DIY Purifi subwoofers.

[Paul7777x]

I think I saw here a year ago, or perhaps more, a diy build of a pair of subs using the new ten inch Purifi driver. But I can’t find it now.

Has anyone done this yet?

I have good enough timber working skills, but little idea of box size calculation or the best way to decently brace the box.

It’ll be a pair of passive subs I’ll want to build.

Cheers.

 

[Head_Unit]

The point of bracing is to reduce vibrational sound radiated into the air. So bracing along the box internal edges, as I did back when I was a teen starting my journey to become a loudspeaker engineer, is not too helpful ha ha. You want to brace front-to-back, top-to-bottom, side-to side but ideally NOT to the center of the panels. You want off-center so the remaining "free to vibrate" portions are each different sizes which will resonate at different frequencies.

I like to use 1x1" dowel, and have them all meet in the middle. I cut the dowels very slightly too long, then twist fit in place, then glue on on side. Dry like a day, rotate, glue the next side, repeat repeat. Also some kind of anti-vibration coating would be good, and also stuffing. For stuffing get Vance Dickason's seminal Loudspeaker Cookbook which at least in the 7th edition has a chapter about that. Even more extreme you can make the walls a sandwich of wood-stuff-wood where sorry I forget what the absorbent stuff in the middle is.

Are you doing sealed or ported? Ports are a whole 'nother thing.

And you are making two subs, to put in different locations? You have room correction that can adjust two independently?

To calculate the box size, you need the Thiele-Small parameters for the driver. There are several 10" Purifi it seems, so you would have to decide which you will use and by the way you know they are like $800+ apiece?

 

[DVDdoug]

I have good enough timber working skills, but little idea of box size calculation

Plug the Thiele-Small parameters into speaker design software. (WinISD is free.)

With a "small" sealed box you'll probably need some EQ to compensate for the low frequency roll-off and the software will show you the (predicted) performance. With active sealed designs, the EQ is normally built-in so once the speaker is done you don't have to think about it.

Ported boxes usually don't need EQ, and it doesn't work as well because of the steeper roll-off. But box size (and port dimensions) are more critical. Again, the software will help you with all of that and it will help you decide to go sealed or ported.

or the best way to decently brace the box.

There are lots of ways to stiffen the box (and a smaller box is naturally stiffer). With a subwoofer it's often less critical because the box resonance tends to be well above the subwoofer's operating frequency. (That's the box-vibration resonances, not the port tuning.) On the other hand, "pressure" in a subwoofer is higher.

 

[kemmler3D]

@DVDdoug with solid info per usual.

My advice is simply to say that I think the Purifi 10" is overkill for a sub unless your system is overall "money no object". I think the CSS or SEAS 10"s are similarly capable with low enough distortion that it shouldn't matter. But it will be some damn clean bass if you use the Purifi. I was looking into building some top-end 3-ways and these drivers were all on my list at one point.

I think it was @CINERAMAX that used these drivers for subs, although it was a much more extensive HT build IIRC.

 

[ShadowFiend]

Honestly, Purifi 10" will be wasted in subwoofer only (high pass at 80-100Hz), as its strength is the ability to play mid cleanly with extremely low distortion while producing excellent bass even at high excursion. There are cheaper and no less excellent drivers for subwoofer duty, like Wavecor SW275. SW259 or SEAS L26RO4Y or CSS SDX10 XBL2

 

[mocenigo]

Honestly, Purifi 10" will be wasted in subwoofer only (high pass at 80-100Hz), as its strength is the ability to play mid cleanly with extremely low distortion while producing excellent bass even at high excursion. There are cheaper and no less excellent drivers for subwoofer duty, like Wavecor SW275. SW259 or SEAS L26RO4Y or CSS SDX10 XBL2

For sub duty–one sub per channel that works also as a stand–I used four GOLDWOOD SOUND GW-215/40/8 CAD, to build two ripples. And then I equalised them using the softer for the Hypex Fusion plates. They only work from 64 Hz down.