openly baffled!!! noobish help wanted

[psychosteve]

i just picked up a set of audax ap210m0 drivers, the qts makes me think they should be open baffle, can any one help with the design ideas for this as im kinda new to speakers. cheers guys, steve.. ..

[454Casull]

The Fs on the spec sheet says 46Hz, yet the impedance curve says it's about 140Hz. What gives?

http://www.audax.fr/docs/@ap210m0.jpg

Anyway, what frequency do you plan to high-pass this thing? Or will it be used to fill in the entire bottom range?

[GM]

Greets!

Obviously they superimposed the wrong impedance plot onto the FR plot since not only is it off Fs-wise, but the impedance peak is of a much lower Qt driver.

Spec-wise, this driver can be used in OB, TL, aperiodic, or very large sealed depending on the intended app/desired performance parameters (within the limits of the driver and your available space of course).

GM

[psychosteve]

i was intending to use it to fill the entire bottom end, hopefully in an open baffle box, but i wanted to know does it matter what size box?

i was thinking about some 30 litre boxes i have built before, but with metal mesh (the kind for the front of PA boxes) across the back???

also if it doesnt matter to much on size can i make them thinner (less deep) ??

any help apreciated, steve.. ..

[GM]

Greets!

Of course the box size affects performance! About the only way for 30L to be of any use down low is to put them in the corner such that the open back loads the apex to make a small conical corner horn.

GM

[Andersonix]

Noob or not, read as much Linkwitz as you can. Then go back for more...

[Paradise_Ice]

Your not alone!

The amount of people that want an open baffel or di-pole subwoofer is amazing me as i dont know what an ideal drive unit would be for an open di-pole, until today that is!

I had to e-mail Siegfried Linkwitz and ask him what the best parameters are for a woofer in this type of applications.

Words from the kind gentelman himself.

"The primary requirement is large volume displacement capability, because of the acoustic short circuit that the open baffle presents. This should be at low distortion and without shuffling noise. The acoustic output will have to be boosted electrically at a rate of 6 dB/oct with decreasing frequency. If the driver has Qts = 1.0, then the boost should shelve at Fs in order to obtain a 3rd order Butterworth acoustic highpass filter response. Fs is preferably below 25 Hz. Values of Qts below 0.5 make correct equalization a little more involved, Cms should be governed by maximum linear range requirements. Usually it takes little power to obtain full excursion at low frequencies, but the high end of the woofer range, the mass controlled region, can be problematic."


The open di-pole woofer is my new pet project, to design a driver just for open di-pole is the challenge

If anybody wants to let me in on any tips please feel free, i hate to waste perfectly good dampers and cones as i work with alot of trial and error, hoping for a Eureka moment

[GM]

Greets!

He speaks the truth, so assuming a 80-100Hz XO point, this should thrill: http://www.ascendantaudio.com/Avalanche%2018.htm

GM

[Paradise_Ice]

Goodness me!

Its rather large for the typical British room.
Its looks very much like a MMATs Juggernaught bass unit? the cone profile and some of the specs, do you know how they measure the linear travel?

The power requirements on that unit are rather large for a domestic amplifier, but am sure it would sweep some large amounts of air if a PA amplifier was used.

alot of my customers wants arrays over a pairs of large units in a di-pole, i wonder why.