Re-Jigging the jig: Speaker testing device for Arta, Speaker Workshop & HOLMImpulse

[MJL21193]

Ok, I'm back in business. I just bought the motherboard on Ebay. $41.00 for the board (INTEL 815 D815EEA), it comes with a spare CPU (733MHZ) and 384 MB of ram PLUS a 128 MB ATI Radeon video card.
Not a bad deal, IF it works

[anatech]

Hi John,
Best of luck on that. If it works, you'll be just fine.

That 'scope I'm using is the DSO-2150 USB. Newer software for it will probably fix the only things that bug me about it. Overall, it's pretty nifty.

The only problem with using a sound card is the high frequency limitations. You might be able to get up to 96 KHz with a really nice card. My EMU1212 just came and I haven't even had a chance to test it yet. The SoundBlaster X-FI Music Extreme will run 24 bit at 96 KHz, which is excellent for a sound ard. One of the few Soundblaster products that doesn't resample (That I know of). I have tried others and always end up with a filter just over 20 KHz. Next to useless!

-Chris

[Vikash]

I've had a case and parts ready with intention of merging the jig/amp/mic preamp into an all-in-one jobby for well over a year now - but still little progress.

Good to see some people getting on with it

Originally posted by pinkmouse
My mic pre is the kit that Vikash sells, AFAIK, it's not disimilar to the Wallin one

More than not dissimilar, it's exactly Eric Wallin's design. The new revised PCB's should be here soon if you're up for testing one?

I'll be using a lm3875 for the amp. Thinking aloud, perhaps using 2-3 attenuator switches for output @2.83v. I use a EMU0404 USB which has external gain/attenuator controls which I always leave fixed for measuring.

David, could you expand on how you've done the "spectrum analyser function for measuring the frequency response of active crossovers and the like...."

V

[djarchow]

Back when LoudspeakerLab was a viable product, it came with a combination mic preamp/impedance bridge/amplifier so that you could do your impedance measurements without needing a seperate amplifier. The concept was great, however reliability of the units was not so great with mine dying three times before I gave up on it and got a mic preamp from Phil Bamberg/BESL.

Regards,

Dennis

[pinkmouse]

Originally posted by Vikash
The new revised PCB's should be here soon if you're up for testing one?

Time, time, time - I never have enough of it these days, but I might be able to fit it in somewhere!

I thought about using gain setting switches, but ended up using a pot just to get going, otherwise I would still be dithering around. Maybe MkII.

[pinkmouse]

Oh, and now I just need to design a folding 1m square test baffle, adjustable to fit any driver cutout.

[daatkins]

The rotary switches are the best choice or extra functionality.

Two rotary switches certainly make the jig easy to use but they're not really suitable for switching high currents (like the driver test signal) or delicate signals (like the mic feedback signal). The redesign that I'm working on will have the rotary switches control relays in a couple of these situations.

could you expand on how you've done the "spectrum analyser function

I wish I could claim genius on my part but it's really simple! Look at the schematic I posted on the first page: the top switch position of SW2A connects the soundcard output to the active crossover input via J4 (and back to the S/C reference input) and the soundcard measurement input connects to the XO output via J5. In SpeakerWorkshop, create a new driver and simply do a nearfield frequency response measurement. I've only used SW for this but the same trick will almost certainly work with ARTA. The attached pic shows three unsmoothed filter responses for my sub XO: 20Hz high pass filter, a Linkwitz transform and the result of both circuits in series.

Using SW does not give real-time results as you need to wait for acquisition of the MLS signal and additional processing time but SpectraLAB from http://www.soundtechnology.com gives immediate results.

Nice one,
David.

[BlueWizard]

Don't mean to offend, but there is a section of the original schematic that doesn't quite make sense to me, so I revised it.

Please confirm that the attached drawing is correct.

If I am wrong the please ignore this drawing. But at the same time, do explain the purpose of this section of the circuit and the R4/R5 voltage divider that seems to do nothing.

Again, if I'm way off base, then just ignore this.

Steve/bluewizard

[MJL21193]

Hi Steve,

Voltage divider R4 and R5 form the "voltage probe" for input to the left channel during frequency response testing. It samples the full signal that goes from the amp to the speaker (BP1_2).

The changes made would route the amps output through R4 to the speaker - not good.


I have been working on a board layout that will consolidate the jig, amp and preamp on one board. I'll post details when it's done.

[y8s]

This is an inspiring thread. I have a few 3886 chips floating around and was looking to rebuild my soundeasy jig. Project time!