Axiom Home Page Forums General Discussion Home Theater VP150 Calibration Problems

I spent this evening calibrating my M2i/VP150 system and discovered a problem. If I calibrate from the center listening position (75db, C weighting, using the Rat Shack analog meter) when I move to the right and left seats of the couch the left and right speakers remain at 75db, but the center channel drops by 2db to 73db. This would suggest that those seated on either end of the couch will be hearing dialog at a lower level than the central listener. I thought the point of the VP150 layout was to eliminate these variations in a horizontally oriented center. Any ideas as to why this is happening? Could my VP150 be defective?

I don't think there's anythging wrong with the speaker. A drop of 2db is barely noticeable to the human ear. If the difference concerns you, I'd calibrate the VP150 to 76dB so that more of the couch gets 75dB.

Also, remember that every speaker interacts with the room. Do you have a coffee table between you and the center channel?

No coffee table. Clean shot between the speaker and the couch. When I play pink noise and move from the center to the left and right seats, I notice a definite change in the sound, which is why I decided to measure. Other centers I've had did not demonstrate any change in level within the seating area.

I reran the calibration, and the actual db variation is 4. It goes from 77db at the central, seated location, to 73db at the left locaton. Ian is on the case. I'll let you know how it turns out.

Ian emailed me to say this is not normal behavior. Fedex has just picked up the sub and I should know something next week. Hopefully, it's a minor fix, but I knew something was obviously wrong. In fact, I heard something rattling around inside the cabinet when I packaged it up. Maybe shipping damage?

Well, it at least sounds like another case of good customer service. That's a +.

-Nick

Fedex picked up the sub?
I thought it was the vp150 giving you problems.

Oops. I've got subs on the brain. It's the VP150 of course.

Just got an email from Ian. He says my VP150 is working as designed. Has anyone else measured (with the receiver's calibration tone using a Rat Shack meter) the VP150 moving the meter from the central position to the left and right? I have tried this with an NHT Evolution M5 and an Axiom M2i and measure at most a 1 db variation from the central position the left and right couch seats. With the VP150, the variation is 5 db using the same measuring procedure (the center seat reads 75db while the left and right are 70db). I was lead to believe that the novel center channel arrangement of the VP150 lead to a more uniform dispersion pattern. This has not been my experience. Could someone please try this and post your results? At this point, I think I'm going to send back the M2i's and get a credit on the VP150. I had originally intended to get a complete Axiom setup, but the center channel is very important and the VP150, with this type of off-axis performance is a non-starter for me.

What is your current setup? What do you have for mains? A single M2i performed better off-axis than the VP150 as a center channel?

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.

Tony,

My VP150 is mounted on a shelf directly above my 65" Mits. It is 5.5' above the floor, 12' in front of the main listening area. I have the speaker angled down to compensate for it's relatively high placement. It is angled down so the tweeters are pointed at ear level.

After reading your post, I used my RS analog sound meter to make some measurements. Using my receiver's built-in white noise tones, with the sound meter pointed at the ceiling, I adjusted the volume of the receiver until the meter showed 75 dB (C-weighted, slow response) while I was in the middle of the listening area. I've got a 7' couch, and I moved the meter to the left and right edges of the couch while playing the white noise. The meter dropped 1 dB at the left and right edges. The drop-off was linear, in other words it seems to drop off steadily. I would estimate it reaches the 1 dB drop-off at approx 15 degrees off-center. I've got a chair that is quite a bit off-center (I would say it's about 45 degrees), about 10' away from the speaker. At this chair, there was a 3 dB drop-off.

I was curious to see if the angle of the speaker made any difference. So I placed the speaker flat on the shelf, so it was no longer angled down to the listening area. I noticed a 2 db drop-off in the center of the listening area and a 3 dB drop-off at the edges of the couch, so the net effect was the same as before.

HTH,
Jason

Thanks for the response guys. It kind of confirms what I measured. Whether it is audible on voices, it's hard to tell. I haven't seen any NRC measurements of the VP150. I think it would be interesting to see some. Since Ian got my VP150 back, I don't think I'm going to have him send it back to me. I guess I'll just move on. Now what's interesting is that Ian said in his original response to my query, that no way should I measure the differences I measured. One db is all it should differ out to 45 degrees, way beyond my angle. Now, folks are telling me it's normal to measure these differences.

Chess, if what I'm hearing are the artifacts of pink noise, I wonder why Ian had me send the VP150 back instead of giving me that explanation.

Call me confused. Thanks again, guys.

Tony

Tony, the easiest explanation for the differences in people's experience is apples to apples comparisons. Using sound test tones i measure no significant differences until a more extreme off-axis angle with the VP150 is reached. Ian may have also used a range of actual frequency tones. I don't know and hence i cannot explain his results although they do coincide with mine, but of course not with pink noise (apples to apples).
As i said previously, pink noise is part of the problem but all speakers have an off-axis response and this is something normal to expect. It is not a flaw with the VP150 and other centre channels may very well be even worse. Using the M2 as a centre still has an off axis response as well but keep in mind you cannot compare a horizontal vs. a vertical design speaker (apples to apples again). Its off axis vertical sound may be more noticeable or measurable with pink noise compared to its horizontal response. Axiom does ALL these measurements and incorporates this in their designs.

I will be over a friend's place this weekend and he has a Tannoy Saturn centre. I will measure the pink noise tones from his Denon receiver and see if it is any better or worse than the VP150. My guess though is that his sweet spot will be alot smaller but i could be wrong. The Tannoy dual concentric drivers really have a wide, even dispersion themselves.

Wow, that's one fugly center channel! I hope it makes up in sound what it lacks in looks.

How do you get those links to work. I haven't been able to get one to work yet, even when I copy the URL exactly.

Oh, and thanks for the explanation (again).

Take care,

TG

Re "folks are telling me it's normal to measure these differences", all I measured was -2db at 15 deg off axis, whereas you measured -5db. Some of this could be room effects, such as furniture, carpet, reflective walls, etc.

Also if you were off-axis vertically (i.e. VP150 points too high or too low), as you move laterally you'd get faster drop off. Just a possibility.

The off-axis problems of any stereo system (and the center channel is merely augmented stereo) are so well known Dr. Floyd Toole refers to it as an "antisocial" system -- it's optimized for a narrow sweet spot. IOW you can't have a large lateral audience who get equal sonic imaging, so it encourages solo listening. Floyd Toole White Paper

To me issues like off-axis behavior are minor next to the huge differences of room effects, good vs poorly mixed material, sub calibration problems, etc.

Joe:

True re room effects. But interestingly enough, neither the M2i nor the NHT M5 I had on hand exhibited these effects. The reason I was in a sense looking at this issue rather closely is that the layout of the VP150 is very unusual (in fact no other manufacturer has picked up on it) and seems prone to comb filtering which is what I think I was hearing and measuring. But I'm sure Ian knows a lot more than I do about speaker design!

I would just ask Axiom to send you a new VP150, since many of us are not experiencing your problem with our VP150's.

Jason

tonygeno,
Regarding the comb filtering.
Read this post by Ian and this thread.

I had seen those threads, Chess, which is why I ordered the VP150. However, in my environment, I noticed a very significant drop-off in output as I moved off axis, one that I heard with my ears. The meter just confirmed it. I have been emailing a couple of guys who notice this as a "muffling" of the center, but neither of them has calibrated their systems, so I don't know if it's what they're hearing. If this were such a great center channel layout, I wonder why others haven't picked up on it, though.

Jason:

Ian has measured my VP150 and says all is well with it, so I don't think a new VP150 will resolve my issues. Thanks for the suggestion, though.

In reply to:

---

However, in my environment, I noticed a very significant drop-off in output as I moved off axis, one that I heard with my ears. The meter just confirmed it.

---

But you specifically stated this occurred when calibrating with pink noise. As i iterated to previously, this is partly an artifact of pink noise and secondly, this will occur with any horizontal centre.
Does this equate to the same 'sound' during a test tone playback or real music?
Not that i've heard and certainly not measured with an SPL. Play a song in DPLII such that the centre channel is being used and then do your SPL test from left to right. I can just about guarantee the results will not be the same as you measured with pink noise.
Keep in mind that your original measured values were 2-3dB which is at the marginal range for human perception as significantly different volume (this number seemed to increase as your later posts came along, i don't know how). If the right and left channels are working and placed for optimum performance, you should not detect any dropoffs or suckouts.
If you do not like the VP150 for this sound, then logically you should not buy towers either since they have the same 'problem' just in a different plane. Someone posted an article recently about the omnidirectinal Beolab5 speakers. You could always give them a try.

As for the design concept, everyone has different ideas for what sounds good as a speaker and not all use measurements like Axiom at the NRC. Many design speakers off the top of their heads based on principles they know, and everyone wants to have something unique. Very few companies like to copy each other, but note how recently many companies have jumped on this multi-directional driver dispersion idea like the QS8s. Sometimes the concepts take time to catch on and be accepted.
Maybe there is a company that does have the best centre channel design for off-axis response.
Who knows?
But from what i've seen so far, many centre channels are very simple. Usually one or two drivers and that's it. I find this style to have a real point source for sound such that localizing the near exact position of dialogue is distracting as it comes from above or below the viewing screen. I think this is far more a negative property compared to the VP150 shift in response by moving left or right 4 feet or more. The distance to ones listening location from the main/centre channels will greatly alter such perceived sounds.

Hi,

Thanks, Joema, for the mention and link to Floyd Toole's white paper. It was Floyd who first demonstrated to me (back in the late '70s) the effects of comb filtering and the limitations inherent in 2-channel stereo playback.

Tony, ALL speakers at the front of a room produce comb filtering and uneven response as a result. It's yet a further liability of stereo listening and is quite audible using pink noise as a test signal. The explanation is too long to go into at length here but while it's audible with pink noise, it's not a significant factor that seriously undermines our enjoyment of music, movies, or even stereo playback, nor is it identifiable using music as a test signal. (Music has a wonderful masking effect of tiny and even large distortions.)

Plus I believe you had your VP150 stuck in an entertainment center, correct? I would suspect that the interference effects of the EC would have the potential to significantly alter the dispersion of the VP150 and introduce some of the anomalies you seem to find with it. A speaker with a smaller enclosure might be less affected, which might explain why you aren't finding the same effects with the smaller M2i on its side.

All of that said, I would point out that the stereo illusion and that with multichannel is always compromised to a greater or lesser degree. What is astonishing is that with neutral, transparent, and accurate speakers like Axiom (and some others) that the movie soundtrack soundfield reproduction with 5.1 or multichannel music is so convincing and enjoyable much of the time!

Given the vagaries of listening rooms, furniture and the like, it's a hopeless and frustrating odyssey trying to find the "perfect" center channel. There isn't one. But the VP100 and VP150, when properly set up, deliver a convincing and seamless soundstage and intelligible dialog for a reasonable number of listeners in most average rooms.

Regards,

Tony, one more item: if you want a higher degree of off-axis capability you could investigate speakers specifically designed for this. One brand I've heard is Mirage, another Canadian company. http://www.miragespeakers.com

I auditioned the Mirage Omnisat and Omni 60 several times. Moving around the room, the stereo image wasn't affected as much as traditional direct radiating speakers. However the tradeoff was an overall sound I didn't like -- diffuse, blurred, and spread out, even when on axis. In A/B testing with direct radiating speakers I greatly preferred them over the Mirages. Other people love the Mirage sound.

My M60/VP150/QS8/VTF-3 config are the best speakers I've heard at any price, so naturally I'm satisfied with them. If there's an abnormal off-axis problem, I haven't heard it. However 95% of my listening is 1 or 2 people, directly on axis, so I wouldn't be affected by it even if it existed.

Hi Alan:

This odd (to me) behavior was noticeable even after I took the VP150 off the shelf (it's not really a cabinet) and placed it where the left speaker was (essentially free space). I noticed the exact same behavior, so I doubt it was the placement.

The other center I have on hand (an NHT M5) uses a three way arrangement ( two woofers flanked by a centrally located midrange with tweeter above or below the midrange, depending on placement) and I neither heard (nor measured) any such frequency or output aberrations. Now, if you guys are telling me that these aberrations are inaudible with music or movies, that's fine. But I would be interested to see the NRC measurements of the VP150 on axis and off-axis to see if what I'm hearing shows up in as measured anomalies.

"But you specifically stated this occurred when calibrating with pink noise. As i iterated to previously, this is partly an artifact of pink noise and secondly, this will occur with any horizontal centre."

It does not occur with my NHT M5, nor did it occur with the CSW MC500 I once owned, both 3 way centers.

I keep trying my best to NOT read any more of this thread. To no avail. I'm glad so many people are happy with the VP150. I'm sorry Tony is not.

Now, go to the beer thread.

If you didn't post to it, Tom, you wouldn't help to keep it alive. No need to be sorry I'm not happy. I'm glad everyone is happy too. I'm also happy, just not with the VP150. I am very happy with the M2i: absolutely amazing value and a good sounding speaker, irrespective of price or listening axis!

Tony, have you tried using one of your M2is as a center? Be interesting as a point of comparison.

Yes I did and it sounded pretty good. Problem is though, that it's too tall for my cabinet and doesn't work so well on its side.

Thanks for the info. Did the M2i have off-axis issues, or were you unable to tell because you couldn't place it vertically? I need to just break down and buy one to do a center-test, but I'm too lazy ... and a bit too embarassed with the SAAF (that's Spousal Audioholic Abuse Factor).

The M2i had 0 off-axis issues in my tests.