Cornscala Crossover Options?

[Tag 1.7]

Hi There,

I'm planning on building myself a pair of Cornscala's. I'll be using drivers from Bob Crites and a pair of Trachorns from ALK. For the crossovers, I'm trying to decide between Bob's Cornscala crossover or a set of ALK's AP12-500 & ES5800 networks. Can anyone offer an opinion between these two choices? I know that the ALK's are three times the price so they should be better. Any opinions are greatly appreciated.

Thanks.

[CIGARBUM]

Dean did my crossovers for my Cornscalas, in one word---perfect

CB

[Deang]

A different animal though since you're using the driver from Great Plains (Altec 902 clone) and the Beyma tweeter.

I will say that I think the midrange will be cleaner, and the power response smoother -- if you use a higher crossover point. Also, because of the higher volume levels most are listening at, I think a 3rd order butterworth filter is preferred. This also reduces comb filtering between the midrange and tweeter which improves imaging. As for the midhorn, my opinion is simply that to obtain lower distortion, the crossover point should be at least a half octave above cutoff. For example, crossing a horn with a 400Hz cutoff at 400Hz is probably not the best way to go.

[kg4guy]

Dean after putting in the drivers ohms and the cut off frequencies and octaves in a crossover calculator program and the schematic is generated if you are using a autoformer to cut the cap values where do you connect the driver wires from the terminal strip to the caps and inductors to the autoformer?

[Guest David H]

Dean after putting in the drivers ohms and the cut off frequencies and octaves in a crossover calculator program and the schematic is generated if you are using a autoformer to cut the cap values where do you connect the driver wires from the terminal strip to the caps and inductors to the autoformer?

You need to figure out what taps you are going to use before inputing to the calculator.

The autoformer is an impedence doubler, for instance if you have a 16 ohm driver connected to tap 4 you calculate for (32) ohms, if its connected to tap 3 (64 ohms) etc. I believe tap 3 is used for most Cornwall / Cornscala.

Corrected, thanks Dean.

[Deang]

Dean after putting in the drivers ohms and the cut off frequencies and octaves in a crossover calculator program and the schematic is generated if you are using a autoformer to cut the cap values where do you connect the driver wires from the terminal strip to the caps and inductors to the autoformer?

I've seen pictures of networks you've built, so I know you know how to build them. So, is this a quiz?

[kg4guy]

Yes and you passed.[]

[Deang]

The autoformer is an impedence doubler, for instance if you have a 16 ohm driver connected to tap 5 you calculate for (32) ohms, if its connected to tap 4 (64 ohms) etc. I believe tap 4 is used for most Cornwall / Cornscala.

Tap 5 is your input tap. What changes the impedance are your output taps -- which reflect the impedance back through tap 5. With the Cornwall/CornScala, the squawker is off of tap 3, and the tweeter is off of tap 4. It's a "16 ohm driver", but the actual impedance is 15 ohms.

Tap 4 = 2 x the impedance

Tap 3 = 4 x the impedance

Tap 2 = 8 x the impedance

Tap 1 = 16 x the impedance

So, with the squawker off of tap 3, you calculate based on 60 ohms. The actual value of the capacitor will be determined by the combination of the reflected impedance and the crossover point you choose.

[jwc]

I went through several networks for the cornscala. My favorite was the ESN700 with the ESN5800. I could really crank the volume and get smacked down with punch w/o killing my ears. Flexible enough to use with different midranges and tweeters.

jc

[BEC]

In case anyone wants to work with values between 3,6,9 and 12 db like the 3636 autotransformer can do, I decided to work out the impedance multipliers. My brain still hurts from figuring these, so might as well share them.

Bob Crites

3636ATZ.pdf

[BEC]

Also, here is measured impedance vs frequency for the K-55V and K-55M on a K-400 horn.

Bob Crites

k-55mimp.pdf

[Deang]

I assume those numbers are out of network. When you add the network, all that changes (because of the reactance caused by the components).

For example, your chart shows 13.7 ohms at 400Hz for the K-55-V, which means we'd need a 14uF cap instead of a 13uF for a 400Hz crossover point.

[BEC]

If you mean how the K-55s were tested, yes, they were on a horn on the bench. Notice that they K-55M and K-55V are a bit difference on impedance. 1/2 ohm different at 400 hz and 1 ohm different at 600 hz. Also you can see the resonate frequency of the K-55M is 296 hz and for the K-55V it is 286 hz.

Bob

[Deang]

Notice that they K-55M and K-55V are a bit difference on impedance.

Yeah, kind of irritating. I suggest we ignore the numbers to maintain peace of mind.

[Guest David H]

Tap 5 is your input tap. What changes the impedance are your output taps -- which reflect the impedance back through tap 5. With the Cornwall/CornScala, the squawker is off of tap 3, and the tweeter is off of tap 4. It's a "16 ohm driver", but the actual impedance is 15 ohms.

I knew as soon as soon as I wrote that I was going to get corrected. I was going from memory. The actual impedence of a K-55v is 15 ohms, I understand this, however I was using a driver impedence as a sample, I did not assume the driver he was using a K-55v.