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audiomagnate 24th January 2013 03:04 PM

Lowering Fs.
 
I have a pair of discontinued Dayton 15" PA woofers I would like to use in a pair of home subwoofers: Dayton Audio PF385-8 15" Cast Frame Driver 4" VC 295-080

38 Hz seems a little high for a subwoofer, and the sensitivity is high so I though adding mass to the woofers might be the way to go. I know some of the classic British manufacturers used to use something that looked like epoxy and sand to add mass to their woofers, and JBL adds lead mass rings to the top of the voice coil assembly.

Opinions, ideas, comments?

sreten 24th January 2013 03:39 PM

Hi,

In theory you can add about 100g to the 100g cone to drop
Fs to 27Hz and bump up the Qts to 0.5. AS Vas remains
the same due to higher Qts the ideal box size increases.

How the suspension and surround would cope with
the extra mass I'm not sure, probably would be OK.

rgds, sreten.

tb46 24th January 2013 03:57 PM

Hi audiomagnate,

For home use you may want to look around for information on the RiPol (Ripole) by Axel Ridtahler. Here is one link: RiPol-Subwoofer .

Regards,

audiomagnate 24th January 2013 04:17 PM

I already have a pair of very nice cabinets, 3^ft in size.

turbodawg 24th January 2013 04:18 PM

I would just put them in decent sized sealed boxes (Q=.707), eq/transform the heck out of them, and a 8th order butterworth high pass at about 25-30hz to keep from bottoming them out.

audiomagnate 24th January 2013 04:50 PM

BIG sealed boxes- around 7^ft!

Any input on the epoxy/sand mixture?

DSP_Geek 24th January 2013 07:16 PM

What you want is a Linkwitz transform. Park the woofers in your boxes, figure out the system Q & F3, then LT to the desired cutoff.

David_Web 24th January 2013 08:47 PM

I don't see any advantage in adding mass. Just use EQ like LT or PEQ.

The only help you could get by adding mass is if the suspension is very non linear and swamping the cone motion, and the added mass pushes the mass controlled region down enough to limit the distortion, assuming the electrical motor is linear enough. Although by that point it's better to get another driver. IMHO.

Fs is an outdated way to look at subwoofers from an age where passive crossover was the only option and EQ was unheard of. IMHO of course.

I would take advantage of the relatively low Qes and large box and go with it. Fair amount of stuffing too.

tinitus 24th January 2013 09:31 PM

with 100gr added to 100gr cone, your 95db SPL will dump to 88db
but is it really only 100gr ?

had it been at around 20hz I would say fine, but considering its around 30hz, I would say its a bit on the low side
also consider the lowish Xmax is made to match the higher 38hz Fs

sounds like they could be very nice bass guitar woofers :D

audiomagnate 25th January 2013 02:57 PM

Quote:

Originally Posted by tinitus (Post 3340729)
with 100gr added to 100gr cone, your 95db SPL will dump to 88db
but is it really only 100gr ?

had it been at around 20hz I would say fine, but considering its around 30hz, I would say its a bit on the low side
also consider the lowish Xmax is made to match the higher 38hz Fs

sounds like they could be very nice bass guitar woofers :D

Had what "been around 20hz?"

I really don't like the way it sounds now in the 3^ft cabinet, sealed or vented, boomy and thumpy, so I'm going to give it a shot. I can keep one cabinet stock and listen to the difference. They will be used in a multi sub (five) system for smoothing in a low sensitivity setup, so the sensitivity cut doesn't matter to me.


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