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Seperate drivers for LF and ULF or one driver? - Page 2

post #31 of 354
Quote:
Originally Posted by desertdome View Post

Don't these charts of Ricci's show that at 63 Hz, the JBL was over 10 dB higher with less distortion than the PB13-Ultra?

I was only looking at the prog sweeps graphs which reflect the headroom across the subs BW. Using the 115dB sweep for each, where the JBL is already exceeding 10% THD at 40 Hz, the JBL gives 9% THD at 60 Hz and the PB Ultra gives 5%. Of course, the JBL will play louder above 40 Hz because that's what it's designed to do, but it's claimed to be tuned to 25 Hz, so I look at the system when looking at a single frequency. This is part of the problem. When the JBL is pushed to it's maximum output numbers, it reeks of harmonics above and below tune, giving over 300% THD below 20 Hz, which unquestionably changes subjective perception of its SQ.

Filtering the sub as part of a 2-way will change the subs headroom numbers dramatically, so the OP is doing the right thing. I just have 2 issues: 1) 60 Hz is 60 Hz. It's far less troublesome and cheaper to just use the proper drivers in a smaller package and avoid a crossover altogether and 2) I would choose a higher cross point for the reasons I've mentioned and looking at the subs actual FR.
post #32 of 354
"'Exactly' how does a subwoofer change the volume of a room?"

is this a trick question?

when the driver moves out from the sub, the volume of the sub increases and the pressure goes down. it doesn't just disappear, it is offset by a corresponding increase in pressure in the room. of course, the volume of the sub tends to be small compared to the volume of air in the room, so the pressure difference will be proportional to the two volumes.

the barometric pressure in the room is changing. even a fraction of a change in psi is enough to knock your house over. this is why subwoofers can shake violently walls even though you won't observe the barometric pressure making big swings.

earbuds work on the same principle. if they are in your ear "loose", you will get no bass because air pressure in your ear canal isn't changing. lock your earbuds in tight and the air has no escape, as a result the pressure increases and decreases and you get a ton of bass.
post #33 of 354
here is an example:

if you have a subwoofer that displaces 10 liters and a room that is 8x15x20 feet (2400 cubic feet, or 67,200 liters), each time the sub makes its sweep, the volume of the room will change by 10 liters / 67,200 liters, which is about 0.015%.

that might not seem like a lot. if we take average air pressure to be around 15psi, a 0.015% is 0.00223 change in psi. standing a half mile away from a 1 kiloton tactical nuke will generate about 2.0 psi. that is going to blow out windows, knock down weak buildings and leave many folks dead.

so 10 liters of displacement in the above mentioned room will give you about 1/1000th the effect of a tactical nuke at 1/2 mile.

it doesn't work quite like that, but close enough.

:-)
post #34 of 354
Quote:
Originally Posted by antisuck View Post

It seems pretty clear to me that the volume of the room could be said to change by (Sd * xmax) at a rate of f times/second. The absurd example being if one entire wall of the room was constructed as the cone of a driver, moving in and out and obviously changing the room's volume in the process.
While we're being absurd, let f approach zero and wave propagation stops mattering. Set f at one cycle per hour and put everything in an ideal perfectly sealed room, and indeed the salient result is that the barometric pressure rises and falls.
I don't know at what point (if ever) this model becomes a useful way of thinking about ULF in audio, but it's possibly worth discussing.

Pretty much sums up what I was gonna say.

A test I thought of may prove interesting.

Start with a regularly shaped room.
Put a sub on one end of the room.
Play a low frequency, something below the room being able to have influence it (if possible).
An indicator could be SPL being uniform throughout the room.
Next, you would need to measure particle velocity at various distances from the speaker.
If particle velocity is the same regardless of how far you are from the speaker, low frequencies do indeed bounce all around the room.
If particle velocity is maximum at the speaker and approaches zero as you get to the far wall, then the speaker does indeed raise and lower the pressure in the entire room.

Not sure if this has been suggested or tried before, or if it even a valid test, but it made a lot of sense as I was thinking about it.

Also, Boyle's Law states P1 * V1 = P2 * V2
Given a room of 1000 cubic feet with an initial pressure of 14.7 psi and a subwoofer capable of displacing 1 cubic foot, then
14.7 psi * 1000 cubic feet = x psi * 999 cubic feet

so x = 14.7147 psi, an increase of .0147 psi. Not sure how that translates to dB, but it's a start.
Edited by Nardokor - 7/31/12 at 10:19pm
post #35 of 354
nard, scroll back to post 33. your example uses more displacement and a smaller room, but we are on the same page. :-)

btw, 1 Pa 1 N-m^-2 = 93.98 dB SPL = 0.000145 psi

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

edit: 0.0147 psi is about 100X more than the above equation, so that is about 114db?
Edited by LTD02 - 7/31/12 at 11:27pm
post #36 of 354
I saw post 33, I just wanted to apply Boyle's law as well.

And according to that, a 0.0147 psi change would be 113 dB?
post #37 of 354
~yes, good catch. i caught that one after the fact as well. updated #35. our calculations are similar +/- 1db, which isn't significant. :-)
Edited by LTD02 - 8/1/12 at 12:38am
post #38 of 354
we are now comparing sub systems to tactical nukes. haha, i LIKE this thread!
post #39 of 354
Quote:
Originally Posted by LTD02 View Post

"'Exactly' how does a subwoofer change the volume of a room?"
is this a trick question?
when the driver moves out from the sub, the volume of the sub increases and the pressure goes down. it doesn't just disappear, it is offset by a corresponding increase in pressure in the room. of course, the volume of the sub tends to be small compared to the volume of air in the room, so the pressure difference will be proportional to the two volumes.
the barometric pressure in the room is changing. even a fraction of a change in psi is enough to knock your house over. this is why subwoofers can shake violently walls even though you won't observe the barometric pressure making big swings.
earbuds work on the same principle. if they are in your ear "loose", you will get no bass because air pressure in your ear canal isn't changing. lock your earbuds in tight and the air has no escape, as a result the pressure increases and decreases and you get a ton of bass.

Is this a trick answer?

So, how does a ported sub or a dipole work? Why doesn't the room shake violently when you enter it, since you're displacing far more volume than a drivers cone moving 20 mm? Standing in the room holding and oscillating a piece of plywood can produce a pressure wave but it doesn't 'change the volume' of or in any way 'pressurize' a room one iota.

Assuming a perfectly sealed room is a flawed approach. There's no such thing. If there were, it would be called a hyperbaric chamber, not a home theater, and an HVAC system with an air return located outside the room would be impossible because it's actually introducing more medium from an outside source, akin to pumping up a bicycle tire. A typical HVAC system can move 1,000 liters of air per second. If an oscillating 12" cone could change the barometric pressure in a room, the HVAC system would kill you.

The pressure wave is a compression/rarefaction of the air molecules as the wave moves through the air (medium). The density of the medium in the room, or the number of air molecules per square inch, does not change as the pressure wave moves through it. If you move a new piece of furniture into the room you may be displacing 1,500 liters of volume, but you aren't changing the ambient air pressure at all.

The barometric pressure in the room is not changing. A subwoofer, regardless of its displacement capability, cannot, does not, will not 'pressurize' a room. That's so absurd a claim as to border on humorous. If there is any evidence anywhere to support it, please post a link.

You're only confusing a local pressure change with an ambient pressure change. The former occurs during the passing of a sound pressure wave, the latter remains unchanged. Going a step further, to associate this claim of pressurization with only a specific slice of the audio spectrum is even more baffling.
post #40 of 354
I have owned many different subs and speakers. Folded 18 inch horns, big JBL 15's, sealed, ported, tapped horns, you name it. The difference people hear within the midbass is sheer spl! The JBL's have awesome midbass because they can play very loud spl within that region. I just went from F-20's(horn loaded subs) to CHT sealed subs(very sensitive in the midbass but more displacement for down low than the F-20's) to eD 13's which were built more for the low end and not as sensitive in the midbass. Once you have enough displacement and power where no compression or distortion creeps in it is very difficult to tell the difference between the systems. There is only one place you can tell, the low end. It is the exact opposite most people say around here that they can not tell the difference with the low end and just go with ported subs. I think why they do not experience the difference is because they never have enough displacement from the sealed subs to matter. They always compare a very powerful ported sub to a powerful sealed but not as powerful around tune. They also do not boost the low end of the sealed system. I saw one time a bunch of guys did boost the low end of all subs and the sealed sub was preferred. My eD system I have now is not even close in sensitivity compared to my F-20's, CHT's, DTS-10's, etc... I bought enough of them to match the sensitivity and guess what, the midbass is the same during a movie. The only difference now is that the seats, pants, chairs wobble more than before. I know what you guys are talking about having better midbass but the JBL subs can play 130 dBs and the SVS can not. Get 4 SVS subs and tell me how the midbass is then and you will have much more low frequencies to boot!
post #41 of 354
Quote:
Originally Posted by beastaudio View Post

we are now comparing sub systems to tactical nukes. haha, i LIKE this thread!

That's the effect I'm going for! biggrin.gif
post #42 of 354
Quote:
Originally Posted by bossobass View Post

Is this a trick answer?
So, how does a ported sub or a dipole work? Why doesn't the room shake violently when you enter it, since you're displacing far more volume than a drivers cone moving 20 mm? Standing in the room holding and oscillating a piece of plywood can produce a pressure wave but it doesn't 'change the volume' of or in any way 'pressurize' a room one iota.
Assuming a perfectly sealed room is a flawed approach. There's no such thing. If there were, it would be called a hyperbaric chamber, not a home theater, and an HVAC system with an air return located outside the room would be impossible because it's actually introducing more medium from an outside source, akin to pumping up a bicycle tire. A typical HVAC system can move 1,000 liters of air per second. If an oscillating 12" cone could change the barometric pressure in a room, the HVAC system would kill you.
The pressure wave is a compression/rarefaction of the air molecules as the wave moves through the air (medium). The density of the medium in the room, or the number of air molecules per square inch, does not change as the pressure wave moves through it. If you move a new piece of furniture into the room you may be displacing 1,500 liters of volume, but you aren't changing the ambient air pressure at all.
The barometric pressure in the room is not changing. A subwoofer, regardless of its displacement capability, cannot, does not, will not 'pressurize' a room. That's so absurd a claim as to border on humorous. If there is any evidence anywhere to support it, please post a link.
You're only confusing a local pressure change with an ambient pressure change. The former occurs during the passing of a sound pressure wave, the latter remains unchanged. Going a step further, to associate this claim of pressurization with only a specific slice of the audio spectrum is even more baffling.

dipoles don't pressurize a room. ported subs won't pressurize a room below their below their tuning frequency.

sealed subs do (and so do infinite baffle subs). it is why you get 12db/oct below the pressure vessel gain point. when you get below the point where the long dimension of the room is less than 1/2 wavelength, all the air molecules begin to be compressed at the same time. you no longer have waves reflecting around the room. the whole room is being compressed and decompressed like a balloon, but since the room is solid, the volume doesn't change, so the pressure rises and falls. the room behaves much like your hyperbaric chamber example. if it were a hyperbaric chamber, you would get the full 12db/oct. the more openings that you have in the room, the less the pressure builds and the less gain that you get. as you note, all rooms have some air leaks, so nobody gets the full 12db/oct.

do the experiment with headphones. when the headphones are "air tight" to your head, you have a hyperbaric chamber and 12db/oct. hold the headphones just slightly away from your head and you lose the 12db/oct and all the bass goes away.
post #43 of 354
Quote:
Originally Posted by bossobass View Post

Assuming a perfectly sealed room is a flawed approach. There's no such thing. If there were, it would be called a hyperbaric chamber, not a home theater, and an HVAC system with an air return located outside the room would be impossible because it's actually introducing more medium from an outside source, akin to pumping up a bicycle tire. A typical HVAC system can move 1,000 liters of air per second. If an oscillating 12" cone could change the barometric pressure in a room, the HVAC system would kill you.
The pressure wave is a compression/rarefaction of the air molecules as the wave moves through the air (medium). The density of the medium in the room, or the number of air molecules per square inch, does not change as the pressure wave moves through it. If you move a new piece of furniture into the room you may be displacing 1,500 liters of volume, but you aren't changing the ambient air pressure at all.
The barometric pressure in the room is not changing. A subwoofer, regardless of its displacement capability, cannot, does not, will not 'pressurize' a room. That's so absurd a claim as to border on humorous. If there is any evidence anywhere to support it, please post a link.
You're only confusing a local pressure change with an ambient pressure change. The former occurs during the passing of a sound pressure wave, the latter remains unchanged. Going a step further, to associate this claim of pressurization with only a specific slice of the audio spectrum is even more baffling.

Since I don't even see the point of arguing your examples, here are some more numbers for you.

A single LMS ultra is capable of displacing 3.5 liters of air. At 20 Hz, the outward stroke of the subwoofer takes 1/40th of a second. So the outward stroke is equivalent to a fan capable of moving 3.5 liters every 1/40th of a second, or 295 cubic feet per minute. If you were to take a theater room, and install a fan on the door capable of moving 295 cfm, I would bet you there would indeed be a pressure increase in the room. The magnitude of the pressure increase would depend on how well the room is sealed, but there would be a pressure increase.
post #44 of 354
Quote:
Originally Posted by Nardokor View Post

If you were to take a theater room, and install a fan on the door capable of moving 295 cfm, I would bet you there would indeed be a pressure increase in the room. The magnitude of the pressure increase would depend on how well the room is sealed, but there would be a pressure increase.

What if you took the same fan and placed it in the middle of the room. Does the pressure increase in the room?
post #45 of 354
Wow what a lack of understanding. I suppose a 25mm dome tweeter can pressurize a room? How about light waves?
post #46 of 354
Quote:
Originally Posted by LTD02 View Post


do the experiment with headphones. when the headphones are "air tight" to your head, you have a hyperbaric chamber and 12db/oct. hold the headphones just slightly away from your head and you lose the 12db/oct and all the bass goes away.

Actually, the bass, mid bass, and a lot of mids go away when you do this, because the only thing you hear are the directional frequencies of the particular headset. So you're pretty much left with high mids and treble.
Edited by tuxedocivic - 8/2/12 at 7:31am
post #47 of 354
Quote:
Originally Posted by LTD02 View Post

dipoles don't pressurize a room. ported subs won't pressurize a room below their below their tuning frequency.
sealed subs do (and so do infinite baffle subs). it is why you get 12db/oct below the pressure vessel gain point. when you get below the point where the long dimension of the room is less than 1/2 wavelength, all the air molecules begin to be compressed at the same time. you no longer have waves reflecting around the room. the whole room is being compressed and decompressed like a balloon, but since the room is solid, the volume doesn't change, so the pressure rises and falls. the room behaves much like your hyperbaric chamber example. if it were a hyperbaric chamber, you would get the full 12db/oct. as you note, all rooms have some air leaks, so nobody gets the full 12db/oct.
do the experiment with headphones. when the headphones are "air tight" to your head, you have a hyperbaric chamber and 12db/oct. hold the headphones just slightly away from your head and you lose the 12db/oct and all the bass goes away.

"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.
post #48 of 354
Quote:
Originally Posted by Aknot5 View Post

What if you took the same fan and placed it in the middle of the room. Does the pressure increase in the room?

That would just move air around the room, not at all what a sub does.
Quote:
Originally Posted by tuxedocivic View Post

Wow what a lack of understanding. I suppose a 25mm dome tweeter can pressurize a room? How about light waves?

This discussion only concerns very low frequencies, read the thread.
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.

So, according to your logic, say I have a small syringe and move the plunger at a rage of 1 Hz. You are telling me that there is a 1 Hz sound wave bouncing around in there hundreds of times? What seems more realistic in that case, the pressure changing or the bouncing sound wave? And don't even try to tell me it is completely different. The scale is off, and extremely simplified, but that doesn't make a difference. It is a chamber, with an opening simulating all the leaks in a room and the plunger simulating a subwoofer.

And opening a window will have a small effect. You are opening just a few square feet of the several hundred of most rooms. The effect will not be pronounced until you open much more of the room up.

And I especially like the fact that you have completely ignored all calculations in the thread and have in stead relied on theory. If you want to leave, go ahead, but that looks like a rage quit to me.
post #49 of 354
Would an IB with 8-18" would pressurize the room? creating temporary pressure and rarefaction of air in this room?
post #50 of 354
With either a subwoofer in a room or a syringe, is it being suggested that the pressure instantly increases to the same value at every point in the space? In other words, at the exact moment the driver or plunger reaches its peak, the pressure will have increased to the same value at every point in the room or syringe? I don't see how that is possible.
From my understanding, the driver or plunger creates a pressure wave that propagates through the space. That wave will reflect off any boundary and will lose energy as it propagates. If the volume is perfectly sealed, the piston does not return to its original position and remains at its peak, after the wave propagates and the air molecules reach a new equilibrium state, the pressure and temperature will have increased.

For a subwoofer driver, isn't it moving in and out faster than it takes the pressure wave to move through the room, so an equilibrium state is never reached and the room pressure does not increase.

I am definitely not an expert so please point out any mistakes.

-Mike
post #51 of 354
Quote:
Originally Posted by Nardokor View Post

That would just move air around the room, not at all what a sub does.
This discussion only concerns very low frequencies, read the thread.
So, according to your logic, say I have a small syringe and move the plunger at a rage of 1 Hz. You are telling me that there is a 1 Hz sound wave bouncing around in there hundreds of times? What seems more realistic in that case, the pressure changing or the bouncing sound wave? And don't even try to tell me it is completely different. The scale is off, and extremely simplified, but that doesn't make a difference. It is a chamber, with an opening simulating all the leaks in a room and the plunger simulating a subwoofer.
And opening a window will have a small effect. You are opening just a few square feet of the several hundred of most rooms. The effect will not be pronounced until you open much more of the room up.
And I especially like the fact that you have completely ignored all calculations in the thread and have in stead relied on theory. If you want to leave, go ahead, but that looks like a rage quit to me.

Good freakin' golly, so now we're climbing into a syringe with a microphone while someone moves the plunger that simulates a subwoofer!!??

What next? rolleyes.gif

I asked for evidence from a credible source, not another irrelevant illustration.

Can you please tell us why the ULF level increased when the window was opened? Feel free to include calculations with your answer if it makes you feel more credible.

Just so we have this perfectly clear; you and LTD are saying that room gain results from an increase and decrease of ambient barometric pressure that's caused by a drivers cone moving in and out and that reflected sound pressure waves have nothing to do with the phenomenon because those sound waves are not reflecting off anything. You're also saying that poking a 10 square foot hole in the wall to the outside world will double the level of measurable sound because 10 square feet is an insignificant hole.
post #52 of 354
Quote:
Originally Posted by Nardokor View Post

That would just move air around the room, not at all what a sub does.

How in the world is moving air "not at all" what a subwoofer does?
post #53 of 354
Quote:
Originally Posted by maxserg View Post

Would an IB with 8-18" would pressurize the room? creating temporary pressure and rarefaction of air in this room?

Yes and no.

No, it will not pressurize a room.

Yes, the sound pressure waves it produces will create a transient compression/rarefaction of the air molecules as the sound wave moves through the room.

As I've mentioned already, they are confusing an ambient pressure change with a local pressure change.
post #54 of 354
Quote:
Originally Posted by bossobass View Post

No, it will not pressurize a room.
Yes, the sound pressure waves it produces will create a transient compression/rarefaction of the air molecules as the sound wave moves through the room.
As I've mentioned already, they are confusing an ambient pressure change with a local pressure change.

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.
post #55 of 354
I don't remember my college physics days, I will leave that to the resident experts? Anyways, my room is a sealed as one can get, the only two openings are the very small cracks in the double doors and the area around my projector. I don't have a HVAC but I do keep a fan in their for summer. It is great to be in a basement and keeps cool. 3 walls are concrete and I have dual layers of 3/4 sheet rock, dual layers of sound board, and 11 inches of insulation all around. This does not include the bass traps and wall treatments. OK, when I run some serious bass scenes I feel sound waves, pressure, whatever. When someone tries to open the doors it is very difficult because it created a seal or vacuum. People actually find it funny and crazy at the same time. So, something is happening for sure. My raw uneq'd response looks like this(peak at 52hz) with an 80hz crossover.

uneqd.jpg
post #56 of 354
Quote:
Originally Posted by MKtheater View Post

OK, when I run some serious bass scenes I feel sound waves, pressure, whatever. When someone tries to open the doors it is very difficult because it created a seal or vacuum. People actually find it funny and crazy at the same time.


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?
post #57 of 354
Quote:
Originally Posted by Aknot5 View Post

How in the world is moving air "not at all" what a subwoofer does?

That is why I said "around" the room. A subwoofer does not move air from one place to another.
Quote:
Originally Posted by bossobass View Post

Good freakin' golly, so now we're climbing into a syringe with a microphone while someone moves the plunger that simulates a subwoofer!!??

A plunger is all a subwoofer is, the scale is just off. Scale the syringe to the size of a room, and you get a chamber with a speaker the size of a wall.
Quote:
Originally Posted by bossobass View Post

Can you please tell us why the ULF level increased when the window was opened? Feel free to include calculations with your answer if it makes you feel more credible.

Not hard, no idea how big your room is, say 2000 cubic feet, 10 square foot hole 6 inches deep. I sense a helmholtz resonator with a tuning around 7 hz.
post #58 of 354
Quote:
Originally Posted by Nardokor View Post


This discussion only concerns very low frequencies, read the thread.
.

I've read every post. I understand what's being discussed. 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. Just like how the 40 to 300hz range behaves differently with the room. At VLF the sound waves are always summing whereas above that you can have summing and canceling. It's not (static/atmospheric) pressure increases. It's still sound pressure, which is a wave.

Geddes once said you can't have room gain because all rooms leak. He'd be right if he meant you can't increase atmospheric pressure because all rooms leak.
post #59 of 354
Ugh.

The use of seperate LF and ULF drivers and how well that would work was the subject of this thread, wasn't it?
post #60 of 354
Yes, i've been following along til the physics talk zoomed over my simple head.
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