Axiom Home Page Forums General Discussion Home Theater VP150 Calibration Problems

Lexicon MC12, Sherbourn 5/1500A, NHT T5s in front, M5 center.

Yes, the m2i layed on its side performed MUCH better than the VP150, at least from the point of view of equal output at all listening positions.

hmmm...that's interesting. I'd love to hear what Alan can come up with to explain that. Alan? Any ideas?

What Ian seemed to suggest is that in his measurements my VP150 did not exhibit this behavior. I'm not making it up, which is why I'd like someone to confirm or deny my findings. In my readings about the VP150 I have come across several listeners who complain of the sound being centered around the VP150 and not being well dispersed. I would call it a kind of "megaphoning". I'd be interested for someone to perform the test I did. Maybe the reason Ian didn't duplicate my results is that my processor outputs its test tones in specific frequencies that are highlighting this dispersion problem. Just a thought.

It could be a unique characteristic of your room. The primary reflections (from the side walls and/or ceiling) may be partially cancelling out with the direct sound to the left and right of the sweet spot.

Just to be sure, I'd try moving the VP150 a couple feet to the left or right and redoing your measurements.

I no longer have it, Ian has it. However, he had me move it to where the left speaker was and measure it. It demonstrated the same problem: 75db on axis and 71 db 3 feet off axis. As I moved from directly in front of it to the side I could hear what I would describe as "suckouts" as the output was reduced. Neither my NHT M5 nor the Axiom M2i exhibited any such behavior. I would like someone to perform a similar test to see if they can duplicate my findings.

tonygeno,
Ian is correct. There is nothing wrong with the VP150.
What you are measuriing is an effect of pink noise, off axis reponse as well as the difference between drivers as you move right to left (tweeter W W W tweeter). To better demonstrate how the VP150 drivers create this effect, try out the following:
If you use your pink noise calibration on your main speakers (i have M60s), hold the SPL about 8cm away from the top driver and measure the dB. Then measure at the same distance moving down to the next driver and so on.
You will notice that each driver does not produce the same exact dB output with the pink noise. This is normal and occurs with the VP150 as well. The tweeters will not measure the exact same dB as the woofers. For a partial explanation, see this link especially the short paragraph on the characteristics of pink noise.

As for the VP150 dispersion, you are reading into the dB measurements too much. The VP150 is so good at dispersion based partly on its great width. I've heard other single driver centre channels that really direct the ears to a single point. The multi driver and extra wide VP150 removes that effect very nicely while creating a wider sweet spot.

Keep in mind that sound will always change as you move in a room, not only because of room reflections but also because of the off axis response your ears perceive from each individual speaker. Try standing on your couch and listen to a song then drop down into the couch and listen again, then drop to the floor and once again listen how the sound changes. Off axis tests are fun but often make the family think you are truly a bizarre and confused individual.

So if I understand you correctly, it's ok that the VP150 shows output variations of 5 db as I move off axis (this is at a distance of 11 feet)? And, why doesn't either my M5 or M2i exhibit the same behavior? The tonal (and output) variations I heard were rather extreme, and were not duplicated with the other speakers. Why would this be?

FWIW, I remember playing with this last time I saw the thread. I just tried again. I see no such variation (or less that 1 db) as I try five different positions (one sofa, small chair on either side). So the spread is about 11 feet.. I'm about 15 feet from the VP150 center. I see the other speakers vary as I change positions (e.g. left gets weaker as I move far right, but not the center). I'm using the built-in tones from Onkyo receiver and an RS spl meter.

Thanks for the reply. so I guess I just have an incompatability with the VP150 and my system. Ian says he sees no such variation when he tests my speaker, but I got tremendous variation. Oh well. Onward and upward.

I have an M60/VP150/QS8 config. I used an analog RS meter, (C weighting, slow) to measure pink noise on-axis and 15 deg (3 ft laterally) off-axis from the VP150 at a distance of 11 ft. Left or right 15 degrees off-axis, the output dropped about 2 db (about 70db to 68db).

Since my QS8s are only about 9' away and positioned at about 90 degrees, moving left or right 3' puts you significantly closer to one and further from another. In my room this effect outstrips the relatively minor VP150 off-axis effect. The sad truth is like stereo before it, surround is significantly optimized for a sweet spot. At least it's better than Quad
At least for HT it seems to matter less than music.

There are definitely complications in dealing with surround audio, but mine don't come from off-axis Axiom speakers behavior. Rather getting my sub calibrated when SACDs and DVDs evidently have two different bass output levels is a problem, as is doing two separate calibrations for digital Dolby sources vs 6 channel analog sources like SACD. Receiver or even calibration disc test tones don't seem to help much, as there doesn't seem to be any level standard for how SACDs (or even CDs) are recorded. After calibrating, I ultimately adjust the speaker and sub levels until it sounds right, which can vary from disc to disc.