Hoops Speaker Roundabout

HiFi
1

As ever, these things go round in circles!

I had been planning an Open Baffle project for a while since my Supravox 165-2000 full-range drivers arrived.


Supravox 165-2000 by Robert Seymour, on Flickr

So far, I have been using them in a ~100 Litre Aperiodic enclosure, not bad at all but not really what these drivers were made for, and although they do a reasonable job in the bass, its not the most ‘distinguished’ .

I have just bought myself a pair of Supravox 285GMF Mid-Bass drivers :smiley:

Unfortunatly I don’t have the budget for the AlNiCo or Field Coil versions to match the AlNiCo 165-2000 drivers.

I currently have two plans, mirroring a project I tried a few years back, with a Full-Range Driver with Bass support and a 2-way/3-way horn based speaker with a 400Hz Stereolab Horn/Radian 850PB and Volt BM251.3 Mid-Bass driver, all with the original MiniDSP 2x4.

Plan A - Open Baffle
MiniDSP 2x4HD
Supravox 165-2000 from ~300Hz and up (Decware Zen)
Supravox 285GMF ~60Hz to 300Hz (CA A5 for the moment)

This is the initial plan, mainly as I will have everything here ready. The plan for the bass is to make a small ‘H’ baffle for the 285GMF to give me a overall baffle width of 900mm.
The 285GMF is not the best suited for the deepest bass extension in OB, but Supravox themselves use it in a couple of designs this way. I don’t have the space for massive baffles or multiple 15" bass drivers so it may turn into using a small closed sub below the ~60Hz that the 285GMFs should get down to.
I also still have a pair of Veravox 5S full-range drivers I may try as well.

Plan B - Horns
MiniDSP 2x4HD
1" CD (BMS 4550, Radian 475PB etc) ~1200Hz and up (Decware Zen)
Supravox 285GMF ~60Hz to ~1200Hz (CA A5 for the moment)

This is more of a longer term project, and one of the reasons why I decided on buying the 285GMFs as they will be quite flexible, being able to use for bass support for Plan A, and comfortable as a 2-way and match with a 1" CD, which there are quite a few project similar online.
The big decision is the 1" CD and horn, I had great results with the Radian 850PB before so the 475PB is a natural choice, and happy to be crossed as low as 800Hz for home use. It is however quite expensive so that might be a one to wait for a pair to come up second hand.
I’ve seen some good projects using the Classic B&C DE250, BMS 4550 and 18Sound NSD1095N as used by Troels
http://www.troelsgravesen.dk/The-Loudspeaker.htm
I’ve also read some good reports on the Tymphany DFM-2535R00-08
https://www.audioxpress.com/article/peerless-by-tymphany-dfm-2535r00-08-compression-driver
This one requires quite a bit more research!

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I would build a folded open baffle - basically a box open at the back - for the bass. Then you can plonk the horns or whatever on top.

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Thats essentially what the test cabs are, an open backed cabinet with two types of foam density at the back


Build by Robert Seymour, on Flickr

For the OBs, I plan to use the existing front panel, mount the 285GMF near the bottom and add on some wings to creat the ‘H’ Baffle.

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Do they sound boxy?

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Not really at the moment, there is around 2" of two density foam covering the back making it a leaky/Aperiodic box, designed for the high Q (Qts 1.1) Supravox 165-2000 drivers.

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Bass drivers arrived


Supravox 285GMF by Robert Seymour, on Flickr

And impedance sweep, not bad. Pretty close to manufacturer spec


Supravox 285GMF by Robert Seymour, on Flickr

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Which type of enclosure will these go in?

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Open Baffle, managed to knock these up today…


Supravox OB by Robert Seymour, on Flickr

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What thickness baffle? I somehow ended up believing I needed a massively thick and mega braced bass baffle today.

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The plywood is 20mm as thats just what I ordered. No other bracing at the moment.
The thickness and bracing is not too much of an issue unless you have a single large baffle I guess, to help with stopping the baffle itself moving with the vibrations.

I believe the ultimate goal is no baffle at all and just the drivers naked, although as you have huge cancellation from the back wave/front wave you need a LOT more bass driver surface area and displacement.

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I thought a sphere was the ultimate baffle.

Anyway my baffles are poop and need some remedial work.

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That Supravox driver has a Qts of about 0.38. Are you getting decent bass from it?

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I’ve got it wired up but not had a chance to try them yet, I’ll leave that to the weekend when I can have a play around with the Mic/REW and see whats what.

I’m not expecting deep bass, my ~3m x 5.5m room does not help with that.

The goal is from my xbaffle spreadsheet, they are predicted to be around -3dB @ 80Hz from reference, at around 2.83V(~99dB). This however is not taking into account for the room only the immediate boundry. Being so efficient means I can add a little eq, especially as I plan to cross them around 200Hz to help out.

Supravox themselves use it in their Open Baffle design here:

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I think that as long as you use decent birch plywood, 15 or 18mm is fine. I get mine cut by my local timber merchant, they do clean accurate cuts.

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I doubt those supravox drivers will take much power. Check the Xmax.

You will need far beefier drivers and an absolute fuck ton of power for that approach.

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Yes, I agree.
The plan is any low bass (<60Hz) is to be covered by a small sealed sub. I don’t have the space/power for multiple 15"+ bass drivers! :grinning:

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I love it when engineers get technical

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Does not compute.

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I was rounding down. :grinning:

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First pass at a few measurements yesterday evening.

The 285GMF on baffle, measurement taken nearfield (~20cm) showing full-range and also LR24 filter @ 120Hz


Supravox 285GMF Full-Range & LR24@120Hz by Robert Seymour, on Flickr

Distortion as above, looking good so far


Supravox 285GMF LR24@120Hz Distortion by Robert Seymour, on Flickr

And the first pass at a full-range plot (285GMF <120Hz, 165-2000 >120Hz), with the original plot of the 165-2000 in the Aperiodic Enclosure.


OB1 & AP Box Comparison by Robert Seymour, on Flickr

No PEQ or other filters added in these plots so far.

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