Open baffle woofer line array concept.

[oon_the_kid]

Hi,

I've been playing with my new SEAS FR22 in a sealed box for a while now. And I really like the sound.

I am thinking of moving to the next step and build a OB for it. I intend to make it 2 or more ways by adding an additional woofer to it. I have two choices, either a

a) use a sealed box for the bass
b) Build an open baffle for the bass.

They will have separate amplifiers (with equalisation), since I don't belive any woofers out there has the same sensitivity as the SEAS full range.

Option a) is quite straight forward. Option b), the most commonly used speaker is the eminnence 15" beta/alpha etc, whihch I think the missus will not take too kindly to a 2 foot wide speaker, even if I paint it red like a Jamo 909. An alternative, I am considering is to use 4 8" woofer for the bass (perchannel) in a line array, and reduce the baffle width to about a foot. From what I understand, the speakers should have an Qts of about 0.7. Is there any other requirement.

One driver candidate for this project could be this.

http://www.parts-express.com/pe/show...number=299-934
or
JAMO 20418 8" Treated Paper Cone Woofer 299-913
or
JAMO 20316 8" Paper Cone Woofer 299-939

This will be my first time building an open baffle, so any advice of any sorts would be very much appreciated.

Oon

[chazdrumzalot]

A low Fs is also important. 48hz is too high I think.

[oon_the_kid]

Originally Posted by chazdrumzalot

A low Fs is also important. 48hz is too high I think.

I will most likely crank up the bass electronically for low frequency.

Oon

[oon_the_kid]

Originally Posted by oon_the_kid

I will most likely crank up the bass electronically for low frequency.

Oon

On a slitghtly different note, how much is the distance between this speaker and the wall at the back (or it might be generalised for all open baffles.)

Oon

[Rudolf]

Originally Posted by oon_the_kid

I will most likely crank up the bass electronically for low frequency.

Trying to crank it up below Fs will easily lead to excessive excursion. Better look for low Fs (and some excursion) in the first place.
These are budget 10" drivers that worked well for me:
Visaton WS 25 E and Monacor SPP 250

Just check the parameters to see, what you should look for. Qts>0.7 is not wrong, if it does not signal poor driver quality. Try to have at least 3 mm linear excursion to each side - that's absolute minimum. 6 mm would be much better.

Any wall distance below 3 feet WILL be detrimental for various reasons. 5-6 feet instead of 3 will significantly help with the bass.

[sreten]

Hi,

The problem with a narrow baffle is that it forces the c/o point for the O/B
to be higher that one would really want, only way round it to keep it low
is some form of active lower boost and the whole project becomes quite
complicated, ideally requiring measuring equipment, a least some serious
simming, and some serious active analogue EQ analogue c/o design.

See Linkwitz's Orion project for the sort of EQ needed.

http://seas.no/images/stories/presti...cz_appnote.pdf

Are you using an RL combo on the driver as detailed above ? If using a low
powered (valve) amplifier EQ is best done line level before the amplifier.

I've attached a sealed versus vented, 1.5cuft versus 2.5cuft comparison.

The very decent excursion of the driver, compared to the pathetic 1mm
or so of many 8" FR's, means its it capable of extended bass at decent
volumes, for low power (valve) amplifiers the extra bass efficiency really
can make a difference as well as the extra bass extension / max SPL.

Nothing against OB's, but IMO a vented floorstander suits the Seas 8"
FR the best. Very simple compared to the complications of a narrow OB.

Line level or passive EQ is a must to get a balanced tonality.

Relatively simple OB's do need to be wide for relatively simple c/o + EQ,
and TBH unless you need high volumes a smaller driver is best for 2 way.

A further option would be to build a 0.5 way, with an 8" helper woofer,
sealed or vented, if 4 ohm bass is OK and more SPL is wanted, but
that will ~ double box size, but reduce the driver EQ needed.

rgds, sreten.

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http://speakerdesignworks.com/
http://www.htguide.com/forum/showthread.php4?t=28655
http://www.troelsgravesen.dk/Diy_Lou...r_Projects.htm
http://www.humblehomemadehifi.com/download.html
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http://www.linkwitzlab.com/
http://www.musicanddesign.com/

Great free SPICE Emulator : http://focus.ti.com/docs/toolsw/fold...t/tina-ti.html

[oon_the_kid]

Originally Posted by Rudolf

Trying to crank it up below Fs will easily lead to excessive excursion. Better look for low Fs (and some excursion) in the first place.
These are budget 10" drivers that worked well for me:
Visaton WS 25 E and Monacor SPP 250

Any wall distance below 3 feet WILL be detrimental for various reasons. 5-6 feet instead of 3 will significantly help with the bass.

Dear Rudolf,

Thanks for the tip. I think the Visaton has real potential. The grand orgue and the petite orgue looks like both interesting project.

Actually I think my requirements for open baffle should be it should have a nice and narrow front, 12" would be good, and can be placed close to the wall (I live in an apartment). The grand orgue would have been nice, but since it can't be placed close to the wall, it is going to be a bit of a challenge.

Just wondering, I believe you have quite a bit of experience in this. What are the other alternative open baffle design that could fit my needs?

I am thinking of something like the petite orgue but I face the rear slot to the top and let it face the ceiling instead. That way I can have the clearence Either that or go with the slot bass

Nelson Pass: The Slot Loaded Open Baffle Project

Oon

[oon_the_kid]

Dear Sreten,

Thanks for your lengthy reply. The was originally thinking of it as a 1.5 way, OB for the fullrange and sealed for the woofer. But thinking more about it, heck, let's go all the way and see what this nice uncoloured bass that everybody is talking about sounds like. I have actually heard the Jamo R909 before once, and was quite impressed.

I already have other BR or sealed speakers, and I want this one to be a bit different. I was planning on doing some form of equalisation and power all the woofers with tripath class D amps. So that is not a problem.

The probelm is like the post befor ethis mentions... the space...

Oon

[Rudolf]

Originally Posted by oon_the_kid

Actually I think my requirements for open baffle should be it should have a nice and narrow front, 12" would be good, ...

Having the front no wider than 12" should be no problem, but ...

... and can be placed close to the wall (I live in an apartment). The grand orgue would have been nice, but since it can't be placed close to the wall, it is going to be a bit of a challenge.

Even with a W frame (like the orgues) you would at least need 50 cm distance to the wall. The only exception would be to place the W frames parallel to the front wall:

If you manage to have them far enough to the sides, you would be in the dipole 8 (green radii). But now you need to have 50 cm free space where indicated in the diagram.

[oon_the_kid]

Dear Rudolf,

Thanks for the quick reply. It makes sense, Pretty much listening to the orque from the side rather than from the front. In which case I could potentially do it in an S-frame (half an orgue) Would be slimmer and higher WAF.....

Will think about it...

Oon