LWB
Well-Known Member
In about 1995 I purchased a pair of low-end Mission 761i bookshelf speakers at a red-hot clearance price. I couldn’t resist grabbing a pair to try them, maybe use them as satellites. I took them home and swapped them into my system to see what they sounded like.
Sitting in the stereo sweet spot they worked well, but their sound output was very directional. I couldn’t move about the room and enjoy them. They couldn't compete with my old speakers, so they were relegated to a corner of the basement where they sat unused for many years.
A few months ago I was given an old pair of Mission Cyrus 782 speakers. These retailed in the USA for about $900/pair in 1990. The Cyrus 782 is a two-way design with dual 7" polypropylene woofers and a single ¾" dome tweeter mounted between the bass drivers. Rated at 4 ohms impedance, the 782’s physical configuration was the same as that of the 8-ohm 761i’s: two bass drivers mounted one above the other, with a dome tweeter mounted between the bass drivers. However, the 782 is much larger. The 761i looks like a down-sized, de-contented 782. Both use the same Mission fabric dome tweeter (R76/78-HFU-D20). They have similar crossovers, except the 782 will accommodate bi-wiring, while the 761i won’t. Each has two inductors, but the bass side in the 761i is ferrite-cored, while in the 782 the bass-side inductor is air-cored. The low-pass filter in both was an electrolytic capacitor; the high-pass filter in the 761i is an electrolytic cap, but in the 782, the high-pass is a pair of film caps (4.7uF and 1uF in parallel).
The 782 cabinet is walnut(?) veneered 3/4” chipboard; the 761i cabinet is 1/2” wood-grained black vinyl-clad chipboard. Inside the 782, Mission filled the cavities with what looks like fairly dense spun polyester, but the cabinet is also partially lined with a thick acoustimat-type product (about 3/16” thick) to dampen vibration. The 761i’s have just cheap 1” foam lining against the bare chipboard. The front panel of the 761i is a rigid diecast plastic (ABS, I’m guessing) face in which the drivers are mounted; the 782 front panel is mdf. Added note: the 761i front panel has two elongated tunnel ports flanking the tweeter, whereas the 782 front panel is not ported.
I was immediately impressed with the sound of the 782’s, even with their old electrolytic crossover caps, which I feel certain must have drifted in value with their age. Now that I’d compared the construction of both models, I could see that the schmutzy bass and directional sound of the 761i was due to cabinet reverberation. The old electrolytic caps in the 761i crossovers needed checking, too. Time for some experimentation!
Here’s what I found in the 761i: the 4.7uF high pass filter cap measured 6.7uF. The low-pass 8uF cap measured 8.65uF. I replaced these with Dayton polypropylene film caps. I used a 7.5uF + 0.47uF in parallel in place of the 8uF low-pass cap, and a 4.7 uF film cap for the high-pass. I probably didn’t burn these in long enough, because I wasn’t impressed. I added a 1uF bypass film cap across the high-pass filter and this brightened up the high frequencies to my liking. But the bass still sounded like it was impaired by the vibrations and resonance of thin cabinetry, and the sound was no less directional than before.
First thing I tried was the addition of a hardwood cabinet brace glued on each side, inside the 761‘s; this yielded a small improvement in sound, but not much. I decided to try 3M Sound Reduction Mat, because I had some left over from another project. It is about 1/8” thick and comes in 10” x 18” self-adhesive sheets. Mission used something like it in the 782 - why not try it in the 761i? I lined the 761i’s sides with the 3M. This produced a dramatic improvement, but I could still hear some cabinet. So I went back in and lined the top, bottom and backsides with more 3M. The 761i’s are now generously, but not perfectly, lined with 3M on all sides but the plastic front panel.
The Sound Reduction Mat has cleared up the cabinet resonance problem, I’d say completely. With a few hours use, the new caps have smoothed out, and these 761i’s now produce sound of quite shockingly good quality considering their cheap, entry-level build constraints. I am astounded at the results, which have invited many hours of listening to favorite tracks. On stands, properly placed, they sound quite amazing, and their directional quality has abated so that one can move freely about the room and still enjoy their output, which is now sweetly room-filling. The stereo sweet spot still yields best critical listening, but the character and quality of these speakers has been completely changed by these simple mods.
If you find a pair of 761i’s at the local thrift or at a garage sale, grab them and follow my upgrade path. You won’t be disappointed!
Sitting in the stereo sweet spot they worked well, but their sound output was very directional. I couldn’t move about the room and enjoy them. They couldn't compete with my old speakers, so they were relegated to a corner of the basement where they sat unused for many years.
A few months ago I was given an old pair of Mission Cyrus 782 speakers. These retailed in the USA for about $900/pair in 1990. The Cyrus 782 is a two-way design with dual 7" polypropylene woofers and a single ¾" dome tweeter mounted between the bass drivers. Rated at 4 ohms impedance, the 782’s physical configuration was the same as that of the 8-ohm 761i’s: two bass drivers mounted one above the other, with a dome tweeter mounted between the bass drivers. However, the 782 is much larger. The 761i looks like a down-sized, de-contented 782. Both use the same Mission fabric dome tweeter (R76/78-HFU-D20). They have similar crossovers, except the 782 will accommodate bi-wiring, while the 761i won’t. Each has two inductors, but the bass side in the 761i is ferrite-cored, while in the 782 the bass-side inductor is air-cored. The low-pass filter in both was an electrolytic capacitor; the high-pass filter in the 761i is an electrolytic cap, but in the 782, the high-pass is a pair of film caps (4.7uF and 1uF in parallel).
The 782 cabinet is walnut(?) veneered 3/4” chipboard; the 761i cabinet is 1/2” wood-grained black vinyl-clad chipboard. Inside the 782, Mission filled the cavities with what looks like fairly dense spun polyester, but the cabinet is also partially lined with a thick acoustimat-type product (about 3/16” thick) to dampen vibration. The 761i’s have just cheap 1” foam lining against the bare chipboard. The front panel of the 761i is a rigid diecast plastic (ABS, I’m guessing) face in which the drivers are mounted; the 782 front panel is mdf. Added note: the 761i front panel has two elongated tunnel ports flanking the tweeter, whereas the 782 front panel is not ported.
I was immediately impressed with the sound of the 782’s, even with their old electrolytic crossover caps, which I feel certain must have drifted in value with their age. Now that I’d compared the construction of both models, I could see that the schmutzy bass and directional sound of the 761i was due to cabinet reverberation. The old electrolytic caps in the 761i crossovers needed checking, too. Time for some experimentation!
Here’s what I found in the 761i: the 4.7uF high pass filter cap measured 6.7uF. The low-pass 8uF cap measured 8.65uF. I replaced these with Dayton polypropylene film caps. I used a 7.5uF + 0.47uF in parallel in place of the 8uF low-pass cap, and a 4.7 uF film cap for the high-pass. I probably didn’t burn these in long enough, because I wasn’t impressed. I added a 1uF bypass film cap across the high-pass filter and this brightened up the high frequencies to my liking. But the bass still sounded like it was impaired by the vibrations and resonance of thin cabinetry, and the sound was no less directional than before.
First thing I tried was the addition of a hardwood cabinet brace glued on each side, inside the 761‘s; this yielded a small improvement in sound, but not much. I decided to try 3M Sound Reduction Mat, because I had some left over from another project. It is about 1/8” thick and comes in 10” x 18” self-adhesive sheets. Mission used something like it in the 782 - why not try it in the 761i? I lined the 761i’s sides with the 3M. This produced a dramatic improvement, but I could still hear some cabinet. So I went back in and lined the top, bottom and backsides with more 3M. The 761i’s are now generously, but not perfectly, lined with 3M on all sides but the plastic front panel.
The Sound Reduction Mat has cleared up the cabinet resonance problem, I’d say completely. With a few hours use, the new caps have smoothed out, and these 761i’s now produce sound of quite shockingly good quality considering their cheap, entry-level build constraints. I am astounded at the results, which have invited many hours of listening to favorite tracks. On stands, properly placed, they sound quite amazing, and their directional quality has abated so that one can move freely about the room and still enjoy their output, which is now sweetly room-filling. The stereo sweet spot still yields best critical listening, but the character and quality of these speakers has been completely changed by these simple mods.
If you find a pair of 761i’s at the local thrift or at a garage sale, grab them and follow my upgrade path. You won’t be disappointed!
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