Meridian Unplugged - Powered by MrTechGuy.co.uk Forums Discussion Meridian - Systems Treble tilt to compensate for microperf screen

I have 3 DSP6000's behind my Stewart microperf screen. I have a substantial dip in the treble, perhaps 10db. I am assuming that this is due to the microperf screen, but Stewart's web site indicates that the treble dip should not be so large. I thought that I could compensate by adjusting the treble tilt for the speakers. I find that I have to adjust it a lot, setting it to +8 to get a flat response.

Has anybody else found a similar need to employ so much treble tilt to get flat response? Any other experiences behind microperf screens?

BTW, in the process of putting measurement signals through the speakers with the treble boosted, I blew the tweeters. Much thanks to Meridian for sending me the replacement tweeters quickly. I installed them myself and they are working fine.

I also once raised this issue as a pre-destined issue for the 861 room correction. Should the room correction board ever see the daylight, it should be switchable to "on/off" in any preset. It would even be better to have 3 curves as well as "on/off" for each preset. That way one could do one correction curve with the screen as 1) and a second curve as 2) for "without screen", if you want to listen to music and roll up the screen for it. "Off" would be cool for demonstrations without room correction. You can do two presets one with and one without the correction to show off the supiority of Meridian....

Maybe you are a 568 owner, then of course the options will be limited.

How far away is your tweeter from the screen ? Is your room rather "live" sounding (little furniture and /or wood floor/ or alot of free walls and hard surfaces/ big windows)?

How large is your screen ?

Cheers,
Andreas



[This message has been edited by Andreas (edited 02-28-2002).]

Thanks, Andreas. To answer your questions:

• 
  * I do have an 861. I would love to have room correction, I would be the first to buy it if they ever sell it.
  * The speakers are unavoidably very close to the screen. Perhaps only two inches or so.
  * The room is very dead to higher frequencies but some of that might be tunable. There are large windows and doors that have heavy drapes in front of them during normal usage. I should try the same measurements with the drapes pulled and see how much the treble changes.
  * The screen is about 10 feet diagonal.

The room correction card would do no good here as it only deals with 200 Hz and below.

I realize that the room correction card doesn't handle higher frequencies, but I also have some bass problems. I have some pretty substantial peaks at 40, 71, and 120 Hz. Using the bass cut on the DSP6000's is a too-crude way of compensating for these problems.

A few possibilities:

Tweeter too close to the screen. Not allowing the peforations to be seen as accoustically transparent. Pull back the speaker if possible (even if it is to test) to see if there is any difference.

Sound of the midrange and bass might escape to the room via some other way (around the screen, through the side wall) but the HF cannot.) Maybe the tweeter's off-axis radiation is being absorbed by the screen. You could try pulling speaker back (as noted above) or adjusting reflective/absorbive properties behind screen.

The stuart chart does not indicate how much loss there is on sound that hits the screen off-axis, which might be useful for situations like yours.

hehe,

Stacey got me. BTW: did you get the "glasses" yet ?

Seriously, I keep forgetting about the correction limitation, but wouldn't it be great to have a functionality up to the treble as well, maybe just for the center and this one special case ? Anyway.


This could be one reason, I constantly keep reading of distances that should be used of around one food or larger for the speaker and the perf-screen. I have only experimented with one feet high samples from Stewart in front of my center, but then walked away from it, as I prefer close viewing ratios of 1,5 the screen width and could see wholes with perf. screens and microperf was really a tad too expensive for my taste over here. Well, actually Stewart is in generall a tad too expensive for the moment. They are sure worth it and I like their products.

What I ment is that maybe, although your room is damped (as you perceive it!) that the speakers are sustained by the room. Holman once wrote in articles that he found in Cinemas the treble to be caught behind the screen too a significant extent, although we have to admit that the screen is covering the complete area in a cinema, not your 10 feet screen. But maybe the speaker is really significantly cut in your case by the close screen, as the 6Ks are pretty linear as I recall. Then maybe also the screen takes away the room support for the center as well. So overall the difference might be quite hearable in comparision.

In my case the center has different room modes in relation to the sweet spot and sound subjectively although the same type differently. So taking away a little treble can shift the perceived balance of that speaker. In my case the center is so annoying around 50Hz that I sometimes considered runnig it although large as small. But now I have new stands and everything is a little more balanced as the Center is a tad higher. I assume your 6Ks are positioned good enough so that the tweeter can fire away through the holes...

You really should play around. Also try out the screen forum in www.avsforum.com, which I have not visited in a very long time.

Good luck.

Andreas

[This message has been edited by Andreas (edited 02-28-2002).]

Yes, thank you. They arrived on Monday. Someone must have drank the beer as there was none in the boxes.

Stacey,

The room correction of 200 Hz and below is an artificial limitation. Meridian can easily add high frequency correction and they were thinking of adding at least one correction curve for the Stewart microperf screen. It would be an excellent feature and if the room correction card is ever released, it will probably be included. That feature alone would switch some very high end installations to Meridian equipment. Since these installations can easily add $100,000+ worth of equipment, it would be commercially a very smart move. Of course, it's all academic, because we will never see the room correction card.

Odyssey is quite right. Although we consider problems above say 500 Hz as no "room modes" anymore, but a problem of reflections and reverb, which is normally treated with acoustic material, it would be very fine if Meridian would include a "switchable" screen compensation feature for just the center channel (pure EQ could help).

However, I'm being realistic too. I have no experience with fixed pixel projectors, that make up already the majority of projectors, and their described "moiree" problems with microperf holes. If that holds true, only CRT projections, which is slowly phasing out, would be the customers of such a feature. Anybody with experience on fixed pixel projectors and microperf screens ? I can imagine that Dila with a fill rate of 93% or so could work well, which would increase the customer base.

[This message has been edited by Andreas (edited 03-01-2002).]

Andreas,

The interference pattern of digital projectors and the Stewart microperf screen is only for sceen sizes below a specific minimum for each type of projector. For example, a 1280x720 DLP like the Sharp 9000 only shows the problem if the screen is less than about 88" wide. In most cases, this minimum size is less than a typical installation would use for a specific projector.



[This message has been edited by odyssey (edited 03-01-2002).]

[This message has been edited by odyssey (edited 03-01-2002).]