Doc modding Marantz imperial 7

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r3xj0hn570n
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Re: Doc modding Marantz imperial 7

Unread post by r3xj0hn570n »

I enjoying seeing these experiments and hearing your impressions.

Just a note though, baffle step compensation is to compensate for narrowing radiation as the frequency goes up, from 360 to 180 degrees. That doesn't apply if you are spreading that radiation pattern out again mechanically. There are complications but that is the general gist...
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karatestu (Thu Oct 21, 2021 5:11 am)

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Re: Doc modding Marantz imperial 7

Unread post by karatestu »

r3xj0hn570n wrote: Wed Oct 20, 2021 10:58 pm I enjoying seeing these experiments and hearing your impressions.

Just a note though, baffle step compensation is to compensate for narrowing radiation as the frequency goes up, from 360 to 180 degrees. That doesn't apply if you are spreading that radiation pattern out again mechanically. There are complications but that is the general gist...
Hello Rex, I hope you are OK. Thanks for your comment, I am having so much fun and I am glad others are enjoying watching me fumble from one thing to the next. No point me posting all this otherwise, I could do it all privately and keep all the laughs for myself.

Four years ago when this started I knew little about speaker design. I know a little more now but I have no measurements to validate any of my subjective views. I can only guess why things are happening and try and correlate that with what is written on the Internet.

Your comment on baffle step is interesting because I couldn't find any information on the net when I tried to look into it. All that is mentioned is about flat baffles and no mechanical spreading of radiation ie diffusers. Do you know of any online resource where I can learn about what is actually going on ? Or do you have time to explain it to me (a numpty) here ?

Many thanks Rex :guiness;
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Re: Doc modding Marantz imperial 7

Unread post by karatestu »

Thinking again about the high frequencies firing up into a diffuser. Manufacturers who use it claim it to be the only way to get point source omni up high. Bass is omni anyway and the mid frequencies are easier than treble to spread out (you don't strictly need a diffuser as nva cubes prove).

Most yse compression drivers for the treble I think. Maybe it requires a lot higher sensitivity and rising response to make it work ? The most expensive models use exponential concave cone shapes rather than balls. What is clear to me from my heath Robinson experiment is that if you plonk a big globe above a cone tweeter it chokes the high frequencies (which are beaming). Where do they go ? Straight back at the cone and through it into the back wave enclosure ?

Maybe a small 13mm or 19mm dome tweeter would work better as they beam higher up. A compression driver probably is the best thing to try to I am not taking the concept any further as it is clear I am in way over my head.
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Re: Doc modding Marantz imperial 7

Unread post by karatestu »

I know a little about line arrays but never really considered it because it goes against my omni loving tendencies. I did briefly try a D'appolito (MTM) style thing with a mid bass below (firing up) and above (firing down) at the tweeter sphere. It sounded like shit so I didn't bother mentioning it. There were resonances and diffractions going on. A point & squirt MTM all forward firing would be a different outcome I am sure.

These little full range drivers are intriguing and on my mind :roll: Their problem is the "woeful sensitivity" as Rex aptly put it :grin: They are a similar figure to the doc mod drivers though when they have been doped (especially the 5,25 " which is only 84dB before doping).

This low efficiency is what got me thinking about using more of them. Being small with very light metal cones they are very fast sounding even though they are only 84dB. I can increase the overall sensitivity by adding more of them and wiring in series parallel or parallel series for the same 4 ohm load as a single one. So this idea ends up as a mini four or eight driver line array with a down firing bass driver in the 30cm sphere at rthe bottom. Luckily these FR drivers are only £25 each.

Can I resist giving it a try ? Line array comes with its own set of problems and comprises. If EQ/ DSP has to be involved then I am not interested :hand:
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Re: Doc modding Marantz imperial 7

Unread post by r3xj0hn570n »

Rod Elliot's page is worth reading

https://sound-au.com/bafflestep.htm

He isn't really all that clear on the differentiation between driver beaming and wave formation due to the width of the baffle.
I've used his circuit in the past (variation on fig 3).

A laudable goal is constant beam width, on diyaudio there is much on this. It means over a wide range of frequencies, the ratio of direct to reflected sound is constant. Dipoles, while not perfect have wider frequency range for which this is true. Omni's, with 360 degree beam width over all frequencies this is also true, but with a much greater room involvement.
I've just become a little bit interested in cardoid, which i think might be an interesting future experiment.
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karatestu (Thu Oct 21, 2021 6:48 am)

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Re: Doc modding Marantz imperial 7

Unread post by karatestu »

r3xj0hn570n wrote: Thu Oct 21, 2021 6:12 am Rod Elliot's page is worth reading

https://sound-au.com/bafflestep.htm

He isn't really all that clear on the differentiation between driver beaming and wave formation due to the width of the baffle.
I've used his circuit in the past (variation on fig 3).

A laudable goal is constant beam width, on diyaudio there is much on this. It means over a wide range of frequencies, the ratio of direct to reflected sound is constant. Dipoles, while not perfect have wider frequency range for which this is true. Omni's, with 360 degree beam width over all frequencies this is also true, but with a much greater room involvement.
I've just become a little bit interested in cardoid, which i think might be an interesting future experiment.
Thanks Rex.

Floyd Toole apparently said comb filtering looks bad on a graph but the brain is expecting it. Anybody have a view on that statement ?
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Re: Doc modding Marantz imperial 7

Unread post by karatestu »

Something just occurred to me. My suspected left right ear imbalance isn't as bad as i thought it was. My reasoning for this is now that I am using a single full range for treble the problem has improved.

This must be due to the three tweeter arrangement with the left channel being on a totally flat wall whilst the right channelis in front of a ribbed central heating radiator. This must be affecting the right channel. It's the only reason I can come up with to explain this. Swapping the speakers round did not change anything. The single full range is much more directional so the radiator won't be coming in to play as much.

If I am right about this then it reinforces the thought that what is near your speakers is very important. Symmetry is important . It makes me rethink what my plans are as when the final speakers go to my house the walls they adjoin won't be exactly the same and there will be bits of other furniture around to complicate things. Maybe I am better off with point & squirt except for the bass which doesn't care.

I can't quite believe I am talking myself out of omni like this. Somebody stop me :confusion-helpsos: :confusion-helpsign:
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Re: Doc modding Marantz imperial 7

Unread post by karatestu »

Listening now to the full rangers with a full range signal - unlike tweeters they can handle it.

Well it's louder obviously but the FR drivers acoustically roll off much sooner in the bass than the doped 6.5". The 6.5" start acoustically rolling off about 6Khz unlike the FR which goes all the way up so I am left with a sound which has too much mid range volume compared to the extremes. Just to be expected I suppose. this was more to do with hearing how the FR's cope with a bit of bass up their arse. There is also a very wide frequency overlap between the two drivers.

It's not a bad sound by any means but the frequency response is off and not how I like it. The higher frequencies do suffer when the FR has to deal with a full range signal. When high passed at 300Hz then I expect the loss of fidelity will not be an issue or less of an issue. That is when extra FR drivers come into play. The mid bass obviously will need a low pass filter.

Going to put the FR's back to high frequencies only before I get a headache and plan my next move :think:
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Re: Doc modding Marantz imperial 7

Unread post by Latteman »

I have / had a similar imbalance between speakers and used mono volume controls to assist- with the Richard Allan CB4 tweeters this has not become a problem for me as the sound seems to be balanced better
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karatestu (Thu Oct 21, 2021 7:02 pm)
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Re: Doc modding Marantz imperial 7

Unread post by karatestu »

Latteman wrote: Thu Oct 21, 2021 2:12 pm I have / had a similar imbalance between speakers and used mono volume controls to assist- with the Richard Allan CB4 tweeters this has not become a problem for me as the sound seems to be balanced better
I have considered dual volume controls but not sure the family will like them. Anyway, first things first - I haven't even got a volume control at the moment :lol: For whatever set up I keep at work I don't think I will use one and just keep using a potential divider made of two resistors soldered together per channel. As a treat for myself I might get some bulk foil resistors for it :guiness; . I won't be needing a source selector either :dance:

Home is a different story though as there will be two or three sources and I want it to be family friendly. Nobody will be allowed to touch the turntable however :grin:
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