Doc modding Marantz imperial 7

A place for DIY project discussions.
User avatar
karatestu
Posts: 5945
Joined: Sun Jan 08, 2017 4:40 pm
Location: North Yorkshire
Has thanked: 1865 times
Been thanked: 1378 times
Great Britain

Re: Doc modding Marantz imperial 7

Unread post by karatestu »

Converted my pair of 30cm cubes that I used to try down firing isobaric 6.5 inchers and up firing 5 incher( me no likey) back to up and down firing 6,5".

I knew the box was too small so went back to aperiodic loading. What a difference and it showed what I was missing with the dipole 12 incher (bass). I can't help but like aperiodic loading :naughty: and my small almost square room seems to prefer it. It is just a 3" circular hole with some open cell foam stuffed in it. The foam if cut slightly too big, expands to completely fill the hole and the box is 3cm thick here as I reinforced all four walls with bits of plywood.

To me it seems to be a half way house between open baffle and closed box. It's not a port either as it's not tuned, is only the thickness of the back panel and is stuffed with resistive material. Works wonders with a box which is too small as it lowers bass output (hump) and seems to alleviate any little bass modes in my crap room. When I build the speakers into those oak tables I found the enclosure will be 25 litres so I might not need the aperiodic vent.

Next thing is to take the 12 incher off the 5" dipole speakers and try it on the 6.5" version. I could even block the vent by screwing a larger wooden circle over the hole. See what that does. There is something magical about the dipole 12 incher that means trying it on the 6.5" dipole is something I just have to do. Nothing lost if it doesn't work out.
DIY FREE ZONE

User avatar
karatestu
Posts: 5945
Joined: Sun Jan 08, 2017 4:40 pm
Location: North Yorkshire
Has thanked: 1865 times
Been thanked: 1378 times
Great Britain

Re: Doc modding Marantz imperial 7

Unread post by karatestu »

When I build the speakers into the oak tables I have come up with a way of making all four sides sand filled without making the panels too thick. 9mm of birch ply on the outside, 10mm of kiln dried sand and an inner panel of 3mm steel. I can do this by putting 10mm x 25mm aluminum bar into the groove that will run down the legs. The groove will be 1cm deep which leaves 15mm sticking out. The birck ply and steel can be attached either side of it. That leaves a 10mm gap for sand :dance:

The top and bottom panels will be harder to do this "sandwich" :lol: but it can be done. Sand filled panels are said to work really well.
DIY FREE ZONE

antonio66
Posts: 1006
Joined: Mon Jul 29, 2019 8:16 am
Location: Grimsby/Phnom Penh
Has thanked: 1449 times
Been thanked: 408 times
Great Britain

Re: Doc modding Marantz imperial 7

Unread post by antonio66 »

I've never heard of sand filled panels, they're certainly going to be thick enough to do the job
These users thanked the author antonio66 for the post:
karatestu (Sat Feb 06, 2021 7:31 am)

User avatar
Fretless
Posts: 9290
Joined: Wed Nov 12, 2014 12:15 pm
Location: Somewhere in Holland
Has thanked: 1487 times
Been thanked: 2280 times
Netherlands

Re: Doc modding Marantz imperial 7

Unread post by Fretless »

Sand-sandwiches! Well they should be, in resonance terms, as dead as the proverbial Dodo.

Groovy, Stu. :dance:
These users thanked the author Fretless for the post:
karatestu (Sat Feb 06, 2021 9:59 am)

Upstairs:
Vinyl
Pro-Ject 1.2 + Grado Sig Jr + Cambridge Alva Duo
DigiVolumio PC + Kiss DP-500 + Sabaj A20d
NVA: P50sa - Cube2 - SSP - LS6+ Sabaj A10a (x2)
Downstairs:
Vinyl
Logic DM101 + Syrinx LE1 + Grado Sig MCX
DigiDenafrips Ares II + Volumio PC + Cambridge CXC
NVA: P50 - BMU+ Aiyima A07 MAX (x2) + Arcam One
HP: HifiBerry Digi+ PRO + Sabaj A10d
Office:
Allo DigiOne SIG + SMSL M300se + Douk G4 (x2)
Mission 760 + Monolith THX AAA 887
Headphones: German Maestro, Monolith & AQ

User avatar
karatestu
Posts: 5945
Joined: Sun Jan 08, 2017 4:40 pm
Location: North Yorkshire
Has thanked: 1865 times
Been thanked: 1378 times
Great Britain

Re: Doc modding Marantz imperial 7

Unread post by karatestu »

Not many commercial speakers use sand which panels but Wharfedale have and there are a few diy versions. There is nothing new under the sun as they say. Also, reading about sand filled panels will bring as many differing views as just things in this ocd marketing led hobby. Some say it is good for midrange and not so good for bass where stiffness rules.

As usual it is a minefield and the devil is in the detail. An inner box (that the drivers are attached to) that does not touch the outer one is probably best but I can't achieve that.

Designing a box for bass and mid is tough because I think they require different construction and materials. There needs to be a compromise that can work for both- probably not ideal for either but hey, what can ya do.

Stiffness for bass, low mass for low energy storage and some damping so the thing doesn't ring. I think combining several different materials in layers might be a way to minimise one material's property dominating.

3mm steel inner, 10mm sand, 6mm aluminum and 3mm birch ply outer. The metal should provide the necessary stiffness. The sand should hopefully stop the metal ringing and the birch ply should help damp the aluminum and be suitable aesthetically on the outside. Some bison kit between the aluminum and ply should help and maybe form a kind of constrained layer damping.

Or it could be a complete waste of time and effort :roll:
DIY FREE ZONE

User avatar
karatestu
Posts: 5945
Joined: Sun Jan 08, 2017 4:40 pm
Location: North Yorkshire
Has thanked: 1865 times
Been thanked: 1378 times
Great Britain

Re: Doc modding Marantz imperial 7

Unread post by karatestu »

Wharfedale SFB/3 sand filled baffle (sfb).

https://www.inner-magazines.com/audiop ... e-sfb3/
These users thanked the author karatestu for the post:
savvypaul (Sat Feb 06, 2021 11:54 am)
DIY FREE ZONE

User avatar
savvypaul
Posts: 8635
Joined: Tue Oct 11, 2016 7:14 pm
Location: Durham
Has thanked: 1657 times
Been thanked: 2978 times
Contact:
Great Britain

Re: Doc modding Marantz imperial 7

Unread post by savvypaul »

Good read, that , Stu...
These users thanked the author savvypaul for the post:
karatestu (Sat Feb 06, 2021 12:05 pm)
I am in the hi-fi trade
Status: Manufacturer
Company Name: NVA Hi-Fi
https://nvahifi.co.uk/

User avatar
Ithilstone
Posts: 570
Joined: Mon Jun 01, 2015 10:54 am
Has thanked: 73 times
Been thanked: 61 times
EUROPEAN_UNION

Re: Doc modding Marantz imperial 7

Unread post by Ithilstone »

And here I was worried that the whole Stu DIY Speaker saga is at its end... :mrgreen:
now I am confident that you didn't even reached half way ;]]]]
I will be very disappointed if you finish it before you reach 200 pages! :mrgreen: :mrgreen: :mrgreen:
These users thanked the author Ithilstone for the post:
karatestu (Sat Feb 06, 2021 1:46 pm)
Nothing to see here...
I am in the hi-fi trade
Status: Manufacturer
Company Name: NVA Hi-Fi
https://nvahifi.co.uk/

User avatar
Fretless
Posts: 9290
Joined: Wed Nov 12, 2014 12:15 pm
Location: Somewhere in Holland
Has thanked: 1487 times
Been thanked: 2280 times
Netherlands

Re: Doc modding Marantz imperial 7

Unread post by Fretless »

What about a mix of sand and polystyrene beads (like you find in beanbags)?
These users thanked the author Fretless for the post:
karatestu (Sat Feb 06, 2021 1:59 pm)

Upstairs:
Vinyl
Pro-Ject 1.2 + Grado Sig Jr + Cambridge Alva Duo
DigiVolumio PC + Kiss DP-500 + Sabaj A20d
NVA: P50sa - Cube2 - SSP - LS6+ Sabaj A10a (x2)
Downstairs:
Vinyl
Logic DM101 + Syrinx LE1 + Grado Sig MCX
DigiDenafrips Ares II + Volumio PC + Cambridge CXC
NVA: P50 - BMU+ Aiyima A07 MAX (x2) + Arcam One
HP: HifiBerry Digi+ PRO + Sabaj A10d
Office:
Allo DigiOne SIG + SMSL M300se + Douk G4 (x2)
Mission 760 + Monolith THX AAA 887
Headphones: German Maestro, Monolith & AQ

User avatar
karatestu
Posts: 5945
Joined: Sun Jan 08, 2017 4:40 pm
Location: North Yorkshire
Has thanked: 1865 times
Been thanked: 1378 times
Great Britain

Re: Doc modding Marantz imperial 7

Unread post by karatestu »

I am not sure I can do another 80 pages :shifty: but I'll give it my best shot :grin:

There's not many things left to experiment with :whistle: apart from materials, box shape, diffraction minimisation, joining the bipole mid bass mechanically and the 12" dipole add on.

Even when they are finished it probably won't be the end of my speaker thread :lol: I have to make my speakers that will stay at the farm then. I fancy OB or quadpole with four 5 inchers ( front, up, in and out firing) which are vented aperiodically into a larger closed box like the Dynaco A25.
These users thanked the author karatestu for the post:
Ithilstone (Sat Feb 06, 2021 7:40 pm)
DIY FREE ZONE

Post Reply