Added a center channel to my OB LA

GuyPanico · 29th October 2005, 08:01 PM

I made a down and dirty center channel to match my line array. This is only for TV and movie surround sound use. I run stereo for music. I'm using 4 NSB's wired to 8ohm, and a single dayton tweet and simply crossing them at 5900hz/6db. Going to try a much lower xover and see what happens. I tried running the NSB's full range, but it was horrid. At the moment the center is OB. But I think I will make it sealed. Also a 12db LW crossover would be in order.

Something I noticed is that the high end doesn't drop out like it does when I run my LA's stereo and stand up. If I move above or below my tweeter line, the sound doesnt turn dull and muddy. It behaves like a point source, not the line source with short tweeter line that it is.

GuyPanico · 29th October 2005, 08:26 PM

_

johninCR · 29th October 2005, 09:17 PM

Since you want to change it, I'd suggest trying 6 nsb's and a tweet and wire the nsb's in a bessel alignment. That way you end up with point source dispersion of the array, so with it horizontal you still have good horizontal dispersion.

My personal preference is to leave it open, especially for a center channel for more natural sounding dialogue.

GuyPanico · 30th October 2005, 10:54 AM

What if I were to angle the front like this > at a 30* angle. Then run 2nsb's + 1tweet on each side. Or would there be ill effects that would ruin the added horizontal dispersion?

johninCR · 30th October 2005, 02:06 PM

MTM's are already poor enough as center channels. A double MTM set at angles is just begging for trouble.

My testing of bessels for center channels has worked fine. That's what I would use with a TV, but I use a projector and no center. I understand your need for a center because your arrays give too large an audio image for the TV.

If the 7 driver bessel (6 plus equal space in the middle for the tweet) is too wide, then you could try a 5 driver bessel and squeeze the tweet in like you currently have.

The power factors for a 5 driver bessel from left to right are:
1 2 2 -2 1 The -2 means out of phase and double power compared to the 1's. This can easily be achieved via 2 different combinations of series parallel wiring depending on which overall impedance is better for you. The 7 driver is wired 1 2 2 0 -2 2 -1 and the tweeter is place in the 0 power position in the center, but an equal space needs to be give to the tweet.

GuyPanico · 31st October 2005, 12:41 AM

Pardon my newbie confusion. So you're saying wire one side out of phase? I'm intrigued, an you explain how the bessel works?

johninCR · 31st October 2005, 01:14 AM

On the 5 driver unit only one driver is wired out of phase.

A bessel array radiates sound like a single point source, not like an array. An array on its side will radiate poorly to the left and right. How it works is beyond my understanding. I just obtained a copy of wiring schemes for amplitude weighted bessels.

You already have a 5 driver array and just need to change the wiring to make it a bessel. With drivers A thru E they need power factors of 1 2 2 -2 1 . The easiest is to wire B, C, D in parallel with D wired out of phase. Then put A & E in series with each other and put that in parallel with others. That results in a low impedance array. For high impedance. For high impedance wire B,C,D in series with D out of phase. Then wire A & E in parallel with each other and put that pair in series with the others. With either wiring you get half the power to A & E which is necessary.

If you have 4 more tweets then you can wire them in a bessel as well to balance with the mid array. Otherwise you'll probably need an Lpad to balance the tweet with your mid array.

planet10 · 31st October 2005, 07:17 AM

Quote:

Originally posted by johninCR
MTM's are already poor enough as center channels. A double MTM set at angles is just begging for trouble.

And i ask why a centre channel at all? With those line arrays so close together a virtual centre channel should easily outperform anything you can put on top of the TV.

When you are watching a movie where do people sit relative to the speakers.

dave

GuyPanico · 31st October 2005, 11:59 AM

Right now they're so close because they dont have a proper base. They are actually leaning against the mantle. Once they're able to stand on thier own, I will move them further apart, and forward some.

I always sit front and center. So it's not much of an issue for me. But others sit at a 45* angle to the TV. From my limited seat time in that position, I can say it's not the optimal place for how the speakers/room are layed out.

GuyPanico · 2nd November 2005, 05:58 PM

I think a bessel array center isn't for me. After doing some searching for information regarding this type of speaker, it only works well in the far field. On the order of 10x or greater the length of the array. So if I have a 5 x 4" driver array, it would be at a minimum 21". So I would have to be at a listening position of 17.5ft to get optimal sound.

Still looking for more suggestions on a center channel solution if anybody has any

29th October 2005, 09:17 PM	#3
johninCR diyAudio Member Join Date: Apr 2004 Location: Costa Rica	Since you want to change it, I'd suggest trying 6 nsb's and a tweet and wire the nsb's in a bessel alignment. That way you end up with point source dispersion of the array, so with it horizontal you still have good horizontal dispersion. My personal preference is to leave it open, especially for a center channel for more natural sounding dialogue. __________________ Everyone has a photographic memory. It's just that most are out of film.

30th October 2005, 02:06 PM	#5
johninCR diyAudio Member Join Date: Apr 2004 Location: Costa Rica	MTM's are already poor enough as center channels. A double MTM set at angles is just begging for trouble. My testing of bessels for center channels has worked fine. That's what I would use with a TV, but I use a projector and no center. I understand your need for a center because your arrays give too large an audio image for the TV. If the 7 driver bessel (6 plus equal space in the middle for the tweet) is too wide, then you could try a 5 driver bessel and squeeze the tweet in like you currently have. The power factors for a 5 driver bessel from left to right are: 1 2 2 -2 1 The -2 means out of phase and double power compared to the 1's. This can easily be achieved via 2 different combinations of series parallel wiring depending on which overall impedance is better for you. The 7 driver is wired 1 2 2 0 -2 2 -1 and the tweeter is place in the 0 power position in the center, but an equal space needs to be give to the tweet. __________________ Everyone has a photographic memory. It's just that most are out of film.

31st October 2005, 01:14 AM	#7
johninCR diyAudio Member Join Date: Apr 2004 Location: Costa Rica	On the 5 driver unit only one driver is wired out of phase. A bessel array radiates sound like a single point source, not like an array. An array on its side will radiate poorly to the left and right. How it works is beyond my understanding. I just obtained a copy of wiring schemes for amplitude weighted bessels. You already have a 5 driver array and just need to change the wiring to make it a bessel. With drivers A thru E they need power factors of 1 2 2 -2 1 . The easiest is to wire B, C, D in parallel with D wired out of phase. Then put A & E in series with each other and put that in parallel with others. That results in a low impedance array. For high impedance. For high impedance wire B,C,D in series with D out of phase. Then wire A & E in parallel with each other and put that pair in series with the others. With either wiring you get half the power to A & E which is necessary. If you have 4 more tweets then you can wire them in a bessel as well to balance with the mid array. Otherwise you'll probably need an Lpad to balance the tweet with your mid array. __________________ Everyone has a photographic memory. It's just that most are out of film.

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30th October 2005, 10:54 AM	#4
GuyPanico diyAudio Member Join Date: Mar 2005 Location: Euless, TX	What if I were to angle the front like this > at a 30* angle. Then run 2nsb's + 1tweet on each side. Or would there be ill effects that would ruin the added horizontal dispersion?

31st October 2005, 12:41 AM	#6
GuyPanico diyAudio Member Join Date: Mar 2005 Location: Euless, TX	Pardon my newbie confusion. So you're saying wire one side out of phase? I'm intrigued, an you explain how the bessel works?

31st October 2005, 11:59 AM	#9
GuyPanico diyAudio Member Join Date: Mar 2005 Location: Euless, TX	Right now they're so close because they dont have a proper base. They are actually leaning against the mantle. Once they're able to stand on thier own, I will move them further apart, and forward some. I always sit front and center. So it's not much of an issue for me. But others sit at a 45* angle to the TV. From my limited seat time in that position, I can say it's not the optimal place for how the speakers/room are layed out.

2nd November 2005, 05:58 PM	#10
GuyPanico diyAudio Member Join Date: Mar 2005 Location: Euless, TX	I think a bessel array center isn't for me. After doing some searching for information regarding this type of speaker, it only works well in the far field. On the order of 10x or greater the length of the array. So if I have a 5 x 4" driver array, it would be at a minimum 21". So I would have to be at a listening position of 17.5ft to get optimal sound. Still looking for more suggestions on a center channel solution if anybody has any

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