Wanna hear your soundstage walk around ???

Courtesy of Bob Bundus, i was able to see just how much "image shift" i've been experiencing. Remind me to "kick him" next time i see him : )

Bob was kind enough to lend em a disc put out by Ayre Acoustics entitled "Irrational, But Efficacious !". If i recall correctly, he picked this up from Bes at Music Direct but i'm sure that other Ayre dealers may have it in stock. You can also probably pick it up directly from Ayre at www.ayre.com

This disc has several different types of noise patterns ( white, pink, brown, mono brown, out of phase brown, etc...) on it. You can use these for various aspects of setting up a system, testing components, etc... It also has two "Glide Tones" on it. These are actually full audio spectrum "sweep tones" that start out at 5 Hz and climb to 20 KHz at a gradual rate. One is of short duration ( 45 seconds ) and the other is appr 4.5 minutes long. Ayre recommends using these "glide tones" occasionally as they supposedly "clean out" your system. If i recall correctly, i think that Cardas also has some discs to this effect ( Cardas Sweep ??? ) as the Ayre disc gives special thanks to "George Cardas, the ever curious audio explorer".

There are several very "neat" things about these "glide tones". First of all, they start out VERY low in frequency. I was amazed that one set of my speakers was actually reproducing the 5 Hz signal at high amplitude as soon as it started playing. This sounded like the flutter that you hear from a helicopter approaching. The driver was making MASSIVE excursions to do this. As such, i don't recommend playing this disc at any type of volume as it may do damage to your speakers or amp. I contacted Ayre about this with some other questions and they too suggested playback at reduced volume.

However, being the "audio geek" that i am, i couldn't resist turning up the power quite a bit. The effect that this generates at volume is pretty incredible and WILL shake your house and the contents IF your speakers and amp are up to the task. Obviously, the faster your speakers roll off in bottom end, the less output and "impressive" this would be.

In the first system that i tested, i was actually able to drive my amp into SEVERE clipping. It is the first time that i have EVER heard this in my life. The amp in question is rated for 200 @ 8, 400 @ 4, etc... so it is not a "gutless wonder". The speakers in question are rated at a nominal 4 ohm load but i know for a fact that they dip well below 2 ohms at low frequencies. As such, they have been a good test for many amps. Some well respected makes and models have failed miserably with these speakers for obvious reasons.

The sound produced when the clipping took place was similar to the "snap" or "pop" that one might hear on a very dirty record. To get the same effect that i heard though, you would have to drop the frequency of that "pop" down quite a bit and make it much more intense i.e. more of a "CRACK" sound. It was not the speaker itself bottoming out, as i've had that experience before. This happened at two different spots in the frequency range and was consistent, as i repeated the test a few times. I did give the driver time between tests to thermally "heat down" though, as i didn't want to cook the voice coil. As such, the speaker is obviously pulling MUCH harder on the amp at those specific frequencies due to impedance / reactance and the amp simply couldn't keep up. Scary and interesting all at the same time : ) I was able to find out one thing though. This amp had "instant" recovery as you heard the "crack" and the tone kept playing with nary a waver or flutter on either side of that frequency.

Secondly, you can check how linear the output of your system is. As the tone rises, you will hear different levels of output from your system. This demonstrates that you DO have more than a few peaks and dips due to standing waves and reflections in the room. Obviously, the most noticeable frequency "should" be the point of resonance of the woofer resonating in your room, but this may vary if you've got REAL problems with room reinforcement / cancellation nodes taking place. Unfortunately, the tone is of continuous output and ever rising, so there is no real way to judge "exactly" what frequencies are "nulled" or "peaked". One could do this with a calibrated disc of test tones or by using an spl meter and a tone generator in similar fashion to what this disc does.

The next "neato" ( am i old or what ??? ) thing about the "glide tone" is the effect it has on imaging and soundstage. Due to various nodes and points of reflection in your room, you can literally hear the placement of the sound "walk around" your room. Depending on how well the room is acoustically treated and the radiation pattern of your speakers, this can range from interesting to phenomenally "weird". Since i have various types of speakers ( 360* omni's, large towers, horns, etc...) in different systems, this in itself was a rather unique learning experience.

As a general rule, i was able to hear the signal shift from side to side, between the speakers, WAY above and outside of either speaker, etc... as the pitch varied. Since the signal is on a continuous climb that never stops until the end of the track, you literally hear the point of least cancellation racing from place to place.

This in itself is a phenomenal test for room acoustics. For those that think that "room treatments" aren't important, think again. I'd like to see a system / room that could hold the image centered, as it would have to have one HELLUVA lot of work into it.

If it wasn't SO dissapointing to hear how "off center" many of these images were, it would make one helluva "sonic demonstration" to people just entering the hobby. This could INSTANTLY demonstrate what "imaging" really is and how sound can be "focused" or projected into specific areas. Of course, it would be MUCH better if this was happening under "controlled conditions" and not just at random due to "room bounce" : )

If this has been interesting to read, believe me, it was even more "fun" and "educational" first hand. I can't guarantee that you'll have the same results that i did ( hope you don't ), but this disc was able to show me that i need a LOT more attention paid to room acoustics and speaker placement. Then again, you might NOT want to experience this first hand, as you may want to commit "hari-kari" if your results were like mine : ) Sean
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