DIY 33" Subwoofer

blaze182

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Feb 7, 2021
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Hello everyone, thanks for reading.

I'm curious to hear your thoughts on ultra large subwoofers.

I'm contemplating building a single 33" subwoofer into a coffee table, with cross-over at about 25hz. The purpose of this, aside from the obvious, is to avoid using multiple smaller subwoofer units dispersed in the room.

Can anyone share some thoughts as to why such a large subwoofer is not preferable? Are there problems with a single sub placed centrally into the room playing exclusively below 25hz?

I see people sporting multiple 15-24" subwoofers in a single HT/living room application, and, assuming those subs are playing exclusively below 30hz, then why are multiple smaller subs a preferred technical choice, placement notwithstanding.
 

Kal Rubinson

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May 4, 2010
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Multiple subs placed around the room with a little care will smooth the in-room response over a large listening area without heroic room correction or massive acoustic devices. The output of a single sub, wherever placed, is subject to the effects of room dimensions and will produce a highly irregular frequency response unless other steps are taken to compensate for those effects. Size of sub is not an issue but one sub cannot be in two (or more) acoustical locations at the same tiime!
See: https://www.harman.com/documents/multsubs_0.pdf but there are many other reports.
Here is one of my personal experiences with the difference between just one and two subs: https://www.stereophile.com/content/jl-audio-fathom-f110v2-powered-subwoofer-measurements
 
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ddk

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May 18, 2013
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Hello everyone, thanks for reading.

I'm curious to hear your thoughts on ultra large subwoofers.

I'm contemplating building a single 33" subwoofer into a coffee table, with cross-over at about 25hz. The purpose of this, aside from the obvious, is to avoid using multiple smaller subwoofer units dispersed in the room.

Can anyone share some thoughts as to why such a large subwoofer is not preferable? Are there problems with a single sub placed centrally into the room playing exclusively below 25hz?

I see people sporting multiple 15-24" subwoofers in a single HT/living room application, and, assuming those subs are playing exclusively below 30hz, then why are multiple smaller subs a preferred technical choice, placement notwithstanding.
HT application is not critical you can use anything to go boom as long as placement doesn’t cancel other bass nodes in the room, but that’s true for any size subwoofer. If you take care of that I think a 33” driver can actually be cool.

david
 
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Kal Rubinson

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Wouldn't a sub that large be pretty slow, sonically speaking?
Possibly but it really depends on how it is built, driven and loaded.
HT application is not critical you can use anything to go boom as long as placement doesn’t cancel other bass nodes in the room, but that’s true for any size subwoofer.
A bit cynical and dismissive of serious HT, imho, but I am not sure what you mean by "as long as placement doesn’t cancel other bass nodes in the room." Cancellation of nodes is exactly what one wants for a flat response and it can be accomplished by the use of DSP, heroic acoustical treatment or multiple subs.
 
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ddk

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May 18, 2013
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Possibly but it really depends on how it is built, driven and loaded.

A bit cynical and dismissive of serious HT, imho,
Neither, what’s there below 25hz in a typical movie soundtrack today aside from digitized fake sound effects?
but I am not sure what you mean by "as long as placement doesn’t cancel other bass nodes in the room." Cancellation of nodes is exactly what one wants for a flat response and it can be accomplished by the use of DSP, heroic acoustical treatment or multiple subs.
What I meant was in the wrong place a sub can cancel out the bass output from the main speakers and you’ll end up with an audible dip or hole or whatever you want to call it. Just because there’s a low pass filter it doesn’t mean that the sub is only operating below the set frequency, reality is that it’s operating continuously at much higher frequencies, some depending on the driver and the filter can still be heard into thousands of hertz. Positioning and setup matters.

I use subs in many two channel installations but never as a bandaid for poor setup or poor acoustics only to extend/support the system’s low frequencies. Maybe he is but I don’t think that OP’s question had anything to do with flattening bass response with a 33” driver.

I realize DSP is a given in a typical surround system and people can use it to “flatten the response” but IME there’s not much point fussing over sound quality once you take that route.

david
 
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Kal Rubinson

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Neither, what’s there below 25hz in a typical movie soundtrack today aside from digitized fake sound effects?
Dunno but that does not mean one wants it to be poorly reproduced. OTOH, the same principles apply to music low frequencies on the same system.
What I meant was in the wrong place a sub can cancel out the bass output from the main speakers and you’ll end up with an audible dip or hole or whatever you want to call it.
Ah. So, you are referring to an interaction between the sub and the main, both of which are subject to the same acoustical constraints (nodes. nulls) and, again, the best approach is to have all sources placed to avoid this. In the majority of real domestic rooms, there is no "perfect" place for the sub or the mains that completely avoids nulls and/or nodes, so the use of multiple, even if smaller, subs is a reliable approach.

Unfortunately, one has to deal additional constraints with the main speakers. Their placement (and there are 2 or more of them) also affects frequency balance, imaging and soundstage and, generally, these dominate the placement choices, thereby justifying the addition of subs.
I use subs in many two channel installations but never as a bandaid for poor setup or poor acoustics only to extend/support the system’s low frequencies.
Agreed. Never said otherwise.
 
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blaze182

Member
Feb 7, 2021
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1
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34
HT application is not critical you can use anything to go boom as long as placement doesn’t cancel other bass nodes in the room, but that’s true for any size subwoofer. If you take care of that I think a 33” driver can actually be cool.

david

Yes, I thought it could be cool, too, and well concealed.

Multiple subs placed around the room with a little care will smooth the in-room response over a large listening area without heroic room correction or massive acoustic devices. The output of a single sub, wherever placed, is subject to the effects of room dimensions and will produce a highly irregular frequency response unless other steps are taken to compensate for those effects. Size of sub is not an issue but one sub cannot be in two (or more) acoustical locations at the same tiime!
See: https://www.harman.com/documents/multsubs_0.pdf but there are many other reports.
Here is one of my personal experiences with the difference between just one and two subs: https://www.stereophile.com/content/jl-audio-fathom-f110v2-powered-subwoofer-measurements

Thanks for sharing both the links, they were very helpful.

What would be the designer-intended use case, or any good case, for such large subwoofers typically?

Is there benefit to placing subwoofers in the nearfield so as to offset the presence of room interference/nulls at the listening position? Is this a solution, or just a part of one?

Wouldn't a sub that large be pretty slow, sonically speaking?

I would think so, though it's only playing very low frequency. I would expect to trade some speed for displacement.
 

Kal Rubinson

Well-Known Member
May 4, 2010
2,360
697
1,700
NYC
www.stereophile.com
What would be the designer-intended use case, or any good case, for such large subwoofers typically?
Depends on the situation. If you have a very large space to fill, you might need fewer of these than the number of smaller subs to get sufficient output. Also, if you are pursuing extreme low frequencies at high levels. Otherwise, imho, it mostly for bragging rights.
Is there benefit to placing subwoofers in the nearfield so as to offset the presence of room interference/nulls at the listening position? Is this a solution, or just a part of one?
That can work but, in most rooms, a single nearfield sub is tricky because, despite the low frequencies involved, one tends to localize the low sounds as weighted to that side/direction. Might work best in a very large space where it would not preferentially load the adjacent room corner.
 
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