diyAudio reference speaker project

Hi guys,

Here's my versions of Rabbitz' speakers (with no veneer as yet).

An externally hosted image should be here but it was not working when we last tested it.


They're made from 16mm MDF, with 4mm deep rebates in the top, bottom, and side. It's probably excessive complexity, but it makes them really well sealed.

An externally hosted image should be here but it was not working when we last tested it.


I put a 16mm radius on the front sides, mainly because I thought it looked nice. They're wonderfully dense little speakers - each one weighs about 5kg. It's been a blast playing with my router.

Now I get to play with crossovers :)

Cheers,

Suzy
 
Hello,

Of course I would advise that you, just as I did, try the several crossovers posted in this threat. But if you are looking to the best result I think you will also find the AR series crossover to sound best.

Try to use the best components that you can affort. As I understood the small coil in parallel to the tweeter needs to be very good quality (I use a copperfoil coil). For the big coil in series with the woofer you also need a good one (I used a 2.0mm2 coil wounded with a wire that consists out out 7 seperate wires).

I am not sure how important the capacitor is. A very good one of 22uF will cost serious money. I used a 22uF 400V MKP first but now I have added a 4.7uF 800V and 0.1uF 1200V in parallel. This gives a little smoother sound in my opinion. Here is my crossover (I know it looks a bit messy but it is difficult to get the components in and solder true the small woofer cutout):

http://img76.imageshack.us/img76/7360/pa260058hq0.jpg

Best regards,

Walt
 
I'll certainly try a few different crossovers. Probably a 4.7uF cap for starters, and the AR series crossover. I've also been thinking about a simple 12dB/octave parallel crossover (a simplification of the Esquire crossover) with 4.7mH inductors and 6.8uF caps, and the tweeter padded out a tad to account for its higher efficiency and lower impedance, using a 22Ohm resistor across the tweeter, with a 3.3Ohm resistor in series.

I'm a little leery of using really huge low resistance inductors. The woofer Re is 5.7Ohms. Surely once you get down to a few hundred milliohms you're not going to see any difference (except perhaps for reducing the enclosure volume with an enormous inductor).

Cheers,

Suzy
 
AR Crossover

I've been simulating different crossovers with LTspice (using a 6Ohm resistor to approximate the tweeter and an 8Ohm resistor to simulate the woofer).

The AR series crossover gives a surprisingly low crossover point of around 800Hz. Is this deliberate? The Esquire has a crossover point of 3KHz.

Anyway, I halved the value of the inductors and capacitors, and came up with L1=0.68mH, L2=0.047mH, C1=10uF, and R1=6R8, and increased the crossover point to 1600Hz.

It's certainly a very kind crossover on amplifiers, as the minimum impedance is 8 Ohms, rising to 10 at high frequencies. The parallel crossover has a dip at the crossover point to about 4R5.

Cheers,

Suzy
 
Hi Suzy, nice work on the speakers. Keep the x-overs simple. Start at the half way point of the 3db down points of both drivers, and start with 6db/octave.
Somewhere I recently saw a novel idea for the hi-pass where attenuation is required. A series resistor to match sensitivity, and a shunt inductor to control the 3db down point of the tweeter. The shunt inductor should dampen the lower resonance of the tweeter.

BTW. The ETI477 fired up OK. Iq a bit high, heatsinks went to 80 odd degrees in 20 minutes!

Geoff.
 
Hello,

I am not sure about the crossover frequency of the AR crossover but with this filter the tweeter seems less stressed than with the single 4.7uF capacitor.

Did you use the measured impedance graph of both tweeter and woofer in your simulation? (Obviously using the DC resistance will give a wrong result)

As mentioned on the AR website the small parallel coil should almost always be 0.11mH for Vifa and Scan Speak tweeters. I did an RTA measurement and the AR crossover measured very flat both on axis and off axis.

Best regards,

Walt
 
Re: AR Crossover

suzyj said:
The AR series crossover gives a surprisingly low crossover point of around 800Hz. Is this deliberate? The Esquire has a crossover point of 3KHz

The AR xo crosses over at about 3400Hz.

You can't use the nominal impedance when working out the xo point and the impedance of the woofer and tweeter are around 15R and 5R3 respectively at the xo point. Series xo's need a low DCR in the inductor (protects the tweeter) and as a general rule it should be less than 5% of the driver's Re in any type of xo, series or parallel (Thiele's reasoning).

Have a look at the AR xo page for some background on this type of xo and Andy G's info on series xo's.

Contour
Great to hear some feedback on the crossovers you tried and IMO the AR does have the edge as you reported.
 
Just a tad of damping material on the back, top and bottom. Long haired wool is the best if you can find it but the stuff from Jaycar is what I use and I split it to half thickness.... about 20mm thick.

It's odd that in Australia that has more sheep than people, it's hard to find long haired wool.
 
Long haired wool. Have you tried craft shops? Wool spinners often go for a double fleece.

None of the synthetics seem to do the job. Prior to tontine, we used a fluffy cotton based stuff. I have asked a few friends what it was called, they remember the material, but no name has come forth.

Rockwool was good, but that was replaced with fibreglass.

Cheers