3-way + sub woofer near field "mid" to HI-FI PC speaker system - diyAudio
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Old 9th September 2008, 11:36 AM   #1
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Lightbulb 3-way + sub woofer near field "mid" to HI-FI PC speaker system

I manage to get a few magnetically shielded speakers from two pairs of (plastic :X ) powered PC speakers.

one of them were 2-way (passive capacitor crossover) and the other were full range.
all the speakers have 4ohm nominal impedance and about 8W rms on the small 3.5" woofer, 5W rms on the 2" full range (for the mids) and enough power in the (about) 1.5" tweeter Cheesy For the sub I will be using a 10'' about 30Wrms bass woofer (possibly) in a sealed box.

My Intention: Make a 3-way + sub woofer near field "mid" to HI-FI PC speaker system.

for the sub it will be the plain n' simple active crossover & independent amp.
for the speakers I want to make an (temporary) passive crossover network because later on (if the speaker design fits the eye and ears) turn the system into an active 3 way + sub speaker system! Cheesy (since the power is low and really near-field it would not be very hard to make...)

so I want help in the cross over... I need a program or a tutorial in How to calculate & build a crossover

the details on this crossover will be simple since I don't have the parameters of the speakers, the design will mind the nominal impedance and the cut frequency only.
since the mid-range is a full-range, I can push the mid down to 200Hz flat Cheesy
My goal in the crossover is a 3Khz and around 230Hz cutoff at 6dB per octave (since being a near field a 12, 18 or 24dB per octave would be to harsh.)

for the box I will use WINISD (or, if any better tell me! Cheesy)
and to get the parameters I will use the information in ESP (website) articles (http://sound.westhost.com/tsp.htm) to get the T/S parameters and design the box better.

for the box I will use (heavy) medium density fiber board (MDF) to be able to round'en up the edges and make it look good! (since they are small I will be able to make them very neat ^^ )

for the power amp I'm looking at the LM1875 IC (http://sound.westhost.com/project72.htm) for the speakers it will do and for the sub (8ohm) an LM3886.

so for now I need help for the crossover... if anyone know how/were I could find help I would Really appreciate it!

thanks in advance!
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Old 9th September 2008, 11:19 PM   #2
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You're probably best to stick with a 2-way for nearfield.
Looks like you've come across some of these links, but here's my list:
Getting started in Crossover Design

The basics (You've got to understand the rules before you can break them :-)
http://sound.westhost.com/lr-passive.htm
choosing xover point:
http://www.speakerbuilder.net/web_fi...xpointmain.htm
Baffle Step Compensation: http://sound.westhost.com/bafflestep.htm

Getting it done:
Jay has a page on designing xovers using manufacturers specs without measuring:
http://www.geocities.com/woove99/Sp...DesigningXO.htm

Calculators:
http://ccs.exl.info/calc_cr.html#second
http://www.sengpielaudio.com/calculator-Lpad.htm

Measurement freeware:
Synrta - http://libinst.com/SynRTA.htm
ARTA http://www.fesb.hr/~mateljan/arta/download.htm
ARTA Jig - http://zobsky.blogspot.com/2008/01/s...t-jig-for.html

Examples from the designs of others can be quite instructive:
http://www.zaphaudio.com/
http://www.troelsgravesen.dk/Diy_Lou...r_Projects.htm
http://www.rjbaudio.com/projects.html
http://www.humblehomemadehifi.com/
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Impedance varies with frequency, use impedance plots of your drivers and make crossover calculations using the actual impedance of the driver at the crossover frequency
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Old 10th September 2008, 12:07 AM   #3
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Well! great! ^^ I'll check that and get in the way of things.
thank you!

I've been analyzing my mid-range and tweeter for better idea of their response and one thing I know... a 2 Way wont work... the mid-range does not respond well in high frequency and the tweeter could be better but I can't find a magnetically shielded one around so it will have to do.

the frequency of the crossover might just be around 300Hz and 4Khz since all the speaker sound better in that range... (sound level measurement and "quick" listen on harmonics with white & pink noise ant freq sweep.)

(I don't like it but...) later on I might make the system hybrid with bi-amping on the satellites and a passive crossover for the mid & highs...

having a active channel for this low power tweeter seems to me a bit odd
even so I'm wondering about it...
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