I thought you folks here, especially Hutzal, might be interested in
Mark Fleischmann's recent blog post about using a centre speaker which matches your fronts. There's a link in his post about lobing which has some revealing graphs and would make for some interesting discussion/debate here.
the only reason I am using 2 M2s, one above, and one below my screen is because of JohnK. If it was not for him, I would have opted for the bookshelf centres. I love how it sounds and I wouldn't have it any other way.
I really must say that anyone hesitant of getting M2 centres shouldn't be, they are an amazing speaker. I was hesitant at first which is why I got the M3s, but after realizing that I could actually hear the difference from the M22s, I replaced them with M2s, and they are amazing speakers.
Do a searching for combing and lobing.
It has been discussed already in the past.
Ian weighed in with some thoughts if i recall.
Yes and in the words of many people: to D'Appolito or to not D'Appolito that is the question.
The main reason most people don't use three identical speakers is because its impractical and once you leave the plane of the mains, alot of acoustical complications kick in. Joseph D'Appolito got it right with his asymetrical MTM configuration as the best solution to this problem. Fleishman's views are very out of date.
Krunch, yes that was an interesting discussion, both as to an MTM center speaker and none at all, employing a "phantom" center. These options have been discussed here several times in the past, and it has been pointed out that others, such as Tom Nousaine, have described essentially the same difficulties. It should be remembered that the MTM arrangement devised by Dr. D'Appolito was specifically intended to have broad horizontal dispersion when positioned vertically and to narrow vertical dispersion to help minimize problems with floor and ceiling bounce. When positioned horizontally the opposite result occurs.
Thanks for the input guys.
I've been learning about all things home theatre for a couple of years now and this is the first time I'd come across the terms combing (aside from the similarly named "comb" filters used by composite video connections) and lobing. I'll dig through the forum for the past discussions as mentioned.
Just when you think you're getting a handle on all of this, you realize just how much more there is. It's all good fun, though.
So what would happen if say you were to have 2 M80's as your fronts and had 2 M80's set up on either side of your display acting as a dual center channel? Sorry if this is an ignorant post.
Kyle, there wouldn't be a speaker literally right in the center, but the two M80s at the side would make the center channel sound fed to them appear to come from the center of the screen for someone sitting midway between them. If the listener moved to the side, the center image would move with them, but not farther out than the M80 center to that side.
I want an amplifier than can drive two M80s as a center channel.
So then that seems as if that could be a better set up than a standard center channel configuration? Am I understanding correctly or is it more suited to personal taste? And for purpose of discussion, wouldn't the Emotiva MPS-1 work? 1 mono for each M80?
Sure, for those who'd find the described result to be better, two M80s(or M60s, M22s or even M2s)would make them happy. If lowered impedance when driving them in parallel with one amplifier was in fact a problem(wouldn't necessarily occur), then two amplifiers could be fed the center channel material and one would drive each speaker.
Ok cool. So really it is just a personal preference kind of thing. Are there any reasons why someone would not want that type of set up?
Well, again the point is if the small shift of the center image to the side for off-center listeners would be acceptable because it nevertheless would sound better than a centralized horizontal MTM . Using one vertical speaker in the center(either above or below the screen)or using two, one above the screen and one below(as Robb Hutzel does)doesn't have any shift with horizontal listener placement.
Ok that makes sense, I'm with you now. Do you think you could mount the M80 above the screen? LOL
If the glue was strong enough; if not, use center speakers very similar to the mains above 80Hz or so, but much smaller and lighter.
I understand. It was a joke. However the 2 M80's on either side of the picture really is something I may be looking into. Would that be overkill if my mains are also M80's?
I'd say so. Use a smaller speaker(s)in the center.
As you go through the practicalities one can see how the horizontal D'appolito configuration provides the optimal solution to these problems. Anchoring the centre channel to the centre of the screen is very important to acheiving theatrical effect. The MTM configuration involves tradeoffs as well but set up properly it results in a well-balanced, wide dispersion of sound and increased off-axis response. The challenge is that the horizontal centre is in most cases still off plane with the mains. Hence even with the same drivers as the mains there will be a slight change in tonality and timbre.
interesting discussion here.
I was thinking about Axioms VP150, I wonder if Axiom has ever tried a MMTTMM configuration? This is similar to the D'appolito layout with more woofers and tweeters.
Perhaps Allan will chime in? Would this not be a better config than TMMMT?
It is essentially 2 M22s on their sides with the tweeters facing inwards.
The VP150s were originally MTMTM. I don't know if that ever made it to production, but they discovered that the TMMMT sounded better.
At some point (whenever I upgrade my CRT TV to a wall mounted LCD) I plan on replacing my M80's with W22's. Based on discussions about using matching speakers for LCR, I was thinking about using another pair of W22's as centers, one above and one below. My thought was to have the tweeters on the horizontally mounted centers positioned on the outside. Is this flawed thinking or would that work? (Using a another pair of W22's as centers that is.)
I think I'd use a pair of W100s before using a pair of W22s in a horizontal array.
Joe Vassallo told me a story in July, 2005 about its origins. Apparently Joe was unhappy with the falloff in dispersion at the back of his HT with the the more conventional MTMTM configuration and invited Ian over to listen for himself. They then experimented with the present TMMMT in the vp150 to achieve a better off axis response in Joe's HT.
Thanks, Jakeman, for telling the story of the listening comparisons with Joe and the array of drivers in the center channel speakers.
Your quote below prompted an added thought:
"Hence even with the same drivers as the mains there will be a slight change in tonality and timbre."
What is interesting is that even using identical speakers--not just identical drivers-- for the front left, center, and right channels, if you use pink noise as the test signal, the three identical speakers may have audible differences in tonality and timbre because of interactions with room boundaries and reflections.
These are detectable with pink noise, but once you use vocalists or dialogue as signals, the differences become difficult to detect, unless of course there are gross location differences in the room, e.g. if the left speaker was in or very close to a corner, and the right speaker was not, with the center between them.
You can even experiment with this with left and right mains and pink noise in stereo only. Depending on variables in your room, they may not sound identical using pink noise. It's an illustration of just how influential the room is in affecting the timbral balance of each speaker.
Regards,
Regards,
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It's an illustration of just how influential the room is in affecting the timbral balance of each speaker.
Yeah. Rooms suck.
I thought the idea was to use the same speakers across the front if possible. Or am I missing the point of the discussion ?
I agree. I thought that the same speaker would give the best sound but wasn't practical due to the fact that the speaker would likely be into the monitor. Which led to the discussion of putting either 2 of the same speaker (say M80's) on either side of the monitor, or 2 matching speakers above and below the monitor. I think I am more confused now than I was last night at 2 AM. LOL. I guess I am just a newbie too because I have no idea what pink noise is. Sorry
Pink noise is the test signal receivers send to each channel during the calibration process. It contains an equal level of sound energy across the entire audible sound spectrum. Here's a sample:
http://www.luxevivant.com/samples/DigitalPinkNoiseSample.mp3
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Yeah. Rooms suck.
X2
Kyle, yes the ideal would be to have a center speaker identical to the mains, if possible. This is possble, for example, when there's enough room beneath a projection screen or a flat panel TV to use even a speaker as large as an M80 there. Where this isn't possible one alternative which in my experience works very well is to use a small vertical speaker(e.g. M2, etc.)which has similar response to the mains above the low bass, and place it immediately above or below the screen. Yet another option is to use dual center speakers either directly at the side of the screen or at the top and bottom edges.
The frequently adopted solution of course is to use an MTM configuration which as was said before was designed by Dr. D'Appolito for vertical use with a narrowed vertical dispersion, and instead for aesthetic reasons place it horizontally, contrary to the intent of the design. While this may be acceptable in general, the tests showing off-axis irregularities illustrate that it's far from optimal.
Other solutions using a horizontal shape include the TMMMT configuration of the VP150, which is said to be better in this respect. The best horizontal center I've heard used a W T/M W configuration which in essense is a small vertical speaker handling the mids and treble flanked by two woofers. At least two members here have centers from manufacturers who use that design. In the past I've wondered how an Axiom center using two of the 6 1/2" drivers flanking the regular tweeter above the 4" mid from the QS4 would do in a roughly 9" x 25" enclosure.
John, I think you have cleared that up for me. Thanks.
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The frequently adopted solution of course is to use an MTM configuration which as was said before was designed by Dr. D'Appolito for vertical use with a narrowed vertical dispersion, and instead for aesthetic reasons place it horizontally, contrary to the intent of the design. While this may be acceptable in general, the tests showing off-axis irregularities illustrate that it's far from optimal.
Other solutions using a horizontal shape include the TMMMT configuration of the VP150, which is said to be better in this respect. The best horizontal center I've heard used a W T/M W configuration which in essense is a small vertical speaker handling the mids and treble flanked by two woofers. At least two members here have centers from manufacturers who use that design. In the past I've wondered how an Axiom center using two of the 6 1/2" drivers flanking the regular tweeter above the 4" mid from the QS4 would do in a roughly 9" x 25" enclosure.
It certainly is true that a properly positioned identical speaker on the same plane would be an ideal configuration, however few people can set up the centre that way. Using a similar vertical speaker or monitor as suggested is another alternative but such a setup will also come with its own set of off vertical axis dispersion problems and timbre differences off plane. In a wide HT with rows of seats, such a setup is less than ideal. Placing dual identical monitors above and below the screen has promise but the effectiveness of this situation depends on where one sits, room acoustics and the speakers radiation patterns. I've heard lobing with friends using this configuration plenty of times.
I often suspect that the knock on D'Appolito horizontal centre speakers has more to do with poor design choices than the physics of the design. Choices must be made regarding the size of enclosure, distance between drivers, crossover point and size of drivers. A wrong choice in any of these results in poor off-axis dispersion or lobing. I have an old CW centre which sounds awful and does not follow the most basic principles. The drivers are too large and too close together to a large horn tweeter. And I can only guess how far off the crossover point must be. A badly designed speaker is just that, however it does not follow that all MTM designs suffer from lobing or poor off axis response as has been suggested. Nor was the use of horizontal made for simple aesthetic choices. Rather it was more to deal with the tradeoffs in off-axis radiation patterns.
If you take a look at the VP100 you can see an example of a good D'appolito design. A pair of 5.25" mids crossed at 2.7Khz to a single 1" tweeter aligned geometrically with the tweeter equidistant to the two mids. At the crossover point, one wavelength is 5" (13,503"per sec/2700hz) which is the ideal distance from the centre of the tweeter driver to the mid drivers. One often sees tweeters in MTM speakers placed off centre to stay within this one wavelength criteria. Such a configuration effectively minimizes or eliminates lobing in both vertical and horizontal placement.
Off axis dispersion is very important and again all speakers are not created equal. While a vertically aligned speaker will always have better dispersion off axis vertically, the fall off in response at the sides of the room are less than ideal. Where a properly designed horizontal centre with the requisite drivers will perform better off axis than the vertically oriented speaker, is if it is aimed directly at the listeners across rows of seats or across a single wide sofa . The Axiom and many other horizontal centre speakers follow these important design criteria, while my CW centre does not. The sweeping generalizations in the original Fleishmann article forced him to backtrack and write that rebuttal. One can always find a bad horizontal centre that lobes and has lousy off axis response, but that is not always the case with well designed speakers.
Excellent post Jakeman. I can see a couple of VP150's in my very near future.