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loudspeaker distance from front wall...guidelines?

I generally adhere to the often-recommended convention of having front L & R loudspeakers form an equilateral triangle with me, the listener, with the Center (my setup is 5.1) lying midway between them. A separate question is how far this front line (L C R) is from the front wall. I'm lucky enough to have free rein in a dedicated room. In my 15-foot x 14-foot room, I've generally left a distance of 2-3 feet between the front baffle of the speakers and the wall behind them (the front wall, from the listener perspective). There's no solid rationale behind that distance other than a vague idea of reducing boundary interference which creates 'comb filtering' cancellations. Lately I've been trying to get a little more science behind front line speaker positions. One reference I've found are pages on this site.

My listening seat is generally placed according to the so-called 38% rule . So my seat is at a point 5.7 ft from the rear wall (38% of 15 ft) . I also have 4" thick , 2' x 4' absorbers on the walls between me and the front line, at the 1st reflection points, and between the L&C and C&R . My subwoofer is in a front corner, which excites maximally excites room modes, which is OK since I can then use DSP (Audyssey) to tame excessive bass frequencies.

In some high-end recording studios, speakers are mounted within the front wall so the baffles are flush with the surface (a so-called 'infinite baffle'). This eliminates front-wall boundary effects . I can't do that. Another way is to place the speakers far enough from the wall to reduce the effects to inaudibility. This distance can be calculated. For my room and loudspeakers, that would be a bit over 5 feet ....not great, since to basically places me just five feet from the front line... a true 'near field' setup, but rather claustrophobic! (Though I might try it for fun...IME actual 'near field' setups create incredible deep images at the expense of having speakers right in your face).

Another way is to position the speakers very close to the front wall, which raises the cancellation notch frequency as high as it can go, then insert 4" absorbers behind them to reduce those frequencies*. I've now tried this (adjusting the side absorber positions too, to cover the new 1st reflection points.) It has two effects. One, given that my listening position stays the same, the equilateral triangle becomes huge, and thus the soundstage too, as the speakers are >11 ft apart. Two, there seems to be a loss of image depth; the sound is spread out across the stage but it's 'flat', lacking front to back image depth. I'm not at all sure I like it, but plan to experiment more. One undeniable good thing it does is to open up more free space in the room itself.


Has anyone else experimented with front speaker /wall distance, and have impressions to report?


*Interesting to note that in the relevant room setup/treatment diagrams in Floyd Toole's book, speakers are positioned with their backs right up against the walls.

Re: loudspeaker distance from front wall...guidelines?

Reply #1
Don't forget the main purpose is enjoyment!!!  (That's assuming you're not talking about a studio used for music/sound production.)      You can start by "following the rules" but then you can do whatever sounds best to you!

Before you go too crazy trying to "calculate" reflections (and the results of reflections) I'd recommend you measure the room.     You don't have to do that but if you are adding acoustic treatment (especially if you are spending money on treatment) remember that "diagnosis comes before treatment."   (You would need to buy a calibrated microphone, but you can use free software.)

Quote
My subwoofer is in a front corner, which excites maximally excites room modes, which is OK since I can then use DSP (Audyssey) to tame excessive bass frequencies.
You can tame antinodes (peaks) to some extent but you can't fix nodes (dips/cancelations) because it takes nearly infinite amplifier power and huge woofers/subwoofers to overcome the cancelation.    You also can't fix ringing with EQ.     These things can be fixed (or at least improved) with bass traps.   Bass traps trap the reflected bass, which means less cancelation and tamed peaks.  

I'm not saying you need bass traps (or any acoustic treatment) but bass traps and woofer placement is the best way to deal with "bass problems".    

Quote
One reference I've found are pages onthis site.
There is one thing I'm highly skeptical about - He recommends isolation stands.     I've only seen ONE measurement-test of speaker isolators and there was essentially no difference (with the speakers at the same height-location without the isolators).  These (skeptical) testers also didn't hear any difference.        ...I've read lots of worthless positive reviews with non-blind, non-scientific, listening tests.   And of course the isolators may change the height or angle of the speaker which CAN change the sound, especially if the listener is close to the speaker/monitor.

 

Re: loudspeaker distance from front wall...guidelines?

Reply #2
I've been in this hobby a looong time.  I only do things I enjoy at this point.  And one thing I like to do is see how what you are 'supposed' to do, sounds to me.

Most of your points are things I know already (e.g. antinodes, ringing, physical treatment vs DSP)

Certainly REW or analogous measurement tool  would be the way to go for diagnosis.    It's in my future.  Btw I have seen many go 'too crazy' using it.

But for now this is why I put the word 'guidelines' in the title.  I know there's no ironclad here.  For once, I'm interested in hearing about other people's investigations into this, with their own setups, even sighted-only.   (Usually I couldn't care less.)

The site I linked to -- Arquen -- is new to me and has some more or less quasi-substantive stuff on it, as every audio site I've ever been to does, none are perfectly objectivist; he's also trying to cater to home studio users *and to* home audio listeners, which is tough.  But it's one of the few that attempts to give testable 'guidelines' and he's at  least aware of relevant audio research (unless he's faking having read Toole's book), and he does recommend taking actual measurements to go beyond simply 'guidelines'.




Re: loudspeaker distance from front wall...guidelines?

Reply #3
Where you are "supposed" to place your speakers is where it sounds "good" to you. The End.

What page in Tooles book does it show the diagrams and/or side absorbers like you have in your attempted studio recreation room?
Loudspeaker manufacturer

Re: loudspeaker distance from front wall...guidelines?

Reply #4
I have to say the DSPs in AVRs these days has come a long way. I appreciate they're not perfect but they do a damned good job of sorting stuff out. Certainly going from a top end pre-lossless surround AVR with an early version of Audyssey onto a nearly bottom of the range one with 15 years between them, I would never go back to the old one even if it is supposed to be technically better.

Re: loudspeaker distance from front wall...guidelines?

Reply #5
Where you are "supposed" to place your speakers is where it sounds "good" to you. The End.

What page in Tooles book does it show the diagrams and/or side absorbers like you have in your attempted studio recreation room?


Third edition, p. 423, Figure 15.10a, illustrating an apparent 9-channel system* in a home theater with three rows of listeners. 
'(a) shows the horizontal plan for room acoustical treatment based on the notion of assisting spatial illusions. The materials described here apply to a horizontal band around the middle of the room, around and above seated ear height. Front side walls** are 'optional' territory'.  If stereo listening is to be part of the entertainment in the room,Chapter 7 discusses the choice of reflecting, absorbing, or diffusing the first reflections from the side walls.  For dedicated multichannel/home theater use, absorption is advised. [...]"


Mine is a 'dedicated multichannel' room, not a 'studio recreation room', unless Toole's diagram is too -- his diagrammed room has a *sh-t*-ton of treatment, comprising absorbers and diffusers (mostly for diffusing sound from the surround speakers).  Currently I'm trying absorption on the front and rear walls (shown in Toole's diagram) and on the side walls in the 'optional' area.  I don't have any purpose-built diffusers.  The room is carpeted as recommended by Toole as well, in this same book (look it up yourself).

And again, you don't have to be an ankle-biter all the time, AJ. 


*with corners reserved for 'low-frequency absorbers if they are needed, or for subwoofers in a multi-sub configuration'.

**the side-wall areas between the loudspeakers (which are shown positioned against front wall, L&R toed in) and the first row of listeners.

 
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