Topic: AT 853 2 wire distortion tests..

[Church-Audio]

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

[SparkE!]

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.)

[Church-Audio]

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

[Chuck]

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.

[Church-Audio]

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