I guess I had time to waste, so I did some measurements on a pair of Mission M70's I've been using as rear speakers in the surround system. I bought them on a flea-market a few years ago, and I listened to them in stereo then, and found them too bright(typical for Mission speakers), but not too bad in general.
I did all the measurements on one speaker (FR, phase, impedance and driver offsets), and ran some simulations in XSim. The phase integration was a bit off, so the ideal listening position was not on-axis, but quite a bit higher (woofer being on top). I decided to adjust the phase and pad the tweeter some.
Now when I listen, I think they still sound a bit bright, but better then before.
Sadly I found that the second speaker did not measure the same after the same mods. It turned out the tweeter was to blame. The ferro fluid had 'gummed up' so it had lost performance in the 2kHz area. I tried to 'massage' it a little, but it only improved a little. Since they are miniature tweeters and glued together, I could not take it apart to clean it either. As a final desperate measure, I used a syringe with needle, and injected a little degreaser through the tweeter surround, and glued the small hole with speaker surround glue after. This did the trick, and the FR was back to the same as the other tweeter. Impedance bump at resonance was higher though. I guess it's behaving as a 'non FF tweeter'. Distortion is also slightly higher around 2kHz compared to the un-modified tweeter, but it's better than gummed up FF.
Modifications to the XO:
-Higher series resistance to the tweeter. Was 2,2, is now 4,2 ohm. I think even higher could be good, depending on taste and room.
-On the woofer I increased the resistor to GND from 1ohm to 3,3ohm. This aligned the phase, but also did not give the same LP slope for the woofer. The 'Q-hump' at just over 1k was sightly reduced from this too. Flatter LP slope was not good since the woofer has a significant 7kHz breakup. I added R3 & C4 to correct this. R3 could actually be lower, down to abt 10ohm to notch the 7kHz even more, but I happened to have 20 Ohm resistors, so in they went. As it is here, 7k is at the same level as the std XO.
I did not replace any electrolyte caps since they measured to spec, but I guess a better cap for the tweeter could be worth a try. I wanted to do this on the cheap, since I only paid abt 15EUR for the speaker pair.
Forgot to mention, I also lined the inside walls of the cabinet with felt.
I just wanted to share this, in case somebody feel like modifying their Mission M70's.
I did all the measurements on one speaker (FR, phase, impedance and driver offsets), and ran some simulations in XSim. The phase integration was a bit off, so the ideal listening position was not on-axis, but quite a bit higher (woofer being on top). I decided to adjust the phase and pad the tweeter some.
Now when I listen, I think they still sound a bit bright, but better then before.
Sadly I found that the second speaker did not measure the same after the same mods. It turned out the tweeter was to blame. The ferro fluid had 'gummed up' so it had lost performance in the 2kHz area. I tried to 'massage' it a little, but it only improved a little. Since they are miniature tweeters and glued together, I could not take it apart to clean it either. As a final desperate measure, I used a syringe with needle, and injected a little degreaser through the tweeter surround, and glued the small hole with speaker surround glue after. This did the trick, and the FR was back to the same as the other tweeter. Impedance bump at resonance was higher though. I guess it's behaving as a 'non FF tweeter'. Distortion is also slightly higher around 2kHz compared to the un-modified tweeter, but it's better than gummed up FF.
Modifications to the XO:
-Higher series resistance to the tweeter. Was 2,2, is now 4,2 ohm. I think even higher could be good, depending on taste and room.
-On the woofer I increased the resistor to GND from 1ohm to 3,3ohm. This aligned the phase, but also did not give the same LP slope for the woofer. The 'Q-hump' at just over 1k was sightly reduced from this too. Flatter LP slope was not good since the woofer has a significant 7kHz breakup. I added R3 & C4 to correct this. R3 could actually be lower, down to abt 10ohm to notch the 7kHz even more, but I happened to have 20 Ohm resistors, so in they went. As it is here, 7k is at the same level as the std XO.
I did not replace any electrolyte caps since they measured to spec, but I guess a better cap for the tweeter could be worth a try. I wanted to do this on the cheap, since I only paid abt 15EUR for the speaker pair.
Forgot to mention, I also lined the inside walls of the cabinet with felt.
I just wanted to share this, in case somebody feel like modifying their Mission M70's.
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Old post I know, but I played around with positioning my M70's at my desk - I found raising them so the tweeter is just slightly above ear level helped reduce the harshness, and still found it had a good soundstage. Not sure i'd bother modding this. If this was a bit bigger with just a hair more bass i would settle and keep them...but i'm searching for my desktop speaker endgame so far. Looking at the Emotiva B1+