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Old 22nd February 2008, 05:00 PM   #1
rwo is offline rwo  Australia
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Default Vifa P17SJ and Vifa D27TG Large Bookshelf MTM

I'm sure this has been posted 100 times already, but I couldn't find it!

I'm looking to build a set of large bookshelf speakers for a HT setup as my first project. I would like to use the Vifa P17SJ woofer and Vifa D27TG tweeter.

Are there any tried and tested designs based on these drivers that I can follow? I have done plenty of searching but couldn't really find anything suitable.

The cabinet work will be no problem, but I don't really know where to start with the crossover. I don't have the technical expertise or equipment to do my own crossover design, but I am more than capable of soldering a few components together if I have some schematics to follow.

Basically, i'm new to this and looking for some plans to get started, has anyone who has built a similar project got a worklog or something to follow?
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Old 22nd February 2008, 05:26 PM   #2
croat47 is offline croat47  United States
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Location: Eastern Shore, Maryland
It has been, sort of...

New house, new HT ...

http://www.geocities.com/etude317/TLconstruction.html
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Aaron
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Old 22nd February 2008, 06:29 PM   #3
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I'm pretty new to this too, and I'm still trying to get people to give me guidelines that help me separate the 'impossible' speaker combinations from the 'maybes'.

There are actually two models of that tweeter -

Vifa D27TG-05 1" Silk Dome Tweeter
http://www.partsexpress.com/pe/showd...number=264-524
Frequency range: 2,500-30,000 Hz
Fs: 1000 Hz

Vifa D27TG-35 1" Silk Dome Tweeter
http://www.partsexpress.com/pe/showd...number=264-526
Frequency range: 1,500-30,000 Hz
Fs: 650 Hz

Vifa P17SJ-00 6-1/2" Shielded Woofer
http://www.partsexpress.com/pe/pshow...TOKEN=45209297
Frequency range: 35-5,000 Hz

On the surface, that would seem good. We have tweeters that go down to 2,500hz or 1,500hz and a woofer that goes up to 5,000hz. It would seem that is enough room for us to work with.

Now look at the spec sheets for these speakers -

Vifa D27TG-05 1" Silk Dome Tweeter SPECS
http://www.partsexpress.com/pdf/264-524.pdf

Vifa D27TG-35 1" Silk Dome Tweeter SPECS
http://www.partsexpress.com/pdf/264-526.pdf


Vifa P17SJ-00 6-1/2" Shielded Woofer SPECS
http://www.partsexpress.com/pdf/297-308.pdf

Look at the frequency response graphs.

Notice on the woofer there are three colors; I'm guessing the Blue is the on-axis 0 degrees response, green is 30 degrees off-axis, and Red is 60 degrees off-axis. Off-axis means off the center line, off center, or to the side by the number of degree specified.

Now we see that what we thought was 5000hz, is really 2khz. Now, I suppose if you don't mind the woofer starting to beam or narrow the field of sound coming from it, we could maybe squeeze this up to 3k, but that would be pushing it. I would be reluctant to crossover at above 2k.

Now the tweeters. If we look at the model that ends in '-05', and we look at the bottom line on the frequency response graph, we see a line with a small hill on the left, a valley in the middle, and a gradual slope on the right. That is the impedance graph. It shows how the speaker impedance changes with frequency.

I've been told as a general rule that you want to crossover at 2 octaves or more above the resonance frequency (Fs), that little hill on the left.

For the '-05' model that is 1khz; one octave up it 2khz, two octaves up is 4,000hz. if you look at the frequency response graph alone, it would seem that you could use anything 1.5khz or above. But our rule of thumb says nothing less than 4khz, thought the spec sheet recommend and gives you the values necessary for a 3.5khz crossover.

For the '-35' model the resonance frequency(Fs) is 650hz; one octave up is 1300hz, two octave up is 2600hz. As a rule of thumb that is the lowest, the tweeter should be crossed over. Again, the specs sheet gives you the values for a 3500hz crossover.

Now back to the woofer. Again, looking at the frequency response graph. I decided from looking at it, that the best highest crossover would be 2000hz. But that could possible be squeeze up to 2500hz. At 2500hz, 30 degrees off center the sound level is down about 2db to 3db, at 60 degrees off center the sound is down about 7db to 8db. It's tolerable at 2000hz, but very marginal at 2500hz.

So, of the components we have looked at, only the woofer and the D27TG-35 tweeter have a chance of working together. And, only a crossover of 2000hz to at the most 2500hz have a chance of working well. At this stage I am assuming a crossover with 12db slopes, a 2nd order crossover; the most common type.

I suppose you could try to raise the crossover to something like 2.2khz. Every thing we do is a compromise, it is just a question of whether this is a compromise you are willing to make.

As a side note: You will notice on the right of the suggested crossover on the spec sheet, a series combination of Rc, Cc, and Lc. These values are flattening the slope on the right side of the impedance graph. Regardless of where you crossover, you can still use these values. This is called a Zobel Network, and you will probably have to create on for your woofer too. But it's not that hard. I don't have the formula readily available, but it is calculated using Le, which is the inductance of the voice coil of the speaker. If you search 'Zobel network' in Google, tons of information will come up.

For specifics of crossover design, I would recommend searching the internet for free speaker design software. There are several of them out there. WinISD is a relatively popular one. SpeakerWorks is another. They will take all the T/S parameters of your speaker and model them for different box sizes and designs and help with crossover design.

In this case, if you follow what I said, you are pushing both the woofers and tweeters to the limits of their truly workable range.

That is about the limit of what I know. There are a lot more details to consider, and hopefully someone will jump in here, and help you with those, and will also correct any mistakes I might have made.

You can certainly pick two reasonable speaker off the shelf, made a reasonable determination of a crossover point, add an off the shelf crossover plus the Zobel networks, and have an OK set of speakers. The question is, is 'OK' good enough? If you want good to great speakers, it means investing some time and money, and a lot of work and study, to get it right. How far you are wiling to take it, is up to you.

Steve/bluewizard
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Old 22nd February 2008, 07:29 PM   #4
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Curious about what people think of this tweeter as a substitute for the Vifa D27TG-35 1" Silk Dome?

Vifa DX25TG-05-04 1" Fabric Dome Tweeter
http://www.partsexpress.com/pe/showd...Number=264-578

Vifa DX25Tg-05-04 Freq & Impedance Graph
http://www.partsexpress.com/pdf/264-578g.pdf

Vifa DX25Tg-05-04 Specs
http://www.partsexpress.com/pdf/264-578.pdf

This tweeter has a Fs resonance of about 650. Two octaves up would be 2600 hz. It's rated frequency response is 2,000-40,000 Hz but it has smooth flat response down to 800 or 900hz. It's off axis response is pretty bad above 10khz, but most tweeter are. The Fs impedance peak is relatively low at about 17 ohms.

Also, you might want to consider this as an alternative. Here is a Georgia Tech student who build speakers based on different Vifa models -

http://users.ece.gatech.edu/~mleach/labsp2/

Just trying to help.

Steve/bluewizard
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Old 23rd February 2008, 08:53 AM   #5
rwo is offline rwo  Australia
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Quote:
Originally posted by BlueWizard
Curious about what people think of this tweeter as a substitute for the Vifa D27TG-35 1" Silk Dome?

Vifa DX25TG-05-04 1" Fabric Dome Tweeter
http://www.partsexpress.com/pe/showd...Number=264-578

Vifa DX25Tg-05-04 Freq & Impedance Graph
http://www.partsexpress.com/pdf/264-578g.pdf

Vifa DX25Tg-05-04 Specs
http://www.partsexpress.com/pdf/264-578.pdf

This tweeter has a Fs resonance of about 650. Two octaves up would be 2600 hz. It's rated frequency response is 2,000-40,000 Hz but it has smooth flat response down to 800 or 900hz. It's off axis response is pretty bad above 10khz, but most tweeter are. The Fs impedance peak is relatively low at about 17 ohms.

Also, you might want to consider this as an alternative. Here is a Georgia Tech student who build speakers based on different Vifa models -

http://users.ece.gatech.edu/~mleach/labsp2/

Just trying to help.

Steve/bluewizard

It's interesting that you mentioned that BlueWizzard. After having a look around an australian parts supplier site I found that same tweeter and was curious as to how it would go.

I did a search on the forums here and found a post by someone who used this combo in a HT, but with 3 tweeters and 2 woofers. Can't rember the user, but i'm sure a search will turn it up.
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Old 23rd February 2008, 10:00 AM   #6
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I would suggest that you both read this page on John Krutke's site, Zaph Audio:

http://www.zaphaudio.com/audio-speaker19.html

For a start, you will find accurate FR graphs for the vifa d27sg-15 and some information about the different versions, SG-05, TG-05, TG-15 etc.

Then you get to see how someone who is willing to take into account (as everyone really should) the acoustic rolloffs of the drivers involved can do away with the rules of thumb such as crossing over 2 octaves or more above tweeter resonance and so on. In this case, the tweeter resonant frequency is about 1100Hz and the crossover point is around 1700Hz.

If you want only the electric crossover used to determine the slope and xo points of the crossover, I should imagine that, using 24db/oct crossovers, 1.5-2 octaves overlap should be sufficient. Driver excursion is unlikely to be an issue with such steep slopes.

rwo, if you don't have your heart set on the vifa woofer, I would consider building this vifa/hi-vi design because it has been designed to be useable on it's side as a HT centre. The page is definately worth reading either way.

My only other comment would be that I don't personally think that it's a good tradeoff to use MTM so that you can have all 5 (or 7) surround speakers looking the same. A small 2-way the right way up or on it's side has the potential, if the lobing is symmetrical (once again see Zaph's design), to make a better centre speaker and would be cheaper to build a whole set of.

If you decide to go ahead with the vifa/vifa combo, good luck and make sure that whichever design you choose, if you can find one, takes into account the tweeter's rolloff, baffle-step compensation, and the need to cross low. So the fairly extended response of the P17 will not be much of an advantage.
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Old 23rd February 2008, 05:54 PM   #7
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Here is a link to a description of the design process used for a speaker using the Vifa P17SJ-00-08 woofer and the Vifa D25ASG05-06 tweeter. It doesn't really have plans but it does nicely discuss the design process.

http://speaker.rosaryshop.com/index.php/r/tutorial

I think what RWO was hoping for is a link to an existing project using the same or similar components. That would save him a lot of headaches in the design process.

I went through the basic analysis that I did, to demonstrate the feasibility of using the components he had selected.

The '-05' tweeter has a resonance at just below 1000hz, it has a moderately high resonant peak of abut 15 ohms, it's flat down to 1khz, and rolls off quickly. The 2 octave Rule of Thumb, is just that a rule of thumb not an absolute rule. It gives you some idea of the tweeters potential.

Since it is reasonable flat and rolls of sharply, you could certainly use a lower crossover. But I would be reluctant to go much below 2khz.

The '-35' tweeter has a resonance at about 650 hz with a resonant peak of a low 10 ohms, but it rolls off very slowly and starts to roll off at about 2khz. So, again, I would be reluctant to crossover below 2khz.

The other tweeter (DX25TG-05-04) is a 4 ohm tweeter. For some reason I though RWO was trying to build a TMM or MTM speaker which is why I thought a 4ohm tweeter would work. Though if you are building at straight forwards 2-way woofer/tweeter speaker an 8 ohm version of the tweeter would be better.

Again, if you can't find a project that matches your need exactly, you can do well with some free speaker design software.

Alternately abandon the idea of using Vifa speakers, and find a speaker design close to what you want and use the speakers it suggests.

The zaphaudio.com site has several. You can also find projects at Parts Express -

http://www.partsexpress.com/projects...ojectindex.cfm

and many other sites.

Consider this Parts Express project -
http://www.partsexpress.com/projects...cfm?project=vd

If other could recommend their favorite project sites that would be a big step in the right direction.

Sorry I can't be more help.

steve/bluewizard
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Old 24th February 2008, 04:47 PM   #8
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I'm surprised more people aren't responding, it seems like a prefectly reasonable question.

Here are some links to additional project sites.

Humble Homemade HiFi-
http://www.humblehomemadehifi.com/

Troels Gravesen -
http://www.troelsgravesen.dk/Diy_Lou...r_Projects.htm

Of course-

Zaph Audio-
http://www.zaphaudio.com/

And-

Parts Express-
http://www.partsexpress.com/projects...ojectindex.cfm

The above are trusted and proven design, and are frequently used by beginners.

Below are randomly selected websites from a search of Google.

A simple search of Google turned up these websites-

Search for 'DIY speaker projects'.

Audio DIY Central-
http://www.audiodiycentral.com/g_s_1000.shtml

DIY Speaker Projects-
http://www.cross-spectrum.com/audio/myspeakerproject/

DIY Audio Projects-
http://diyaudioprojects.com/Speakers/speakers.htm

DIY Speakers-
http://www.diyspeakers.net/projects.php

RJB Audio- (**looks good)
http://www.rjbaudio.com/projects.html

Hope that leads you to something you can use.


Steve/bluewizard
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