Doc modding Marantz imperial 7

[karatestu]

Toeing these speakers in severely so that one of the corners is pointing right at me improves the imaging no end. But i am not sure i prefer it to flat against the wall. Something is missing now that i had previously. Can't put my finger on it. I wish i had RD golden ears , not sure mine even reach bronze.

[karatestu]

Speakers put back how they were (flat back against the wall).

That's better. I was missing a bit of bass because the cabs were slightly further away from the wall. Not missing the sharper imaging at all or am i just too used to listening to them in the current position. Anyway, it is good that i am able to push them right back to the wall as room wise that is preferable for me.

[karatestu]

Dispensed with the blutack and polystyrene beads on my up firing 5".

I tried sand at the dust cap / cone interface and it sounded horrid (well of course it would) but i had to try it. Distortion from the sound of the sand rattling around on the cone and dust cap. Tried pulling tiny irregular shaped bits off some foam and throwing them on. Didn't do enough attenuating and as with polystyrene beads it flew up and down in random projections. Polystyrene beads were the best out of that lot (except the blutack which combined with polystyrene beads really did have an effect). But at higher volume you can hear the strange sound of the polystyrene beads rubbing together - it can't be doing any good.

So i have sprayed more plastidip on them but only on the dust caps. I got the nozzle quite close and limited the force at which the spray came out. Doing that it was possible to just spray it on the dust cap without it splattering everywhere. Putting plenty on resulted in a puddle of it accumulating at the interface of the dust cap and cone and it levelled itself around the circumference of the dust cap much like bison kit would do.

I thought i would have a go at doing it this way. Not because i am scared of bison kit (i don't like the fumes though) but to try something a little different. More can be added in the same way. It would be useful to know for anyone trying doping so they don't have to go to the expense of buying loads of bison kit and could just buy plastidip.

Will there be any difference in sound between bison kit and plastidip versus just plastidip ? Well i am listening to my efforts now even though it is not completely dry. I just waited long enough so it would not jump about with the excursion of the cone. Sounds good to me so far so maybe on to something here. I find it easier and more consistent in application than bison kit.

[karatestu]

I am not going to do any more doping until my new 1 uf PIO K75-10 caps arrive. It would be unwise to do anything until then.

The units do sound more alive when only lightly doped. Maybe that is the break up resonances which are not attenuated enough. Who knows. It doesn't sound awful like my B&W P4 6.5" kevlar drivers (or MS902S) did when i removed the inductor (coil).

I tried some sheets of foam and fibre glass wool over the 5 incher before i added the plastidip and it did attenuate really well but there was a closed in quality to the mid range. Anyway, one cannot simply go around shoving large blocks of foam on top of mid bass drivers. The only way to do it is mount the drivers on the inside of a thick baffle (like 25 - 30 mm) and put the same depth of foam in the cut out. Might get some nasty resonances doing that though from sound waves bouncing around off the cut out walls. There may be ways to mitigate that by rounding off or tapering but quite frankly i can't be arsed to go down that rabbit hole.

[Latteman]

I use peelable (rubber like) paint - it’s all I can find in Doncaster
I have used it as u say above with the pooling etc
It’s neater than the doping and u can get colours too

[karatestu]

Oooh, pink speaker drivers

Plastidip is available online and it too comes in different colours i think

[karatestu]

The pool of plastidip almost disappeared when it had dried I know bison kit reduces as it dries but i wasn't expecting that to happen with plastidip. I know i said i was going to wait.......but i'm not too good at doing that.

So i am currently sat in a room getting high on Bison kit. Headache coming on as i type. This container has been opened over a year and it still pours but is a bit thicker than i remember. I am hoping some of the volatile gas it gives off has gone already. It has run in to an even ring around the dust cap. I did pour it on the dust cap but you know that thing called gravity.

Did you know you can listen to your doped drivers straight after pouring Just don't put anything on with too much bass content. We don't want it splattering about all over the shop

[karatestu]

It is immediately apparent that these drivers do need quite a bit of dope. This is miles smoother than before. I was just fannying around the edges. Sounds brill even though the dope is still wet Volume has gone down a smidge though.

[Daniel Quinn]

I was wising Richard was alive for kara. Hes the only one who could have given him a few choice words to stop him looking for answers in the dark.

[karatestu]

I'm in the light now It's all a journey of discovery and i have tried a few things which i had to in order to satisfy my curiosity.

RD would probably have had a few choice words without a doubt

Sounding the best it has so far since i added the new extra 5". I could have saved myself some time and gone straight for the bison kit but i thought i could be clever (how wrong i was ). There was some attenuation of higher frequencies before but obviously not enough. Doc was right when he said to put lots on. At least i can make the whole speaker more efficient by adding more 5 inchers

I have ordered two small value polystyrene film caps which when added in the tweeter amps input stage should give me the first order high pass filter knee frequency i need. If it sounds any good then i can dispense with the big Russian PIO caps between the amplifier and tweeter. Then there will be nothing between any of my amps and any of the drivers, not even a resistor. All i am doing is removing one capacitor and inserting another (much smaller value) somewhere else.

If it sounds better then they will stay if not will revert back to the big PIO caps. There is no modification to do to the amp boards so easily reversible.