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Inactive speakers in the room...any effect?

A recent thread degenerated into a discussion about whether an inactive speaker in the listening room affects the sound of active speakers. I should have been more tactful, and called it a "hypothesis" instead of a "myth".

Now, a hypothesis can be proven by analytic means or by experiment. This particular hypothesis, from the analytic approach, is very unlikely to be true. So, we go on to an experiment.

A listening test was described where a group of listeners were unanimous in saying that sound quality was degraded by an inactive speaker. (By the way, I don't understand why, if there were any effect, it would have to be a degradation rather than an improvement).

However, to be acceptable as a proof, the experiment would need to be done as follows:
1. The inactive speaker should be introduced and removed from the room in such a way that the subjects, and the person conducting the experiment, cannot tell if it is in or out.
2. The listening test should be performed a number of times. A dozen might be sufficient. More would be better, but the subjects would get bored and results would be degraded.
3. The subjects should record their observations (Speaker IN/Speaker OUT) in such a manner that they do not know how the others are voting.
4. The results must be tabulated and analyzed in a statistically valid way.

I doubt that the reported experiment was done this way. It apparently convinced the subjects, but does not constitute a proof acceptable to an objective non-participant like me. Lacking a valid experiment, I must rely on the analytic approach, and find the hypothesis untrue.

Another game that would be fun would be to conduct the experiment in the manner that I suspect it was done, where everyone knew when the speaker was in or out, but use a speaker that, unknown to the subjects, has had its cones immobilized with glue and the vent (if any) closed off.
I think I know how that would come out if the subjects were believers. (Or, for that matter, if they were nonbelievers). This exercise would indicate how much confidence should be put in the experiment that was done.

Are we having fun yet?
eldartford
eldartford OP
4,262 posts
 
Sean...Your point about subtractive differences is very well-taken. The best known example of this is that a performance hall has very different acoustic characteristics when it is full of people vs when it is empty.

Of course speakers function as microphones, many (if not most) handheld communication devices make the speaker do double duty. Just for fun I will measure the output of a box speaker/microphone at some measured SPL. But what to do with this data? Perhaps I should express the signal in terms of the SPL which the speaker would produce if that voltage were applied. The idea is to assess whether the effect, which certainly exists, is of any practical significance.
subaruguru
1,376 posts
 
Rather than go through the hassle of repeated trials with a bunch of humans (audiophiles, even!), it'd be easier to just set up a RatShack mic on a tripod and run the S'phile or other 1/3 octave bass warble tracks and compare the curves with and without the added speaker "traps" (which is predominantly what they'll be, I suspect). Who knows, you may get smoother response after some experimentation!
After pondering Twl's telly-on-the-table trick, I wonder if it isn't the 1" diaphragm that's operative here, but the altered total reflective package in the upper mids...ESPECIALLY off a hard horizontal surface near the listener, that's changed their responses. I too doubt that it could be constructive/destructive waveform in the bass, but just a normal change in the diffraction mix when you start tossing stuff around the cofeetable type thing...especially hard-edged solids. Again, this could be measured, but is trickier as you have to be more careful to keep the effects of hand and head movements cloned in repeated trials in the uppermids. So I think Twl's customers heard something, but related to the phone's CASE, not its SPEAKER! Cheers. Ern
dannylw's avatar
dannylw
172 posts
 
The Linn dealers used to demonstrate the single speaker pair effect vs. multiples in a room. Each time a pair of unused speakers was removed the quality of the sound increased. Even non-audiophiles noticed it.
eldartford OP
4,262 posts
 
Linn is the "certain British manufacturer" who tried to pressure dealers into having a dedicated Linn room. The extra speaker thing was part of it.
wellfed's avatar
wellfed
690 posts
 
I had a conversation with Geoff Kait recently about the effect Marigo dots have on walls and received an explanation so simple even I could understand it.

I was mentioning that image locations moved during installation of these dots in a room. Specifically during installation of the dots I would stop and listen after installing a portion of the treatment, say to one side of the listening room only (asymmetrical).

Geoff explained that by treating the room in this fashion I was, in effect, eliminating additional "speakers" from contributing to the sound in the room. This makes a profound amount of sense to me. In the past I never could explain why the Marigo dots did what they did, all I knew was I really liked the results.

One more effect that I didn't broach with Geoff, but would enjoy the feedback available here is regarding the use of Marigo dots on windows. I find that, in addition to controlling high-frequency distortion issues caused by or exacerbated by windows, the Marigo dots in this location (windows) reduced phasey effects and really tightened the focus of images. Is this also the effect of eliminating/reducing windows as a "speaker" in the room?
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