Doc modding Marantz imperial 7

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karatestu
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Re: Doc modding Marantz imperial 7

Unread post by karatestu »

Oops, one of the dimensions on that drawing is wrong. 95mm should be 65mm :oops:

And not shown is the cone diameter - 105mm.
DIY inspired by Richard "The Doc" Dunn RIP

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Re: Doc modding Marantz imperial 7

Unread post by karatestu »

I am considering using a flexible stiff gooseneck lamp holder (like the one below ) to connect my tweeter sphere to the mid bass sphere.

Image

They come in several different lengths and finishes. Obviously being made for lamps they have provision for wiring to be passed through the centre. Just the job for that. There are male 10mm threads on both ends and so easy to connect at each end as long as a hole is put in the right place and tapped acurately.

I am thinking putting the mount round the back of the sphere as far away from the tweeter as I can. I can see only one support being beneficial as there is less to block the sound wave and to re radiate off but I may be being too anal here :hand:

This will be serving three purposes (1) to get wiring between the two spheres invisibly (2) to hold the tweeter sphere up (3) to position the down pointing cone on the under side of the tweeter directly above the centre of the up firing mid bass' dust cap / voice coil.

It will therefore need to be stiff enough to hold the weight of the tweeter sphere without sagging. The tweeter sphere doesn't weigh that much as it is made of 3mm thick polyethylene plastic and the driver doesn't weigh that much due to it being small, frame made of plastic and having a small neodymium magnet.

Also I need to accurately place the sphere above the mid bass and be able to duplicate the positioning on the second speaker as well.

What d'ya reckon ? A good idea or not ? Aesthetically it does it for me :dance:
DIY inspired by Richard "The Doc" Dunn RIP

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Re: Doc modding Marantz imperial 7

Unread post by slinger »

karatestu wrote: Tue Mar 01, 2022 6:16 pm I am considering using a flexible stiff gooseneck lamp holder (like the one below ) to connect my tweeter sphere to the mid bass sphere.

Image

They come in several different lengths and finishes. Obviously being made for lamps they have provision for wiring to be passed through the centre. Just the job for that. There are male 10mm threads on both ends and so easy to connect at each end as long as a hole is put in the right place and tapped acurately.

I am thinking putting the mount round the back of the sphere as far away from the tweeter as I can. I can see only one support being beneficial as there is less to block the sound wave and to re radiate off but I may be being too anal here :hand:

This will be serving three purposes (1) to get wiring between the two spheres invisibly (2) to hold the tweeter sphere up (3) to position the down pointing cone on the under side of the tweeter directly above the centre of the up firing mid bass' dust cap / voice coil.

It will therefore need to be stiff enough to hold the weight of the tweeter sphere without sagging. The tweeter sphere doesn't weigh that much as it is made of 3mm thick polyethylene plastic and the driver doesn't weigh that much due to it being small, frame made of plastic and having a small neodymium magnet.

Also I need to accurately place the sphere above the mid bass and be able to duplicate the positioning on the second speaker as well.

What d'ya reckon ? A good idea or not ? Aesthetically it does it for me :dance:
I don't see an immediate problem, but might it become a weak point over time? Maybe something like a small Sorbothane hemisphere attached to the lower section, for the top section to rest against might give more support without affecting the decoupling too much?

Just thinking out loud, but not necessarily in joined-up. :lol:
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karatestu (Tue Mar 01, 2022 9:29 pm)
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Re: Doc modding Marantz imperial 7

Unread post by Firebug1 »

I think it would be good and at a quick look, it will probably look like the tweeter sphere is floating in the air above the mid sphere.
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karatestu (Tue Mar 01, 2022 9:29 pm)
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Re: Doc modding Marantz imperial 7

Unread post by TheMadMick »

In case you need an alternative support, these are sold as mic supports and you can get mounting plates for them. If interested, I think I have some somewhere and you could have them for the postage. They are chrome finish.
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karatestu (Tue Mar 01, 2022 9:29 pm)
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Re: Doc modding Marantz imperial 7

Unread post by karatestu »

slinger wrote: Tue Mar 01, 2022 7:01 pm
karatestu wrote: Tue Mar 01, 2022 6:16 pm I am considering using a flexible stiff gooseneck lamp holder (like the one below ) to connect my tweeter sphere to the mid bass sphere.

Image

They come in several different lengths and finishes. Obviously being made for lamps they have provision for wiring to be passed through the centre. Just the job for that. There are male 10mm threads on both ends and so easy to connect at each end as long as a hole is put in the right place and tapped acurately.

I am thinking putting the mount round the back of the sphere as far away from the tweeter as I can. I can see only one support being beneficial as there is less to block the sound wave and to re radiate off but I may be being too anal here :hand:

This will be serving three purposes (1) to get wiring between the two spheres invisibly (2) to hold the tweeter sphere up (3) to position the down pointing cone on the under side of the tweeter directly above the centre of the up firing mid bass' dust cap / voice coil.

It will therefore need to be stiff enough to hold the weight of the tweeter sphere without sagging. The tweeter sphere doesn't weigh that much as it is made of 3mm thick polyethylene plastic and the driver doesn't weigh that much due to it being small, frame made of plastic and having a small neodymium magnet.

Also I need to accurately place the sphere above the mid bass and be able to duplicate the positioning on the second speaker as well.

What d'ya reckon ? A good idea or not ? Aesthetically it does it for me :dance:
I don't see an immediate problem, but might it become a weak point over time? Maybe something like a small Sorbothane hemisphere attached to the lower section, for the top section to rest against might give more support without affecting the decoupling too much?

Just thinking out loud, but not necessarily in joined-up. :lol:
Wow, I didn't know you read this thread Paul. :dance: I mentioned I was worried about it sagging but I won't know what will happen until I get my hands on one.

They seem ideal in so many ways. It's just I don't know how stiff they will be and how easy it will be to position the tweeter sphere in exactly the same place. Oh and I hope they don't rattle. If it doesn't work out I will have to build a couple of lamps :lol:
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Re: Doc modding Marantz imperial 7

Unread post by karatestu »

Firebug1 wrote: Tue Mar 01, 2022 7:08 pm I think it would be good and at a quick look, it will probably look like the tweeter sphere is floating in the air above the mid sphere.
That will be interesting 8-)
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Re: Doc modding Marantz imperial 7

Unread post by karatestu »

TheMadMick wrote: Tue Mar 01, 2022 8:32 pm In case you need an alternative support, these are sold as mic supports and you can get mounting plates for them. If interested, I think I have some somewhere and you could have them for the postage. They are chrome finish.
Thanks Mick that is a very kind offer.
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Re: Doc modding Marantz imperial 7

Unread post by slinger »

I read through most of the threads at some time, Stu. Unlike a lot of forum dwellers throughout the universe though, I generally don't say anything until I've actually got something to say (or I feel like derailing the thread with something stupid, obviously). :lol: :lol: :lol:
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Ithilstone (Thu Mar 10, 2022 3:05 pm)
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Re: Doc modding Marantz imperial 7

Unread post by karatestu »

Increasing the distance between the tweeter diffuser sphere and the up firing mid bass improved the sound for me with the problem I had - resonance at that wavelength. However :roll: I still wasn't happy. Something was amiss and it should have been the first thing that I thought of but here in numpty land the limited supply of brain cells don't always work the way you want them to.

Latteman will concur with the following I think. Isolating the speakers from the floor does a lot of wonderful things for me but it has done something that I was not aware of that has just dawned on me. It has increased the level of the lower treble relative to everything else. Don't get me wrong, bass isn't lacking at all but the higher output from the driver seems to be unmasked for want of better word.

Isolating the drivers from their enclosures has elevated this even more. I am so glad I did it as for me it brings many improvements (for me) but the effect of this is my frequency response is too hot in the lower treble. I don't need to measure anything to realise this. I should have known that the main reason for my dissatisfaction was a frequency response hump. Although here we collectively like to believe that a flat response is not the most important speaker parameter this has highlighted the fact that it is important. I wouldn't sacrifice the other things for a table top flat FR but I can't live with what I had. After the initial wow had worn off it was evident that something needed tweaking.

First port of call was the passive line level 1st order high pass filter. I had set it at approx 7KHz for the old drivers. Never bothered to change it. But many things have changed since then. So for a quick experiment I went back to speaker level 1st order (cos it was easier and quicker) with a single 3.3uf cap. Yes the FR was better as the xover has been pushed higher to approx 12KHz. Big change and it did solve the problem but now a bit of a dip in the FR.

Next I tried 4.7uf which was better - xover around 8.5KHz. Still a smidge hot with the flute track. Running out of cap values so paralleled a 3.3 and 1uf for 4.3uf. That is about right. Can't quite believe I am having to xover so high now (9.5KHz)after this driver and speaker isolation. Other things have changed as well but I will come to that later. No pics to show, sorry.

Whilst I had found the right xover frequency I was aware that something was missing and assumed it was the change from passive line level 1st order high pass (between pre and power amps) to speaker level capacitors. So I decided to go back to passive line level and changed the polystyrene cap I use for that for a lower value. Put some 330pf in and bingo. Xover is now at approx 10.2 KHz and sounds about right to me.

After all that I could have just said I needed to change the high pass filter and that would have sufficed but you got this essay instead. :roll:
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antonio66 (Fri Mar 11, 2022 4:42 am)
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