Doc modding Marantz imperial 7

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Daniel Quinn
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Re: Doc modding Marantz imperial 7

Unread post by Daniel Quinn » Mon Jun 03, 2019 8:02 am

Not more, but a comparable amount, that you need not worry about lack of effeciency in doped drivers.

I've tried the drivers before and after doping, if you factor in increased ineffeciency due to crossover, you are talking about negligible amounts.

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karatestu
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Re: Doc modding Marantz imperial 7

Unread post by karatestu » Wed Jun 05, 2019 8:31 pm

More thoughts.

Doc's bbc were modular like cubix so you could buy one cube and add more. I will be going for three isobaric 12 inchers straight off so the cabinet can be all one instead of three different parts. The drivers are really made to be mounted on the inside of the cabinet and i think that is what i will do for bass and mid drivers. Decorators caulk and crews. No more silicone sealant for drivers as last time i used it i had to put a bottle jack inside the speaker and jack the bugger out :lol:

As usual i will do a prototype out of crap chipboard first. Got some old ikea stuff floating about somewhere. Box will have to be a boring rectangle due the isobaricness :think: . Width 35cm, depth 35cm, height ~ 100cm. I save some height by only having one thickness of wood between each cube. Back panel will obviously have to be removable otherwise i wont be able to get the drivers in :doh: .

So drivers required = 6 x 12", 6 x 5" and not sure about tweeters yet. At least one per speaker :lol: . But do i need three per speaker ? Getting complicated and expensive but i have four bass drivers, two mids and two tweeters already.

Have to give thought to every section being the same as far as bass and mids go. Each section needs one 12 " and one 5 " due to mid sharing the cube with the bass driver. But not sure if ineed more than one tweeter per channel as they are enclosed .

Then thoughts turn to loading of amplifiers. One amp for the whole thing may be a challenge - would require a lot of series connections between bass an mid drivers with tweeters in parallel. Tweeter load is 20 ohms as visaton is 8 ohms but there is a 12 ohm resistor in series added on to that. As i have 6 channels of nva amplification at my disposable then i might as well design the speakers with that in mind. If only one cube has a tweeter then the loading on that amp will be different to the other two

More thinking to do :think:
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 » Wed Jun 05, 2019 8:33 pm

Can't believe this saga has reached 50 pages :o
DIY inspired by Richard "The Doc" Dunn RIP

jimbob
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Re: Doc modding Marantz imperial 7

Unread post by jimbob » Wed Jun 05, 2019 10:38 pm

I think the cubix pro had 3 tweeters? One forward and one to either side
Squeezebox Touch - Colin Wonfor mini pre - EWA M50 Power Amp - Modified NVA Cube 2 mk1 - SSP MK2 - LS6

NVA P90sa - NVA A60 MK1 - DIY Cubettes - SSC - LS3

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karatestu
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Re: Doc modding Marantz imperial 7

Unread post by karatestu » Thu Jun 06, 2019 6:13 am

Yes, the cubix had a tweeter per cube . But they only had one other driver - the 8" mid / bass.

Two possible reasons why Doc did this. It sounded better having tweeters on the sides of the cabinet. He wanted each amp to be loaded EXACTLY the same. The amp that has the tweeter in paralell with the bass will be loaded at say 4 ohms rather than 8 ohms with just bass. For the isobaric thing to work best it will probably require all amps loaded exactly the same.

Ways around it. (1) Have 8 channels of amplification with 2 of them driving a tweeter each. (2) all 12 inchers wired in series and driven by one amp, all 5 inchers wired in series and driven by another amp, tweeter driven by its own dedicated amp.

Dont fancy 8 channels of amplification so maybe no.2 would work and save buying two more tweeters. Amp on the bass drivers will see a 24 ohm load 8+8+8) as will the amp on the mid drivers. Tweeter amp with see 20 ohms (8 + 12 ohm resistor).
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 » Thu Jun 06, 2019 6:22 am

Just thought that if the bass and mid drivers are mounted from inside the cabinet then the grilles used can be totally flat and if a rebate is routed then they will sit flush with the baffle :dance:

Tweeter will need a domed grille. Smaller is better aesthetically for my tastes. One that just covers the tweeter face plate (100 mm) if i can find one.

Sorry for boring yall. This thread is where i dump my ideas so i don't forget and can look back in the future. No doc to keep me on the right track :cry:

Stu
DIY inspired by Richard "The Doc" Dunn RIP

jimbob
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Re: Doc modding Marantz imperial 7

Unread post by jimbob » Thu Jun 06, 2019 8:51 pm

This isn’t boring at all, I’m looking forward to reading more about this project!
Squeezebox Touch - Colin Wonfor mini pre - EWA M50 Power Amp - Modified NVA Cube 2 mk1 - SSP MK2 - LS6

NVA P90sa - NVA A60 MK1 - DIY Cubettes - SSC - LS3

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karatestu
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Re: Doc modding Marantz imperial 7

Unread post by karatestu » Fri Jun 07, 2019 7:06 am

jimbob wrote:
Thu Jun 06, 2019 8:51 pm
This isn’t boring at all, I’m looking forward to reading more about this project!
:guiness;
DIY inspired by Richard "The Doc" Dunn RIP

Daniel Quinn
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Re: Doc modding Marantz imperial 7

Unread post by Daniel Quinn » Fri Jun 07, 2019 8:07 am

Mounting from the inside will assist in them being air tight but you will need a precise cut out.

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karatestu
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Re: Doc modding Marantz imperial 7

Unread post by karatestu » Fri Jun 07, 2019 8:13 am

Daniel Quinn wrote:
Fri Jun 07, 2019 8:07 am
Mounting from the inside will assist in them being air tight but you will need a precise cut out.
Very true Dan. Need to practice my routing skills. Messy cut outs can't be hidden . Same goes with rebating for a flat grille.
DIY inspired by Richard "The Doc" Dunn RIP

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