I use a 25W tube amp with a diy loudspeaker. This loudspeaker is made with a Fostex FE206E + FT17H on open baffle upon a bass enclosure with an Eminence Delta 12 LF. The problem is that the damping factor of this amplifier is not friendly with Delta 12LF and I have not enough dynamic and efficiency on basses. I need a RLC series notch filter before using bi amplification but I'm not sure how to calculate it. Does somebody could help me ? :(

Thanks.

Eminence Delta 12LF :

Re = 6,06 ohms
fs = 45 Hz
Qes = 0,45
Qms = 7,28
Impedance at fs = 93 ohms

Pascal / France

I recommend that you either run the woofers with a separate amplifier, or perhaps substitute a Delta 15 woofer in place of the Delta 12LF. That of course will require a pretty large box, so it may not be your favorite option.

Sorry, but I'm afraid those are the best things I can suggest. But I think you'll find one of them will satisfy you, and it's better than attempting to use a notch filter to solve this problem.

Thank you for your answer. The problem for me at this time is that I can't build active filter. For the future, yes, I will build a tube crossover and a mosfet amplifier for basses. But at this time I can only use a passive filter or replace the Delta 12LF by another 12" wich can be work in a 100 Litres box.
I have read on the net that at the resonnance frequency, the power fall down with the peak impedance. For a driver wich have 6 ohms at 200Hz, and wich have 45 ohms at Fs, if you have 100W at 200Hz you have only 13W at Fs. So it certainly my problem with tube amp. I have tried my loudspeaker with a solid state amplifier (yamaha of my home theater system) and the problem is not so perceptible/discernible.
I have found a link to calculate series notch filter on the net, but I'm not sure of the quality http://www.mhsoft.nl/SeriesNotchfilter.asp.
Do you know this link ?

Thank you for all

Cordialement.

Pascal.

thank you very much, after I have adding a LPad on Fostex drivers (more than 100db) the result is better. And I have added a little bit of "gaze" (in french) in vents. I have raise up the front of loudspeaker a little and give a slope/tilt to front baffle. Basses are more present and good. I think it will be better with active filter but at this time I'have not filter and second amplifier. This loudspeakers are made for the room where I work, and in this room I have only one amplifier. Others tube amplifiers and home theater are in my living room.
On "money" of Pink Floyd, basses are very good, and medium + trebles are precise/definite . And "shine on you crazy diamond" is fabulous.

Cordialement.

Pascal.