Questions regarding electronic crossovers, bi-amping and impedance equalization

[Davey]

Maybe I missed it but, is this passive crossover you want to "ditch" an existing crossover (that was designed by someone else) and is in use on the speakers currently? And it sounds good?

If so, that might help your progress (and establish a good base line) considerably when trying to go the active direction.

Cheers,

Dave.

[Dissi]

Hi Rodeodave,

The impedance correction (zobel) of the woofer is only used by the passive low-pass filter, you do not need it in an active setup. To convert a passive design to active, you have to find filters giving exactly the same transfer function as the passive crossover does at the driver terminals. I know the review of this speaker in K+T 4-2008 and also have a simulation of it. Therefore I can retrieve the driver voltages from my speaker simulation program:

DriverVoltagesPipeSix.jpg

Unfortunately the passive filter interacts with the driver impedances and yields transfer functions far from text book. You will have to design active filters having approximately the same response. Good luck!

[Pano]

Thanks Dissi, that's pretty much what my sims show. This may have been done to correct for baffle peak.
Dave, if you have any way to measure the frequency response, it would be a great help.

[Davey]

Originally Posted by Dissi

Hi Rodeodave,

The impedance correction (zobel) of the woofer is only used by the passive low-pass filter, you do not need it in an active setup. To convert a passive design to active, you have to find filters giving exactly the same transfer function as the passive crossover does at the driver terminals. I know the review of this speaker in K+T 4-2008 and also have a simulation of it. Therefore I can retrieve the driver voltages from my speaker simulation program:

Attachment 319305

Unfortunately the passive filter interacts with the driver impedances and yields transfer functions far from text book. You will have to design active filters having approximately the same response. Good luck!

If that transfer function plot uses measured driver impedances (and it looks like they do), then the results contain the interaction with driver impedances and those would be equivalent to actual electrical measurements taken at the driver terminals. This would be the "baseline" I was referring to.

Cheers,

Dave.

[Pano]

Dave, here is what I get from the published impedance plots, which looks a lot like the graph above.

[Rodeodave]

Originally Posted by Davey

Maybe I missed it but, is this passive crossover you want to "ditch" an existing crossover (that was designed by someone else) and is in use on the speakers currently? And it sounds good?

If so, that might help your progress (and establish a good base line) considerably when trying to go the active direction.

Cheers,

Dave.

The speaker design and passive crossover were published in K+T in 2008, and it has been built by numerous people (though not by me yet), and is received quite well from what I read.
I can get the drivers for very little money, and at a first uninitiated glance the crossover network seemed to be straight forward and easy enough to replace by an active design. Little did I know...

Originally Posted by Dissi

Hi Rodeodave,

The impedance correction (zobel) of the woofer is only used by the passive low-pass filter, you do not need it in an active setup. To convert a passive design to active, you have to find filters giving exactly the same transfer function as the passive crossover does at the driver terminals. I know the review of this speaker in K+T 4-2008 and also have a simulation of it. Therefore I can retrieve the driver voltages from my speaker simulation program:

Attachment 319305

Unfortunately the passive filter interacts with the driver impedances and yields transfer functions far from text book. You will have to design active filters having approximately the same response. Good luck!

Thanks, I think I get it now. It's there to keep the woofer's rising impedance from messing with the low pass filter response, right? It's not there for the amp, it's for the LCL filter's sake.
Your whole response has been very helpful, thanks!

Originally Posted by Pano

Thanks Dissi, that's pretty much what my sims show. This may have been done to correct for baffle peak.
Dave, if you have any way to measure the frequency response, it would be a great help.

Well, I do have RTA/spectrum analyzer apps on my phone (Galaxy S), and have calibrated/zeroed them as the apps demand. They are quite sensitive, but I doubt that the microphone's response is sufficiently linear in terms of SPL. I can definitely measure something though, for instance a relative change in SPL at a certain frequncy.

Originally Posted by Pano

Dave, here is what I get from the published impedance plots, which looks a lot like the graph above.

Are you saying you plugged the driver and passive crossover data into a simulator and got that plot? And it's similar to Dissi's simulation? Well, at least that would be consistent then.


And thanks for the links, sreten, they should keep me busy for some time.


I guess I'll have to look further into filter design to emulate the odd LP behaviour. I'll get there eventually. Thanks for your input, guys!

[Pano]

Originally Posted by Rodeodave

Well, I do have RTA/spectrum analyzer apps on my phone (Galaxy S), and have calibrated/zeroed them as the apps demand.

How do you use it? Play pink noise and look at it on the app? That would be interesting. Of course, you have to build the speaker first.

Are you saying you plugged the driver and passive crossover data into a simulator and got that plot? And it's similar to Dissi's simulation?

Yes, that's right. That's the electrical response those passive components would give with those drivers. Since the drivers are pretty flat thru the crossover range, acoustic response should be close. With that box, there should be a baffle peak from about 600-1200Hz, tho not a very big bump. Don't know if that's why the weird shelf in the low pass.

You don't have to this crossover, you can do your own. We can help.

[Rodeodave]

Originally Posted by Pano

How do you use it? Play pink noise and look at it on the app? That would be interesting. Of course, you have to build the speaker first.
...

Exactly, somehow suspend the phone in mid air on some sort of stand in front of the speaker, play pink noise, observe graphs. I have these: https://play.google.com/store/apps/d...oft.net.rtapro and https://play.google.com/store/apps/d...ectrumAnalyzer. For calibration one can either play pink noise through a known-good system (yeah, not that lucky...) or have it auto zero in a very low noise environment (my parents live in a very rural area, zero measurable noise there). I did the latter and it seems fairly usable, but like I said, the mic's linearity regarding SPL response is questionable when calibrated below target SPL. Still better than nothing.

Originally Posted by Pano

...
Yes, that's right. That's the electrical response those passive components would give with those drivers. Since the drivers are pretty flat thru the crossover range, acoustic response should be close. With that box, there should be a baffle peak from about 600-1200Hz, tho not a very big bump. Don't know if that's why the weird shelf in the low pass.

You don't have to this crossover, you can do your own. We can help.

I like that attitude. Would you still recommend a 3rd order design?

[Pano]

Yeah, 3rd order electrical usually sounds good. It's a good place to go.
My guess is that your phone will be OK for most of the range around the crossover area, so you can use that to measure with.

[Rodeodave]

I tried to simulate the enclosure/woofer combination in hornresp, but of course I'm not sure if I'm doing it right since I first opened the program only like an hour ago, and I'm under the influence of eggnog. I'm using hornresp version 30.20

The driver parameters are seemingly straight forward and can be copied from the datasheet or published specs.

Ang is set to 2pi halfspace
Eg is set to 2,83V
Rg is set to 0,2Ohms

S1, area at the beginning of the TQWT, is 5,6*18,7=104,72cm^2
S2, area at the position of the driver (center), is 11,05*18,7=206,64cm^2
S3, area at the end of the TQWT, is 17,3*18,7=323,51cm^2
S4, area of the port, is 3,5^2*pi=38,48cm^2
S5, since the port is not expanding, is S4

L12, distance from TQQT's beginning to driver (center), is 86,7-18,7=68cm
L23, distance from chassis to TQWT's end (tricky because of the fold), is 11,4+86,7=98,1cm
L34, ?, is set to 0,01
L45, the port length, is 10cm

For contour I chose "Par", though I'm not exactly sure what it implies.

Vrc, Lrc, Fr, Tal, Vtc, and Atc are set to zero.

I chose "Offset driver horn", hit calculate, chose "combined response" in the tools section, and then entered a distance of -28,6cm since the port of the horn is on the backside.

Attached you'll find what the program computed. Does that make any sense? What can we learn from it?