How can I emphasize the super-highs (10k+) with the cross-over ?

[Blitz]

Hi,

I am building currently a line-array using the big newform ribbons and eton chassis. The result is quite impressive, the only thing I can imagine a bit better are the super-high frequency above 12-15Khz. Here do other tweeters more pressure. So, are there ways to amplify the super-high-frequency through the cross-over ? I heard that it would be possible with an active cross-over, but is this visible as well with a passive one ? Nevertheless I have no documentation at hand for a active solution as well, so any hintis highly welcome.

Best Regards

 

[Ap]

A parallel cap. & res. in series with the tweeter will do it.
The value of the cap. determines the freq. & the res. determnies boost.

 

[Centauri]

A parallel cap. & res. in series with the tweeter will do it.

Actually this gives less attenuation at higher frequencies - the resistor drops the level to the tweeters. Also be aware that additional resistance in series with the tweeter will change the impedance seen by the crossover and therefore change its operation.

If your crossover already has an attenuation network (resistors) to feed the tweeters, then a parallel cap across the series resistor will work - you will have to experiment with value (start off with around 0.5uF).

Cheers

 

[Blitz]

Well, I need every bit of effieciency already....

...as the woofer have in total something around 98 db efficiecy and the newform has only 91 db, I have currently the resistor network on the woofers, not on the tweeter. How effieciency do I loose typically with such a setup ?

Best Regards

 

[Centauri]

You would probably have to lose well over 6dB of overall level for this simple circuit to work at all, which in your case would not be an option.

Probably the next best way of acheiving the desired result is to modify the response of the power amp using resistor/capacitor network on the amp's feedback network - would require some knowlege of the amp and procedures though....

Cheers

 

[Blitz]

Well, but how would an active cross-over do it ?

Yes, that's an idea...I use though tube equipment without any feedback...so in my case as well no option.

If I have not taken it wrong, there are circuits which are used in active fcross-avers to achieve that effect. Has anyone experiences with this ? Wouldn't it be some king of treble-cicuit like in non-audiophile preamps ?

Best Regards

 

[Centauri]

Yes, many active crossovers have what they call "CD horn equalisation" which gives a 6dB/octave boost above a certain frequency. The normal teble tone circuit usually gives much more boost than this, which is probably not necessary in your case. A small capacitor in parallel with a large resistor inserted in series somewhere in your tube circuit would give the required 6dB/octave, however the values and location of such a mod would depend a lot on your amp circuitry and gain available.

Cheers

 

[kelticwizard]

Well, this is rather unorthodox, perhaps just plain silly, but here goes. Have you considered adding a high efficiency dome tweeter and crossing it over at 12K? The Newform would play up throughout the top range, only the dome would start also adding output above 10K Hz or so.

For a spacious effect, you can mount the dome on the back, and the speaker can be bipole from 10k on up.

It's a suggestion offered as experimentation more than a definitive answer, but it sure wouldn't cost much to try. Granted, you paid good money for the Newform for a reason, but this dome would be only active over a fraction of an octave.

 

[Blitz]

Thanks for the hint on modifying the amp.. need to understand this better...


Regarding the Super-tweeter: This was the first thing I thought about, but I want to have a real line source and not a mixture between point-source and line-source as this will certainly mess up the concept. If you are in the theory of line sources, you know that the tweeters have to be very tightly to each other in order not to have comb-filter-effects. The varies with frequency, so that especially in the super-highs you can't get the tweeters tights enough together. Therefore the ribbon.

 

[Ap]

Have you seen VMPS new RMX design?
They use mutilpe line source planars with a single tweeter - seems to have gotten positive reviews.