If you want to know how something works...

[Reid Malenfant]

Then buy it & get in there with some test gear (http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=290522288517&ssPageName=STRK:MEWNX:IT) :lolsign:

I don't go buying subwoofers willy nilly, but for years i have been fascinated by how Stahls' Ace Bass subwoofers work. They control cone using electronics ahead of the power amp & a sense resistor for measuring current in series with the driver, effectively it's an amplifier with negative output impedance. Stahl took the concept a good bit further & apparently mass can be added electronically to the driver cone (:scratch:) to get it to reproduce down to silly frequencies with low distortion & at a high level..

We'll see, as this little thing is capable of 100Db @ 30Hz from an 8" driver :eek:

At the end of the day i'll learn something, as to get the gist of this i need some kind of circuit to look at & parameters to play with. I also end up with a nice compact sub that i'll use in my workshop once i get an empty room :eyebrows:

[Jac Hawk]

i was gonna buy that sub, but was a bit put off by the 8" driver, let us know how you get on with it, i'm still of the opinion that to get real low Hz you need a big cone to move the air, but i really would be interested to find out how it performs as a movie sub, if it has the grunt needed to shake your fillings out. As a side note i'm still on the lookout for a Rogers JR Super Woofer, i used to have one and it was awsome.

[Beechwoods]

As a side note i'm still on the lookout for a Rogers JR Super Woofer, i used to have one and it was awsome.

I must admit I'd like to have one of those. I don't particularly feel like I need a sub, but having got 149s as my main speakers, I'd be interested to hear how a paired JR Super Woofer would sound, particularly with dance music, or death metal.

[Reid Malenfant]

i was gonna buy that sub, but was a bit put off by the 8" driver, let us know how you get on with it, i'm still of the opinion that to get real low Hz you need a big cone to move the air, but i really would be interested to find out how it performs as a movie sub, if it has the grunt needed to shake your fillings out. As a side note i'm still on the lookout for a Rogers JR Super Woofer, i used to have one and it was awsome.
:lolsign: You really shouldn't have let the 8" cone put you off Mike ;) I know you probably don't understand what the Ace Bass principle is & i'm sure i'd have been bidding against you if you happened to.

Negative impedance amps can generally only be used with sealed box enclosures because they don't like working with ported speakers (the output would have a huge peak at port resonance). What they do is force the cone to do exactly what it's told to do via negative feedback, so they are fast & accurate. Stahl managed to design the same kind of thing for use with ported enclosures, the bass from this thing will still be very fast & accurate as the amp will be damping the driver more than the port will.

Keeping it accurate along with the vast increase in output that the port allows means this thing can generate 30Hz @ 100Db with very low distortion (take it from me that is remarkable). Admittedly it'll go down to only 28Hz but the thing is only a tad bigger than a 1ft cube. What i want to do is see how each section of this thing works & how it affects the driver (which i'll remove & test the parameters of). I'm hoping i get to understand the thing & be able to design my own :)


I'll keep an eye out for a Rogers JR super woofer for you, & Nick to by the look of it :eyebrows:

[Jac Hawk]

I must admit I'd like to have one of those. I don't particularly feel like I need a sub, but having got 149s as my main speakers, I'd be interested to hear how a paired JR Super Woofer would sound, particularly with dance music, or death metal.

As i remember they came out with 2 variants one of them had a built in amp and the other had it's own seperate amp, i had the latter and had it set up with my kef reference 101's like i said it was awsome, big though, about the size of a large lamp table, christ i think i'm having a moment just thinking about it :eek: