Bipole ML TL with TB W871 – feed back on sims please

[Forsman]

I have done some simulations with the Tang Band W 871 driver. I have quite a couple of them at home and want to try them in a bipolar arrangement.

Recently I’ve built Bjohannesen TABAQ with the same driver. I’m very happy with this nice sounding little speaker but am curious how the same driver will perform as bipolar in a Metronome style cabinet.

The internal hight is 31"

An externally hosted image should be here but it was not working when we last tested it.

The worksheet

Grateful for some feed back!

/Forsman

 

[GM]

Bipolar designs are for creating an acoustic baffle step compensation filter to keep from giving away any efficiency, so the rear driver is typically rolled off as required, ergo AFA sims go, if it works for you, then build and adjust it for best blend to the room by experimenting with stuffing density and port tuning same as any vented speaker.

GM

 

[Forsman]

Hi GM

I’m not sure I understand you perfectly, English isn´t my first language.

I’ve seen bipolar arrangements where the rear driver is rolled off approximately where the baffle step starts but I’m not sure I’ve got that right.

Could you also please elaborate on this:

ergo AFA sims go, if it works for you,

/Forsman

 

[Forsman]

Ok, now I think I understamd, AFA stands for As Far As. Sorry

 

[planet10]

I’ve seen bipolar arrangements where the rear driver is rolled off approximately where the baffle step starts but I’m not sure I’ve got that right.

If you are going to roll it off (i have not found a need) that would be your starting point, perhaps a bit lower so as to further reduce the bipole dip.

Another option which we have started playing with is mounting the 2nd driver on the side (to keep the magnets from trying to occupy the same space, the front driver is shifted up half a driver diameter, the side driver lowered by the same amount.

dave

 

[Forsman]

I had hoped to be able to avoid any filter circuits in the signal path if possible. I consider that possibility together with the rise in efficiency to be very appealing.

I´ve found it hard to tune the pipe to 55 Hz and still keep the SPL response flat. I have little experience of this but to me it looks pretty ok.

 

[hm]

trombone

Hello Forsman,

do you know my double bipol horn
for 3" driver, i prefer to take the second
invers with +- change to need less
filtering.

 

[GM]

I had hoped to be able to avoid any filter circuits in the signal path if possible.

As Dave alluded to, if the surrounding boundaries are either HF BW absorptive and/or diffuse in nature and/or you prefer the added ambiance of audibly late arriving reflections, then no need to roll the rear driver off or at least not as much as is required for BSC.

FWIW, I'm a believer in acoustic solutions for acoustic problems, so adding an absorptive filter over the rear driver is how I recommend doing it.

GM

 

[Forsman]

hm

It is impressive that you have mange to tune a small 3” driver down to 38 Hz. However your cabinet is unfortunately too big for the porous I’ve intended this build.

As Dave alluded to, if the surrounding boundaries are either HF BW absorptive and/or diffuse in nature and/or you prefer the added ambiance of audibly late arriving reflections, then no need to roll the rear driver off or at least not as much as is required for BSC.

FWIW, I'm a believer in acoustic solutions for acoustic problems, so adding an absorptive filter over the rear driver is how I recommend doing it. GM

Thanks for that tip. I think I’ll go that way and try.