Speaker Asylum General speaker questions for audio and home theater.

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Average the frequency response at multiple seats "smooths" the bass (average enough seats and standing waves disappear!)

Posted by Richard BassNut Greene on March 8, 2007 at 09:47:21

In Reply to: It takes one to know one ... ;o) posted by Duke on March 7, 2007 at 10:13:33:

Forum thread "death spiral"? You mean like when I compare your family to farm animals and then compare you to Hitler? I was saving that for a future post!

Forget averages -- at every INDIVIDUAL seat the bass frequency response is still uneven no matter how many subwoofers you use (unless every listener gets his own near field subwoofer).

Computer simulations are not data from real rooms.
They merely suggest subwoofer set-ups that ought to be measured, and more important -- listened to in real rooms.

Side and rear subwoofers have no place in two-channel audio -- they upset the intended up-front stereo image/sound stage.

Averaging bass measurements hides reality.

Two-channel audiophiles care about their one-chair sweet spot.
Bass frequency response elsewhere is mainly irrelevant.

The sweet SPOTS for home theater are usually considered to be at least three locations across a couch or three/four seats in one row.
Consistency (standard deviations) among the seats are considered more important than sub-optimizing the frequency response at one seat (which is the primary goal for a two-channel sweet spot).

Why not add Tom Nousaine to your list of "experts":

Nousaine recommended one or two subwoofers in the nearest room corner based on a comparison with five surround sound subs (details and real measurements in his AES paper in the late 1990's).

Welti recommended four subs at mid-wall positions -- Nousaine tested Welti's theory in a real room and reported on-line that all subs in one corner were better!

Geddes recommended three subs -- one near the ceiling.

The other guy, I forget his name, recommended left-right subwoofers connected out of phase, the last time I read his paper.

Linkwitz goes for dipole bass which reduces excitation of most room modes -- perhaps the best advice of all for those unwilling to parametrically equalize their subwoofer, or buy a batch of bass traps.

Note that all these recommendations are different and all (except Linkwitz) are for home theater where sound comes at the listener from the front left, front right, front center, left side, right side, and sometimes from the rear.

The home theater is energized from at least 5 different locations versus two locations for typical 2 speaker two-channel audio -- the room acoustics are absolutely not the same as two-channel with the need to sit equal distances from the two stereo speakers to get the proper "phantom center image".

There is no evidence from real rooms that more than one subwoofer in one location is needed for decent bass under 80Hz. (other than SPL requirements that require more than one subwoofer)

Using two (left-right) subwoofers simplies subwoofer-main speaker integration by preventing potential integration problems possible with one mono subwoofer located off-center.

Sometimes using left-right subwoofers, which prevents a the first order axial side-wall-to-side-wall standing wave, makes the bass sound better at the sweet-spot listening position, and sometimes it does not.

There is a potential for improved bass frequency response at the sweet-spot position from using left-right ceiling subwoofers and left right floor subwoofers (4 in total) to prevent the very important first-order axial floor-to-ceiling standing wave in addition to the first-order axial side-wall-to-side-wall standing wave.

Unfortunately ceilings usually rattle from a nearby subwoofer, even assuming there is no WAF problem.

Much more can be accomplished with one subwoofer and a $150 digital parametric EQ which will completely eliminate all bass peaks at one sweet-spot listening position.

A lot of bass traps will reduce the partial nulls too, particularly above 80Hz. where bass traps work best (not that they are ever efficient tools at any frequencies).

As soon as you scatter subwoofers beyond positions that are close to the two main speakers, you start deteriorating the intended stereo image soundstage.

And the closest thing to a bass transient, the slap of a hammer on a kick drum, will not have the best possible sound quality if the two to three drivers in each channel (subwoofer driver, bass driver and mid-range driver ... or subwoofer driver and bass-mid-driver) that reproduce its sound are not located near one another.

Whether adding an additional subwoofer (beyond two) will improve the bass frequency response at the sweet spot seat (or at any other seat)is like flipping a coin. The correct answer is "maybe".
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Richard BassNut Greene
Subjective Audiophile 2007

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