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Gear / Technical Help => Microphones & Setup => Topic started by: Church-Audio on May 10, 2007, 02:49:51 PM
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I was going to do this a while ago and never got around to sending these pictures up for you guys so here goes..
I have done distortion measurements on the AT-853 Wired 2 wire to a 3.5 mm stereo plug with a voltage input of 9 volts..
The first picture shows a distortion of 10% at an output of -23db at 114db @ 1k..
The second picture is after the 4.7k mod I have come up with it shows a distortion of 0.6% @ 114db at 1k with an output of -35db
I am not selling mods here, I just wanted to show you guys the performance advantage of my mod. If anyone wants me to show you how to do it. I would be more then happy.. I do not charge for the information..
Chris
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So, what is the source of the excitation? I'm assuming it is acoustic and I'm assuming that it's a 1 kHz tone. Was it at the same level each time? If it is, you lost almost 13 dB in sensitivity. That's not a bad thing if you've still got enough signal left to drive the input to your recorder, though.
Your 1 kHz tone is still a little bit better than 70 dB above the noise floor. I wonder if that is the noise floor of the mic or of the tone you generated?
Did you do a plot of silence? (That's hard to do, by the way... It' hard to find a place that is truly silent. Some people do it by drawing a vacuum on the mic in a bell jar. No air = no sound.)
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So, what is the source of the excitation? I'm assuming it is acoustic and I'm assuming that it's a 1 kHz tone. Was it at the same level each time? If it is, you lost almost 13 dB in sensitivity. That's not a bad thing if you've still got enough signal left to drive the input to your recorder, though.
Your 1 kHz tone is still a little bit better than 70 dB above the noise floor. I wonder if that is the noise floor of the mic or of the tone you generated?
Did you do a plot of silence? (That's hard to do, by the way... It' hard to find a place that is truly silent. Some people do it by drawing a vacuum on the mic in a bell jar. No air = no sound.)
I use an ultra low distortion source.. A burrbrown signwave generator block going into a Mylar driver that has been acoustically coupled to the microphone this chamber was designed for this type of work. I have measured the baseline distortion of this driver/sine wave generator at less then 0.002% distortion at 1k at 114db. The residual noise you see on my plot is acoustic noise because the test is not conducted in a chamber..
As for doing noise measurements I have an acoustic chamber I have purchased its still sitting in Texas.. I have to find a way to get it here lol its 175 lbs.. And shipping is going to be $400 I am still looking into cheaper methods to get it here. When I have that the inside SPL level is only 23 db.. When the 75lb door is closed.. :) Then I can do measurements for noise but again I cant really do anything less then 23db. I have a mic with a self noise of 26db So I can confirm the results..
As for the air vacuum it would work if there was a way to make the mic wireless :) with out introducing noise.. The cable will conduct noise from the outside to the mic capsule.. That's a huge problem for vacuum tests. The acoustic chamber that I have sitting in Texas has several audio connectors to "pass the signal" thru the enclosure. So I dont have to worry about the cable transferring the outside noise into my measurement..
Its very hard doing tests on a budget.. :)
As I am sure you are very aware test gear especially the kind you guys have is very expensive.. I am working on getting a standalone Distortion analyzer. Then I want an impedance meter... But I have to wait for that..
This software is very good. As long as you have a very good audio interface the results are very accurate. I can measure up to 24bit at 192khz.. with this software.
Chris
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Sounds good, Chris. I hope having that chamber helps you with your microphone building.
BTW, I just used a pair of your STC-11's for the first time on Wednesday night. I haven't done any critical listening yet, but my first impressioin was favourable. I do want to make a DIN bar for them. I have some idea's, but haven't started working on it yet.
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Sounds good, Chris. I hope having that chamber helps you with your microphone building.
BTW, I just used a pair of your STC-11's for the first time on Wednesday night. I haven't done any critical listening yet, but my first impression was favourable. I do want to make a DIN bar for them. I have some idea's, but haven't started working on it yet.
If you come up with anything let me know I wish I had time to figure that out.. I have a lot of customers that want a simple solution.. I am glad you like your mics..
Thanks Chuck.
Chris