Infinite Baffle. Best bet if possible?

[dhenryp]

You've got good drivers, so the benefit of push/pull is probably small, but if Linkwitz uses it for his dipole woofers then why not? The harmonic distortion at lower frequency may not very audible at low frequencies, but they do tend to make things rattle more in the room.

I agree that there is no reason not to try it as long as you have a well vented spider so you don't get turbulence noise from the back of the driver.

I'm not sure harmonic distortion causes more rattling but I can assure you that the main cause of rattling with my IB are things in the room moving around because of high levels of low frequencies.

When you get the other driver back, just mount the 2 difficult to get to drivers from the inside and the 2 that are easy to get to as seen in your attic pic from the outside. I'd think that push/pull with opposing drivers would be better than your trial setup anyway because it would be a true push/pull instead of a push/push, pull/pull.

I've got all four drivers installed now, all facing inward. I don't think my original configuration would produce different results than what you describe as true push-pull. In my original configuration, at a given instant in time you have two cones radiating from the front of drivers and two radiating from the back. If anything, my "push-push, pull-pull" would have a very slight advantage in cancellation of opposing forces. thi is because the opposing cones would be absolutely symetrical-and opposite in their cone motion. e.g.. on two opposing faces you have both cones moving toward the front of the driver while on the other two faces you would have the two cones moving toward the rear of the drivers. I think this improvement is inconsequential. I'm not sure what advantage the push-pull configuration would have, especially when you consider the wavelengths involved.

No matter, I've decided that neither the push-pull or push-push, pull-pull are worth the hassle of reconfiguring my IB. YRMV.

 

[johninCR]

Dhenry,

I've done some A/Bing to satisfy myself that distorted bass starts room rattles at much lower output than clean bass.

Regarding push/pull, it's my understanding that it helps offset distortion caused by non-linearities in the operation of a pair of drivers. If that is true, then the drivers would need to operate in the same plane.

You've got an impressive setup that I'm sure sounds great. With everything already in place, I wouldn't make any changes either.

 

[Hybrid fourdoor]

Wow! You guys are under the wrong impression that I want super cowabunga bass. I just want some nice "tufts" to go along with everything. A little bit of couch shaking, and the occasional window rattle is what I'm looking for. I'm sure that one 15" would probably be enough for me, but I'll do 4 just incase, and that way the drivers hardly get strained.

I mean your talking to a guy who lived with Magnepan bass for several years

Also what about adding particle board between the rafters, securing the sheetrock to the rafters? Would this help eleiminate rattles? Probably make it more sound proof.

I think I'm gonna talk to the wife and see what she thinks about putting folded fabric on the walls, to elminate ambiant light, and have a nice theater look. But who knows

The other problem is that this is the room you walk into when you come up stairs, and then all the other rooms branch off from there. So one side of me wants this room to be a nice cozy theater, but the other side wants a room thats a little bright and has some atmoshphere. Choices!!!

 

[ThomasW]

fourdoor

Also what about adding particle board between the rafters, securing the sheetrock to the rafters? Would this help eleiminate rattles? Probably make it more sound proof.

Particleboard has no structural integrity. It will add mass, lowering the Fs of where ever it's installed. If you use OSB, that will stiffen the ceiling and add mass as well.

A frequent choice for dedicated HT's is double up the drywall. There are some metal channels that separate the two layers of drywall so the vibration isn't transmitted from one layer to another. Also there are some lossey membranes that are placed between the studs and the drywall. These dampen the vibrations transferred to the studs from the drywall.

You might want to 'google' HT room construction techniques or grab a couple of books if it's not too late


JohninCR,

I've done some A/Bing to satisfy myself that distorted bass starts room rattles at much lower output than clean bass.

Nousaine uses 10% THD levels as the standard for all his subwoofer testing. His opinion is that for subwoofers, 10% or lower is inaudible. And if it's inaudible, it of course has no impact on output levels.

Everyone will be interested in seeing your test data.

Regarding push/pull, it's my understanding that it helps offset distortion caused by non-linearities in the operation of a pair of drivers. If that is true, then the drivers would need to operate in the same plane.

Given the wavelengths in the passband of a subwoofer there's certainly some latitude in woofer placement.

but high gain screens have their compromises too including narrow viewing angles.

This isn't true of retro-reflective high-gain screens

 

[johninCR]

A 1500 lumen or so projector will work fine or a 2K lumen with an economy mode setting on the lamp. Then if you can get away with a dark color on the ceiling at least withing 6-8 feet of the screen and the ability to completely shut out natural light through the windows, then bright colors in the rest of the room are fine. Try to avoid glossy paint though. Recessed lighting with a dimmer switch is a good addition, so you can still have quite a bit of light for stuff like superbowl parties, but still can go all the way dark for a great theater effect.

I wouldn't incur the extra expense of a second layer of wood on the ceiling. If you try to avoid a manifold alignment, afterward you would wish you hadn't. Maybe a double walls with interior airspace for the walls segregating this room from the rest of the upstairs would be money well spent. In that case you'd want to invest in good doors too for an effective sound barrier.

 

[johninCR]

This isn't true of retro-reflective high-gain screens

I'm not sure what promotional BS you've fallen prey to, but all high gain screens have serious compromises including a narrowed viewing angle. The only time I ever recommend a high gain screen for an HT setup is when high ambient light cannot be avoided and in those cases a dual screen setup is usually employed with a high gain screen for daytime use and a normal screen for night.

 

[ThomasW]

I'm not sure what promotional BS you've fallen prey to, but all high gain screens have serious compromises including a narrowed viewing angle.

I have a DaLite highpower, 2.8 gain (note that it IS a retro-reflective screen). And I have a megabuck tab-tensioned powered Steward with a 1.3 gain. The video sources include both a 8" gun CRT projector, and a LCD projector. So it's not too difficult to separate out the hype and hyperbole with regards to screens.

BTW when I want recommendations regarding video equipment, I have our engineer pick up the phone and call Bill Cushman.

Perhaps you've heard of him....

 

[Jennice]

The other problem is that this is the room you walk into when you come up stairs, and then all the other rooms branch off from there. So one side of me wants this room to be a nice cozy theater, but the other side wants a room thats a little bright and has some atmoshphere. Choices!!!

H4D,
You don't need a black or overwhelmingly dark room in order to have decent HT.

I have pretty much the same dilemma. It's a comfortable room, and my g/f won't let me change anything in order to get some projetion stuff in.

The result is a drop down screen, and the projector would go either on the table when in use, or on a bracked from the ceiling. Mind you, the timber you plan to cover and use for subwoofer placement is free an visible in my home, so I'll have a good place for the projector. (only thing is, my g/f doesn't like to have it there).
Regarding the colors, my walls are a soft orange tone, but as long as the sun-light is blocked out fairly good (direct light is the main problem), I had no problems getting a nice picture on a borrowed Sanyo PLV-Z2 projector.
This way, I'll have my comfy room, and yet the ability to watch movies in style

Jennice

 

[johninCR]

ThomasW,

I'm sure you have a setup that we all would envy and it would be great if everyone had your kind of resources. I was just stating a simple fact that ALL high gain projection screens have the compromise of decreased image brightness as the off axis viewing angle increases, whether they are Reflective or Retro-reflective. Retro-reflective just means that light is reflected back at the light source instead of at a mirrored angle. The primary benefit of retro-reflective is that with the projector in an elevated position, "hotspots" resulting from the use of a high gain screen will be up out of the viewing area.

I'm sure that Mr. Cushman would agree that considering the power of modern projectors the use of high gain screens in an HT setup should be limited to only very specific circumstances.

 

[ThomasW]

The primary benefit of retro-reflective is that with the projector in an elevated position, "hotspots" resulting from the use of a high gain screen will be up out of the viewing area.

Actually that's backwards. Retro-reflective screens work 'best' with low mounted PJ's. If the PJ is ceiling mounted the screen tends to illuminate the ceiling

I'm sure that Mr. Cushman would agree that considering the power of modern projectors the use of high gain screens in an HT setup should be limited to only very specific circumstances.

Bill's preference for 'best' picture quality is to avoid the so called 'light cannons', (aka high lumen output PJ's). So with Bill Cushman; we have a man with access to virtually ANY video gear on the planet, and he's using a DaLite high-power in his home system.

I trust that clarifies things...........

fourdoor,

We now return control of this tread to your original questions.

Regards
ThomasW

 

[johninCR]

ThomasW,

With a 400 lumen projector, of course a high gain screen is needed and you'd want the light reflected back to the viewing area. I'm sorry but that kind of setup just isn't typical anymore. Even one of the high end 1000 lumen projectors is going to be way too bright in a dark room with the screen setup you are saying is the holy graile.