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Post Number: 55
Registered: 2-2004
| | Posted on Saturday, September 22, 2007 - 7:24 pm: | 
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Reducing the Sensitivity of the Astatic D-104 Desk Microphone Without losing Audio Quality.
An Article Written
By
Penrider ~ Sean
CEF#867 ~ CVC#081
I own 3 different D-104 desk microphones, and have used nearly every other model they made.
They all have the same things in common ~ extremely loud and clear audio, and entirely too Sensitive to background noises.
The one I am using now is a D-104 T-UG8 4-wire, I also have a Silver Eagle and a Night Eagle.
The T-UG8 is so sensitive; it can pick up my wife and kids talking downstairs!
The two newer ones are even more sensitive! I have tried to adjust the mic gain on the radio and on the microphone in every combination I can think of. If I turn either one or both down enough to not pick up so much background noise, I lose a serious amount of modulation. It will not achieve 100% modulation, even while speaking into it like a hand mike, without picking up every other sound in the room.
The normal answer to this would be, Use a Different type of microphone. I have a Turner +3, a Galaxy Echomax 2000, and a Workman Mini Mic.
The Turner is an ongoing repair/restoration project, the Echomax goes through batteries very quickly, and the Workman doesn't have very good audio quality. And, to tell the truth, I just plain like Lollipops!
I have heard of and read many different ways to fix this problem. Most involve minor to major electrical modifications. Some even involve replacing the element or the amplifier circuit. If we do these things, it will no longer be a D-104! This wouldn't matter very much if the D-104 weren’t a Collector's Item! So, I felt it important to find a way to fix the problem without major modification.
Now, let's examine how this microphone is constructed.
It has a 2 1/4" x 1/2" element. That is huge for a microphone.
The element is encased in a steel head with a steel grille cover. Steel Absorbs sound waves many times better than plastic. so, how do we reduce the amount of incoming sound waves without reducing audio volume or sound quality?
Simple, we find a way to limit where the sound waves enter the element.
In stock form, the element picks up sound waves from all four directions.
The front is just louder and clearer. so we find a way to force the element to only pick up sound waves from the front grille.
If we disassemble the head of the microphone itself you will notice a few things.
The element floats in the head via a couple of pieces of foam. There is one layer of thin foam on the back cover to protect the wiring on the element. There is about 1/4" of fiberglass insulation plus a very thin layer of felt over the front of the element.
I have even seen a couple of heads that the element rattles around inside the head!
Now, to remedy this situation I cut a piece of 1/8" thick solid rubber (car floor mat) to fit the back cover and glued it on.
Then, I cut a one-piece ring of 1/2" solid rubber (boot heel material) to fit the element snugly centered in the head without glue.
I used solid rubber for these pieces to block sound waves entirely from the back and side edges.
Now we want the front of the element to pick up sound waves without being muffled.
For this I used Craft Felt. It will take up the space in the head without blocking sound waves.
I cut pieces of this felt to fit the front grill and fitted enough of these pieces over top of the stock insulation just to take up the space in the head.
These minor modifications do not harm the microphone in any way, and cannot be seen.
Results:
My T-UG8 is now much less sensitive to background noises.
When set for 100% modulation with 110% peak, it still will pick up a loud voice in the shack.
But, no more voices from other rooms and it no longer picks up the computer fans and floor fan.
So far all reports say it still sounds loud and clear with no reports of muffled audio.
I very strongly believe that limiting the audio pickup to the front grille only is what greatly reduced the sensitivity of the microphone.
These are my observations and results on my rigs in my shack.
If any of you that read this have any other ideas or experiences, please post them. This is, was, and will be a learning experience.
Respectfully Submitted,
Sean
Penrider
CEF#867 ~ CVC#081 |
