Kappa 8 bi-amping/amp suggestions

[RogerM]

So I've finally gotten around to entertaining the active crossover again. I have 2 Adcom 565's mono blocks and am working on getting a Adcom 555 for the mids and highs.

I just wanted to make sure that the active crossover was still a recommended solution for these speakers. From what I was reading it seems as much.

What crossovers do you guys like?

Thanks a bunch and talk about reviving an old thread

 

[whoaru99]

So I've finally gotten around to entertaining the active crossover again. I have 2 Adcom 565's mono blocks and am working on getting a Adcom 555 for the mids and highs.

I just wanted to make sure that the active crossover was still a recommended solution for these speakers. From what I was reading it seems as much.

What crossovers do you guys like?

Thanks a bunch and talk about reviving an old thread

I'm not sure if it's been mentioned, but to "properly" use either line level passive filters, or an active crossover, the crossovers in your speakers should be bypassed. Given the quality of the Infinities, I'm of the opinion that you're unlikely to do better than what Infinity designed. No doubt you'll be able to change the sound, but whether or not it'll be better is the big question.

There are things in complex crossovers that can't simply be recreated by using generic off-the-shelf active boxes.

For an amp, I might recommend something like a Crown K1 or K2 for your low end. Pick what you prefer for the mid/high as long as it's got enough power to keep up with the Crown on the lows. The K2 seem to be going for ~$600, give or take, these days.

 

[Bunny]

An active X-over is better in every perspective. But it is possible that you speaker is build around the passive X-over and that you'll need a LOT of finetuning to get a good sound again. I would risk it but hey, who am I...

 

[phaedrus]

I'm not sure if it's been mentioned, but to "properly" use either line level passive filters, or an active crossover, the crossovers in your speakers should be bypassed. Given the quality of the Infinities, I'm of the opinion that you're unlikely to do better than what Infinity designed. No doubt you'll be able to change the sound, but whether or not it'll be better is the big question.

The Kappa 8's were designed with bi-amping in mind. There are two inputs - one for the woofers and one for the high/mids - which are normally strapped together.

If he uses an active crossover, all he'll need to do is unstrap the inputs, and set the crossover to send the bass to the bass inputs and the remainder to the mid/high inputs. He shouldn't need to mess with the passive crossovers at all.

David

 

[RogerM]

I already have Adcom 565's which run the bottom end just fine. I amo not going to (nor plan to) bypass the crossovers in the speakers. What is the disadvantage to leaving the built in crossovers inline?

My main purpose in thinking about the crossover was eliminating the lows frequencies from the amplifier connected to the upper end of the speakers and doing the same for the lower end of the speakers. I guess the better question is will this be an audible difference. I'm imagining this will result in the amps not working as hard because they don't have to run full spectrum which in turn should (in theory) result in better sound.

Thanks

 

[whoaru99]

The Kappa 8's were designed with bi-amping in mind. There are two inputs - one for the woofers and one for the high/mids - which are normally strapped together.

If he uses an active crossover, all he'll need to do is unstrap the inputs, and set the crossover to send the bass to the bass inputs and the remainder to the mid/high inputs. He shouldn't need to mess with the passive crossovers at all.

David

I know how the binding posts work. I have a few pair of speakers with that capability.

My point is that it essentially doubles up on the crossovers. If you set the active crossover near the same frequencies as the speaker's crossover, the slope of the crossover has been altered significantly - probably developing a "hole" in the response pattern.

If the active crossover is set with the frequencies far enough above and below the speaker's crossover point, you're probably not unloading the amps enough to make that big of a difference, or your making an even bigger hole in the response, depending on which way you go with the settings.

Of course, there is some dependency on the specifics, but you get the drift.

 

[RogerM]

What would a "hole" in the response pattern sound like? I mean what are the end results of said hole?

 

[phaedrus]

My point is that it essentially doubles up on the crossovers. If you set the active crossover near the same frequencies as the speaker's crossover, the slope of the crossover has been altered significantly - probably developing a "hole" in the response pattern.

If the active crossover is set with the frequencies far enough above and below the speaker's crossover point, you're probably not unloading the amps enough to make that big of a difference, or your making an even bigger hole in the response, depending on which way you go with the settings.

Of course, there is some dependency on the specifics, but you get the drift.

Well, I guess I don't get the drift.

The Kappa 8 crosses over the woofer at either 80 or 90 Hz. There is a single passive crossover network for the woofers, and a separate one for all the mid/high drivers. The two networks are connected by the bridging straps. The passive network for the woofer rolls off everything above 90Hz at some predetermined rate, and the mid/high network does the reverse.

If he sets his active crossover to pass 90 Hz and below to the woofer, with say a 6dB/octave rolloff above 90 Hz, and sets the high pass the same way (pass everything above 90Hz with a 6dB/octave rolloff below), I don't see where I'm getting a "hole".

I don't know what kind of crossover slope Infinity used in the Kappas, but guaranteed it's at least 6 dB/octave, and probably more. So, the woofer is still getting the relevant portion of the signal, as are the mid/highs.

If Infinity used a 6 db/octave rolloff, there won't be any change to the crossover slope. If Infinity used a steeper rolloff curve (12 or 24 dB/octave), the passive networks will take over and filter out the unnecessary frequencies. Either way, the appropriate drivers will still be receiving the proper frequencies.

David

 

[whoaru99]

Mmmm.... I shoulda picked better words.

"...probably developing a "hole" in the frequency response."

By hole I mean a large dip in the frequency response. For an extreme example, envision a 3-way speaker, then disconnect the midrange driver. A hole/large dip in the midrange frequency response of the speaker likely now exists.

 

[whoaru99]

Well, I guess I don't get the drift.

The Kappa 8 crosses over the woofer at either 80 or 90 Hz. There is a single passive crossover network for the woofers, and a separate one for all the mid/high drivers. The two networks are connected by the bridging straps. The passive network for the woofer rolls off everything above 90Hz at some predetermined rate, and the mid/high network does the reverse.

If he sets his active crossover to pass 90 Hz and below to the woofer, with say a 6dB/octave rolloff above 90 Hz, and sets the high pass the same way (pass everything above 90Hz with a 6dB/octave rolloff below), I don't see where I'm getting a "hole".

I don't know what kind of crossover slope Infinity used in the Kappas, but guaranteed it's at least 6 dB/octave, and probably more. So, the woofer is still getting the relevant portion of the signal, as are the mid/highs.

If Infinity used a 6 db/octave rolloff, there won't be any change to the crossover slope. If Infinity used a steeper rolloff curve (12 or 24 dB/octave), the passive networks will take over and filter out the unnecessary frequencies. Either way, the appropriate drivers will still be receiving the proper frequencies.

David

You're right, adding the external crossover doesn't change the slope of the Infinity crossover per se, but the slopes will add together, afaik.

So, if the external is 6dB/octave and the internal is 6dB/octave, it would be a sum total of 12dB/octave.

I'll have to think about the "hole" theory a bit more. If the crossover slopes are symmetrical and one gets the center frequency of the external crossover matched to the internal crossover, then it might not be an issue - albeit steeper than the design intent.

EDIT: I have a Behringer DCX2496 on order for my "garage system" - due to arrive later this week. Since it's much too cold in the garage this time of year, I may have to do some experimenting with some other speakers along the lines of doubling up on crossovers, varying slopes, and varying center frequencies to gauge the various results.

 

[Vitopanch]

Well, I guess I don't get the drift.

The Kappa 8 crosses over the woofer at either 80 or 90 Hz. There is a single passive crossover network for the woofers, and a separate one for all the mid/high drivers. The two networks are connected by the bridging straps. The passive network for the woofer rolls off everything above 90Hz at some predetermined rate, and the mid/high network does the reverse.

If he sets his active crossover to pass 90 Hz and below to the woofer, with say a 6dB/octave rolloff above 90 Hz, and sets the high pass the same way (pass everything above 90Hz with a 6dB/octave rolloff below), I don't see where I'm getting a "hole".

I don't know what kind of crossover slope Infinity used in the Kappas, but guaranteed it's at least 6 dB/octave, and probably more. So, the woofer is still getting the relevant portion of the signal, as are the mid/highs.

If Infinity used a 6 db/octave rolloff, there won't be any change to the crossover slope. If Infinity used a steeper rolloff curve (12 or 24 dB/octave), the passive networks will take over and filter out the unnecessary frequencies. Either way, the appropriate drivers will still be receiving the proper frequencies.

David

Stated very well.

Vito

 

[rroobbcc]

You're right, adding the external crossover doesn't change the slope of the Infinity crossover per se, but the slopes will add together, afaik.

So, if the external is 6dB/octave and the internal is 6dB/octave, it would be a sum total of 12dB/octave.

I'll have to think about the "hole" theory a bit more. If the crossover slopes are symmetrical and one gets the center frequency of the external crossover matched to the internal crossover, then it might not be an issue - albeit steeper than the design intent.

EDIT: I have a Behringer DCX2496 on order for my "garage system" - due to arrive later this week. Since it's much too cold in the garage this time of year, I may have to do some experimenting with some other speakers along the lines of doubling up on crossovers, varying slopes, and varying center frequencies to gauge the various results.

whoaru99, is correct that using an external x-over will have an accumulative effect with the speakers own passive x-over and result in a dip in the frequency response. Remember that a x-over is not like a light switch, it is not on/off. The x-over "rolls off" the signal beyond its tuned frequency. What this means is that given the 90Hz x-over frequency between woofer and mid-bass of the 8 Kappas, the mid-bass is still producing some of the output below 90Hz and the woofer is still producing some of the output above 90Hz. The crossover must be carefully tuned to ensure that the frequency response of the system remains flat across the spectrum where both drivers are contributing to the audible output.

The level of the output produced beyond the crossover frequency is determined by the slope of the x-over. Assuming a slope of 12db/octave and a x-over point of 90Hz, the signal to the woofers and mid-bass would be attenuated as follows:

Woofer:
22.5 = 0db
45 = 0db
90Hz = 0db
180Hz = -12db (1/16 of original level)
360Hz = -24db (1/256 of orignal level)

Mid-bass
22.5Hz = -24db (1/256 of orignal level)
45Hz = -12db (1/16 of original level)
90Hz = 0db
180Hz = 0db
360Hz = 0db

Now it is important to keep in mind that these are the levels that are required to have a FLAT frequency response. For example, at 180hz a non-attenuated output from the mid-bass combined with an output from the woofer of 1/16 of the original level are BOTH required to have a flat overall response across this area.

So now let's add an external x-over to the system. If we set the external x-over to 90Hz with a slope of 6db/octave, a 180hz signal will already be down 6db (1/4 of original level) by the time it hits the speaker's x-over. The speakers x-over will still do its job and reduce the level it receives by 12db. So our 180Hz signal is now at -18db at the woofer, or 1/64 of the original level... a level that is TOO LOW to produce a flat response when combined with the mid-bass's output. The same effect will occur in the other direction, with the response dipped below the crossover frequency as the mid-bass is no longer contributing enough output to maintain an overall flat output.

In the case of the 8 Kappa there is no reason to us an external active crossover. In fact you are going to negatively effect the response of the speakers if you do. Generally people want to use an active crossover because they believe they are saving the amplifier from doing unnecessary work. This belief comes from a lack of understanding of the basic electronic principles at work. The mechanism that causes a signal to be attenuated at frequencies beyond the x-over point is a rise in impedance. As the frequency of the signal gets further away from the crossover point the impedance of the overall circuit (speaker driver and x-over together) limits the flow of current, which limits driver movement, and thus sound level.

Let's look at this in the context of the 8 Kappas. We will assume the impedence of the mid-bass-and-up circuit is 4ohm. If the slope of this x-over is 12db/octave, then the impedance our amplifier sees on this circuit at 45hz is 64ohm, at 22.5hz it sees 1024ohm. These high impedances limit the flow of current from the amplifier. Since the "work" of the amplifier is the delivery of current (a topic that deserves a thread all its own), the amplifier has less and less "work" to do the further the signal goes beyond the x-over frequency. The only difference between using the active and passive crossover is where the current limiting mechanism occurs, but the end result is the same - an easier job for the amplifier's output stage and power suppply.

The last thing I will say is that on the 8 or 9 Kappas you should be careful with using different amps for the woofers and mid-bass-and-up. About half of the energy in music exists in the 90-900Hz band that is covered by the Kappa's mid-bass coupler. It is logical then that HALF of your amplifier power should be made available in this range. Additionally, if you use different amps, they may have different input impedances which causes more of the signal to be sent to one amp over the other and results in an imbalanced overall response. So keep this in mind if things don't sound right.

HTH,

Rob