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?
I've done the experiment, and in fact have done it many times. I did it with unsuspecting customers at the audio shop I used to work at, and didn't even tell them that I was doing it, or anything. I would tell them afterwards, and they were all typically amazed that it was just another little speaker in the room making the difference.

We had a single speaker(pair) system listening room in the shop for demo purposes of the higher end systems. We'd do the demos and try some different components and speakers until we found something the customer liked pretty well. Only the active set of speakers was present in the room. Then I'd go out of the room, and come back with a cordless telephone handset, like I was just finishing up a call(phone turned off). I'd put the phone down on the small table next to the listening chair, and then put on another record. Almost every time, the customer wondered what happened to the sound of the system. There were no apparent changes to the components. After a little conversation about it, I revealed that I had brought the phone into the room and put it on the table, and that he was hearing the adverse effects of the re-radiations of sound from the telephone speaker. Then I'd take the phone out of the room and play the record again. Sound was magically restored. Then I explained why a single pair of speakers in the demo room was important for auditioning purposes. I probably did this over a hundred times, with as many different customers. To this day, I never have any other speaker in my listening room. Not even a television speaker or computer speaker or a telephone speaker.

Now I'm not going to say that everyone will notice this in every home listening environment. But in a dedicated room with good setup, and a reference grade audio system, it is definitely a factor. Maybe a somewhat minor factor, but an audible one.

Some may doubt this, but I am relating to you a real life experience that we did use in our audio shop for years. I have first hand experience with this, and knew what I was doing. People may nay-say or try to come up with some kind of reason why this can't happen, but I'm here to tell you that it does happen, and is repeatable as per my experiences.
Eldartford, perhaps I was not clear in my original response, But I am comfortable in suggesting that the first 3 criterion were fullfilled ( if not quite a dozen times, quite close, further more some the listeners had the opportunity to do this on more than one occassion spanning a couple of days). As for the statistical tabulation and analysis, I think the unanimous response satisfies that criterion. Do I think that a unanimous response will always be typical, heck no. I do think most people can discern the difference.
Tom, did you ever try putting a pair of inactive speakers in the lower corners of the front wall behind the active speakers?
Wellfed, no I have not tried that, although I have heard of the practice being used for tailoring the room for bass response. However more than just the bass is being re-radiated. I'd prefer to use a more specifically designed item for that purpose.
I think the original thought on the existence of other speakers in the listenroom had less to do with whether or not you could hear the disconnected speaker, but how their presence could alter the sound of the main speakers. The concept was that without other speakers present the sound could only be attributable to the speakers being demo'd. The falacy with this was that the room itself was a major contributor to the sound as was everything else in it. You still wouldn't know how the speakers would really sound 'til you got them home in your room. This was for me just another audio salon gimmick to add credibility to their image. However, regarding testing, I think it is clear that anything introduced into a listening room will alter its sound. If you disagree, just imagine bringing in plain boxes into the room, one at a time, and thereby changing the volume of and reverberation patterns with each box introduced, until the room was full of boxes. Ditto books, plants, vases, etc. When you add speakers you also introduce things which can vibrate and this will further alter the sound. The only remaining question is at what point does the change in the sound become audible? I think the answer to that question is that it will depend on the quality of the listener's hearing and their knowledge of the acoustics of the listening room and its equipment. I've always thought it humerous to read about listening tests, blind or otherwise, done by panels in rooms where the listeners were seated in various positions, as opposed to having one listening position and letting each listener have the sweet seat (after they have accoustomed themselves to the sound of the equipment and the room. In my experience if you are not perfectly positioned any really subtle changes in sound will be lost. And if you can hear differences when you are substantially off axis there are not subtle ones theat needed to be tested to be proved. Anyway, thats my view.
Believers...What you are saying is that a "room treatment" device having only about 1/2 square foot of active area has a significant effect. If this is so, why don't the room treatment merchants design a box with a passive radiator (or an active device) to accomplish their purpose without acres of foam on the walls.

By the way two things I can accept.
1. An inactive speaker placed immediately adjacent to the active speaker will function as a passive radiator, and will have some impact.
2. A small audio shop listening room with the walls lined with dozens of speakers would sound different if they were all removed.

A telephone! Now I know you are spoofing me.
Eldartford, I don't have to believe. I know, because I've done it. No spoof intended or conveyed. Everything I said above is absolutely true in the context that I stated it.

Secondly, there are room treatment devices of small volume that are used and sold by room treatment advocates. They are called helmholz resonators. And they work, in their limited role.
I would be delighted to participate in such an experiment if there is anyone near western Mass who is interested. An audio club perhaps?
If you have a pair of old speakers with a 10" or larger woofer, put them at the front corners behind the main speakers, make sure they are not connected to any amp, short the speaker terminals with bare wires, and play some bass heavy music like the opening track of the movie soundtrack Titanic or the Ray Brown Trio Soular Energy. Now turn the old speakers around so that the woofers are facing the front wall and listen for the difference. I think you will be amazed.
Sidssp...Yes I agree that in close proximity to the active speakers they would function much like passive radiators (which, by the way, some people think are a bad idea).

I can't do that particular experiment because the walls behind my three MG1.6 speakers are already occupied by embedded multiple subwoofer drivers that are very much active.

I remain to be convinced that a couple of inactive box speakers at the opposite end of the room would have any audible effect. As for a telephone...

Regarding helmholz resonators...they were used during WW1, connected by tubes to a set of earpieces, to detect approaching aircraft long before they were detectable by other means. Poor man's radar. It worked.
Actually, they don't act like passive radiators, they act like bass traps.
Our audio club has had a similar problem but with inactive beer cans. Before we get half through a meeting the empty bottles are acting like little Heimholtz resonators and the cans are just playing their own one note tune.

After copious study we decided to go to the foam cooley cups which have a great damping effect. If things sound a unnaturally bright in your system I suggest you clear the room of inactive aluminum cans or go to an audio-grade cooley cup.

I remain
Clueless, I can see it now, specially formulated from a rare an exotic rubber tree, cryongenicly treated and mounted on a sandwich of sorborthane, exotic wood, rare stone and kevlar over tip toes, with a remote controlled blue light that can be programmed to glow ones name at the touch of a remote control, cooley cup. Don't forget the sipfrom coasters!
Unsound: Amazing! I have just such a cup!!
Since it's just a prototype (sorry--can't name the manufacturer as I signed a nondisclosure agreement) I didn't think anyone knew about these yet. As for the sonic effects, I can't say for sure: they require at least 10,000 hours of break-in.
Eldartford asks: "If this is so, why don't the room treatment merchants design a box with a passive radiator?" Well they have. It's called Modex made by RPG. Different volumes and front material determine the frequency. With the speaker design, it is hit or miss in terms of the resonance frequency. It can work to the benefit, if it is resonant at the modal response of the room. It can also work to the deteriment if it's not. It's really hit or miss--not very scientific. As to TWL's phone experiment--seems highly unlikely that a phone would resonate enough energy to make a difference. However, the RF produced by cordless phones is a signficant problem, and I'm not surprised that it being in the room would create a detrimental effect--it's reason though I don't suspect to be the diaphramatic nature of the speaker.
ok, all of this is nice and well, but everyone seems to be skimming on the real question..

How long does it take for a set of inactive speakers placed in the room as treatments to break in?


Hey, does anyone think a modified Perch from Marco could be used as an accoustical lens?

Twl, i totally respect what you say and believe you definatly know what you are talking about. Your contributions to these forums are very well appreciated and your opinions and suggestions are held in high regard, But come on. A telephone speaker? Are you sure yer not pullin our collective leg?

I gotta say, i know alot about audio gear and how it works, but my actual first hand experience on these high end dedicated listening rooms is somewhat limited. But some of the things that people will say really blows my mind.
I guess it is one of those things i will believe when i experience it. Other than that, man that sounds pretty far fetched.

I saw a picture of a guy's listening room, he had all the accoustical treatments. Including what appeared to be a 3x6 foot legnth of foam rubber which looked to be glued to the top front of his speaker and leaning forwared and stapled to the ceiling.
Man that looked rediculous. To each his own though.

I still have a nagging suspicion that alot of these tweaks and stuff are the "Kings new Clothes", I definatly understand the importance and fundementals of accoustics, but man. Some of this just seems kinda... crazy?

I remember this time i was listening to nick caves "O'Malleys Bar" and my dog walked into the room and farted. Man, the soundstage collapsed, the imaging died...
Nothing more to say on this subject. Take it or leave it as you please.
I think there's a very large effect. A very large negative effect to the WAF!
El: If you play music and the music excites specific resonances of items in the room, those resonances contribute to what you hear. If those resonances are of noticeable amplitude due to high level excitation, you will be able to localize where the sound is coming from. It is at this point that most people remove the item from the room or take steps to damp the resonance. Even if the output levels from such resonances aren't strong enough to stand out individually, they are part of the broad-band spl within the room and what you are hearing. Obviously, some items are easier to excite than others and speakers are some of those that are easier. This is especially true if they are of the vented variety. In some cases, you can easily measure this.

By attaching a sensitive voltmeter to the outputs of the unused speakers, you an actually see / measure the amount of energy being developed from the driver acting as a microphone. This becomes even more apparent if you have a raw driver that is large in surface area and makes use of a lightweight cone / loose suspension. Believe me, if there is enough energy to cause a woofer to act as a microphone, you can bet there is enough movement of the cone to alter the spl's / tonal balance within the room.

By the way, the subject at hand is commonly referred to as "sympathetic resonances". I made mention of this a few years back here on Agon. As to what the specific thread was or how it came up, i have no idea. Sean

PS... You folks have to remember that not all "audible differences" result in increases in amplitude or extension of bandwidth. Some changes can be subtractive. These are typically more subtle and take longer to recognize because the differences are not "in your face". While i'm not saying this is what takes place in this specific situation, i did want to make mention of it because cancellation can also take place when dealing with acoustics.
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.
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
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.
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.
agree wholeheartedly with twl about speakers and phones in room
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?