diy passive radiator?

honda cber

how would i ever figure out tuning/weighting?

a little background will make this make more sense. i have just joined another band, this time playing bass. i have an "a" rig, and another, lesser one. this band will NOT rehearse at my place like i am used to, so i want to put together a passable rig with little inherent value (to me) that i can leave there (in a non-climate-controlled space). bass cabs are heavy and awkward!

i have a 2x15 cabinet loaded with two peavey black widow 1502. the thing about these is that they have "field replaceable baskets". well, now one is blown, and i do NOT intend to replace the basket ATM due to finance ($80-100 depending on who has what).

given my love for vintage polk designs, i thought maybe i could use it (sans magnet) as a PR of sorts. i can get t/s parameters for the complete driver. the box is big (40x26x16), and sealed (by me--- used to have a couple of 4" holes in the baffle with no "port" to speak of--- i sealed with 3/4" ply screwed and glued from the inside). can i just goop some blu-tack or something into the v/c former? plenty of room and strength, as it is 4" v/c with kapton former. seems like a very time consuming process without some sort of initial direction. i am hoping not to destroy this cabinets formerly huge low-end response. sensitivity isnt a huge issue, as i will be driving it with ample power (480wrms), and the space isnt that big (prob 25x20' or so).

BTW, the suspension is pretty stiff, and excursion rather smaller than one would think, at least as a complete speaker. problem?

any pointers, ideas, or links?

am i way off base? i am an compulsive tinkerer.

thanks!
a

shadowofnight

I've used both TC Sounds and CSS passive radiators in a couple of builds now, as well as playing around with Polk's 15" radiator in a couple of designs way back before high xmax/tuneable PR's were available. . All 3 have a common design trait, the suspensions ( Both spider and surround ) are designed to be much looser and the cones much heavier and stiffer then most speakers.

Combined it gives them Fs ratings in the single digits to teens ( TC 4Hz to 24Hz adjustable.....CSS 3.6Hz with 2,100 grams ) ...also both have 3 INCH P-P excursions.

Your on the plus side with that stiff cone on the black widow , but that super stiff surround and limited excursion on both the active and passive drivers in that large of an enclosure is going to mean 2 things. The passive isnt going to add much to the sound/output of the enclosure no matter how much you add/subtract weight to it....and in that large of an enclosure the power handling on your single active driver is going to drop way down ...its going to hit its xmax way too soon.

I tried to get the T/S parameters for that driver ( Wanted the Fs and Vas at least ) and Peavey is really stingy with the specs ?


It wont hurt to try it though...thats half the fun...just be careful how much power you feed it

honda cber

well *supposedly* the power rating for the single driver is 1400 peak, 700 program, and 350 rms. i use a compressor, and *never* clip the amp, but then again, i see where you are going about the big azz box. also, i had rather feared the worst for using the "basket" as a PR because of the reasons we have mentioned..

BTW, i *have* used the amp since the driver blew--- it is simply unhooked. somehow i thought maybe taking the magnet off and messing with it might improve things---- the active driver never distorted or sounded bad, but i wasnt cranking either. and no, it (the passive driver) didnt seem to reinforce the sound in any way.

here is the t/s stuff anyway, tiny xmax and all.

Resonant Frequency (fs) 43.1 Hz
Impedance (Re) 3.2 ohms
Coil Inductance (Le) .32
Electromagnetic Q (Qes) .38
Mechanical Q (Qms) 7.9
Total Q (Qts) .36
Compliance Equivalent Vol. (Vas) 192 Liters
Displacement Volume (Vd) 225mL
Voice Coil Overhang (Xmax) 2.8mm
Surface Area Of Cone(Sd) .084m2


i guess it only makes sense to replace the basket. was just hoping to do at least ONE job so it isnt directly out of my featherweight wallet. hey, it was an idea.
a

ShinAce

An overhung voicecoil has more xmax than what is listed. It will progressively lose linearity, as oppsed to a sharper loss for underhung coils. That Xmax figure is only important if you want perfect sound quality.

honda cber

FWIW, i went ahead and tried it. it was..... ok. with the maget assembly off, the driver was more compliant. the excursion of the active driver seemed normal (not much) but the passive one was shaking pretty good on some notes, and with about twice the excursion of the active one. there was an apparent reinforcement to about "A" on the bass, which is about 55Hz, and where the passive driver had the most energy. below that, response dropped off as you would expect it to. as an in-the-pocket kind of bassist (think motown or old atlantic stuff), 55Hz just aint low enough. i might try some ghetto weighting if i get bored, but really, the impracticality of a cabinet this large having just one active driver invokes the law of diminishing return pretty heavily.

but hey, it was a learning exercise.

a

jcaut

I reported this... the spam that's now gone... But it was there. And I reported it.