Doc modding Marantz imperial 7

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karatestu
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Re: Doc modding Marantz imperial 7

Unread post by karatestu »

CycleCoach wrote: Fri Jul 09, 2021 9:07 am I love the idea of a "theoretical speaker suspended in infinite space" but I suspect its behaviour would bear little practical relation to a real speaker in an actual room, where everything in that room plays a part in complicating the scenario.
I think your speakers will work because they will interfere less with the room once they've done their part in energising it.
What do you think?
Anyway, great work Stu! I'm enjoying your experiments immensely.
I don't know exactly what will happen until I have tried it and ironed out any wrinkles as best I can with the limited knowledge J possess. All I know is that spherical tweeter pods with no face plates are amazing and I want more of it :grin: I currently have the spherical pods up and running but tweeters held in with gaffa tape and rested on a crude ring of cardboard on top of my cubes mid bass cabs.

The sound is addictive to the point that I really can't drag myself away or get anymore speaker building done. I truly have never heard anything like it. I don't want to sound like a flowery language newspeak reviewer or come across as overly enthusiastic but it's hard not to convey how much I fecking love the effect it has had.

It produces the most relaxed and easy to listen to music I have ever heard. Others who have done it before have all described the presentation and it is easy to read something like that and think "yeah whatever". But there is such a sense of calm and feeling like being amongst the musicians. All the dynamics, detail and texture is still there but at the same time it sounds quieter and that is impossible because I don't have a volume control. Doc used to say the perception of loud was actually distortion and that loud doesn't sound loud if it's clean and you turn to talk to somebody and find you have to shout. It's the most relaxing, emotional and involving experience I have ever had when listening to reproduced music, and there is still more to do.

As far as taking the room away goes, well you can't. It will always be there unless you listen outside. There are several ways people go off in when it comes to the room. If you are lucky to have a big one :whistle: then you can have the speakers and listening position(s) well away from walls. That doesn't work for speakers with no baffle step compensation though (no bass). Buy or make some highly directional speakers like the ultimate point and squirt which uses a fireman's hose. Or you can throw money at the problem and install ugly and domestically unacceptable room treatments. Or you can follow all the other sheep who want the easy way out and buy a dsp unit which magically sorts it out for you AT ONE LISTENING POSITION ONLY, involves extra circuitry, anologue to digital lies conversion and throws some of the music away for good measure.

Or you can do it like we try to do and use the room for better or for worse.

As I don't measure things then all I can go on is how it sounds, if I like it and try to tie that in with something I have read or other people's comments who have tried it. So far my findings correlate very well with what others have said as regards spherical enclosures.

It is my view that run of the mill enclosures of the usual shape and dimensions are clearly inferior and not just by a little bit. All my speakers will be spherical from now on. Once I had tasted the effect then nothing else will suffice.
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Re: Doc modding Marantz imperial 7

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CN211276 wrote: Fri Jul 09, 2021 11:30 am Certainly thinking well outside the box. :grin: i am interested in how you get on Stu. As far as the main stream speaker manufactures are concerned SQ seems to have gone down at the same rate as prices have gone up.
Thanks for the post and encouragement. Stops me talking to myself and imagining everyone is having a laugh at me.

I stopped going to hifi dealers a long time ago so I am way out of touch with what is on offer these days. I know you have had some experience and it wasn't good. So enjoyment goes down whilst bling and prices go through the roof. Seems to be a good measure of modern life and the way the human race and planet is going.
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Re: Doc modding Marantz imperial 7

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Well the pig balls are going to be unsuitable I think but I will persevere just to be sure. I cut the two opposing holes and sanded down a flange the same width as the drivers. The walls are not as thick as I was hoping and they flex a bit near the cut outs. Added to that the flanges aren't wide enough and when a hole is drilled it breaks through.

A pity but I was half expecting it. They can be progressed by sanding the flanges down a lot further and mounting the driver in a wooden cicle which is wider than the driver. The driver can then be put in a rebate and the periphery of the wooden circle shaped to follow the curve of the sphere. It will require clamping in compression by the four threaded rods running from driver to opposing driver. Lose a tiny bit of volume with this though.

That is the only hope for these plastic pig balls. Some good things have come out of this so far. The ping noise when I hit the complete sphere has now disappeared after I cut the holes and put the drivers in. Also I can now see what the mid bass enclosure looks like with drivers in and I like it a lot.

3mm steel hemispheres are the next to be ordered. Cutting the holes won't be as easy or quick and obviously steel is very resistant to sanding. I have other ideas though and more on that in the next installment of this saga.
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Re: Doc modding Marantz imperial 7

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karatestu wrote: Fri Jul 09, 2021 9:04 pm
CN211276 wrote: Fri Jul 09, 2021 11:30 am Certainly thinking well outside the box. :grin: i am interested in how you get on Stu. As far as the main stream speaker manufactures are concerned SQ seems to have gone down at the same rate as prices have gone up.
Thanks for the post and encouragement. Stops me talking to myself and imagining everyone is having a laugh at me.

I stopped going to hifi dealers a long time ago so I am way out of touch with what is on offer these days. I know you have had some experience and it wasn't good. So enjoyment goes down whilst bling and prices go through the roof. Seems to be a good measure of modern life and the way the human race and planet is going.
Over two years ago now I had a demo through Spendor WAF speakers and it was not a pleasant experience compared to what I was used to at home. Out of politness I did not end it after ten minutes because it must have taken the dealer a while to set everything up and I wanted a loan of the Mscaler. When I was informed that the speakers cost 3.5K you could have knocked me down with a feather.

I do not see the point of manufactures of source components and amps going through dealers if they will be demonstrated through the music stranglers which seem to be all the rage.
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karatestu (Sat Jul 10, 2021 6:01 am)
Main System
NVA BMU, P90SA/A80s (latest spec), Cube 1s, TIS, TISC(LS7)
Sonore OpticalRendu, Chord Mscaler & Qutest, Sbooster PSs
Network Acoustics Eno, ifi iPurifier3, AQ JB FMJ, Cisco 2940 & 2960
DH Labs ethernet, BNC & USB cables, Farnells cat 8 ethernet cable

Second System
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Re: Doc modding Marantz imperial 7

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karatestu wrote: Fri Jul 09, 2021 9:22 pm Well the pig balls are going to be unsuitable I think but I will persevere just to be sure. I cut the two opposing holes and sanded down a flange the same width as the drivers. The walls are not as thick as I was hoping and they flex a bit near the cut outs. Added to that the flanges aren't wide enough and when a hole is drilled it breaks through.
There is a west system epoxy that sticks to polyethylene. It can be plastic welded too. There are heat gun techniques to shape the plastic. You could heat it up to exactly the right temperature, then just place it on a surface and let it's own weight form a thicker flat for the driver frame.
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karatestu (Sat Jul 10, 2021 6:01 am)

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Re: Doc modding Marantz imperial 7

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r3xj0hn570n wrote: Sat Jul 10, 2021 2:06 am
karatestu wrote: Fri Jul 09, 2021 9:22 pm Well the pig balls are going to be unsuitable I think but I will persevere just to be sure. I cut the two opposing holes and sanded down a flange the same width as the drivers. The walls are not as thick as I was hoping and they flex a bit near the cut outs. Added to that the flanges aren't wide enough and when a hole is drilled it breaks through.
There is a west system epoxy that sticks to polyethylene. It can be plastic welded too. There are heat gun techniques to shape the plastic. You could heat it up to exactly the right temperature, then just place it on a surface and let it's own weight form a thicker flat for the driver frame.
Hi Rex,

Thanks for that information, it's news to me. I will have to try and find out what that temperature is and give its a try. I have an old glass table top that is perfectly flat which I could use.

I thought my over enthusiastic subjective drivel had scared you off, I'm glad you are still hanging around :grin:
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Re: Doc modding Marantz imperial 7

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I tried clamping the two drivers to the sphere with 6mm threaded rods that I already have. The rod will only just go through the driver mounting holes. I can actually screw the rod in and it holds. :shock: Saves having to put a nut on. That's ok for one of the drivers but the second can't be installed. I would have to enlarge the driver mounting holes and use nuts on the second.

Added to that the lip on the outside of the driver gets in the way of 6mm nuts and maybe the rubber surround will be compromised too. I will need 4mm threaded rod and nuts which I don't have so will have to order some.

I bought the plastic pig balls because they were cheap, lightweight and easy to machine. I have read that sometimes light but rigid enclosures can sound better than heavy which can resonate for a longer time. I was trying to list my options and what fits my needs the best

1) Translam plywood ring construction- wasteful and expensive plus I don’t have a lathe or the experience to do a good job. Nice to look at and minimum finishing required.
2) Pig balls - cheap, easy to work, lightweight but a bit too flexible for my liking (bass reproduction may suffer), need painting
3) Steel hemispheres- relatively cheap ( compared to acrylic), heavy, prone to ringing, very stiff :dance: , harder to machine, easy to paint
4) Stainless gazing balls- relatively cheap, unknown wall thickness but said to be approx 1.2mm which is very thin for creating a driver mounting flange
5)Acrylic hemispheres - very expensive but probably the ultimate, can get in any wall thickness, hard to machine, relatively low resonance, very stiff, comes ready finished

I thought of another yesterday. Concrete :shock: It is high mass and there is a risk of cracking. I could try and cast it myself in hemispheres with the driver cut outs already done. I will need molds of course, I thought that if the pig balls fail (very likely) then I could chop one in half and use it as the removable inner wall of a mold. The outer would have to be a 35cm diameter hemisphere which I would have to buy. As long as they are sprayed with something non stick then the molds could be used many times.

I would need to perfect my skills ofc. The right mix, vibration to get the air out, something to reinforce the structure. There are some very attractive aggregates that can be used and the external appearance when polished can resemble marble. Seriously considering this option even though some steep learning to do.
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Re: Doc modding Marantz imperial 7

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karatestu wrote: Sat Jul 10, 2021 6:08 am
I thought my over enthusiastic subjective drivel had scared you off, I'm glad you are still hanging around :grin:
Just busy organizing and competing in an archery comp.
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karatestu (Sat Jul 10, 2021 8:56 pm)

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Re: Doc modding Marantz imperial 7

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r3xj0hn570n wrote: Sat Jul 10, 2021 8:24 pm
karatestu wrote: Sat Jul 10, 2021 6:08 am
I thought my over enthusiastic subjective drivel had scared you off, I'm glad you are still hanging around :grin:
Just busy organizing and competing in an archery comp.
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:
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Re: Doc modding Marantz imperial 7

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My thoughts have turned to casting my own concrete hemispheres. :roll:

It would be dirt cheap to do apart from the molds. I could use the pig balls as inners but would need a 35cm outer mold. That would make the walls approx 20 -25 mm thick. You need to get all the air out and avoid using large aggregates. Vibration tables are often mentioned but I thought of strapping the mould to flat sheet of wood etc and putting that on top of a farm implement which is actually being powered slowly (like a power harrow for example). There ya go, a ready made vibration table :lol:

Getting the mix right will take some experimentation to get the right ingredients and consistency. No gravel but there are many additives that could be used like quartz and other decorative stone. Also to reduce weight how about rubber crumb. The mix can also be coloured before pouring.

At least the molds are reusable if some release agent is used but I only need to make four hemispheres , unless I go into production :lol:

So is concrete the ideal material ? As with most things in this hobby some think it is, some don't. It certainly is dense and heavy and does not flex and the resonance frequency is relatively high where energy levels are lower and is harder to excite. High mass stores energy for longer though. As this is for a very wide range doped mid bass with output upto 8kHz and above then I can't expect to push the enclosures resonance frequency above the pass band but hopefully it will be high enough to next get excited much.

Although concrete does not flex the downside of that is it can crack under pressure. That could possibly be a problem in a sub enclosure with 18" driver and lots of internal pressure in a sealed vessel. Not sure it will be a problem for 1" thick walls and a couple of weedy 5.25 inchers. It wouldn't hurt to put some metal reinforcement or glass fibre in but I expect it will be hard to keep the steel central and not visible on the outer surface.

Not a problem if painting or covering the outside of the speaker but may be unsightly if trying to use the outer surface as is and polished up.

Casting concrete seems to be the perfect way to make a bespoke cabinet with rebated driver cut outs taken care of and possibly other little details. I did consider fibre glassing over an inflatable ball or polystyrene ball but that creates a whole lot of pain in getting the outside perfect. With concrete in a mold done properly, the outer surface should be an exact copy of the inner surface of the outer mold. That would have to be strong ofc and a perfect curve.
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