DIY version of the BG Radia DGX-4850 In-Wall subwoofer

fizzylime

Member
Paid Member
2004-11-04 10:49 pm
Fayetteville, AR
DIY version of the BG Radia DGX-4850 In-Wall subwoofer based on THX Balanced Bass Line concept.

Before anyone says it… yes I want to copy a commercial design (to be fair, BG is no longer in business so take that for what it’s worth)… further I’ve read all the arguments for not using small drivers for bass frequencies and I don’t buy it.. that is if you use enough small drivers of appropriate specs, lots of power, and DSP!

Goals are low-distortion, even response, limited mechanical vibration, and low extension (60% movies/40% music). I don’t typically listen at reference levels. Oh and of course hidden speakers (pesky WAF!)

Will be paired with BG Radia SA-320 in-walls

Idea is to prototype one and if happy build three more while sharing my experience with the DIY community here.

Driver I had in mind is Tang Band W4-2089 4.5" RBM Mini Flat Panel Subwoofer 4 Ohm:
Tang Band W4-2089 4.5" RBM Mini Flat Panel Subwoofer 4 Ohm

Other options I should consider are welcome? As these will be placed in-wall I realize that they will not completely fit in a 2x4 wall but as the wall I have in mind has my garage on the other side the back side of the box can extend into that space a bit and not affect my ability to park my car. For this reason should I consider larger drivers (less of them)? Mind I'm not willing to give up too much space in my already cramped garage so let's put a limit on say up to 8" drivers)

What would this design be called? Push Push Slot Loaded Sealed--
How do you model it? Hornresp and/or AkAbak (anybody willing to help? I’m just getting started with these programs!)
Amp to pair with it? (in my head I see using a MiniDSP (read: Linkwitz Transform) but I not sure if say an iNuke amp gets me there without needing the MiniDSP?)

Hopefully this will be a fun and rewarding project (and you guys don't beat me up too bad)!:eek:
 
The thing to consider is that using multiples of small drivers to get the cone area only goes so far. Take for instance, trying to outperform a single JBL GTO1214. Fairly cheap 12" driver. You'd need 4x 6" drivers, or 9x 4" drivers for the equivalent cone area.

The problem here is that each of the small drivers must be capable of the cone excursion of the larger driver its trying to replicate. JBL claim 14.5mm Xmax, though I can say the driver's pretty nonlinear by that point.
Now, to match that with smaller drivers, each will need 14.5mm Xmax, which is rare for a 6" driver, and entirely unrealistic for a 4" driver. A 4" driver with 7.25mm Xmax is more feasible, but still rare. Lets take 3.625mm Xmax (to keep other numbers simple) on a 4" driver. Pretty realistic. You will, however, need 36 of those to keep up with that single 12". That's the cone area of a 24" driver (indeed, the drivers will form a 24" square) all because smaller drivers generally have less excursion available than larger drivers.

You'd need 18 of the drivers you've linked to match the aforementioned JBL on volume displacement (cone area, Sd, multiplied by cone travel, Xmax). Having noted the cost of that Tang Band unit, I don't think this is viable.


8" drivers are where you start being able to displace useful amounts of air. Take this unit for example:
Dayton Audio RSS210HO-4 8" Reference HO Subwoofer 4 Ohm

8" cone (give or take), with 11mm Xmax.
You'd need more than 8 of those TB units to match this 8" driver.


I'd go with a pair of those drivers mounted in-wall as a slot-loaded infinite baffle. Wire them in series for an 8ohm load, and grab an NU3000DSP fitted with a silent fan. That should give you lots of room for adding more of them - that amp can (just about) hack 2ohm per side. You won't need much power, since IB is inherently very efficient at LF.

Hopefully I didn't beat you up too badly, just wanted to make sure the understanding is there - cone area doesn't make bass, volume displacement does.

Chris
 

fizzylime

Member
Paid Member
2004-11-04 10:49 pm
Fayetteville, AR
Thanks!

Thanks Chris! I think I'm going to bag the idea just for the reasons you stated. I started another thread looking at doing dual Rythmik Audio 12's in a similar configuration.

IB is not an option as my bedroom is above the garage (where the subs will be placed) and I need to contain the sound to the listening area.