Doc modding Marantz imperial 7

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karatestu
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Re: Doc modding Marantz imperial 7

Unread post by karatestu »

SteveTheShadow wrote: Fri Mar 11, 2022 11:40 am Joe Ackroyd of Royd fame ran his bass/mid units sans dustcap. His pole pieces were not vented though, so he didn’t have the problem of the cavity resonance. They were decent speakers but lacking in bass, especially the Eden, which had the internal steel plates. Weighed a ton. Nearly killed me carrying the pair I bought, all the way from Sheffield Devonshire Green to the train station. Good job it was downhill and I was still in my twenties at the time. :lol:
I have liked all the Royd speakers I have heard. They need to be right against the wall. I liked Epos speakers as well but not heard any in a long while.
DIY inspired by Richard "The Doc" Dunn RIP

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Re: Doc modding Marantz imperial 7

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Latteman wrote: Fri Mar 11, 2022 12:58 pm I had the minstrels- similar no dust cap design- they were sensitive to sunlight / heat which made the ‘dope’ run into the voice coil killing them if not maintained
What was the dope he used on those ? I can't see blacktack or blutack running like that. I had thought of trying the black gutter sealant as it is butyl rubber based and never goes hard. My new flat dust caps would sit nice on top of it and it does stick things.
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Re: Doc modding Marantz imperial 7

Unread post by karatestu »

I have listened to parts of various albums now with dipole tweeters, mainly jazz as they are on the whole better recordings.

My past brushes with open baffle have been interesting but ultimately flawed and never really satisfying. That was with a mid bass though. I have never tried open baffle tweeters though, until now.

Well what can I say apart from I love it. :romance-smileyheart: The sound is so open and airy with a sense of ease. Every album I have played has been good with no problems. Donald Byrd - Slow Drag, Places and Spaces, Street Lady, Stevie wonder - Songs in the key of life, The police - Synchronicity.

The last track on Slow Drag has some brush work and I have never heard anything like it. Some instruments appear outside the speakers now which has never happened before. It's bloody awesome :dance: No draw backs I can hear. Listening to The Crusaders - Street Life now. The emotion in Randy Crawford's voice is at an all time high.

I now have a problem though. I don't like the look of the naked tweeters as much as when they were in a sphere. From the listening position they look good but not so much from the side. But I much prefer the sound with the dipole tweeters. Other variables have changed too like there is no longer a 15cm diameter sphere over the top of the cone. I don't sonically need the diffuser as the front firing tweeter fills in the top end.

I do worry about the re radiation from the mid bass off the tweeter but I can't hear anything that points at that being a problem. Same with the abrupt edge at the end of the rubber ring I have stuck on the front of the frame. I can't remember at what frequency it will start to diffract from a 95mm circle. I suppose it helps that the high pass filter is at 10KHz and by the time we reach the frequency with a wavelength greater than 95mm the driver's output is 18dB down.

The other thing that has changed is the tweeter is right above the mid bass' voice coil now. When it was mounted in the sphere it was above the surround so it has moved back about 7cm. Sounds good to me, it's hard to say if it has had an effect as other things have changed at the same time.

The goosenecks work really well. The 20cm ones are just the right length to get the tweeter right above the mid bass' voice coil. They are stiff but easy to bend where you want them and they stay in that position. There is bugger all weight on them which helps. It turns out they were made by QTX :lol: :lol: :lol: Where have we heard that name before :grin:

I will have to have a think about ways to make the naked driver look better. The wires will be inside the gooseneck eventually so that's not going to be a problem. You can buy black magicians soft foam balls about 10cm diameter. If I hollowed one of them out to go on the back of the driver maybe ? Would that kill the dipole loveliness ? Or strangle the back wave too much ?
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Re: Doc modding Marantz imperial 7

Unread post by karatestu »

Actually I think I have more of a problem with the looks of the gooseneck than the naked driver. Just doesn't look right to me. I am now considering using a simple rigid pipe with one 90 degree bend in it. Maybe a 15mm copper pipe.
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Re: Doc modding Marantz imperial 7

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I read the whole goodmans thread that popped up and found this quote from Doc

"No, and steel plate is not damping. Damping is a mechanical filter, steel plate is about cabinet rigidity, so mass damping is not an expression I would use. Quite simply steel plate (and the more of it the better) stops the cabinet storing energy and talking.

Initially you will think less bass, but it is real bass that is left and not bloat and you will need to push the speaker further back to the wall."

With the mention of steel lined Royd's being a bit bass shy then I thought it would be relevant here. I agree completely with what RD said apart from the bit about it stopping the cabinet storing energy. It was my belief that mass increased the resonant frequency of the box which made it harder to excite.

Anyway it matters not. The general thing is that when I first moved to extremely rigid 3mm steel spheres I also noticed the dramatic reduction in what I thought was bass. It was of course bloat and cabinet talk which I had previously completely under estimated. What is left now is real bass not stunt bass :grin:

So yes they need to go further back to the wall to get more boundary gain. In my case I was eager to keep the mid bass low down and sk close to the wall / floor junction. As I don't want to introduce baffle step circuitry or the new devilry which is dsp then it is the only thing that can be done.
DIY inspired by Richard "The Doc" Dunn RIP

antonio66
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Re: Doc modding Marantz imperial 7

Unread post by antonio66 »

I quite liked the 'gooseneck', reminded me of War of the Worlds for some reason, but pleased you enjoyed your experiments.
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karatestu (Sat Mar 12, 2022 5:11 pm)

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Re: Doc modding Marantz imperial 7

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antonio66 wrote: Sat Mar 12, 2022 4:47 pm I quite liked the 'gooseneck', reminded me of War of the Worlds for some reason, but pleased you enjoyed your experiments.
You are not the only one who likes it Dave :shock: Maybe it will grow on me. Whatever happens there will only be one pipe to mount the tweeter - centrally on the back of it's magnet. That maybe the gooseneck or a rigid pipe with one 90 degree bend in it.

The dipole tweeter (no enclosure) effect is so nice it has to stay. With it being a figure ov eight sound pattern thd side walls do no reflecting. It kind of goes against the omni direction of the mid bass but imo the two go together really well. The imaging and soundstage are very good and I have said before that those attributes weren't something I would pursue if other things were affected.

Well it seems I can have my cake and eat it :grin:
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antonio66 (Sun Mar 13, 2022 8:04 am)
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Re: Doc modding Marantz imperial 7

Unread post by karatestu »

My speaker ends up being more and more like the Linkwitz Pluto. But no transmission lines to soak up the back wave and I cross high whilst the Pluto crosses low and the tweeter is moved to the front of the mid bass to avoid reflections and then delayed.

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Re: Doc modding Marantz imperial 7

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Talking to speedysteve he urges me to take measurements and use holmimpulse to time align the drivers. I feel honoured that somebody as skilled as Steve took the time to give his thoughts. Here is what he said looking at my pic with ob tweeter and gooseneck

"Sort of snake charming vibe🙂
Like it

If you have a measuring mic and free software like Holmimpulse, you can accurately time align.
Very worthwhile.

You can do an approx by ear though, as you have found. Just sorta sounds right and snaps in.

The high frequencies of tweeters mean only small amounts of movement (millimeters) are needed.

Deep bass needs metres and metres so not practical physically. You don't have that problem though"



Yes, things just kind of snaps in and sounds right. Doing it by ear isn't as accurate but you can hear when it is right or thereabouts. I have more tweeter positioning to do. I will measure distances and take notes. Moving it a few mm and taking more notes I should find the right spot. I do know I can't be far away or might already be there. The tweeter is directly above the mid bass voice coil.

It is amazing what a difference it makes getting this time alignment right (with ears only).
DIY inspired by Richard "The Doc" Dunn RIP

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Re: Doc modding Marantz imperial 7

Unread post by karatestu »

Some Green Mountain Audio speakers (RIP Roy) have the mid and tweeter on tracks so the user can fine tune the positioning depending on how high their ears are from the floor when listening. Roy of course was a very vocal advocate of 1st order xovers with driver impedance flattening and time alignment.

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