Help with notch filter for Beta 12LTA?

[bigaudioscotto]

Can any of you guys recommend a good notch filter
to tame the peaks of this driver.

[Up_3dB]

I recommend using a 31-band graphic equalizer (GEQ). I have some 12LTA cabs and a 15-band GEQ, and it sounds really good, but a 31-band GEQ would allow even better 'taming' of the peaks AND valleys.

[Pano]

Have a look at what is used on the Hammer Dynamic, it's basically a 12LTA.
Hammer Dynamics Super 12 Loudspeaker Kit

There are other versions of this filter. Also look for the Afterburner project.

[norman bates]

try asking over at the full range driver forum.

Fullrangedriver Forum

Norman

[freddi]

I'm not sure if its "that peaky" on-axis - IIRC the afterburner notch values didn't do much. Your best bet is to mount the speaker in desired enclosure or baffle, measure in real time and do some adjustments to the LCR trap


here's 3 cases outdoors where I've measured that speaker - the last one shows on and ~20 degree off axis where a typical for fullrange speaker hole appears and a peak

12LTA in a little K12 Karlson enclosure on and 45 off at several mic heights

12LTA in an Aristocrat (1953 EV/klipsch design)

12LTA mounted in the top right corner of an inappropriately tuned
4.6 cubic foot tapered pipe


12LTA would probably work very nice in a Karlson enclosure with ~2.2 cubic foot rear chamber and about half that front. A slotted waveguide tube tweeter would be nice.

although there's not much motor on 12LTA and can be weak on dynamics, it did an admirable job with.Danley's Harley recording in the Karlson 12. That would kill AN Super 10 in a reflex - the cone with AN10 jumped like crazy in a 70liter/41Hz reflex trying to play that Harley. AN10's cone excursion in a Karlson coupler is generally under control and will do useful work.

[Godzilla]

Beta 12LTA in a 3cf box - port size

I'd just cut out the dustcap and add a phase plug... done. That's how i enjoy them... i love the EQ idea but i don't have any desire to run one thru my tube amps. I would if i were using solid state tho. I'd imagine that if one were willing to use the EQ you'd have the most amount of control of the overall balance of sound.

[bigaudioscotto]

Thanks for all the input guys.

[norman bates]

godzilla, what'd ya use as a phase plug ?

Like Home Depot ? and what size so anyone can go in and buy one....


Norman

[wintermute]

I found this wikipedia page invaluable for making notch filters. Takes the guess work out of it!

RLC circuit - Wikipedia, the free encyclopedia

go to the parallel RLC section (but it helps to read the preceding stuff as well.

If you are like me and shy away from maths, it looks intimidating but if you can get your head around at least the Q formula and the Wo formula you should be able to work out a filter suitable for your desired frequency. swapping the values for C and L will change the q (without changing the centre frequency) and the resistor determines the amount of cut.

Choose a value for C or L and the frequency and then work out what the value for the unknown component (L if you chose C) is. adjust until you get usable values and the desired Q.

I found this to be a much better starting point for simulation (very close to the desired frequency) than the methods I'd found in my speaker books.

edit: using the Wo formula and the 8.5uF and 0.65mH in the notch filter in pano's post gives a notch frequency of around 13,450 Hz That seems a bit on the high side, I think the formula has been changed to radians (since I last used it), so you also need to divide by 2pi which gives about 2140Hz which seems more reasonable.

Tony.

[norman bates]

I'd use a pot to determine the resistors values, then replace with a fixed one. Remember that the impedance usually increases as the freq goes up, so you may need a 16ohm resistor to cut the peak by 6db using an 8ohm driver.

F = 1 / (2 x Pi x L x C)
so you multiply 2 x Pi x .4 (the inductance) x 10^-3 x 4 (the uF) x 10^-6
then with the result, press the 1/X key, now you have the notch frequency.

It's simple.

Norman