New life for Mission 761i

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!
 

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Interesting, I used to sell those and picked up a pair for my wife's TV set up in her sewing room. They did really weird things as you moved around, not pleasant. Changed them for some PSB Alpha B which work fine in her set up.

Did you change the placement at all? Part of the issue is no doubt inherent in the driver layout and though your other changes may have improved things in other ways I would not expect them to have any great affect on the lobing behavior:

https://en.wikipedia.org/wiki/Midwoofer-tweeter-midwoofer
 
I left their position in the room alone so as to ensure I was hearing the effects of my tweaks. You're right, as they came from the factory, their sound did really weird things as you moved around. What I've done seems to have tamed that lobing behaviour, their behaviour has really changed. I'm surprised at the results, too. I didn't want to dis their original performance too badly, but I found them unlistenable to begin with. Now I'm enjoying them to no end and I'm going to give them to our daughter for a system in her living room, they are that good after my tweaking.
 
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Very interesting indeed, well done!

It was not a favorite of mine when I was in retail, I did not sell many. I grabbed that pair recently as it was at a very flappable price and I did so.
 
Today I have the 782's apart and have made some edits to my first posting accordingly.
 
Also hve pair 761i's bought at a thrift. Agreed, not memorable sound. Sit unused. Glad you are finding some improvement. Maybe they're better as large desktop speakers, given directionality.
 
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I thought I'd eliminated all cabinet sounds....Nope. The last tweak to these 761i's was to open them up again and pull out the 1" thick foam cabinet lining and stuff each of the boxes with 15 ounces of polyester fiber fill. That works out to 1.5 pounds per cubic foot. The big brother Mission Cyrus 782 cabinets are stuffed with polyester, rather than lined with open-cell foam like the 761i. Plugged them back into the system and they are definitely improved, sounding quite wonderful and truly beyond all recognition from their original state. According to my test CD, they are reproducing down to 32 Hz; not a lot of energy at that frequency, but exceeding my expectations for these little boxes.
 
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Very interesting
I'm picking a pair of these up next week.
I will definitely follow the crossover mods and increasing the acoustic wadding.
I find the later improves most cheaper speakers
 
I picked up a pair last week Saturday in very good condition for $80. Upon first listen, they sounded very nice. After seeing these posts, I got polyfill and filled the cabinets through the back speaker connection plate.
Seems to sound better, with very nice highs and a nice low end kick. Really a good sounding pair - used in my home office with the new Yamaha A-S801.
Debating on whether to re do the caps.
 
I bit and did the re-cap. At first listen, they seem a bit strained - and different somehow from their original sound. I will let them burning in for some hours and listen again. I may just need to get used to their sound again.
 
They do need to burn in, that was my experience.

They have been playing through the night, and just between you and I, listening to the same source material, they did sound better this AM. Less harsh, more rounded out sound. I will leave them playing and see how they respond tomorrow as well.
 
Did you take the cheap grey foam out before stuffing the cabinets? And I do strongly recommend the "acoustimat" cabinet liner. I used 3M Sound Reduction Mat that I bought on sale at an auto parts store. It really works!
 
Yes, I did take out the foam. I have spent the last couple of hours with them listening to all kinds of music. They are really sounding good. I will take a look at the 3M stuff. Thank you for your input, I really appreciate it.
 
Nice :thumbsup:
Glad there starting to come on song. It took my 770 a while to sound right after the recap but they sound much more open now than they ever did with the old caps in them.
 
Did they use different woofers? You say the 782s were 4 ohm and the 761s were 8 ohm.

Lee.
 
Hello LWB, I hope you still react to this thread. I just got a pair of 761i and I want to pimp them.
First problem: How do I get inside the speaker to line the inside with reduction mat?

Greatings from The Netherlands!

Bas
 
If I recall correctly you can do all work necessary by removing the drivers from the front baffle - they screw in and the wiring is a removable clip, no desoldering required. Then pull the foam out, it's not glued. The crossover panel comes out, too, so you can get into front and sides of the cabinet. You may find that even after removing the screws that hold the drivers in place, that the drivers are stuck to the front panel. I think I used a small pointed pry tool to gently loosen them. You'll find the cabinet loosely lined with the cheapest 1" open cell foam, get rid of it! Then line and stuff them as I've described.
 
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Thx! The openings are bigger then I thought. Now just trying to find out what material "polyster fiber fill" is in Dutch. I keep you posted with the progress and mayby more questions.
 
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