Vifa TC9FD18-08 in Zaph's B3S cabinet - diyAudio
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Old 1st February 2012, 12:55 PM   #1
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Default Vifa TC9FD18-08 in Zaph's B3S cabinet

Hi all,
I have a couple of the Vifa TC9FD18-08 drivers mounted in cabinets with the same baffle size as Zaph's B3S design (Zaph|Audio). Which I'm planning on running full range with an active or passive line level crossover to a sub at approx 150Hz.

There are two issues that I'd like to address with a passive crossover
1. Baffle Step
2. Rising response above 10KHz

So question is:
am I right in thinking I can combine the baffle step component from Zaph's design (L1 and R2 below) to address point 1:
Click the image to open in full size.

..and the notch filter from this design (L2 and R1) to address point 2:
Fast, fun, Inexpensive OB project
Click the image to open in full size.


Or will each of these sections affect the other significantly such that I need to recalculate all the components?

Thanks
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Old 1st February 2012, 01:26 PM   #2
sreten is offline sreten  United Kingdom
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Hi,

Why not do all your EQ at passive line level ?

For some BSC you could put an inductor across the second circuits 4.5R.

rgds, sreten.
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Old 3rd February 2012, 09:12 PM   #3
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I don't think there is any need for a notch filter on the Vifa unit. You can't judge by the OB design because this is very special. Look, Zaph has also measured the Vifa in his Blog part. Judging by his measurements the Vifa has a flatter response than he ends up with in the B3S design after his corrections. The baffle step will be needed.

/Erling
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Old 4th February 2012, 10:40 AM   #4
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Thanks for the responses. The eq at line level is quite tempting - I might have some more questions once I've looked into that a bit more.

I've just fired them up for the first time without any filtering (apart from using the 150hz high pass from my preamp) and they sound pretty good as is.

So perhaps I'll try starting with the passive baffle step filter above for starters and take it from there..
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Old 4th February 2012, 11:56 AM   #5
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I don't think that you need a notch with the tc9..........
The rising response past 9khz, just sit a squeek off axis and that should be lessened.

But baffle step almost always helps.
I have a buddy that swears that line level baffle step is the only way to go.

That's a nice driver.

Norman
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Old 4th February 2012, 12:40 PM   #6
sreten is offline sreten  United Kingdom
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Hi,

FWIW I don't not why the "special trap" filter isn't simply called what it is.
Its not a notch filter, its a low pass step filter and is doing the equivalent
of a BSC filter, it has nothing to do with the top octave response.

Sorry I didn't notice that before when replying, I didn't notice the values.
You can't combine the two filters, just use the first one.

FWIW with a passive BSC filter in place the top response will tend to rise
due to the 0.3mH inductance of the driver with the BSC resistor value.
You can control this by putting a RC across the driver, it doesn't have
to be zobel values, by making the zobel resistor a little lower and/or the
zobel capacitor a little bigger you can tweak the top-end of the driver.

rgds, sreten.

A back of an envelope calculation indicates the driver inductance
= the BSC resistor value (8ohm) plus driver DCR (6 ohms) @ 7.5KHz.
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Last edited by sreten; 4th February 2012 at 01:08 PM.
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Old 4th February 2012, 01:12 PM   #7
sreten is offline sreten  United Kingdom
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Hi, classic zobel values seem to be 7.75R (8R) and 5uF (4.7uF), rgds, sreten.

Though the calculators don't seem to want to agree with
each other, which is a real pain. I've got results for the
capacitor of 1.2uF, 5.uF, 5.5uF, 8uF, 9uF, go figure ......

Checking the theory 4.7uF is right for an 8R zobel on a 6.2R 0.31mH driver.
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Last edited by sreten; 4th February 2012 at 01:40 PM.
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Old 4th February 2012, 04:44 PM   #8
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Great - thanks Sreten.
I may even have those zobel values to hand so no reason not to give it a try really.

Be interesting to try and then compare with line level BSC.
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Old 4th February 2012, 09:15 PM   #9
sreten is offline sreten  United Kingdom
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Quote:
Originally Posted by big russ View Post
Great - thanks Sreten.

Be interesting to try and then compare with line level BSC.
Hi,

Line level BSC won't have the zobelling issues, and adding a RC in
parallel with the driver will have no practical effect, so the fact
you can't easily tune the treble end may be a disadvantage.

Line level BSC comes into its own with low powered amplifiers,
T-amps or valve. It effectively quadruples the amplifier power
above the BSC transition (assuming its 6dB). if you already
have plenty enough power perhaps passive BSC with its
attendant treble tweaking options is the better choice.

(Assuming you don't have tone controls and/or you don't
want to include passive tone controls in the line level EQ.
Again, like BSC, treble cut EQ at line level is very easy,
in a general sense, its much harder to make it localised.)

TBH without off axis curves the top-end is anyones guess.
I'd say forget about it and experiment with toe-in angle.

rgds, sreten.
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There is nothing so practical as a really good theory - Ludwig Boltzmann
When your only tool is a hammer, every problem looks like a nail - Abraham Maslow

Last edited by sreten; 4th February 2012 at 09:31 PM.
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