audio-talk

I've been pondering over some changes to my speakers and have some ideas. But I don't have that much expertise with speakers and there are lots here who do so I'd be grateful for thoughts .

My starting point is what came to Owston last year - Fostex 208E sigma "full range" in small OB (approx 450mm square) on top of Supravox 285GMF bass helper in a H frame baffle (450mm square x 500mm deep), with a Fostex T90A supertweeter, in a room approx. 4m square. And it does a lot of nice things I like.

But I felt the bass didn't go particularly low and there was probably music I was missing down there. Understanding how the speakers actually performed was the start of the journey to get more bass, and I took some measurements with REW which showed the bass starting to roll off at around 100Hz. No surprise considering physics tells us that 1m diameter baffle will roll off at around 105Hz.

So, what to do?

I had a "chat" with Chris who suggested building some sealed boxes for the 285GMFs as his suspicion was that the room gain from a sealed box could work well. So I built some 75L boxes based on a sim, which predicted an F3 of 87Hz.
And then I measured them, and in my room they get down to a F3 around 50Hz.

The 285s work well in the sealed boxes, and most normal people would stop now and enjoy. But after 3 months living with them, as much as I like what they do lower down compared to the H frames I miss the, er, openness of the OBs. There's just something a little more funky about the OB bass.

The reason why I moved away from the Quasars, a well trodden path to OB, is partly because of the imposing size, but mostly because the side wings seemed to be create a rather unpleasant peak in the 208's response around 3kHz - going to the flat baffle much reduced this.

So unless I start again with drivers, which I'm not ruling out, I want to maximise the OB-ness within size constraints.

This is the measurements of all the drivers - they're not level matched so you'll need to use your imagination, but you can see how the 285 in a box goes usefully lower than in a smallish baffle. I'm leaning towards going back to the H frames, but then add a subwoofer below, with a low pass filter perhaps around 80ish Hz. But then these are 4 way speakers, and will the sub blend with 285s successfully?

So is this a reasonable idea? Or asking for trouble? Or perhaps there's a better way? Grateful for any thoughts on this.

I would have expected the 285's to roll off rather earlier with sealed box than on OB to be honest. Looking at it quickly on Hornresp does confirm that, for volumes in range 75 to 85L. Great lower-mid solution though
They have rather too high Fs to be a real bass solution with sealed box - the resnance goes higher as you add the box loading.

We need to think about this carefully. Incidentally, Chris V gave me some pointers to other bass units the other day. Check out the new 380mm Supravoxes if you have some coin hanging around ... there is an alnico one !
But.. there is a 15" Fane one with not too high rms that looks quite nice on its response.

ps. the 208 to my ears , and on graphs, needs some work on the 4kHz peak. I did develop a crossover for that and the G3 ribbon that used a shallow notch on the 208, it sounded pretty tasty.

I guess it's the difference between dipole losses and sealed room gain Mark? As Chris has said, the benefits of measuring what's actually happening are significant.

I've had a quick look at the 380GF - not cheap at €1500 a pair! And a ported box is in the region of 200+L, so probably a bit big for my room. I'd be interested in which Fane driver. I've looked at some and they're pretty big boxes again, and don't go especially low in a simple sim at least. The Impulse 18XL looks impressive though, but I'm not sure I'd get a 500L cab up the stairs!

Edit - just noticed Fane's dataset recommends a volume of 60L to 230L. That's nothing like the quick sim I did so they must be using a lot more intelligence! Shame they don't have suggested cabinets as examples.

Must get to bed... but :
https://www.diyaudio.com/forums/multi-w ... es-20.html
So are you sticking with sealed, or going back to OB, for the bass ?
Bi-amped between bass and mids ?

If 15” too big what about...https://www.falconacoustics.co.uk/sb-ac ... oofer.html. There is a 16 ohm version for OB, some discussion of this drivers use on diyaudio

IslandPink wrote: ↑Wed Dec 30, 2020 12:38 am Must get to bed... but :
https://www.diyaudio.com/forums/multi-w ... es-20.html

Interesting thread, I've read from your link to the end. 8x15" is tempting but altogether too much for me!

IslandPink wrote: ↑Wed Dec 30, 2020 12:38 am So are you sticking with sealed, or going back to OB, for the bass ?

I think this is the crux of the matter. Ideally I'd like OB. But physics demands a large baffle and the right drivers. James' Quasars use a series crossover to get lower bass from the 285GMF, more on this below. So, unless there's a clever way of getting lower bass from an OB in a smallish room then a compromise is needed. (For now at least I don't want to go DSP.) So if I do go OB with what I have I need to fill in the lower bass with something else.

IslandPink wrote: ↑Wed Dec 30, 2020 12:38 am Bi-amped between bass and mids ?

Yes, that's what I'm using at the moment - GM70 for the 208 wide band, and class D 3116 for the 285s and T90As. When I was using the Quasars I experimented with biamping and got tremendous improvement in clarity. Biamping brings a different set of problems of course, not least that the 285s don't go as low anymore.

vinylnvalves wrote: ↑Wed Dec 30, 2020 8:04 am If 15” too big what about...https://www.falconacoustics.co.uk/sb-ac ... oofer.html. There is a 16 ohm version for OB, some discussion of this drivers use on diyaudio

I have one of those in a sealed sub for the TV and it's nice. I'd been considering adding one to this system as it models well, most likely as a sub below 80Hz, but also as bass drivers replacing the 285s. But I didn't know there was a 16ohm version, or that it had been tried in OB, I'll see if I can find the discussion on DIYAudio.

So unless I start again with drivers, which I'm not ruling out, I want to maximise the OB-ness within size constraints.

what about a pair of these? http://www.rythmikaudio.com/GRci_OB.html

I noticed this on Colins link.

"SW12-08FR is on back order till further notice."

Cool, you got the sealed boxes built. The extra LF extension isn't much of a surprise.

Simon, did you, by any chance, take some measurements of the 285 at the listening position?
IME, once you get below a few hundred Hz, you need to be treating the room + speaker as one, and acting accordingly. The sealed box will be activating a different set of room modes compared to the dipole version, and of course will be operating without dipole losses. It's possible there's some cancellation (there appears to be one already showing at 1m) which could be eliminated with careful positioning.

If possible, I'd also take an impedance sweep of the sealed box, and make sure there aren't any secondary resonances (standing waves etc) which will show up as small peaks. An irregular internal surface and/or absorption inside the cabinet will help there.

I haven't checked out your LF amp, but if you've got some spare gain available (via turning the volume control up a bit, changing resistors or whatever), you could probably put together a shelving cut with some caps and resistors to drop the level above 50Hz. Totally passive, just put it on the input of the amp. Add the required gain back in, and the <50Hz range should be boosted.

First, though, I'd take some measurements at the listening position and see what your room's doing below 100Hz or so.

Chris

pre65 wrote: ↑Wed Dec 30, 2020 1:42 pm I noticed this on Colins link.

"SW12-08FR is on back order till further notice."

Still appear to be available direct from GR Research: https://www.gr-research.com/store/p37/S ... oofer.html
Direct servo amps here: https://www.gr-research.com/direct-serv ... fiers.html

Links to their H-frame & W frame are currently broken, but the Wayback Machine is your friend:
https://web.archive.org/web/20180521081 ... me%202.pdf
https://web.archive.org/web/20181123121 ... /obsub.pdf

Simon i think I have a pair of 15" vintage fane drivers, I think they are 15" versions of what phil uses. Your welcome to try them, but I'd need to check as I've got rid of a bit of my stuff..
They are more suited to low wattage use than alot of the modern stuff in my view.

simon wrote: ↑Wed Dec 30, 2020 10:14 am Interesting thread, I've read from your link to the end. 8x15" is tempting but altogether too much for me!

Ha - no, I mean the driver is interesting, as a single.
They are only about £100 each on EBay.
Would be a good idea to take up Steve on his offer though, I think.
In the meantime i will check that driver at least on Hornresp for IB to see if it goes any deeper than the 285.

Part of your problem is that you need to get up to at least 500Hz to blend to the 208's which have a significantly rising response through the midrange.