Fostex FE207E with Eminence Alpha 15 open baffle

[sharpi31]

I am about to try out open baffle speakers for the first time (other than my Maggies). I have both a pair of fostex fe207e and a pair of eminence alpha 15.

My plan is to use a baffle about 600mm x 1000mm, sloping backwards slightly with 200-300mm side cheeks.

I am keen to keep things very simple initially, with a single inductor on the bass driver and the fostex running full range. I've played around with The Edge software but would appreciate some advice.

What inductor value would you recommend for starters? I have read about similar systems using from 3.9mH to 7mH.

Does the baffle size seem appropriate?

I don't want to get bogged down with BSC filter etc. as my next purchase will probably be a DEQ2496.

Any advice would be appreciated.

 

[ttan98]

Martin King has developed a Mathcad program which allows you to determine baffle width and high required and also the roll-off frequency for the bass end.

Contact him, he is most helpful.

 

[sharpi31]

Many thanks ttan98 - I've ordered a mathcad model from Martin.

 

[Ricky]

I am about to try out open baffle speakers for the first time (other than my Maggies). I have both a pair of fostex fe207e and a pair of eminence alpha 15.

My plan is to use a baffle about 600mm x 1000mm, sloping backwards slightly with 200-300mm side cheeks.

Hi.

I've had a lot of experience with Eminence Alpha's in OB situ's.

I feel your choice is a good one. You may have to go to a 2nd order filter for the Emmy tho or else you might not be able to make it "shut up". A frequency of about 500Hz should do it. When you go to the DCX, using the same frequency, shut it off at 24dB/Octave or steeper and put a bottom limit on it of around 40Hz with a 2nd order roll.

You can also tame the top end of the Fozzie with a 6dB slope at around 8K.

Look forward to your results.

Ricky.

 

[sreten]

Hi,

The Fostex run full range does not sound like a good idea due to xmax.

I'd say you should use a series 1st order crossover at least.
1st order series should work better than the normal 1st order parallel.

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

4mH / 80uF are very ball park values.

/sreten.

 

[felixx]

What do you think about this?

http://www.diyaudio.com/forums/showthread.php?s=&threadid=23208&perpage=10&pagenumber=118

 

[OzMikeH]

I have found my Fostex Fe207E somewhat flat in the extreme high end.
I may be doing something wrong for that result though, they only have about 50 hours on them.

 

[sharpi31]

Those are beautiful felixx.

How do you cross them over?

Did you use a BSC or equalization?

I think my first pair will look a bit less impressive than yours

 

[felixx]

I use Alpha15A for woofers and works very well.
The cross is active only for Alpha's.
The cuttoff is 250hz with Burr Brown OPA2134.
I have an active filter "a la Linkwitz" 3db and could be modified easy.
The Supravox is free of any components and it goes superb(xmax. is 4mm).

Here is an impressive work with Fostex into open baffle:
http://www.bd-design.nl/
Quasar.

 

[sreten]

Hi,

Note that open baffles do not have BSC (baffle step)
as such, they have baffle roll-off at 6dB/octave.

You can use 2 bass units in a 0.5 way configuration to
compensate for 6dB of this roll-off, i.e. extend one octave.

/sreten.

Active EQ and bi-amping you can do anything with the lower unit.
You can reduce the Fostex amplifiers input capacitor to cut low bass.

 

[HiFiNutNut]

Using such a wide baffle moves the first dipole null lower that would be very difficult to deal with in an XO. You can simulate the baffle response from Edge, BSC and A B C Dipole.

 

[barackuda]

A how to...

Hi folks....i am very interested in such design, like felixxx build him self.is there any proven or well known design that i could "copy"? i mean drawing, drivers used, wiring, etc etc.....you know, everithing allready done.I've searched the forum, but the search engine give strange results....

Thanks alot.

 

[sharpi31]

Well I have been enjoying the speakers for a month or two now, and am very happy overall. There is no shortage of bass weight or warmth, but the detail and imaging are also excellent.

 

[sharpi31]

I am currently using a series first order crossover (4.1mH air core inductor and 75uF caps). Today I received some new monster Russian military PIO caps from Estonia (below) and am keen to try pushing the crossover point down an octave or so to about 145Hz. Two of my new caps measure the same at 114.3uF, so I will first try 7.0mH inductors and take it from there.

Will the fostex be happy working down to to this point? With a 145Hz crossover the fostex will be 6dB down at 72.5Hz and 9dB down at 36.25Hz, which I hope should prevent over excursion of the driver.

Any advice would be appreciated

 

[sreten]

I am currently using a series first order crossover (4.1mH air core inductor and 75uF caps). Today I received some new monster Russian military PIO caps from Estonia (below) and am keen to try pushing the crossover point down an octave or so to about 145Hz. Two of my new caps measure the same at 114.3uF, so I will first try 7.0mH inductors and take it from there.

Will the fostex be happy working down to to this point? With a 145Hz crossover the fostex will be 6dB down at 72.5Hz and 9dB down at 36.25Hz, which I hope should prevent over excursion of the driver.

Any advice would be appreciated

Hi,

Hand waving I'd say it would not work well as the fostex is too
near the edge of the baffle, you will have substantial baffle loss
for it at 140Hz, but suck it and see. You may have to go series
capacitor on the fostex and higher 2nd order on the Alpha.

/sreten.

 

[Geoff H]

By all means give it a go. If sreten's warning is valid, and I think it is, a "shelf" above the main driver could be a solution.

I prefer the crossover to the main as low as 80 Hz. Can't always get there.

Have a look at: www.contrabass.com/pages/frequency.html

Good luck,

Geoff.

edit: the series xo is the way for passive use. You need to take into account the z at such low freqs, usually much higher than nominal.