Did I create the correct electrical schematic of my existing crossover?

[JayGilb]

Welcome to ASR. Glad you found us.

This is exactly why I enjoy the forum.

 

[motleypixel]

I can't see the AK images, I'm not a member over there. Not sure if they are the same circuit with fewer parallel components, or if it is new. This 90 uF capacitor could replace the three film capacitors in your woofer crossover (75, 15, and 0.1 uF) for example. 90 uF and 90.1 uF are sonically equivalent to much better than 0.1dB. It was (and still is) popular to add a small-value capacitor in parallel with larger caps, allegedly improves transients (it does not), it all could be replaced with one big 90 uF capacitor.

I'm attaching screen images from that AK post. I tried and tried to squeeze as much info/history out of this from an audio engineer at Soundtube that reports to a Vice President Ken Hecht (former CEO of PhaseTech and again son of Bill Hecht founder and creator of the soft dome tweeter). He was absolutely reluctant to give any crossover specs/drawings and any data of either the tweeter or woofer. But he did suggest the version I have are few and far in the wild even when the maufacturing was underway because they switched to this version I'm about to show here quickly. All I can figure here is they simplified and saved money. The original (ones I have) contain more components, AL anodized back plate etc. So I am just curious if that simplification was an improvement or minor hit to the sonic response of the entire speaker?

That 90uF film is HUGE and I am very concerned it's not going to fit well which is why I did not buy it. So for now I will parallel the 68/22 smaller electrolytic along with the .1 film but sounds like that's a "snake oil" thing about higher freq. bypass etc.?

Thank you!

 

[bmc0]

I will lift leads and measure the inductors with my fluke multimeter.

FWIW, the DATS can be used to measure inductors and capacitors as well.

For ESR this is only on the capacitors?

I probably should have written "DCR" instead of "ESR" there. Inductors in crossovers (especially air core) tend to have significant DC resistance which must be considered as part of the circuit design. So to properly model an existing crossover (or to design a new one), you need the inductance as well as the DC resistance.

Film capacitors usually have negligible ESR, but electrolytics can have ESR high enough for it to be important. I see that you're intending to replace the electrolytics with film—that should be fine in this case because the 1.8R resistor to ground should be large enough to swamp the ESR of the capacitors (making the exact ESR value not so important). In some cases, it is necessary to add a resistor when changing electrolytics to film.

should I measure them out of the speaker box, in the speaker box with the acostastuff and back sealed or both?

No need to measure in free air (i.e. outside the box) unless you're planning to design a new enclosure with a different internal volume/tuning. For modeling and/or tweaking the crossover, the in-box impedance is what you want.

When you mean "omit it and not to be too cavalier with the volume knob" you mean take out the POT and not drive the speakers too loud with my pre-amp volume control/knob right?

I was referring to the breaker there, but otherwise yes.

I wonder if folks have killed drivers using REW before?

I'm sure it's happened. Not to me though (at least not yet ). ~75dB isn't particularly loud for a speaker, especially if you consider the fairly short duration. Most speakers (even small ones) won't be damaged by a short sweep even 20-30dB louder than that.

 

[a4eaudio]

.... So for now I will parallel the 68/22 smaller electrolytic along with the .1 film but sounds like that's a "snake oil" thing about higher freq. bypass etc.?...

Probably snake oil, but it's snake oil for a few dollars rather than $2,000 speaker cables.

 

[motleypixel]

@bmc0 thanks again for the reply. For now I'm reading and watching videos etc. I think because I am not building a new box (cabinet) I just want to do some measurements and use them to model what a decent cross-over might be, for both exercise/practice and to see how the model differs from my existing XO.

So far I think what I will need are:

With the woofer and tweeter both screwed into the cabinet with stock stuffing inside as well and two short pig tail pairs exiting out the rear marked tweeter/woofer and that large square hole in the rear taped closed, perform the following:

Woofer only:
Run a 50-4k phase and impedance sweep with the DATS V3 and export that as .zma file

Tweeter only:
Run a 1K to 10k phase and impedance sweep with the DATS V3 and export that as .zma file

I'm just a little confused in the DATS user interface and manual for the "measure free air parameters" as to me this means just hooking up the driver, set the sweep freq appropriate for the driver in the "open free air" and not in the box/cabinet? IDK, this is just all the jargon/naming conventions I'm learning for the first time.

I don't think I need to conduct the weight method Vas measurement since I'm using the stock non-ported cabinet?

Then, and not sure if I should, but since I'm setup do the following with REW which I have experience using:

Woofer only:
With my horizontal umik-1 cal file in use, place the mic very close to the center of the woofer about 1in away and run a 50-4k sweep at 75dbcs and save that. Also near field like this it should be okay in my living room just so long as it's out in the open area and not near a wall?

Do the same with the tweeter but sweep it for 1K to 10K and save that.

Measure the volume of my non-ported cabinet.

So all in all this should provide me all the data I need to use with XO simulation tools correct? I won't need to run the phase/impedance sweep with DATS with the driver out of the box at all correct?

Thank you.

 

[bmc0]

and that large square hole in the rear taped closed

I'd suggest something with more structural integrity than just tape.

Run a 50-4k phase and impedance sweep with the DATS V3 and export that as .zma file

You should run the impedance sweeps full range for both drivers. The input level is low enough that it won't cause any problem.

I'm just a little confused in the DATS user interface and manual for the "measure free air parameters" as to me this means just hooking up the driver, set the sweep freq appropriate for the driver in the "open free air" and not in the box/cabinet?

That is indeed what "free air" means, but there's no need to actually do it this way in this case since you're not designing a cabinet. What you want is the complex impedance (i.e. impedance magnitude and phase) of the drivers in the cabinet.

I don't think I need to conduct the weight method Vas measurement since I'm using the stock non-ported cabinet?

Correct. That is only if you need to determine the woofer's Thiele/Small (T/S) parameters in order to design a cabinet.

place the mic very close to the center of the woofer about 1in away

To properly model the crossover, you need to measure with the mic 1-2 meters away and apply a time window to remove all the reflected sound. Simple nearfield measurements can be useful for low frequencies, but do not accurately represent far-field acoustic output at higher frequencies where wavelengths are shorter than a few times the baffle/driver dimensions.