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 Aug 12, 2019 9:02 am

I don't think shape would make a difference. Sounds to me what they were made of is responsible for the bass

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Re: Doc modding Marantz imperial 7

Unread post by _D_S_J_R_ » Mon Aug 12, 2019 12:18 pm

karatestu wrote:
Mon Aug 12, 2019 8:26 am
I was thinking yesterday (dangerous) why the 3 way semi omni design using the original Marantz cabs didn't work (yeah remember those ?). The small cabs on their own with just up firing 5" and front firing tweeter worked straight off. The cab volume is a little more than what they need so they are over damped.

The Marantz cabs however with single forward firing 12 " was another matter. The bass was overblown on bass heavy music like Portishead, jamiroquai and Morcheeba. I thought it was the box volume being too low. But i think i was wrong. Doc successfully used a 15" cube for his BBC(ubes) which i am guessing from the context of the previous posts was the outside measurements. Take the acrylic thickness out of the equation and you are left with a cabinet volume of just under 40 Litres.

The Marantz cabs were about 43 Litres from memory. So my conclusion is that it was the box shape which fooked things up. The Marantz are tall and not so deep like many speakers of the early 70's era. If my thinking is correct then the idea of using cubes does everything that the Doc said it did :guiness; But then my little cabs with up firing mid are not cubes either.

Flawed logic ?
Was the sound bad with original Marantz bass units or when they were heavily doped? Bass is omni-directional anyway but if the midrange was all but removed by excessive doping, that could also explain it perhaps? The drivers NVA used were good for doping but maybe not all if they're well enough behaved without it? I don't even begin to understand it taken as a whole, but drivers have suspensions and other characteristics meaning to me anyway, that you can't treat them all the same - some are designed to use ported boxes and others not for example.

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karatestu
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Re: Doc modding Marantz imperial 7

Unread post by karatestu » Mon Aug 12, 2019 1:33 pm

I used Doc's ready doped kevlar 12 inchers in the Marantz cabs, i never used the original bass drivers.The mid was removed from the Marantz but i was using one of docs 5" ready doped drivers as a mid in a seperate enclosure along with the tweeter. The Marantz cab housed the docs 12 " bass drivers and nothing else. Smaller cab plonked on top with 5" mid firing up

Marantz cab set up was like this Image

But smaller cab had 5" mid moved to an up firing position like this Image

This is the set up i use now with same original smaller cab on top of a big ass cube (which then turned in to an isobaric cube).

Image

Tomasz will love to see these pics :lol:

The marantz cabs are chipboard but every square inch of them was covered in 5mm steel and i even have 5mm steel angle in the corners. The cabs could not have been any more rigid. The big 80 odd litre cube cabs that replaced them are made out of crappy ikea chipboard with no steel added at all and there have never been any problems with these.
DIY inspired by Richard "The Doc" Dunn RIP

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Re: Doc modding Marantz imperial 7

Unread post by _D_S_J_R_ » Mon Aug 12, 2019 1:43 pm

I think the idea of wall tiles seems good, as the adhesive used would damp the wooden enclosure and the tile itself is very stiff and not prone to bending.

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Re: Doc modding Marantz imperial 7

Unread post by Daniel Quinn » Mon Aug 12, 2019 2:07 pm

They don't look equal volume and the drivers are placed differently. I would be very surprised if the shape itself was responsible for what you heared.

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karatestu
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Re: Doc modding Marantz imperial 7

Unread post by karatestu » Mon Aug 12, 2019 2:32 pm

The marantz cabs are a slightly larger volume than the BBCube that Doc came up with just before he passed (RIP). The big bass cubes of mine are over 80 Litres (but there are two 12" bass drivers per cab in isobaric configuration).

I won't be using the Marantz cabs in my main system but want to use them with an electronic drum kit . Solving the overblown bass would be useful as i still want to use the same kind of drivers, sealed box with up firing mid and front firing tweeter.

I wish i knew exactly what the problem was. Back when i was doing it i put it down to too small a volume as the specs of the raw drivers give a required volume of roughly 80Litres, but Doc has made me think again. Cabinet was maybe vibrating or something was loose. I will have to revisit those marantz cabs, shame to discard them as i spent a good deal of time on them.
DIY inspired by Richard "The Doc" Dunn RIP

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Re: Doc modding Marantz imperial 7

Unread post by _D_S_J_R_ » Mon Aug 12, 2019 2:41 pm

Have you tried turning the cabs so the bass driver is further from the floor?

A pal recently sold a pair of Goodmans Magnums with good drivers but shit boxes and despite their size, they did sound better balanced off the floor on low stands, as did most speakers like this I heard from the late 60's to early 70's I remember.

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karatestu
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Re: Doc modding Marantz imperial 7

Unread post by karatestu » Mon Aug 12, 2019 5:00 pm

_D_S_J_R_ wrote:
Mon Aug 12, 2019 2:41 pm
Have you tried turning the cabs so the bass driver is further from the floor?
I think i tried them turned upside down but can't remember. I will have to read the early part of this thread as i think i would have mentioned it.
DIY inspired by Richard "The Doc" Dunn RIP

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Re: Doc modding Marantz imperial 7

Unread post by karatestu » Wed Aug 14, 2019 6:24 am

I am going to revisit the down firing bass cab as i dont think i tried it in isobaric configuration. Will play with distance between driver and floor if there is promise. If it works then i will have downward firing isobaric bass and up firing 5". If the mid has its own enclosure at the top then i would only need one. Same goes for tweeter, just one forward firing. That will keep cost and complexity down and i can still add a third 12 incher.

Choices, choices .
DIY inspired by Richard "The Doc" Dunn RIP

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Re: Doc modding Marantz imperial 7

Unread post by karatestu » Fri Aug 16, 2019 11:24 am

It seems you can have isobaric bass drivers at 90 degree angles to each other. Who knew. :geek:

This is copied from diyaudio.com

"I had some speakers that used Dynaudio 30W54 in isobaric loading, but ran them right up into the midrange. No problems- but they used a trick to get around the issue. Front driver mounted in a smallish subchamber on the front wall. Back driver mounted on the bottom wall, i.e., 90 degrees with respect to the front driver. And the back driver fired into the subenclosure through a Variovent. This way, the speaker was isobaric at low frequencies, but not in the midrange. Tradeoff was some extra volume, but the bass quality was some of the best I've ever heard."

Richard would have probably tried this but who knows. :think:
DIY inspired by Richard "The Doc" Dunn RIP

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