Don't set your subwoofer on the floor

[carewser]

Heh. I saw this guy a while back. I think I was researching room treatment. My BS detector went off far too late. But it was the fantastical quasi-scientific lingo that sounded the alarm.

For subs, the more stationary the enclosure, the lower the THD. While a heavier cabinet is better, I use carpet spikes to keep my subs from walking around. Both the JBL 550P and SB2000pro just want to get up and take a walk with the standard rubber mounts.

Even with rubber feet your subs move around? I agree and think the knock test is legit, that is, to knock on your speaker/subwoofers enclosure and if it sounds solid it's better, of course a heavy enclosure is all part of that as well. Since I like my music loud countless times my speakers have moved around on their own and I blame the enclosure

 

[carewser]

I've not watched the videos

I don't expect many here have even though both videos combined are less than 11 minutes

 

[NTK]

That still doesn’t make it the best location

Why waste boundary gains?

 

[voodooless]

Why waste boundary gains?

I just explained.

 

[youngho]

Yes, you get maximum room gain, but that does not mean it’s the best location for an even frequency response. A better location is actually along a wall right in the middle. Especially with multiple subs.

If you're referring to Welti's multisub paper, that came out of Harman. The Powerpoint is no longer linked here, but I recall that the frequency response measurements of the Reference Room were extremely even, despite your concerns. They used four corner subwoofers along with Sound Field Management, as mentioned in the comments. You can read more from Welti and Toole.

 

[voodooless]

If you're referring to Welti's multisub paper, that came out of Harman. The Powerpoint is no longer linked here, but I recall that the frequency response measurements of the Reference Room were extremely even, despite your concerns. They used four corner subwoofers along with Sound Field Management, as mentioned in the comments.

Yes, that’s the one! I was looking for that

 

[abdo123]

i feel you're guys missing few points:

1) Hi-Fi advice =/= Home Cinema Advice where there are multiple seats.

2) Even if he thinks a certain way, the customer is always right.

His advice is usually legit in a "Minimize Compromises in anyway even if it means barricading your windows" kind of way.

 

[pozz]

diaphragmatic absorption

Aka panel absorbers. These are one of the few kinds of treatments that work for bass.

His main thing is to sell very expensive absorbers which have activated carbon cores and huge diffusors. Their effectiveness and his data are really questionable, and the prices are nuts. He rode the YouTube wave a few years ago as this kind of content began appearing online and managed to get a following.

He has no formal background in acoustics, but did work on projects and room construction. All of his advice is half informed at best.

His videos irritate me to no end.

RPG Modex Edge a Resonator Bass Absorber

https://www.rpgacoustic.com/modex-edge/ I see RPG has a new to me product, any inputs would be appreciated. It looks to me like it is some kind Hemholtz Resonator type product. The Modex Edges are dedicated, broadband, low frequency sound absorbers designed to balance the modal distribution...

www.audiosciencereview.com

 

[digitalfrost]

If your subwoofer is transferring vibration into the floor through direct contact it is not heavy/sturdy enough.

This. I built a couple of DIY subwoofers and most would wander on the floor even at medium volume. This also happened with subwoofers that I considered quite heavy. Nowadays I simply built impulse compensated subs, they are inert. You can even put them on a desk without anything rattling.

 

[frankrcarter]

Why would moving the subwoofer in the Z axis be less valid a solution to smoother frequency response than the X and Y axis?

I’ve always wondered if I do 4 subs in the bottom left/right and front top left/right (possibly behind baffle wall), I’ve covered the 4 corners and would it have the same effect as the 4 corners on the ground?

 

[tecnogadget]

Yes, you get maximum room gain, but that does not mean it’s the best location for an even frequency response. A better location is actually along a wall right in the middle. Especially with multiple subs.

I understand your point and already seen several examples, with simulations and measurements of good locations for subwoofer response.

Why waste boundary gains?



View attachment 156242

But I’m on NKT side, since when you are dealing with non optimum, unregular shaped room, most simulations or predictions loose sense, and most of the time makes it imposible to pinpoint the best placement beforehand. Thus measurement becoming mandatory to get a glimpse of whats happening at different locations.

A good solution would be to take advantage of boundary gain free extra output boost, shaping or tailoring the response by DSP. Thanks to all that extra output, you are given with more freedom to tame and cut the peaks, and shape the response with negative filters, not loosing that much gain in between.

 

[Weeb Labs]

Why would moving the subwoofer in the Z axis be less valid a solution to smoother frequency response than the X and Y axis?

Can't imagine why, Superman.

 

[617]

Why?

(hint: wavelength at 50 Hz is about 20 feet)

Even better than that - for a pitch to be recognized you need about 3-5 wavelengths at that frequency, so the path length is more like 60-100'

 

[SIY]

Even better than that - for a pitch to be recognized you need about 3-5 wavelengths at that frequency, so the path length is more like 60-100'

I was thinking more of interference effects (or lack of same). After all, we can distinguish bass pitch with headphones.

 

[Blumlein 88]

I've not put my subs anywhere except on the floor. However, if you look at sims, the one in REW will do, you activate somewhat different room modes by varying the height of the sub as well as its x-y positioning. Enough that different heights can allow you to get smoother response over two or three octaves in the bass there. Or so the various sims software predict.

As a thought experiment I've wondered about 4 subs in the front 4 corners of a room. This gets you all the same room modes, but with use of the upper front corners lets you sling about more subs without eating up precious room real estate out in the room. Then being the devious and impractical audiophile I am, my mind went immediately to the idea of a stacked column floor to ceiling in the front two corners for maximum sub output capability. Like maybe a solid stack of Dayton Audio 12 inch subs or some such crazy idea. Eventually of course I end up with a Grateful Dead-like wall of sound. But then the Wall of Sound reminds me of Phil Spector sound and I write the whole thing off as a bad idea.

 

[thewas]

Yes, you get maximum room gain, but that does not mean it’s the best location for an even frequency response. A better location is actually along a wall right in the middle. Especially with multiple subs.

Exactly the mid of a wall has also its own peculiarities/problems like exciting maximally the symmetric modes on that axis, that's why often (usually for only 1-2 subs) rather positions like 1/3 and 2/3 of the wall length are recommended (for example by Neumann).

 

[youngho]

Why would moving the subwoofer in the Z axis be less valid a solution to smoother frequency response than the X and Y axis?

I’ve always wondered if I do 4 subs in the bottom left/right and front top left/right (possibly behind baffle wall), I’ve covered the 4 corners and would it have the same effect as the 4 corners on the ground?

Hi Frank,

Usually, most listeners in a home theater or listening room context have their heads at a relatively similar height along the Z axis, as opposed to a significant variability along the X-axis and less so along the Y-axis, assuming 1-3 rows of listeners. Since most listeners end up with their ears relatively close to 35-38" from the floor in a seated position, that puts them relatively close to 33-38% of most typical home theater or listening room heights in the US domestic setting. The most significant axial modal frequencies occur at even fractions of room dimensions, so for ceiling height, that's likely to occur outside of the subwoofer frequency range in terms of what I'm discussing here.

However, in theory, you are absolutely correct, especially when we're talking about larger rooms, and there are alternate models of multiple subwoofer configuration called the double bass array. See here for more information, also for the source-sink approach: https://www.researchgate.net/public...reference_of_modal_control_in_listening_rooms

Young-Ho

 

[youngho]

Exactly the mid of a wall has also its own peculiarities/problems like exciting maximally the symmetric modes on that axis, that's why often (usually for only 1-2 subs) rather positions like 1/3 and 2/3 of the wall length are recommended (for example by Neumann).

I think by symmetric you mean even-order modes, but yes, you're right. Still, one could potentially adjust the crossover between the speakers and the subwoofers to take that into account. Similarly, one could potentially adjust the listener position, accordingly.

For example, for a 14'x20' room, if the speakers were positioned along the short wall axis and the subwoofers were positioned in the midpoints of the long walls, and if the listeners were close to the center of the room, a lower crossover like 60-70 Hz would not result in the subwoofers activating the second order mode. Alternatively, if the speakers were positioned along the long wall axis and the subwoofers were positioned in the midpoints of the short walls, then one could position the listeners a little closer to the back (hence the 38% rule) out of the anti-node of the second order mode, accordingly.

Young-Ho

 

[MikeMc Retired]

I built my dual 12" sub (a very long time ago) from 1.25" MDF, including the internal bracing. At my age, the only way I'm getting it off the floor is with a couple of pullies and a winch!

 

[Ultrasonic]

Having now had chance to watch the two videos (the second of which was a complete waste of time) I'll say they include two main points that I actually think it's hard to argue with (and one I struggle with).

The idea of using a variety of heights to improve overall bass response is accurate, and the concept of wanting to decouple a sub from a suspended wooden floor is hardly new either. I'm lucky enough to have a solid floor but when I had a downfiring sub I did notice I could feel (not hear) vibration travelling through the carpet and underlay which could be distracting but I solved this by using spike to couple to the concrete below.

What I struggle with is the concept of using a large diaphragmatic absorber, since wouldn't this be essentially absorbing significant acoustic output from the initial boundary reflection?