Using only the mid / high portion of the A/4500 crossover

[jjbraga]

Hi, I have A/4500 crossovers in my LaScala (with the CT125 tweeters).  I am going to bi-amp the LaScala, using an active crossover feeding two amps.  One amp will feed only the woofer (which would mean disconnecting the woofer from the crossover), the other I want to keep hooked to the A/4500 and use it to do the splitting between the squawker and tweeter.

That would leave nothing connected to the woofer output on the crossover.  Would that hurt the crossover at all, or affect the operation of the mid / high section?

If so, would putting a 8 ohm (non inductive of course) resistor across the woofer output terminals on the A/4500 "correct" things?

Thanks!

Edited November 6, 2021 by jjbraga
Had tweeter model wrong

[mboxler]

On 11/6/2021 at 2:33 PM, jjbraga said:

Hi, I have A/4500 crossovers in my LaScala (with the CT125 tweeters).  I am going to bi-amp the LaScala, using an active crossover feeding two amps.  One amp will feed only the woofer (which would mean disconnecting the woofer from the crossover), the other I want to keep hooked to the A/4500 and use it to do the splitting between the squawker and tweeter.

That would leave nothing connected to the woofer output on the crossover.  Would that hurt the crossover at all, or affect the operation of the mid / high section?

If so, would putting a 8 ohm (non inductive of course) resistor across the woofer output terminals on the A/4500 "correct" things?

Thanks!

 

Will your active crossover be sending the low-pass signal to the woofer amp and the high-pass signal to the A/4500 amp?  Or will you be sending the 

full signal to the A/4500 amp?  

 

Mike

[OO1]

On 11/6/2021 at 4:33 PM, jjbraga said:

I want to keep hooked to the A/4500 and use it to do the splitting between the squawker and tweeter.

 

not sure why you want to keep the A/4500 , when you have an Active crossover that can do away with the A/4500 , either you run full passive or full active , and active is better than passive 

[Marvel]

3 hours ago, RandyH001 said:

not sure why you want to keep the A/4500 , when you have an Active crossover that can do away with the A/4500 , either you run full passive or full active , and active is better than passive 

If you only have 4 channels of amplification and you still need the tweeter, it makes sense. The LS  midrange won't exactly work in a two way.

[KT88]

It is often handled in such a way that mid-range channel to high tone channel remains passive so that it does not become too costly. Even here at Klipsch in the cinema department, for example, if the K402 runs in systems as midrange only, the tweeter is switched or can be switched to it so far I know in passive mode regardless of possible disadvantages or advantages.

 

To the question of the topic opener, do you use just an active xover where you can set the points and probably the kind of slope or do you use a full working dsp?  

 

If you make use of an dsp then skip the coil is series in the bass section and set an imitating filter. You could even go further if you want to correct some areas in the bass response, but I would start with the same properties the coil would give in terms of slope etc. Funnily enough I would compare the sound with the passive coil in place with the active solution when listening to the total speaker system finally. Be fair enough and chose what you like more, not what is more fancy.

 

To the mid/high section. If the woofer is out of the game by now why imitate it by using a 8 ohm resistor in shunt? May be I do not understand this point in a way I should and others may be of better help. May be you are thinking you want to keep the mod/treble section of the xover free of unwanted oscillations or something like that?

 

When using a dsp  mid/high section can be delayed from now on. You can also make use of the dsp in the way an overall e.q. would do it if you like (stuff you may know anyway).

 

One point where I cannot give a recommendation is the following. On one hand you will protect the mid/treble section-amp, so you would cut out the bass energy, very important should it be a tube amp. But I have no idea how much lower freq. you must allow to send to the mid/treble amp so that the result sounds good. For example if you divide passive at 500 hz with a lets say 12 or 18 dB slope of a given filter form…how much bass frequency must be send to this passive mid/treble xover so that the lower but necessary to be adressed frequencies are not cut out in a double way if that makes sense. 

Have we to send at least one octave lower without diminuation in case of a 12 dB slope or minimum 1.5 octaves? Others will know better.

And below this point of slope effects, would it be of benefit to cut even lower freq. by using a much sharper slope to keep the (tube) amp protection?

[mboxler]

If using active filter for high pass...

 

It would be best to bypass the 13uf capacitor.  Disconnect the 13uf capacitor from the crossover input, and run a wire from that same spot to tap 5 of the autoformer.  If you are not comfortable with soldering you could use an alligator clip to connect to that tap for testing.

 

Unfortunately, the 4uf capacitor is in series with the 13uf capacitor, effectively creating a 3uf capacitor to the tweeter.   Once you bypass the 13uf capacitor, the 4uf capacitor is on it's own.  The voltage across the tweeter will increase sooner than it would with the 13uf connected.