Is home theater the ideal environment for open baffle?

[pellothed1]

Bear with me here. I'm currently in a situation where I would like to timbre match all of my surround speakers, back/forward/side-to-side, you get the idea. The problem is cost (for me) as using matching bookshelf's all the way around is going to be expensive (for a good speaker).

I initially entertained the idea of rolling my own, but unfortunately the cost of the enclosure negates the use of expensive drivers. HOWEVER, in 2 channel audio, I've always liked the dipole sound. While I'm not entirely sure about how that translates to 7.1 HT, I'm entertaining the idea.

My question, aside from the almost philosophical (backed by science of course) question in my title, is this: assuming a crossover of 80Hz or 60Hz (THX standard I think) to a sub, would a narrow baffle, ceiling mounted OB provide the best (in my circumstance) way to achieve higher-fi in HT?

AND, exactly how narrow could the baffle be to achieve said crossover? Would something say, a 10" Silver Iris in a baffle of 12"x40" horizontally mounted to the ceiling (which would provide reinforcement) do what I want?

[italynstylion]

I'd say that for HT you'd want to stay away from OB unless we're talking about IB manifold subs that have their rear wave concealed into the attic or something.

The main reason would be that movie sound is VERY loud and dynamic and you'll run out of Xmax with most drivers relatively quick.

[preiter]

Ideally, you want an OB to be as far away from the wall (or ceiling) as possible. Otherwise the back wave is going to bounce off the wall and combine with the front wave too soon. That would be a limitation for home theater unless you have a whole lot of space to mount all of those baffles well away from the walls.

They have a do have a home theater forum on the Hawthorne site now. I'm sure they have some advice.

[chrisb]

Originally Posted by preiter

Ideally, you want an OB to be as far away from the wall (or ceiling) as possible. Otherwise the back wave is going to bounce off the wall and combine with the front wave too soon. That would be a limitation for home theater unless you have a whole lot of space to mount all of those baffles well away from the walls.

They have a do have a home theater forum on the Hawthorne site now. I'm sure they have some advice.

Bob in St Louis among others would certainly have some comments on the subject. Note that many of these guys take the "theater" part quite seriously - certainly in terms of the size of the rooms involved.

Once again, at the risk of sounding like a publisher's shill, highly recommended reading on the subject would be:

Amazon.com: Sound Reproduction: The Acoustics and Psychoacoustics of Loudspeakers and Rooms (9780240520094): Floyd Toole: Books

Don't need to buy from Amazon, but certainly worth adding to your collection.

The history of the evolution of multi-channel audio, particularly as it relates to movie watching is very informative. As the the number of discrete / surround and LF channels continue to increase, "satisfactory" implementation in non-dedicated rooms becomes exponentially problematic.

[human.bin]

not that i've tried... but the image you get form OB is a fake, it adds ambience by delayed reflections of the rear wave, so if you use it on a good multichannel recording, where the sourround channels are meant for ambience sounds it would probably mess things up...

also given that a sub or two is a must for HT building 4 or 5 spheres with some fullrange like the chr-70 won't be that expensive... also i think that you can use more refined drivers for the main and cheaper for the rear (like alpair 10 or 7 for the fronts, and chr for the rears) and still get good tonality match...

(also there is a cheap kenwood ht amplifier outthere that people say to be very wortwhile)

[pellothed1]

Originally Posted by italynstylion

I'd say that for HT you'd want to stay away from OB unless we're talking about IB manifold subs that have their rear wave concealed into the attic or something.

The main reason would be that movie sound is VERY loud and dynamic and you'll run out of Xmax with most drivers relatively quick.

Would Xmax still be a problem with a crossover point of 80Hz? I ask because many of the pro-audio drivers have relatively low Xmax's compared with home audio counterparts. Being that pro-audio is usually much louder, I guess I'm left a little confused. Not trying to be argumentative, just trying to get everything straight.

Audio is always a trade-off, I'm just trying to figure out what I can keep and what I can't.

[pellothed1]

human.bi, actually, I'm pretty much set as far as my electronics. I'm currently using a Pioneer SC-25 ICE Powered receiver that I got at a steal. That being said, I was quite surprised how much better my speakers sounded with the electronics upgrade (usually people preach that electronics don't have a large impact).

Again, my goal here isn't necessarily the least expensive option, but the most frugal, or the best bang for the buck, whether that be at $1K or $2K etc.

But, my requirement be that whatever I buy/build, it must be ceiling mounted/able so the typical tower type speaker isn't going to be ideal for me and it must look fairly decent.

[human.bin]

well 1-2k$ isn't my same class of cost problem

there is a thread going on about ikea spheres as frugal ideal enclousers, four or five alpair-7 sealed would make for a interesting fullrangers HT i think. just my 2cents

[italynstylion]

Originally Posted by pellothed1

Would Xmax still be a problem with a crossover point of 80Hz? I ask because many of the pro-audio drivers have relatively low Xmax's compared with home audio counterparts. Being that pro-audio is usually much louder, I guess I'm left a little confused. Not trying to be argumentative, just trying to get everything straight.

Audio is always a trade-off, I'm just trying to figure out what I can keep and what I can't.

You're exactly right, most pro audio drivers are typically very very efficient (like 95db+) and don't have a lot of Xmax. They are usually in enclosures though and not OB. I know the silver iris driver you're looking at is designed for OB use but the 2.7mm of xmax does worry me when listening at HT levels. With a xover of 80hz you might be able to get by though. You should model it IB and check the excursion vs frequency with a given power rating just to make sure.

PS: It's also worth mentioning my frame of reference for HT. On The Home Theater Shack forum, two 12's isn't nearly enough so that should help put things in perspective.

[pellothed1]

Originally Posted by italynstylion

You're exactly right, most pro audio drivers are typically very very efficient (like 95db+) and don't have a lot of Xmax. They are usually in enclosures though and not OB. I know the silver iris driver you're looking at is designed for OB use but the 2.7mm of xmax does worry me when listening at HT levels. With a xover of 80hz you might be able to get by though. You should model it IB and check the excursion vs frequency with a given power rating just to make sure.

Thanks for the response. I was wondering, what is the best way to go about this type of modeling and is it possible to do so while taking the room into consideration? Is there a PC based program that allows for this?

And, if I don't pursue an OB solution, is there a single driver design (non-horn) that can achieve theater levels? I really like (from what I've read about it) the Alpair 12, but with it's ~89db sensitivity and 50watt power handling, I'm unsure it would meet theater demands in a 20x30 room.