# My Micro Acoustic FRM 1A Spruce up project



## fdrahuse (Oct 30, 2014)

I am starting this thread to document the restoration, tweaking, improving etc. of my old speakers from the past as a nostalgia project. I want to keep the feel and character of these speakers, but make them more enjoyable to listen to. I will post pictures after my five posts are done. 

These speakers feature a 10" woofer, sealed box, and a five tweeter array. When I first bought these back in the seventies, They just seamed to sound better than the brand names I "knew" should be better.

I think these are a good project, because you will not see a two way acoustic suspension system with a five tweeter array ever produced again. And they bring back good memories for me. Many hours spent listening to my old pair.

So, I will update as I go along. Any comments or help from the peanut gallery appreciated.

First problem I have is the center tweeter on both units are blown. Due to the unusual wiring, I am not sure if these center tweeters were 8 ohm like the side tweeters. If anyone knows something about these, your input would be appreciated. I am going to design a new crossover around the existing drivers and a new pair of center tweeters anyways, but it would be nice to know the original design.


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## fdrahuse (Oct 30, 2014)

Since I need new center tweeters, I went shopping. So far the Tang Band 28-847SD Shielded Neodymium Dome Tweeter at Parts Express seems to be a good choice. The space available is constricted and I wanted a tweeter that could be crossed over lower than may current set up, and this is the best for the money so far.


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## fdrahuse (Oct 30, 2014)

Here is an picture of what I am working on


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## fdrahuse (Oct 30, 2014)

Replacing this crossover with a much more developed one. And getting adjustable L-pads to replace potentiometers and keeping the design flavor the same.


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## fdrahuse (Oct 30, 2014)

Got my order from Parts express. Two new tweeters some coils and caps to experiment with. Also order from Tayda Electronics. They have very good prices and cheap shipping. Bought some caps to replace in my Nikko receiver.


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## fdrahuse (Oct 30, 2014)

Also ordered a meter to measure capacitance from China (ebay). $12.00 including shipping. Just curious if it works. Will test my new caps against what is currently in my system.


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## fdrahuse (Oct 30, 2014)

Bought a three pack of magnet wire from radioshack for 9 bucks. Its a little thin but good for notch filter coils. The spools seem the right size for forms. 
Will start making my impedance test board today. I will try too post pictures.
I also ordered sockets for 3.5 mm plugs for laptop mic and headphone jack on laptop (from Tayda electronics) 
This should be easier to make the REW set up for testing impedance since the sockets have the signal broken out in laug and I don't have to try and make a custom plug. Just plug a male/male cord from laptop to socket. Not quite clear on the schematic REW shows for the circuit. They have left and right outputs shown only. I guess ground is not used from the soundcard and headphone jack.


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## fdrahuse (Oct 30, 2014)

Received the cheap capacitor meter. Works good. 10.0 uf checked 9.88 uf.


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## fdrahuse (Oct 30, 2014)

Never got the impedance measurement jigs to work, but did measure manually. Using a couple of different microphones, resonant frequency of the side tweeters was about 1550 HZ. 

The tweeter I tested was actually pretty flat and compared well to the new tweeter I bought for the center tweeter. 

Starting to work on testing crossover with the frequency response of the whole array wired together.


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## fdrahuse (Oct 30, 2014)

Just found out the Dayton Audio iMM-6 works with REW. The text calibration file from Dayton loads directly into REW just like the .cal files. No problem


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## fdrahuse (Oct 30, 2014)

Frequency response of tweeter with no baffle


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