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Old 13th April 2004, 04:40 AM   #1
nrgy is offline nrgy  United States
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Default Vifa D27TG Crossover

I've seen numerous threads regarding crossover configurations for this model, however they all seem very different from each other. I would like to build a 2nd order Linkwitz-Riely for the tweeter, and wondered if these values would be ok with a crossover point at 3200hz.

Cap: 4.3uf
L: .60mh

L-Pad: R1= 2.5, R2=10

First off, I've read mixed reports on the use of an L-pad for this tweeter. Necessary or not?

I will be using the P13WH woofer, with plans to not run a XO on this, as several have recommended this.

Should this produce optimal results for this 2-way combonation?

Thanks.
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Old 13th April 2004, 07:10 AM   #2
Jay is offline Jay  Indonesia
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Hello nrgy,

I assumme your D27TG is the double chamber version having resonance at 650Hz.
As I can remember, the Tlb 5uF approach is to cross the D27 at (or a bit higher than) the
P13WH natural rolloff (on-axis) at 5KHz. So Crossing the D27 at 3K2 means that you
will have an overlap, that may create terrible cancelation, IMHO.

If you use fullrange woofer, it is not that important that you select a Linkwiz-Riley
or any specific filter. A second order on the tweeter (worse with L-pad) will not put the
P13WH in real fullrange, anyway.

I have created a second order filter for a tweeter that working with a fullrange woofer.
It was a success (lock-in), but it was a supertweeter (1.5uF). As I can remember, higher
values will create serious delay. Hope anyone with advanced software will confirm this, and
I believe the guys producing the Tlb had tried this if this is really possible.

As for the L-PAD, avoid it where possible (Tlb doesn't use L-pad I'm sure?). I guess the
original idea of the L-pad is to pad down the tweeter sensitivity and then to bring back the
original system impedance. In other words, the L-pad is designed when the rest of the
filter has been decided beforehand (L-pad is not part of the filter design). This I think is
not correct, especially if you know the effect. Tweeter is not sparkling (what the hell I'm
talking about???), overall system transient is worse (in simple crossovers). Or, if you take
the L-pad into design process, you AT LEAST will have to take the L-PAD into account
and change the original crossover values (LR)

You don't have components for playing around? I have whatever LR values for experiment.
For me, trying it out is easier than theory so I will try that tonight. Oh, in the pdf Vifa has
a recommended 2nd order crossover for the D27TG with notch at resonance
(Fc=3K5, C=8.2, L=0.47, L/R/C=0.9/6.8/69)
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Old 14th April 2004, 03:17 AM   #3
nrgy is offline nrgy  United States
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Thank you Jay for the reply. I actually havn't purchased any of the parts or drivers yet, but was nearly one click away from doing so. But I think I need to get a better understanding of the crossover. I am new to this hobby, and my questions sort of stem off of the other thread regarding the beginner 2-way system, however I get lost reading through all the replies.

The tweeter I was referring to is not the double chambered one, but seeing as I have not bought it yet, should I go with this instead?

It sounds like there are a couple options in terms of a crossover for the D27, and from what I gather, simple is better for this particular tweeter.

A single 5uf cap on the tweeter. - My only concern is some have said this is not enough filtration.

OR

8.2uf cap and .47mh as suggested by the specs you posted from VIFA. - Would this require the notch too?

As far as the woofer, it sounds like it is ok to go ahead and NOT use a crossover on this?

As I said, I'm fairly new to all of this and am to the point where even though I don't fully understand everything, I'm ready to buy some parts and start putting something together.

Thanks again for your help.
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Old 14th April 2004, 02:26 PM   #4
Jay is offline Jay  Indonesia
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Hello again nrgy,

The single chamber D27, I don't have experience with them. Whether you should
go with the dual chamber or not, I think I have no idea as I don't know your objectives.
The single chamber one is cheaper, have higher Fs (but acceptable, you can cross
it at 2K5, or 3K with high power system), not many reputations, not many design
examples. What I know is that bad tweeter or wrong HP filter will ruin your day.

Vifa reccommend at least 2nd order filter for D27. And I don't think that simple is
better with this tweeter. I feel the other way around. The single cap 5uF idea is fine
because it crosses the tweeter at relatively high frequency (far from resonance point),
the system concentrates on the P13WH (not the tweeter), and if you use suitable
amplifier then you sure have an objective.

5uF is not enough? Yes, nothing is enough But if you have a low wattage amplifier
(especially if you use tube amp) this problem has less effect than if you use a high
wattage system. The notch filter is optional. It is recommended only in high power
system.

You can run P13WH crossoverless (it has been proven by many people), the problem
is you cannot assumme that you can match the woofer with any tweeter running
any kind of filter. As you are a newcomer to this hobby, I think you're not using
tube amp (or class-A amp, or even low wattage chip amp), and I believe that you
value BASS highly. The problem with P13 bookshelf is you will not have that BASS,
but a great midrange sound.

BTW, why do you want to run the P13 crossoverless? Is it because you don't want
to spend $$? If that's the reason you should use a proven design, or any design
from experts. If you're a hobbyst and want to have fun and learn, you will have to
waste some $$ anyway, sooner or later.

So P13 is a good choice (if bass is not that important), and D27 double-chamber is
a good mate, because if you failed with one design, you can use other people designs
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Old 14th April 2004, 05:22 PM   #5
nrgy is offline nrgy  United States
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My orignal intention was to use a crossover on the P13, using 1st order, however the reason why I am leaning towards no XO on the P13 is mainly that is what I see recommended, and saving $$ is also nice, but not my main motivation. Do you think it would be easier to get a better sound by XO the P13? I know you stated you do not no what my objectives are, but I can't say I have any specific objectives, other than a fun project.

I can say this, after I build a pair of bookshelf speakers I do plan to build a sub unit as well. I'm assuming this will supplment the P13 and D27, and cover for any lacking bass? Your right, I am not using any fancy amp, just plan to run the speakers off a branded receiver.

A little off topic, but aren't most bookshelf speakers intended to shine in the high and midrange, but lack in bass? Or are many bookshelf systems designed to cover the full range, with no need for a dedicated subwoofer? I would think any bookshelf with anything less than a 7" woofer would need a dedicated subwoofer to really cover the bottom end.

Back to the D27, I will take your advice and use the double chambered version. Your right, I do see more examples of this tweeter being used, and actually I didn't realize it, but this is the tweeter I intended to use.

As for crossover values, I'm very torn on what to do, as there are so many different configurations and I really don't know what to expect from one configuration to another. I trust your opinion, and was wondering if you could simply tell me what crossover components to buy for the D27 (and P13 if you think this would be better). I would like to keep costs as low as possible, but not to sacrifice decent sound quality.

Or should I simply follow Vifa's crossover recommendations, with the exception of the notch?

Thank you again, I very much value your help!
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Old 14th April 2004, 06:01 PM   #6
Vivek is offline Vivek  India
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Hi,
Whether you choose a Butterworth, LR or a Bessel type is not an issue. Formulae to calculate crossover component values are available on the net. Just put in the impedance value of the driver and the crossover frequency and you get the values. You can tweak it later also if you do not like the sound.
If you want to be more sophisticated use a software like speaker workshop to simulate the crossover response.
An L Pad would be required on the driver which has the higher sensitivity. If your tweeter is 90dB and woofer is 86dB, then the prominence will be in the higher frequencies. Having both sensitivities equal would be better in my opinion.
By the way, I am making a 2-way speaker with a Vifa tc18wg48 and a d27tg-05-06. I am using a second order bessel for both with the crossover point being 2500Hz.
Good luck with your project.

Vivek
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Old 15th April 2004, 12:31 AM   #7
nrgy is offline nrgy  United States
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"Whether you choose a Butterworth, LR or a Bessel type is not an issue."

I'm glad to hear someone say this, as this is just added confusion for a newcomer like me. I assume you're basically saying that I shouldn't be too concerned with what type of 2nd order to use, as they all pretty much achieve the same thing.

I have found those crossover calculators, which are quite useful and easy to use, which is actually how arrived at the first set of crossover values, however my only concern with going by the numbers it calculates is whether or not I can trust them. The reason being, I have plugged in crossover points as shown on proven designs using the crossover calculator, and I never come up with the same values as their crossovers. I realize this is because each design is tweaked for individual and driver preferences, however how much variation can their really be with a 1st or 2nd order filter using the same driver?

I wish I was reading into this crossover deal too much, but I've heard too many people say the crossover is the most critical part of a speaker system.
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Old 15th April 2004, 02:08 AM   #8
nrgy is offline nrgy  United States
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Just to provide an example my concerns using the crossover caluclators, Vifa recommends a 2nd order crossover at 3500hz, with C=8.2, L=.47

However, when I calculate a 2nd order Butterworth at 3,500hz, as I assume this is what they are using (since the other XO are further off), it shows me C=5.3, L=.38

I would imagine these two crossovers would provide different results, however which one do you trust/go by?
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Old 15th April 2004, 07:06 AM   #9
Vivek is offline Vivek  India
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Obviously, the crossover suggested by Vifa has been tweaked after computer simulation.
As I told you earlier, I used formulae to calculate second order Bessel filters for both the woofer and tweeter and will be using the same values.
To get an idea about the various types of crossovers and their characteristics, see Rod Elliott's article at

http://www.sound.westhost.com./lr-passive.htm

Vivek
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Old 15th April 2004, 07:58 AM   #10
sreten is online now sreten  United Kingdom
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Regardless of what you've read IMO your plan will give poor results.

The TLb from which the simple crossover was derived is far more
subtly designed than first appearances would suggest, whether
this is through design or accident I don't know, it that application
(bipole) the simple crossover works, two units in a box it doesn't.

http://www.t-linespeakers.org/projects/tlB/

The bizzarre thing is for such a popular driver I can't find a
decent design for a straight 2-way that doesn't have any
fundamental design errors in it.

You could do a lot worse than building the ME2 or the TLb.

http://www.nutshellhifi.com/Ariel.html#index

sreten.
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