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A tool for calculating front wall SBIR
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dodittydada
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#1
25th March 2013
Old 25th March 2013
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A tool for calculating front wall SBIR

Hi All,

Here is a tool I thought many of us, as well as futurer visitors will find very useful.

mh-audio.nl - Acoustic

Obviously ,as well noted , getting your speakers up and close to the front wall has a major benefit in that that it raises the frequency that SBIR occurs, hence it is easier to treat with traps that dont have to be especially massive.

Interestingly, at 1.5 mtrs (5ft) off the front wall, the range that SBIR is going to hurt you is around 57hz or so. Virtually pointless in trying to treat with porous absorbtion, yet is around the distance many recommend to get your speakers from the front wall.

Even at 1mtr distance, another common distance you see recommended everywhere, we are around 86hz. Still going to require very thick traps behind the monitors to effectively treat that.

In my own case for an example, at 170mm off the front wall, we are at 505khz 1/4 wavelength. That we may have a chance of hitting to an effective degree with a 4 inch thick panel.

Hope this of use to someone out there.
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25th March 2013
Old 25th March 2013
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Great timing! I started emptying my family room today; officially claiming it as "mine". My wife laughed when I asked if she was OK with it, pointing to the mountain of gear that has taken up residency there.

I'll be positioning monitors tonight- have a few positions I want to try- then rebuilding the room around the mix position. The vaulted ceiling seems promising, even before treatment.

Sent from my SAMSUNG-SGH-I717
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26th March 2013
Old 26th March 2013
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Nice link! I still use Thomas Barefoots Excel calulator.

Quote:
Originally Posted by dodittydada View Post
........ it raises the frequency that SBIR occurs, hence it is easier to treat with traps that dont have to be especially massive.
.........Still going to require very thick traps behind the monitors to effectively treat that.
I just want to point out that trying to treat an anomaly is near futile, especially below about 200Hz. You may have a wall bounce at, say 100 Hz, and effectively treat the bounce with trapping. The trapping will prevent that frequency from resonating.. maybe no more than 20-30 times... but can you stop that frequency for resonating more than once? Not gonna happen.

This is a fundamental. As Scotty used to say "Ye canno' change th' laws 'o physics!"

It's best to adjust your speaker/listener position of obtain the 'best' response in the sweet spot. You're not going to be able to the 'treat' the bounce economically, unless it's above the Shroeder frequency of the room.

Cheers,
John
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dodittydada
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26th March 2013
Old 26th March 2013
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John,

Does your vast experience put monitors at their best place in the room often close to the front wall? I have found this in various rooms I have been in and Im not sure I fully understand why. Im also not sure if its best for imaging this way either.
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26th March 2013
Old 26th March 2013
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Quote:
Originally Posted by dodittydada View Post
John,

Does your vast experience put monitors at their best place in the room often close to the front wall? I have found this in various rooms I have been in and Im not sure I fully understand why. Im also not sure if its best for imaging this way either.
It's usually best to put the monitors IN the front wall.
i suspect being close to the front wall has something to do with this (though you won't gain the full benefit of flush-mounted in a free-standing implementation)
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26th March 2013
Old 26th March 2013
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In a flush/soffit arrangment there are formula's to work out where the low end boost will be based around the size of the soffit face and a bunch of other stuff. If your free standing and close to the front wall, is there a way to work out where this low end boost will be?
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26th March 2013
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+1 agreed.

I was reading through the mh-audio page for wall bounce calculations and though they do not advocate flush mounting, they recommend filling the space around the speakers that are next to the wall with rock wool....

This is called 'soft-sofit' or 'soft-mounting'. I NEVER do this. It has serious drawbacks compared to proper, hard-wall flush mounting.

But, it is way better than a 'poke in the eye'.... and better than free standing too far from the boundary. so, pick your poison...

Cheers,
John
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26th March 2013
Old 26th March 2013
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Is it really better than a poke in the eye John?

A "soft soffit" is going to do sweet bugger all for speaker cabinet edge diffraction right? A proper flush/soffit mount eliminates this.

Its not going to tighten the bass and improve imaging, as a proper soffit can.

May as well just use a wall mounted panel behind each monitor, it would be much more practical and easy for one. So what is the point?

On the other hand, I think DanDan claims one of his clients, I think its a client, has done this with what he says is very good results.

Ahh, so many ways to skin a cat!
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26th March 2013
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poor cat!
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26th March 2013
Old 26th March 2013
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Great link.. Not that I always end up with the monitors close to the wall but in most smaller rooms it is recommend.
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26th March 2013
Old 26th March 2013
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A room with only one wall (and a sound transparent floor)

doditty,

If we reduce the (Speaker) Boundary Interferense Response ”problem” to
a room with only one rigid wall this calculation works. A huge simplification. SBIR is more than that.

The calculator in itself is OK...

In reality (in a room) there are many more surfaces close to the loudspeaker. The floor, often hard and reflective, the ceiling, often hard and reflective. The side wall, often hard and reflective. And a number of other surfaces just a little longer away especially if the room is small.

As John H Brandt points out ”find out the best speaker/listener positions”.

Here are some ways to practically do just that:
Speaker Stands/Behaviour of speakers mounted on desktop
Check the link in the post.


BTW I often wonder why a professional monitor speaker manufacturer simplifies the position ”problem”like this.
Is this a ”don’t scare the customer” type of advice”?

Cheers

ake
#12
26th March 2013
Old 26th March 2013
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Great

Nice thread. Wes Lachot afaik came up with an interesting statistical study concluding that 38% was a potentially great listening position.
But it was in a Soffit room. So the rule of thumb is of no use generally.

Bob Clearmountain used Yamaha NS10 speakers with toilet paper obscuring the tweeters, to mix huge hits. Yamaha sold millions of them as a result.
BUT the product they sold the NS10M bear little similarity to the original rather sweet sounding bottom of the range speaker.

So while it is IMO helpful, and we may like to use shock to diss the assumed truth that speakers need to be out from the wall, another rule of thumb is hardly welcome.

Testing is really the only way to go here. With no assumptions.

Another parable...well it's near Easter...;-)

I have tried FWBIR panels many times with no result at all. One sees traps behind speakers all the time but in testing I have seen no benefit.
But LOL, on one occasion.....Eureka SBIR
DD
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26th March 2013
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Thats interesting Dan.

Im thinking more so than ever that the wall composition has a huge effect on this. Im seeing very minimal FW SBIR in my new room , at THIS stage, speakers 170mm from the wall. The front wall is only 10mm drywall, seven inchs of insulation, then the outer wall which is only very thin metal (typical tin garage).

Maybe a very low mass wall greatly reduces this effect, which is no revelation of course, just saying. Or theorising...
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26th March 2013
Old 26th March 2013
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Hard

The FW in my exception test was 9 inch wide brick, cemented and plastered both sides to about 12" total.
DD
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26th March 2013
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jeez, scrap that theory then
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26th March 2013
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Reverse

Aaah. Nope dddd, I think your first thoughts were correct. An LF HARD wall like mine will show noticeable BIR due to the strong reflection.
On the other hand LF will partly pass through your FW, less refection, less FWBIR.
DD
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26th March 2013
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Ah sorry, I misread your post. Looking at your FR graph you have linked to...thats an incredible difference. Look at those nulls now gone! And only 100mm of absorbtion.
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26th March 2013
Old 26th March 2013
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Exception

It is kind of hard to believe but there you have. I must repeat the test some day to be sure.

DD
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27th March 2013
Old 27th March 2013
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Quote:
Originally Posted by DanDan View Post
Aaah. Nope dddd, I think your first thoughts were correct. An LF HARD wall like mine will show noticeable BIR due to the strong reflection.
On the other hand LF will partly pass through your FW, less refection, less FWBIR.
DD
My Front wall is interior : 5/8 inch sheetrock on either side of the 2x4 frame, plus wood panel on the opposite side(covered with thick rug). That room used to be the band rehearsal / tracking room, but now its just for overdubs...

So I started thinking why not cut some holes in it? No reason i couldn't also do it behind the speaker or along the floor - ceiling boundaries
That can only help it "breathe", and let all those bad bass reflections out, right? (its about 35 feet to the real foundation).

Security is not really an issue so I figure I can replace it the sheet rock with some flimsy pegboard.

I've probably got bigger problems with a cement floor and low ceiling, but every little bit helps - and this is easy.

I started cutting some 1' x 2' holes in the corners (no measurements yet)
A question coming to mind is - if I succeed in making the corner no longer look like a corner, bass-wise, am i wasting the effort of having a large corner bass trap there? Maybe I can relocate some of it...

Another situation: Let's say I have a 4", 2'x4' OC703 panel hanging on the wall behind the speaker (over the existing sheetrock etc). If I cut hole approximately the size of the panel (replace with just pegboard ) is there any point to having the trap there anymore?
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27th March 2013
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Quote:
Originally Posted by jeff_free69 View Post
...why not cut some holes in it?...
That can only help it "breathe", and let all those bad bass reflections out, right?
I started cutting some 1' x 2' holes in the corners...
Why not make them 2'x4' or 4'x8' or... Why stop with the front wall? Why not holes on the sides or back? Why not holes in the ceiling and floor?
Why have any walls?
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27th March 2013
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27th March 2013
Old 27th March 2013
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Quote:
Originally Posted by John White View Post
Why not make them 2'x4' or 4'x8' or... Why stop with the front wall? Why not holes on the sides or back? Why not holes in the ceiling and floor?
Why have any walls?
Yes indeed, when the weather warms up I'm moving it all out into the yard!

Until then I'm still working on a way to put holes in the cement floor.

Actually I already have openings in one side (interior) wall.
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27th March 2013
Old 27th March 2013
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Holes

LOL. Not following the train of thought jeff.
I thought that you didn't have strong FWBIR?
Plasterboard on studs can be a useful panel trap if the internal damping is right.
Andre calls this Invisible Alpha.
Holes would, I guess raise the peak absorption frequency.
But it's a good week to go Holy.
DD
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27th March 2013
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Quote:
Originally Posted by akebrake View Post
...........
BTW I often wonder why a professional monitor speaker manufacturer simplifies the position ”problem”like this.
Is this a ”don’t scare the customer” type of advice”?
.........
Most probably. If one manufacturer tell to potential customers that their speakers needs "special postioning", nobody will buy it, because other speakers "doesn't need special positioning".

I always use "soft" soffit or "soft" mounting, or heavy bass traps behind speakers, at their sides and above them. Ordinary checking which boundary-speaker (mirror) images generate interferences will show where we need absorption to solve this problems a bit, but AFTER proper loudspeaker/listener positioning...

Hard wall soffit mounting cannot solve interferences with ceiling, floor and side walls... only back wall, and loudspeaker cabinet difraction may be solved. But there must be clear that we do not have too much speakers which can be soffit mounted in hard wall, without serious loudspeaker crossover modification (baffle step compensation must be disabled). Nearly all today loudspeakers are designed to be "free standing"

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Better control room needs:
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-speaker stands
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-a broader and thicker cloud
-a broader and thicker wall panels
-more super chunks in all corners
-a binary diffuser slats over proposed treatment
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28th March 2013
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Quote:
Originally Posted by boggy View Post
Most probably. If one manufacturer tell to potential customers that their speakers needs "special postioning", nobody will buy it, because other speakers "doesn't need special positioning".
Triple +1 I love it! LOL

Sums it up perfectly. Well, like we all keep saying, A critical listening room IS a system. - Correct room treatment and alignment of speakers, listener, and the room system is critical to getting the most out of any particular arrangement.

Cheers,
John
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28th March 2013
Old 28th March 2013
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Quote:
Originally Posted by jhbrandt View Post
Triple +1 I love it! LOL

Quote:
Originally Posted by jhbrandt View Post
Sums it up perfectly. Well, like we all keep saying, A critical listening room IS a system. ....
I don't agree...
Firstly, critical listening room is a politics...


#27
31st March 2013
Old 31st March 2013
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[QUOTE=boggy;8887253]

Quote:
Most probably. If one manufacturer tell to potential customers that their speakers needs "special postioning", nobody will buy it, because other speakers "doesn't need special positioning".
Nice!
Thanks for great comments (as usual) and sharing your wievs.

Quote:
... Ordinary checking which boundary-speaker (mirror) images generate interferences will show where we need absorption to solve this problems a bit, but AFTER proper loudspeaker/ listener positioning...
I am a little curious about your "ordinary checking". Would you mind expand a little on that?

And also... You seem to prefer searching for "the best" loudspeaker/ listener position before installing acoustical treatment.


Quote:
Hard wall soffit mounting cannot solve interferences with ceiling, floor and side walls... only back wall, and loudspeaker cabinet difraction may be solved.
(Bolded mine)

I guess you meant the loudspeaker wall (in front of the listener) ?

Best

Ake
#28
13th April 2013
Old 13th April 2013
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Quote:
Originally Posted by akebrake View Post


Nice!
Thanks for great comments (as usual) and sharing your wievs.
You're welcome
Quote:
Originally Posted by akebrake View Post


I am a little curious about your "ordinary checking". Would you mind expand a little on that?
It is nothing spectacular. I plan to write a paper about treatment of non resonant interferences (SBIR), mainly because that only Newell's N-E design seriously takes it into account. I don't have time now...
Quote:
Originally Posted by akebrake View Post
And also... You seem to prefer searching for "the best" loudspeaker/ listener position before installing acoustical treatment.
Yes, because I use "positioning before" mostly to reduce cost of LF treatment. I know that (strong) LF treatment change room response usually in non predictable way (looking from loudspeaker position response perspective), but, from my experience, positioning "before" treatment is less wrong way (or something like "pick your poison")... at least because I always do fixed treatment so there aren't too much space for experimenting, as people here may do with modular elements.
Quote:
Originally Posted by akebrake View Post
I guess you meant the loudspeaker wall (in front of the listener) ?
....
Yes. I look often at room from loudspeaker's perspective


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16th April 2013
Old 16th April 2013
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Quote:
Originally Posted by boggy View Post
You're welcome

It is nothing spectacular. I plan to write a paper about treatment of non resonant interferences (SBIR), mainly because that only Newell's N-E design seriously takes it into account. I don't have time now...
Ahh, that's interesting! Looking forward to that paper

Quote:
Originally Posted by boggy View Post
Yes, because I use "positioning before" mostly to reduce cost of LF treatment. I know that (strong) LF treatment change room response usually in non predictable way ...
Makes perfectly sence, thanks for the explanation

Quote:
Originally Posted by boggy View Post
Yes. I look often at room from loudspeaker's perspective

Another good idea when it comes to understanding of what surfaces and obstacles the soundwave will meet after leaving the speaker.

Best

Ake
#30
17th April 2013
Old 17th April 2013
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So, there seems to be three potentially useful ways of placing a speaker system when trying to avoid front wall SBIR related problems:

1) Flush mounted (full-range speaker)
2) Very close to the front wall (full-range speaker)
3) Subwoofer(s) close to the front wall and satellites far enough to lower the SBIR frequency below the crossover frequency. (Bass-managed system)

Are there any major drawbacks to number 3?
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