Fountek FE85 Bipole

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I am about to order two pairs of the Fountek FE85 for a small bipole speaker.
Would I have any advantage ordering double and have two firing forward, two firing back on each speaker. (as they are under 10Euro each)
I know about lobing, but some people have used similar sized drivers together (like the Jordan and Bandor ones) without any filters between them.

It would be similar to these (a previous design I have done with Bandor 50mm drivers)


Bandor Tower 1 by hoopsontoast, on Flickr

But with two on the back, and no Volt Radial Subwoofer.

Thanks, Rob
 
My previous ones i designed a few years ago, worked really well in the near-field. (placed a good bit further out into the room)

3667098657_6ae824528a_b.jpg
 
Those speakers look great, by the way.

Thanks I have made a quick CAD Model, which is what I am planning, except that the drivers are back ordered a month, every supplier does not have any stock.

6765666905_539287ccd2_b.jpg


Very simple, with the two FE85's mounted magnet to magnet, in a small sealed box with extra wide baffles. Its around 960mm x 600mm x 130mm.
Its roughly the Golden Ratio in dimensions (except depth), and with the driver placement.

Aiming for something a little like electrostatic speakers, but to be used in the near-field (around 1.5m from the listener, and around 1m from the rear walls.)
 
I had thought about it, as the fs-125 being not too low the line length would not be too long, I get confused with the maths of working out the TL path. I understand that I would would want a 2.7m line (or 675mm if 1/4 wave) going from an area at the top roughly equal to the SD (1>1.2*sd) which is 27cm2 and a ratio of the line from 10>1 for a sealed Transmission line.
I do have a copy of the MJK Alignment Table paper, but I just get confused.
 
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I am going to go with the FE87, side by side they look the same cone, just one with the shielded magnet.
And the FE87 has a higher Qts, which gives me 100Hz@-3db in a sealed 4Litre box with two of them.
And mainly as everywhere in Europe is out of stock atm with the FE85, but lots of Fe87 :)
 
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My previous ones i designed a few years ago, worked really well in the near-field. (placed a good bit further out into the room)

3667098657_6ae824528a_b.jpg

I think remember this speaker, I think you made it as part of a course you were qualifying from if I remember correctly, I even think I have a copy of this image somewhere. You do some nice work.
 
Yes it was for my Final Degree show project in Transport and Product Design.
The design itself was not the most advanced, but it worked quite well, although I made a mistake of selling the drivers Veravox 5S @ 150Euro/ea for around £150 for the 4 as I was really skint at the time. :(

It was a good couple of years ago now, well remembered!
 
Hi Rob,

Very nice designs..! But I think you will get less (very little) high frequency with your design and with FE87 in particular. This is due to the very wide baffle dimension. Because of the baffle dimension you will get a very flat on axis response above the step frequency. But the power response will fall in high frequency (above ~4kHz). That’s why, in these configuration, you have to listen so close (1,5m) to the speaker.
If you want to keep this design, you will have to choose a driver with a rising frequency response above ~4kHz, like Fostex FF85k, Monacor SPH-30X, etc….
For the FE87 I suggest an approach quite the opposite: Very narrow front baffle and a very deep loudspeaker so that the cancelation between front and rear speakers occur below 400Hz (this is important!. try to keep cancelation frequency well bellow the critical frequency of your ears!). This way, the front baffle step will be at a high frequency and you will have a natural on axis rising frequency and a more flat power response. You may have to use a little notch filter at high frequency (tipical ~3kHz) to “adjust” the power response, but the final results are very very good (from my experience).

Cheers,
Esaú
 
Hi Rob,

If you tried the FE87 in OB and you like it, then go for it! This configuration works fine in near field listening. I think it is a question of taste. I usually like to listen to music in no specific place of the room. I like the music to “fill” the room, and bipoles can do that very well. For this purpose, I found that narrow baffles works best, although room acoustic and loudspeaker placement may be critical.
Any way I will be following your design!

Esaú
 
I have put them in a new OB, using two drivers each side, and using the bass treble tone controls helps. I can get as much output from these running full-range at the moment.
Sounds really really good with electronic music, not so good with vocals which seem a bit recessed. This could be the cardboard baffles, probably adding quite a lot of resonances.

One thing i have noticed with these drivers, they have to be rear-mounted, the connections wont fit through a cutout that is big enough to get round the large magnet.
Also the connectors need to be manually bent outwards, as they are very close to the magnet and one of them shorted onto it and put the amp into protection mode.

Build quality is very good on these considering they are 10Euro/ea, not quite as nice as the Veravox 3/Omnes Audio BB3.AL but they were a good bit more and quite an old design with a nice cast chassis. Much nicer than the Visaton FR 10 8.
 
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