Is infrasonic output with authority possible with dynamic drivers?

[yepimonfire]

@yepimonfire

"You'd need a large room for room gain to actually be beneficial"

This is completely false.

"small rooms can actually push the -3dB point up, for example, my 12x11 bedroom has modes at ~50 and 45hz, since it's nearly square, I get a nice 10dB bump centered on 50hz, pushing my small subs 30hz f3 down 6dB."

Half of this is nearly nonsensical. The other half seems to be your anecdotal experience with your *very* small room.

"Let's say a sealed sub starts next rolling off anechoically at 35hz, and it's down 12dB at 20hz. We would need a room that was at least 25' long"

Now you're making stuff up...

It's really simple. If you do that formula you'll have a good idea where your room gain will begin to build, generally at 6dB per octave. YMMV, but generally the larger the room, the less impact room gain will have, not the other way around. Yes, you'll get room modes which can occur with infinite randomness based on your room, but the room gain will still occur.

What's the difference between room gain and room modes then? According to you calculation my room gain begins at 60hz. If you do 565/L, you get 28hz, for a 20' long room, which is exactly what I said originally.

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[Irvrobinson]

FWIW, room gain is a very tricky affair. It's not just a matter of room dimensions, but room construction as well. Even then, calculations are only an approximation of what is really happening, not to mention the issues that occur in the modal region.

My personal case is somewhat interesting.
FR:
View attachment 21756
EQ (white line is the cumulative effect of the various filters employed):
View attachment 21757
Actual Native Response:
View attachment 21758

First thing to note is that most of what I'm doing is cutting out peaks in the response. The second is that with those peaks removed, it takes very little boost to get a reasonably flat response down to 20Hz. Given that the native response is more than 15dB down at 20Hz relative to the 50+Hz range, I consider myself fortunate in that regard. I also doubt that's an effect of room gain, but instead part of the room's modal response. You can also see the effects of room gain on the far left side of the FR graph where there is minimal boost occurring: the room is perfectly supplementing the 12dB/octave rolloff of the system. At that point, I only really need a shelf filter to raise the low end response further (and sufficient output to back it up, which is coming).

As for the room itself, it's one half of a basement, separated only by a bit of drywall. The exterior walls are all cinder block, with a concrete slab floor, and a sturdier than average ceiling. The way I figure it, the layer of drywall splitting the basement doesn't do much to stop a 50+ foot long sound wave, so the effective space for a room gain calc is much more than you might expect. OTOH, the sturdy construction means that the gain I do get is quite good. Not a bad trade-off in my view.

Your technique for tuning your system is similar to what I do. Are you running your mains without a high-pass filter?

 

[Irvrobinson]

Depends on your point of view I suppose. As I see it, a subwoofer system that can effectively deliver solid 10Hz performance isn't all that costly; a quad pack of Seaton F18's will set you back roughly $6k. That's chump change for people shopping in the KEF Reference / Revel Ultima range, and less than some high end power cords for those so inclined.

Chump change? Let's not get carried away.

 

[yepimonfire]

Thinking that 'room gain' is going to solve any problem is also wasted time. The flexibility of DSP allows most of that to be nonsense, accepting that adequate power and diaphragm (total) radiating area vs. cubic volume of listening space is a usable ratio. (size of one driver is meaningless; Assuming multiple subs are used, you need to be able to vibrate enough particles in your listening space to NOT make an audible difference seat to seat. Calculating room modes vs. L,W,H, dimensions gives you a 'map' pf sorts to work with)

I think both of you guys need to buy Floyd Toole's 'Sound Reproduction' 3rd edition.... I know I still need more studying!

I agree. Expecting room interaction to correct any deficiency in a speaker is a shot in the dark. In a sealed room, maybe, but in real houses, those are far and few between. That's not to say placing a sub in a corner won't help you get an extra 6dB out of it, because it generally does, but it does so centered at the room modes frequency. If I put my sub in the corner of my 20x12 room, I'm going to get reinforcement at 28hz, 47hz, and 70hz. I am lucky enough that these dimension actually make for an ideal room gain scenario. My sub is 18" from the front wall, and 24" from the side wall, so I do get some corner reinforcement, but the response is relatively flat.

We can further improve atlaudios calculation by breaking it down into each dimension of the room, so 565/L, 565/W, and 565/H.

The 47hz gain along the width of the room causes my fronts, center, and surrounds, which all roll off at 63hz anechoic, to extend flat down to 50hz -3dB. My height speakers are -3dB anechoic at 90hz. They are mounted 1/2 space towards the ceiling, the 7.9' height of the room gives a boost centered at 70hz, this has given me a -3dB in room response of 80hz for the heights.

I don't see how a large room would be worse when we are talking subwoofers. If my room were something like 30'x20', it would obviously fail to help extend my speakers response to 50hz, however, if a subwoofer started rolling off at 35hz, 12dB per octave, you'd be -6dB at 26hz, placed in a corner, you'd get a 6dB boost at 28hz, with a second order rolloff (12dB/octave), which means at 21hz the effect would be 6dB down, the second dimension of 30' would give you a 6dB boost at 20hz, extending the response to 20hz almost flat.

If you put a subwoofer in a small, square room, you're just going to get boomy one note bass, which is the point I made before.

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[Steve81]

Your technique for tuning your system is similar to what I do. Are you running your mains without a high-pass filter?

No, I seal my speakers with the supplied plugs and then cross at 120Hz with a 2nd order filter. Overall it results in a smoother response, and with the Funk carrying the heavy load of the low end, the R500s have a much easier job at higher output levels.

Chump change? Let's not get carried away.

Heck, I assume 1%ers like you, Rich, and ATDG just burn 100's like firewood to keep warm in the winter.

 

[Irvrobinson]

No, I seal my speakers with the supplied plugs and then cross at 120Hz with a 2nd order filter. Overall it results in a smoother response, and with the Funk carrying the heavy load of the low end, the R500s have a much easier job at higher output levels.

Ah, KEF R500s. Understood.

Amazing that you get such a smooth response with only one sub. That's why I run the Salon2s full-range; for anything musical it's like having three subs. Or do you really have two Funk 21.0s?

Heck, I assume 1%ers like you, Rich, and ATDG just burn 100's like firewood to keep warm in the winter.

Speaking for myself, only 1s. I think ADTG does 20s.

 

[panteragstk]

This discussion got very interesting. Especially when it comes to the sealed vs ported in relation to room gain.

That brings up a concern/question for me. I had a theater room added on to my house while it was being built. It is about 16x14x8 and has two exterior walls that are siding with blown in insulation. The back wall has the attic behind with blown in insulation and a barrier to keep it in place. The last wall has the game room on the other side. There is also insulation in that wall because I had asked for it.

I had wanted to do rock wool or something else that would act as a sound barrier, but what I got was the best I was going to get.

Having said all that, I have 2 infinity 1260w and 2 1262w drivers that I plan to put into 1.25 cu ft sealed enclosures. I'll run about 262w through each of the 1262w and 387w through each 1260w. They will each be in corners of the room and may be used near field if I can do it.

How much sound could potentially get out of the room the way it is constructed? I'm concerned I won't get much room gain after reading through this thread.

 

[Steve81]

Ah, KEF R500s. Understood.

Amazing that you get such a smooth response with only one sub. That's why I run the Salon2s full-range; for anything musical it's like having three subs. Or do you really have two Funk 21.0s?

That response was with a single 18.0, which I'll run together with the 21.0LX (different driver from the 21.0 and 21.0L) when it arrives. Really, getting a flat response isn't a big challenge with EQ. Where multiple subs help is seat to seat variation. Not really a big concern for me as I'm the only one in the house who remotely cares in the first place, and I get the good seat.

 

[Irvrobinson]

That response was with a single 18.0, which I'll run together with the 21.0LX (different driver from the 21.0 and 21.0L) when it arrives. Really, getting a flat response isn't a big challenge with EQ. Where multiple subs help is seat to seat variation. Not really a big concern for me as I'm the only one in the house who remotely cares in the first place, and I get the good seat.

What is a 21.0LX? I only saw the 21.0L on their website.

 

[Steve81]

The 21.0LX uses a variant of the GUJ21 driver (21.0L) with the much more powerful magnet structure from the TSAD21 driver (21.0). By Nathan's reckoning, the 21.0LX should be able to deliver +6dB on the low end, and +2-3 dB on the top relative to the 18.0, in a cabinet that isn't massively larger than the 18.0 (4.5 cu ft vs 3.5). The extreme motor force also translates into a very low Q in that 4.5 cu ft cabinet. More details on the driver can be found on the DB forum.

 

[yepimonfire]

This discussion got very interesting. Especially when it comes to the sealed vs ported in relation to room gain.

That brings up a concern/question for me. I had a theater room added on to my house while it was being built. It is about 16x14x8 and has two exterior walls that are siding with blown in insulation. The back wall has the attic behind with blown in insulation and a barrier to keep it in place. The last wall has the game room on the other side. There is also insulation in that wall because I had asked for it.

I had wanted to do rock wool or something else that would act as a sound barrier, but what I got was the best I was going to get.

Having said all that, I have 2 infinity 1260w and 2 1262w drivers that I plan to put into 1.25 cu ft sealed enclosures. I'll run about 262w through each of the 1262w and 387w through each 1260w. They will each be in corners of the room and may be used near field if I can do it.

How much sound could potentially get out of the room the way it is constructed? I'm concerned I won't get much room gain after reading through this thread.

What do you mean siding with blown in insulation? No solid drywall? If the siding is thin, bass might pass right through it.

You're room modes are 35hz, 40hz, and 70hz. At 35hz, you should see a 6dB increase rolling off at 12dB per octave. Since 35hz and 40hz are close together, it may be something like 10-12dB, which is similar to what I experienced in my almost square room. You could eq the hump flat and boost 20hz, the room should have a mild effect down to 17hz.

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[TheWarrior]

What do you mean siding with blown in insulation? No solid drywall? If the siding is thin, bass might pass right through it.

You're room modes are 35hz, 40hz, and 70hz. At 35hz, you should see a 6dB increase rolling off at 12dB per octave. Since 35hz and 40hz are close together, it may be something like 10-12dB, which is similar to what I experienced in my almost square room. You could eq the hump flat and boost 20hz, the room should have a mild effect down to 17hz.

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Mmmmm no.

1130fps/room dimension in feet gives modes. Likewise - 1130/frequency gives dimension (unless you live in Denver) Then you still need to multiply to get the higher order modes because sound waves don't dissipate after only reflecting once. And those are the tricky ones because they are often above the crossover frequency of the subwoofer.

@panteragstk It sounds like this was a bonus room added in a space where there would have been roof only. More description would be needed to understand what you're dealing with there!

 

[panteragstk]

What do you mean siding with blown in insulation? No solid drywall? If the siding is thin, bass might pass right through it.

Sorry, drywall was assumed by me. Yes, siding on the outside of the house. Blown in insulation then drywall.

 

[panteragstk]

Mmmmm no.

1130fps/room dimension in feet gives modes. Likewise - 1130/frequency gives dimension (unless you live in Denver) Then you still need to multiply to get the higher order modes because sound waves don't dissipate after only reflecting once. And those are the tricky ones because they are often above the crossover frequency of the subwoofer.

@panteragstk It sounds like this was a bonus room added in a space where there would have been roof only. More description would be needed to understand what you're dealing with there!

It was an addition to the floorplan when we built the house. What other info can I provide that will help?

 

[yepimonfire]

Mmmmm no.

1130fps/room dimension in feet gives modes. Likewise - 1130/frequency gives dimension (unless you live in Denver) Then you still need to multiply to get the higher order modes because sound waves don't dissipate after only reflecting once. And those are the tricky ones because they are often above the crossover frequency of the subwoofer.

@panteragstk It sounds like this was a bonus room added in a space where there would have been roof only. More description would be needed to understand what you're dealing with there!

The modes I quoted we're derived using REW's room simulator.

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[ATLAudio]

@panteragstk

I'm confident that you'll get copious amounts of room gain in a room that measures 16x14x8. How much headroom with those subs/amps is another question. You'll likely have to run some DSP correction here and there, but barring odd construction surprises, it should be fairly easy.

 

[panteragstk]

@panteragstk

I'm confident that you'll get copious amounts of room gain in a room that measures 16x14x8. How much headroom with those subs/amps is another question. You'll likely have to run some DSP correction here and there, but barring odd construction surprises, it should be fairly easy.

Thanks. When I ran two of those subs in my 13x17x8 room they did a great job. That was with only 300w each. I have a plan to get larger drivers and adding more amps, but that's going to wait a bit.

 

[TheWarrior]

The modes I quoted we're derived using REW's room simulator.

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Refer back to 'Sound Reproduction' look for Back of the Envelope calculations pg 203.

Predicted modes are sometimes higher than actual due to doors and windows allowing flex in the structure, lowering the resonant frequency.

Write out your list for height, width, length measurements and use it to refer back to when analyzing the acoustic measurement. When running multiple subs, understanding where your subwoofer is relative to the boundaries causing resonance allows you to constructively or destructively drive those standing waves.

 

[yepimonfire]

Refer back to 'Sound Reproduction' look for Back of the Envelope calculations pg 203.

Predicted modes are sometimes higher than actual due to doors and windows allowing flex in the structure, lowering the resonant frequency.

Write out your list for height, width, length measurements and use it to refer back to when analyzing the acoustic measurement. When running multiple subs, understanding where your subwoofer is relative to the boundaries causing resonance allows you to constructively or destructively drive those standing waves.

Slightly off topic, what sort of effect would an open closet with thin sliding (read: an ineffective boundary at low frequencies) doors have on room resonances? In my nearly square bedroom system, I get a huge bass suck out on the front right side (where the closet is) of the room, and very poor bass response if I place the sub on either the rear wall, near the closet, or the side wall of that side of the room.

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[rojo]

Slightly off topic, what sort of effect would an open closet with thin sliding (read: an ineffective boundary at low frequencies) doors have on room resonances? In my nearly square bedroom system, I get a huge bass suck out on the front right side (where the closet is) of the room, and very poor bass response if I place the sub on either the rear wall, near the closet, or the side wall of that side of the room.

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Sounds like you need dual subs. Shove one of these under your bed to supplement your primary sub.