Easy way to explain center?

[PeruvianSkies]

A buddy of mine recently starting messing around in the world of Home Theater and has been buying deals from eEbay, Craigslist, etc. He informed me that he was using a monitor speaker for his center channel, I think he said it was a Polk Monitor 40. I have been trying to explain to him that it's not ideal to use a monitor speaker for a center channel and that he should invest in a proper center channel speaker, but he just isn't "getting it".

Can anyone figure out an easy way to explain this to him without getting too technical?

Much appreciated friends.

[audio amateur]

What's wrong with a monitor? Idealy you want 3 matching speakers in front. In fact if I remember correctly the 40's are MTM configuration too just like your average center speaker.

[kexodusc]

Without getting overly technical, in a lot of ways a monitor speaker is better than a horizontally oriented MTM (midwoofer-tweeter-midwoofer) speaker for center channel dutires...yet the MTM's still seem to be popular. MTM's oriented that way have some challenges off axis.
In a perfect world, the center speaker should be identical to the monitors and placed at the same height. For practical reasons we can't always do that.

[Geoffcin]

For horizontal center channels MTM's are only going to show their "off" colors if your more than about 30 degrees off axis. For most of the HT's that use a couch or 3 chair seating it would be hard to tell if the speaker is upright or horizontal. I did notice a shift with the large Axiom 150, but it is nearly 30" across and I was sitting better than 60 degrees off axis.

I think in a perfect world the speakers, fronts, center and surrounds, should have matched timber down to 100Hz or so. If you can achieve that wheter it be with a monitor or MTM then you will have an excellent chance to balance the speakers for output correctly. Once that is done you'll have quality HT.

[kexodusc]

Yeah, much off 30 degrees and some lobing issues often occur. To be fair, that's about a sofa width or more in most rooms.

Part of the problem using a monitor speaker as a center channel is that the monitor is usually voiced to operate in an open space. If it's mounted on top of, or near a large display, that can reenforce some of the midrange and lower frequencies and throw off the timber a bit. MTM centers are usually voiced with this in mind (though not always).

I tend to like the MTM's in most budget systems because the extra driver keeps distortion down in the critical midrange at higher volumes...any off-axis issues are usually not as offensive to me. As you climb the price scale you'll see more 2.5, 3 and even 3.5 way speakers that are better optimized to be placed horizontally.

[Geoffcin]

Yeah, much off 30 degrees and some lobing issues often occur. To be fair, that's about a sofa width or more in most rooms.

Part of the problem using a monitor speaker as a center channel is that the monitor is usually voiced to operate in an open space. If it's mounted on top of, or near a large display, that can reenforce some of the midrange and lower frequencies and throw off the timber a bit. MTM centers are usually voiced with this in mind (though not always).

Exactly! Although the horizontal driver pattern is not optimal, the designer has taken that into account and voiced the speaker accordingly, and even more important, specifically for HT use.

The saving grace for all of these problems (sans dispersion) is that most modern receivers use a time delay/output adjusting/EQ protocal in their setup initialization. This has been by far the best thing to happen to HT since the invention of the sub-woofer. Mine uses a pretty sophisticated 9 band EQ with standing wave detection. The difference is pretty remarkable, and I use a non-traditional mix of planar and dynamic speakers which I don't even think would be possible without it!

[Hyfi]

Maybe it's just a Polk?

[poppachubby]

We had a HUGE thread on this not too long ago. All the H/T pros chimed in but yes, it was agreed that a "regular" speaker is preferrable to a conventional center speaker. The problem, as I recall, was that the speaker has to be level to the mains.

[Geoffcin]

We had a HUGE thread on this not too long ago. All the H/T pros chimed in but yes, it was agreed that a "regular" speaker is preferrable to a conventional center speaker. The problem, as I recall, was that the speaker has to be level to the mains.

How absurd. Exactly how did the "experts" decide to get around the fact that a large optical display sits in the center of every home theater?

It's like saying the optimal position for a car driver is exactly in the center of the cars moment of inertia. Yes I agree, but look at the logistics of doing it that way?!

I've had center speakers both above and below the screen, and if properly angled toward the seating position the effect of it's position is mostly undetectable.

[JoeE SP9]

Gee Geoff! One of my favorite cars is the McLaren F-1. It has three seats. The driver sits front and center. The two passenger seats are behind the drivers seat.

[Hyfi]

Gee Geoff! One of my favorite cars is the McLaren F-1. It has three seats. The driver sits front and center. The two passenger seats are behind the drivers seat.

I'll bet it turns both left and right with same ease as opposed to american cars that turn one way better than the other.

[audio amateur]

Geoffcin, you can achieve it if you have an acoustically transparent projection screen.
Pops was saying what the theory says, not that it is feasible.

[Geoffcin]

Geoffcin, you can achieve it if you have an acoustically transparent projection screen.
Pops was saying what the theory says, not that it is feasible.

I know, I came across a bit terse too. Sorry Poppa!!

[Geoffcin]

Gee Geoff! One of my favorite cars is the McLaren F-1. It has three seats. The driver sits front and center. The two passenger seats are behind the drivers seat.

I've seen one up close and personal, but alas I've never had the pleasure of driving one. You can give me that or a Saleen S7 and I'll be a happy puppy!

[poppachubby]

Ya don't get mad at me. I have a regular center channel that sits on top of my TV, much higher than my mains.

[Sir Terrence the Terrible]

How absurd. Exactly how did the "experts" decide to get around the fact that a large optical display sits in the center of every home theater?

You raise the television so that the bottom of the screen is aligned with your eyes. Then you place the center speaker under it so that the top of the speaker is just below the bottom of the set. I do this in two of my smaller theaters. This puts the center height more aligned with that of the L/R speakers(and your ears) which allows panning across the frontal sound stage with no image jump.




I've had center speakers both above and below the screen, and if properly angled toward the seating position the effect of it's position is mostly undetectable.

Agreed, The ear and brain does all the rest.

[Sir Terrence the Terrible]

Exactly! Although the horizontal driver pattern is not optimal, the designer has taken that into account and voiced the speaker accordingly, and even more important, specifically for HT use.

Not exactly. Remember, your L/R mains are vertically positioned, and the center speaker horizontally will not have the same radiation pattern as the L/R speakers. The L/R will have a wide horizontal dispersion pattern, but relatively narrow dispersion in the vertical plane. A horizontal center will have a wide vertical dispersion pattern, and a narrow horizontal one. The center will fully interact with the floor and ceiling(destructive reflections), and the L/R will engage the side walls more (constructive if not too early), and the ceiling less). A strong floor bounce will change the timbre and frequency response of the center speaker relative to the left and right ones that don't exhibit this characteristic. This is why all the front speakers should be placed identically, as it give all speakers essentially the same radiation characteristics.


The saving grace for all of these problems (sans dispersion) is that most modern receivers use a time delay/output adjusting/EQ protocal in their setup initialization. This has been by far the best thing to happen to HT since the invention of the sub-woofer. Mine uses a pretty sophisticated 9 band EQ with standing wave detection. The difference is pretty remarkable, and I use a non-traditional mix of planar and dynamic speakers which I don't even think would be possible without it!

Man, you are really working the processing of your setup with this combination. I prefer my setup processing to work a bit less, as to not introduce any errors that can crop up with digital processing. For me, it is better to start of close to ideal as possible, and then let the processing fill in any gaps I cannot account for.

[Sir Terrence the Terrible]

For horizontal center channels MTM's are only going to show their "off" colors if your more than about 30 degrees off axis. For most of the HT's that use a couch or 3 chair seating it would be hard to tell if the speaker is upright or horizontal. I did notice a shift with the large Axiom 150, but it is nearly 30" across and I was sitting better than 60 degrees off axis.

With some horizontal center speakers, the lobing happens far less than 30 degrees. It really depends on how wide the distance is between the two mid/bass drivers. The Axiom 150 is not designed like other center channels. It widely spaces the tweeters as opposed to the mid/woofer drivers which are tightly clustered together, so lobing is less an issue with this speaker than you would normally have with MTM set ups.


I think in a perfect world the speakers, fronts, center and surrounds, should have matched timber down to 100Hz or so. If you can achieve that wheter it be with a monitor or MTM then you will have an excellent chance to balance the speakers for output correctly. Once that is done you'll have quality HT.

Ideally, all of the speakers should be timbre matched down to 100hz, but they should also have the same radiation pattern as well. A horizontal center speaker does not meet that criteria unless the designer can closely cluster the two spaced mid/woofer driver together, and taper their response to reduce driver interaction. Or you could design a horizontal three way with the midrange and tweeter stacked vertically, and taper the woofers response to reduce driver interaction at higher frequencies, but allow them to work together at the lower frequencies. These center speakers are usually pretty expensive though.