front-line speaker placement and image depth

[ssully]

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 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 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.

 

[windhoek]

My Kralk Audio BC-30 speakers are placed tight against the wall to benefit from boundary reinforcement as intended by the manufacturer - presumably because they're bass-lite and reinforcement is calculated into end-user operation norms.

 

[skherbeck]

You just made me realize... I have know idea what I'm doing here.

 

[ssully]

My Kralk Audio BC-30 speakers are placed tight against the wall to benefit from boundary reinforcement as intended by the manufacturer - presumably because they're bass-lite and reinforcement is calculated into end-user operation norms.

Good point. Some models are definitely designed to be placed like so.

Mine are near-field studio monitors -- Behringer 'Truth' B2030p. They are not designed for on-wall placement, so I'm basically trying to work around their design with my experiments (by reducing the near-wall bass boost via DSP, and using absorbers to reduce mid-frequency boundary effects)

 

[windhoek]

Good point. Some models are definitely designed to be placed like so.

Mine are near-field studio monitors -- Behringer 'Truth' B2030p. They are not designed for on-wall placement, so I'm basically trying to work around their design with my experiments (by reducing the near-wall bass boost via DSP, and using absorbers to reduce mid-frequency boundary effects)

I had a quick look at that article and the word compromise seems to be the order of the day - even if you've got means of measuring your room with REW and a Umik-1 mic.

 

[ssully]

Absolutely. This is a reason to try different things. See which compromises are acceptable ;>

I've been putting off learning REW forever, I already have a calibrated mic, it might be time.

 

[MCDave]

My listening seat is generally placed according to the 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.

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).

*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.

I have Toole's book as well. Required reading for any audiophile. Just to comment on the bolded items above:

I'm sure you're aware that Floyd's research shows that in most normal room, it's a mistake to try to tame "first" reflections (and by the way, every square millimeter in the room is a first reflection point). That common practice began in the early days of home theater about 20 years ago when it was thought that the room shouldn't contribute to the soundfield, only the surround speaker system. As a result, most professionally built home theaters from those days have WAY too much absorption. Toole's research generally refutes this idea.

I also have a dedicated space for my surround listening, a 23' x 15' room I built earlier this year. I too use 4" thick 2x4 absorbers on the walls and ceiling, but only enough to bring RT60 down to around 3.8, and NONE are at a so-called first reflection point. They are hanging from the ceiling or mounted in the corners of the room only. The room sounds very spacious this way. Read again what Floyd says about absorbing reflections, and give this a try in your room - you might find it sounds even better.

IMO, the most important section of his entire book is where he talks about using multiple subwoofers in different configurations. I personally use 2 identical subs at the half way points on the sidewalls, as he (and Sean Olive, who actually did this research) recommends. The bass at my seat (at approximately 42% of the front-back distance) is excellent, and I use no DSP of any kind. If you can, I highly recommend getting a second sub to complement the one you have, as long as it's the same model or the same specs. The primary purpose of multiple subs is to smooth out the bass in the room rather than to increase output (you'll get a 3 dB boost).

Floyd also describes what "near-field" means. I think you'd need to be within 2-3 feet to qualify, but it's technical. I don't recall exactly what the definition is. Something about wave lengths, IIRC.

My front L-C-R array is about 4 feet from the front wall, in a semi-circle pattern (so all 3 are equidistant from my ears), with the L and R 2.5 feet from the sides. My 2 surround speakers are 6' from the back wall and 2.5 feet from the sides. This places the surround speakers subjectively further to the sides from my listening position. About 140° or so. I've played around with various speaker positions in this room, as well as front-back seat position, and found this arrangement to give the best results with regard to imaging and soundstage.

 

[ssully]

Thanks. I've bought and read both editions of his book and much of his published work elsewhere, so I'm well aware of Toole's view and agree with it, but I am also using a *much* barer room that he envisions -- basically unfurnished, nearly square, with no drapes, just a carpeted floor and drywall on studs. Not a 'normal' room (and not like his own!). He is not adamantly against treating first reflections (of which, from the *single listener* perspective, there are only a limited number that matter), he just knows that's it's not always necessary to treat them (witness that his diagrams for rooms actually include treatments...as options)....and FWIW, his advice has an *important* caveat, namely that it apples when the loudspeakers have good off-axis performance. Mine happen to be pretty good in that regard, from the few measurements I've been able to find, but I've found that my room, not unsurprisingly, is far too 'live' without some absorption at the FRP (and elsewhere). But I am always open to experimenting with placement of the absorbers, and I have by no means tried every option; I've also begun building a ceiling cloud but haven't hung it yet, and I am aware that actual corner bass traps would be a plus too. Multiple subs are also on the to-do list....I plan to eventually ditch the 15" one I have and get two 12". I've read Todd Weltis' work (and Earl Geddes's) and I'm aware of the benefits of multi subs (though they are typically aimed at getting the best bass response across *multiple* seats, i.e. home theater)

'Near field' whether defined as 2-3 feet or ~5 feet, is still nearer than I prefer to be. I have experimented with that too! I suppose an ideal I aim for could be written as, near-field-like sound image depth , from mid-field listening.

When not trying against-the-wall, my front line is either semicircular in fact, or made so virtually, via speaker delay ('distance') DSP. and my rear speaker distances are virtually equalized the same way ( SL and SR are physically a foot or more away from the walls , at 110 degrees from the Center line, i.e, 20 degrees behind me -- of less concern to me generally, as I feel it's more important to experiment with the front line first). Did your choice of 4 feet from front wall come from trial and error, measurement, or both?

 

[MCDave]

Did your choice of 4 feet from front wall come from trial and error, measurement, or both?

Trial and error mostly. I knew I wanted the speakers well away from the walls to minimize boundary effects, and I moved them around a number of times before I settled on their current position. They're not exactly 4', more like 44". I have plenty of length in my room to play with (23 ft) so I was generous with placement.

You made a good point about speaker off-axis response in relation to the need for absorbing reflections. I forgot about Toole's comments on that. Actually, I bought 5 identical Revel M106 speakers specifically because of their superbly smooth on- and off-axis frequency response. So in my room, minimal absorption works well.

 

[hobie1dog]

When you have a small room such as a bedroom, there's very little room to move speakers around. If I use normal placement methods, all 4 speakers are around 5 ft from my ears, so there's simply a very restricted area for placement.