D9 Crossover Redo...

[jbeckva]

Ah, here's another point to ponder too... Given the 3 circuits above, what are the associated phase shifts of each, and given that, can the woof/mid/tweets REALLY be configured to be in phase with each other? I'm just thinking here... I know when I pulled my tweeters, the spades were reversed.

Hmmm.... maybe a redo might give way to a redesign?

 

[Gepetto]

Putting a poly in for the woofer shunt cap. Inductor is "ok" - I would replace it, but not sure what value it is. Hmmm... maybe Joe would know... given the following parameters...

Xover frequency - 500hz
Woofer impedance - 8 ohms
Value of C - 100uF

(what's the value of L in the woofer circuit above??)

Which leads me to this point too, so MAYBE I might end up with a poly in there... Seems to me that 100uF is pretty high, given all the calculators I have used to calculate based on just the woofer impedance, xover freq, and desired slope.. They come up with a 20uF cap and 5mH inductor.

So yeah, that's another way of going about it too - junk the inductor, and go with one that doesn't require such a big cap.

The series inductor to the woofer is what provides the 6 dB/octave rolloff of the woofer reproducing or trying to reproduce higher frequencies. The addition of the capacitor makes it roll off faster acoustically (and electrically) at 12dB/octave

 

[jbeckva]

The series inductor to the woofer is what provides the 6 dB/octave rolloff of the woofer reproducing or trying to reproduce higher frequencies. The addition of the capacitor makes it roll off faster acoustically (and electrically) at 12dB/octave

Correct, sir! But can you tell me what the value of L may be, given the "knowns" below? I'm curious to know what the value of the inductor I currently have in there may be.

Xover frequency - 500hz
Woofer impedance - 8 ohms
Value of C - 100uF

 

[laatsch55]

Jer, I know there are phase shifts with any capacitor usage. On my K's crosses, the way Al treated the mid horn the phase was completely reversed on those and had to be shifted back.

 

[jbeckva]

Jer, I know there are phase shifts with any capacitor usage. On my K's crosses, the way Al treated the mid horn the phase was completely reversed on those and had to be shifted back.

Yep and current phase shifts with inductors.. something like that.. Just trying to line em all up and say "hmm.. if it's 90 degrees total shift for the mids and -90 for the woofs.. and so on.. then I should wire the drivers 'this and that' way". All this pondering about the crossovers has me thinking about how the woofers were hooked up when I first saw them at the seller's house versus now... long story, but I may have some NOT in the correct phase with the others.

 

[Gepetto]

Correct, sir! But can you tell me what the value of L may be, given the "knowns" below? I'm curious to know what the value of the inductor I currently have in there may be.

Xover frequency - 500hz
Woofer impedance - 8 ohms
Value of C - 100uF

1.0132836 mH

Basically ~1mH

 

[jbeckva]

1.0132836 mH

Basically ~1mH

So do you think they designed it so that the inductor would be smaller, thus taking up less space?

For example, a 5mH I am looking at measures 2.36" x 1.18", while the 1mH equivalent measures 2.05" x 0.60". (hmmm.. that's not much)

What typically goes into the decision on what to size the cap at versus the inductor, as far as the ratio between the two versus the desired frequency cutoff?

 

[Gepetto]

Hi Jer
Not fully sure I understand your question.

CV designed the crossover to hit a crossover frequency. Generally speaking, manufacturers will use the smallest value inductor possible because this inductor element is in series with the woofer and every inductor has a DCR (DC Resistance). Generally speaking, for a given inductor frame size, when the inductance goes up its resistance goes up more significantly than the inductance does and the inductor Q goes down as well. You do not want to be dissipating your amplifier power in heating up the inductor of your crossover. You want to be moving your speaker cone with that power instead.


Why do you want to change the inductor size to 5mH?

 

[jbeckva]

Hi Jer
Not fully sure I understand your question.

CV designed the crossover to hit a crossover frequency. Generally speaking, manufacturers will use the smallest value inductor possible because this inductor element is in series with the woofer and every inductor has a DCR (DC Resistance). Generally speaking, for a given inductor frame size, when the inductance goes up its resistance goes up more significantly than the inductance does and the inductor Q goes down as well. You do not want to be dissipating your amplifier power in heating up the inductor of your crossover. You want to be moving your speaker cone with that power instead.


Why do you want to change the inductor size to 5mH?

Well, because the xover calcs I have seen online tell me that.. I was wondering why the results on most range the cap between 28 and 33uF when the current crossover I have is populated with a 100uF. With the cap at 20uF, the calculated coil was 5mH. But as you've indicated above, having less inductance, and less DCR, makes a whole lot more sense in a woofer circuit where current will be a bigger factor.

That settled it... Went ahead and ordered the metal polys for all. I'll make them big bama-jama's fit on the back of the plate somehow, heheh.

 

[Gepetto]

Well, because the xover calcs I have seen online tell me that.. I was wondering why the results on most range the cap between 28 and 33uF when the current crossover I have is populated with a 100uF. With the cap at 20uF, the calculated coil was 5mH. But as you've indicated above, having less inductance, and less DCR, makes a whole lot more sense in a woofer circuit where current will be a bigger factor.

That settled it... Went ahead and ordered the metal polys for all. I'll make them big bama-jama's fit on the back of the plate somehow, heheh.

The low DCR is why there is a market for copper foil audio air core chokes like Alpha-Core out of CT makes. The perfect inductor has zero DCR and the ideal inductance value. Those do not exist.

It is like the old saying, every microfarad has its own nanohenry. Caps and inductors are not perfect.

Big caps with good specs are cheaper than big inductors with good specs are however.

 

[laatsch55]

Why all the worry about DCR if we are dealing with AC sinewaves??

 

[Gepetto]

Are you busting my chops Lee

 

[Gepetto]

Well, because the xover calcs I have seen online tell me that.. I was wondering why the results on most range the cap between 28 and 33uF when the current crossover I have is populated with a 100uF. With the cap at 20uF, the calculated coil was 5mH. But as you've indicated above, having less inductance, and less DCR, makes a whole lot more sense in a woofer circuit where current will be a bigger factor.

That settled it... Went ahead and ordered the metal polys for all. I'll make them big bama-jama's fit on the back of the plate somehow, heheh.

Hi Jer

5mH X 20uF = 1mH X100uf

The 1mH is better from the DCR and Q perspective than the 5mH is.

500uH and 200uF would be even better
250uH and 400uF would be even better...and so on.

The rule of practicality comes into play eventually.

Now here is an inductor

http://www.goertzaudio.com/contents/en-us/d6_Goertz_Audio_Store_Foil_Inductors.html

 

[jbeckva]

Well, I sure hope that getting the metal poly's was worth it... LOL.. look at the size of 'em - that shiny thing is a quarter!




Well, no better time than the present... dum dum dee dum...

 

[laatsch55]

Nice!!!!!

 

[Gepetto]

Well, I sure hope that getting the metal poly's was worth it... LOL.. look at the size of 'em - that shiny thing is a quarter!


View attachment 9638

Well, no better time than the present... dum dum dee dum...

We know you will sleep better at night Jer knowing that you have these in your crossover. Very nice quality.

 

[Web Police]

You do not want to be dissipating your amplifier power in heating up the inductor of your crossover. You want to be moving your speaker cone with that power instead.


Why do you want to change the inductor size to 5mH?

CV's were designed with one thing in mind, why would you want to lessen that thing?

 

[laatsch55]

Might be a better thing!

 

[jbeckva]

Well, the patient "lives" hehe. Sorry was in a hurry to start listenin, so no pics .. But suffice to say, I got 'em in there ..heheh. Aint hot glue guns great???

Anyway... Like all new caps, especially crossover caps so I've been told... I'll let 'em burn in for a week or so before passing judgement.

 

[laatsch55]

No initial impressions??