Where 2 sit audio quiz

Sean/Rives, I had a question, the answer to which might help demonstrate each of your points of view.
I was pretty astounded at the effect of simply walking backwards through the room, from the 12' point to the 20' point, centrally of course and facing the speakers (which are now toed in only around 5* since the listening seat is so far back).

Forgetting about mid to heigher frequency anomolies and low frequency response, the thing that got to me was the shear change in volume... moving back through the 16-17 area, the volume reduced considerably then increased sharpley at the 18-19' area. I know this is somewhat indicated by the spl reading on the chart, but the actual experience of hearing this in the room was quite surprising and almost unnatural!!. Having had my original seat somewhere in the 16-17' area for a while, I'd been fighting gain issues with my LS15 preamp (another thread posted a while ago). Even after installing the ARC approved hi-gain modification, I couldn't get satisfactory volume in the 16-17' area. Now I'm sitting some 3-4' further away from the speakers, the volume has increased to more realistic levels without further equipment changes.

I'm curious to know more about the 'theory' of what is happening here. Is the 'dead-spot' at the 16' area actually the most neutral place to be? As mentioned previously, the sonic's lacked some depth and warmth and certainly lacked absolute low frequency extension in the 15' area.

Is this spl phenomenon common in room installations of these dimensions?
Is there a way somehow to treat the room to create more spl in the 15-16' area?.....this I would think is the most desireble area to sit. I've heard others offer as a rule of thumb:- measure the distance between speakers (12') and add 2-3 feet for the distance to the chair (15').
So I'm curious as to what changes in the room might equalize the spl more in the 15' area with that which is heard at both the 12 and 20' points.
Given that there is so much clearance between each speaker and the side walls, is it impossible to introduce any kind of side-wall reflective, diffuser or absorber that could be angled (perhaps) to create a higher spl in a given zone. ( the room width is 45' with the right side speaker approx. 10' from the side wall).

I've always understood the importance of room acoustics in arriving at good sound, but I've never had this kind of experience where differences are so marked within different 'zones' of the listening space.

Rooze

This is strictly a guess, so take it for what it is worth.

My "guess" is that the reflection from the back wave of your Maggies is "colliding" with the front wave at these distances. As such, you're experiencing out of phase cancellation, reducing the spl. The reason that this takes place over a specific area is that sound waves are all different lengths. One batch of frequencies is nulled at 16', another batch at 18' and the frequencies between those points at 17'. As such, you have a noticeable broad band dip at this specific distance.

In front and behind those distances, you'll experience reinforcement of those frequencies ( to varying degrees ) but cancellation of other frequencies. The key is to find the point that allows the most neutral tonal balance while still allowing good to optimum soundstaging / imaging. Since a microphone and test gear don't hear or process information the same as our brain does, using equipment and tools to get you in the area is fine, but trust your ears.

As far as doing the math to figure out the wavelengths and reflected paths, a room with irregular shapes, sizes and / or irregular non-solid objects that break up reflections can cause pretty erratic results. This is the reason that the acoustic modeling program called C.A.R.A. wants to know as much as possible about your room, it's shape and size, what you have in it, the speakers radiation pattern, etc... The more info that one can provide an acoustician or a program similar to CARA with, the more likely the results are to be accurate.

As far as "boosting" the spl's and linearizing the frequency response at that distance, this can be done. It will take a lot of work and will completely change the presentation that you hear at any given distance. This is because you'll be "squashing" the back wave to minimize cancellations and reflections. In effect, you will probably end up losing many of the desirable attributes of the Maggies that attracted you to them to begin with.

As a side note, with Maggies at 12' apart with a very mild amount of toe-in, 16' - 18' is too far back in my opinion. Then again, i don't know the specifics of the room or anything else about this installation, so keep experimenting and learning as you go. This can be a very educational and beneficial time for you in terms of learning via first hand experience. If you really get serious and start doing a lot of experimenting, keep a notebook. I would also make cohesive notes, not just jot down things at random. You might not look at these notes for a while and by that time, you may have forgotten some of the specifics of your "abbreviated" notes. Sean
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Sean, you make the point that speakers beam at higher frequencies and are less linear off axis. Are you then of the opinion that speakers should be toe'd in for best overall frequency response?

If there is a high frequency hole at the listening area, can it be boosted by toeing in the speakers to get a more direct on axis presentation?

I am aware that while many speaker placement methods recommend some toe in, at least one major speaker manufacturer states that best results are achieved with little or no toe in.

Also for both of you, what are the effects on sound stage width and depth as one adds toe in? Can it be predicted or is it room dependent?

Thanks,

I did a post not that long ago giving a brief run-down on the method that i generally use for setting up speakers. It is somewhat of a universal approach that works regardless of room or speaker size and takes into account tonal balance and soundstage / imaging. Only problem is, i can't remember what thread it was in and it's too long to type out again. I'll see if i can find it or hopefully, someone else will point us to it. Sean
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PS... As a general rule, i prefer little to no toe in. Then again, that is with using the approach that i mentioned above.

Aargon: Found the thread that i posted a basic and relatively universal speaker set up method in. It it just so happens that Rooze started that one too : )

Look for a thread of his entitled "problems with Maggie 3.6's" or something to that effect. This should answer your questions and then some. Sean
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