Can this be doped ?

[karatestu]

More work done on these MS902S



Mid/ bass driver put back in. Just need to attach one steelplate to the side of each cab.



Tweeters have been put back together after adding some IPA around the voicecoil gap to freshen up the ferrofluid. I have also poured some bison kit in some voids in the tweeter housing to help deaden it a bit. Have to wait for it to go off now before putting them back in the cabs.



I am still messing about with the back panel of the cab. Port was easily pushed out by hand I have temporarily stuck a small circle of wood on the inner face with two holes to pass the high frequency send & 0V wires through. The mid / bass will be soldered directly to the binding posts internally but whilst I have to muck around with the tweeters capacitor and resistor (not sure what value of resistor needed yet if any) it is easier to have them on the outside of the cab. I will block around the wire holes to keep things airtight and join the wiring to the low frequency binding posts externally. When all tweaking is finished I will remove the wooden circle over the port hole and cover it with something neater and more permanent. The cap and resistor can then go inside the cab and be wired to the HF binding posts.



This is the inner face of the back panel. I have removed all of the old crossover components (2 of) and removed some plastic which was sticking out in to the cab. I should get some steel plate over the back panel (when tweaking is finished) taking care not to short any of the binding posts together.

I should be able to listen to these soon .Getting excited about playing with more dope on the mid / bass, plastidip over the top and discovering if I need a padding resistor and if so what value.

Some more progress also made with my doc mod Marantz but that is for another day.

[karatestu]

Well, I am finally listening to the doc modded MS902S. I thought the day would never come with 2 doc mod projects on the go and a load of other stuff. I had no idea of what to expect.

I used the original drivers and so they are run in already. The bison kit on the mid/ bass and plastidip on the tweeter are not run in however . I don't even know if there is any run in with bison kit ? Also the Russian PIO caps are new and so will probably run in over time. 3.3uf is the value that MS used on these anyway. No padding resistor as yet as MS didn't use one either.

System is Cambridge audio CD5 through SSC to AP20 through LS2. Playing Stevie Wonder Songs in the key of life at the moment

Initial impressions are they are a bit bass light but then I have blocked the ports and I don't have them back to a wall yet as they are just plonked on top of my floorstanders. The bass has tightened up also (a lot) and is more tuneful (no port farting). High frequencies seem a bit too prominent so not sure if a padding resistor will ultimately be needed after all or whether more bison kit on the mid bass will sort that out. I will live with them like this for a while to see if the sound changes before tinkering.

They are amazingly tight & fast and that is probably down to the massive amounts of steel that went into these. I have not weighed them yet but will when finished - they do weigh a ton for a small stand mount.

They are also very open, clean and detailed. Musical?? - yes, yes, yes. Even though I have a way to go with tweaking I have a silly grin on my face and toe is tapping. I can hear right in to the music and am really enjoying the presentation on the end of the little AP20. Getting rid of the bass inductor really is a good thing.

More to report in time. Need to try them with my other system as well and biamp them as well. Need to go back to the wall to help the bass output. I will not be measuring their frequency response as I don't have the kit or the inclination.

[antonio66]

Well done Stu.

[karatestu]

Well done Stu.

Thanks, it has been done at a snails pace and not finished yet, but at least i can listen to them.

One mistake i have made is not doing it in stages. Take wadding out, listen. Steel line, listen. block port, listen, dope drivers & remove crossover, listen. Done it all in one step. Never mind.

It is clear to me now that i will need a padding resistor. The doping of the mid bass (although i have not put much on yet) will have lowered their sensitivity so tweeter output will be too high.

I am also going to add more bison kit as i dont think there is enough on. Also need to get them up against the wall. These speakers will ultimately be going in my kitchen diner. One speaker on an oak shelf and the other on top of a display cabinet. They will be almost in the corners of the room at equal height and about 3 feet from the ceiling. Challenging in terms of positioning.

Stu

[Simon Hickie]

Good stuff! Really looking forward to making my semi-omnis too.

[karatestu]

I am finding listening to these speakers rather addictive even though they are no way near being finished. More doping to add and padding resistor.

They do so many things right and are a joy to listen to even though certain frequencies are too prominent compared to others. Bass is not shattering but as I said earlier I don't have them back to the wall yet. Other things affecting bass output will be the fact they are only small stand mounts with a 5" mid/bass driver and I have sealed the port and reduced the internal volume of the cabs a little with all that steel. What bass there is, is as fast as a rat up an aqua duct with no boom at all. That steel must be doing a good job.

Phase and other issues from using inductors really does the music no good at all.

Currently have my much modified Naim CD3.5 hooked up to the AP20 instead of the Cambridge CD5. It clearly shows that CD player a thing or two but then it ought to with a fancy clock with dedicated psu, dedicated dac psu, digital psu and anologue stage psu. Four transformers in total. Playing Morcheeba big calm and loving it.

[karatestu]

Been thinking about these. They are obviously inferior compared to my little home made cuboid 3.

Pic of the back and the arrangement so I can play with cap & resistor easily without opening up the cab.



This (I think) is the way forward with these to get the frequency response more even

1) Put them right back to a wall (reinforces bass output) and listen
2) Add lots more bison kit dope and listen
3) Spray with plastidip when I think I have enough and listen
4) Add padding resistor starting at 1.5R and going up until I get it right and listen
5) If still not happy, reduce cap on tweeter to 2.2uf listen & increase resistor value if needed. Listen

This will hopefully get the bass output up relative to the rest of the frequency spectrum.

Is it possible to add too much steel

What effect does having an air leak have on the sound ????

[Simon Hickie]

Looks like the back of my speakers! A leaky box might give aperiodic vent type effects - typically reduced internal box pressure at higher SPL and at lower frequencies plus a possible lowering of the impedance peak at bass resonance. As for what that means for the sound, I have no idea!

[Daniel Quinn]

I will wait in the hope that one day ill be able to piss about with hifi

[Dr Bunsen Honeydew]

Press the cone in on the bass driver, if you hear a hiss you have a leak. Also does the driver feel like a spring or does it go down and then slowly come up. It should be a spring, if it isn't you have a leak.