Axiom Home Page Forums General Discussion Advice from Axiom Owners VP 100 or VP 150 paired with M3ti?

hello all, my question is witch center will match the best with the M3ti bookshelf speakers the room size is 14'L x 14W'x 7'H I have a built in entertainment center that does not allow tower speakers or the M22ti. I will most likely go with 4 QS4 surround speakers with a SVS PB1-ISD sub. For the receiver I will be going with ether the Denon 2803 or the HK AVR 525. thanks for the help.

Logan, I have a different suggestion. Since you're getting a very good sub, M2s should be excellent as mains where you're facing space limitations. Then, the best match as center to M2s is a third M2, positioned vertically. If for some reason it has to be a horizontal center, the general opinion is that the VP150 is significantly better(the possibility of placing 2 M2s horizontally, woofer to woofer in a TMMT configuration shouldn't be overlooked).

John, I am curious about the option of using two M2s (placed horizontally TMMT) in a center channel configuration. My receiver has only one speaker input for a center channel -- would I simply connect both speakers to the same input and program the receiver as if there were only one speaker? Is there anything else which must be done in this sort of set-up? Thanks!

Correct me if I'm wrong, everyone, but I believe the way to hook up the two speakers correctly to one output is to do them in series. You'll need 3 separate speaker wires:

• One to go between the red terminal on your receiver and the red terminal on the first M2.
• One to go between the black terminal on first M2 and the red terminal on the second M2.
• One to go between the black terminal on the second M2 and the black terminal on the receiver.
  

Hi pmbuko,

Yikes. The proper way to hook up a pair of speakers to the same output is in parallel, not in series. A parallel hookup will, of course, present a lower impedance (two 8-ohm speakers in parallel will present a 4-ohm load to the amp), but you'll preserve the correct tonal balance of each speaker.

When you hook up speakers in series, the impedance curve of one speaker interacts with that of the other speaker, and the speakers may sound quite different, depending on frequency and the shape of the curves themselves. Series hookup should be strictly a last resort when your amp can't drive the lower impedance of a parallel connection.

Regards,

That would take the impedence up to 16, which is probably no good on modern amps (anyone?). I would think that parallel would be better, which would take the impendence to 4 ohms. No biggie, there!

As an aside, I was thinking about a pair of M2s for a center, but having them both vertical and very close to the TV. I figure the TV has speakers at the corners, and the sound seems fine, so this could work. However, I could be insane.

Alan - so if I have this right, I run a connection from each speaker to the single center channel input on the receiver. This is considered parallel? Something else you mentioned about impedance gives me pause, however. The two speakers I am considering using for the center channel are rated at 6-ohms. My receiver only has an 8 or 4-ohm setting, and I am running M22ti as my mains. What are my options?

Yes, running a pair (+ and -) for each speaker to the receiver is correct (try drawing a picture, it makes more sense, then). I'd be a little concerned about the 6 ohm thing (it would take it down to 3 ohms), but I'll let the experts speak to that.

Does your reciever actually have switches between 8 and 4 ohms?

Oops! I knew I was quite possibly wrong, which is why I invited correction in the first sentence. Not more wiring advice from me. :P

Yes bigrocks, as Alan indicated, since no two speakers(even of the same model)are precisely identical, differences in impedance curves can cause interference when they're connnected in series(although 2 speakers of the same model should have only a small problem)and it's generally better to connect them in parallel if the resulting impedance is acceptable. There's various ways of doing this so that the positive amp terminal is connected to the positive terminal of each speaker and likewise for the amp and speaker negative terminals.

Ken, there shouldn't be any significant problem with setting up center speakers right up against the side of the TV(so that the center image wouldn't shift farther outside than that)although some might worry about the exaggerated problem comb-filtering is supposed to cause when two widely separated speakers play the same material.

Comb filtering? I thought that was a video thing...

No Ken, it's an audio thing in this context, but an over-exaggerated thing. Unless someone's listening in an anechoic chamber the reflections in the average listening room cause comb-filtering all over the place when the reflections of the same sound reach the listener at different times, so I don't worry about a little more caused by multiple speakers.

Unfortunately, with my TV, they won't be widely separated. 27" CRT.

No, it wouldn't be "unfortunately" Ken, because those who worry about comb-filtering would want the speakers to be as close to each other as possible, and your separation would be considered "wide". Again, I don't think there's any significant problem with that sort of twin speaker setup.

For those of you who are curious, "comb-filtering" is a fancy way of describing "phase-cancelations."

Suppose you are in an anechoic chamber, listening to two small single-driver speakers driven by the same sine-wave signals. If one speaker is placed further from you than the other by exactly half the wavelength of the sine-wave sound, then the sounds from the two speakers reach you at a 180-degree phase shift. That will result in a severe cancelation of sound.

For example, the wavelength of 250Hz sound is about 4 feet. So, if one speaker is 2-feet more distant from you than the other, the 250Hz sound will cancel out, creating a big dip in the frequency response at 250Hz.

Now, consider the 750Hz sound, with wavelength of 1.3 feet -- for that frequency, the 2-feet distance between the two speaker represents 1.5x wavelength and will induce a 540-degree phaseshift (360+180), again resulting in a big dip in frequency response at 750Hz.

Similarly, the next dip will happen at 1250Hz, 1750Hz, etc... In the end, the entire frequency response will look like a comb.

Damn you're good!!

Hi Sushi,

All true, and you don't have to be in an anechoic chamber to experiment with comb filtering and its effects. Just sit exactly in the sweet spot between your main speakers, and play a sustained pink-noise test signal in stereo (no center, no surrounds).

Now, while you're staring at the midpoint between your two front speakers, move your head to one side a few inches--don't turn it to the side--and then back and a few inches to the other side. You'll hear the mid and high-frequency response change noticeably and fluctuate as you move your head and body a few inches either way.

Regards,

Can you draw a picture of that?

Alan,

Damn you're good, of course!

One important point in this experiment: You have to use a MONO pink noise, so that the two speakers receive an identical signal. Some test CDs/DVDs include "de-correlated" or "de-synchronized" pink noise (in which the actual instantaneous wave forms sent to each channel are always different from each other -- it produces a very diffuse feel without any imaging whatsoever). The experiment won't work with it.

Incidentally, I had actually done this exact experiment with my VP150 alone, to examine the possible comb-filtering among the drivers, especially between the two outside tweeters. And boy, Ian is right!!! At least in my room, the noise timbre is VERY uniform until I go almost 30-degrees off axis, where the highs start to roll off as expected.

I LOVE this very "unusual" center channel -- it defies conventional wisdom, yet it performs!!!

You might want to try Alan's test when there is no one around.
Not unless your family and/or roomates already know you are a bit nutsy about the audio thing lest you look like Stevie Wonder with your eyes closed, head swaying back and forth listening to pink noise.

Chess,

This is of couse a comb-filter for the video application, but the frequency response is essentially identical for audio and other applications.

Actually sushi i was hoping for something even more simple.
Perhaps something in crayon with stick figures.
(just kidding)

Ian's comments here about the real world significance of comb-filtering and his thoughts on down-axis lobing effects may be of interest.