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Old 27th September 2013, 03:14 PM   #21
AllenB is offline AllenB  Australia
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Quote:
Originally Posted by Michael Chua View Post
Vifa D19TD-05 tweeter
I had a set of these about 20 years ago. They are nice tweeters but I found problems crossing them low enough to match anything but a small woofer. Otherwise the system's directivity would narrow below the crossover and present harshness from the treble.
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Old 27th September 2013, 05:44 PM   #22
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Allen,
Again thanks for your insight. I'm a speaker building amateur, but isn't the resonant frequency 1700hz. If I cross them at 3500hz wouldn't they work? I pretty sure the Altec woofer can handle it, because they came out with a Series II version of the same speaker and changed the cabinet volume by about +130 cu in and raised the xover from 3khz to 3.5 khz. Wouldn't your 3.3uf cap recommendation earlier work?
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Old 27th September 2013, 07:35 PM   #23
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Originally Posted by mjatabor View Post
Speaker manufactured in 1976. Tweeters look like there is some wear, surrounds are good but paper cone a bit distorted.
Solen makes caps inexpensive caps. What you say? Any recommendation of other brands of metalized film caps?
Jantzen, Dayton Audio, and many others. The brand isn't as important as the type -

Film and Foil Capacitors -

Film and Foil Capacitors in the Speaker Components Department at Parts Express | 295

Metalized Polypropylene -

Metalized Polypropylene Capacitors in the Speaker Components Department at Parts Express | 294

Here is a Dayton Audio 6.2uF for $2.83 -

Dayton Audio DMPC-6.2 6.2uF 250V Polypropylene Capacitor 027-427

And a Dayton 2uF for $1.48 -

Dayton Audio DMPC-2.0 2.0uF 250V Polypropylene Capacitor 027-414

The thing you probably do NOT want is the Non-Polarized Electrolytic -

2.2uF 100V Non-Polarized Capacitor 027-324

For the slight difference in price, there is simply no point in buying the Non-Polar Electrolytic.

Steve/bluewizard
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Old 27th September 2013, 07:43 PM   #24
balerit is offline balerit  South Africa
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As someone mentioned you have to measure the impedance at the crossover point. Is there an impedance curve for the tweeter you want to use? It sounds like you are hearing the classic problem of a 1st order network namely that whenever the two speakers are reproducing the same frequency at roughly the same levels, there will be interference between them, reinforcing some frequencies or cancelling others.

Last edited by balerit; 27th September 2013 at 07:46 PM.
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Old 28th September 2013, 02:57 AM   #25
AllenB is offline AllenB  Australia
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Quote:
Originally Posted by mjatabor View Post
Allen,
Again thanks for your insight. I'm a speaker building amateur, but isn't the resonant frequency 1700hz. If I cross them at 3500hz wouldn't they work?
There are some things to keep in mind when running a woofer at high frequencies which have small wavelengths compared with the size of the cone. The woofer will produce more sound to the front of the speaker, ie less to the sides. These may sound OK when you sit closer but in a room, you tend to hear all the sound because it eventually bounces around the room and comes back to you. So, if you get the higher woofer frequencies to sound right from the front, they can be less strong in the bigger picture.

If you then cross to a tweeter which has wide dispersion and make it sound good from the front, the treble may sound too heavy in the room and the region of frequencies below the crossover where the woofer is running out may expose a harshness in the treble which is otherwise undeserved (ie no other reason it should be a problem).

One option is to keep the 8" crossed perhaps lower than 2k. You could also use a tweeter with more narrow dispersion and then you might cross the woofer higher (not too high). Such tweeters might be a larger coned tweeter or perhaps one that is waveguided.

Some of this is generalising, of course. You may like the tweeter. If I had some still I'd probably put them into something.
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Old 28th September 2013, 03:05 AM   #26
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That's interesting info Allen. I had the Dynaco A25xl speakers and like the Altec didn't use a xover for the woofer either, but used the woofers natural roll off at the up end. The Dynaco used a 1" dome tweeter and it seemed to integrate very well with its 10" woofer.
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Old 28th September 2013, 09:46 AM   #27
AllenB is offline AllenB  Australia
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The reason a simple crossover (ie one capacitor total) may work is that the tweeter will be producing more energy at its resonance, which is below the crossover and this might happen to fill in a little for the woofer at its top end.

Since a small capacitor is used to compensate somewhat for the resonance peaking, the tweeter response just above this is normally slightly low. The woofer may tend to have some peaking at its most upper region (called breakup) just above the crossover which may fill in this second hole.

When you use a second order filter (preferrably around an octave or more higher than the tweeter resonance but still maybe lower than for first order) the peaking is not as profound. There is a certain immunity to it compared with the capacitor on its own and the response should be closer to what it ought to be.

When you use a second order on the tweeter you might use one order on the woofer to help keep them in line

Last edited by AllenB; 28th September 2013 at 09:48 AM.
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Old 28th September 2013, 08:02 PM   #28
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Allen, this makes sense and keeps it into perspective.

If I go the route of the Vifa d19, which is a drop in w/o cabinet modification, I should consider at least a 2nd order xover. It might be surprisingly good. There is no way for me to do any impedance measuring so it will be hit or miss w/ an online calculator.
Vifa D19TD-05 3/4" Poly Dome Tweeter 264-500

Or maybe just purchase a phenolic ring tweeter, which I've read is a slight improvement of stock cone tweeters w/o any crossover mod other than a new poly cap.
Phenolic Ring Tweeter 8 Ohm 270-252

What you say?
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Old 28th September 2013, 11:28 PM   #29
AllenB is offline AllenB  Australia
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The D19 tweeter if I remember correctly gave a slightly relaxed performance when used without equalising and larger cone tweeters sometimes do the same. This is probably only of interest if you plan to use a straightforward crossover. I probably used it down to 3kHz and I did use it first order sometimes but second fitted better with what I was doing and allowed a lower cross point. I also appreciate a good cone tweeter or small full range driver for what it's worth. Steve (System7) has previously recommended this one.

With a second order filter, the capacitor and inductor have a shared control that gives the impression of partially ignoring the impedance. If you are not doing measurements it can become a sensible choice for this reason.

If you do decide to cross the woofer you should probably use impedance rise compensation with the inductor as shown below if you aren't going to use measurements. The values should be easy enough to work out.
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Old 29th September 2013, 12:06 AM   #30
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Quote:
Originally Posted by mjatabor View Post
If I go the route of the Vifa d19, which is a drop in w/o cabinet modification, I should consider at least a 2nd order xover.
If you don't mind paying a bit more, the Vifa XT25TG30 is a better choice. You can go 1st order (Red trace below) with this tweeter. More information can be found at SWIFT-IIIb.

Click the image to open in full size.

The XT25 can easily be crossed at 2.5kHz with 2nd order. All in, it's more flexible. The D19 on the other hand, is more suitable for 2nd order at 3kHz to 3.5kHz.

By the way, 8" with a dome is quite difficult. I usually use a compression driver but it's costly and complicated.
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