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IMPORTANT - Compensation component values [message #33815] Fri, 07 September 2001 02:49 Go to next message
Wayne Parham is currently offline  Wayne Parham
Messages: 18670
Registered: January 2001
Illuminati (33rd Degree)
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
====================================



Re: IMPORTANT - Compensation component values [message #33816 is a reply to message #33815] Fri, 07 September 2001 04:19 Go to previous messageGo to next message
Rich B is currently offline  Rich B
Messages: 4
Registered: May 2009
Esquire
The table is a great idea!

Thanks

Rich

Re: IMPORTANT - Compensation component values [message #33817 is a reply to message #33816] Fri, 07 September 2001 06:19 Go to previous messageGo to next message
Mike Borzcik is currently offline  Mike Borzcik
Messages: 14
Registered: May 2009
Chancellor
I built some speakers and find them to have just a hair too much treble, so I suppose this would help that, right?

Thanks,
Mike Borzcik

Re: IMPORTANT - Compensation component values [message #33818 is a reply to message #33817] Fri, 07 September 2001 15:51 Go to previous messageGo to next message
Wayne Parham is currently offline  Wayne Parham
Messages: 18670
Registered: January 2001
Illuminati (33rd Degree)
If your tweeter circuit is like the Pi crossover, and you're using a compression driver with CD horn, then this is the approach you'll want to take. It will make your speakers very smooth, not lacking in treble but not too bright either. You just have to match the efficiency of the woofer with the tweeter output, using the compensation values in the chart.

However, if your tweeter is not a compression driver, or if it is but is mounted on a horn that has collapsing directivity, then this crossover arrangement may not be right for you. It's perfect for Pi's and speakers like them, but no single crossover is right for all loudspeaker configurations.

Compensation components [message #33821 is a reply to message #33818] Fri, 07 September 2001 17:27 Go to previous messageGo to next message
Art J. is currently offline  Art J.
Messages: 16
Registered: May 2009
Chancellor
Hi Wayne, Ive been looking over a Klipsh Cornwall
crossover schematic and they use a transformer
for compensation. Is their any advantage to that over
resistors and L pad ? Thanks Art.
Re: IMPORTANT - Compensation component values [message #33822 is a reply to message #33815] Fri, 07 September 2001 19:10 Go to previous messageGo to next message
James W. Johnson is currently offline  James W. Johnson
Messages: 199
Registered: May 2009
Master
Excellent... that's just what I was looking for.

Out of curiosity, is there anything that uses more than 10-12dB attenuation?

Re: IMPORTANT - Compensation component values [message #33823 is a reply to message #33822] Fri, 07 September 2001 19:55 Go to previous messageGo to next message
Wayne Parham is currently offline  Wayne Parham
Messages: 18670
Registered: January 2001
Illuminati (33rd Degree)
No, and I wouldn't recommend it if there were. The best match is a high efficiency woofer that's only about 10dB lower than the tweeter, just enough for passive EQ of the power response using the R1/R2/C1 network. A woofer that is less efficient than that - needing more than 12-14dB attenuation - is probably not a good match for this kind of system. I've calculated values well above and below what I'd actually recommend using.
Re: Compensation components [message #33824 is a reply to message #33821] Fri, 07 September 2001 20:44 Go to previous messageGo to next message
Wayne Parham is currently offline  Wayne Parham
Messages: 18670
Registered: January 2001
Illuminati (33rd Degree)
There may be an advantage for their application, but for what we're doing, the RRC approach works best. The initial load resistor R2 provides a specific amount of damping for the splitter filter to provide an initial shelf of flat response, followed by 6dB/octave rising response above 4kHz via R1/C1 to compensate for the falling power response of the driver. A transformer would not do this.

One benefit from using step-down transformers is they transform the energy rather than dissipating it, so they don't get as hot when current is high. On the other hand, I don't expect the Klipsch transformers are made to take a whole lot of power, so this might be a mute point. However, another aspect of this is the impedance transformation which effectively increases tweeter damping when a step-down transformer is used to lower the drive voltage to a tweeter. The output coil from the step-down transformer has lower impedance and is therefore a better current sink, providing better damping. Here again though, I'm not sure this is very relevant in practice because tweeters do not require a lot of electrical damping, particularly compression horns which are extremely well damped acoustically.

Re: IMPORTANT - Compensation component values [message #33825 is a reply to message #33816] Fri, 07 September 2001 21:11 Go to previous messageGo to next message
Wayne Parham is currently offline  Wayne Parham
Messages: 18670
Registered: January 2001
Illuminati (33rd Degree)
Thanks! I hope it helps. I'm only sorry that I didn't think to post it sooner. Everyone doing a custom job asks what values I'd suggest they use, so here it is.

Note that if you're building from the plans, you won't need this chart. Use the values specified in the plans. The chart is for people that are doing their own thing, and gives them a place to start.

Re: Compensation components [message #33827 is a reply to message #33824] Sat, 08 September 2001 04:11 Go to previous messageGo to previous message
Art J. is currently offline  Art J.
Messages: 16
Registered: May 2009
Chancellor
Thanks, To fully cover the subject;
What do you think of variable L Pads ?

They are my choice because you can further compensate
for room conditions and peircing headaches.

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