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Old 30th November 2003, 08:10 PM   #1
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Default Speaker Workshop + Microphone = invaluable

I hadn't taken any measurements using a mic and Speaker Workshop before because I didn't think there was any point until I got a decent mic. Man was I wrong!!!

I've only got a cheap and nasty computer mic, specs something like 80Hz - 10Khz +- 3db, but curiousity got the better of me yesterday and I decided to do some crude measurements.

To my surprise I discovered that my Mids were wired up out of phase!!! I'd been unhappy with the sound since I put them back in (they'ed been replaced with cheap polycones for a while since I thought I'd cooked them). I put it down to the fact that they were partially cooked, but they still sounded better than the polycones so I decided to live with it.

I reversed the wiring and they sound heaps better, pretty much managed to remove that somewhat nasal sound from peoples voices. Now I want to get a decent mic, and a mic preamp so I can do some proper testing, esp once I start work on my new set of speakers!

I've attached the plots. Don't pay too much attention to the relative level below 500 Hz, this is partially due to the position of the mic when doing the test (about 30 cm from mid and tweet), although the dip from 200Hz to 500Hz does indicate a problem with my box tuning (probably due to leaks). I'm unsure whether teh 5Khz peak is in the mic response or the tweeter, but for now I'm happy that I identified a major problem and my speakers now sound better for it.

The plots are 1/3 octave smoothed.

Regards,

Tony.
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Old 1st December 2003, 07:53 AM   #2
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The dip at 500hz is probably from baffle step.
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Old 1st December 2003, 11:11 AM   #3
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Hadn't thought of that, but I think with the width of the baffle (49cm) that it would be lower than that.

The mike is pretty dodgy, so it could be mic response too, and I haven't done any amp response tests either.

Here is a nearfield plot of the woofer no XO (well its a bit dodgy actually as only one of the leads to the XO was disconnected and I was running another lead from the amp in through one of the vents) Hey I was just trying to get an idea whether the 500Hz dip was XO related or maybe the box. Published specs of the Vifa M26WR-09-08 do show a slight dip from 200 to 500 Hz but nowhere near this dramatic. Looked a bit like some of the response curves I modeled when the tuning was off.

Once again, I'm not sure of the mic, the modeled -3db point for this speaker was around 36Hz, this plot is nowhere near it (more like 57Hz). I'm not going to read too much into it until I can get myself a panasonic electret and fully calibrate speaker workshop with my new Audigy 2 ZS.

I just thought it was cool that it was so obvious that the mids were out of phase, from looking at the first plot....... I never would have picked it by ear! (well maybe I would now, but.....)

My mic placement for the plot below (about 2 cm from the dust cap) was probably dodgy as well, All part of the fun though

edit: Oh and it doesn't help that the mid shouldn't be crossed as low as 500Hz either

Regards,

Tony.
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Old 1st December 2003, 11:43 AM   #4
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Yea with a 49cm baffle it would be lower than 500hz, hmm, have you got a spare peice of wood to temporally mount the woofer in, open baffle style?

I've found that good to get a "reference" response out of the driver, since they tend to give the flattest response (above the baffle step rise of course, use a big baffle) like that and you can tell if baffle step or enclosure colouration is causing problems when you mount the driver in a "normal" enclosure.
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Old 1st December 2003, 12:03 PM   #5
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Thanks for the tip, I'll have to try that when I get to the point of making some new cabinets for the woofers. The existing boxes are atrocious! It would be interesting to see just how much they are colouring the sound, and how much better the new enclosures are. A reference response would be very usefull.

I think I may have to resort to buying a mic from OS. Shipping should be next to nothing for something that small.

I haven't got any large bits of wood at the moment, but I'm sure if I was carefull, I could use a sheet of MDF which I was intending to make into cabinets , just have to measure real carefully!!!!

Either that or cut a hole in a wall

Regards,

Tony.
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Old 3rd December 2003, 04:49 AM   #6
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wm-60 from digikey.com

cheap and good

Some are skeptical of its capabilities,however many people reccomend it for value for money.

plugs into an RS spl meter ,or perhaps make own circuit.
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Old 3rd December 2003, 11:25 AM   #7
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I submitted a form on their web site last night asking what the shipping cost would be for 5 of the WM60AY's.

The cheapest international shipping they have listed is $18US for up to one lb, I'm sure it wouldn't be more than that. It's kind of ironic that 5 mic's costs about $13.50US, shipping is $18US handling is $5US and international extra handling is $6US! so my original $13.50 becomes probably about $42.50US, or about $58 Aus. Still ME were selling the lesser WM60AT's for $10AUS each with $8 for shipping so that's pretty much exactly the same cost

Maybe I should get 10! at least then the unit price would come down a bit, and maybe I could flog some off on ebay

Regards,

Tony.
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Old 3rd December 2003, 11:31 AM   #8
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heaps of ppl i know cant get speaker workshop to work properly....i may use it nextyear.

I know 2guys whove used it, at PI forum ..
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Old 3rd December 2003, 11:51 AM   #9
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I was getting wildly varying results with it at first, but once I made a proper jig, and started running it from my amp, rather than directly off the sound card (original SB 16 at the time), I started getting more consistency.

It's been quite a while since I used it for measuring T/S params (probably close to two years at a guess) but I think (from memory) one of the keys was to get the output levels right (which was why the amp helped).... too low and it was all over the shop, and same if it was too high. Just required some patience and multiple test runs. I think also one of the tricks was to up the sample size to the max (It basically sends a much longer pulse if you do).

Unfortunately I had a HD crash and didn't have a backup of my SW files (although I do have printouts). The stupid thing was, that the files were still there, I just forgot to back them up before I sent the drive away, as they were in the SW dir and not my data dir, doh....

The last tests I did were with a TB montego II (which doesn't like my new computer) so I went and bought a creative labs Audigy 2 ZS. This sound card has seriously good specs, and when I tested it with RMAA 5.1 it lived up to those specs! I'm hoping it should give me some very accurate measurments.

Regards,

Tony.
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Old 3rd December 2003, 11:58 AM   #10
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I also use Speaker Workshop - works very well. Also use WM60 mic mounted in long tube - my unit had a calibration file from ME Technologies as part of the IMP analysing system (unfortunately ME are no longer running - auction of all equipment on 7th December).

I do recommend the Wallin jig and mic preamp linked from Speaker Workshop site - I built my jig into a drive bay panel on my PC and built the preamp into a gutted dynamic mic case, which the measuring wand plugs into.

Haven't been able to find an Australian supplier of the mic capsule....

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