Doc modding Marantz imperial 7

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karatestu
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Re: Doc modding Marantz imperial 7

Unread post by karatestu »

Having a bipole design where two woofers are on opposing cabinet panels and wired in phase provides baffle step correction. The low frequency that wraps around the front baffle and goes to the rear is compensated for by the rear facing woofer which does exactly the same thing.

https://www.diyaudio.com/forums/atta ... n-png

This is what i have with the two 5" firing up and down. I have one with cone facing out and one with magnet side facing out. This is said to cancel some distortion.

Also with woofers on opposing panels there is some force cancellation as well which reduces a lot of cabinet vibration.

Happy days.
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karatestu
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Re: Doc modding Marantz imperial 7

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I have finally been able to think about diy audio again :dance: . Maybe I am just sick of my thoughts being all about Coronavirus, lock down, incompetent government.

Part of it will be just having bought four visaton tweeters from zebbo (thanks). I have totry and pick up from where I left off but the train of thought will need a little remembering. I suppose documenting it all here is going to be useful as I can just read the thread again but only the later part as i haven't time for 82 pages.
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savvypaul (Sun May 31, 2020 3:03 pm) • Ithilstone (Mon Jun 08, 2020 9:59 pm) • Stentor2020 (Mon Jun 08, 2020 10:18 pm)
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Re: Doc modding Marantz imperial 7

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Anybody heard speakers like these which use EMI drivers ? Two angled tweeters mounted in front of the mid bass oval cone. Scroll through the pics. This is the first time i have seen something like these. Like a crude coaxial.


https://www.ebay.co.uk/itm/Vintage-t ... bile
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Re: Doc modding Marantz imperial 7

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I just can't get the idea of true infinite baffle bass loading out of my head. Why ? Because it gets rid of large visible enclosures, does not sound boxy (allegedly ) and gives low frequency bass output.

Only down side I can see is destroying the 12 inchers with too much excursion. In floor 12 inchers here we come.
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Re: Doc modding Marantz imperial 7

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It would seem I am not being very successful at getting this thread up to 100 pages. Must try harder.

How to sum this thread up in a sentence? Total numpty tries to make some party speakers with nothing but a chainsaw, copious amounts of dope and a couple of ears.
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Daniel Quinn
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Re: Doc modding Marantz imperial 7

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Or. You do it, so nobody else has to.
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karatestu (Sat Jul 04, 2020 8:20 pm)

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Re: Doc modding Marantz imperial 7

Unread post by karatestu »

I managed to find on the tinterweb some work by John Kreskovsky who experimented with U frame open baffles which have the uframe stuffed. Apparently this creates a quasi cardioid bass loading which if you read pfm's audio room then you will be getting all moist in the groin area right about now.

But, but, but the amount of stuffing must be exactly the right amount otherwise you are left with just a crap dipole. This must be the new name for my speakers. Crap dipole has a certain ring to it.

By the way some ATC speakers got a right slating on audiosciencereview. Pah. Who gives a fook anyway?
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Re: Doc modding Marantz imperial 7

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I have been wondering about what finish to give my diy speakers when the final build happens :pray:

I have never done any veneering before but am not scared of having a go. If the bass boxes end up in concrete then I believe they can't be veneered anyway. So they will be plastered, sanded and painted.

The upper cab will more likely be baltic birch ply which is quite attractive in it's own right.

How about painting the whole lot in cream with lacquer over the top ? I quite like the look of cream and it goes with most things decor wise. Also the contrast of cream and the black of the drivers might be just the ticket. Another plus for cream is I think they will disappear in the room easier (they will be of substantial size :shock: ). The grilles will be black as I am not sure cream grille cloth is available.

Any thoughts from you guys ??
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Re: Doc modding Marantz imperial 7

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Nobody had an opinion on cream speakers :violin: :cry: Doesn't matter as I have just about decided they are going to be cream. Not done any diy recently unless thinking about it actually counts ?

I have however ordered some tools :happy-partydance: so I have intent :twisted: Ordered a new circular saw with matching 2.8M track. The one I have is bolloxed and I have never had a track before :dance: Bought a wood blade with lots of teeth for a fine cut so hopefully no plywood chipping (and swearing) will be occurring :pray:

But I also got a blade for concrete. The lower bass cabs are going to be made out of recycled (ofc) concrete paving slabs 50 mm thick which i will plaster when finished. I am going to reduce the thickness of the slabs to 25 mm except for a 50 mm band all around the outside where they will be joining other panels at 90 degrees. Going to do this by cutting 25 mm deep lines a couple of centimetres apart and then using a chisel to remove what i don't want. It won't be smooth but as it will be inside it doesn't matter plus I thought it might be good for them sound / pressure waves to be coming up against uneven surfaces rather than flat.

This helps keep the box size down and I am not sure any more than one inch thickness is really needed. My listening room has carpet and always will so I am not going to bother having a base panel on the bass enclosures. But it won't be a sealed box I hear you cry. Well it will be as near as damn it. It will be a slightly leaky bass enclosure but that is not for worrying about. If I end up going aperiodic again then it won't matter. Also this will help give me a smaller enclosure (do you see where this is going ?)

Yes it is about keeping the enclosure to a manageable size without effecting the performance. Not sure about stuffing yet, the jury is out but if going for a quasi cardioid bass loading then it will be needed and it might be useful in lowering the volume of enclosure required. I will add a bit and listen in stages to see if I can actually hear any difference (cloth ears ).

The baffle holding the isobaric bass drivers (there won't be much of it) is going to be 6 mm aluminum as it's bloody stiff and the relatively low thickness will again save a little on box size (every little helps). I know the baffle is the most important panel on a loud speaker but there is going to very little of it once a 280 mm hole has been cut in a 400 mm square panel. Plus it overlaps the 50 mm thick concrete panels on all four sides. If you had taken notice earlier when I was talking about reducing the concrete slab thickness to 25 mm you will have noticed I will be leaving the slabs at full thickness in a 50 mm band (like a picture frame) all around their perimeter.

At least with no base panel I won't need a removable panel to access inside. Just tip the buggers over and crawl in :lol: The top enclosure housing the mid bass drivers (not sure how many yet but at least two in total one of which will be down firing with magnet outwards ) and tweeters (at least four) is going to be made from 19 mm baltic birch ply as I can't be bothered to cut all them holes in concrete :hand: Plus I need to keep the weight down as they will weigh a ton as it is.

I thought possibly the upper cab could be slightly smaller as regards width and depth compared to the lower cab. The gap between the two cabs will need to be covered with grille cloth or something as I don't want to see the arse end of a 12 incher and a 5 incher kissing :lol: . But I have mid bass drivers and a tweeter firing up as well as front and side firing tweeters. I can't leave them all open to little fingers so I was thinking of making a one piece grille covered in cloth (like an open ended box) that fits over the upper cab and space between the cabs. If the bass box is slightly larger then this grille could sit on it and be the same external width and depth as the bass box. Make sense ?

Why go to all this bother you may be thinking ? And it might be a bag of sh*te. Well I know the concept works already. My crap chipboard cabs sing along at a certain bass frequency. I just need to make the frequency response and polar response as flat as I can with what I have to work with. It's a bit of a juggling act with drivers that have different efficiencies, frequency response , dispersion and impedance. Plus I have differing numbers of each type of driver. The isobaric bass drivers can only count as one driver. Two, three or four mid bass and four tweeters. Thank god I have things to play with like direction of fire and how to wire them up - this will help to even things out. Just look how I managed to remove the padding resistor on the tweeter by adding more of them firing in different directions and I wired them all in series.

Sorry for the essay. I had to write that lot down so if my head explodes it won't be lost.
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Re: Doc modding Marantz imperial 7

Unread post by Daniel Quinn »

I like cream in my coffee, whether it's good for you I haven't a clue. Some pictures may help.

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