Doc modding Marantz imperial 7

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r3xj0hn570n
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Re: Doc modding Marantz imperial 7

Unread post by r3xj0hn570n »

Thought of the day regarding loading...

An unbaffled speaker in free space doesn't work very well due to cancellation, simply S + -S = 0. Typical loading like a sealed box mostly removes -S leaving just S, except below resonance etc etc. Resonant loading (port) inverts -S to be S at one particular frequency so we now have 2S at that frequency, all others be damned. Horns introduce the concepts of (usually) frequency dependent asymmetric loading. It is this asymmetry that is key to reducing cancellation. Static objects close to the loudspeaker cone are going to load it up more at only low frequencies, the closer you get the higher up the loading will extend. Of course if your static object is elastic, you are introducing another variable...
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karatestu (Tue Sep 28, 2021 6:05 am)

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Re: Doc modding Marantz imperial 7

Unread post by karatestu »

r3xj0hn570n wrote: Mon Sep 27, 2021 10:03 pm Thought of the day regarding loading...

An unbaffled speaker in free space doesn't work very well due to cancellation, simply S + -S = 0. Typical loading like a sealed box mostly removes -S leaving just S, except below resonance etc etc. Resonant loading (port) inverts -S to be S at one particular frequency so we now have 2S at that frequency, all others be damned. Horns introduce the concepts of (usually) frequency dependent asymmetric loading. It is this asymmetry that is key to reducing cancellation. Static objects close to the loudspeaker cone are going to load it up more at only low frequencies, the closer you get the higher up the loading will extend. Of course if your static object is elastic, you are introducing another variable...
Thanks Rex, what you have written above is certainly steering my thoughts in a useful direction. :clap:

My 3D sphere is supposed to be static but won't be as it is just resting in a circular container, the sphere is very light and the plastic is not strong enough to resist deformation (so is slightly elastic). If this "loading" sphere is going to be a permanent feature then it will eventually be concrete or steel.

So I have created a horn by pushing the sphere close to the flat bottom of the wooden cube enclosure ? I will have to research the asymmetric aspect, horns are not something I have bothered to learn about because I never thought I would ever be building one.

I am familiar with destructive cancellation - distance to nearby walls and sound bouncing off out of phase. The recent revelation with this sphere under the down firing MB has led to a suspicion in my mind about the down firing concept. It is not a popular thing to do and I wonder what problems it is creating . My 5.25" down firing MB is on a 28cm square baffle and currently 43cm from the floor.

After a bit of experimentation I settled on a distance between sphere and driver of 5cm (2") and there is a 8cm distance between the bottom of the 30cm sphere and the floor. I expect my results may change once my mid bass enclosure becomes a sphere. I was also going to saw 7cm off the legs of my speakers so the sphere rests on the floor. I expect that will change results also.

This experience has been a bit of a downer for me. I thought my speakers were good enough to progress to a final build but clearly they were not, very humbling. I am again completely aware of how little knowledge I have and when I start feeling like this then the thoughts of throwing it all in a skip start to grow like a snowball rolling down a hill
:angry-screaming:
DIY inspired by Richard "The Doc" Dunn RIP

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Re: Doc modding Marantz imperial 7

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karatestu wrote: Tue Sep 28, 2021 6:44 am
So I have created a horn by pushing thesphere close to the flat bottom of the wooden cube enclosure ? I will have to research the asymmetric aspect, horns are not something I have bothered to learn about because I never thought I would ever be building one.
Loudspeakers are horribly inefficient. This is mainly due to poor coupling between the cone/dome and the air, a mechanical impedance mismatch if you will. Horns constrain the air near the cone/dome and reduce this impedance mismatch.
karatestu wrote: Tue Sep 28, 2021 6:44 am
I am familiar with destructive cancellation - distance to nearby walls and sound bouncing off our of phase. The recent revelation with this sphere under the down firing MB has led to a suspicion in my mind about the down firing concept. It is not a popular thing to do and I wonder what problems it is creating . My 5.25" down firing MB is on a 28cm square baffle and currently 42cm from the floor.
Downward firing bass units are more common than you'd think. Lots of speakers have them, usually only on bass duty.
karatestu wrote: Tue Sep 28, 2021 6:44 am
This experience has been a bit of a downer for me. I thought my speakers were good enough to progress to a final build but clearly they were not, very humbling. I am now completely aware of how little knowledge I have and when I start feeling like this then the thoughts of throwing it all in a skip start to grow like a snowball rolling down a hill
:angry-screaming:
Where is the fun in that? Making stuff is cathartic, for me anyway, and a day when i don't learn something is another meh day.
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karatestu (Tue Sep 28, 2021 8:37 am)

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Re: Doc modding Marantz imperial 7

Unread post by karatestu »

r3xj0hn570n wrote: Tue Sep 28, 2021 8:21 am
karatestu wrote: Tue Sep 28, 2021 6:44 am
So I have created a horn by pushing thesphere close to the flat bottom of the wooden cube enclosure ? I will have to research the asymmetric aspect, horns are not something I have bothered to learn about because I never thought I would ever be building one.
Loudspeakers are horribly inefficient. This is mainly due to poor coupling between the cone/dome and the air, a mechanical impedance mismatch if you will. Horns constrain the air near the cone/dome and reduce this impedance mismatch.
karatestu wrote: Tue Sep 28, 2021 6:44 am
I am familiar with destructive cancellation - distance to nearby walls and sound bouncing off our of phase. The recent revelation with this sphere under the down firing MB has led to a suspicion in my mind about the down firing concept. It is not a popular thing to do and I wonder what problems it is creating . My 5.25" down firing MB is on a 28cm square baffle and currently 42cm from the floor.
Downward firing bass units are more common than you'd think. Lots of speakers have them, usually only on bass duty.
karatestu wrote: Tue Sep 28, 2021 6:44 am
This experience has been a bit of a downer for me. I thought my speakers were good enough to progress to a final build but clearly they were not, very humbling. I am now completely aware of how little knowledge I have and when I start feeling like this then the thoughts of throwing it all in a skip start to grow like a snowball rolling down a hill
:angry-screaming:
Where is the fun in that? Making stuff is cathartic, for me anyway, and a day when i don't learn something is another meh day.
Thanks for your opinion and help with this rex, much appreciated. Your last comment has bucked my spirits somewhat :clap: Unfortunately I am one of those glass half empty types and a little setback or something that makes me question my own ability can have a dramatic effect, hence the throwing it in a skip comments which pop up at various stages of this thread. It doesn't help that I am a perfectionist (which you wouldn't realise by looking at the quality of my prototypes so far :lol: ) and it really gets quite exhausting after a while.

Sometimes it makes me want to just buy a ready designed and made Frugal horn with a single Mark Audio full range in it. When I manage to get a bit of perspective then I usually pick up where I left off and continue until the next blip. You have reminded me that I think I am addicted to this learning process - I get a huge buzz when I manage to successfully pull something off (oo errr). I have come a long way in five years all mostly through trying things and trying to work out what and why.

Oh god, I can't believe I am boring everybody with my personality defects. :obscene-hanged:

I'll be back to talk about speakers, promise :whistle:
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antonio66 (Wed Sep 29, 2021 11:52 pm)
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Re: Doc modding Marantz imperial 7

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I cut 8cm off the legs of these speakers so the 30cm sphere was on the floor with a 5cm (2") distance from top of the sphere to the down firing driver. I listened to that for a while.

Put a small round container plastic container under each sphere so the distance between sphere and driver is now 1cm. Listening to that now and I think I like really close best so far so me saying I preferred 2" distance earlier is complete boolox.

Maybe it's time to saw another 4cm off the legs of the speakers. These are getting shorter by the minute :lol: I am changing other variables at the same time though so run the risk of not knowing what the feck is going on (as usual). There is a bipole dip which doesn't occur 90 deg off axis fortunately. The lower the enclosure gets the more I can see of the up firing mid bass from my seated position. The tweeter height isn't important as I can easily change the angle of that.
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Re: Doc modding Marantz imperial 7

Unread post by karatestu »

I have cut another 4cm off the legs. The whole speaker is now only 78cm tall to the very top of the tweeter sphere.

What I know about horns is very limited but the main issue is resonances. Bass horns have to be very big to increase the spl. That is not what I want to achieve, just use the sphere to even out the low frequency response which it is doing surprisingly well.

What complicates things in my case is the down firing mid bass running wide open. The mid range was a bit hot for my liking. I have now stuffed around the driver between the sphere and the mid bass enclosure with open cell foam all the way around. That is much more like the frequency response I want and doesn't give me a headache.

I suppose the best thing to do would be to go to a three way design or a 2.5 way with the down firing driver handling only up the -3dB point of baffle step transition. In the case of a 30cm sphere enclosure that would be 383Hz. With a 2.5 way the up firing driver would be run fully open. Of course a three way would require a low pass filter on the down firing driver and a high pass filter on the up firing driver. The up firing driver might not need a low pass filter when handing over to the tweeters as long as it was well behaved like the Monacor SPH-145HQ

I have found a suitable mid driver if i go three way . The Monacor MSH-115 is available now https://www.monacor.com/products/comp ... sh-115/
The bass driver is proving a bit harder to find. I could use a SPH-145HQ but with the mid taking up a bit less internal volume I might be able to squeeze a 6.5" driver in and get a bit lower output.

My B&W P4 6.5" drivers have unknown TSP so It would be a shot in the dark trying to use them. No idea if Qts is high enough or what the VAS is so enclosure volume could only be found be trial and error. It would save me a bit of money if I could use them and they are good quality drivers. If I used them I could buy the MSH-115 and not have to wait around for drivers that are unavailable at the moment - there are a lot unavailable.
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Re: Doc modding Marantz imperial 7

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Look what was waiting for me when I got home. Wish I had some drivers to put in them :roll:

Image

I also wish they made bigger ones :drool:
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Latteman (Wed Sep 29, 2021 7:38 am) • CycleCoach (Thu Sep 30, 2021 12:06 pm)
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Re: Doc modding Marantz imperial 7

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karatestu (Thu Sep 30, 2021 5:20 am)

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Re: Doc modding Marantz imperial 7

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r3xj0hn570n wrote: Wed Sep 29, 2021 8:44 pm https://www.morrisonaudio.com/reviews
Thanks for that link Rex. I have seen it before but I only just took notice of how close the sphere is to the up firing mid bass. Mine is several centimetres higher. I was going to try mine lower and that pic of the Morrison has spurred me on. Getting the tweeter closer to the mid bass can only be a good thing especially at the high frequency (7 kHz) I am crossing over at - getting the centres of the drivers within 1/4 wavelength at these higher frequencies is impossible. Lowering the xover requires a low pass filter being introduced on the MB but I try to avoid those if possible (blame RD for that one).

The tweeter firing into a smaller sphere is also something I had considered but it takes a tweeter with certain parameters J believe to be able to pull it off - rising response?

I did look at long column mid bass enclosure like the Morriston but with my obsession with spheres I ended up blending it into a spherical end and if looked too much like a penis with a massive bell end :grin:

The Morrison is closer to a true omni than my effort.
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Re: Doc modding Marantz imperial 7

Unread post by karatestu »

I have been playing around with the steel hemispheres. On their own when held in a suitable way and tapped they ring for a long time. When a sheet of plywood is inserted between them the response is a short dull noise that does not ring at all. I believe these spheres can be made inert. If I can avoid using bitumen damping sheets then I will .

When I cut two opposing holes this may start some ringing off again but with a flange welded in and a driver plugging the hole I hope that will stop it. Plus I intend mounting the drivers with threaded rods which go to either the opposing driver (if using the same driver) or to the plywood between the two hemispheres. This will clamp the two hemispheres to the dividing plywood (nof tightened too much though as that could deform the driver basket).

With this clamping effect I might be able to get away with not having to use any adhesive which means the enclosure can be easily taken apart for internal tweaks. I do prefer a small amount of stuffing to non at all (sorry Doc) and that is likely to be fibreglass and placed in the centre of the enclosure where it is more effective.
DIY inspired by Richard "The Doc" Dunn RIP

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