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Where 2 sit audio quiz

Ok folks, don't take this too seriously now!

It's cold and cloudy here in Wisconsin and I'm bored out of my skull.

I've been messing around with different seating positions and trying to form a pattern between measured results and audible results.
I thought it might be interesting to put up measured results at 3 widely varying seating positions, and see if anyone could suggest ideas on a range of different issues. There's a $1 Million cash prize for whoever get's it right, redeemable 11/22/2064

First the setup:
Meter used is the RS digital set to slow response and C weighted.
Test tones from Rives CD 2
The Rives CD say's to use tracks 32 - 62 which are compensated for the non-linearity of the RS analogue meter. It doesn't say what to use for the digital meter, so I tried both, and the most consistent seemed to be tracks 1-31.
Anyway, the numbers are more indicative than they are absolute. If I need to re-do the test using tracks 32+ then so be it.
I used 3 different 'practical' seating locations at 12', 17' and 20.5' from the speakers.
The 20.5' position is up against the wall, which is central on a large un-draped window (a clue perhaps.. [14'x 4' approx window dimension]). I'm showing the 3 sets of results in tabular form (wasn't bored enough to bother making a graph).
Also, I'm not saying at this point which reading relates to which seating position....(perhaps the SPL level will provide the answer?)

Speakers are Maggie 3.6R's, amps are Cary V12 Mono's with ARC LS15.
I thought I would have to adjust the preamp gain at the farthest position, but it didn't require it, so all 3 positions are measured using the same volume setting on the LS15 preamp.
Questions that spring to mind....(add more if you wish).
From the results shown at http://thenaturalshopper.com/audiohell.htm

1 - which position would seem to suggest the best sonics
2 - what do the readings say about room layout and frequency response
3 - what do they indicate as far as equipment selection(speakers) for the particular room layout (example - insufficient bass response at any position, harsh treble response, or whatever?)
4 - which position do you thinks is the 12', 17' and 20.5' seating position
5 - given that the spl's are almost identical at higher frequencies, what does that say about the room layout. (given that there is a 8.5' difference between the closest and farthest seat position, shouldn't one of the columns show a consistent reduction in SPL?).
6 - what does all of this say about people from Wisconsin

What the heck!

Rooze
rooze
sean
6,231 posts
 
Rives: I hope that you don't take this as a personal attack, only an open discussion of differing points of view.

I assume that Rooze basically took these readings walking away from the speakers in a straight line in what would be termed the "sweet spot". Then again, this is not mentioned but would be taken for granted as being the common sense approach by most readers.

As a side note, ALL speakers are directional and beam sound as frequency is raised. Obviously, some are worse than others in this regard, but they all do it. This happens not only horizontally, but also vertically. On top of this, the angle of incidence can vary quite a bit as distance is altered. Much of this will depend on whether the speakers are flat-faced or are toe'd ( sp ??? ) in.

If you look at any frequency response chart of a driver, off axis response becomes FAR less linear as one is moved further off axis. Going from 10* off axis to 30* off axis, which isn't that much, can make a huge difference in terms of frequency response linearity. Not only will this affect tonal balance, but also the soundstage, imaging and transient presentation of the system.

I have no idea what you or various dealers are using as a reference in terms of measuring frequency response and / or dispersion patterns. I would hope that it would be measurably more accurate than a stock Rat Shack meter. The non-linearities of this device itself, primarily in terms of frequency response and directionality, make the results very "questionable" under anything less than optimum conditions in skilled hands. As a generic tool used in the hands of civilians, it can be quite useful to study trends and average out results. As such, averaging is not a bad thing so long as the results are viewed in the right perspective. After all, Rooze verified that my observations, which were derived from averaging and following trends, were pretty consistent with what he was hearing.

Suffice it to say that we will probably end up agreeing to disagree here. Sean
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rooze's avatar
rooze OP
645 posts
 
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
sean
6,231 posts
 
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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zargon's avatar
zargon
453 posts
 
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,
sean
6,231 posts
 
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.
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