AL-3 Question(s)

[geoff.]

Question 1:

 

Is 13uF the correct value for the T4A with 4db of attenuation? From another post (by DJK) the correct value was calculated at 10.36 uF. So would a 10 be more appropriate than a 13?

 

Question 2:

Why is the tweeter coil value (125uh) between the same two 2uF capacitors in the AL-3 half of the value of the coil in the AA crossover (245mH)? If I run the AL-3 without the elliptical filter would their be a more appropriate coil value? 

 

 

The reason I ask is I recently built a pair of AL-3s, and a pair of AAs, with some cheap ERSE polyester caps I’ve had sitting on a shelf since before everything doubled in price and I was surprised to find I preferred the AAs over the AL-3s, apples to apples. I was not expecting that.
 

My first experience with La Scalas was with a pair having the AL-3s and what’s left of my memory recalls them being all that and a bag of chips. But this time around my brass ears found the AL-3s a little reserved. Like there was a hole in lower midrange/upper bass. 

 

I should mention these crossovers are in (on top of for now) LSI Splits with K-43 woofers, K-55M squawkers, and a variety of tweeters floating on top. I removed the grab handles and stuck a barrier strip on top of the opening for fast changes. Internal driver wires to the bottom and crossover wires to the top. 

 

 

 

 

 

 

 

[mboxler]

11 hours ago, geoff. said:

Question 1:

 

Is 13uF the correct value for the T4A with 4db of attenuation? From another post (by DJK) the correct value was calculated at 10.36 uF. So would a 10 be more appropriate than a 13?

 

Without a link to DJK's post, I can only make an uneducated guess as to how the 10.36uf value was reached.

 

If you assume that Tap 4 on the T2A is -3db, then the reflected impedance would be 2 times the impedance of the K55.  

Tap 3 on the T4A is -4db, therefore the reflected impedance would be 2.51 times the impedance of the K55.  

 

2 / 2.51 = .797.  .797 * 13 = 10.36.

 

In reality, tap 4 on the T4A is -3.35db, and the reflected impedance is 2.16 times the impedance of the K55

 

2.16/2.51 = .86.  .86 * 13 = 11.19.

 

In reality, the AL3 and AA filters are completely different, so I'd leave the 13uf as is.

 

 

11 hours ago, geoff. said:

 

Question 2:

Why is the tweeter coil value (125uh) between the same two 2uF capacitors in the AL-3 half of the value of the coil in the AA crossover (245mH)? If I run the AL-3 without the elliptical filter would their be a more appropriate coil value? 

 

 

The reason I ask is I recently built a pair of AL-3s, and a pair of AAs, with some cheap ERSE polyester caps I’ve had sitting on a shelf since before everything doubled in price and I was surprised to find I preferred the AAs over the AL-3s, apples to apples. I was not expecting that.
 

My first experience with La Scalas was with a pair having the AL-3s and what’s left of my memory recalls them being all that and a bag of chips. But this time around my brass ears found the AL-3s a little reserved. Like there was a hole in lower midrange/upper bass. 

 

I should mention these crossovers are in (on top of for now) LSI Splits with K-43 woofers, K-55M squawkers, and a variety of tweeters floating on top. I removed the grab handles and stuck a barrier strip on top of the opening for fast changes. Internal driver wires to the bottom and crossover wires to the top. 

 

 

 

 

 

 

 

 

The 125uh value is needed to compliment the deep notch in the elliptical filter.  If you remove the deep notch and leave the 125uh inductor as is, the transfer function across the tweeter will be a little shallower and peak later than with the 245uh of the AA.   

 

Mike

[Deang]

 

@geoff. Just curious if you used a T4A and other Klipsch parts, or after market?

 

AL-3. Steeper slopes. Turn it up.

[geoff.]

Gentlemen, thanks for the replies.

 

I'm using the real deal T4A. I do remember some posts on here stating the aftermarket autoformers have slightly different values.

 

I guess I could always listen louder, lol

 

 

 

 

[mboxler]

I am curious how others define attenuation.  Yes, the voltage on Tap 4 of a T2A is 3.35db lower than the voltage on Tap 5.  And the voltage on Tap 3 of a T4A is 4db lower than the voltage on Tap K.

 

However, unlike the AA, the tweeter circuit of the AL-3 is separated from the squawker circuit.  With the AL-3 circuit, the voltage across the squawker increases with frequency until it levels off at -4db.  This is the amplifier voltage minus 4db.  This is because the load on the 13uf capacitor is fairly constant from 300hz on up.

 

With the AA, the parallel tweeter circuit affects the load on the 13uf capacitor.  Like the AL-3, the load on the 13uf capacitor is fairly constant UNTIL the impedance of the tweeter circuit drops enough to affect the parallel impedance of the squawker/tweeter circuits.  As a result, the voltage across the squawker rises to around -4.5db then levels off as the load on the 13uf capacitor steadily drops to around 8 ohms.  Again, this the amplifier voltage minus 4.5db.

 

In other words, I believe the AA attenuates the squawker more than the AL-3???  I think I've tested this before.  If not I may have to test it again 😎
 

Mike

[mboxler]

I decided just to rerun the AA test using a K55M and K77M.

 

I had forgotten that the AA tweeter circuit actually dips down to around 5 ohms at 5000hz before quickly bouncing back.  That results in the sudden voltage increase across the K55M at that frequency.

 

At the point before this increase at around 5000hz the voltage across the K55M is down around 6db.

 

Mike