[zobsky]

I've decided to build a line array using 12 foster woofers per side (  http://www.madisound.com/cgi-bin/index.cgi?cart_id=6931163.5636&pid=1902 ) and a tweeter line

Open Baffle is one alternative I'm considering.

Here's my situation:
This is going to be for a HT/music application. My room is about 11 ft wide x 14 ft long with an 8 ft projector screen in the center of the room. Therefore the baffles can't be more than 1.5 ft wide and would have to be along the side walls / corner loaded.

1. I'm concerned about how low I can get with such an arrangement. Ideally I'd like to be able to  do 70Hz which allows me to cross to a single subwoofer . Would this be possible with an OB LA within my constraints?

2. I thought about building a bass module + plate amp for each LA and tapping a low frequency signal from the speaker level input to the LA. There would be 2 issues with this.
a. some plate amps don't have high pass filters, ... which means that I could still be running bass to the OBs. I'm not sure how much of an issue this would be, .. as I expect the array to be close to 100dB efficient.
b. for those that do have a high pass (typically around 150 - 200Hz), I imagine that it can't be of high quality to keep cost low(I fully expect to find cheapo electrolytic caps in the crossover if I looked)
c.  fully active multi-amping is not an option for this project .
d. Going totally passive, the cost of caps & inductors at say , 2nd order, 200Hz seems kind of high. Maybe I'm wrong, here.

Help set me on the right path.

Thanks

[Rick Craig]

I've decided to build a line array using 12 foster woofers per side (  http://www.madisound.com/cgi-bin/index.cgi?cart_id=6931163.5636&pid=1902 ) and a tweeter line

Open Baffle is one alternative I'm considering.

Here's my situation:
This is going to be for a HT/music application. My room is about 11 ft wide x 14 ft long with an 8 ft projector screen in the center of the room. Therefore the baffles can't be more than 1.5 ft wide and would have to be along the side walls / corner loaded.

1. I'm concerned about how low I can get with such an arrangement. Ideally I'd like to be able to  do 70Hz which allows me to cross to a single subwoofer . Would this be possible with an OB LA within my constraints?

2. I thought about building a bass module + plate amp for each LA and tapping a low frequency signal from the speaker level input to the LA. There would be 2 issues with this.
a. some plate amps don't have high pass filters, ... which means that I could still be running bass to the OBs. I'm not sure how much of an issue this would be, .. as I expect the array to be close to 100dB efficient.
b. for those that do have a high pass (typically around 150 - 200Hz), I imagine that it can't be of high quality to keep cost low(I fully expect to find cheapo electrolytic caps in the crossover if I looked)
c.  fully active multi-amping is not an option for this project .
d. Going totally passive, the cost of caps & inductors at say , 2nd order, 200Hz seems kind of high. Maybe I'm wrong, here.

Help set me on the right path.

Thanks

Even though the Fostex driver has a high Q the resonant frequency is too high for an open baffle to extend very low. Without active equalization you won't be able to cross them over to a subwoofer.

[robert1325]

put in some Hawthorne SI's!!! that would give you a crazy line array!!!   (15inch )

[zobsky]

put in some Hawthorne SI's!!! that would give you a crazy line array!!!   (15inch )

Comb filtering would be an issue with 15"

Thanks, though.

[zobsky]

[
Even though the Fostex driver has a high Q the resonant frequency is too high for an open baffle to extend very low. Without active equalization you won't be able to cross them over to a subwoofer.

Thanks Rick, ..

what would my options be if I wanted to cross over higher (say 200Hz) to stereo bass modules? My first post listed out my questions about this alternative.

[Rick Craig]

[
Even though the Fostex driver has a high Q the resonant frequency is too high for an open baffle to extend very low. Without active equalization you won't be able to cross them over to a subwoofer.

Thanks Rick, ..

what would my options be if I wanted to cross over higher (say 200Hz) to stereo bass modules? My first post listed out my questions about this alternative.

It's hard to say if 200hz is possible without testing the driver on a baffle. You might try buying one woofer and see how it works.

[zobsky]

I'm pretty sure it will (I bought a couple a month ago to evaluate them and they seemed to go lower than that, just lying on the floor).

This should be easy to verify since my HT source on that system is a PC, .. WinISD's tone generator should tell me pretty easily. Just need to buy a sheet of posterboard to hack up as a temporary baffle. Hello walmart, here I come.

[tubamark]

Zobsky:

Are the bass modules you're considering dipoles, or monopoles?  I wasn't clear from the post(s).

The reason I ask is that given your room dimensions, Dipole bass will disappear below 40 Hz.
That's fine for most music, but a serious shortfall for home theatre . . . especially when compared the size/efficiency of your LA's.

If you can get your mains down to 150 Hz (should be easy), any plate amp will let you integrate the stereo bass units fine.  Yes, avoid the high-pass built-into the plate amps.
A first order passive hybrid (electrolytic combined w/good poly) high-pass XO is inexpensive, and can still integrate well** and keep the deep stuff out of the LA.  Given the number of drivers and efficiency you are contemplating, I can't imagine that a higher-order highpass is really "protecting" the drivers that much.
**The good MCM plate amps offer a constantly variable phase adjustment if you are worried about integration with a 1st order highpass.

Just my 2 cents.

[zobsky]

Zobsky:

Are the bass modules you're considering dipoles, or monopoles?  I wasn't clear from the post(s).

The reason I ask is that given your room dimensions, Dipole bass will disappear below 40 Hz.
That's fine for most music, but a serious shortfall for home theatre . . . especially when compared the size/efficiency of your LA's.

If you can get your mains down to 150 Hz (should be easy), any plate amp will let you integrate the stereo bass units fine.  Yes, avoid the high-pass built-into the plate amps.
A first order passive hybrid (electrolytic combined w/good poly) high-pass XO is inexpensive, and can still integrate well** and keep the deep stuff out of the LA.  Given the number of drivers and efficiency you are contemplating, I can't imagine that a higher-order highpass is really "protecting" the drivers that much.
**The good MCM plate amps offer a constantly variable phase adjustment if you are worried about integration with a 1st order highpass.

Just my 2 cents.

Thanks for the tip on the hybrid 1st order crossover.

Re. the subs, .. I haven't made up my mind yet, .. I only need to go down to an honest 40 -50 Hz or so though at high efficiency, since I have a bunch of suitable drivers lying around. Probably a couple of small horn loaded midbass/bass units (or is that an oxymoron) to cover the 1-2 octaves. I'll have to factor in the cost of plywood though, .. and see if it makes more sense to do OB bass at that level of efficiency. A seperate horn sub will do the 20-50Hz

[zobsky]

Could someone tell me whether a flat baffle or a fixed U-baffle would work better in this case? I can only pull the speakers out around 1 - 2 ft from the rear wall.

Links to useful info would work too. I'm a relative novice to this OB stuff.

Thanks

[thuthriller]

i am using the foster drivers 4 per side with a planar tweeter. i can tell you that they will do 200hz easily. with the number you intend to use you should be fine. and by the way they sound great.

[zobsky]

Thanks, I have a heap of them lying around the house, but work has kept me busy this week ...

What kind of response do you get from them (and on what baffle type/size )? What do you do for a bass solution?

I started my "official" build thread on diyaudio.com, though I haven't got down to business yet.

FWIW, here are some "fanciful" renderings I came up with

U-baffle
http://img128.imageshack.us/img128/1998/baffleuik8.jpg

K-baffle
http://img404.imageshack.us/img404/7159/bafflekeq2.jpg

t-line
http://img404.imageshack.us/img404/1893/baffletlinehe7.jpg

baffle with helper woofer
http://img402.imageshack.us/img402/9168/bafflehornke6.jpg

[thuthriller]

i run mine wwtww on a 9" wide baffle 48" tall. they are crossed over at 3.6k with a rane ac-22 active crossover. you will need help below @100hz, but any decent sub should handle that. they are a steal at that price. one of the tweeters i use costs as much as 20 of the woofers!

[zobsky]

Thanks, I'm playing with 4 on a cardboard baffle for now (wired for 8 ohm) . I'd estimate somewhere in the early 90 dB efficient

... pix of my initial (crude) experiments with the woofers . They're work well to 100Hz and 80 Hz is clearly audible in room . I miss the mid-bass slam though. Is that something that I'm not going to get with this configuration (without going to a helper woofer)?

I plan to end up with 12 per channel once I nail down the final configuration.

http://img180.imageshack.us/img180/3563/img2461zr2.jpg
http://img180.imageshack.us/img180/5773/img2463ti0.jpg

I could use my active x-over , but am trying to stay away from the whole multi-amping can of worms as this application will be for HT mains.

[zobsky]

How do I decide / calculate the driver distance from the baffle walls? ie. for a U-baffle, would positioning a driver equidistant to the L and R edges be optimal or would an offset be better? The "Edge" baffle step program tells me that an extreme offset to either side is better but that program isn't for OPEN baffles per se.

[JohninCR]

I thought you had a tweeter array, so that gives you inherent offset in front.  WRT to the "wings" of a U-baffle shape, use a slightly different depth for the inside and outside tapered wings (you end up with L and R speakers, so plan that properly). 1-2" is plenty of difference, since that's equal to 2-4" difference on a flat baffle.  Since you are working with corners, I'd recommend burning a little extra wood and experiment with some temporarily screwed in "wings" and different amounts of rearside damping.  There's no modeling that can tell you exactly what will happen with a tapered U-baffle array near a corner, so some easy and cheap experimentation is the best way to ensure you are happy with the end result.

Personally, I would go with as narrow a front as the drivers and roundover will allow.  That will permit angled wings.  I had success with tapered angled wings and a narrow front, 8" wood, and all I used was a layer of polyfill batting and 1/2" open cell foam over the back of the drivers, and that's with placement of the bottom corners of the wings against a concrete wall.  I didn't have corners, which will likely add more bass and make damping & diffusion of the first reflection of the side walls pretty much mandatory.

[zobsky]

I thought you had a tweeter array, so that gives you inherent offset in front.  WRT to the "wings" of a U-baffle shape, use a slightly different depth for the inside and outside tapered wings (you end up with L and R speakers, so plan that properly). 1-2" is plenty of difference, since that's equal to 2-4" difference on a flat baffle.  Since you are working with corners, I'd recommend burning a little extra wood and experiment with some temporarily screwed in "wings" and different amounts of rearside damping.  There's no modeling that can tell you exactly what will happen with a tapered U-baffle array near a corner, so some easy and cheap experimentation is the best way to ensure you are happy with the end result.

Personally, I would go with as narrow a front as the drivers and roundover will allow.  That will permit angled wings.  I had success with tapered angled wings and a narrow front, 8" wood, and all I used was a layer of polyfill batting and 1/2" open cell foam over the back of the drivers, and that's with placement of the bottom corners of the wings against a concrete wall.  I didn't have corners, which will likely add more bass and make damping & diffusion of the first reflection of the side walls pretty much mandatory.

Thanks for all the good advice, John,

...would driver offset be a valid substitute for different sized wings? I ask because I also had other experiments in mind, . .such as a K-baffle screwed onto the rear wings (easier to do this with  equal sized wings)

I've had some plywood cut up this evening, . My baffles are 6 ft x 1 ft (drivers are 5.25" and 2.5")

[JohninCR]

I thought you had a tweeter array, so that gives you inherent offset in front.  WRT to the "wings" of a U-baffle shape, use a slightly different depth for the inside and outside tapered wings (you end up with L and R speakers, so plan that properly). 1-2" is plenty of difference, since that's equal to 2-4" difference on a flat baffle.  Since you are working with corners, I'd recommend burning a little extra wood and experiment with some temporarily screwed in "wings" and different amounts of rearside damping.  There's no modeling that can tell you exactly what will happen with a tapered U-baffle array near a corner, so some easy and cheap experimentation is the best way to ensure you are happy with the end result.

Personally, I would go with as narrow a front as the drivers and roundover will allow.  That will permit angled wings.  I had success with tapered angled wings and a narrow front, 8" wood, and all I used was a layer of polyfill batting and 1/2" open cell foam over the back of the drivers, and that's with placement of the bottom corners of the wings against a concrete wall.  I didn't have corners, which will likely add more bass and make damping & diffusion of the first reflection of the side walls pretty much mandatory.

Thanks for all the good advice, John,

...would driver offset be a valid substitute for different sized wings? I ask because I also had other experiments in mind, . .such as a K-baffle screwed onto the rear wings (easier to do this with  equal sized wings)

I've had some plywood cut up this evening, . My baffles are 6 ft x 1 ft (drivers are 5.25" and 2.something)

If the front is large enough to override the wings, then the wings become rear wave reflectors.  As part of your K trials, why not use the corner and exponentially tapered wings to create K-slot(s) with the walls?

[el`Ol]

Having the baffles in touch with the side walls gives bass reinforcement (similar to floor reinforcement) and helps to keep the baffle size small (I can tell from my own experience). However I would try to get some distance to the rear wall if possible.
If I were going to build an OB line array I would use the Ciare CW250 plus BG Neo8 with 800Hz x-over, though I have heard neither of them yet.
http://www.teleprodottistore.it/shop/ciare/cw250.pdf

[JLM]

You're using $3 drivers and a mile of wiring for 24 of them and worrying about what??