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Howard Ferstler

Allison room-response curves

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When I reviewed speakers for The Sensible Sound and The Audiophile Voice I also did measurements, although those measurements were secondary to the level-matched A/B comparisons I did between the speakers under review and my reference speakers. The measurements were basically just starting points that helped me understand some of what I was hearing. They did help me separate the good and great speakers from the real dogs, however. What we have below are readouts of several Allison models I checked out over the years (I did not formally review any for magazine reports, because when I did the measurements the company was already out of business), plus readouts of several other brands for reference purposes.

Basically, I would use the 20-second integration feature of my AudioControl 1/3-octave, SA-3051 RTA. The curves are hand drawn, using the readouts on the RTA front panel.

The test is simple. I would feed decorrelated pink-noise signals to the speaker pair, and then SLOWLY move the measurement microphone over a roughly 1 x 1 x 5 area at ear height at the listening couch. While the microphone was being moved the RTA would average out the sound being picked up and then give me a cumulative result of the 20-second input. The technique helped to reduce hot-spot reflection effects and standing-wave artifacts that one gets with measurements at a fixed location. Note that the result would be a blend of the direct and reverberant-field output, with wider dispersing speakers favoring the latter and narrower-dispersing speakers favoring the former. The idea was to get a fix on the spectral balance of the speaker at the best listening location in the room, with a mix between the direct and reverberant fields.

The couch was 14 feet from the front wall, although many free-standing speakers would be pulled out some distance, with a corresponding increase in the strength of the direct-field balance. When sub/sat speakers were measured, the subwoofer was usually in the left-front corner, about 17 feet from the center of the couch. The speakers were 10-12 feet apart, depending upon how far out they were located.

Note that these curves will give one an idea of spectral balance, but they will not determine things like imaging tightness, focus, soundstage envelopment and spaciousness. I would use my single-presentation and A/B comparisons to determine those attributes.

All were run in my main, roughly 22 x 18 x 8.5 foot AV room, with the exception fo the Bose 901 pair curve, which was run in a still larger room belonging to a friend of mine.

Curve One: IC-20 pair. These are mine. Note the room-gain at the low end. I have no explanation for the dip at 1250 Hz, but when equalized out there is no particular change to the musical sound at all. These speakers can be seen in the photo I posted some time back showing my main AV system. In my current arrangement I use a Velodyne subwoofer to handle the very low range.

Curve Two: AL-130 pair. These belong to a friend of mine.

Curve Three: CD-8 pair. These belong to a friend, also.

Curve Four: Model 8 pair. Again, also belonging to a friend.

Curve Five: Model 4 pair. This pair is also used as surround speakers in my smaller AV system. I have four more used as surrounds in my main system.

Curve Six: The left and right speakers in my smaller AV system, made from scratch, which use two RDL tweeters each and one 6.5-inch Allison woofer each, with two TB Systems 4.5-inch midranges each. These speakers are illustrated in some photos I submitted of that system a short while back. The woofer is not large enough to handle low bass happily, so I use a big Hsu subwoofer for that range.

Curve Seven: The center speaker in my main system. I also made it from scratch, and it uses two Allison tweeters and two Allison mids, in a vertical MTTM array, just like a single panel on an IC-20. A single IC-20 woofer handles the bass. The crossover network is a combination of what we have with the Model One and CD-9. This speaker can be seen in the same main system photo I submitted a while back, along with the IC-20s. To do this measurement I located the speaker at the left postion and fed it mono pink noise. Had to do this, because there is only one of them.

Curve Eight: An NHT "Evolution" sub/sat system, with the M6 satellites and two W-1 subwoofers. I reviewed this package for The Audiophile Voice. This package listed for about $2500 when I reviewed it. Look at that tweeter response. Very clean sounding speakers, but with limited spaciousness when set up optimally.

Curve Nine: Polk LSi-25 speakers. These are large systems, with powered woofer drivers. I reviewed them for The Sensible Sound. These speakers listed for about $3000 when I reviewed them. I thought they sounded a tad bass heavy.

Curve Ten: Dunlavy Cantata systems that I had for some time in my smaller AV systems. I also reviewed them for The Sensible Sound. They employ a vertical MTM array using 6.5-inch midrange drivers, and with a downfiring 10-inch woofer on the bottom. Very directional speakers with a very clean sound and superb imaging, but not with particular spaciousness. These speakers listed for about $5500 when I reviewed them.

Curve Eleven: Bose 901 systems in a friend's very large room (31 x 21 feet, with a cathedral ceiling running 8-10 feet) at a roughly 16 foot measuring distance. The active equalizer had been set up by him for his preferred balance. Very realistic sound with small-ensemble source materials, but anything but pinpoint imaging. The curve almost looks like what one would get with a mid-level three-way conventional speaker.

Curve Twelve: Waveform MC sub/sat system. The satellite enclosures were cast-aluminum and egg shaped (exhibiting essentially zero diffraction), with a one-inch tweeter and 6-inch midrange. Two Waveform subs were used, and the crossover network was a fourth-order type. This package listed for about $5400 when I reviewed it. Very clean sounding systems

Curve Thirteen: Eminent Technology LFT-8 system. This one was also reviewed for The Sensible Sound. It has dual line-source planar-magnetic tweeter and midrange drivers, with an 8-inch dynamiv woofer. The treble rolloff is not all that apparent with musical sources. These speakers listed for about $1200 when I reviewed them.

Remember, curves like these are but starting points when auditioning speakers. The bottom line involves additional things like solid listening evaluations, but I feel that a speaker has to at least have decent performance with a test like this to qualify as a high-fidelity item.

Howard Ferstler

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Guest Donn

My 1st thought when seeing the Allison curve is its curve looks odd! I think the abnormal non-flat freq response (at low feq) probably helps when listening to low volume but at high volume it is bass dominated. Is such feature desired in the Allison design?

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