Progress on 620A with 604D (ping GM)

[lhgin]

Hi GM/guys,

After I've installed the 3R/2uF network in series with the N1600 crossover box, the bass improved substantially!

I've changed the 3R to 5R in parallel and I've got even more out of the speakers. Thanks GM! It really helped.

What's happening by adding in this resistor/capacitor network? Is there any calculation/method of determining what's the value needed for the capacitor and resistor?

I'm thinking of rebuilding the crossover with optimized version this cap/resistor network + T-pad attenuator instead of L-pad. The woofer would be connected directly to the amplifier.

Please advise.

Many thanks!

Rgds,
Heng Gin

[GM]

>I've changed the 3R to 5R in parallel and I've got even more out of the speakers. Thanks GM! It really helped.

====

You're welcome, but understand that you didn't gain any bass, just traded efficiency for a more correct tonal balance over a wider BW.

====

>What's happening by adding in this resistor/capacitor network?

====

The resistor acts as a voltage divider, shunting some of the amp's output away as heat so it needs to have a high enough current rating to run cool otherwise the response won't be linear over time and varying loads. The cap in parallel acts to bypass the resistor with increasing frequency so that it will get more power up where the roll off is increasing.

====

>Is there any calculation/method of determining what's the value needed for the capacitor and resistor?

====

Yes, the added resistance changes the effective Qes/Qts, so its effects can be calculated/modeled in box programs:

Qes' = Qes*(1+Rs/Rvc), where Rs is the series
resistance and Rvc is the driver's DC resistance, so:

Rs = (Qes'/Qes-1)*Rvc. Remember to include the series
resistances of your amplifier/cable/inductors in Rs,
so the actual resistor you buy may be somewhat
smaller than calculated value. Or do as I do and just
use a pot to dial in the sound, then measure it for
the fixed resistor value.

Qts' = Qes'*Qms/(Qes'+Qms)

Vas is unchanged

n0 = 9.614*10^-10*Fs^3*Vas(liters)/Qes'

SPL = 112.02+10*Log(n0)


The cap requires you to measure the impedance at whatever XO point you want the cap to 'lift' the HF response, then:

C = 1e6/(2*pi*F*Z)

====

>I'm thinking of rebuilding the crossover with optimized version this cap/resistor network + T-pad attenuator instead of L-pad. The woofer would be connected directly to the amplifier.

====

If you're going to go to all this trouble, then add time delay to the HF horn and/or experiment with a different XO point closer to the ideal, and instead of a series resistor per se, calculate the necessary baffle step requirements and wind an inductor with the desired DCR to 'kill two birds with one stone'.

GM

[lhgin]

Hi GM,

Many thanks for the reply!

Just to double confirm, the C formula is
C = 1,000,000/(2*pi*F*Z), correct?

How do I obtain the impedance at the crossover point that's needed to fit in this equation? Say if it's at 1.5kHz?

I think what I'll do is to get a pot and try it till I get the best point by experimentation.

What I've in mind is a simple Butterworth crossover. i.e. with a cap (6.63uf) connecting in series with the horn.

Something as follow:

(L/T-pad)
o--+--wwww--+--+--wwww--+----||-------o +tweeter
| | | |
+---||---+ | W
| W
| |
o--------------|--------+-------------o -ve
|
|
o--------------+----------------------o +woofer


I'm not sure of what do you mean by getting an inductor to replace the resistor. Could you kindly explain furthermore please what's necessary to be done if I chosed this path?

Many, many thanks!

Rgds,
HG

[lhgin]

Hi,

The diagram didn't turn out to be ok. I'm reposting again, pls ignore the dots.

..................(L/T-pad)
o--+--wwww--+--+--wwww--+----||-------o +tweeter
...|........|..|........|
...+---||---+..|........W
...............|........W
...............|........|
o--------------|--------+-------------o -ve
...............|
...............|
o--------------+----------------------o +woofer


Rgds,
HG

[lhgin]

Hi,

Ooo... This is tough. Repost again.


......................................(L/T-pad)
o--+--wwww--+--+--wwww--+----||-------o +tweeter
......|....................|.....|................ ....|
.....+-----||-----+.....|...................W
.................................|................ ...W
.................................|................ ....|
o------------------|------------+-------------o -ve
.................................|
.................................|
o------------------+-------------------------o +woofer


Rgds,
HG