KEF Cresta 10 Crossover

[ccschua]

Hi,

I have below the above cross over which is a 3rd order.
The original cap was electrolytic.I have replace all the cap with Jantzen Crosscap and resistors to Kiwame. What I found is better clarity but the bass is lacking.


1. Should I follow the capacacitor printed in the label or based on measurement. I actually measure 11.9uF on the electrolytic on one of them and the other 11.5uF? Which one to follow ??

2. I change R2 from 1R5 to 1R8, and I get better bass response. However I found the sound slightly compress, not so open. Why ?

3. What software do I use to simulate if the crossover is still at 3kHz.

[PeteMcK]

Re: the caps, I'd go with what's on the label; electros change value over time.

I'd leave R2 as it is (I think it's there to change the Q of the driver) - increasing it will waste power. I'd increase R1 instead to get the balance you want.

If you have measured the actual impedance of the drivers at 3 KHz, you can plug the numbers into the calculator here:
http://ccs.exl.info/calc_cr.html#second

[ccschua]

Below is the spec of the speaker : -


Design 2 way bookshelf
Drive units HF: 25 mm (1”) silk dome tweeter
LF: 130 mm (5.25”) pp coated cone
Frequency response at ±3 dB 52 Hz - 20 kHz
Crossover frequency 3 kHz
Amplifier requirements 10 - 100W
Sensitivity (2.83V/1m) 90 dB
[bold]Impedance 8 Ohms [/bold]
Maximum output 108 dB

Can I assume 8 ohms is the impedance at 3khz. or do I ulsolder the wire and measure the resistance.


I plug in the figure and it seems a little different. Is it due to the speaker driver acutal response.

[PeteMcK]

Re: "Can I assume 8 ohms is the impedance at 3khz. or do I ulsolder the wire and measure the resistance."

No and No.
What you need to measure is the ac impedance at 3KHz.
This can be done with a signal generator and an AC voltmeter, but the easy way nowadays is to make a simple jig and download ARTA software, and use you computer to do the measurement.

ARTA http://www.fesb.hr/~mateljan/arta/download.htm
ARTA Jig - http://zobsky.blogspot.com/2008/01/s...t-jig-for.html

[Inductor]

Originally posted by PeteMcK

I'd leave R2 as it is (I think it's there to change the Q of the driver) - increasing it will waste power. I'd increase R1 instead to get the balance you want.

I would do the opposite and test. Maybe also testing it with less R2 (or without it, if not changing a lot of things like xover freq) and adjusting R1. If you have to leave R2 as it is (R2=1.5) make sure you use adequate power (W) or 4 resistors in series/parallel (for the same/similar speaker power).

[wxa666]

Originally posted by ccschua
Hi,

I have below the above cross over which is a 3rd order.
The original cap was electrolytic.I have replace all the cap with Jantzen Crosscap and resistors to Kiwame. What I found is better clarity but the bass is lacking.


1. Should I follow the capacacitor printed in the label or based on measurement. I actually measure 11.9uF on the electrolytic on one of them and the other 11.5uF? Which one to follow ??

2. I change R2 from 1R5 to 1R8, and I get better bass response. However I found the sound slightly compress, not so open. Why ?

3. What software do I use to simulate if the crossover is still at 3kHz.

1) The difference from 11.5 to 11.9 and finally to -12- shouldn't affect Your pleasure.

2) Very sensible to really hear a difference. With the bigger R You attentuate the lower mids more related to bass and treble.

3) You wouldn't gain insight from that. The simulation would lack original data on speakers impedance and amplitude and phase in the peticular cabinet.

Nice speaker though. Best You leave it as it is. If You HAD to change the caps because they MEASURED bad You probably should add resistors ~ 0.5 .. 2Ohm to make more modern caps appear as electrolytics.

have fun

[ccschua]

Originally posted by Inductor


I would do the opposite and test. Maybe also testing it with less R2 (or without it, if not changing a lot of things like xover freq) and adjusting R1. If you have to leave R2 as it is (R2=1.5) make sure you use adequate power (W) or 4 resistors in series/parallel (for the same/similar speaker power).

I tested R2 using 1R3 and the bass response is reduced. I also increase R2 to 2R3 but found the bass to be boomy.

[ccschua]

1) The difference from 11.5 to 11.9 and finally to -12- shouldn't affect Your pleasure.

I mean C2 was 10uF but when I measure I got 11.5uF and 11.9uF for left/right channel.

2) Very sensible to really hear a difference. With the bigger R You attentuate the lower mids more related to bass and treble.

I felt this way too. But when I listen to PEPE Romero flamenco, the feet thumping effect is less if I reduced R2.

[ccschua]

The original R1 and R2 were using ceramic resistor. First I change the high pass R1 from original Ceramic resistor to Kiwame 2R7. Not much differerence here, although I was told it is supposed to be smoother.

Then I changed driver resistor R2 to Mills MRA 1R5 (for trial) but found the bass lacking.

Is Mills resistor fit for crossover ? what do you recommend the resistor type.

Next I will do is replace R1 with say 3R to see if the bass is more prominent while Maintain 1R5.

[Inductor]

Originally posted by ccschua

Is Mills resistor fit for crossover ? what do you recommend the resistor type.

What's the power for this resistor (R2-5/10W?)
Do you know if the original ceramic resistor (R2) had any inductance that this one you are using lacks. (Now I am more confused. Maybe not because there's a lot of things going on now.) You are saying that what ever you do to R2 you always end losing bass.