[PaulP]

Originally Posted by SAC

1/4 wavelength - from which surface? And at which frequency?

My understanding is that the 1/4 wavelength only applies to the first order
axial mode that has a null in the middle of the room. This null is a plane
across the center of the room. To attack it properly would probably
require a bipolar planar speaker the size of the room. Given this is somewhat
impractical the sub on either side of the plane is a compromise. Apparently
still effective enough to have a beneficial effect.

While wavelengths less than 1/4 wavelength will couple, you still have the additional reflective surfaces! In fact, you have at least 5 of them - and you must deal with those reflections as well!

I don't see what reflections at other frequencies has to do with anything.
The only ones we're interested in are the ones related to the modes.

- despite the fact that, in addition (for starters), the study conveniently chooses to ignore the oblique and tangential modes for simplicity, as if they would never sum to cause a problem...

You must admit that they will be lower in level compared to the axial
modes. Perhaps they aren't as bothersome.

And after all, your head never changes vertical elevation - well except when you stand or sit - and modes don't apparently don't operate vertically as well. Wait, you mean they do?

I noticed this lack as well. It seems to me that it would be better if the
four subs were mounted halfway up the wall. Perhaps they found it impractical
(or figured an end-user would find it impractical) to mount a sub in the
middle of a wall, not to mention in the center of the ceiling and in the
middle of the floor. They wouldn't be the first to ignore the vertical.

And the commonly drawn conclusion that 4 subs are 'best' is questionable

Actually they said that 5000 subs is best.

even by their own mention compared to two subs (none of which can be localized...or so they claim!!!! another assumption). Two subs provide substantially less loss of low frequency response than four at 1/2 the cost, with only a slightly greater increase in (only axial) modal activity

They did say as much.

Folks need to review the Toole sub study more closely. It provides a very general guideline within a set of very constrained conditions. It does not provide as much information as some think nor the broad conclusions that some draw! - in fact it provides much less when you realize the conditions assumed and what they simply ignore! And they choose to ignore (and assume!) ALLOT.

My understanding of the study is that they were looking for a practical
method that caused a noticeable improvement in the modal reponse of a
room. I don't believe they say anywhere that they solved all the problems.

To me it looks to have more potential than absorption for the treatment of
modes. How much absorption would you need to tackle a 25 hz mode ?

Oh, and ANY attempt to apply this study to the vertical use of subs violates the very conditions assumed by the study as well!

How is that ? You don't think Toole thought of this ? Seriously ?

Paul P