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In Reply to: RE: Felt to absorb tweeter reflections? posted by KanedaK on April 10, 2017 at 02:31:34
I would try to figure out what the 8k peak is from first, move the speaker to a neutral location like outside or the middle of large quiet room.
If it's still there when you move around in front,its not reflected sound then consider a series RLC tank with an 8 k notch.
If it's a lobe / directional then try;
If you have an electronic crossover handy, set up a band pass filter from say 6 to 12Khz then play pink noise through it (leaving the 8k much more audible).
Then walk around it, see if you can localize it, take a chunk of foam and see if you can find it blocking things off or absorbing. do not put foam anywhere you could see if you were looking through the driver mounting hole, if anything on your horn, continue the horn progression at the top and bottom with foam, that is the likely diffraction point on that shape.
If you measure, set up and rta when you do this and then you have a objective indicator when you hit gold with the foam or moving the mic around you may find a lobe or null (the two are usually found together)
Edits: 04/10/17Follow Ups:
Looking at the BEYMA CP35 frequency graph shows a broad peak centered around 8KHz, roughly 6 dB in amplitude.
I've ordered components to make a notch filter starting at 6500Hz and stopping at 9500Hz with a 6dB max attenuation. I'll see where that takes me, as I understand it the only way to know for sure is to try...
i hope to flatten the tweeter response enough to be able to remove the variable L-pad I'm currently using.
Agreed, try the notch filter.
I can't tell off hand if/what effect absorption would have on that, it's way smaller than what i have a feel for.
In any case, it wouldn't hurt and on that shape it would be the sides where you would want to put it
I'm currently trying the notch filter.
It does work - it does as predicted, removing the 8KHz bump and allowing me to remove the l-pad (with the bump, the tweeter was really too hot), effectively boosting the relative level of frequencies above 10KHz.
But I have yet to decide if I like the result.
The new extended treble makes the sound more detailed but also more rough and unforgiving.
I still don't know if:
1) the new response shows all the flaws of my equipment
2) the notch filter caps sound rough because they are not broken in yet
2) the notch filter caps (Jantzen cross-caps) aren't good enough
3) putting a notch filter wasn't a good idea.
So I will now wait until the caps settle down and re-evaluate.
I was wondering.
Does that Manger also produce that 90 degree phase shift
at midband with flat frequency response, like direct radiators do?
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