two way design, first project

[dj_smilee]

This is effectively my first scratch build of a speaker system. I'm downsizing from a pair of Cambridge R50 TL clones, to a sub and two smaller speakers. The sub is a seperate project for now; a TC Sounds 15" TC2000 in a LT'd sealed box. I plan to cross the sub actively to the mains at around 50hz, this will depend on the mains capabilities I guess...

For the mains i've got a pair of Visaton GF200 8" woofers and Vifa D27TG-35-06 tweeters.

Visaton Specs
Vifa Specs

Looking at the drivers responses, It looks like the XO might be around 2khz, however I know very little about XO design.

It would be nice to build the main enclosures as to offer a better bass response when not in use with the active crossover/sub config. However integration with the sub is more important at the moment, I figured a box F3 of 50hz would be practical. Is this possible in a sealed enclosure? I'm thinking simple standmount monitor, size isnt too much of an issue but smaller the better

As for woodworking and electronics experience, I can get my head round tutorials quite easily. building the boxes and crossovers should be painless(ish!) I just need some design ideas to get the ball rolling! thanks!

[PeteMcK]

Have a look at the enclosures the GF200 is used in on the visaton page, plenty of clues there for how to proceed;
the VIB 2000 GF is a 2-way.

Pete McK

[tade]

take the step initially and go active with your crossover. With this in mind you can incorporate your LT for the sub. You could even LT sealed monitor cabinets which could be advantageous because the LT is supposed to improve phase performance as well as extend bass response. Then you must establish the acoustic behavior of the drivers in question. ie, the acoustical rolloff will sum with the electrical so taking the acoustic response into effect is key. It is regarded that leaving an octave on either side of the crossover point of smooth FR will keep things safe though in the case of large peaks such as break up, more attention must be paid.

My next project will be to LT my sealed subwoofers. an extra octave of superb bass, yay!

[Jay_WJ]

Why not first model a box using Unibox at FRD Consortium? From the spec, I think this woofer will require rather large a box even with a sealed design. F3 of 50 Hz is not necessary if you use a sub with them. A sealed design will integrate better with your sub.

For XO, I'd try asymmetric Likwitz-Riley acoustic 4th order crossed at around 1800 Hz. Lower XO point is better for an 8" woofer.

[dj_smilee]

Time to update on whats happening! My original intention was to build a sub and monitor pair to use together for music production. Well I've built the sub, crossed it over and EQ'd it with a linkwitz transform and its a monster. however its enormous, along with the crown amp to power it. I'm going to stick to a pair of full range speakers for the music production and leave the sub for foundation demolition or something... (pic included for good measure)

Have a look at the enclosures the GF200 is used in on the visaton page, plenty of clues there for how to proceed;

Thanks for the tip Pete, their design includes a crossover network set at 2.5khz with a parralel resonant circuit to flatten the midrange. I dont know what order or type their crossover is, could someone elighten me?
Visaton suggested crossover

Their design would work ok, as my tweeter matches the sensitivity. However the GF200 seems to break up immediately after 2.5k.. and my Vifa tweeters can go much lower than the visatons.

So would it be easy to modify it to cross at a lower frequency? Could i get away with a 1.8 cross?

As for the cabinets, i'm aiming around 35 litres in a ported alignment. I may try a slot port too as KRK use on their monitors.

[PeteMcK]

electrically, tweeter xover is 3rd order (although it looks like the 6.8 ohm resistor is tweaking the slope a little); woofer is 2nd order with notch as you note;
I should be easy to cross over a bit lower, maybe even tweaking one of the components in the woofer xover will get you what you want (the 33u cap a bit larger? )
You would need to recalculate the tweeter xover parts values for the impedance of the vifa tweeter at the xover point anyway

cheers,
Pete McK

[Inductor]

Hi,
Nice design for an old school 2-way, I guess. Well maybe not since you are using a double voice-coil with the Visaton GF 200. You could test a 1200Hz xover (+/-) for that effect dj.

Conservative upper limit is for a 8" 1,23K. Keep in mind that this will cut the voices mid-band in a half, this is just for purists. Highest recommended frequency with this woofer will be the band 1-2k, because of break-up as you said and there is enough room to play.

note: Svante do you remember if the parameters for this GF 200 are right from their website Visaton factory work sheet (?), I remember they messed with parallel and series connections.

[Inductor]

The D27TG-35-06 and D27TG-45-06 spec a lower 650 Hz resonance, which should make crossover design less critical.

Warning! My respondents tell me that the Fs of current production units consistently measures around 850-950 Hz. The difference is enough to require a completely different crossover design. These units are therefore only conditionally recommended!

in "Driver recommendations - Vifa"
http://ldsg.snippets.org/vendors/vifa.php

it's always the same... %&/($)/ new drivers from China. They are not even measured in the factory, unless they run out of ferrofluid ?!...

dj do you have the new kit from PE to measure impedance vs frequency in speakers?

[dj_smilee]

The only measurement tools I have are a digital multimeter and an oscilloscope. I've not looked into measuring impedance before..

I bought the tweeters approximately 2 years ago, perhaps they're not the chinese ones?

2-way designs with 8" woofers can't be terrible as Visaton offer the GF 200 in such a config. I know of many studio monitors with 8 inchers too...

Rod Elliot's pages have some useful information on passive xover design that I can understand. Its probably easier to design the xover from scratch than modify Visaton's suggested plans. If the Vifa's Fs is 650 then a 2nd order at 1.8khz seems reasonable.
I only bought the GF200's because I got them very cheap, if I could get a pair of P13's that'd make an awesome 3-way, but i'm quite determined to nail a 2-way design.

[Inductor]

Originally posted by dj_smilee
If the Vifa's Fs is 650 then a 2nd order at 1.8khz seems reasonable.

I think the problem here was originaly the ferrofluid. (Again, I can be wrong.)
Type 1 w/out ferrofluid fs=1000Hz and type 2 with ferrofluid fs=650Hz.

The type 1 ones: D27TG0506, D27TG1506.
The type 2 ones: D27TG3506, D27TG4506.

They are used in various set-ups like Kefs and other pro stuff. You will be fine.

We should try 2 or 3 different set-ups/x-overs (and be patiente) before some good results.

Now if you agree (I don't want to be pretencious here) I would make a first shot on a 1.order/3order x-over and if "I" would not like it (meaning you) or you found it unreasonable we would then change it for a 1.order/1.order or 2.order/2.order. There's plenty of material to work on. But probably I would finish with 2 x-overs at the end to chose from or something similar.