Doc modding Marantz imperial 7

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r3xj0hn570n
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Re: Doc modding Marantz imperial 7

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karatestu wrote: Sun Jul 11, 2021 6:41 am
Good work. Did you do well ? I am hopless at it as well as most other sports apart from tennis and table tennis) I taught my son how to make a bow from a Sycamore (-type of maple) branch a couple of weeks ago :grin:
2nd highest score in the competition, the guy who beat me was using long stabilizers and a scope. I won my class (hunter class).
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karatestu (Mon Jul 12, 2021 8:16 am)

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Re: Doc modding Marantz imperial 7

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karatestu wrote: Sun Jul 11, 2021 7:22 am My thoughts have turned to casting my own concrete hemispheres. :roll:
I made a set of concrete lines speakers once. Serious threat to my toes, back, children, pets. Glad i didn't have them when the earthquake struck.
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karatestu (Mon Jul 12, 2021 8:16 am)

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Re: Doc modding Marantz imperial 7

Unread post by karatestu »

r3xj0hn570n wrote: Mon Jul 12, 2021 7:16 am
karatestu wrote: Sun Jul 11, 2021 7:22 am My thoughts have turned to casting my own concrete hemispheres. :roll:
I made a set of concrete lines speakers once. Serious threat to my toes, back, children, pets. Glad i didn't have them when the earthquake struck.
Yeah that worries me too so the stand/legs will have to be super robust and sturdy.
DIY inspired by Richard "The Doc" Dunn RIP

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karatestu
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Re: Doc modding Marantz imperial 7

Unread post by karatestu »

Here's what a 5.25" mid bass looks like in a 30cm pig ball.

Image

No rebating as the walls aren't thick enough. If I go concrete then the outside dimension wil be 35cm to allow for the wall thickness required. I can then rebate the drivers for as smooth a transition from cone to cabinet as possible. I will probably removing the foam like ring which is around the outside of the surround with something that is rounded over to meet the cabinet and extend the smooth curve right up to the driver surround. I think it will be worth doing seeing as though the mid bass is more or less run full range and producing output up to 8kHz and above. It will be beaming by that point though.
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Latteman (Mon Jul 12, 2021 9:42 am) • CycleCoach (Mon Jul 12, 2021 1:09 pm)
DIY inspired by Richard "The Doc" Dunn RIP

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Re: Doc modding Marantz imperial 7

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Further ridiculous goings on here with aesthetically challenged speakers. :grin:

Picture from the side of tweeter without face plate (bit blurry as both my hands were shaking)

Image

You can see all the dome from the side. Compare that to with the face plate on

Image

Not much of it now visible. Removing the face plate has changed the directivity of the tweeter quite a lot. More output at 90 degrees. The lower frequencies that the tweeter is producing are no longer funnelled forwards like with a wave guide. The text book experts and graph lovers would say I have done the wrong thing and made it worse. Well I can't prove it measures better but it will definitely measure different. All I know is it sounds different and I think much much better for what i am trying to achieve here.

Now I have all my tweeters minus face plates and gaffa taped into spheres I thought I would make some crude and quick supports as I had them sat on bits of chipboard with holes cut out :roll: . As the pods aren't balanced for weight (there is no back firing tweeter) they always want to roll over forwards.

I made a quick loop out of steel wire and fixed it in to a 4cm long piece of old broom handle which is hot melt glued to the mid bass cube.

Image

As I wanted to try the tweeter pod directly over the up firing mid bass I positioned it as in the pic. The spherical underside and back of the sphere will act as a sort of diffuser although not a perfect one as it four flat sides with tweeters in. More on this later.

I placed the tweeter pod in the loop and watched it sag down at the front as the pod is front heavy. Four tweeters weigh a surprising amount. The glue and loop held so I added a front support made of a screw and hot melt glued that to the steel loop.

Image

That worked out nicely so I placed the tweeter pods in their temporary stands.

Image

I managed to get the pods at the right angles and so sat down to listen. TBC.............
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CycleCoach (Mon Jul 12, 2021 1:10 pm)
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Re: Doc modding Marantz imperial 7

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I never drew the side view of the speaker with tweeter pod directly above the up firing mid bass.

Well here it is

Image

I think it looks better than having it half way over the mid bass or completely behind. Can't go on just looks though.
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Re: Doc modding Marantz imperial 7

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When I switched on and started playing it sounded awful. I soon realised there was no sound form the left hand tweeters :roll: I took one of the tweeters out and sure enough one connector had come orf. Ofc if you have several tweeters wired in series and lose a connection then non of them work. I corrected that before proceeding.

Having listened to quite a few albums I can find nothing not to like about this experiment with tweeter pod directly above the mid bass. :dance: It certainly is not ideal because I have tweeters held in with tape that is wrinkled a bit, the tweeters are not all flush with the ring of the cut out at all points and the crappy wire cradle is not helping.

Even so it sounds bloody good. There are some changes that at first I could not get my head around. I don't know what is exactly going on but there is more fine detail on offer and spaciousness. No harshness at all that I have tuned in to yet but there are many more albums to test it with yet. It is a slightly more energetic presentation but not too far the wrong way.

I had a bit of a mid band dip built into these speakers to start with because certain frequencies annoy the feck out of my ears. This has boosted the mid range a very small amount I think because the top three octaves from this mid bass start to get directional and eventually beam straight at the ceiling. I expect the underside of the tweeter sphere is dispersing those frequencies in other directions including straight at me. Drivers that fire up (and down, to the sides etc) lose a bit of sensitivity doing so but the upside is any remaining break up is not heard.

I have not really heard any issues with time alignment although that is hard to spot the difference between mounting a tweeter on the front of a cube and then moving it to where the mid bass is located is quite staggering. Yes there will be wave interference from the top of the mid bass cab and the mid bass itself but that is a very small price to pay IME.

All the tweeters except the up firing one are above the periphery of the up firing mid bass. Before moving the pod, it was behind the mid bass with the front firing dome above the back edge of the MB. I think the way I have it now might actually be an improvement as all the tweeters are now over the mid bass. The up firing tweeter may be spoiling things a little, I don't know. I may try removing that one and see what happens. the tweeters volume will go up a little as the load on the amp reduces from 21 ohms to about 16 ohms. I may end up reverting back to an up firing tweeter but don't know til I try without. I never liked one on the back when I tried it.

If I continue to be as happy with this pod placement then it will be staying :dance: It looks better to me from all angles not just the side.

I think I need to get my tweeters into the pods without gaffer tape as the next step on this road. That will surely help clean things up even further. Then I need to construct a better way of suspending this pod above the MB by one pipe only into the back of it like in the last drawing above. Cables can go in through there. At the moment I am trying not to irreversibly modify the pod so making it unsuitable for the final build. But I am at some point going to have to drill a hole for a pipe and support it inside the pod to take the weight. That time looks like being soon.

I want to be able to play around with the height of the pod above the mid bass so the support will have to be height adjustable.
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CycleCoach (Mon Jul 12, 2021 6:12 pm) • Toontrev (Tue Jul 13, 2021 11:10 am)
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Re: Doc modding Marantz imperial 7

Unread post by karatestu »

Listened to Kate Bush Ths whole story, best of Gerry Rafferty, The Crusaders Street Life, Stevie Wonder Innervisions, The Police Synchronicity, Donald Byrd Places and Spaces, Herbie Hancock Headhunters, Black Byrds City Life and Unfinished business.

The music never put a foot wrong, it was inviting, spacious, relaxing, dynamic and incredibly detailed without fatigue. I've listened more or less all day and I could carry on til bed time.

The last album I played was The Police Zenyetta Mondatta and that just blew me away, never heard it so good.

This tweeter pod directly above the up firing mid bass is staying I think :guiness;
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CycleCoach (Mon Jul 12, 2021 6:12 pm) • Latteman (Tue Jul 13, 2021 4:25 pm)
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Re: Doc modding Marantz imperial 7

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Possible alternative to bison kit maybe ?

https://uk.rs-online.com/web/p/adhesi ... chtype=
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Re: Doc modding Marantz imperial 7

Unread post by Latteman »

karatestu wrote: Mon Jul 12, 2021 3:20 pm Having listened to quite a few albums I can find nothing not to like about this experiment with tweeter pod directly above the mid bass. :dance: It certainly is not ideal because I have tweeters held in with tape that is wrinkled a bit, the tweeters are not all flush with the ring of the cut out at all points and the crappy wire cradle is not helping.

Even so it sounds bloody good. There are some changes that at first I could not get my head around. I don't know what is exactly going on but there is more fine detail on offer and spaciousness. No harshness at all that I have tuned in to yet but there are many more albums to test it with yet. It is a slightly more energetic presentation but not too far the wrong way.
Although our systems are very different I implement some of the ideas u post- I will agree placing tweeter pods over the mid bass does energise and promote the mid bass.
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karatestu (Thu Jul 15, 2021 6:50 pm)
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