AR3 subwoofer

[Ragnwald]

Thinking of building two subwoofers on the AR3 concept, a 2 cubic foot closed box. There were a modell with just a woofer in the box, called AR3W, i think.
First woofer made by Acoustic Research, had Fs=14Hz and later went upp to FS=18Hz and Fc=43Hz.
Woofer sold as service replacement for AR3 to day, have Fs=26Hz and Fc=49Hz.
Anyone knowing the TS-parameters of the good old 12", and perhaps a recommendation of a useful substitute?

Is this one usefull, or what parameters are wrong? What´s important?
Europe Audio
Grateful for any help.

[bentoronto]

Help... I'd like help myself.

I have an AR-1 with a very heavy, thick, solid cone and cloth accordion surround.

Great speaker.

I can't figure out why the idea of a Fs=12 Hz driver in a profoundly solid 1.4 cu foot box isn't found more. Why can't you buy such drivers?

Makes a lot of sense to me. I don't think they had too many mechanical failures. Mine is 50 years old and it pairs really nicely with my equally old Klipschorn.

Maybe like with 18 inch drivers, it might be plain hard to get the parameters and mechanicals to work properly together in that configuration.

Except for movie earthquakes, a speaker like the AR-3 that played just fine down to about 37 Hz, is playing almost anything you'll find on recordings.

BTW, the AR-1 has the individual drivers' terminals accessible from the outside. Did they have bi-amping in mind in 1954?

Footnote: I tried to sell my rather beat-up speaker on eBay, figuring it had great historic value. Not much interest. Sad.

[Ragnwald]

bentoronto, don´t forget roomgain, 20Hz is no problem for this speaker.
Magnetism can have weakened in the alnico driver, as a lot of other age phenomenon and brute use.
In bass drivers, there is a difference is sonic character because of differences in flux modulation and temperature curves of the different magnetic materials.

[GM]

Originally Posted by Ragnwald

Is this one usefull, or what parameters are wrong? What´s important?
Europe Audio

Never really got into the acoustic suspension 'thing', but the classic math says that this driver wants a ~1.2 ft^3 net cab for a 0.7Qtc with minimal damping.

WRT what's important, guess that's a matter of personal preference. It's my understanding though that we want the net Vb to be < 1/3 Vas, so that the cab's air mass 'spring' dominates, making Qtc = 2x Qts. For a 2 ft^3 gross cab then, this driver's Vas is ideally a little low, so Qtc will be < 0.7 unless there's some series resistance to raise its effective Qts.

GM

[Ragnwald]

Thanks GM.
The AR3 box is 1,7cf, 48 liter, i relalized. Seams to be ok then.
Is there someone that can tell me about the relationship between Fs and VAS ?

[GM]

You're welcome!

Vas is the system's compliance (Cms), so for a given moving mass (Mms), increasing Cms lowers Fs, ergo reducing Cms raises Fs. From this we see that for a given Cms, increasing/decreasing Mms lowers/raises Fs.

GM

[Ragnwald]

Originally Posted by GM

You're welcome!

Vas is the system's compliance (Cms), so for a given moving mass (Mms), increasing Cms lowers Fs, ergo reducing Cms raises Fs. From this we see that for a given Cms, increasing/decreasing Mms lowers/raises Fs.

GM

Thanks again GM.
There must be a limit, when a high compilant cone get flappy of to high mass.
But a look at the original AR3 woofer, we see a relatively weak motor drive and a (as it looks) high mass cone. The pressure in a closed box is enormous and i can´t see how this come together?

[GM]

You're welcome!

Well, not until both mass and compliance becomes infinite, though of course there is a point of diminishing returns.

Consider a passive radiator (PR) that can have thousands of grams of mass and even more in liters of compliance to make it resonate down in the infrasonic BW in an acoustically tiny cab. A typical acoustic suspension driver is a stiff mouse trampoline in comparison.

Don't know the math for calculating the force on the driver, but didn't think it was 'enormous'. Regardless, even a high Qes (weak) motor will work, just the system's Qtc goes up more than with a stronger motor for a given net Vb, so it's about getting the right mass/compliance/motor strength for the desired Vb, Qtc.

GM

[Ragnwald]

Now you've got me working.
For the movement doing simulations.

[GM]

About time.