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post #1 of 56 Old 06-04-2014, 01:43 PM - Thread Starter
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What would be better for an open room a sealed dual opposed 18 setup with 2 daytons, or a properly ported setup with 1 dayton 18 ( a marty build to be exact). The single would be the HO and the dual would probably be the ultimax. How much of a difference between the two would really be noticeable?
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post #2 of 56 Old 06-04-2014, 03:00 PM
 
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Sealed subs rely on room gain to get below 35Hz or so. If your longest room dimension is more than 18 feet or so you won't get room gain, so ported is usually better, unless you use a lot of subs to make up for the lack of room gain.
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post #3 of 56 Old 06-04-2014, 03:14 PM
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Once again Bill you're wrong about sealed subs. And I have the data to prove it. My 33ft long room has room gain from 50hz and down.

OP, depends on your goals. If you want ULF the sealed. High output, then ported.

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post #4 of 56 Old 06-04-2014, 03:18 PM
 
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I'm not sure about room gain, but my single sealed 18 sounds really good and really loud ( louder than comfortable), really deep, shakes everything, and my room is about 24 x 40 and is open to multiple other rooms and hallways.
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post #5 of 56 Old 06-04-2014, 05:18 PM
 
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Quote:
Originally Posted by JWagstaff View Post

I'm not sure about room gain, but my single sealed 18 sounds really good and really loud ( louder than comfortable), really deep, shakes everything, and my room is about 24 x 40 and is open to multiple other rooms and hallways.
How does the in-room response measure? You don't need to go to 20Hz at 105dB to experience what you have. But it's a lot more fun when you do. wink.gif
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post #6 of 56 Old 06-04-2014, 05:22 PM
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If you have the space, go ported. If not, that's a shame wink.gif
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post #7 of 56 Old 06-04-2014, 05:30 PM
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^^^LOL!!!

"And I have the data to prove it. My 33ft long room has room gain from 50hz and down."

where was the sub? where was the mic?

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post #8 of 56 Old 06-04-2014, 05:32 PM
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op, generally, at least two subs is better than 1 for cancelling room modes, so if you can try to find a way to do that, even if the two subs are slightly smaller than one mega sub.

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post #9 of 56 Old 06-04-2014, 06:12 PM
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Originally Posted by LTD02 View Post

^^^LOL!!!

"And I have the data to prove it. My 33ft long room has room gain from 50hz and down."

where was the sub? where was the mic?

Thanks for making me check my facts. I would be more correct to say below 35hz based on re-evaluating my measurements. It was my 50hz mode that tricked me. I hadn't look at these measurements for a year or so, so I had forgotten the details.

Here it is. Blue is a GP measurement with the mic 1m away in an open environment (I think my drive way). Green is the subwoofer along my front wall, which is the long 33ft wall, about 1/4 distance along that wall at the bottom right of my screen. The microphone was at my LP.



You can see a positive mode at 50hz and then from 35hz down it's all gain. About 20db worth where it counts down low. That measurement was taken with my receiver XO set to 200hz so the speakers are out of the way. A little unsure what my room is doing at 80 to 120hz I could even overlay that GP measurement lower. That's a single CSS Trio 12 subwoofer in a 65L sealed box.

I should add, my room opens to various other rooms and a staircase. It's nearly an open floor plan. Concrete floor but wood framed ceiling and walls. So not much concrete bunker type gain to push on here.
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post #10 of 56 Old 06-04-2014, 06:32 PM
 
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Quote:
Originally Posted by tuxedocivic View Post

Here it is. Blue is a GP measurement with the mic 1m away in an open environment (I think my drive way). Green is the subwoofer along my front wall, which is the long 33ft wall, about 1/4 distance along that wall at the bottom right of my screen. The microphone was at my LP.
.
What you're seeing isn't exclusively room gain but the combination of room gain and boundary reinforcement, which can be quite substantial compared to half-space. At best room gain will deliver 12dB/octave, with 8-9dB being more typical. You've got a lot more than that, so room gain alone doesn't account for what you have.
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post #11 of 56 Old 06-04-2014, 06:58 PM
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Quote:
Originally Posted by Bill Fitzmaurice View Post

What you're seeing isn't exclusively room gain but the combination of room gain and boundary reinforcement, which can be quite substantial compared to half-space. At best room gain will deliver 12dB/octave, with 8-9dB being more typical. You've got a lot more than that, so room gain alone doesn't account for what you have.

So you admit your initial assertion is wrong?

Given your previous misinformation and my willingness to put my money where my mouth is I'm not willing accept your statement as given. Please explain this more thoroughly rather than just bat away my data like its worthless.

For the record, I've always submitted that room gain = increasing boundary reinforcement with decreasing frequency. I reject the idea that room gain is room pressurization.
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post #12 of 56 Old 06-04-2014, 06:58 PM
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Originally Posted by JWagstaff View Post

I'm not sure about room gain, but my single sealed 18 sounds really good and really loud ( louder than comfortable), really deep, shakes everything, and my room is about 24 x 40 and is open to multiple other rooms and hallways.

One 18 in a 8000 plus cuft open room shaking everything..... Not a bass hound smile.gif
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post #13 of 56 Old 06-04-2014, 09:22 PM
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Originally Posted by chalugadp View Post

One 18 in a 8000 plus cuft open room shaking everything..... Not a bass hound smile.gif

lol so true
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post #14 of 56 Old 06-05-2014, 05:23 AM
 
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Quote:
Originally Posted by tuxedocivic View Post

So you admit your initial assertion is wrong?
.
Room gain is a well documented phenomenon, starting at the frequency where the longest room dimension is 1/2 wavelength. In a 33 foot long room that's 17Hz. I have no issues with your charts, only with the conclusions drawn. Room gain will be one factor in play, but it's not the only factor in play.
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post #15 of 56 Old 06-05-2014, 05:58 AM
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So if a room with a 33ft dimension can have RG below 17hz (I still don't necessarily agree with your statement as I have many more examples) why can't a room with an 18ft longest dimension not have room gain at all? That was your initial statement. But by the statement in you last post it should have room gain below 30hz.

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post #16 of 56 Old 06-05-2014, 06:09 AM
 
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Quote:
Originally Posted by chalugadp View Post

One 18 in a 8000 plus cuft open room shaking everything..... Not a bass hound smile.gif
Quote:
Originally Posted by notnyt View Post

lol so true

hey I didn't say I wasn't buying more subs in the future :P It's only temporary in this room, it's going in a 10x16x8 sealed room soon smile.gif

Random stuff in my house is falling off walls and shelves -.- In the future when I get a dedicated theater I can get more subs without wrecking everything.

I was just saying that you don't necessarily need ported for a large room in response to the second post - for lots of people it would be enough bass.
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post #17 of 56 Old 06-05-2014, 06:29 AM
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Quote:
Originally Posted by Bill Fitzmaurice View Post

Sealed subs rely on room gain to get below 35Hz or so.

 

 

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Originally Posted by tuxedocivic View Post

Once again Bill you're wrong about sealed subs. And I have the data to prove it. My 33ft long room has room gain from 50hz and down.
 

 

 

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Originally Posted by tuxedocivic View Post


Thanks for making me check my facts. I would be more correct to say below 35hz based on re-evaluating my measurements. 
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post #18 of 56 Old 06-05-2014, 06:52 AM
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Bear, that wasn't my objection. This was.
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Originally Posted by Bill Fitzmaurice View Post

If your longest room dimension is more than 18 feet or so you won't get room gain

I'm saying that is incorrect.

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post #19 of 56 Old 06-05-2014, 08:20 AM
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Just to add to the data, here's a snippet of something Bossobass posted in popalock's build thread a while ago.
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As Josh and I have noticed over the years (and commented on), many larger rooms show a dip in the 10-15 Hz area and some rooms show a resonance peak from large frame boundaries (vs a room on slab), but the general Room Gain Profiles are (+/-) 2dB, starting in the 30s Hz.

The rooms are every size from your 1500 cubes to not's 6000 cubes.

You can see despite room dimensions greater than 18ft there's gains from the room (ie. room gain) starting at around 35hz.



Once again as I previously stated, for the OP, the decision should be about extension, or output. I'm not pushing sealed or ported, it's your preference between those two goals.

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post #20 of 56 Old 06-05-2014, 09:09 AM
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Quote:
Originally Posted by tuxedocivic View Post

Just to add to the data, here's a snippet of something Bossobass posted in popalock's build thread a while ago.
You can see despite room dimensions greater than 18ft there's gains from the room (ie. room gain) starting at around 35hz.



Once again as I previously stated, for the OP, the decision should be about extension, or output. I'm not pushing sealed or ported, it's your preference between those two goals.

What is "well documented" is that a room cannot support a standing wave at any frequency whose wavelength is greater than L2 (the rooms longest dimension times 2). It's a simple math formula, although actually measuring the longest dimension of most rooms is not so simple.

The idea that below L2 some weird pressure-thingy happens has not been presented in documented form on this forum to my knowledge.

Tux is correct. "Room Gain" is a phenomenon resulting from boundary gain.

Placing a point source (subs driver) within 1/8 wavelength of a corner assures only constructive reinforcement from corner reflections (left wall, right wall, floor) to the typical 80 Hz crossover point. Of course, there are many more boundaries in our rooms (opposite walls, ceiling, chases, offsets, etc.) that are further distances and which will cause reflections that are either a) destructive, b) neutral or c) constructive, as well as standing waves.

As frequency decreases, wavelength increases and the result is that more and more of the reflections become constructive and less and less of the reflections are destructive or neutral.

This is evident in every collected posted in-room FR by members over the years. All gain profiles begin in the 30-40 Hz decade, regardless of room size or whether or not the room is closed or open to the floor plan.

The amount of gain is entirely dependent on the transmission losses of the boundaries. That is, if only half of a wave is reflected back into the room and the other half is lost through the wall, the net result will be less than if the wall is concrete-filled 12" cinder block where 90% of the wave is reflected back into the room.

The ultimate extension on the low end is dominated by the cumulative signal chain roll off, which all systems have to a greater or lesser extent.

So, to answer the OP, Tux is correct. If the goal is maximum output from a given system but extension is not and system size is irrelevant, ported is the way to go. If the goal is maximum bandwidth in the smallest system size, sealed is the way to go. If multiples are in the future plans, output is irrelevant as both systems are able to exceed human tolerances of that goal.
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post #21 of 56 Old 06-05-2014, 09:43 AM
 
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Quote:
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So if a room with a 33ft dimension can have RG below 17hz (I still don't necessarily agree with your statement as I have many more examples) why can't a room with an 18ft longest dimension not have room gain at all? That was your initial statement. But by the statement in you last post it should have room gain below 30hz.
An 18 foot longest dimension gets room gain below 32Hz. That meshes very well with the f3 of the average sealed sub. My point is that if you have a sealed sub and you're counting on room gain alone to fill in below f3 then don't expect it to do so with a dimension longer than that. Other contributing factors may do so. In your case obviously all of the factors involved resulted in a favorable result. But it wasn't just room gain alone. Resonant modes and boundary effects would also be contributory. A better understanding of room gain can be seen in charts like those shown here, comparing an auto sound sub in and out of a car:
http://s3.amazonaws.com/szmanuals/7ac06dac885eff9d6bd160d9969c9eb0

Here room gain dominates the result because the 'room' is much too small for resonant modes and boundary effects to have as much effect as in a larger space.
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post #22 of 56 Old 06-05-2014, 09:50 AM
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Ok I think I understand your position better Bill. I'm still unsure what you think room gain must be.

So far every sealed sub build I've watched where the user measured his results, I've seen gains from at least 30hz and down despite room dimensions in excess of 18ft. So our disagreement is there I think. Could you clarify what you consider to be strictly room gain, how we could measure it discretely to better understand the subject, and why the OP or anyone else shouldn't rely on boundary reinforcement despite the overwhelming examples in favor? Thanks.

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post #23 of 56 Old 06-05-2014, 10:02 AM
 
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Quote:
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Ok I think I understand your position better Bill. I'm still unsure what you think room gain must be.

So far every sealed sub build I've watched where the user measured his results, I've seen gains from at least 30hz and down despite room dimensions in excess of 18ft. So our disagreement is there I think. Could you clarify what you consider to be strictly room gain, how we could measure it discretely to better understand the subject, and why the OP or anyone else shouldn't rely on boundary reinforcement despite the overwhelming examples in favor? Thanks.
It gets complicated. Toole does a pretty good job of summarizing all the contributory factors here:
https://www.harmanaudio.com/all_about_audio/loudspeakers_rooms.pdf
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post #24 of 56 Old 06-05-2014, 11:15 AM
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Quote:
Originally Posted by Bill Fitzmaurice View Post

A better understanding of room gain can be seen in charts like those shown here, comparing an auto sound sub in and out of a car:
http://s3.amazonaws.com/szmanuals/7ac06dac885eff9d6bd160d9969c9eb0

Here room gain dominates the result because the 'room' is much too small for resonant modes and boundary effects to have as much effect as in a larger space.

This was added after my reply. I see there nothing more than what I'm saying. In a car the mode lengths are even shorter, and the gain starts ealier. Nothing surprising there. Still not sure what room gain is to you.
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It gets complicated. Toole does a pretty good job of summarizing all the contributory factors here:
https://www.harmanaudio.com/all_about_audio/loudspeakers_rooms.pdf

That's a nice article, but it doesn't differentiate room gain any differently than what I'm saying. Once again, room gain is increasing boundary reinforcement with decreasing frequency. Seems like Toole agrees with me. Note, he didn't mention any kind of pressure vessel gain at all! Thanks for posting a link that reinforces my point. But I'm still interested in what room gain is to you and why it's only available at a maximum of 12db/oct below 17hz in my room?? And how I'd be able to measure it discretely from modes? Perhaps you could share some measurements of sealed subwoofers in various rooms that offer a counter perspective?

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post #25 of 56 Old 06-05-2014, 03:51 PM
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"The idea that below L2 some weird pressure-thingy happens has not been presented in documented form on this forum to my knowledge."

it is semantics. both give the same result.

in a solid room, the wave equation gives a rising 12db/octave result which provides a conjugate for the 12db/octave rolloff of sealed subs.



in a solid room, the pressure theory (aka using the ideal gas law to predict spl) doesn't rely gain from the room, just the fact that more pressure modulation is required from the driver for the same spl as frequency falls.



the fact that these two provide the same solution is not immediately obvious. i hope that we can all be forgiven for that.

it wasn't until i found a spreadsheet that codes the wave equation that i realized what was going on.

what complicates things one step further is that many sounds are transient in nature, while the measurements are something closer to steady-state. the former don't allow room modes to build up, while the latter does.

so even a good "sweep" measurement in a room doesn't fully capture the difference in sound.

this may be what 'not experienced in his room when he switched from sealed to ported subs. the sealed subs rely on multiple reflections / boundary gain (depending on which way you want to describe it) to provide the rise in the low end of bass, where the ported cabs don't. they just fire out with about 12db more spl directly before any reflections / boundary gain.

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post #26 of 56 Old 06-05-2014, 04:44 PM
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then there is also sound intensity, as distinct from sound pressure level, which complicates things one further... ;-)

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post #27 of 56 Old 06-05-2014, 04:49 PM
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Quote:
Originally Posted by LTD02 View Post

"The idea that below L2 some weird pressure-thingy happens has not been presented in documented form on this forum to my knowledge."

it is semantics. both give the same result.

in a solid room, the wave equation gives a rising 12db/octave result which provides a conjugate for the 12db/octave rolloff of sealed subs.



in a solid room, the pressure theory (aka using the ideal gas law to predict spl) doesn't rely gain from the room, just the fact that more pressure modulation is required from the driver for the same spl as frequency falls.



the fact that these two provide the same solution is not immediately obvious. i hope that we can all be forgiven for that.

it wasn't until i found a spreadsheet that codes the wave equation that i realized what was going on.

what complicates things one step further is that many sounds are transient in nature, while the measurements are something closer to steady-state. the former don't allow room modes to build up, while the latter does.

so even a good "sweep" measurement in a room doesn't fully capture the difference in sound.

this may be what 'not experienced in his room when he switched from sealed to ported subs. the sealed subs rely on multiple reflections / boundary gain (depending on which way you want to describe it) to provide the rise in the low end of bass, where the ported cabs don't. they just fire out with about 12db more spl directly before any reflections / boundary gain.

Siegfried's formula is a prediction of atmospheric pressure in a rigid (theoretically rigid, since one of the walls of the enclosure is a drivers cone) and airtight enclosure. It is not frequency dependent and has nothing to do with sound.

I wonder why you insist on making a simple fact of physics so ethereal and beyond comprehension. Accurately measured in-room responses against accurately measured GP responses show that room size is irrelevant and that only transmission losses alter the averages gathered from the data. There simply is no data to support gas/liquid behavior from subwoofers in our rooms.

Although I agree that steady state signals are largely irrelevant for anything beyond a basic frequency response measurement, complex dynamic source does not complicate anything. It's been shown many times that complex dynamic source translates exactly from encoded digits to sound reproduction.

b267ecba8a2643309819e750787162a8.jpg

All not hears is a difference in frequency response. At the levels he listens, soon he will hear not much of anything.

I see a 10dB difference <10 Hz but only a few dB difference at tune to 125dB.

bd3146c5953a030bdc9edaa84dc3e269.png
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post #28 of 56 Old 06-05-2014, 05:06 PM
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"Siegfried's formula is a prediction of atmospheric pressure in a rigid (theoretically rigid, since one of the walls of the enclosure is a drivers cone) and airtight enclosure. It is not frequency dependent and has nothing to do with sound."

the frequency dependency goes away below the 1/2 wavelength point. he notes it in the picture as a condition: F (less than) C/2L. if i use the less than symbol, the text becomes invisible. :-)

todd welti also refers to the zone below the first mode as the "pressure zone".* again though, same result, so use whichever term you like.





* Welti, T. (2002) How many subwoofers are enough, Proceedings of the 112 Audio Engineering Society Convention, Munich, Germany, Paper 5602. This was the paper summarized in the JBL multsubs.pdf presentation.

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post #29 of 56 Old 06-05-2014, 07:45 PM
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Hmm, déjà vu. Ya know Bosso, I'm starting to see why you've constantly preached "show the data" in the past. We've got one side saying RG is constructive reflections and another side saying its some kind of pressure thing without much of a clear definition (and a idealized gas law that simply doesn't apply). And which side "shows the data"?

LTD02, I respect what you do around here. I appreciate that you are able to dig up interesting articles, contribute to discussions, and help people design subs. Bill, I also respect you. I appreciate your no BS stance, your patience with newbs and myself, and your high level of knowledge of audio in general. Unfortunately sometimes we have to call each other out. I've shown the data. I've read the linked articles (which only support my position thanks). I'm flat out saying your wrong. I'd love to come to an agreement. I'm a humble person (different than loud mouth, I'm that too). I admit when I'm wrong. Show me where I'm wrong. Answer my previous questions (what is room gain, how do you measure it discretely, how come all examples show gain below 30hz, etc). If you can't, then consider that you might be wrong.

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post #30 of 56 Old 06-05-2014, 07:47 PM
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Originally Posted by LTD02 View Post


* Welti, T. (2002) How many subwoofers are enough, Proceedings of the 112 Audio Engineering Society Convention, Munich, Germany, Paper 5602. This was the paper summarized in the JBL multsubs.pdf presentation.

Is this accessible anywhere convenient? I'd like to read it.

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