Doc modding Marantz imperial 7

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karatestu
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Re: Doc modding Marantz imperial 7

Unread post by karatestu »

Latteman wrote: Thu Oct 14, 2021 3:26 pm I also found some bass heavy music was ‘difficult’ with the bipolar - what helped mine was ‘blocking’ the rear magnet port on the doc mod drivers-
It's because there is the full 6dB baffle step compensation with bipolar. Add room gain to that and some things can get a bit too bass heavy. That's why it only worked with the little 5.25" drivers. My 6.5" bipole cube was a total no go with anything like Portishead and similar. Even well away from walls it was overblown. Lovely though on things you wish had more bass :grin:

For me it was an attempt to get more sensitivity by adding another driver (3dB extra). If you wireit in parallel with the other identical driver then that's another 3dB (6dB) total. Now I plan on using a more sensitive, slightly larger driver then that is not so much of an issue.

The options for me now are single up firing 6.5" mid bass run full range (no filter) or a down firing 6.5" bass with a low pass passive line level xover (1st order) at approx 250 Hz. That will need a dedicated mid driver from 250 hz up. It will of course need a high pass passive line level filter. The one I am thinking of has a smooth roll off so I will try and get away with not low passing it if possible. tweeter arrangement will stay the same.

If I xover at 250 Hz then that keeps the filters out of the range which our ears are most sensitive and the mid and bass drivers will still be within a quarter wavelength away from each other at xover even though they are on opposite ends of a 30cm sphere.

Just need to dust the mothballs off my wallet :roll: (again)
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Re: Doc modding Marantz imperial 7

Unread post by Latteman »

The number of permutations you have tried or conceived is huge with no sign of slowing down- I think it’s time you review this blog and decide.
Having followed and tried several- BBCs, 12” 6.5” & tweeter to more unorthodox boxes I believe the bipolar with close multiple tweeters to be the best compromise.
I’ve decided on bipolar 5.25” up and 6.5” down it’s tweeter pod below- one at 3.3uf the other at 2.2uf. The most significant improvement was the double tweeter followed by the bipolar- so pull your fingers out and build 😂😎👍🏼🍺
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karatestu (Fri Oct 15, 2021 8:03 am)
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Re: Doc modding Marantz imperial 7

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:crying-yellow: :confusion-helpsign:
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Re: Doc modding Marantz imperial 7

Unread post by TheMadMick »

Latteman wrote: Thu Oct 14, 2021 7:06 pm The number of permutations you have tried or conceived is huge with no sign of slowing down- I think it’s time you review this blog and decide.
Having followed and tried several- BBCs, 12” 6.5” & tweeter to more unorthodox boxes I believe the bipolar with close multiple tweeters to be the best compromise.
I’ve decided on bipolar 5.25” up and 6.5” down it’s tweeter pod below- one at 3.3uf the other at 2.2uf. The most significant improvement was the double tweeter followed by the bipolar- so pull your fingers out and build 😂😎👍🏼🍺
Don't say that, what are we going to do without a major source of entertainment - and quite a bit of learning.

Keep it up Stu!!!
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karatestu (Fri Oct 15, 2021 8:26 pm)
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Re: Doc modding Marantz imperial 7

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This is probably going do do Peter's head in (sorry Peter) but next experiment up inolves the use of a passive speaker level xover. Not spent much time on it and it will be the usual first order single series inductor for the bass driver low pass filter and a single series capacitor for the mid tweeter high pass filter. I am combining a doped 6.5" down firing mid bass with one of the little SB Acoustics 2.5" full rangers up firing into a 10cm plastic sphere.

The only reason I am using a passive speaker level xover is because I can't be bothered to rip my nva amp boards out for surgery just yet. Prove the concept first.

Why ? Well I'm all up for a quick experiment that doesn't take much effort and I am keen to hear what this full ranger sounds like. I looked at the crossover components that I pulled out of the old Marantz Imperial 7 way back. Turns out that I have two little crappy inductors of 3.9mH :dance: With a 7.5 Ohm bass driver that will give me a low pass -3dB point of 306 Hz. That is right in the area that I was looking at (somewhere between 250 and 380Hz).

The high pass for the 3.6 ohm full ranger requires a capacitor of 144.5uf. They don't exist and I don't have a suitable cap anywhere near that value. But I do have a draw full of 47uf film caps - three of them in parallel will give me 141uf which gives a filter -3dB point of 313 Hz. Close enough.

I have to build a quick and dirty top baffle for my cubes each with a little back box to keep the woofer and mid tweeter's back wave separate. But luckily the cube's dimensions work out almost ideal when both drivers box volume requirements are taken into account. I love it when things work out like this :guiness; The sensitivities of the two drivers don't match up but the woofer is doped so will not be 88dB as the suspect TS parameters suggest. The full ranger has a rising response and it will be interesting to see what happens when it is up fired into a diffuser.

One of the aims of this is to see what the bass sounds like with it firing into the convex hemisphere at the base of the speaker and a mid up firing. As my hearing tops out at 13 kHz then it might be "oven ready". Then again it might not.
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Re: Doc modding Marantz imperial 7

Unread post by karatestu »

I put these little 2.5" full range drivers in 3mm x 150mm plastic spheres (1.5 litres). Put some stuffing inside . Bodged in of course in a ring of ply with no rebating as yet but I did chamfer the back side of the 9mm ply wood and splodged some decorators caulk about. I will smooth this area off after a while but it's always a rush to hear things and I haven't bought a router yet (can't decide which one to get :roll: ).

I decided against putting it in the cube enclosure for now as it is much easier to try a few things whilst it is in a little sphere. I can play with angle of firing very easily. I have had it facing straight forward, crossed over in front of me and various angles of pointing at the ceiling including straight up :grin:

Lots and lots of fun :dance: At the moment I am only using it over the same frequencies that my three tweeters were covering but I will be lowering that down so it covers from 300 Hz or so in due course. I am reserving judgement for a while. One thing I can say is there is a slight beaming compared to using 19mm dome tweeters but I suspected that would be the case from a 50mm cone. And the cone is metal which I did have reservations about but early thoughts about that are favourable :grin:

Pointing straight ahead

Image

At 45 degrees

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Pointing straight up (no diffuser as yet but that is to tried)

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Idea for a quick experimental diffuser. You could say it was a lightbulb moment :lol:

Image
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Latteman (Wed Oct 20, 2021 6:14 pm)
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Re: Doc modding Marantz imperial 7

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Lightbulb suspended on cotton from above . Was a b'stard to get right.

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Latteman (Wed Oct 20, 2021 6:14 pm)
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Re: Doc modding Marantz imperial 7

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Tried a candle shaped lightbulb anorl .

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Re: Doc modding Marantz imperial 7

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A few things have become clear after this latest round of faffing about. A very enlightening experience. I can now say there is no point in trying to make the higher frequencies omni directional through pointing it at the ceiling and trying to use a diffuser.

The little full ranger sounded better pointing up with no diffuser at all. The larger globe strangled the highest frequencies altogether :( The candle lightbulb was didn't strangle things but was not much better than no diffuser. It is clear that either my drivers are no good for this type of thing or the diffusers are just not optimised enough. I suppose I can't expert great things from something cobbled together in a hurry. The 2.5" FR drivers have a rising top end but that didn't help.

I can now put that idea to bed :dance: :(
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Re: Doc modding Marantz imperial 7

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Now some initial thoughts about the little 2.5" full range jobbie. It's not run in, only a few hours on them. I don't know if these little drivers need running in like bigger ones do to loosen up the suspension. I suspect they do, not that it should effect the outcome too much.

They are a very nice sounding little thing with one replacing my three tweeters per channel. I haven't tried them covering down to 300 Hz yet but you can be sure I will do before long. I can't say a bad thing about them expect they beam earlier than the 19mm soft dome tweeters. That is not a problem as long as you don't sit directly on axis of them.

They are metal cones with a soft dust cap but don't shout "METAL" at you like I feared, they have an even natural sound. The sound is as detailed as you could wish for and certainly on a par with three tweeters in that respect. They are not rebated into the little ply baffle I made so I expect things will get better once that is done.

Putting them in spheres works really well. I can adjust the horizontal and vertical angle of fire infinitely to my heart's content. That is a very valuable tweaking option to have, they sound quite different depending on what you do with them in that sense.

They are only 84dB sensitivity which is a shame but the higher frequencies seem to be as strong as with three 88dB tweeters wired in series. Things sound a little crisper if I am honest but in a good way. The bass and mid and high frequency balance seems to be to my liking which I am a little surprised with. It just goes to show that a 88dB 6.5" mid bass when lightly doped and pointed at the ceiling loses quite a bit of sensitivity and is about on par with a forward firing 84dB full ranger.

I think the imaging is tightened up compared to three tweeters all firing at 90 degrees to each other. I suppose I expected that would happen but I'm not a big imaging freak. The sphere must be helping with that. What I go for is clarity, transparency and detail which improved every time I added an extra tweeter. Less work for each of them to do really did pay big dividends when there is only a first order 6dB per octave high pass filter. The 2.5" full ranger has non of those issues as far as I can hear, it is as clear and detailed as the three tweeter option (I will go back to the tweeter sphere just to check that).

I don't really prefer one over the other at this stage so I will probably end up doing both. It will be nice to have options. One option is to use the FR up firing where the mid bass is now and use the tweeters in the sphere to supplement the full range. The bass would be down firing though in that set up. There is the option to run two or four of these FR's per channel once they are covering down to 300 Hz. Will have to see how they sound covering all those octaves.

I've got options coming out my flaming ears (sorry Peter). A larger 4" mid may be needed.

I plan to have a good play with these
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Latteman (Wed Oct 20, 2021 6:14 pm)
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