Hello
New to these forums, but not new to IMFs.
I have a pair of IMF CM2 and a pair of CM2A. and also had a set of TSL80Mk2 for quite a while.
The CM2s I have had seen new, and the CM2As bought 2nd hand 15 years ago. (I’m guessing they are both about the same age, manufactured 1980-81, (both with the foam grills that have now fallen apart...but made some nice new cloth framed ones that use the orignal velcro holders)
As far as I can tell the speakers are identical apart from the CM2 being ported?
Ok, here is my problem. Even though when I bought the cm2A I was satisfied with the sound and a full frequency sweep revealed that both tweeters and woofers were working correctly, I have now identified a problem with them.
They are currently being used as surround speakers in my home theatre. I am running a Denon receiver which runs the Audyssey microphone calibration set up. In looking at the equalisation curve for the cm2A it was showing that they are flat up to 2 kHz , but needed 6dB(that the maximum Audyssey can give) of boost in the 4, 8 and 16k bands, whereas the CM2s were relatively flat across the spectrum. Swapping speakers about the room and indeed using the cm2A by themselves as mainspeakers showed that they were consistently down by 6 dB above 2 kHz, possibly more given that is the max boost audyssey adds.
Were the tweeters not working? Well testing with high frequency tones revealed there were(and physically blocking the tweeter directly did have an effect on the output-so it wasn’t just high frequency getting reproduced by the woofer), just quite a bit down compared to the CM2s. Interestingly Audyssey was showing that within the pairs each speaker was within 1 dB of being identical to the other.
Interestingly I hadn’t use either pair as my main speakers for over 20 years and was surprised to see how good they still sounded when driven hard when I was comparing their responses..
Questions:
1. Was that the way they were made(the CM2A), or have they deteriorated.(unlikely they would have been 6 dB in the top end at the time?)
2. My understanding of the audax tw1500F tweeters is they work or they don’t work, their output shouldn’t decrease with time?
3. Are we looking at problems in the cross overs of the CM2As……..I suppose I could answer this for myself if I opened both speakers up and played tones through the respective woofers and tweeters bypassing the crossovers.
4. Are the crossovers different for the two types of speaker, or perhaps made at a time when one supplied component was not up to it?
At the moment, given Audyssey has spectrally taken care of the problem in my home theatre setup, it perhaps doesn’t matter, but would still like to get on the problem if we decide to do something else with the cm2A
Suggestions on where to go from here. (apologise if this is covered somewhere in the 84 pages so far)
Thanks
Sac