the parallel surfaces. They will excite sympathetic resonances. At some room dimension-dependent frequency a room will no longer have the ability to support a standing wave (this does not mean the room exhibits no modal behavior below that point). As frequency decreases below that point, more and more of the rooms surfaces will cause only constructive reflections.

This is where I'm coming from, based on my own experiences and measurements. I would appreciate actual data or evidence that adds to or refutes any of the following:

Air losses (increase or decrease) do not change room gain. I've documented this with accurate-to-4 Hz measurements. I've done measurement comparisons with the doorway open vs sealed, with a window open vs sealed and with all 3 openings open vs sealed. All results in the so-called PVG region were either unchanged or the opposite of what would be predicted if the pressure pot theory were correct.

Separate placement of multiple subs can cause cancellation in the so-called PVG region. I've documented this with accurate-to-4 Hz measurements, many times. If there are no reflections of sound waves, if the pressure pot theory is correct, this result would be at least worth examination.

The SPL varies by varying the position of the microphone in the room. If there are no reflections, this also would at least be worth examination.

If the pressure pot theory is correct, how exactly does the room gain increase as frequency decreases? In nearly every sub I've built, I model to limit excursion with enclosure size and signal chain roll off. This means that driver excursion at 5 Hz is approximately the same as it is at 10 Hz, yet from 10 Hz to 5 Hz there is a room gain increase of +13dB.
post #83 of 354
Quote:
Originally Posted by LTD02 View Post

boundary gain (moving from 1/2 to 1/4 to 1/8 space gives you a non frequency dependant increase of 6db spl assuming a theoretical boundary loaded point source per halving of space)
Boundary gain is very frequency dependent.
http://www.synaudcon.com/site/author/pat-brown/how-boundaries-affect-loudspeakers/
post #84 of 354
Quote:
Originally Posted by bossobass View Post

The theory that the cone causes an ambient atmospheric change simply by reducing the frequency of of it's motion is... well, silly.

Yep; good thing no one said that.
Quote:
Originally Posted by bossobass View Post

If the pressure pot theory is correct, how exactly does the room gain increase as frequency decreases? In nearly every sub I've built, I model to limit excursion with enclosure size and signal chain roll off. This means that driver excursion at 5 Hz is approximately the same as it is at 10 Hz, yet from 10 Hz to 5 Hz there is a room gain increase of +13dB.

As freq decreases, the wave more closely approaches being in phase everywhere in the room; there is less time for a "ripple" to form and travel away from the source.

As waves travel away from the source and expand, they become weaker, and they do this progressively less as freq decreases.

What's your explanation?

If you're going to say "room gain", explain how that works.
Edited by noah katz - 8/4/12 at 3:12pm
post #85 of 354
I think he already explained how room gain works. I said it previously as well. As frequency decreases, the waves become more and more constructive. At VLF there's no destructive waves. That's how it works. Really, it's a simpler explanation than ambient pressure fluctuation. That calls in all kinds of wave behaviour questions.

I thought this was a given. Had no idea this was so misunderstood. I don't normally participate in the subwoofer threads. This is Physics 101. I'll go dig out my text book and do some reading...
post #86 of 354
I'm not debating what room gain is or how it works, I'm just making a very simple statement of a physical fact.

P in SPL is for pressure, and it's a simple units conversion from psi to SPL.

From http://www.silcom.com/~aludwig/Physics/UNITS&.html

1 atm = 14.7 psi = 197.1 dB SPL

By definition, if the SPL is greater, pressure is greater.

If the SPL is higher, the pressure moving the mike diaphragm which measures SPL is higher, no?

If not, what's making it move?
post #87 of 354
I'll keep reading my book to be sure, but it's about pressure differential. If ambient pressure increases, then the mic sees no change, because pressure on both sides of the diaphragm will be the same. I'm not 100% on this though.
post #88 of 354
"Boundary gain is very frequency dependent."

for speakers, yes, but that is not what i said. i said theoretical point source.
post #89 of 354
geddes, who did his phd work in the acoustics of small rooms, said that from the modal region down, the entire pressure rises and falls with no apparent wave propagation (i added the bold).

"In a small room in the modal region, the SPL rises rather slowly at the individual modes as the energy builds up. The point about this NOT being like a propagating sound wave is quite correct. The pressure throughout the room basically rise and falls virtually in unison at every point. Think about the rise time of a mode compared with the wave propagation time. If you plot out the pressure around the room you will see that the wave travels around faster than the pressure can respond and the entire room pressure rises and falls with no apparent wave propagtion. Once we reach the modaly dense region then this effect goes away because the wavelengths are shorter and the modes are denser."

http://www.diyaudio.com/forums/multi-way/121590-cardioid-bass-13.html

i'll keep looking around for something a little better.
post #90 of 354
the geddess quote above is not completely accurate, as when you are in the modal region, there are still high pressure and high velocity zones, so pressure won't be identical everywhere in the room and this is what causes the peaks and nulls. what he is saying would more precisely be said as in the "pressure zones" in the modal region the pressure rises and falls everywhere at the same time...below the lowest room mode, which is the "magic frequency", the whole room behaves as a pressure zone, so pressure rises and falls everywhere.
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