U baffle line array

[goldyrathore]

Hi,

I am thinking of an active line array (U frame) with the following drivers.

Brand/Size: Eastech 65mm fullrange drivers.
Driver parameters: Qts 1.2, Fs 135Hz. Power about 15 watts RMS and 2 mm xmax.
Vas: Not measured( Guess it wil not be more than a litre or two).
No of drivers per side: 20
Crossover to woofer: 120Hz 24db/octave slope. The lower end will be handled by 8" drivers.
Crossover to tweeters: 3500 Hz at 24db/octave slope. The higher end will be handled by Dayton neo tweeters.

I already have the drivers. These are usually used in OEM HT package as fullrangers in a sealed cabinet.

I am willing to use stuffing (light stuffing in the U frames and then some denser damping on the rear) to get the response lower if it helps.

I still have many unanswered questions:-
1) Can I achieve the goal of 120hz lower response and be able to place it at about a foot from the wall at its rear?
2) What are the approximate minimum dimensions (width and depth) for the array?
3) Is the lower response achievable?
4) Should I go for OB or sealed instead?
5) Is there any excel sheet that can help me simulate the response when T/S parameters are known?

Can someone with experience on U OB arrays help me figure out?

Thanks,
Goldy

[LineArray]

Hi there Goldy,

i cannot give exact answers or guarantees but hints:

1) a) Can I achieve the goal of 120hz lower response

> with OB and rightly damped U-Frame it is possible but definately not in front of a
wall in case of OB.

b) and be able to place it at about a foot from the wall at its rear?
> OB: NO!
> U-Frame: Should work depending on damping -> seamless transition to
closed box with/without leakage possible.

2) What are the approximate minimum dimensions (width and depth) for the array?

- for OB i recomend max width: Driver diameter X 2.2, but not feasible because rear wall proximity
check using "The EDGE" baffle simulator. It does not simulate
the rollof due to the driver parameters below fs but with Q around 1
Edge output will be usable down to 130Hz (fs of your driver)

- if you go to deep and - correctly damped - U Frame you may go narrower but:
Try to evaluate Vas of your drivers and ensure that the volume of the
damped U-Frame is significantly larger than N X Vas X number of drivers.

In your case a factor N of 2 or even much more does not harm ... calculate a closed
box volume which rises your resonance as little as possible, which you can tolerate
from the space needed.

Then you can close the U-Frame if the result does not meet your taste and you have a
closed box of sufficient size. If you go for depth you get lower bass than going for width
when using a U-Frame.

3) Is the (a ?) lower response achievable? > No. Not with that driver without compensation.
There may be BR alignments ... but this is not a BR recommended driver.

4) Should I go for OB or sealed instead? > See above.

5) Is there any excel sheet that can help me simulate the response when T/S parameters are known?
> Nearly. You can at least estimate the "break even" point e.g. where the displaced volume of the
driver mounted in an OB causes the same sound pressure as if it were mounted in an
(infinetely large) closed box.

This gives a hint on the minimum dipole path length "D" you should have.
That "break even point" should be estimated to be significantly below your desired
cutoff say 100 ...110 Hz. Then you have a measure for your desired
"dipole path length".

That path length is the average path length from the driver to the edge of the baffle
in the OB case, which is needed.

A damped U-Frame needs half the depth of that estimated path length: "D/2".

All your possible systems built will most probably have to be compensated in some way ...


I recommend these sources:

John Kreskovsky: U-Frames and damped U-Frames
DIY-dipole-1

Siegfried Linkwitz: displaced volume/path length/sound pressure
http://www.linkwitzlab.com/spl_max1.xls

Tolvan Data: The edge baffle simulator
Home of the Edge


Kind Regards

[LineArray]

I have to make clear:

Reaching 120 Hz with OB one foot from the wall may work,
but the sonic result will be very poor due to comb filtering
and reflections.

The bass to lower midrange will sound somewhat weak and
resonant.

http://www.pvconsultants.com/audio/reflection/rrc.htm

You might go there and check the "room reflection calculator".

Download, set the sound source to "Dipole" and see what happens
with different distances from the wall.

But the dipole modelled there is not a line array, you may just
get a feeling for the effect of the rear wall.

Kind Regards