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zydeco

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

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My experience has been to set-up speakers on the short wall firing so as to optimise bass. The downside, for those of us with small rooms, was the first reflection points so this saw me move to speakers with controlled, off-axis, response. All this made sense in the days before sub-woofers and DSP but, now, I’m wondering if it’s still the starting point for room set-up. Is it the case that, with bass performance partially decoupled from main speaker location as a result of sub-woofers and DSP, the long-wall set-up is worth re-visiting?

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You make some great points. There are lots of simple, cheap, and elegant solutions for first reflection points now. Multiple subs and dsp can fix most bass issues.

Often the issue with long wall placement is that the listening pisition is too close to the rear wall, however, even this can be addressed with diffusers.

So it often comes down to aesthetics and room functionality.

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On 04/08/2019 at 9:01 AM, zydeco said:

My experience has been to set-up speakers on the short wall firing so as to optimise bass.

I'm unsure of the rationale to setup on the short wall to optimise bass? - below the room's transition zone (say below 250Hz), the bass won't care which way the speakers are oriented inside the room - long wall vs short wall...

...but sub positioning is critical, and may change based on LP changes with long wall vs short wall

On 04/08/2019 at 9:01 AM, zydeco said:

the long-wall set-up is worth re-visiting?

certainly - if it works for main speaker placement for imaging/sound stage - and tweak sub positions accordingly.

 

IMO short wall vs long wall was never about bass, but all about main speaker placement for imaging/sound stage.

 

cheers

Mike

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Is there a thread specifically on subs x2 positioning in relation to main speakers etc, or with plenty of info ...?

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On 14/08/2019 at 7:43 AM, jamesg11 said:

Is there a thread specifically on subs x2 positioning in relation to main speakers etc, or with plenty of info ...?

 

Paul Spencer's Bass Integration Guide parts 1, 2 and 3 have plenty of info

Part 1 linked here: 

https://www.hifizine.com/2011/06/bass-integration-guide-part-1/

 

I would recommend reading them all, but part 3 discusses main speaker and 1 or more sub positioning.

 

To implement the guidelines you'll need a measurement rig and DSP capability for EQ and delay - particularly delay of the mains - which is usually the tricky part with a "normal" setup.

When you read the guide it will explain why you need to delay the mains so the subs can catch up, but essentially the filters involved in the crossover between sub and mains will have an inherent delay (all filters have delay), where the subs are delayed more than the mains, so the mains require further delay (usually with DSP) to enable time alignment between mains and subs for proper integration.

 

If you don't have EQ/delay capability of your main speakers you can still apply a bunch of the theory in the papers regarding mains and sub/s placement if you have a measurement rig (U-Mike, mike stand, laptop and REW software).

 

The method of placing a sub at the listening position and moving the mike to all the likely sub positions will save you hours and save your back - highly recommended!

 

If your subs have DSP EQ/delay,  you will still be able to tweak the room's bass response to a reasonable degree even if you can't delay the mains.

 

Free software like Multi Sub Optimizer (MSO) https://www.andyc.diy-audio-engineering.org/mso/html/index.html

can also assist in getting the best room bass response from multiple subs - but requires DSP EQ/delay capability.

Others on this forum @Snoopy8 have used MSO to great effect with minimal/no room treatment in a shared space (ie a lounge room, not a dedicated room).

 

If you can get away with it, IME all rooms benefit greatly with some absorption targeted at the lower frequencies to clean up the 100 - 300Hz range, but absorption that works < 150Hz or so gets big.

 

IMO to achieve great "in room" bass - a combination of main/subs positioning, room treatment and DSP EQ/delay capability across mains and subs is essential.

 

cheers

Mike

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On 04/08/2019 at 9:57 AM, AudioGeek said:

the issue with long wall placement is that the listening position is too close to the rear wall, however, even this can be addressed with diffusers.

The challenge with diffusers is sitting far enough away for a diffuse field to be generated...the gurus of diffusion are Cox and D'Antonio - and I don't have one of their reference texts at hand, but my recollection is that they recommend sitting > 3 times the wavelength of the lowest frequency diffused.

This guideline could likely be relaxed (ie you can sit closer) for diffusers like 1D and 2D BAD panels compared to say QRD diffusers...as BAD panels don't diffuse as much as QRDs.

...but you still don't want to sit too close to a diffuser on the rear wall, which could be the case with the mains across the long wall.

 

Mike

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On 04/08/2019 at 9:57 AM, AudioGeek said:

Multiple subs and dsp can fix most bass issues.

I wouldn't start with DSP to fix bass issues - although I accept many don't have the option of deploying treatment, especially in shared spaces, so after positioning main speakers and adding 1 or more subs the only option left is DSP.

For those that can get away with installing treatment in their room, managing bass with treatment 1st, then adding DSP EQ for remaining issues, IME will provide a superior result to EQ on its own.

 

DSP/EQ has a deservedly bad name - poorly applied it can do great evil...

...as can poorly applied treatment - the best example being egg crate foam on the walls of band rehearsal rooms with besser block walls (rigid walls reflecting all the bass and the foam soaking up treble - truly awful sound)...

...and there's no way you'd be able to fix the above band rehearsal room issue with EQ :(

 

For me DSP/EQ is an essential tool to achieve great "in room" bass, but is applied judiciously/selectively after room treatment - well applied it can achieve great good.

 

I have a lightly constructed room with a lot of absorption, decent bass capability on my mains, a single sub, and DSP capability across all...it's the combination of all that working together that provides a nice dry "in room" bass response...

...Put the whole system (including absorption) into a rigid room and there wouldn't be enough low bass absorption - it may be ameliorated with more EQ cut in the bottom end, but likely specialist bass traps would sound better.

 

If possible, treat 1st, then use EQ is the approach I use.

 

cheers

Mike

 

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On 13/08/2019 at 10:34 PM, almikel said:

I'm unsure of the rationale to setup on the short wall to optimise bass? - below the room's transition zone (say below 250Hz), the bass won't care which way the speakers are oriented inside the room - long wall vs short wall...

...but sub positioning is critical, and may change based on LP changes with long wall vs short wall

certainly - if it works for main speaker placement for imaging/sound stage - and tweak sub positions accordingly.

If you use the long wall(s) then it affects your sitting position so you're most likely going to be sitting closer to the rear wall.

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On 04/08/2019 at 9:01 AM, zydeco said:

My experience has been to set-up speakers on the short wall firing so as to optimise bass. The downside, for those of us with small rooms, was the first reflection points so this saw me move to speakers with controlled, off-axis, response. All this made sense in the days before sub-woofers and DSP but, now, I’m wondering if it’s still the starting point for room set-up. Is it the case that, with bass performance partially decoupled from main speaker location as a result of sub-woofers and DSP, the long-wall set-up is worth re-visiting?

People should do what avoids the biggest problem(s), rather than what seems "most right".

On 16/08/2019 at 11:11 PM, Satanica said:

If you use the long wall(s) then it affects your sitting position so you're most likely going to be sitting closer to the rear wall.

 

1000%
 

The most important thing.... by far .... is having enough space behind the listening position.    This is to ensure that after the first (groups) of arriving sound, eg, direct and from the sidewalls, floor and ceiling ...... that there is a long gap between the next group of sound which arrives (eg. reflected from behind you).

 

Lateral reflections are not so bad.

 

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PS.  You will see many people breaking this rule - so don't go on what you see.     Sometime they have no choice (system in a living room, etc.) ..... and other times is a downright cringe-worthy.

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On 16/08/2019 at 11:11 PM, Satanica said:

If you use the long wall(s) then it affects your sitting position so you're most likely going to be sitting closer to the rear wall.

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

 

On 04/08/2019 at 9:01 AM, zydeco said:

My experience has been to set-up speakers on the short wall firing so as to optimise bass.

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.

On 18/08/2019 at 5:46 PM, davewantsmoore said:

1000%
 

The most important thing.... by far .... is having enough space behind the listening position.    This is to ensure that after the first (groups) of arriving sound, eg, direct and from the sidewalls, floor and ceiling ...... that there is a long gap between the next group of sound which arrives (eg. reflected from behind you).

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

 

 

 

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2 hours ago, almikel said:

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

I think that gives new meaning to the term "basshead". 😏

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17 hours ago, almikel said:

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

Bass is omnidirectional, so neither do I.

Quote

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.

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  ;)

Edited by davewantsmoore

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Similar discussion from another post and someone simulated not always so bad aligned on the longer wall with head against rear wall. Try whatever is practical and gauge the sound results, try both ways. In my case with 5 x 3.6 x 3.2m high room the longer wall is much better in a 2m equidistant listening triangle. Simulation below didn’t manifest those problems too badly nor am I hearing issues. Room has ample furniture with lots of reflection breakup instead of a bare very reflective room as many dedicated audio rooms seem to be.

06D81178-2FC6-40E7-98F2-43C4D30B9878.png

D8153C0E-FA7E-4BE2-B5CC-5B04823AB63A.png

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13 hours ago, Al.M said:

Similar discussion from another post and someone simulated not always so bad aligned on the longer wall with head against rear wall. Try whatever is practical and gauge the sound results, try both ways. In my case with 5 x 3.6 x 3.2m high room the longer wall is much better in a 2m equidistant listening triangle. Simulation below didn’t manifest those problems too badly nor am I hearing issues. Room has ample furniture with lots of reflection breakup instead of a bare very reflective room as many dedicated audio rooms seem to be.

What I was talking about isn't an issue with the frequency response.

It's to do with the arrival times of reflected sounds (above the bass regions, eg. 300Hz+)

Sounds which reaches you directly from the speakers, or from the reflections at the front of the room, are ok .... but once the sound has passed behind you ..... you want it to return to you with quite a lot of delay, and quite a lot of attenuation.... ie. you don't want a back wall behind you.

This is related to the clarity and imaging of the entire frequency range.

For the bass.... no matter which way around you have your room (long short), you can use positioning, multiple woofers, and EQ to solve the bass problems.

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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.

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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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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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