Upgrading drivers

[vandevoordekoen]

I have a conventional electronic cross-over. It has no CD-compensation function. But I checked some measurements of the de250 with Wayne's H290C horn, without compensation:



Will there be an audible difference with CD-compensation? The response of the driver-horn combination seems quite good to me, even without compensation!

However, I sent Wayne a mail with the question which passive adjustments are required with active X-over.

[dumptruck]

Yeah, you might want a bit of a downward tilt to the overall system response (I do with this type of speaker), but the uncompensated response is not a great starting point. I think you'd find that to avoid excessive "bright" sound, you would have to turn the HF attenuation down to the point of not really having any upper treble.

[vandevoordekoen]

You mean, attenuate the overal response of the de250? Or just the highest frequencies?

[dumptruck]

I meant overall - the main HF level knob on the crossover. The shelf-like 2-5kHz response caused by the waveguide will sound bright, unless you turn it down enough for that part to match the woofer level, and if you do that the 10-20kHz octave will be quite low.

[vandevoordekoen]

Thank you for the explanation, Dumptruck. I read through the forum of Waynes website to understand completely what CD compensation is.

Here I found a good explanation (read Waynes answer):
AudioRoundTable.com: Pi Speakers => Erse caps, attenuation circuits.

Wayne uses a R1/R2/C1 configuration to adjust the frequency response of the HF driver. The specific values he uses for the 4pi speakers:
Pi Speaker Forum - Clarification of attenuation values - Wayne Parham, August 01, 2002 at 12:48:20

This is the schematic of the 4pi passive cross-over design:


If I'm right, I just have to use use the R1 and R2 for the b&c de250 (C1 can be omitted).

Till here my 'knowledge'. I'm not an engineer, so here is my question to the members of the forum: Can I use the same values for my active setup (same drivers, same h290C horn, same enclosure) for CD compensation. I'd like to obtain a similar top octave compensation response curve as obtained with the passive crossover.

Thank you very much!

[Inductor]

Originally Posted by vandevoordekoen

If I'm right, I just have to use use the R1 and R2 for the b&c de250 (C1 can be omitted).

Till here my 'knowledge'. I'm not an engineer, so here is my question to the members of the forum: Can I use the same values for my active setup (same drivers, same h290C horn, same enclosure) for CD compensation. I'd like to obtain a similar top octave compensation response curve as obtained with the passive crossover.

Thank you very much!

No.
R1/C1 is the compensation.

[Inductor]

C2/L1/C3 it's a 3. order.
R2 is part of the l-pad.
hope this is clear like water...

[vandevoordekoen]

I'm sorry, I don't understand at all
I thought that CD compensation is done by 2 resistors and a capacitator.
The values of the components vary in accordance with the tweeter compensation you want to do. (correct me if I'm wrong)

Here I copied a chart of this configuration, found on Waynes forum:

Here's a chart that shows the appropriate values of R1, R2 and C1 compensation components for the Pi crossover. The way it works is the level of attenuation shown in the "dB" column is what the circuit presents to the tweeter below mass rolloff. Above that, attenuation is removed at 6dB/octave. So if you use R1/R2/C1 values that give 10dB attenuation, the tweeter will be -10dB from crossover up to 6kHz, at 12kHz it will be -4dB and by 20kHz there is no attenuation at all.

dB R1 R2 C1
====================================
6dB 12 ohm 30 ohm 0.47uF
8dB 12 ohm 20 ohm 0.47uF
10dB 16 ohm 16 ohm 0.47uF
12dB 25 ohm 16 ohm 0.47uF
14dB 30 ohm 14 ohm 0.33uF
16dB 40 ohm 12 ohm 0.33uF
18dB 50 ohm 12 ohm 0.22uF
20dB 75 ohm 12 ohm 0.22uF
====================================

For 12dB attenuation, I'd need the following values:
R1 = 25 ohm
R2 = 16 ohm
C1 = 0.47uF

But looking at the cross-over for the 4pi speaker, I saw there is a little adjustment in the tweeter compensation configuration for de de250 driver: point 8: C1 is 0,47µF for 2426H tweeter, omitted for de250 and psd2002.



I concluded (please correct me if I'm wrong!) that just R1 and R2 compensate the tweeter response.


However, Wayne mailed me that I wouldn't need a 12dB equalization.
Looking at the following response curve of the de250 on a h290c horn, I think an attenuation of 3dB (or 6dB) before mass rolloff would be ok (active crossover: 1,6khz, so don't look at the lower frequencies)



I hope that you can help me with this
thanks!

[vandevoordekoen]

I think I'm wrong here.
Wayne mailed me about this, he's extremely helpfull.
(and I understand now what you want to say Inductor )
But I'll have to read a lot to find out which components and which values I have to use to compensate the mass rolloff of the tweeter.
If somebody has done this before, don't hesitate to inform me

[Inductor]

Originally Posted by vandevoordekoen

I think I'm wrong here.
Wayne mailed me about this, he's extremely helpfull.
(and I understand now what you want to say Inductor )

Not a problem. He's very professional.

1. Invert polarity for JBL's woofers as Black>+2/Red>-2
2. n.a.
3. DE250 tweeter Black>+1/Red>-1
4. n.a.
5. R2 = 15R/10Wn.i.
6. DE250 tweeter R1a/R1c = 20R/n.i., R1b/R1d = 30R/n.i.
7. C1 is omitted for DE250 tweeter (no compensation)
8.
9.
10.

I translated this (not complicated) for you. Hope this helps. You might not need it by now...

Originally Posted by vandevoordekoen

For 12dB attenuation, I'd need the following values:
R1 = 25 ohm
R2 = 16 ohm
C1 = 0.47uF

But looking at the cross-over for the 4pi speaker, I saw there is a little adjustment in the tweeter compensation configuration for de de250 driver: point 8: C1 is 0,47µF for 2426H tweeter, omitted for de250 and psd2002.

I concluded (please correct me if I'm wrong!) that just R1 and R2 compensate the tweeter response.

"They attenuate the tweeter response 12dB's."
(ps: we are already repeating ourselves, have a nice time. )