Speaker Rescue!


The AWA Omnidirectionals

I didn't know AWA had ever built speakers like this! I suspect it was a very limited run. They were once a major electronics company and supplied a lot of radio equipment to the Defence Forces. I was once involved in Navy supply work, and the Naval Transmitting Stations back then used a lot of AWA transmitters, up to about 40kw!

Having seen them advertised on ebay, and being rather interested in omni-directionals, I had to get them whatever the cost: big spender - anything up to $50. As luck would have it I did get them for $50, although there have been further outlays (entirely to be expected) so the initial price was about right. I reasoned that I couldn't put together the fairly complicated cabinets for that cost, so even if all the drivers were rubbish, I could move on from there and make something of them.

Description: three-way design, with a downward firing woofer, five midranges in the top cabinet section (2 forward, one each side, one rear) and a tweeter mounted firing downwards onto a conical disperser, the HF then being channelled in all directions via the gap between the upper and lower cabinets.

Initial listening suggested many of the faults of old speakers were present. Boomy bass, backward midrange, lack of top detail. One tweeter was dead - then later I found that actually both tweeters (Foster Horn loaded models) were dead and I'd been hearing treble output from the oval midranges, (which are paper cones with AlniCo magnets) and not the tweeters at all.

The Foster 8" bass drivers suffered from old treated cloth roll surrounds which had firmed up, limiting their overall reach and speed. They had to go. A pity, as they would have been quite nice woofers in their day.

The major leap that I had to make in the process was to ditch entirely the rather elaborate crossovers. These featured two large inductors, two volume controls, and assorted capacitors. Experience has shown that the simpler the crossovers the better the results.

As well as finding replacement tweeters that fitted the place (tucked under the top chamber, firing downwards, and ideally around 105mm in diameter) I decided to try the Foster SLE 8" woofers I had left over from another project. These are an unusual construction, having no roll surround at all, just a small air gap. The cone is located by a double spider. The intention of this design is to add speed of response and longer throw - SLE = Super Long Excursions. I used another pair in an otherwise more conventional floor speaker - all forward firing drivers - to good effect, and they are the right size for the job.

While I had the various sections of the cabinets apart I took the opportunity to respray the black surfaces, which had become dusty-looking and spotty here and there, generally dull. For the moment I've used some rubber feet under the boxes, but may install spikes later. The veneers are in quite good condition for speakers that must be around 40 years old.

Once the woofers were in, together with two new paper cone tweeters - selected over new horn-loaded ones for the characteristics of (a) efficiency, (b) frequency range, and (c) wider dispersion - I could settle the design of the crossover.

Keep it as simple as possible is a good rule. New binding posts were installed as a first step in the rewiring. If I could get away with one small inductor and two capacitors, I would. But an issue arose with an overly forward midrange, which was coming on so strong that the other sections couldn't get a look in. That old crossover network with its two volume pots and two large coils would have been about matching volumes and possibly also impedances. I had to decide whether to control the midrange with a potentiometer or just resistors. The latter won out, and a good balance was achieved. What remains to be done is to do some extended listeing and fine tuning to achieve a result I can say does everything well.

At the time of tweeter testing I'd say that they did classical very well indeed and Jazz during the tweeter trials (forward firing - picture below) was great, bass not really where I wanted it. Now with the tweeters installed properly in the down-firing spot, the choice of amplifier has become important. Too weak (i.e. the B terminals off a surround reciver, even in two channel mode!) and the system loses the immediacy and the bass that it can achieve. Even so, a fairly everyday Yamaha AX-396 integrated ran them reasonably well during testing. They have improved out of sight as better amps were hooked up. Currently running the Yamaha MX-830 but will give the Accuphase E-303 a go soon.

I can say right now that it has been a most interesting and rewarding project, breathing new life into a pair of speakers that might not have found a new home with anyone, due partly to their size and looks (not the most wife-friendly), and to the sound, which did need a lot of overhaul. This one falls somewhere between a simple rescue and a complete rebuild. More like some organ transplants!

My wife Barbara reckons that without their grilles on the front, these speakers look like Owls! She has a point. See picture below!

Dimensions: 865x445x370mm (hwd), weight 27kg each. Impedance: 8 ohms at rest. Efficiency: I'm guessing around 91dB or a bit higher - they are run easily by the Yamaha AX-396, but sounding much better with the higher powered Yamaha MX-830. Frequency response: some audible output at 25Hz, bit of a dip at present at 40Hz, back strong at 50Hz, and with this tweeter probably only up to 13kHz at the top end. Midrange is excellent.

Adding photos below:

Would have interspersed these through the text but they were playing up so I opted for the simpler remedy!