Doc modding Marantz imperial 7

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r3xj0hn570n
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Re: Doc modding Marantz imperial 7

Unread post by r3xj0hn570n »

karatestu wrote: Sat Sep 25, 2021 5:46 pm That produced the lowest amount of perceivable bass and as it gets further away the bass becomes more prominent but less detailed. I am a bit of a bass head which is why I like the bipolar opposing driver baffle step compensation but with this sphere at a certain distance from the driver the frequency balance is still to my liking but the bass is more detailed. That's my second hang up - detail. If the artist wanted you to hear it then I want to hear it.
One of the things i've noticed with my latest set of speakers is that some music sounds quite different. I've put it down to lack of low frequency harmonic distortion. Low bass is (comparatively) difficult to engineer and less easily perceived and what you hear as bass on most systems is mainly harmonics generated by the speakers and the fundamental is masked. Remove these harmonics and music can now sound fast and punchy AND have lots of bass without boom. How you remove these harmonics is the question. Most bass units have horrible distortion measurements due to all sorts of things, including loading which is what you are up to here.

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Re: Doc modding Marantz imperial 7

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karatestu wrote: Sat Sep 25, 2021 8:08 pm
I have found a suitable driver which has a published FR graph which is about as smooth as I am going to get. Starts to roll off naturally about 7 kHz so ideal. It's also a 5,25" which when modelled in winisd gives a suitable enclosure size. It is also 88d so 4dB more efficient than the cheap Chinese jobbies (84dB even before doping).
Looks good. Q is high enough, coated paper, Le is OK. Monacor make some interesting drivers. I remember spending hours pouring over datasheets from Vifa, Peerless, Focal, Dynaudio, Scanspeak.
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karatestu (Sat Sep 25, 2021 8:27 pm)

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Re: Doc modding Marantz imperial 7

Unread post by karatestu »

r3xj0hn570n wrote: Sat Sep 25, 2021 8:22 pm
karatestu wrote: Sat Sep 25, 2021 8:08 pm
I have found a suitable driver which has a published FR graph which is about as smooth as I am going to get. Starts to roll off naturally about 7 kHz so ideal. It's also a 5,25" which when modelled in winisd gives a suitable enclosure size. It is also 88d so 4dB more efficient than the cheap Chinese jobbies (84dB even before doping).
Looks good. Q is high enough, coated paper, Le is OK. Monacor make some interesting drivers. I remember spending hours pouring over datasheets from Vifa, Peerless, Focal, Dynaudio, Scanspeak.
Yes, one can lose days looking over data sheets. This Monacor driver looks just the job for what I need. A member here replaced the drivers in his original 1990's ?? Nva cubix speakers with the 8" big bother (SPH-220HQ) of the ones I am buying. Unfortunately a sphere big enough for two of the SPH-220HQ in bipolar opposing fashion was going to be of gigantic proportions. Even for a single driver it was going to be at least a 35cm diameter sphere. I suppose going isobaric would reduce that but then it starts getting very expensive ( four drivers per channel).

I guess I'm just not serious enough but I have bad memories of awakening the evil room mode gods with some 12 inchers. :grin:
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Re: Doc modding Marantz imperial 7

Unread post by karatestu »

I realise that the monacor drivers will be more efficient than the cheap Chinese kevlar jobbies. 88dB for the monacor versus 84dB for the kevlar and that is before doping. Once heavily doped the kevlar will be even lower efficiency.

The added efficiency will be very welcome but it will cause me a problem with balancing the tweeters output to the mid bass. I have managed to balance them without a padding resistor by wiring several tweeters in series with only one pointing at the listening positions. I may need to drop to three tweeters to reduce impedance and thus up the tweeter amps output.

I am certain it can be done without any added components. Last resort is having independent volume controls for mid bass and tweeters.
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Re: Doc modding Marantz imperial 7

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Costing these speakers not including all my time, money spent on drivers and other parts I won't be using;

Steel hemispheres (four of) 300mm x3mm £150
Dog indestructible balls (two of) 150mm x 3mm £20
Monacor SPH145HQ (four of) £240
Visaton G20sc (eight of) £320 if all bought new - I got four from zebbo at £10 Inc postage :dance:

That comes to £730 already and there are other things yet to add like plywood, legs, internal wiring, binding posts (six of) very small amounts of bitumen damping and fibre glass stuffing, paint, threaded rods, nuts ............

Say £850 all in. If sold in a shop then times that by ten = £8500. I'm not saying these sound as good as a professionally designed and manufactured speaker costing £8.5k as i have no idea what a typical speaker sounds like in that price bracket. Probably sound nothing like these will.

I am under no illusions that my speakers will be anything special. They will be the essence of me and probably the best speaker I could build for my ears, room and preferences at this particular point in time.
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Latteman (Sun Sep 26, 2021 7:31 pm)
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Re: Doc modding Marantz imperial 7

Unread post by karatestu »

Not sure if I have linked to this speaker before. A bit of Linkwitz Pluto mixed with a hexagonal tweeter enclosure above the up firing mid bass.

Image

Image

So, six tweeters per channel in all. Xover done with dsp (new devilry) at 700 Hz. I think the long hexagonal column is stuffed like a closed end transmission line to soak up all the back wave rather than have a vent which supplements the low frequency.

Some people describe these type of speakers as omni when really they are not. There are tweeters only in the horizontal axis not up or down. Some say bipole designs have an aspect of omni about them. I think whilst this is true for lower frequencies it doesn't hold true for high frequencies.

I think they look really nice and he has done an excellent job of the construction. I don't like the sharp edges on the tweeter housing though. You could get six tweeters in a sphere if it was of adequate diameter but I don;t think it can be too big otherwise there may be problems with it's diffusing properties of the up firing mid bass (depending on where xover is - low frequencies won't know it is there. But there is much more to this than meets the eye - I have been awoken to that by the effect a 30cm ball has when placed under my down firing mid bass.

What I will glean from the above speakers is how the tweeter housing goes to a point above the up firing mid bass. Lots of speakers do this. The Duevel range starts with The planets which use spherical diffusers but as you up the range that changes to exponential cone shapes.
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Re: Doc modding Marantz imperial 7

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Well fook me backwards.

I have played a number of albums including The Police - Zenyetta Mondatta, Ghost in the machine, Synchronicity. Donald Byrd - Places & spaces, Street Lady, The Crusaders - Street Life.

Putting those 30cm spheres under the down firing mid bass has had a remarkable effect. I have been mostly concentrating on the bass (but not exclusively) and the effect is like somebody magically transported this ragged collection of sound reproduction equipment in to a much better sounding room. Or they used dsp to smooth out the room related peaks and dips in the lower frequencies - although I have never used EQ so don't know exactly what it sounds like.

There is much going on here that I don't completely understand. The Loading brought up by Rex up thread intrigues me and seems completely plausible. It is hard to research such things though as most comment on loading seems to be related to horns. Not much is mentioned about 3D shapes plonked in front of drivers.

I don't see how I can ignore the effect it has had. At first I thought it was less bass but I can see past that now. It's just better behaved. I would much rather chase improvements through mechanical means than electrical (hello Doc). I am not sure where this is going to lead (certainly not in to conventional horns I can assure you) but there is experimentation to do with distance from driver to sphere and if I had different sized spheres I would experiment with that too.

It does mean I will have to try adding an exponential cone on to the bottom of the tweeter sphere (smoothly blended in ofc) and possibly one on top of the sphere that the down firing mid bass fires in to (although I don't see it making as much difference as the one with the tweeters in it).
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antonio66 (Mon Sep 27, 2021 8:18 pm)
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Re: Doc modding Marantz imperial 7

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It's pissing it down here so I get speaker play time :dance:

I suppose the validity of these experiments is questionable at the moment as I still have the steel lined chipboard cubes housing the opposing mid bass drivers. Once I have spheres for the mid bass enclosures then results may be changed. Add to that the fact that I will hopefully be using Monacor SPH-145HQ mid bass drivers. I haven't got the tweeter spheres finished yet - the latest spheres need the tweeters modifying, at the moment i have them gaffa taped :lol: into the previous spheres .

I do know that if i use the 30cm plastic pig balls under the down firing mid bass then I will be filling them with sand or something to stop them being the source of any vibrational output.

Then I get to thinking about what a wasted space that is :think: What could I use it for ? Another driver? To house the three nva amplifier boards per channel (psu's remote) ? A disco light ball ? :laughing-rolling:
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Re: Doc modding Marantz imperial 7

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I am just rambling on to myself now :whistle: Excuse me, I need to record my ridiculous thoughts before they evaporate into the vacuum that is age related memory loss. :character-oldtimer:
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Re: Doc modding Marantz imperial 7

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Monacor has no stock of SPH-145HQ and can't give a date to when they will be available which suggests to me that they are not currently being manufactured. :cry: Covid ?????

Might be months before any are available so that has brought this project to a bit of a halt sadly. Gutted. I am not going to design the spheres for the Qtx drivers and then have to do it all again later. The Monacor drivers are 13mm wider and the cut out required is slightly larger as well (119mm vs 112mm).

I can progress with the tweeter pods I suppose, they won't be changing. Will keep me busy for a while.
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CycleCoach (Mon Sep 27, 2021 6:30 pm)
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