Sonics of Soundlabs

Mcreyn -- you are incorrect. When a half wavelength (~ 28 ft for a 20 cycle/sec tone) is longer than the longest dimension of the room, it cannot fully form in space before hitting a wall and reflecting. causing it to double back on itself, producing points of both cancellation and reinforcement. If you happen to be at one of the reinforcing points, it may appear that the bass is very loud, but just a few feet away there may be a null point with very little bass due to cancellation. Right at a wall surface, there is always louder bass because that's where the wave changes direction, therefore releasing a lot of energy when it momentarily stops before being reflected in the opposite direction. That phenomena happens in all rooms though, regardless of size.

If your analysis was correct, then shorter organ pipes would produce lower notes :~)

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You are speaking about standing waves, which is different than room gain. Room gain results from the maximum length of the wavelength being longer than the room. You do not have standing waves at frequencies below this fundamental frequency, only above. The way to compute the lowest resonant frequency of the room it to take 1127 (or if metric 343) divided by (longest room dimension x2). The result is the lowest freqency that you can have a standing wave and the knee freqeuncy below which you experience room gain.

You analogy of an organ pipe is incorrect as an organ depends on resonance to produce sound. This is far different than sitting in an enclosed area (a room) with a device that puts out an accoustic signal.

Here is a quote from Tom Noussaine on the subject:

"2. Room gain: Room gain starts at roughly the frequency of your lowest axial mode. The pressure gain is 12 dB per octave as frequency falls. In a car its at 60-70 hz depending on size. In my 2136 cubic foot older listening room it started at just below 30 Hz. In my 7500 cubic foot current room it starts at 16 Hz. A Velodyne FSR-15 had 8 dB less output at 2 meters in the larger room with idntical placement."

http://archive.avsforum.com/avs-vb/history/topic/39249-1.html

Mcreyn -- standing waves are only produced when a room dimension is a whole multiple (not a fraction) of the half wavelength of the frequency in question. The room will gain in dB (more SPL than the speaker is putting out) by resonating at the frequency in question (like an organ pipe) and that is why bigger rooms have lower resonant frequencies (per Mr. Noussaine's remarks)

Once again, a room smaller than a certain frequency's half wavelength cannot resonate at that frequency and thus the SPL cannot increase over what the speaker is putting out by itself.

I also read Mr. Noussain's remarks on avht. The smallest room he mentions (assuming an 8 foot ceiling) is quite big enough to develop a full 20 cycle wave (roughly 13x20), and so standing waves (and room gain) are definitely possible at that frequency -- however, in a room too small for the 20 cycle wave to form in the air, standing waves, and therefore room gain are not possible.

As for his weird experience with the Velodyne: A loudspeaker will always put out the same SPL (at a given frequency, at a given power input, at a given distance away from it) in any environment (or even outdoors) at normal atmospheric pressure UNLESS there is either cancellation or reinforcement at the point where the measurement is being taken (which is probably what happened to Mr. Noussaine, and he just didn't realize it.)

I had trouble visualizing how he placed a speaker "identically" in two rooms of different size -- so I'm not sure what the heck he meant; maybe he meant "proportionately" since "identically" would be geometrically impossible. It sounds like he once again stumbled onto a null point without realizing it.

In any case, I would not be especially drawn to his remarks in the future.

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Well guy's,

I went to hear these speakers today and was dissapointed. Only one was working.......... the upgraded backplate had not arrived from Soundlabs for the other yet, and there was a lot of distortion from the one that was working. I think it was the gentleman's amp that was clipping, but I am not positive. He was using a monster SS Crown PA amp. The sound was pretty harsh all the way around.

Anyway, to make a long story short we agreed to do another audition when both speakers are up and running (hopefully next week). Any thoughts anyone on this experience? I am hoping this isn't typical for these speakers. Question: Are Soundlabs unreliable? I am starting to not feel real good about this pair of speakers.

Chris

I will try this one last time and then quit wasting my time, as it appears you are more concerned with running your mouth than hearing the truth. Below the resonate frequency of the room, there is what is termed transfer function gain, room gain, or cabin gain. All are the same thing. Below the knee frequency, there are no standing waves, only the 12db/octave rise.

Try this little experement. Take your subwoofer, run a 20hz signal through it. Measure the output at 10 different locations in your listening room with an SPL meter. Don't change any levels and take that subwoofer and put it in a closet with a door. Close the door and stand in there with the sub. Measure the SPL reading there in 10 different locations. Guess what the SPL reading is higher and very close all around. Can't find any standing waves, because there are none.

Now, I know you think you are smarter than Tom Nussane, so here are a few more links that discuss the transfer function, but I will guess that you will continue to argue until you are blue in the face that you are right and scientific fact is wrong.

http://www.linkwitzlab.com/rooms.htm#Standing%20waves

http://www.linkwitzlab.com/thor-intro.htm

http://www.linkwitzlab.com/images/graphics/enclosure-spl.gif

http://www.caraudiohelp.com/newsletter/cabin_gain.htm