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Old 4th April 2012, 02:32 AM   #41
toobhed is offline toobhed  United States
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I can second uv's opinion. My recently finished MA Alpair7.3 pencils sound great (much better than might be implied from tech stats) from diy bottlehead paramour 2A3 monoblks...
Mario
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Old 4th April 2012, 03:07 AM   #42
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Often we see Diyers complaining about maker's data having run their own independent tests. However, the independent testers too often make the critical error of assuming their test equipment and methodology is to laboratory standard and is free of error.
So how would you explain if someone gets data that clearly resembles that of a manufacturer, such as peerless, and then in the exact conditions and methods finds the data of another manufacturer to be different from the manufacturer's data. And what if this is repeated many times across many manufacturers and among many DIY'er.

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A typical error is the assumption that accurate emittance measurement is possible without the use of adequate anechoic isolation.
Would ground plane, or 5m off the ground be close enough to anechoic to you? Even an anechoic chamber has reflections. Outside though, there is only 1, the ground.
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Old 4th April 2012, 03:33 AM   #43
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Quote:
Originally Posted by tuxedocivic View Post
So how would you explain if someone gets data that clearly resembles that of a manufacturer, such as peerless, and then in the exact conditions and methods finds the data of another manufacturer to be different from the manufacturer's data. And what if this is repeated many times across many manufacturers and among many DIY'er.
If the data we measureis similar to the manufacturers it means that the T/S curves of that driver are close to a horizontal line.

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Old 4th April 2012, 04:23 AM   #44
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I meant frequency response.

I don't trust my impedance and TS measurements worth a hoot. And I don't understand TS parameters all to well.
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Old 4th April 2012, 05:21 AM   #45
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Originally Posted by tuxedocivic View Post
I meant frequency response.
"Move an inch, get a different response..." Ed Schilling

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Old 4th April 2012, 08:25 AM   #46
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Quote:
Originally Posted by tuxedocivic View Post

1 - So how would you explain if someone gets data that clearly resembles that of a manufacturer, such as peerless, and then in the exact conditions and methods finds the data of another manufacturer to be different from the manufacturer's data. And what if this is repeated many times across many manufacturers and among many DIY'er.

2 - Would ground plane, or 5m off the ground be close enough to anechoic to you? Even an anechoic chamber has reflections. Outside though, there is only 1, the ground.
Hi Tux (Guys),
For your first question, I've witnessed factory tests on several competitor makes including the one you mention that don't match. There are many variables that affect test outcomes. From the effectiveness of the anechoic isolation (chamber size and type), accuracy and working range of the mic, accuracy of the calibration, test equipment type and environmental conditions (temperature, humidity and barometric pressure) and so on.

Interestingly, Markaudio has a reasonable record on independent close data. I remembered some of the first independent tests and reviews done in Germany where 2 sets of tests using different equipment gave close results:

Markaudio Alpair 10 - ein Kurzbericht

Japan's MJ magazine did a large scale review of the Alpair 12 and got close results. But there's been a few guys who've got different results from my data, some spending their time complaining to me, or knocking my work down publicly on the net. Usually, those tests that close match mine are anechoic or near anechoic, done by guys who have good knowledge on driver construction, operation and have spent some time getting their test set-ups properly sorted. The point is its a random situation. There's bound to some results that will match and some that won't.

As I've said soooooo mannnnnny times: Until there's a comprehensive universal single standard that all use (pro and amature alike), there will always be variation.

2 - This is a more practical and useful question. For those guys who want to do full-range frequency testing at home (note the words "Full-Range"). Here's my advice: (Tux, note the positions, dimensions and foam isolation requirements):

A - Invest is a decent mic. Don't buy the cheapo mics that cost below US$300. They are fine for general set-up but Not for accurate testing below 50Hz and past 15-kHz. Take a look at the Earthworks measurement series, at the very least, their M23 but this is only good up to 20-kHz. Expect to pay around US$500 for a M23. You'll need the M30 or the M50 is you really want to find out more:

Measurement Series | Earthworks Audio

B - Try to get hold of hardware/software like Linear X V4, DAAS, MLSSA and similar test gear. There's also something available for Mac that Dave (Planet 10 uses - Dave please mention as I can't remember the name).

C - Beg, borrow (or steal) your wife's, granny's, friend's spare room, basement etc. and set about creating an isolation chamber within: see my sketch pic attached (dimensions = Metres).

Regarding the acoustic foam on the floor, you'l need to carefully cut large rectangles, treating them as mats to be lifted and put down during the measurement process. For siting the mic and driver, buy a small laser pen and place in the same clamp as the mic. Aim it directly at the centre of the driver's dust cap. Once aligned, carefully exchange it for the mic. Just 10-mm off alignment will create measurement error so take lots of practice to get it right.

Could be a great collective project for a group of audio buddies. Remember, this is an isolation chamber, unlikely to become anechoic, but at least its a reasonable opportunity to remove the worst of the external variables.

Phew.....I've got to go, its Easter day off and need a rest.

Cheers
Mark.
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File Type: jpg a-chamber1.jpg (192.2 KB, 416 views)

Last edited by markaudio; 4th April 2012 at 08:57 AM.
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Old 4th April 2012, 11:30 AM   #47
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Ah ha! The answer to one of my questions.You use a 1.5m square baffle with the driver centered. I know you know, but neophytes might not -- The shape of the roll-off below 200-300Hz is almost entirely dependent on the baffle. Some manufactures will put a sealed box behind the baffle and that totally changes the shape of the response curve.

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Old 4th April 2012, 12:05 PM   #48
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Quote:
Originally Posted by Bob Brines View Post
Ah ha! The answer to one of my questions.You use a 1.5m square baffle with the driver centered. I know you know, but neophytes might not -- The shape of the roll-off below 200-300Hz is almost entirely dependent on the baffle. Some manufactures will put a sealed box behind the baffle and that totally changes the shape of the response curve.

Bob
Hi Bob,
Actually, we use large volume sealed box with interchangeable front mounts. Best I take some pics when time permits. I'm flat out busy at the moment.

Given that I'm suggesting a simple DIY isolation arrangement as possible, a large sealed test box needs +1 metre clearance around it, so will increase the size of the isolation chamber.

Cheers
Mark.

Last edited by markaudio; 4th April 2012 at 12:12 PM.
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Old 4th April 2012, 04:10 PM   #49
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"Move an inch, get a different response..." Ed Schilling

dave

we still talking measuring drivers?
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Old 4th April 2012, 04:14 PM   #50
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Dave: 1inch would maybe change the response by less than 1db.

Mark: thanks for the feedback. I've coveted an ACO Pacific mic for a while and would love an earthworks m30. Pricey though. I suppose I'm only interested in 200 to 10,000hz. For this I go outside and use a gated impulse response. I am able to replicate many spec sheets to within a couple db (considering baffle effects), consistently. This is good enough for a DIYer. Thanks for the professional feedback.

I think Bob meant below the baffle effects there will be baffle step losses. You don't use an IB?

Sorry to derail a good thread. If there is interest I wouldn't mind a separate thread on this. I love measuring more than building Nice to have feedback from a manufacturer.
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