ABR tip for speaker builders!

[walpurgis]

Hi all, if you fancy using an ABR (auxiliary bass radiator) in one of your speaker projects, remember that you can use an ordinary bass drive unit for this function (with a suitably low natural resonance) and this has two big advantages. Firstly bass units are easier to obtain and also, if you put a capacitor across the terminals of your proposed driver it becomes resistive at higher frequencies due to the reaction of the motor assembly (coil/magnet) and will actually fight against resonating at higher bass and midrange frequencies, thereby keeping colourations down. You would have to experiment with capacitor values. Geoff.

[nat8808]

I like the capacitor tip.

Could the generated current be tapped into to say charge your mobile? More bass = more the phone charges...

[walpurgis]

Yes, I'm sure you could eventually charge a mobile. Good tip, I should have thought of that. Maybe you could even feed the power back to your amplifier and have a self perpetuating Hi-Fi?

I suppose you could also have a bit of fun seeing if there's enough energy to drive an LED or two and mount them on the front panel of the speaker! Geoff.

[nat8808]

Hehe - like some kind of bass energy metre.

[Reid Malenfant]

Getting away from some of the daftness :eyebrows:

You can also tune a bass driver used as an ABR by adding mass to the cone to lower the tuning frequency. If you are going to do this while keeping the magnet assembly in place it's best to distribute the added mass evenly around the cone.

The capacitor idea is pretty good, you can also add damping to the driver by using a low value resistor across the voicecoil terminals ;)

[walpurgis]

Yes, the added mass idea is employed on a number of ABRs which were derived from regular bass drivers. There is a mass ring in the rear of the KEF BD200 ABR I have (which I've been trying so far unsuccessfully, to flog on eBay for a while). If I recall, something similar was used on the BD139. Another more complicated trick is to use two ABRs, one behind the other. This causes the main driver/cabinet system to think it 'sees' an ABR of greater mass and lower resonance, not sure its worth the extra work though. Might be worthwhile in a semi-isobaric design with a second main driver inside the cabinet part of the way down from the front driver. The lower resonance of the paired ABRs could help combat the compromised cabinet volume.

I do love messing about with speaker designs. Here's another, a distributed port transmission line. Never seen anybody build one. A characteristic of transmission line cabinet systems is a response 'hump' around the port resonance frequency. Some IMFs had this amongst others, that's why they gave that initially impressive but rather unrealistic deep bass thump. But, if as well as the main port you include a few smaller ports of decreasing size going back up the acoustic line from the main port, energy starts being dissipated earlier and is spread over a wider range of the lower bass, reducing the more obvious main port output and creating a more balanced bass output. I thought this one up myself donkeys years ago (I'm sure it has occured to other people) and have to admit I haven't built one, but the physical principals say it has to work.

A design you do see, but as far as I'm aware only on PA and Disco production speakers, is the large flare coupled reflex. I have built these and it works well. It looks like a cabinet with a horn mouth, but is basically a Hemholtz design, coupled to the room with a flare or horn mouth. It certainly gives tight bass.

[nat8808]

The whole "suck it and see" speaker experimentation is interesting to me - just a shame I don't have the time or space to do anything..