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View Full Version : Calibrator Adapter for SIA/EAW RTA-410 Mic?



Arthur Skudra
May 27th, 2008, 07:08 PM
Anyone know of any sources of calibrator adapters for the SIA/EAW RTA-420 measurement microphone? 3/8" is pretty hard to find! Maybe I should get myself a Taig lathe and turn my own? Another tool for my workshop that I can write off! Yay! :)

Harry Brill Jr.
May 28th, 2008, 09:04 PM
I plan to make my own.

I'll use my drill press to get the inside diameter. I'll mount it on a mandrill and shave the outside down to size. Shouldn't be too hard.

I just picked up (on your advice) an OLD calibrator (when I say old, I mean it looks like it's at least 30 years old) on ebay. It should get me by until I can get something smaller. I really like the size of the B&K unit. It only does 114dB, so I need to figure out how to pad it down to 94dB so I can use it for RF packs. It accepts 1" and 1/2" so I need to get an adaptor for my M30 and make something for the SIA mic.

Arthur Skudra
May 28th, 2008, 10:14 PM
Hey Harry,

You might inquire of Earthworks, several years ago I sent my calibrator to them, and they custom milled the adapter for me to fit my M30, complete with inner o-ring for an airtight seal. My Simpson calibrator needs an adapter just shy of 15/16" to fit, so 1" adapters won't work! Back then it cost me in the neighborhood of $75. I don't know how kind they would be to mill an adapter to fit my 3/8" SIA mics though...

Arthur

Harry Brill Jr.
May 29th, 2008, 10:09 PM
I think I can use an off the shelf earthworks adaptor for both. One just need to be drilled out to 3/8". My calibrator does 1" and 1/2" We'll see how well it works when it gets here.

Calvert Dayton
June 2nd, 2008, 09:13 PM
The thing is, there's an O-ring inside the cavity in the calibrator cup to make an airtight seal -- it has to have an airtight seal to work properly. So in addition to enlarging the cavity in the adapter, you would also need to cut a channel inside the opening and fit a new, larger O-ring. That would be a pretty daunting undertaking without the proper tools. Have you considered building up the diameter of the microphone tube instead? You might be able to find a piece of plastic tubing to slip over the end of the mic that would give you a snug fit in a standard 1/2" calibrator cavity.

BTW, I also have a hand turned 1/4"-to-1" adapter cup somewhere that the guys at Earthworks whipped up for us out of billet stock, once upon a time when the earth was young. I keep it around for sentimental value, because it's the single most expensive piece of plastic I have ever been a party to purchasing. I vividly recall that we paid them almost $100 for the thing (in 1998 dollars), which is more than we're going to be selling the RTA-420 microphone for (in 2008 dollars) once the store goes live. I kind of doubt Earthworks does much of that sort of thing anymore in any case.

Harry Brill Jr.
June 2nd, 2008, 10:33 PM
I will be including an O Ring. It won't be that hard. I have a drill press. I figure if I cut it at the right spot, then cut a 1/4 groove in each half, then glue it back together I'll have the space I need for the O Ring. It will be plastic. I can't really work with anything else unless it's wood which I suspect would not last.

Calvert Dayton
June 3rd, 2008, 01:18 AM
Sounds like quite a project. I think I'll just take my 420 to the hardware store though, and see if I can find myself about a one inch length of plastic tubing with an inside diameter around 3/8" (10 mm if you want to be picky) and approximately 1/16" wall thickness. I wouldn't be too surprised if such a thing does in fact exist.

Harry Brill Jr.
June 3rd, 2008, 04:23 PM
Sounds like quite a project. I think I'll just take my 420 to the hardware store though, and see if I can find myself about a one inch length of plastic tubing with an inside diameter around 3/8" (10 mm if you want to be picky) and approximately 1/16" wall thickness. I wouldn't be too surprised if such a thing does in fact exist.

Yep I just did that. It will at the very least be a good temporary fix. The issue at hand is no stop edge on the other end, and it's a real tight fit. Not exactly convenient, but it'l get me through the next couple weeks.

Calvert Dayton
June 5th, 2008, 09:23 AM
Oh cool. Any old port in a storm, as they say. I'll keep a lookout though. There are about a bajillion kinds of plastic tubing in the world. I wouldn't give up on finding a perfect fit and if one did, the stop on the calibrator cup ought to work well enough. I don't see why you couldn't come right up flush with the end of the mic with your sleeve since even if there are openings on the side of the capsule, that part is typically covered during calibration anyway.

kwindrem
August 19th, 2008, 01:03 PM
+1 for needing a low cost calibrator. The Galaxy CM-C200 appears to come with 1/2" and 1/4" adapters. Maybe Rational Acoustics can make a deal with Galaxy for the proper adapters for the mics in the store???

Bob Hulme
August 19th, 2008, 07:55 PM
The thing is, there's an O-ring inside the cavity in the calibrator cup to make an airtight seal -- it has to have an airtight seal to work properly. So in addition to enlarging the cavity in the adapter, you would also need to cut a channel inside the opening and fit a new, larger O-ring. That would be a pretty daunting undertaking without the proper tools. Have you considered building up the diameter of the microphone tube instead? You might be able to find a piece of plastic tubing to slip over the end of the mic that would give you a snug fit in a standard 1/2" calibrator cavity.

BTW, I also have a hand turned 1/4"-to-1" adapter cup somewhere that the guys at Earthworks whipped up for us out of billet stock, once upon a time when the earth was young. I keep it around for sentimental value, because it's the single most expensive piece of plastic I have ever been a party to purchasing. I vividly recall that we paid them almost $100 for the thing (in 1998 dollars), which is more than we're going to be selling the RTA-420 microphone for (in 2008 dollars) once the store goes live. I kind of doubt Earthworks does much of that sort of thing anymore in any case.

Has anyone thought about checking out the cost at a machine shop? One would no doubt be quite a bit but if you needed a bunch the cost would come down a lot because of setup time.

Just a thought, Bob H

Michael Häck
August 24th, 2008, 11:01 AM
Hi to everybody,

I found out a german company which sells a calibrator and additionals adapters from 1" to 1/4" and also a custom made model:

http://www.content.ibf-acoustic.com

I also found a very helpfull shock mounted Microphonclamp from Sennheiser which is called MZS6 for 35,00€.

Best regards

Michael Häck