Doc modding Marantz imperial 7

A place for DIY project discussions.
Forum rules
1. No ad-hominem
2. No spamming or shilling
User avatar
Toontrev
Posts: 120
Joined: Mon Aug 22, 2016 12:48 pm
Location: Chester le Street

Re: Doc modding Marantz imperial 7

Unread post by Toontrev » Sun Jun 02, 2019 3:11 pm

This is the info the Doc gave me when I modded my 12"'ers a few years back. -

'Bison first plastidip second. You have two choices depending on whether you bought a can of Bison or are relying on tubes. If only tubes then a nice *thick* worm all around junction between dustcap and cone. It will settle then put another worm. If you have loads then the method I use is to dribble it around the edge of the cone and it will flow down fill in gaps so it flows down evenly across and from the cone to gather at the place you would have had the worm. It will look too much but it dries back a lot so don't worry. Then do the same with the dustcap dribble to cover. Let completely dry over a few day and then spray twice with plastidip all over (dry time between) - job done.'

As I'm in my late 50's, dribbling around the edges seemed the most appropriate method. As pointed out, does seem to be an excessive amount of adhesive at the time, but dries right back and is barley noticeable.

Regards Trevor

User avatar
karatestu
Posts: 1801
Joined: Sun Jan 08, 2017 4:40 pm
Location: North Yorkshire
Great Britain

Re: Doc modding Marantz imperial 7

Unread post by karatestu » Sun Jun 02, 2019 3:34 pm

Thanks for that Trev, very helpful.

I have loads of bison kit so can do the dribbling method. Cheers.

I can feel the bison headache already :lol:
DIY inspired by Richard "The Doc" Dunn RIP

User avatar
Ithilstone
Posts: 496
Joined: Mon Jun 01, 2015 10:54 am
Swaziland

Re: Doc modding Marantz imperial 7

Unread post by Ithilstone » Sun Jun 02, 2019 6:46 pm

There is more to doping Doc's way that just splash it on driver - actually a lot more. But principle is quite simple - physically limiting the driver. If one think about it it is common sense in how it need to be done - just don't overdo it as too much doping is worst than not enough.

I had a chance to listen BBCubes in both configurations - BBCube is made of 3 drivers. Up firing low end, forward firing tweeter and mid driver that can be set inward or outward ( simple swapping left with right ) From my experience inward is good but surprisingly comes close to point and squirt sound when mid is outward it sound like cube 1 on steroids just way way more of all the goodness;]
Nothing to see here...

_D_S_J_R_
Posts: 4188
Joined: Mon Feb 03, 2014 9:53 am
Location: The end of the road in Suffolk Coastal.
Wales

Re: Doc modding Marantz imperial 7

Unread post by _D_S_J_R_ » Sun Jun 02, 2019 7:50 pm

Daniel Quinn wrote:
Sun Jun 02, 2019 10:24 am
The resistor on the tweeter is dependant. I use expensivec scans peak tweeters with a 5 ohmn resistor..

Doping increases the effeciency it deos not destroy it. There is an argument to say its the same as a passive xover
How can doping do that? You're increasing the mass of the cone (the driver suspensions can take it though) and audibly as much as anything else, it takes more electrical energy to get the cone moving and a rather higher volume control setting. Passive crossovers, if not done to excess, don't lose the efficiency, but may well cause other problems - depends on the speaker. If you wish to read up, I'm sure there are many good references to explain it. Using the room to spray the sound all over doesn't always make up for this. Anyway, I appreciated the Doc-Mod B&W's but have never liked omni's whatever the make, but fans of the Cube concept swear by them and if owning and using them makes people go out and buy even more music (as I was told a few days ago), then that's what it's all about isn't it?

Daniel Quinn
Posts: 7610
Joined: Thu Jul 12, 2012 7:16 am
Wales

Re: Doc modding Marantz imperial 7

Unread post by Daniel Quinn » Sun Jun 02, 2019 7:57 pm

Passive crossovers lose effeciency. Go and do some reading then you can apologise

User avatar
karatestu
Posts: 1801
Joined: Sun Jan 08, 2017 4:40 pm
Location: North Yorkshire
Great Britain

Re: Doc modding Marantz imperial 7

Unread post by karatestu » Sun Jun 02, 2019 8:11 pm

Ithilstone wrote:
Sun Jun 02, 2019 6:46 pm
There is more to doping Doac's way that just splash it on driver - actually a lot more. But principle is quite simple - physically limiting the driver. If one think about it it is common sense in how it need to be done - just don't overdo it as too much doping is worst than not enough.

I had a chance to listen BBCubes in both configurations - BBCube is made of 3 drivers. Up firing low end, forward firing tweeter and mid driver that can be set inward or outward ( simple swapping left with right ) From my experience inward is good but surprisingly comes close to point and squirt sound when mid is outward it sound like cube 1 on steroids just way way more of all the goodness;]
Thanks for your input Tom. I have over doped and it sounded bad - no life or get up and go. I remember doc saying it was surprising how little was needed with the drivers firing up (much of the unwanted frequencies and rough output is directional and the driver is not fpointing at you). When i got my 5 inch mids they were for a doc mod 3 way point & squirt project (marantz imperial 7). That is probably why doc filled the cone with bison leaving only a few millimeters of the cone visible. Its almost full to the top. They dont sound bad, in fact they sound damn good although now used firing upwards.

With my isobaric configuration it is even more complicated. There needs to be a 5" midrange for each bass driver to make things equal ( mid has to share the enclosure with a bass driver). So i will end up needing four more mid drivers as well as two bass drivers. Two on one side and one on the other ? Also three bass drivers means height of cabinet will be just over a metre. Not a problem in my book.

Stu
DIY inspired by Richard "The Doc" Dunn RIP

_D_S_J_R_
Posts: 4188
Joined: Mon Feb 03, 2014 9:53 am
Location: The end of the road in Suffolk Coastal.
Wales

Re: Doc modding Marantz imperial 7

Unread post by _D_S_J_R_ » Sun Jun 02, 2019 9:41 pm

Daniel Quinn wrote:
Sun Jun 02, 2019 7:57 pm
Passive crossovers lose effeciency. Go and do some reading then you can apologise
Apologise for what exactly? I know I'm right - mostly :lol:

valvesRus
Posts: 204
Joined: Sat Feb 24, 2018 2:34 pm
Great Britain

Re: Doc modding Marantz imperial 7

Unread post by valvesRus » Sun Jun 02, 2019 10:18 pm

_D_S_J_R_ wrote:
Sun Jun 02, 2019 9:41 pm
Daniel Quinn wrote:
Sun Jun 02, 2019 7:57 pm
Passive crossovers lose effeciency. Go and do some reading then you can apologise
Apologise for what exactly? I know I'm right - mostly :lol:
You are right Dave, and DQ is wrong.

Gunged up drivers need more power to get similar sound levels (even without crossovers) so they must be less efficient.

It could (no doubt) be measurable. :)

User avatar
savvypaul
Posts: 3299
Joined: Tue Oct 11, 2016 7:14 pm
Location: Durham
Contact:
Great Britain

Re: Doc modding Marantz imperial 7

Unread post by savvypaul » Sun Jun 02, 2019 10:20 pm

The Cubes are the least efficient (db/1w) speaker that I've owned but still plenty of volume at midday on the p90sa dials...
"The one who would whistle to Throbbing Gristle through harsh times in Umberstone Covert."

HiFi Foo Fight Blog
NVA BMU / BTE Designs Lenco 59 / ATP-12t / Denon 103 / NVA Phono2 / GSP Revelation / Vortexbox Appliance / Sonore microRendu USB streamer w/ LPSU / RME ADI-2 dac / NVA P90sa / NVA A80MK2 (bass) / NVA A70 MK2 (tweeters) / Marantz 2015 / NVA Cube 1 / Klipsch Heresy 3 /NVA TIS MK1 / NVA SSPMK2 / NVA LS6 / NVA AP10H / Grado sr225e

User avatar
karatestu
Posts: 1801
Joined: Sun Jan 08, 2017 4:40 pm
Location: North Yorkshire
Great Britain

Re: Doc modding Marantz imperial 7

Unread post by karatestu » Mon Jun 03, 2019 6:38 am

I think Daniel's argument is that passive xovers reduce efficiency more than doping the cone. That might be the case with the experience that he has. A 5 ohm resistor is nowhere near the 12 ohm that most of us use and the xover may have had a damping resistor for the tweeter already. I suppose it would depend on the design of the actual xover removed and the amount of dope applied.

I do know doping reduces the efficiency but not sure how much. I have never heard the doc's drivers before doping ( yet).
DIY inspired by Richard "The Doc" Dunn RIP

Post Reply