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zydeco

Short vs Long Wall Set-up in the age of subs + DSP

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22 hours ago, Al.M said:

Not technically ideal but my setup sounds better on long wall with head against rear wall not only because I have no option but also that it sounds quite acceptable with plenty of clarity and imaging still retained and not audibly worse than other more technically ideal setups I’ve heard and in comparison to some scenarios better sounding. Perhaps not all of the potential issues involved are explained by the technical reasons given so far.

One tricky but key thing when auditioning different setups like this, is you need to do something to account for the huge differences/errors in the LF (eg. <300Hz) ..... otherwise, when you listen to the different setups, then THAT is all you will hear.

 

So perhaps (rhetorical q) your 'sitting against the wall' setup just happens to have the best/better LF performance ..... but EQing each location, and optimising woofer positions (if you have subs) would allow the direct/reflected issues I'm talking about to show up more.   ; )

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On 19/08/2019 at 7:58 PM, almikel said:

agreed - but sitting too close to the rear wall will impact all freq - eg comb filtering higher freq, boomy bass from room modes.

 

I still don't understand how short wall would optimise bass over long wall.

I accept that having the LP as far off boundaries as possible is a good thing - but it's not about bass response...

...I love putting my head into the room corners to hear a bit more bass now and then.

Agreed for everything above the transition zone of the room.

Below the transition zone of the room there is no "long gap" to the next group of sound - we "hear" the the room's resonant behaviour.

 

Mike

 

 

 

 

On 20/08/2019 at 1:12 PM, davewantsmoore said:

Bass is omnidirectional, so neither do I.

Yes.   It is not a consideration for the bass.

 

 

I bought it up because it is the single most important thing for choosing room layout, etc......  and extreme lengths are worthwhile to optimise it over all else.

 

If it means putting the speakers on the short wall.   Do it.

If it means sitting only 1m back from the speakers  (so you have 2.5m behind you) .... Do it.

 

It might look and feel dumb, and audiophiles might laugh, but they are dumb  ;)

 

Interesting. I've always had speakers set-up against the short wall either (a) pushed to the front wall so that the cancellation from the front wall reflection is at higher frequencies or (b) pulled well out of the front wall so that this cancellation is down low. And thought of the additional distance behind the listening position as a consequential benefit and the early arrival sidewall reflections as a downside. Re the distance behind the listening position: is it correct that the research shows that these are beneficial (and thus treating the rear wall with absorption is a poor idea.)

 

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3 hours ago, zydeco said:

Re the distance behind the listening position: is it correct that the research shows that these are beneficial (and thus treating the rear wall with absorption is a poor idea.)

no - you've misinterpreted something - reflections from the rear wall are to be avoided.

 

In my very small room, I have no choice but to sit close to the rear wall, and have around 400mm of absorption on the rear wall - diffusion is fine also if you can sit far enough away (off the rear wall) - I don't have that option.

 

Toole considers sidewall reflection to be ok provided the speakers have even "off axis" response (as yours do), and the reflections have the same spectral content - ie don't treat 1st sidewall reflections with thin absorbers (which will absorb top end and not bottom end - hence change the spectral content).

 

3 hours ago, zydeco said:

set-up against the short wall either (a) pushed to the front wall so that the cancellation from the front wall reflection is at higher frequencies or (b) pulled well out of the front wall so that this cancellation is down low

My room is so small (roughly 4m x 4m), I've gone for your option (a) - main speakers pushed back into the corners up against absorption - I'd have to check an SBIR calculator to confirm, but close enough (to front and side walls) so that the SBIR cancellation from front and sidewalls should be above the Xover to my midwoofers which is 350Hz.

My mid woofers are also close to the floor to ameliorate SBIR floor bounce.

 

4 hours ago, zydeco said:

(b) pulled well out of the front wall so that this cancellation is down low

front wall or sidewall...and you'll find you don't have a big enough room not to have an SBIR dip somewhere you don't want it with the typical audiophile approach of lots of space between speakers and boundaries.

 

More space is better - but in typical rooms this often puts a big SBIR dip in the bass response at the LP.

If it's below 80Hz, the easy fix is 1 or more subs.

 

cheers

Mike

 

 

 

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On 23/08/2019 at 4:51 PM, zydeco said:

and the early arrival sidewall reflections as a downside

Depends on how early they arrive.   If they're very very early (like in a <3m wide room) then perhaps.

 

On 23/08/2019 at 4:51 PM, zydeco said:

Re the distance behind the listening position: is it correct that the research shows that these are beneficial (and thus treating the rear wall with absorption is a poor idea.)

Not really... it's hard to generalise.    Any type of specific direct reflection isn't beneficial...... really the big issues, baring any strong and/or very early reflections (ie. diffraction from the speaker, or nearby)  ....  is overall ratio of direct to reflected sound .... when the later arriving sound arrives.

 

I'd put absorption on the rear wall if I had to sit too close to it.....   speakers with good polar response are much more important than "room treatment for reflections" IMHO.

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Posted (edited)
On 23/08/2019 at 9:18 PM, almikel said:

Tole considers sidewall reflection to be ok provided the speakers have even "off axis" response (as yours do), and the reflections have the same spectral content - ie don't treat 1st sidewall reflections with thin absorbers (which will absorb top end and not bottom end - hence change the spectral content).

 

True but need to be careful as rooms get bigger when set up across the room. The delay time between direct and side wall reflections gets too large and you lose clarity. Sensed like a small reverb issue but not.

 

I'm in need of treatment and had to mitigate this by increasing speaker spacing to bring them closer to the side walls than ideal to reduce the delay time and then add a bit of toe in as I was getting too far off axis.  

 

As it is the side walls create a little ghosting in the imaging and the sweet spot is narrower than I'd like. Mates holding up some batts pulled from under the house on the reflection points snapped the imaging tighter but my RTs are already not bad so want to use diffusion when time allows. 

 

Length ways was problematic for me with doors in three corners making speaker positioning and cabling impractical with them in good locations. In an untreated room long ways was actually worse than what I have now as rear wall reflections were so delayed they were audible as a discreet flutter at the buzz/ring end of flutter. 7m length room by 4.5m. Seat was about 1/3 to 1/4 from front wall. 

 

To control rear reflection etc in the across ways set up I brought the seating position to about 1/3 room width from the rear wall. Close to the rear wall you boost low frequency and lose imaging as the direct and reflected time delay is close. Your ears feel 'filled' and you can't pick direction like being in a room mode when a tone is played. It's imperative for imaging that your brain knows what is the direct signal, it can deal with other stuff once it has locked that in which is why diffusion works so well. At 1/3 distance the sound from the rear wall has had to travel twice as far (further actually as the speakers are out from the front wall) to get to you than the direct signal and will have dispersed further and be at a lower level. I tend to think in terms of image sources as a starting point as you can recreate any regular physical room using image sources. 

 

While tuning rear wall distance this I also played with distance of the speakers from the rear wall since they will couple across the room as well then retuned the seating position.  Speaker width also changed the coupling at the lower end in the room. 

 

I'd recommend playing around a whole lot. I tuned by ear all the positioning to within 10cm and was surprised how good it got without any treatment. I then modeled it which confirmed what I could hear. 

Edited by DrSK

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