H-frame woofer mania
Apr 21, 2012 3:26:07 GMT
Post by jeffc on Apr 21, 2012 3:26:07 GMT
Hi Guys,
Before these get locked away in my man cave as spider homes and to augment bass of my DML panels, though I'd let them see the light and snap a couple of pics.
The drivers are 15" Eminence Alpha-15A pro-woofers that I've had for ages and played about for a while in OB with 8" Visaton B200s as well as Sabre greencone 8" mids and 4" tweeters.
Anyways, they got put away when the grotto was tiled quite some time ago now.
I thought it was time they resurfaced in H-frames, these being compact and offering benefits in OB bass extension without excessive cone excursion as with plain OB. I decided to build one for each driver for placement flexibility and to help limit cone stress at higher volumes. The room they’ll be in is huge.
Internal H-frame dimensions are 420 x 420 mm x 400 mm deep, tops/bottoms 400 x 480 mm and doubled up to add mass/weight and hide screw holes. Woofer mounting panel positioned centrally. All panels cut from 2 sheets of 18 x 2400 x 1200 mm MDF, leaving only a couple of small spare pieces. Cuts done at a local kitchen manufacturer for $60 and the 2 panels cost ~$60, with a bit extra for screws and bolts, $50 for 4 L paint but only used 1/3 of that, so no banks needed to be robbed.
I added a brace as a magnet support with a wedge cut out lined with felt to allow free breathing of the magnet-voice coil/dust cap vent hole. Although hidden for aesthetics, the stamped frames of the woofers are damped expensively with 3M 2552 viscoelastic damping tape. Ping the frames and they sound dead, with little if any ringing. Being wedged between the woofer mounting panel and the magnet brace helps with this too I think. Apparently taking care of these little details lifts performance of the lowly Alpha-15As to something close to much more expensive hi-end woofers. Fingers crossed they do, as a taping and bracing required quite a bit of fiddling.
To provide Xover flexibility, I now have a MiniDSP and MiniDIGI. In addition to this, the active route is also to avoid issues with use of passive Xover parts, as someone I trust did careful measurements of the Alpha-15A and these seem not to behave as predicted, particularly with regard to use of higher value inductors.
First up I'll test the woofers using analogue out of my CDP to the analogue in of the MiniDSP. MiniDSP low pass out will got to a Yamaha RX-V550 6.1 channel receiver I picked up for nix on eBay to allow each H-frame to be amplified by a separate channel. There’s lots of flexibility if the DSP of the receiver is used too, but I’ll be bypassing this initially.
Spdif from the CDP to my DAC > 10K attenuator > Class D Audio amp > DML panels to avoid routing this through the MiniDSP, but I may go that route in the end, depending on how I deal with DSP delays etc and blending the woofers with the DML panels. There’s options galore with the MiniDIGI/MiniDSP, too many really.
Anyway, that's were I am and the initial plan. It should provide some fun over the next month or three trying to get the H-frame woofers to work as planned, and experimenting with woofer placement.
Below are a few pics of the H-frames plus just a few of the many links to H-frame woofers and dipoles and their benefits or otherwise.
www.quarter-wave.com/OBs/U_and_H_Frames.pdf
www.quarter-wave.com/Project08/Jordan.pdf
www.musicanddesign.com/u_frame.html
www.musicanddesign.com/Dipole-offset.html
www.hifizine.com/2012/03/on-dipole-subwoofer-placement/
cheers.. jeffc
Before these get locked away in my man cave as spider homes and to augment bass of my DML panels, though I'd let them see the light and snap a couple of pics.
The drivers are 15" Eminence Alpha-15A pro-woofers that I've had for ages and played about for a while in OB with 8" Visaton B200s as well as Sabre greencone 8" mids and 4" tweeters.
Anyways, they got put away when the grotto was tiled quite some time ago now.
I thought it was time they resurfaced in H-frames, these being compact and offering benefits in OB bass extension without excessive cone excursion as with plain OB. I decided to build one for each driver for placement flexibility and to help limit cone stress at higher volumes. The room they’ll be in is huge.
Internal H-frame dimensions are 420 x 420 mm x 400 mm deep, tops/bottoms 400 x 480 mm and doubled up to add mass/weight and hide screw holes. Woofer mounting panel positioned centrally. All panels cut from 2 sheets of 18 x 2400 x 1200 mm MDF, leaving only a couple of small spare pieces. Cuts done at a local kitchen manufacturer for $60 and the 2 panels cost ~$60, with a bit extra for screws and bolts, $50 for 4 L paint but only used 1/3 of that, so no banks needed to be robbed.
I added a brace as a magnet support with a wedge cut out lined with felt to allow free breathing of the magnet-voice coil/dust cap vent hole. Although hidden for aesthetics, the stamped frames of the woofers are damped expensively with 3M 2552 viscoelastic damping tape. Ping the frames and they sound dead, with little if any ringing. Being wedged between the woofer mounting panel and the magnet brace helps with this too I think. Apparently taking care of these little details lifts performance of the lowly Alpha-15As to something close to much more expensive hi-end woofers. Fingers crossed they do, as a taping and bracing required quite a bit of fiddling.
To provide Xover flexibility, I now have a MiniDSP and MiniDIGI. In addition to this, the active route is also to avoid issues with use of passive Xover parts, as someone I trust did careful measurements of the Alpha-15A and these seem not to behave as predicted, particularly with regard to use of higher value inductors.
First up I'll test the woofers using analogue out of my CDP to the analogue in of the MiniDSP. MiniDSP low pass out will got to a Yamaha RX-V550 6.1 channel receiver I picked up for nix on eBay to allow each H-frame to be amplified by a separate channel. There’s lots of flexibility if the DSP of the receiver is used too, but I’ll be bypassing this initially.
Spdif from the CDP to my DAC > 10K attenuator > Class D Audio amp > DML panels to avoid routing this through the MiniDSP, but I may go that route in the end, depending on how I deal with DSP delays etc and blending the woofers with the DML panels. There’s options galore with the MiniDIGI/MiniDSP, too many really.
Anyway, that's were I am and the initial plan. It should provide some fun over the next month or three trying to get the H-frame woofers to work as planned, and experimenting with woofer placement.
Below are a few pics of the H-frames plus just a few of the many links to H-frame woofers and dipoles and their benefits or otherwise.
www.quarter-wave.com/OBs/U_and_H_Frames.pdf
www.quarter-wave.com/Project08/Jordan.pdf
www.musicanddesign.com/u_frame.html
www.musicanddesign.com/Dipole-offset.html
www.hifizine.com/2012/03/on-dipole-subwoofer-placement/
cheers.. jeffc
, but I had the drivers already and though what the heck, I was going to need 2 x sheets of MDF anyway and the panel cuts for 4 worked out to leave much less waste, plus the room my DML panels are in is ~15 x 7 m with only a couple of cut-ins for stair well and toilet/shower. Being able to play each woofer at a lower vol should help reduce distortion too.
Unfortunately with the panel distance from the front wall combined with where I like to listen near-field, there's always been a bit of a null at low frequencies. Problem now solved, and H-frames sounded closest to right when positioned 40 cm or so forward of the panels mainly to account for the short DSP delay.
. 
