Doc modding Marantz imperial 7

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karatestu
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Re: Doc modding Marantz imperial 7

Unread post by karatestu »

I expect I will have to tweak these speakers once they go into the steel and wood speakers. The plywood I am putting between the two hemispheres was originally to increase the volume a bit but I don't really need thd extra anymore. Even so I am going to keep it for a humber of reasons.

I am going to make holes in it to connect the two hemispheres which will hopefully help break up the internal spherical shape. Also it will have a bolt thru it to clamp the lower hemisphere to the ply and threaded rods put through it and the mid bass mounting holes for the top hemisphere so both hemispheres can be clamped down against the ply in the middle. That should be enough to stop any ringing in the steel but as long as the cut edge of the hemisphere is touching a surface it doesn't ring at all. The last reason to use some wood is to mix up the materials used a bit. I plan to use ply for the leg(s) and baseplate if required.

The only joint in the enclosure will be where the two hemispheres join each side of the plywood spacer. There will be no glue and the clamping of the hemispheres to the ply via bolts should keep it in place. I have to make sure there are no air leaks of course. It will be easily dismantled so if I ever need to change anything inc driver then just need to swap the top hemisphere or one other part.

It should be a super rigid structure due to the strength of a sphere especially in 3mm steel. I am looking forward to what effect this has on the bass which needs rigidity and no bending of panels to be as efficient as possible. Well there are no panels as such. I am expecting this to be a major advantage over the traditional six sided wooden enclosure.

I am also very much looking forward to the effect of having the mid bass in a sphere. As the mid bass is running fully open up to about 7kHz before it rolls off acoustically then I expect there will be benefits from the spherical enclosure. It will hopefully make for a smoother sound as the ripples in response should be vastly reduced. Look at that lovely flat line for the sphere. About the worse thing you can do is put the driver in the middle of a square or circular baffle.

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karatestu
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Re: Doc modding Marantz imperial 7

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I took the base of my drop saw so need to mount it on a vertical surface in order to slice the top off the sphere. As long as the horizontal flat surface that the hemisphere sits on is parallel to the 300mm saw blade then all should be good

I am planning to use 2x3" lengths of wood with threaded rods to clamp the hemisphere and so I don't have to hold on to the sphere directly. I want to be able to spin the sphere so the blade only has to go deep enough to go through the 3mm steel.

I will have a clear shield between me and the saw for safety and a foof on off switch so I can keep both hands on the work piece. The blade will be locked in place so it can't move. The blade pulls the workpiece with it's direction of rotation sk I have to keep that in mind.

This might be a bit of an arse clenching experience. Other options don't give the cleanness and straight cut in my mind. I thought of making a jig which is basically a ring of wood for a guide around the outside of the sphere. Then use a hacksaw blade. That might take me a while to do but could work as long as the guide jig is clamped down securely. Certainly sounds much safer than my other option.
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karatestu
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Re: Doc modding Marantz imperial 7

Unread post by karatestu »

A little tip for those using rockwool / fibreglass insulation in their speakers. Spray it with hairspray to stop any loose fibres floating about.
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karatestu
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Re: Doc modding Marantz imperial 7

Unread post by karatestu »

I'm thinking of getting one of these.

https://www.stanleytools.com/product ... w/20-220

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Re: Doc modding Marantz imperial 7

Unread post by Firebug1 »

It's going to take some time to cut out the top of steel hemisphere with that one :shock:
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karatestu (Thu Nov 04, 2021 5:21 pm)
Rega by Michael Lim\Teac\ASR\NVA\
SA Mantra30\Audeze LCD-2 closed.
...the Gods you worship are steel, at the altar of rock 'n' roll you kneel...

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karatestu
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Re: Doc modding Marantz imperial 7

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Firebug1 wrote: Thu Nov 04, 2021 2:52 pm It's going to take some time to cut out the top of steel hemisphere with that one :shock:
Yeah, I think my arm will be tired :grin:
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Firebug1 (Thu Nov 04, 2021 9:43 pm)
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karatestu
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Re: Doc modding Marantz imperial 7

Unread post by karatestu »

Houston we have lift off :grin:

After much procrastination, chin scratching and general pondering I decided to get going on cutting a hole in these hemispheres. Can't think about it forever otherwise this will end up taking as long as the development of the MDAC2. :lol:

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After lots of measuring and marking I decided to use a plasma cutter - like a knife through butter. That left a shitty looking edge but I cut the hole slightly too small. Angle grinder came out at this point.

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Almost there so the last tool of choice was a trusty belt sander with 60 grit belt. I wasn't too sure on the outcome of this. I made sure as much of the belt was in contact at one time as possible and went round and round with the sander measuring every so often. Not sanding across the thin edge meant I didn't round any edges over and kept the edge flat.

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I'm quite pleased with it so far. A little bit more with the belt sander and it will be done. It is about half a mm out in one area but I am very surprised how fast the belt sander removes the material so should not take long.

I ended up cutting off 3cm of the hemisphere and I am left with a hole 171 mm diameter. The flange I have created all the way around is 4.5mm wide so I have a diameter of 180mm in total. The 4.5mm should be enough for a plywood mounting ring to sit on top of. The driver is 170mm diameter and the cut out needed is 145mm so the mounting ring will be 17.5mm wide.

Onwards :guiness;
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Firebug1 (Fri Nov 05, 2021 1:36 pm) • Latteman (Sat Nov 06, 2021 8:39 am)
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karatestu
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Re: Doc modding Marantz imperial 7

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Got both the cut outs done now :dance: This is the closest I have got to finishing ANYTHING as my attention is wandering all over the place with new ideas and things I have learned. I have done a few mock up's of how it is going to look. I sprayed a circle of cardboard black and put it under the 110mm drain pipe. I sat one of the qtx 6.5" drivers in the hole on top of a length of drain pipe and arranged the tweeter sphere on top.

I am quite liking how these are starting to look. That's a lie, I am really starting to get a hard on with these. Certainly IMO going to be much more interesting than the boring shapes that most people churn out. I think you get a good idea of the aesthetics and proportions except I forgot to spray the tweeter sphere black :roll: Ignore the orange.

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Please let me know what you think (good or bad).
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Latteman (Sat Nov 06, 2021 8:43 am) • Ithilstone (Mon Nov 08, 2021 9:27 am)
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Grumpytim
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Re: Doc modding Marantz imperial 7

Unread post by Grumpytim »

It's looking good, far far better than anything I could have done and far more original.

I'm kind of getting a 'how will it end?' Truman Show vibe in a good way.
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karatestu (Fri Nov 05, 2021 5:46 pm)

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karatestu
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Re: Doc modding Marantz imperial 7

Unread post by karatestu »

The beauty of it all Tim, is that it almost made itself so far :grin: Cut two holes in 3mm steel this shape is tough but that is all I have had to do so far. There will be some routing to do for the driver mounting rings. And the leg and base will need making as well as the final tweeter sphere - might do that in steel anorl but haven't decided yet.

Also the way i am going to support the tweeter sphere above the mid bass is not really decided on yet but it will probably be three little legs like i use now with the cubes. I will try and isolate the tweeter cube from vibration coming from the mid bass cube if i can. Wiring and binding posts to do. Internal stuffing to finalise - fibre glass but just the right amount.

Oh and lets nots not forget the finish of the two spheres. i will have to dust off my spray gun that goes on the compressor which i haven't used for five years or more . I said this almost makes itself as there are no joints to make as such but that list of things to do is quite long :shock:
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