As an aside, add "NHT" to the my "approved marques" list. I recently heard their "Verve" system in the kind of step contemplated in this thread - on-wall, around a big flat panel TV. This setup sounds better than anything else I've heard with those placement constraints, and mostly gets my endorsement. The coaxial mid/tweeter sounds surprisingly good for a non-coincident design, and I don't think turning the center horizontally hurt the sound nearly as much as it usually does. However, getting the mains all above the screen (coaxial drivers all at the same height) helped the coherence of the soundstage quite a bit.
Why qualified endorsement? Well, they do sound a little bright. Not as bad as the typical movie theater or a pair of Klipsch speakers, but not that BBC rounded-off sound either if that's what you're going for. Also, the subwoofer is not very good. However, it is tiny and probably pretty cheap, so maybe three of them placed per Geddes would work OK.
(As a further aside, I also bought some old
NHT Model 2.9 tower speakers off of Craigslist in what I presume is sycamore - I thought they were oak upon looking at them - this weekend. Nice speakers for a temporary dwelling, I think, and if I can't sell them quickly when I leave in August I'll give them to my gf's parents for storage. They're good enough to keep for a second home.)
Quote:
Originally Posted by
ChicagoRon 
Yes, Spezz, I agree about reviewers, but you can't listen to everything.. so it's worth finding someone who reviews w/ similar taste to you so you can choose from a field of 5-6 choices in your price range. And price matters in reviews, but not completely. I would not have known about the amazing value of PSB and Paradigm if not for Stereophile. I also LOVE their cd reviews.
CD reviews, fair enough. But the fact of the matter is, one can find out which speakers are good and which are poorly-engineered vanity projects without reading one line of the prose. Just looking at two measurements in the reviews can narrow down one's listening to only good speakers.
First, look to see that the on-axis frequency response is smooth. It might tilt one direction or another; that's a voicing preference. But make sure the designers took care to eliminate all of the major peaks. (Dips are far less annoying than peaks.)
Second, look at the smoothness off-axis frequency response. A good speaker's off-axis frequency response will track the on-axis response almost exactly, except for a rolloff on the very top. If the speaker has large "horns" in the response anywhere in the 1.5k-4.5k region, where there is more radiated energy off-axis than on axis, then it is a poor design and will not sound good except maybe if one gets really lucky with placement.
Will those two things get one all the way to finding the best speaker for a given application? No way. But because so many so-called high-end speakers are of such abjectly poor design, looking at these two simple measurements will narrow the search down considerably.
Quote:
Originally Posted by
A Y You can make the MTM array work well, but you have to engineer specifically for it. For example, NHT had several speakers where the tweeter was placed very closely to the mids, and the crossover point was very low, so that the interference patterns were greatly reduced.
I would argue that it's just not possible to do it well, because the pattern control is by simple physics exactly 100% wrong: wide open vertically (with a flare-up of upper-midrange energy off axis in most of them, because the directivity of the tweeter at the bottom of its passband is entirely uncontrolled) and restricted horizontally. That combination results in the speaker only sounding right over a very small listening window, between the off-axis midrange nulls and the excess midrange/treble energy bouncing off the floor/ceiling. (Floor not so much if it's carpeted.)
I'm generally a fan of NHT. I hope they come back soon with an interesting line. The Verves I mention above are good HT satelites. And actually, the temporary system I hastily assembled over craigslist for my summer sublet in my living room right now is anchored by Ken Kantor's old model 2.9, thanks to Craigslist. But until the T6 they never got center channels remotely right. Even their other 3-way centers, the ones with the dome mid and dome tweet are poor.
Quote:
Originally Posted by
A Y The other solution as I'm sure Sprezz will mention is a coaxial tweeter-midrange driver, which has the acoustic centers of tweeter and midrange in the same spot. Since there is no physical separation, you can can eliminate interference patterns ... if the crossover is designed correctly.
Well, sort of. Every coaxial driver I've heard (Tannoy, KEF, Thiel, the Seas OEM 7" one and riffs on it for Gradient and Vandersteen, B&C's "professional" line) has a narrow but deep and occasionally audible cancellation notch in the treble. The solution is to mount the center (and therefore
all three front speakers slightly off-axis vertically. Since a concentric/coincidentdriver's polar pattern is basically the same vertically and horizonally (excluding diffraction effects), that doesn't harm the overall sound. I think higher-than-the-listening position sounds better than lower-than-the-listening position.[/quote]
The other other solution is deceptively simple, though sometimes ungainly to look at: just pick out right and left speakers, and buy a third speaker of the same model for the center. Mount them all at the same height, same orientation, apply Audyssey or other room correction, and go.
IMO, the center should be exactly the same as the mains regardless.
Here's an example of a center that's better, with the midrange and tweeter arranged in a vertical line: 
The reason the second center's arrangement is better is because of the sound dispersion pattern at the crossover between the tweeter and the midrange. Because both tweeter and midrange are playing back the same signals at their crossover point, but are also separated in space by some distance, the sound dispersion pattern will have destructive and constructive interference. What that means is that, for the first (MTM) speaker, as you move left to right, the sound will vary in level. The person sitting on the left side of the sofa might not hear something as clearly as someone sitting in the center. This is terrible for movie watching with more than 1 person. The second center, with its vertically stacked mid and tweeter, will still exhibit this uneven dispersion pattern, except the pattern will be vertically oriented, so everyone across the seating area will get a more even sound distribution. Of course, if you stand up and down, you can hear the uneven dispersion pattern, but most people don't do that, so it's OK. You can make the MTM array work well, but you have to engineer specifically for it. For example, NHT had several speakers where the tweeter was placed very closely to the mids, and the crossover point was very low, so that the interference patterns were greatly reduced. The other solution as I'm sure Sprezz will mention is a coaxial tweeter-midrange driver, which has the acoustic centers of tweeter and midrange in the same spot. Since there is no physical separation, you can can eliminate interference patterns ... if the crossover is designed correctly. Another solution is super-steep crossovers made possible these days by DSP, but those speakers are very rare. The basic solution is to make the tweeter and midrange overlap in frequency as small as possible, or reduce the distance between them to less than a quarter of the wavelength of the crossover point. --Andre
