Hi-Vi F8, Vifa Pl27tg-35-06, crossover help! - diyAudio
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Old 20th January 2006, 09:28 AM   #1
crewsa is offline crewsa  United States
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Default Hi-Vi F8, Vifa Pl27tg-35-06, crossover help!

So here it is, I wanted to do my first true DIY home speakers. After some research and my desire to build an "easier" two way, I chose the Hi-Vi F8 mid/woofer and the Vifa PL27TG-35-06. I like the reasonably flat response of both and how they seemed to match up (overlap) around 2,200 Hz (on paper mind you). My question is, what would be the best kind of crossover for this combo. I was thinking a 2nd order linkwitz/riley on both drivers with a Zobel on the woofer and an adjustable 100w L-pad on the tweet. Anybody build this combo before and what woud be some good tactics for me to observe when building? Right now the cabinet is about done with the woofer setting about 3/4 inch further forward to better correct for acoustic center alignment of the drivers. I also will be using a 2" flared vent in a cab thats about 2,200in^3. I'm fairly new to this so any comments will be welcomed, especially recommendation for the crossover. Would a series crossover be better instead of the parallel one I plan on using?
crewsa
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Old 20th January 2006, 01:55 PM   #2
sreten is offline sreten  United Kingdom
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Hmmmm......

An easier two way ? what part of the easy bit am I missing ?

The easy way is build a well documented design with crossover details.

For what it worth :

The crossover must consider baffle step and possibly cabinet diffraction issues.

Parallel 2nd order crossovers are nearly always better than serial 2nd order.
(because they "short" the driver in the stop band)
Note this is just electrical 2nd order, the actual c/o will be a higher acoustic order.
You seem to planning an acoustic 4th order linkwitz riley.
You cannot achieve this without measuring or serious modelling.

The bass driver has a break up mode ~ 800Hz you can see as a dip on the response
curve and as a small peak on the impedance curve, no idea of its seriousness.

/sreten.
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Old 21st January 2006, 09:14 AM   #3
crewsa is offline crewsa  United States
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Oh sorry, I mean "easier 2 way" as in not a 3 way or higher. I'm guessing 2 ways are easier to perfect than 3 and 4 ways??

I can measure most of what I need to to get the crossovers reasonably correct. I can measure the Thiele/Small parameters of my drivers, I have access to an ocilliscope, volt/current/impedance/resistance/capacitance/inductance/frequency capable meter, and a dB meter too boot(cheapo radio shack digital). I guess what I'm asking is who has used these particular drivers together, what they did with them successfully and what they did wrong so I can know the quirks of this particular combo. Any comments are wecome though

BTW, I think Parts Express sent me two different model years (same model though) of the woofers I bought. There were slight physical and functional differences between the two. The fs of one is about 3-4 Hz higher than the other along with other measured inequalities(Zmax, Qts). As far as constuction goes, the tinsel leads on one driver has glue where they go into the cone and the other doesn't, the bolt holes are countersunk to different sizes (slightly), spiders are different shades of tan/yellow, etc. Maybe one cone is heavier than the other and consequently giving a lower fs? Maybe I'm just being overly picky on these points but I would like the drivers to be as close as reasonably possible.

Thanks for the reply Sreten, I guess I'll now have to build in the baffle step circuit too. Should I worry about tweeter impedance compensation too? I need to read up on L/R acoustic fourth order you mention. Does that mean the 2nd order nature of the crossover combined with the 2nd order cutoff nature of ported enclosures equaling a combined 4th order; or am I just missing the boat here?

Anywho, I'm just ranting. I can't wait till the boxes are done and I can start building and tuning the crossovers. I'll post pics of this first of many projects.
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Old 21st January 2006, 01:25 PM   #4
sreten is offline sreten  United Kingdom
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Join Date: Nov 2003
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Hi,

you'll find answers to your L/R questions and a lot more here :

http://www.zaphaudio.com/

/sreten.
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