Super Tweeter Cross Over.....

[tubenut]

I am trying to use a Foster Ribbon Tweeter as an add on super tweeter like Tannoy/Townsend/Murata/Elac....

I have been playing with simple 1st order cross over with cap and resistor in series crossing over at points between 10 and 15 kHz. The results are interesting but everytime I wish to change the x over frequency or level it affects both R and C components.
Would an L Pad feeding a cap in to the tweetwer not be better?
How do I calculate the L Pad for matching 84 dB sensitivity speaker system to a 92 dB tweeter of 8 Ohms crossing at "X" frequency?

I did comms electronics a long time ago and can probably work out a pad with supposed input and output impedance of 8 ohms but is that what is required? Would the pad need to do 6 dB as the cap will do another 2dB? (92-84=8 dB)

[sreten]

Hi,

Would an L Pad feeding a cap in to the tweetwer not be better?

In most cases yes it would. Could use an adjustable 8R L-pad.

Its generally agreed ribbons don't like 1st order crossovers at all,
due to excursion increasing down to its resonant frequency, the
excursion stays ~ constant with 2nd order, decreases with 3rd.

/sreten.

[tubenut]

X over for ribbon I am using should be 6400 Hz at lowest so thought 11k first order should be safe......

G

[DeonC]

Hi tubenut

I read somewhere than one manufacturer uses a cap in each leg of the tweeter. Basically the effect is that you get a 2nd-order roll-off with the low phase deviation and other advantages of a 1st-order XO (or so they said anyway). If this is true, this is something you might try.

Enjoy,
Deon

[Ole Pedersen]

I think the cap most come before the L-pad, og am I wrong !!!

Ole

[sreten]

[

Originally posted by tubenut
X over for ribbon I am using should be 6400 Hz at lowest so thought 11k first order should be safe......
G

Hi,

you can probably use a first order crossover as long as it is fed from the tweeter terminals.

Originally posted by DeonC
Hi tubenut
I read somewhere than one manufacturer uses a cap in each leg of the tweeter. Basically the effect is that you get a 2nd-order roll-off with the low phase deviation and other advantages of a 1st-order XO (or so they said anyway). If this is true, this is something you might try.
Enjoy,
Deon

Hi,

As described you would not get a 2nd order roll-off.

Originally posted by Ole Pedersen
I think the cap most come before the L-pad, og am I wrong !!!
Ole

Hi,

Normally the capacitor should precede the L-pad to prevent bass frying it,
if the supertweeter is fed from the tweeter terminals its not so critical.


/sreten.

[Mark Techer]

Try this -

Rp = 10^A/20 x Rt/(1-10^A/20)

Rs = Rt-(1/Rp+1/Rt)^-1

Where

Rp is the resister in parallel
Rs is hhe resister in series

Rt is the rated tweeter impredance in ohms
A is the amount of attenuation needed in negative dB

Hope this helps...

Mark