Doc modding Marantz imperial 7

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karatestu
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Re: Doc modding Marantz imperial 7

Unread post by karatestu »

Geoff.R.G wrote: Wed Jul 07, 2021 8:00 am
karatestu wrote: Wed Jul 07, 2021 6:47 am A link to spherical speakers that I had not seen before. Interesting stuff, especially the bit about the so called strong "standing wave" :roll: at one frequency due to having one internal dimension where the author found there was not a problem. All very encouraging :dance:

http://www.speakerdesignworks.co ... ns.html
What is it with Hi-Fi and standing waves?
It's written all over the place even by some very knowledgeable EE's and designers. It's one of those things I suppose that gets written and read so many times that it becomes seen as true. I couldn't prove they exist or don't exist in a speaker when playing music, I too thought it was a problem until I joined HFS four years ago.
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Re: Doc modding Marantz imperial 7

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I got a text today whilst out at work in the great outdoors that a parcel was going to be delivered around lunchtime. I assume it is the pig balls :grin: Haven't been home yet to inspect them but will be doing very shortly.

I'm so excited :dance: My kids will probably want to play with them when they see them. That's what happened with a pair of giant foam dice I ordered a while back.
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Re: Doc modding Marantz imperial 7

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The pig balls have landed. They are round which is a good start and after measuring the circumference and dividing by 3.1416 the diameter is indeed 30cm :dance:

Kids reaction was "what the heck are they ?"
"Anti stress balls for pigs'
"What pigs"
:grin:
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Re: Doc modding Marantz imperial 7

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In the hot seat. Specialist subject - being a good little speaker enclosure :grin:

Image

Who knows how this will turn out. It may flex too much for good bass reproduction. It may be slightly too small. It may resonate ruining the mid band. I will see how they perform as they are first. At least it will be easy to try, the enclosure almost comes ready made. No panels to cut and join only two holes to cut and some sanding to make a flange for mounting the driver against.

The procedure goes like this. Measure multiple times to find the centre of the holes and make sure the they are exactly at the poles of the sphere and perfectly opposing. Not so easy to do on a sphere but it's all about the measuring.

I will have to modify my orbital sander by making a wider moving plate to attach the sandpaper. With the sander mounted upside down I will press the hole squarely and evenly against the sandpaper. Keep going and measuring until the flange is exactly wide enough for the driver. When doing this and because of the small hole compared to the diameter of the sphere the holes are near the poles . The side walls are at an angle to the wall and so end up quite a bit wider than the wall thickness of the sphere. This pic of a smaller dog ball shows what I mean but with the 30cm sphere it will be even more pronounced.

[img] /img]

Then drill and fit the opposing drivers making sure that the mounting holes line up. Fit four 6mm threaded rods with nuts and tighten evenly until the two mid bass are pulled against the sphere and it is put under slight compression. There will also be a metal bar mechanically linking the back of the two opposing magnets. That is very important for the force cancellation and vastly reduced cabinet vibrations.. Oh and a very small amount of fibreglass stuffing right in the centre of the sphere.

That will do as a first try and will be listened to. It will be easy to take apart for adjustments Al it will 4ake is loosening four nuts. I can then damp the inside of the walls if needed and damp the threaded rods etc. If it turns out too small then I will chop the sphere in half and insert a 21 or 25 mm ring of plywood jnbetweenthe hemispheres. If it is still no good then I will progress to steel hemispheres .

There are also rounded edge wooden driver mounting rings to think about. When Ido those the holes will need sanding down further to accommodate the thickness of the wood and still maintain the spherical curve right up to the crivers edge (which will be rebated into the wooden mounting ring. The bottom mounting ring will also have three tabs sticking out to attach the three legs (if I go that way rather than single leg).

That's the plan. If it fails then at least it will serve as a visual prop to look at the sizes, shapes and proportions of the thing as a piece of furniture.
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Re: Doc modding Marantz imperial 7

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A bit more reading about spherical enclosures.

http://www.sophera.com.au/index.php/d ... res.html

It's nothing new, Harry Olson's research has been around since the 1950's but spherical enclosures have never become very widespread. Probably due to the complexity and cost of manufacture and as we all know manufacturers want an easy life and as much profit as possible. So spherical full size speakers are mostly expensive any the advantages only appreciated by a few.
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Re: Doc modding Marantz imperial 7

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I am starting to get a bad feeling about these plastic pig balls. How could they be any good, they are so cheap and you can hear a bit of a "ping" when you strike the ball with your ear close up. Doesn't bode well but then my paranoia and my habit of always looking on the dark side of things might be getting the better of me.

Won't stop me giving them a go however, it's all part of the journey and learning experience. Damping was never the RD way for reasons well known so I will be reluctant to have to go down that route.

Anyway, I have eight of the doped 5 inchers so I can build these spheres alongside the steel lined chipboard cubes I have now. That will, make for quite easy comparisons and will, just need the tweeter pods moved over from one to another. The shape doesn't lend well to just plonking on top. The tweeter pod is not weight balanced as there is no tweeter on the back so it has a tendency of wanting to roll away :lol:
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Re: Doc modding Marantz imperial 7

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Copied from a pdf hidden amongst the above site, the last paragraph mirrors what I have found.

"‘Walking into’ the music K.M.Bond BA BE

The profound implication of Olson’s result is that it predicts that a spherical speaker
will be surrounded by a relatively smooth sound pressure field. This potentially
reduces the amount of work we do while listening. For instance, kinaesthetic research
reports that listeners automatically and subconsciously make micro-movements of
their bodies and heads when listening, quite possibly to place sounds accurately in
space: near and far, left and right, up and down. Spheres, with their uniform sound
fields, reduce the amount of work this involves.

To see why, try this virtual experiment. Imagine yourself floating 5 metres away from
a 500 cm spherical speaker that is also floating in infinite, air-filled space. The sphere
is projecting a single, pure tone (say, 600 Hz) that is also diffracting around it.
Floating slowly toward the sphere, you’ll perceive a gradual increase in volume, the
reverse if you back away.

Now replace the sphere with an equivalent speaker box (a parallelepiped). Floating
forward, the increase in volume will be less steady. At some points, volume will rise
quickly with a small forward movement. At other times, you will move some distance
forward before noticing any change. Similar step-like changes in volume are also
heard when moving away from the box. The size and position of the steps is dictated
by the interaction of the main signal from the speaker interacting with the diffracted
signals arriving from the box’s edges.1

Now repeat the experiment with a signal of the same strength at a slightly lower
frequency (say, 580 Hz). For the sphere, the results are very similar as for 600 Hz.
The box will, again, produce step-like changes in volume, although in different
positions than for 600 Hz. The longer wavelength of the signal means that for 580 Hz,
at the same distance from the sphere, the diffracted signals now arrive at different
amplitudes than for the 600 Hz diffractions. To get the same volume at 580 Hz as at
600 Hz at any given point, you may have to move your head a little, a kind of
positional equalisation.

In technical terms, diffraction means that each frequency projected from the box
surrounds it with a uniquely varying sound pressure field. Changing the frequency
emitted from the box changes the box edge diffractions and the total sound pressure at
almost all points in the sound field. This does not happen with a spherical speaker.2
Back in the real world, our ears and brains are already working hard to untangle the
music from sundry room reflections, room resonances and stereophonic artefacts
(such as crosstalk and comb filter effects). Speaker boxes’ non-uniform frequency-
dependent sound fields add to the work load. Spheres, on the other hand, reduce the
listener’s work load and remove a hindrance to the illusion of live performance.
It is understandable that when listeners first hear the relatively smooth sound field of
spheres, they frequently express a sense of relief, or ease. In fact, with a good
recording playing, you’ll feel that you can actually walk into the music.

1) In this thought experiment, there are no reflections and we are well in front of the speaker, so that the
diffractions will arrive at our ears both delayed and out-of-phase. See Wright, J., ‘Fundamentals of
Diffraction’, Journal of the Audio Engineering Society, Vol. 45, No. 5, May 1997, p. 348.

2) ibid., p. 355.
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Re: Doc modding Marantz imperial 7

Unread post by CycleCoach »

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.
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karatestu (Fri Jul 09, 2021 7:56 pm)
I think I might be in the HiFi trade.
I am not currently seeking treatment for this.
Current System: Linn LP12 Lingo Ekos Troika, NVA PHONO2 with BBPSU, NVA AP20 (White), Quad ESL 57s &/or NVA Cube3s (White)

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Re: Doc modding Marantz imperial 7

Unread post by CycleCoach »

:epopc:
I think I might be in the HiFi trade.
I am not currently seeking treatment for this.
Current System: Linn LP12 Lingo Ekos Troika, NVA PHONO2 with BBPSU, NVA AP20 (White), Quad ESL 57s &/or NVA Cube3s (White)

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Re: Doc modding Marantz imperial 7

Unread post by CN211276 »

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.
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karatestu (Fri Jul 09, 2021 7:56 pm)
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
NVA P20/ A20, Cubettes, LS3, SSP, SC
Sonore MicroRendu, Chord Mojo 2 MCRU PSs, AQ Carbon USB cable & JB FMJ

Headphones
Grado SR325e/Chord Mojo, Beyerdynamic Avetho/AQ DF Colbat

RIP Doc

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