Doc modding Marantz imperial 7

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karatestu
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Re: Doc modding Marantz imperial 7

Unread post by karatestu »

Sharpie permanent markers are available in metallic silver :dance: I will give that a go.
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antonio66 (Tue Feb 22, 2022 12:50 am)
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Re: Doc modding Marantz imperial 7

Unread post by karatestu »

I have a problem. My tweeter spheres are too close to the mid bass driver.

I played some jazz music with flute on and a few particular notes went right through me. IOn jacking up the spheres a bit I have noticed it go away. Looking at the Duevel Planets they have the sphere much higher than I had.

So they will have to be higher which doesn't fit with trying to get the mid bass and tweeter as close as possible but you can't have everything.

I currently have an old sphere with a cone added to the bottom which if successful i will say a bit more about and do similar on the final build.
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Re: Doc modding Marantz imperial 7

Unread post by r3xj0hn570n »

The high pass cap will introduce a phase lag (which you can back of an envelope calculate, but it'll only be very approximate) which can be cancelled by placing the high pass driver closer to the listener...
So getting them as close as possible might not be the best strategy.
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karatestu (Wed Feb 23, 2022 8:21 pm)

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Re: Doc modding Marantz imperial 7

Unread post by karatestu »

r3xj0hn570n wrote: Wed Feb 23, 2022 8:17 pm The high pass cap will introduce a phase lag (which you can back of an envelope calculate, but it'll only be very approximate) which can be cancelled by placing the high pass driver closer to the listener...
So getting them as close as possible might not be the best strategy.
Thanks Rex, I was aware of the phase lag between voltage and current but.........

I have my passive high pass filters at line level and the mid bass also has a high pass in the same location (very low Hz to block DC). It ended up like this because I removed the coupling caps from my cdp - I got to remove one cap in the signal chain of the tweeters. That probably makes no sense but there are an equal number of coupling caps between dac and speaker drivers for mid bass and tweeters.

Anyway, I can live with the tweeter a bit higher up . It's worth it to get rid of that resonance. I hope putting a cone on the bottom of the tweeter sphere pointing at the mid bass' dustcap will improve things further.
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Re: Doc modding Marantz imperial 7

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karatestu wrote: Wed Feb 23, 2022 8:37 pm
I have my passive high pass filters at line level and the mid bass also has a high pass in the same location (very low Hz to block DC).
The same rules apply. Same pole, same minimum phase relationship, same phase lag.
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karatestu (Thu Feb 24, 2022 7:14 am)

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Re: Doc modding Marantz imperial 7

Unread post by Geoff.R.G »

r3xj0hn570n wrote: Wed Feb 23, 2022 9:38 pm
karatestu wrote: Wed Feb 23, 2022 8:37 pm
I have my passive high pass filters at line level and the mid bass also has a high pass in the same location (very low Hz to block DC).
The same rules apply. Same pole, same minimum phase relationship, same phase lag.
As one of my college lecturers used to say “phase angles is important”.

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Re: Doc modding Marantz imperial 7

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r3xj0hn570n wrote: Wed Feb 23, 2022 9:38 pm
karatestu wrote: Wed Feb 23, 2022 8:37 pm
I have my passive high pass filters at line level and the mid bass also has a high pass in the same location (very low Hz to block DC).
The same rules apply. Same pole, same minimum phase relationship, same phase lag.
Thanks for your reply Rex. The way I have done things allowed me to have one less capacitor in the chain before the tweeter. It brought increased clarity.

However, I have neglected the fact that the phase shift for a single series cap will not be the same across all frequencies- it will vary between 90 and 0 degrees. So the relative phase will still be different between tweeter and mid bass .

My efforts to get the tweeter and mid gass close together wax more to do with trying to keep them as close to a point source as possible. The filter knee of my first order high pass is 7KHz where the wavelength is small and it is impossible to get the centres of the cones within a quarter wavelength .

Sometimes as somebody without any formal electrical training I find the subject of phase quite hard to follow. What really puzzles me is what the effect of having the two drivers firing at 90 degrees to each other has.

Anyway, as my tweeter sphere is also used as a crude diffuser then it needs to be centred directly above the mid bass. With the tweeter forward facing then it is always going to be nearer my lug holes than the mid bass - it is right above the mounting flange of the mid bass.
I find this to sound much better than having the tweeter on the front of a shared cubic enclosure where it is many inches further forward than the voice coil of the up firing mid bass. The larger the diameter of mid bass that is used the further forward the tweeter becomes.

Increasing the distance between the tweeted sphere and up firing mid bass does move the tweeter closer to my ears but only fractionally . It is worth it to allow thd mid bass to breathe and reduce the amount of sound bouncing around between mid bass cone and bottom of the tweeter sphere. That's what the resonance was due to I think. The distance seemed to correlate well with the frequency wavelength of the flute which brought this ok my attention.

Oh well it's not a big change in design and it does sound subjectively better.
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Re: Doc modding Marantz imperial 7

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I have pulled out all the music I have with flute on and this problem only occurs with this one track. Jaco Pastorius track is as well behaved as are the others. Anyway the problem with that one track is worth correcting because it will be affecting all music even if I can't detect it.

Here is the track

[bbvideo] [/bbvideo]
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Re: Doc modding Marantz imperial 7

Unread post by Fretless »

The opening section of 'Tangram' by Tangerine Dream has a synthesized flute sound that caused tweeter problems on one set of speakers I have.

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karatestu (Sun Feb 27, 2022 9:18 am)

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Re: Doc modding Marantz imperial 7

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karatestu wrote: Sat Feb 26, 2022 9:32 am I have pulled out all the music I have with flute on and this problem only occurs with this one track. Jaco Pastorius track is as well behaved as are the others. Anyway the problem with that one track is worth correcting because it will be affecting all music even if I can't detect it.

Here is the track

[bbvideo] [/bbvideo]
It's one of the high notes on that track that caused the issue. Don't know what the fundamental frequency is but the wavelength probably tallies with the distance between the mid bass' cone / dustcap and the underside of the tweeter sphere.

Raising the tweeter up more sorts it out. I am going to add a cone on the bottom of the tweeter sphere to try and alleviate any sound bouncing around in the gap. This may mean I have to tweak the tweeter's high pass as more of the mid bass' higher frequencies are heard.

Here's a little drawing of what it will look like.

Image

Looks a bit like one of those Google maps placemark icons :lol: I could make the cone exponential but not sure about that.

I have tested a way of doing it. Drill a small hole in the sphere which will be the centre of the cone. Insert a screw just enough so the flat head is 35mm from the sphere. Fill the area around the screw with car body filler in layers and wait until dry until adding more. When the straight edge of a metal ruler is rested on the head of the screw and edge of the sphere it creates the straight line required. The body filler is smoothed out by rotating the ruler round and round using the screwhead as the fulcrum.

The screw is driven in 5 mm more than required as the cone's point will be 5mm above the flat of the screw head. I have tested this method with decorators caulk and it works a treat. The resulting cone is smooth and perfectly uniform. The smallest amount of sanding will be required. Body filler sets hard unlike decorators caulk which stays flexible. There are no cones available to buy with the right geometry that I could glue on :cry: Their height relative to radius is always too high. So I must make my own.

Having the cone permanently adhered to the sphere will mean the tweeter tilt angle will have to be decided on before doing this as the point of the cone must always be in the centre of the mid bass' dust cap / voice coil.
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antonio66 (Sun Feb 27, 2022 11:09 pm)
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