Project - Subwoofer for Apogee Divas

[nautilus]

Hi Guys,
I have been lurking for quite some time and thought I would finally post.

I would like your opinion.

I want to make a pair of subwoofers for a pair of Apogee Divas. What I have in mind is to use the design Apogee use for the Grand. I believe it is a pair of subs using 2x12" woofers in each sub with servo feedback. Minus the Krells of course

I believe they used an accelerometer for feedback.

Based on what I have read in this forum the Rythmik audio kits seem to be the go. I was thinking two dual 12" kits including the amps with servo feedback.

The other option is to develop my own feedback controller and use the ICEpower 1000ASP amps I already have.

Your thoughts?
Cheers
Matthew

[Cloth Ears]

Matthew,

Those Divas are pretty responsive, exactly what are you looking for in a subwoofer, or a pair of bass units (one for each of your Divas). You can produce the notes with a pair of sealed/ported subwoofers, but will the crossover (meaning the psycho-accoustic crossover, not the electronic one) between the 2 match?

A couple of things to think about (or I fear that you will be disappointed with your first effort):
1) What about a (tall, thin) line-array of (say) 8" subwoofer drivers that would line up alongside the vertical edge of your Divas?
2) What about an open baffle or H-frame subwoofer? (Did I suggest that? It must be too early...)
3) What are you trying to achieve with these subwoofers that the Divas cannot do by themselves?

Matching full-range ribbons to a subwoofer is not the easiest thing to do.

[Salas]

I would use a couple of high Q pro drivers angled 45deg to each other's face, keeping the box I see in the pic but with no back baffle. No feedback, just your ICE and a DCX low pass. An RTA and a mic, then use the DCX parametric modules to help the room. Bliss.

[nautilus]

Hi Guys,
The Divas work well down to about 30-40 hz but drop off steeply due to the open baffle design.

For those unfamiliar the Diva is a full range ribbon speaker. For the purists no it's not a true full range ribbon speaker but has the following:
Bass - Al foil coated Kapton panel
Midrange - three strips of Al foil mounted on a Kapton strip.
Tweeter - True Al foil ribbon.

I am more than happy with the response of the Divas in it's range but I would like something to manage the octave or two that the Diva can't do. Also doing sub 30-40 Hz will simplify the integration of the sub.

The picture is not of my speakers (I wish) it just to show what the proposed subs would look like. The picture is a pair of Apogee Grands. The subs have 2x12" drivers per side with active crossovers and Krell amps. I don't want Krells (can't afford them) but I have a pair of ASP1000 digital amp modules to power the sub.

I also want to consider using servo feedback.

More than happy to build my own cabinets, crossovers electronics etc.

Hope that clarifies it.

[Salas]

I have listened to the Divas and I haven't got the feeling of 30Hz, more like 45Hz. But that depends on the room. Wasn't big. In your case I would firstly measure them in room and then see what I need. If you can create 2x15'' open back using a DCX digital controller (affordable) plus your available amps it will be best. Only dipole bass will follow the panel seamlessly. And you NEED digital room modes control for such a performance system. Feedback will not add a real benefit and will complicate things.

[JarreYuri]

Hi!

I am a bit amazed! .... thought the Divas produced lower bass then between 40-30Hz!?
I would NOT think that Your Divas i suffering from frequency cancelation in the bass region at ALL. hehehe
Me myself have a pair of home made La Folia that is mostly based on the Divas in size, and I can ASSURE You that my speakers have flat frequency down to 22Hz!!!
I am NOT kidding! I have tuned them myself and I have NO use for a sub on those panels.

Could it be that You might have to place Your speakers a bit further from the back wall??
Just a thought.

http://picasaweb.google.com/jerker.lindborg/LaFolia

[nautilus]

Hi Guys,
Yes it could be that the speakers are placed badly but I think they are ok.

Don't get me wrong they sound good. Really good. It's just that I am trying to make something similar to the Apogee Grand. The bass was much much better

I have always been baffled how the Diva can have excellent bass with an open panel design (70cm wide) that results in 6dB/octave drop off after (around) 200Hz (not including room loading of course). You can't argue with theory

Anyway the practice is good bass down to about 30Hz. Sure you can get some good lower response but also lots of flap. So I want to take the low end load away from the Divas (and use the sub).

JarreYuri I am impressed by your efforts! How did you find cutting the Al foil and mounting it on the Mylar? And did you use one tuning point or a number over the diaphram?

Cheers
Matthew

[JarreYuri]

Originally posted by nautilus
Hi Guys,
Yes it could be that the speakers are placed badly but I think they are ok.

Don't get me wrong they sound good. Really good. It's just that I am trying to make something similar to the Apogee Grand. The bass was much much better

I have always been baffled how the Diva can have excellent bass with an open panel design (70cm wide) that results in 6dB/octave drop off after (around) 200Hz (not including room loading of course). You can't argue with theory

Anyway the practice is good bass down to about 30Hz. Sure you can get some good lower response but also lots of flap. So I want to take the low end load away from the Divas (and use the sub).

JarreYuri I am impressed by your efforts! How did you find cutting the Al foil and mounting it on the Mylar? And did you use one tuning point or a number over the diaphram?

Cheers
Matthew

I see. Well I have no idea how close the foil is to the magnets on Apogee speakers, so maybee they risk flapping in high volumes.
My speakers have about 5-6 mm space to the magnets and it almost goes without saying that hey are not so efficient. I use ordinary ferrite magnets (for now).

One trick with the aluminium to mylar-mounting is to soap a glas table, roll out the alu-foil, take a rubber scraper and soup and make it flat and nice. Then cut it to Your liking but leave the cut-away strips. Now take some spray-glue and spray evenly over the entire surfice. Take the mylar and stretch it over a padded plywood or similar. Spray the mylar and NOW carefully remove the cut-away strips.
Now You dont have any glue on the glass.
Place the stretched mylar on the pre-glued alu-foil and then remove the paded playwood.
Now take a rubber roller and roll over the mylar to make it get good and even contact with the alu-foil.
Then carefully remove the whole membrane unit from the glass table.

Here is a link to a person I just bought some new treble-ribbons from. He corrugates them very nicely.

http://www.dahlbergaudiodesign.se/del1/del1.htm

[JarreYuri]

PS. Yes, I used multible resonance points to tune the membrane.

[nautilus]

Awesome stuff! Nice link too.

A great place for ribbons is www.apogeeacoustics.com
Graz sells all of the Apogee spares and can do custom jobs. Really nice kit.
I am probably heading off topic for a subwoofer forum so I would be happy to email about the ribbons if you want.
Cheers
Matthew