Hoops Speaker Roundabout

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
I’ve also read some good reports on the Tymphany DFM-2535R00-08

This one requires quite a bit more research!


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.

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.

Do they sound boxy?

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


Which type of enclosure will these go in?

Open Baffle, managed to knock these up today…

Supravox OB by Robert Seymour, on Flickr


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

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.

I thought a sphere was the ultimate baffle.

Anyway my baffles are poop and need some remedial work.

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

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.

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:

I love it when engineers get technical


Does not compute.


I was rounding down. :grinning:


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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