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Don't set your subwoofer on the floor

youngho

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Throwing away boundary reinforcement sounds like a daft idea to me I'm afraid. Possibly there is an upside if EQ isn't being used, but it should be.
I don't think you really understand how diaphragmatic absorbers work. How about this: imagine removing a peak acoustically, instead of using EQ, also potentially addressing some nulls? For example, take the following thought experiment:

You have a 20 foot wide room. This results in width modes due to axial standing waves at about 28.25 Hz, 56.5 Hz, 84.75 Hz, etc. (it's a little more complicated, but let's go with the simplest model). A person sitting in the midline of the room sits at the node of the first-order mode at 28.25 Hz so will experience a relative null at this frequency due to cancellation, especially if the bass source (like a single subwoofer) is positioned closer to a sidewall (unless you have two bass sources positioned close to the sidewalls, but let's stick with the single subwoofer until the next paragraph). They will experience a peak at 56.5 Hz since they're in the antinode for the second-order width mode, a null at 84.75, etc. You could bring down the 56.5 Hz peak with EQ. However, if this were a home theater, there might be multiple seats set up in a row, so a listener sitting near the end of the row, perhaps 5 feet to the side of the midline, is sitting in a node for this second-order width mode, so they were experiencing a null already, and the EQ that you just did to bring down the peak in the midline doesn't help them at all.

You could address the first-order node with two subwoofers, one positioned close to each side wall. This results in mode cancellation for the odd-order modes, but doesn't address the even-order ones. Alternatively, you could position two subwoofers along the midline of the room, maybe one in front and one in back. Because they're positioned in the nodes of the odd-order modes, they don't activate these standing waves, but they still activate the even-order ones because they're positioned in the antinodes for these

Now you take two very large diaphragmatic absorbers tuned to 56.5 Hz and position them along the sidewalls lateral to the listening position. These now address the second-order width mode so that the listener in the midline (who was experiencing a peak) and the listener at the end of the row (who was not experiencing much bass at the frequency at all) now experience much more similar bass levels at this frequency. The subwoofers still have boundary reinforcement, but the listeners are less subject to the frequency response irregularities due to standing waves at the frequencies relevant to the diaphragmatic absorbers.

Hope that makes sense.

Young-Ho

p.s. the first paragraph of the thought experiment goes part of the way towards explaining the 38% "rule" for listener positioning, since this is halfway between the nodes for the first-order and second-order length modes
 
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Ultrasonic

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I don't think you really understand how diaphragmatic absorbers work. How about this: imagine removing a peak acoustically, instead of using EQ, also potentially addressing some nulls? For example, take the following thought experiment:

You have a 20 foot wide room. This results in width modes due to axial standing waves at about 28.25 Hz, 56.5 Hz, 84.75 Hz, etc. (it's a little more complicated, but let's go with the simplest model). A person sitting in the midline of the room sits at the node of the first-order mode at 28.25 Hz so will experience a relative null at this frequency due to cancellation, especially if the bass source (like a single subwoofer) is positioned closer to a sidewall (unless you have two bass sources positioned close to the sidewalls, but let's stick with the single subwoofer until the next paragraph). They will experience a peak at 56.5 Hz since they're in the antinode for the second-order width mode, a null at 84.75, etc. You could bring down the 56.5 Hz peak with EQ. However, if this were a home theater, there might be multiple seats set up in a row, so a listener sitting near the end of the row, perhaps 5 feet to the side of the midline, is sitting in a node for this second-order width mode, so they were experiencing a null already, and the EQ that you just did to bring down the peak in the midline doesn't help them at all.

You could address the first-order node with two subwoofers, one positioned close to each side wall. This results in mode cancellation for the odd-order modes, but doesn't address the even-order ones. Alternatively, you could position two subwoofers along the midline of the room, maybe one in front and one in back. Because they're positioned in the nodes of the odd-order modes, they don't activate these standing waves, but they still activate the even-order ones because they're positioned in the antinodes for these

Now you take two very large diaphragmatic absorbers tuned to 56.5 Hz and position them along the sidewalls lateral to the listening position. These now address the second-order width mode so that the listener in the midline (who was experiencing a peak) and the listener at the end of the row (who was not experiencing much bass at the frequency at all) now experience much more similar bass levels at this frequency. The subwoofers still have boundary reinforcement, but the listeners are less subject to the frequency response irregularities due to standing waves at the frequencies relevant to the diaphragmatic absorbers.

Hope that makes sense.

Young-Ho

p.s. the first paragraph of the thought experiment goes part of the way towards explaining the 38% "rule" for listener positioning, since this is halfway between the nodes for the first-order and second-order length modes
Apologies that my brief replies apparently lead to you writing the above, as I am familiar with everything that you have said. I completely understand the use of diaphragmatic absorbers in general as a targeted solution to room mode issues at partcular frequencies. What I don't 'buy' is the blanket advide to place all subwoofers on one.
 

Spkrdctr

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Well, Rel just posted their "Dial in a Line Array of REL Acoustics Subwoofers" guide; on and off the floor for that matter; Seems like all the science based methods of placing subwoofer in your room (aka Welti research) are not the way to go when we talking audiophiles stuff :)

I see a stupid waste of money. Oh well.
 

Ultrasonic

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Oh, you had said "large diaphragmatic absorber," but I don't consider these products to be large at all.

You may already be familiar with this, but I thought it was quite interesting and counter-intuitive: AES paper and Stereophile discussion. Here are the products in question. One could therefore use a diaphragmatic absorber tuned below 60 Hz, depending on the specifics of one's room and floor construction.

Young-Ho

I'll have a look at the papers later but the product linked to is described as being all about isolation from the floor (which makes sense where floor constuction makes this beneficial) but says nothing about addressing room mode issues (my point).
 

killdozzer

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When I first came here a member recommended this gentleman, but something told me it's not my pair of socks. In theory, you might say that evening out the low freq response in your room might benefit from going up as well. But it's simply not necessary as we can derive from thousands of very good system that didn't lift subs. It's simply not imperative to this specific goal. But what it is, it's very hard to achieve. Imagine 30-40 pounds beast on some legs, those legs would have to be silly heavy and sturdy... Like a concrete column. I just don't see it.
 

Spkrdctr

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When I first came here a member recommended this gentleman, but something told me it's not my pair of socks. In theory, you might say that evening out the low freq response in your room might benefit from going up as well. But it's simply not necessary as we can derive from thousands of very good system that didn't lift subs. It's simply not imperative to this specific goal. But what it is, it's very hard to achieve. Imagine 30-40 pounds beast on some legs, those legs would have to be silly heavy and sturdy... Like a concrete column. I just don't see it.

Subs are not 30-40 pound beasts, they are 100 pound beasts. When 100 lbs. falls to the floor, you will hear it!! If you get in the way you will get a trip to the hospital.
 

killdozzer

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Subs are not 30-40 pound beasts, they are 100 pound beasts. When 100 lbs. falls to the floor, you will hear it!! If you get in the way you will get a trip to the hospital.
:D
Even more so. I didn't want to overdo it! But I agree.
 

Ultrasonic

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Any diaphragmatic absorbers positioned on the floor could be tuned to address height modes.

Sure. Are the products you linked to even diaphragmatic absorbers though? These need to be sealed units whereas what you linked to appears to have open sides. I'm sure these weren't the products being referred to in the original video actually.
 

Ultrasonic

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No, and I never said that that I was linking to diaphragmatic absorbers. What I wrote was "You may already be familiar with this, but I thought it was quite interesting and counter-intuitive: AES paper and Stereophile discussion. Here are the products in question. One could therefore use a diaphragmatic absorber tuned below 60 Hz, depending on the specifics of one's room and floor construction." In the original videos (which I thought were terrible), Dennis Foley seems to discuss using some sort of diaphragmatic absorber platform beneath the subwoofers in order to isolate them. The results of Katz's measurements using EVP isolation products, which are not diaphragmatic absorbers, were interesting: "However, at lower frequencies—below about 60Hz—floor vibrations increased when the isolators were used." This suggests to me that subwoofer isolation products would need to be designed accordingly to prevent this from happening, even in a room-specific way to address floor resonances. I should have written, "[I wonder if or Perhaps] one could therefore use a diaphragmatic absorber tuned below 60 Hz, depending on the specifics of one's room and floor construction[, to address the question of isolation and avoiding excitation of floor resonances.]" On further reflection, however, it does not seem likely to me to be a useful way of approaching this specific problem.

I had trouble finding it earlier, but here is another link to Bob Katz with some measurements from when he used the EVP isolators on a cement slab: https://www.digido.com/installing-d...WpYfm7CpBm4EpbChOwRzCFgso9c_c3m-BIo#technical. The waterfalls in this scenario showed improvement in the subwoofer range.

I think you may be looking to "win" some kind of argument, and I don't really have any interest in participating further in that. I'd rather learn something or else pass along useful information, as I did above with specific links to Welti and Fazenda, among others.

Oh no, very much not the point in bold. I hate that and it really isn't what I try to achieve on forums at all. I absolutely post to learn and apologies that you've clearly got a different impression.

Where we appear to have been talking at cross-purposes is I have no issue whatsoever with trying to decouple subwoofers from problematic floors. I joined this thread at a point where the videos were being dismissed out of hand whilst both decoupling and having subs at a variety of heights are completely valid as far as I'm concerned. It was specifically the the use of diaphragmatic absorption for reasons other than decoupling that I questioned and what I thought you were reponding to.
 

Ultrasonic

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Mulling this over, I also wonder if diaphragmatic absorbers are necessarily the best option for decoupling? Wouldn't this limit the decoupling effectiveness to a narrower frequency range than other options?
 

keenly

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Mulling this over, I also wonder if diaphragmatic absorbers are necessarily the best option for decoupling? Wouldn't this limit the decoupling effectiveness to a narrower frequency range than other options?
What would you say are the best products we can get in the UK for putting under our subs?
 

Spocko

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Subs are not 30-40 pound beasts, they are 100 pound beasts. When 100 lbs. falls to the floor, you will hear it!! If you get in the way you will get a trip to the hospital.
As it pertains to room modes I can see the benefit of vertically raising subs off the floor, consistent with moving subs along the x-y axis. I believe these modes are not vertical columns but rather 3D spheres; however, impractical as the subcrawl is for many, it is still do-able and effective. What I cannot imagine doing is having my wife holding a 100lb sub as I yell "Ok honey, can you lift it another 6 inches while I run REW one more time? OK, no, that didn't work, how about lifting it another 12 inches now..."
 

thorvat

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I had trouble finding it earlier, but here is another link to Bob Katz with some measurements from when he used the EVP isolators on a cement slab: https://www.digido.com/installing-d...WpYfm7CpBm4EpbChOwRzCFgso9c_c3m-BIo#technical. The waterfalls in this scenario showed improvement in the subwoofer range.

Unfortunatetly that particular measurement is hardly done the way it should be. For a start, 2 measurements were not done consecutively, one was done in November, the other in December, which leaves space for speculation about the consistency (mic position, speaker position, etc.).

I also noticed that frequency response changes between measurements, say at app 175Hz, which is hard to explain.

And finally, why would you make the measurement with Acourate and then import it into REW for presentation when you can easilly make that same measurement with REW?
 

thorvat

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Oh no, very much not the point in bold. I hate that and it really isn't what I try to achieve on forums at all. I absolutely post to learn and apologies that you've clearly got a different impression.

From my persepctive you have raised some valid points doing it in a civilised manner, so I see no need to apologise. I was expecting him to answer you, instead it seems he acted as you insulted him. But the fact is you didn't.
 

Spkrdctr

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As it pertains to room modes I can see the benefit of vertically raising subs off the floor, consistent with moving subs along the x-y axis. I believe these modes are not vertical columns but rather 3D spheres; however, impractical as the subcrawl is for many, it is still do-able and effective. What I cannot imagine doing is having my wife holding a 100lb sub as I yell "Ok honey, can you lift it another 6 inches while I run REW one more time? OK, no, that didn't work, how about lifting it another 12 inches now..."

That is TV "Divorce Court" material right there! LOL.
 

Ultrasonic

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This isn't the most modern of websites but for anyone who hasn't seen it the following may be of some interest regarding tyring to meaure any benefits of decoupling in the cotext of a small-ish speaker:


Subwoofers are arguably a rather different subject though.
 

Ultrasonic

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What would you say are the best products we can get in the UK for putting under our subs?

I'm afraid I'm really not sure. I'm lucky to have a solid floor in my lounge so it isn't something I've particularly explored.

Many years ago I did have a sub on a platform made from Auralex Platfoam and a paving slab sat on top of it, but this was in an upstairs flat with pathetic sound-proofing to the room below and so I basically never used the sub at any useful volume. I don't really feel I can draw any conclusions from this therefore.

Townshend Audio demonstrate the effectiveness of their isolation platforms by putting a tablet/phone running a vibrometer app on top of the speakers and then stamping on the floor next to the speaker. I've never been too sure of the validity of this but for what it's worth I've found Auralex Platfoam does basically nothing using this test method, but Sorbothane hemispheres do. This is testing under speakers not a sub thouh, and it's important with Sorbothane to use the right type and number of pads for the weight they are supporting.
 

Spkrdctr

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I'm afraid I'm really not sure. I'm lucky to have a solid floor in my lounge so it isn't something I've particularly explored.

Many years ago I did have a sub on a platform made from Auralex Platfoam and a paving slab sat on top of it, but this was in an upstairs flat with pathetic sound-proofing to the room below and so I basically never used the sub at any useful volume. I don't really feel I can draw any conclusions from this therefore.

Townshend Audio demonstrate the effectiveness of their isolation platforms by putting a tablet/phone running a vibrometer app on top of the speakers and then stamping on the floor next to the speaker. I've never been too sure of the validity of this but for what it's worth I've found Auralex Platfoam does basically nothing using this test method, but Sorbothane hemispheres do. This is testing under speakers not a sub thouh, and it's important with Sorbothane to use the right type and number of pads for the weight they are supporting.

Wow. Stomping on the floor next to a speaker is useless. The things audiophile nuts will do to sell a product. I'm shocked at this one! I think buying metal discs to interfere with the natural magnetic waves from the earth would be better spent money.
 

thorvat

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Wow. Stomping on the floor next to a speaker is useless. The things audiophile nuts will do to sell a product. I'm shocked at this one! I think buying metal discs to interfere with the natural magnetic waves from the earth would be better spent money.

Single sub, when sitting on the floor in the corner can actually do a decent job. That is assuming it is well integrated with mains, of course. Having 2 subs is better, if your floor space and budget can allow it, but in that scenario there are better places then corners. :)
 
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