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Old 23rd March 2015, 05:52 PM   #1
Akhnot is offline Akhnot  United States
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Default New build and a crossover question.

Hi Folks,

I built this new set of two way mini-monitors, to use an oldie-but-a-goodie tweeter I had sitting on my shelf.

Tweeter: Focal T123TiO2 (Yes, it's a real model, they were used in the Wilson Watt Puppy in the mid-90's, I have SN: 3471315, and 3471316)
Woofer: TB W4-1720

My crossover question is:
You'll see two crossover diagrams. I made both in PassiveCrossoverDesigner 7.

The first one is the second order with zobel's and such. I assembled that circuit for both woofer and tweeter, hooked it up and epic fail. It sounded great, until you turned the volume up, and the amplifier started clicking off/on and making the speakers pop.

So I went back to my first order design I had run through the designer, and assembled that one for a test. Worked perfectly.

The first order design is in the final as-built. They sound fantastic, great room filling sound.

Why would the second order cause that issue?



John
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Old 23rd March 2015, 06:59 PM   #2
system7 is offline system7  United Kingdom
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The issue with the first crossover is that the impedance is below 2 ohms for most of the range. And FWIW, I don't see a Zobel in sight. I see an attenuator.

Truly an awful design. 0.33mH bass coil and near 200uF of shunt capacitance is just daft! Sorry. I have simmed this circuit with similar sorts of drivers below. Electrically it's going to be right.

Here's a better one using the same 4 ohm Tang Band W4-1720 4" driver:
Piccolata Mini Monitor
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Old 23rd March 2015, 07:23 PM   #3
Akhnot is offline Akhnot  United States
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Interesting. Those are straight from the Passive Crossover Designer, and just modified from when I used the 'initialize textbook values' function. I did use SPL trace to create the ZMA and FRD files for the woofer, and used the next closest guesstimate for the tweeter (T120tio2) since there are no published specs for the T123.

On the other hand, I'm happy with the first order that I tried. I spent all day listening to them yesterday, and love em. I think they'd be real easy to blow up, but I don't typically push my gear to its limits.

Thanks again Steve.
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Old 23rd March 2015, 07:29 PM   #4
RajkoM is offline RajkoM  Bosnia and Herzegovina
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It's beautiful design.
These are copper ports ???

Last edited by RajkoM; 23rd March 2015 at 07:43 PM.
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Old 23rd March 2015, 07:35 PM   #5
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As for the second order: totally wrong. 0.33mH with the 100uF + 2ohm-200uF cap practically places a nice short circuit on your amp for most of the frequency range.(no wonder it was going to protection mode...) The first order one might work, but it is a better idea to use an L-pad after the cap, OR place the resistor in front of the cap. On the HF part the coil after the cap is 2.2mH? If so, that's wrong too.....

Last edited by dragonweed; 23rd March 2015 at 07:37 PM.
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Old 23rd March 2015, 07:42 PM   #6
Akhnot is offline Akhnot  United States
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Quote:
Originally Posted by RajkoM View Post
It's beautiful.
These are copper ports ???
Thanks! =)

Yes, 1" copper, installed flush to the surface of the box, with polished interior slightly rounded edges on the inside to prevent noise. They're also tarred to the the floor of cabinet to prevent ringing.
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Old 23rd March 2015, 07:46 PM   #7
RajkoM is offline RajkoM  Bosnia and Herzegovina
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Quote:
Originally Posted by Akhnot View Post
Thanks! =)

They're also tarred to the the floor of cabinet to prevent ringing.

That interested me.
Congratulations once again.
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Old 23rd March 2015, 07:50 PM   #8
system7 is offline system7  United Kingdom
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It looks to me like T123 TiO2 just describes a 123mm faceplate:
Le Phenix Noir : Le Coin de l'Audiophile > Base HP
Page 6 for the T120.

Nothing very controversial about a 30mm metal dome tweeter.

Your simpler first order filter doesn't dip below 4 ohms, so no amp cut out. But that's a poor design too, IMO. You're pretty much running the 4" bass full range.

I'd reckon that Piccolata design is going to be much better. Louis Coraggio was a very good designer, and if he has done the bass section for a 3kHz crossover, that's half the battle.
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Old 23rd March 2015, 07:54 PM   #9
Akhnot is offline Akhnot  United States
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Quote:
Originally Posted by dragonweed View Post
As for the second order: totally wrong. 0.33mH with the 100uF + 2ohm-200uF cap practically places a nice short circuit on your amp for most of the frequency range.(no wonder it was going to protection mode...) The first order one might work, but it is a better idea to use an L-pad after the cap, OR place the resistor in front of the cap. On the HF part the coil after the cap is 2.2mH? If so, that's wrong too.....
It seems I may have clicked a few wrong buttons in PCD? :/

On the first order, there shouldn't be a coil in the HF section, just cap and resistor.

On the second order you are correct, it was a 2.2mh.

Starting to wonder if I transcribed positions/values wrong and then built to that.
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Old 23rd March 2015, 08:04 PM   #10
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Personally I'd omit the zobel network. It's not necessary and only adds a potential source of coloration to the sound as well as complexity to the project.

Unless your amplifier is on the fritz, it serves no real benefit, because it's purpose is to stabilize driver impedance over the range of audio frequencies...however most audio amps can handle this type of dynamic load without any such compensation.

My recommendation: Stick with a simple 2-way butterworth crossover. I went with super-simple 2nd order butterworth xovers plus L-pad attenuation to match the tweeter's sensitivity to that of the woofer and my speakers sound great.

BTW - Just pick a good xover point and use a simple calculator to figure out the values of your caps, inductors and l-pad resistors. It's ok to nudge the xover point slightly up or down in order to minimize the number of components you'll actually need.
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