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On Sat, 24 Apr 2004 17:13:36 GMT, (Quan Tran)
wrote:

As mentioned in my first message, the current tweeters are not the
original. When I replaced the old tweeter I also redesigned the high
pass filter to suit the new one.

The old high pass filter had a 4.7uF cap and a 4ohm resistor in
series.

I I designed the new HPF without any quipment but I did refer to the
xover of the NHTpro A10 because they have the same tweeters xovered
at around 2000Hz.

If I got that right you replaced a tweeter that covered 4 kHz to over
20 kHz with a different one that goes down to 2 kHz is a (slightly)
different box. Fine. The new tweeter will not have any problem with
the reduced bandwidth.

Of course you may alter the xover to make use of the extended
frequency range of the new tweeter. As I don't know your speakers
I cannot give you more specific tips.

I do listening test by comparing the sound of the speaker with my
Senheiser 414 headphone.

I'm somewhat sceptical in comparing the sound of a speaker under
construction with the sound of a headphone. I would rather modify
on speaker at a time and compare the modified one with the original,
using a mono signal of course.

With the current 5.5uF (3.3+2.2) cap, 3ohm
and 15.7 ohm Lpad, they sound quite close. I want to fine tune the
xover further. But this is difficult with our measurment equipment.

You need a PC with a soundcard, some software as sound generator and
some software to analyze the results along with a good mic and a mic
amplifier. I use a Behringer ECM-8000 mic and the Behringer Eurack
UB 802 mixer as mic amp. Sound source is some pink noise generated
on a PC and for analysis I use Adobe Audition. There are less
expensive programs than that but I need it as audio editor and
multitrack mixer as well.

As the the Lpad on the A10 has 2.7 and 10 ohm resistors, is it a good
idea to copy this Lpad and change the capacitor value to arrive at a
4000hz xover point? (assume the same efficiency).

Changing the capacitor will change the xover frequency. The
main reason for the resistors is the level match (attenuation) of the
tweeter with the midrange speaker.

The second thing I want to do is to bypass the cap with a small good
quality cap (film and foil?) because many say it improve the sound.

Bypass capacitors are needed for a large frequency range that extends
over several decades. I remember a project where I need a AC impedance
of less than 5 Ohm in the range from 10 Hz through 30 MHz. I used one
bypass cap for every other decade. The largest cap had to cover 10 Hz
to 3 kHz, the next one 3 kHz to 300 kHz etc.

What is your advice on this?

Get a (5.6 ÂµF) condensor of good quality and you're set.

Norbert

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