Open baffle line array

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
This is a new thread to address some questions I had in a different one. My idea is to use 16 Tang Band w3s-881s (each side) in an open baffle (dipole) line array. This would be mounted above a 10" sub of some sort, in a transmission line. The mid drivers will be mounted as close as possible to each other to help lessen comb filtering effects as much as possible.

So my questions are:
-Is this an idea worth pursuing?
-Am I going to be looking at any nasty artifacts by coupling a line array with an open baffle?

The ideas behind the Phoenix really intrigued me, and I was thoroughly impressed by a friend's DIY line array I heard a few months ago. I'm hoping the marriage of the two will give me a room filling sound that other speakers have lacked (I have a loft with 12' ceilings and an enormous amount of space).

I did some quick 3d mockups of the speaker i'm envisioning. Any feedback would be appreciated.

An externally hosted image should be here but it was not working when we last tested it.


The original layout idea came from http://www.angelfire.com/biz/davidson/
 
frugal-phile™
Joined 2001
Paid Member
I was at one point thinking of doing something similar with my ESLs.

You will need to make your baffles wider (or add wings on the sides) to get them down to where you can comfortable XO them to the woofer.

I just posted this nomograph for open baffle cut off http://www.diyaudio.com/forums/showthread.php?s=&postid=111550#post111550.

Looks like 45" will get you down to 150 Hz. Should sound good if you can get it going. A wider baffle will also give you room for a row of magnetostats (or cheap domes -- ApexJr has some suitable -- 100 for $85 IIRC) if you find that the comb filtering is too great.

dave
 
Nielsio said:
What about impedance? Parallelling drivers lowers resistance, right?

What I'm thinking of:
-Using that amount of Tangbands, so it matches the bass drivers' efficiency. And then:
-Parallelling the bass driver also (Magnificat style).

So:
-No filter / x-over
-TB's and bass driver are run full-range

http://melhuish.org/audio/diy5.htm
http://melhuish.org/audio/diy5.htm

Parallel connection soloution - Line Arrays.
In this configuration, drivers recieve different power according to their position in the array - an attempt to to make a point source I think.
In my experience, to run different drivers in parallel, a zero inductance connection is needed between the drivers, and impedence (series RC network) correction is also required.

Eric.

Line array series/parralel connection.
 

Attachments

  • array.jpg
    array.jpg
    16.1 KB · Views: 1,114
In this configuration, drivers recieve different power according to their position in the array - an attempt to to make a point source I think.

I've just held my head vertical, and the center stereo-image disappears, and the closest / strongest source is the point where the brain think it's coming from. But: is that a problem? All the same drivers could be in complete parallel, so the energy is optimally divided.
 
A neat trick that helps with the upper mids and highs on a flat panel is to cover the front surface with felt or foam. It won't change the rolloff on the low end, but it will do a splendid job of eating up highs that want to crawl across the front of the panel and re-radiate from the edges.

Grey
 
"All the same drivers could be in complete parallel, so the energy is optimally divided."
Yeah, except that 12 8 ohm drivers in parallel will give 0.6 ohms total load.
This is ok if you have a <1 ohm capable amplifier, but most amplifiers are not.
An economical soloution would be to run multiple, say gainclone amplifers in each cabinet, and load then appropriately.

Eric.
 
Another thing. Won't putting a low frequency into all those Tangbands make them create tons of IMD? Shouldn't there be a HPF in place to limit displacement at frequencies where they're not effective? I made a similar open panel line array with 9 Fostex 4" drivers a some years ago, and the HPF made a huge difference to the speaker's articulation.
http://www.diyaudio.com/forums/showthread.php?s=&postid=112174#post112174

Setting them up in the wiring configuration Eric posted can have some benefits, but they still went to hell on a complex work like a massed chorus. Speakers, being reactive little beasts, change their parameters with level and so this is a compromise, and will probably only work on a QUAD 63 or similar ESL. The parallel amplifier idea sounds like it might work, but then you'll get delay effects from the furthest spaced drivers, unless you curve the array so that it focuses at a critical distance, and you listen near that.

I'm also a bit confused about Neilso's comment about Thorsten's Alphabet Soup :))) loading arrangement. That was set up for two dissimilar drivers using a common enclosure volume, so how does an OB and TL combo relate?
 
I also think you're going to want a high pass on the TB'S, probably around 200hz or greater. 16 drivers will get effective cone area up, but volume displacement will be limited by the x-max of the individual drivers, which I suspect is less than 1mm. In short they are going to bottom easily on an open baffle below 200hz. Interestingly, less volume displacement is required for a given SPL on an open baffle down to about 200hz ( if the baffle is large enough to support a 200hz wave), compared to a closed box. Below this point, volume displacement requirements increase Quickly.
There will also be a large peak(+6db) at the frequency where the wavelength equals the distance from center driver front, to center driver rear. The front and rear radiation will sum before dipole rolloff begins( might be smoothed by the line?).
I think it's a good idea, but you will need some crossover work.
If You're going to use the transmission line as a diffuser like the Davidson Panga, you're going to need to cover it with some type of acoustic absorption.
regards, Jason
 
Re: baffle size:

So the 45" should be entire baffle size or 45" from each side of the driver? And would having a bent baffle cause any unwanted effects (I'm thinking a box without a back)?

The wiring I'm going to use is a series/parallel mix that should present each speaker with the same amount of power and keep the load at 8 ohms. Turning the line into a point source sounds like a Bessel array and that's not really the effect I'm looking for.

The w3s-881s have an xmax of .5mm :( Not exactly monsters. The pair I'm running off of the Wave 8s and my computer sound good enough running full range that my girlfriend's mother came around the corner to find out what was making that lovely sound (Mel Torme) on Christmas Eve ^_^. Not exactly an audiophile endorsment, but in full range t-line tubes these things are shocking.

I'll be ordering the drivers in the next week or so and start playing with the open baffle idea. Based on the results I'll start tweaking with high pass filters and such.

The other idea I was kicking around was loading each driver in an inverted horn. That's alot of work for 32 drivers which is why I'm going to try the open baffle first. Does anyone know the theory behind inverted horns and perhaps a few formulas to model response? I'm not adverse to writing a program to model responses based on some formulas.

Thank you for the feedback.
 
frugal-phile™
Joined 2001
Paid Member
ryoshu said:
So the 45" should be entire baffle size or 45" from each side of the driver? And would having a bent baffle cause any unwanted effects (I'm thinking a box without a back)?

officially it is the shortest distance from the edge of the cone on the front to the edge of the cone on the back. This applies to folded baffles as well. Folded baffles will have some extra resonances to deal with (box cavity, and air mass resonances), but these can be minimized.

dave
 
"There will also be a large peak(+6db) at the frequency where the wavelength equals the distance from center driver front, to center driver rear. The front and rear radiation will sum before dipole rolloff begins( might be smoothed by the line?)."

If a mid-driver is placed centered on a circular baffle, then you get something like 6dB peak.

If a mid-driver is placed slightly of center on a rectangular baffle the peak can be like 3dB.

Using an array/line source is worse than a single driver on a rectangular baffle. So.. using the array in the first post in this thread would most likely give a 4-6dB peak before roll-off.

Think about it and you´ll understand why...

/Peter
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.