Doc modding Marantz imperial 7

[karatestu]

Two inch thick concrete bass enclosure walls really are a pain in the arse even though they are gonna sound out of this world. The enclosure is much bigger than it ought to be but then i don't think any bracing will be needed so that will save a bit of volume. The width and depth are going to be 40cm at the very least and that is 10 cm thinner than what i have now. I can live with 40 cm width and depth. To get the volume i want and with really thick walls the height is going to be too much.

So i have had an idea enable me to reduce the height of the bass enclosure to what i want . I will cut away half the thickness from the panel to make the panels 1" thick except at the joints where they will still be 2". That gives me quite a surprising amount of extra volume to play with and won't compromise performance i don't think. It will make them a bit lighter as well so more easily moved about. They will still weigh a ton mind

It can be done with my petrol stone cutter . Think lots of lines cut an inch deep and about an inch apart. Then a hammer and chisel will do the rest or an sds drill with chisel bit. Job done and nobody will see it as they will be the inside faces.

[karatestu]

Starting to think of finishes for these speakers ( must be in sight of the end ?)

The wooden top enclosure will be fairly straight forward . But the concrete bass enclosure will be a pita. The slabs are really quite rough and you can't veneer on top of concrete.

Options are;

Plaster or render skim then sand and paint (or wallpaper )
Fabric e.g felt
Leather - if it can be purchased in big enough sheets
Very thin acrylic - they will have an NVA look about them
Very thin metal sheet which can be ploished e.g copper
None of the above

Any other ideas ????

[karatestu]

Just ordered two more 5.25" drivers for £22 inc delivery At that price this could turn into a mid bass driver breeding project The visaton tweeters are much more expensive (£70 a pop) so i am glad i tested to make sure it works with tweeters i already have before splashing out on six or eight more of them

The new 5.25" drivers will oviously need doping but i have loads of bisonkit and plastidip so no problem there. I will use them in the up firing position and use my existing ones in the visible magnet down firing position. If my existing little cuboid is big enough i might initially make a hole in the bottom of it and use that before making a bigger box. Will need some way of supporting it right above the 12inchers magnet (unless the fields are attracting then they might stick themselves together ).

Also found some 5.5" mid bass to replace the nasty aluminum continuous cones in the MS902S that i have doc modded. They should dope well and are suitable for sealed cabinet.

[Latteman]

This is my diy cube that has evolved to front firing, the lid is a snug fit where the 12” used to be- following your ideas earlier on the port I’ve lifted the lid at the front very slight- this has resulted in a lift in volume- more bass & midrange especially at lower volume but will monitor the ‘boom’ at higher levels I think it will be susceptible to

[karatestu]

Morning Peter.

So you have left a gap for the back wave to get out of the box ? Did you put any resistive material in the gap (foam, fibre glass etc) ? If not i would try it with some in and see what you think. That may tame things.

I have found booming bass to be caused by;

* enclosure volume being to small for a said driver
* crappy materials used for the enclosure
* enclosure construction not been up to the job
* drivers not secured properly
* room modes

It's not been plain sailing with my project by any means. I kept assuming any bass problems were due to the box volume being too low when really i should have been looking to the enclosure materials and construction first. Then volume fine tuning after that.

I would advise to make sure the box is as stiff as you can get it. More weight is good for a bass enclosure. Bolt the woofer down as well as you can - i found this helps when i had the little speaker and 56lbs weight on a shelf which rested on top of the woofers magnet.. Don't make a tuned vent as you end up with a farting bass reflex unless you are really lucky to make a good one. What ever hole you have then stuff it and try to not have the opening pointing at you.

Your box looks very big for the driver you have left in it (8" ???) I would be surprised if you got any bass problems apart from lack of it. What Qts has your driver got ? If it is very high (>1) then you might be better off with open baffle .

Anyway you don't have to listen to me. As Fleetwood Mac sang "you can go your own way".

If Doc was here he would be saying something like what the heck are you doing ? Sealed box acoustic suspension was his thing.

[karatestu]

Final ffing about with these speakers before Christmas. Waiting for the two 5.25" drivers that i have ordered to turn up i decided to revisit something i had done before but slightly different this time.

I have removed the back panels again and cut some foam to fit in the hole and completely seal it. I made it slightly over sized so that it sealed itself against the enclosure sides, top and bottom. Last time i did this i shoved old duvets in there and it was quite leaky with the duvets not far from the back of the rear driver. Also i am clamshell isobaric now so the there is now a greater distance between the front and back of the driver pair (in isobaric config they act as one driver).

I am enjoying it very much with a back panel made entirely of foam about three inches in thickness It's not a sealed enclosure and it's not an open baffle. Is it an aperiodic open baffle or what ? The impact of the bass is lower and i may have lost some of the very lowest frequency but there is a lot to like about this - there is more detail and texture to bass guitar and synth. The room seems less pressurised, i don't know how to explain it. There is a calmness now to the bass that the 5" aperiodic hole hinted at but this has taken it to a whole new level. The wooly sounding bass that i had with duvets in the cab is not evident this time with foam

More comments when i have done more listening .

[karatestu]

Other things to try with a whole aperiodic panel.

* Try the two 12 inchers in push push. I don't know if isobaric loading is actually achieving anything in this configuration. Two visible drivers closely coupled will give me more dB if i put them in parallel.

* Push pull (not isobaric) i'm not so sure about. It is said to decrease distortion.

*Then there is slot loading

*Try the bass drivers isobaric up firing with the aperiodic venting done at floor level.


Head is starting to hurt now

[Fretless]

Starting to think of finishes for these speakers ( must be in sight of the end ?)

The wooden top enclosure will be fairly straight forward . But the concrete bass enclosure will be a pita. The slabs are really quite rough and you can't veneer on top of concrete.

Options are;

Plaster or render skim then sand and paint (or wallpaper )
Fabric e.g felt
Leather - if it can be purchased in big enough sheets
Very thin acrylic - they will have an NVA look about them
Very thin metal sheet which can be ploished e.g copper
None of the above

Any other ideas ????

How about using liquid epoxy?

Make a mould around the top surface, fill with epoxy, allow to dry, shift speaker onto side and repeat surface for surface.

Could look great.

[Latteman]

The madness has crept south
Your ‘blog’ gets my imagination going



May connect the 12” what eh!

[karatestu]

Starting to think of finishes for these speakers ( must be in sight of the end ?)

The wooden top enclosure will be fairly straight forward . But the concrete bass enclosure will be a pita. The slabs are really quite rough and you can't veneer on top of concrete.

Options are;

Plaster or render skim then sand and paint (or wallpaper )
Fabric e.g felt
Leather - if it can be purchased in big enough sheets
Very thin acrylic - they will have an NVA look about them
Very thin metal sheet which can be ploished e.g copper
None of the above

Any other ideas ????

How about using liquid epoxy?

Make a mould around the top surface, fill with epoxy, allow to dry, shift speaker onto side and repeat surface for surface.

Could look great.

I will have a look into that, cheers Fret.