Omni Polar speakers and Room Acoustics.

[BigGuy]

I'm starting to get into room tuning now, and i'm getting into the ETF program, trying to figure out what I need to do. One problem that I have is that I use Mirage Om-9 and OM-C2 omnipolar speakers, which use the room walls to reflect the sound to create their sound. I enjoy the sound of the speakers a lot, but how would room dampening effect the speakers? I don't really know where to begin on room acoustics and Omni Polar speakers. I don't have any major complaints about the current sound of the room, but I love this hobby and enjoy tweeking. I know room Acoustics make up 40% of the sound of the system. My theater is in the basement that has cinder block walls with sheet rock on studs with a drop ceiling(normal tiles), wall to wall carpeting with another large rug on top of that. two couches and a large bookcase behind the last couch. 10ft wide 7ft tall 28ft long.(book case is about 15' from the front wall) The room isn't too alive and it isn't too dead, but i'm sure there's room for improvement... any thoughts?

Brian

 

[Ethan Winer]

Brian,

> I know room Acoustics make up 40% of the sound of the system. <

Make that 90 percent and you'll be a lot closer to the truth.

> My theater is in the basement that has cinder block walls ... The room isn't too alive and it isn't too dead, but i'm sure there's room for improvement... >

A room like that needs as much bass trapping as you can manage. When you refer to "alive" and "dead" that's for your perception of mid and high frequencies. But bass frequencies are always a big problem, and hand claps won't reveal that.

I'm not familiar with those speakers, so my best advice is to ask the manufacturer directly for advice. With "normal" loudspeakers you'd treat the front portion of the room, and also the first reflection points on the side walls and ceiling. But Mirage may have other suggestions. If you do ask them, please post here what they tell you.

--Ethan

 

[WmAx]

BigGuy, omnipolar speakers(with true full range omni response) and other speakers with extremely wide full range dispersion require different acoustical treatment as compared to speakers with common dispersion patterns if you want to use the unique ambiance/spatial effects that such provide. Normally (with most speakers) you would to some degree reduce or diffuse the 1st reflections of the back wall and side walls, and sometimes the ceiling, as well as a myriad of other acoustical treatments. An omnipolar, though, has a specific effect that lends to a more realistic sound as a result of tricking[make no mistake, it is a trick] the human perception system with specific delays at different locations(the reflected source points).Also, a very wide/linear dispersion speaker will sound better in a normally reverberant environment as compared to a speaker without linear and wide dispersion. However, an omnipolar[and other speakers with very wide and linear full range dispersion] can be made to sound just like a more standard speaker with treatments[if you prefer this sound], because if you remove the reverberant field effects, you pretty much have removed the difference from omni vs. non-omni. . I know that Mirage says that room placement and set-up is less dependant with omnipolars, and this is true, but primarily only for tonal response and imaging. You can not simply place these speakers anywhere and get the best sound quality. If you place this kind of speaker too close to a wall, you will create a broadband [this is worse, since the speaker also disperses treble in an omnipolar pattern; upper treble is primarily responsible for distance/space perception] reflection that will confuse the brain, and result in what may best be described subjectively as a 'smear/confuse' effect. You should have such speakers set up so that the walls in the rear are about 4'-6' from the back of the speaker, and the side walls are about 2-'3'. The back and side wall distances should be about the same for both channels. Now, do not treat the the 1st reflection point at the side wall or rear wall, if you can manage the distances specified above. But if you have to place the speakers substantially closer, you will need to treat these reflection points like you would with a standard speaker. You will benefit from acoustical treatment elsewhere in the room just as in any other application[but perhaps a little less material for mid/hf absorbtion since you will want to retain more of the live sound field in the room for this type of speaker], and you can use Ethan's acoustic material set up guide as usual in that respect. One additional thing that I prefer with omni type speakers, is to use a large absorber on the center wall(but not at the 1st reflection points relative to your ears on the front wall) that will reduce spurious cross reflections from the omnipolar tweeters.

-Chris

 

[Savant]

Brian,

One problem that I have is that I use Mirage Om-9 and OM-C2 omnipolar speakers, which use the room walls to reflect the sound to create their sound. I enjoy the sound of the speakers a lot, but how would room dampening effect the speakers? I don't really know where to begin on room acoustics and Omni Polar speakers. I don't have any major complaints about the current sound of the room, but I love this hobby and enjoy tweeking.

I underlined some of the above because this first part seemed a little contradictory to me. Is the "problem" experienced, or implied? Have you simply assumed there's a problem because there is so much on the 'net discussing the horrors of reflective sound in residential listening spaces? Further, the inferred or implied "problem" would seem to contradict your assertion that you have no "major complaints" about the sound of the room.

Since it doesn't appear that anything is broke, I would hesitate laying out a whole bunch of suggestions for fixing anything. If you are enjoying the sound of the system (which includes the room and rightfully so), then I would suggest to leave it as is.

If, on the other hand, you are experiencing situations where you feel the sound is suffering as a result of the room, then some possible treatments could justifiably be discussed. That does not appear to be the case, though. Additionally, if the Mirage products are designed to work with the reflective environment typical to many residential spaces, then I'd say the setup you have is doing those loudspeakers justice.

I know room Acoustics make up 40% of the sound of the system. My theater is in the basement that has cinder block walls with sheet rock on studs with a drop ceiling(normal tiles), wall to wall carpeting with another large rug on top of that. two couches and a large bookcase behind the last couch. 10ft wide 7ft tall 28ft long.(book case is about 15' from the front wall) The room isn't too alive and it isn't too dead, but i'm sure there's room for improvement... any thoughts?

Again, if you feel the sound is suffering, then considering treatments would be wise. If you cannot hear any major problems, though, my advice would be to enjoy your system!

 

[BigGuy]

Thank you all for your replys. I would agree that I am not unhappy with the setup, and I shouldn't fix what isn't broken. Honesty I love to learn as much as I can about audio\video systems, and this is the one department where I need more experience. Your replies have given me things to think about. I just ran a room response test using ETF. freq response is +-10 with dips up and down over 6 octaves or so. Low end has a 15db drop out at 75hz but doesn't bottom out. Reverb time is around 8ms for almost all the FQ's. Still trying to figure out how to read the phase results. How this all translates to how good the acoustics are in my room? Im not sure, lol. But i'm not planning on dropping any money until I figure it all out.
I would say the bass would be the only area would my system could use some of improvement. I've also been fooling around with my subs position, there are so many factors it's hard to nail down where to start! Honesty my speakers are my weakest link by far but i'm not planning on upgrading any time soon. Most likely i'll leave it as is, but would like to learn as much as I can about the topic. Thank you all for the great info.

Brian

 

[Savant]

Reverb time is around 8ms for almost all the FQ's.

An RT of 0.008 seconds is - dare I say? - impossibly low. You might want to check the settings on that particular analysis... Even then, it is arguable whether RT is even a useful metric for small rooms. I say it is not. Regardless, the second graph down on this page is what your RT graph should resemble, in a very rough, general sense.

Still trying to figure out how to read the phase results.

Only useful at low frequencies...and even then, not as important as the other metrics. Relevant reading material.

 

[BigGuy]

I'll take a look at my results again... The graph that the software came up with looked like the RT was way to high, the scale on the bottom was 1.5ns... I think it was nanoseconds, not milliseconds... I don't even know what the difference is between the two. I would say that according to ETF my RT was too high, so maybe i misinterpreted the results. My Frequence response was actually +/- 5db, i said 10 because that was the difference between the low point and the high point, which i understand is actually +/- 5db. I'll look over the results again, too bad i can't save them in the unregistered version!. What should the +/- db Frequence response be? Is 5 acceptable? Thanks for your help,
Brian

 

[Savant]

I'll take a look at my results again... The graph that the software came up with looked like the RT was way to high, the scale on the bottom was 1.5ns... I think it was nanoseconds, not milliseconds... I don't even know what the difference is between the two. I would say that according to ETF my RT was too high, so maybe i misinterpreted the results. My Frequence response was actually +/- 5db, i said 10 because that was the difference between the low point and the high point, which i understand is actually +/- 5db. I'll look over the results again, too bad i can't save them in the unregistered version!. What should the +/- db Frequence response be? Is 5 acceptable? Thanks for your help,
Brian

1 millisecond = 1 ms = 1/1000th of a second = 0.001 s
1 nanosecond = 1 ns = 1/1,000,000,000th of a second = 0.000000001 s

If your RT is in the range of nanoseconds, I wish to visit your room soon!!! For reference, the most significant digit we usually get to when talking about RT is 1/10ths of a second. I.e., values to the nearest 0.1 s.

As for the ±5 dB thing, that's up to you. In the most general sense, ±5 dB in the low range is not too shabby. Is this before or after you've established some good locations for the subs?

 

[BigGuy]

The +/-5 db was from 200hz to 20khz, below 200hz, there was a dip of -15db, but that was the lowest and +5db peak. I know my room isn't as good as the results I interpreted, so I have to be reading them wrong, I'll run the test again and fool around with the graphs. ETF is a great program but it takes some learning to understand the results. I spoke to Mirage today, They said that with omni speakers you want to stay away from acoustic treatment on the first reflection point, and just leave the room as is(as someone said before). If anything, use some bass traps in the room corners to tame low frequency modes. I've moved my sub from the front left corner to the left wall, 7ft behind me, and about 5ft from the back left corner, facing the front wall (front firing sub). But this is the only other position I've tried due to limited options (small room). I moved it to begin with because to get the right SPL I had my pre\pro at -10db (lowest it would go) and the gain on the sub almost all the way down (9 O'clock position, 7 o'clock is off) That lowered the SPL a bit and now my pre/pro is at -8.5db, sub still at 9.

Brian

 

[electricdick]

Mirage Omni Polar Speakers

Hey BigGuy.

I have Mirage speakers as well: OM-7, OM-C3, OM-R2 but the 150 Watt/8 inch sub and they are no problem to me. I am extremely pleased with the performance of these speakers but I admit that I covet your 12 inch sub.

If I recall correctly the technical page of the Mirage web site states that the human ear cannot distinguish rear sound reflections of 5 feet or less (time-wise I do not recall). I have placed mine approximately 3 feet from the rear wall.

There is an old thread on this forum that stated one benefit of the omni polar speaker is the ability to widen the sound stage. Coincidently I had taken advantage of this benefit prior to reading that thread and have placed the speakers very far a part. I managed to have surrounded a huge couch and a love seat. One day I’ll post a picture or two.

I do not use meters or tweak my system very much (too many other hobbies on the go) but I took plenty of time to balance the sound it to my ear. I use the system as much as possible and try not to sweat the details. A guy can drive himself crazy on the details.

D ick