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Old 27th July 2008, 08:54 PM   #1
karmik is offline karmik  Italy
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Default Quality floorstanding 3way - Newbie Attempt

Hi, i recently gained the availability to use a pretty decent woodwork lab (but i have to do the work) and having already built some Fostex FE206 and FE126 based bookshelves, i want to make good use of the tools i now have.

I want a 3 way floorstander and i think i'm gonna use multi-layered birch (more durable than mdf and somewhat cheap here.) or something along that line.

I did search the forum but there doesn't seem to be a project that features readily available cones around here (Italy). I chose the cones for their price and their good brand name.

Of course, budget is something i have to consider (i'm not rich) but even something a little pricier than what i added here could be feasible. Other costs like work, wood, tools and everything shouldn't be a problem, the main expenses will be the crossover and the cones.

I've pretty good skills in realizing electronic boards (both cabled and printed circuit) but not having a solid math/electronic background i'm not able of designing my own crossover. A friend of mine offered to design it for me but not wanting to exploit his kindness too much i thought of figuring out the frequencies myself (along with the speakers i've chosen).

Any hint (or even total wreck of my dreams) will very appreciated.

The cones i was looking at were:

Tweeter Vifa DX25TG05 - http://www.audiokit.it/ITAENG/Altopa...X25TG05-04.pdf € 25,00 Cad.
My friend said i should look for linearity through out all the audible spectrum, so looking at the graphs for this tweeter, it looks like cutting it 2000 hz and above should be ok?

Woofer Peerless HDS 205 - http://www.audiokit.it/ITAENG/Altopa...sDK/830884.pdf € 74,00 Cad.
400 hz and below?

Midrange Vifa M10MD-39/08 - http://www.audiokit.it/ITAENG/Altopa...10MD-39-08.pdf € 48.00 Cad
Between those two? (400 hz and 2000 hz?)

*ANY* help is appreciated and i do realize i totally lack any theoretical knowledge. Thank you a lot!
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Old 27th July 2008, 09:58 PM   #2
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Looks like those speakers would work well together; the tweeter is 4 ohms, if you can get an 8 ohm version it might require less padding down; I'd probably cross over the tweeter higher...

there's a good primer on xovers here: http://sound.westhost.com/lr-passive.htm,
and read about BSC: http://sound.westhost.com/bafflestep.htm
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Old 27th July 2008, 10:09 PM   #3
tinitus is offline tinitus  Europe
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Default Re: Quality floorstanding 3way - Newbie Attempt

Quote:
Originally posted by karmik


*ANY* help is appreciated and i do realize i totally lack any theoretical knowledge. Thank you a lot!

You may find something here http://www.troelsgravesen.dk/Diy_Lou...r_Projects.htm anyway, find a proven design as its complicated to design a 3way, and how do I know, well I have used more than 5 years to make mine play
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Old 28th July 2008, 07:26 AM   #4
rabbitz is offline rabbitz  Australia
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I agree with tinitus.... go with a proven design. Believe me, 3-ways can be a nightmare to get right.

Another good source is http://www.humblehomemadehifi.com/

Don't get stuck on a 3-way. Keep your mind open as a good 2-way can out do an average 3-way.
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Old 28th July 2008, 04:16 PM   #5
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Consider also a TMM 2.5-way design - use two 6.5" - 7" woofers (same model), one plays mid & bass (no high pass filter as a dedicated midrange would have), the other (.5) is filtered lower to support the bass output - this filter can be a simple 1st-order (single inductor) or possibly 2nd order.

Simpler (cheaper) crossover design and similar results/performance to a 3-way w/ larger woofer. The .5 woofer can also be ported.
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Old 28th July 2008, 04:59 PM   #6
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As a newbie, go with a proven design or else get some good measurement and simulation software, good test mic and measurement rig and spend a lot of time learning how to do it well.
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Old 28th July 2008, 05:31 PM   #7
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I should have specified that I was recommending an established design when I pitched the 2.5-way - I just wanted to describe it to him so that he had some idea of what it was and how it would be cheaper to execute. I actually didn't have a particular design in mind to recommend, but I do suggest he visit

www.zaphaudio.com
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Old 28th July 2008, 06:22 PM   #8
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The www.audiokit.it site you posted sells a good range of drivers.

Build one of the existing designs at either of these sites. You should be able to source the parts you need from www.audiokit.it.
http://www.troelsgravesen.dk
http://www.zaphaudio.com

You cannot just pick some drivers and put together a 3 way if you have no idea how to design a speaker.

David.
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Old 28th July 2008, 09:27 PM   #9
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despite what the other guys have said, and it's good advice, I think you've made a good choice of drivers. We've all got to start somewhere...
The simplest way ahead is to design a 2 way with the mid and tweeter, (2nd order xover between 3-5Khz) following the instructions on Rod Elliot's site, and then add the woofer as .5 way (incorporating BSC into the xover inductor).
I think you'll have a system that is basically good, which you can tweak to your heart's content...
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Old 29th July 2008, 12:33 PM   #10
sreten is offline sreten  United Kingdom
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Quote:
Originally posted by PeteMcK
despite what the other guys have said, and it's good advice, I think you've made a good choice of drivers. We've all got to start somewhere...
The simplest way ahead is to design a 2 way with the mid and tweeter, (2nd order xover between 3-5Khz) following the instructions on Rod Elliot's site, and then add the woofer as .5 way (incorporating BSC into the xover inductor).
Hi,

0.5 way 8" woofer to a 4" midrange ? I do not think so ....
Rod Elliots primer is too simplistic, though it covers the basics
it does not cover the actual acoustic issues involved or the
correct way to cost effectively build a crossover.

The drivers are a reasonable choice and could be used for a proper 3-way.

http://www.rjbaudio.com/Audiofiles/FRDtools.html
http://www.geocities.com/woove99/Spkrbldg/

/sreten.
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