Mirage Omni Series! (1 Viewer)

[Kevin C Brown]

Tony- Let's see if you understand this:

Some actual calculations to prove you wrong, once and for all.

Let's be conservative and say there is 15" between the acoustic mid-points of the two woofers.

The wavelength at 80 Hz, a common crossover freq to a sub is 13.75 ft. 1.25/13.75 * 360 deg = 33 deg phase difference. You and your infinite intellect and your 30 years of Stereophile reading might say, gee, 33 out of 360 ain't bad, I'll take it. Less than 10%. But you'd be wrong (again), because 180 deg out is actually the worst. So even at 80 Hz you are already 1/6 out of phase. And I can say "1/6" is simply dividing 33/180, but the fact of the matter is, the "relative" effect is actually much more than "1/6" because the slope of a sine wave going through 0 deg is actually much greater than say the slope at 90 deg.

OK, so then let's move up one octave to 160 Hz. Still a very reasonable freq for the woofs in a center to reproduce before they crossover to a midrange. (Following so far?) The wavelength here is 6.875 ft. 1.25 ft/6.875 ft * 360 deg = 65 deg. Remember, that's vs 180 deg, not 360. For example, if you're 210 deg out, as far as the bass quality goes, doesn't sound as bad as 180 deg, just that your time alignment is off. 65 deg is already more than 1/3 of the way to 180 deg. I can hear that. Hopefully you can too.

Let's try one more octave up. 320 Hz, the wavelength is 3.44 ft, 1.25/3.44*360= 131 deg. But that's 131 vs 180. Bad. Very bad. Even though we are heading up the other part of the sine wave curve towards zero again. Above 320, I bet the woofs hand off to the midrange.

Now, all of my calculations above were for 90 deg horiz from the center channel. Worst case.

Let's do 22.5 deg for kicks. Very conservative number. That is well within the limit for a few people sitting across a sofa in a home theater.

22.5/90 = ~0.25 times all of the above numbers. So ... 80 Hz => 8 deg out of 180. Not bad. Probably pretty difficult to hear. 160 Hz => 16 deg out of 180 deg. This pushing it, again, because of the steep slope of a sine wave through zero. I got a buddy in LA who does mastering for DVD soundtracks (Jurassic Park, recent Star Wars flics ring a bell? He says he can hear a 10 deg difference. I believe it. He does this for a living.) 320 Hz => 33 deg out of 180 Hz. Even I can hear that. And I'm sure you can fill in the numbers in between.

Even if you can't hear the distinct effects of that out of phase material, it *will* exhibit itself as smearing, less detail, less sharpness, and a mushiness in those frequencies.

The CC design *is* a better design than most. But completely immune from interference effects between the two woofers? Nope.

 

[Tony Genovese]

Even if you can't hear the distinct effects of that out of phase material, it *will* exhibit itself as smearing, less detail, less sharpness, and a mushiness in those frequencies.

Audible in a double blind test?

Prove it.

 

[Kevin C Brown]

sigh...

 

[Tony Genovese]

Not fun when you get responses out of left field.

You seem to be concerned with smearing. (Or was that just a straw man argument)? If so, why are you buying speakers that bounce the sound off the walls? Talk about smearing.

Why not look at a complete Vandersteen setup, which would appear to follow the design precepts that you so espouse?

 

[Kevin C Brown]

You are amazing. First, you completely deny that any phase issues exist at all with dual woofer center channels with a midrange driver. Then, after I PROVE that they do exist, you stretch your argument to now include listening tests. Yeah, OK.

*You* quoted this, not me:

This arrangement allows both woofers to operate in the bass for maximum power handling, while reducing the speaker's lobing in the midrange.

Reducing, but not eliminating. It exists. It's real. No amount of pretending it's not there, or ignoring it can change that.

Dude, click on the following link. I already *have* a complete Vandersteen setup.

http://www.hometheaterforum.com/bbs/...ent/28962.html

Vandersteen's design for their center channel, using coaxial drivers, is the only way I am familiar with to completely eliminate lobing, other than using a vertically oriented bookshelf speaker.

BTW, I am getting a Mirage setup to compare (NOT replace) the Vandersteen setup. I will probably use the Vandy's for 2 ch audio, and the Mirages for HT.

And before you go spouting off on yet another topic that you know nothing about (bouncing the sound off the walls and "smearing"), go read up on the Haas effect.

And I also recommend you go look up the Dec 2001 review of the OM-5's in WSR. A lot of interesting comments from the designer, Ian Paisley, on the differences between bipolar, omnipolar, and direct radiating speakers.

*Your* turn to get educated. I'm tired of arguing with you. Have a nice day...

 

[Tony Genovese]

If you are a first order zealot, then no amount of discussion regarding the audibility (or lack thereof) of phase and time alignment will satisfy. I have owned over the years a number of fine examples of such speakers, including Vandersteen 2Ci and Duntech PCL3 and PCL5. Ultimately, I chose to go with speakers that had a wider sweet spot, as I find these work better in my setup. I sometimes watch movies with other people, and someone off center from these speakers isn't hearing the speakers as the designer intended anyway. (Whole other kettle of fish). I will not deny that the image cast by the first order speakers can be holographic.

Fact is though, that if this were the only way to audio nirvana, speakers with first order crossovers would dominate the market, and they are clearly a very minor player. We've mentioned the 3 designers on this thread who prefer them, one of whom is out of business, as you pointed out. Here in Massachusetts, you'd have to travel 100 miles if you live near Boston just to see Vandersteen.

Finally, my points here were intended (although I guess I wasn't as clear as I should have been) to be about the audibility of the lobing and your original quote that seems to suggest any speaker used horizontally with dual woofers (whether it uses a dedicated mid-range) is a poor design. If you're a first order zealot, any speaker that uses crossovers with higher slopes I guess would also be "poor" designs.

You said:

Like most centers, the CC is a poor design with the woofer-tweeter-woofer arrangement which creates comb filtering problems off (horizontal) axis as the two woofers deconstructively interfere.

Indeed most centers lack the midrange that the CC has, which as has been pointed out, reduces the lobing. Does it reduce it to below audibility? I guess only double blind listening tests would show either way, or at least listening tests like those conducted at the NRC in Canada.

I do think it odd that if this were such a poor design, that designers such as Michael Kelly, Kevin Voecks, Floyd Toole, and Jim Thiel to name a few, would continue to utilize this poor design in their multi thousand dollar, flagship centers. But, then I guess you're a better man than they are, Gunga Din.

If I knew several posts ago what I know now, particularly regarding where you're coming from, we could have spared ourselves all this typing .

You hava nice day...

 

[David K.]

Im not expert but I have the omni CC currrently as my center channel speaker and I hate it. I can't understand what the heck is playing out of the center channel when 2 people start speaking and sometimes when just one person is speaker. The speaker itself sounds incoherent at times.

I am looking for a CC speaker upgrade or an entire speaker set upgrade.

I currently use omni 60' 50's and cc's

the 50's limited frequency response also bothers me, the 60's are great though, but they need a lot of space to sing.