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building an audio crossover

flippityflop

Feb 2, 2014
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i want to build an audio crossover and by the small amount of reading that i've done online, the most desirable crossover topology is the 4th order Linkwitz-Riley. linear gain in wide ranges, better Q, responsiveness, so forth...

so i found this 4th order LR crossover online http://sound.westhost.com/project09.htm. i'm building the one that separates the signal to 3 passes (hi/mid/low).
p09_fig1b.gif

(i'm thinking of further filtering the mid in the future, but that'll have to wait until the whole speaker system is finished.)

anyways, there are a few things that are not clear to me. the author, mentions that the passes may be a bit of out-of-phase, BUT it's very small, etc... but then i saw that he also provided a small buffer circuit for each signal. so i was wondering:
p09_fig3.gif


1.) can the same buffer circuit can be used to insert a delay in each signal line, so they can be adjusted to be completely in phase with each other (or maybe i'm just getting the concepts from digital circuits mixed-up). i'm no electronics engineer. if not, is there any cheap buffer design out there that might do??
i know that i would be needing an oscilloscope for this (which i don't have, but i'll be putting one together in the coming months). but for the mean time, i might have to do it by ear... or maybe the close tolerances of the parts that i would purchasing online would be good enough that won't be able to hear it in any case.

2.) what are the best cut-off frequencies for high-pass, band-pass, low-pass to drive speakers. i think it might also be a matter of the quality and make of the speakers. so just give me the general values (20-500Hz/500-5000Hz/5000-20000Hz)??
 

Arouse1973

Adam
Dec 18, 2013
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I would add another upper voice speaker as I think you have already mentioned. The cut-offs below are a good starting point which you can adjust for your preference.

Bass 90-120Hz
Lower Voice 120Hz-500Hz
Upper voice 600Hz-4Khz
Tweeter 4Khz-8Khz

As always the author doesn't show the power supply connection. Looking at the connections I think he is using +/- supply. If you are planning on using a single supply you might want to modify your circuit. See diagram attached.

Adam
 

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flippityflop

Feb 2, 2014
13
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Feb 2, 2014
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I would add another upper voice speaker as I think you have already mentioned. The cut-offs below are a good starting point which you can adjust for your preference.

Bass 90-120Hz
Lower Voice 120Hz-500Hz
Upper voice 600Hz-4Khz
Tweeter 4Khz-8Khz

As always the author doesn't show the power supply connection. Looking at the connections I think he is using +/- supply. If you are planning on using a single supply you might want to modify your circuit. See diagram attached.

Adam


sorry, the attached diagram is a sallen-key high pass filter, right?? so should i just substitute that for the high pass filters of the linkwitz-riley?? or is that the phase shifting buffer that i'm asking for??

about the power supply, the author mentioned he was using a +/-15V (does the -15V refer to it being lower than "ground"??). he also provided the schematics for a power supply: http://sound.westhost.com/project05b.htm . but i think i'm just gonna purchase it online from ebay. i'm sure it'll easy to a good and cheap one there. this crossover, though, i'm building myself...
 

Arouse1973

Adam
Dec 18, 2013
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Your diagram is sallen key. You don't need to do anything just if your using single supply just follow my design.
 

flippityflop

Feb 2, 2014
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Your diagram is sallen key. You don't need to do anything just if your using single supply just follow my design.

oh... i misunderstood the purpose of the diagram you provided. yes, i know how to connect a generic opamp to the power.

800px-Generic_741_pinout_top.png

pin 4: -V
pin 7: +V
i've experimented with a few before. needless to say i busted a couple too (overloaded current from feedback).

it's a sallen key?? i was under the impression it was LR... or is it a combination?
 

flippityflop

Feb 2, 2014
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anyways, i did a few modifications. i'm purely an amateur in designing circuits... the most i could do is follow directions written in the datasheet. here it is:

ag1c.png



i've tweeked some of the values to my intended ranges:
high pass: 3000-5000 (4000-higher) Hz
low mid pass: 3000-5000 (4000) Hz
high mid pass: 90-150 (120) Hz
low pass: 90-150 (120) Hz
i've also made them overlap on their boundaries lower and higher by about 25%. i've chosen overall slightly higher capacitances to prevent too much sensitivity from stray capacitance. i've also made the resistance for the higher frequencies lower, so that it wouldn't be attenuated.


there most likely are not ganged potentiometers of:
2 - 2.5k ohms/2 - 5k ohms
4 - 2.5k ohms
2 - 5k ohms/2 - 10k ohms
4 - 100k ohms.

but piher manufactures potentiometers with detachable shafts:
pt15nv%205k.jpg

i figure i could just insert a long shaft or something, going through several of these potentiometers. voila! now i've got meeself a custom ganged potentiometer. unfortunately, piher aren't not that big yet, so not many north american suppliers carry them.

another option is to buys these potentiometers (categorized as trimmers in digikey, though i think they're quite big to called "trimmers"), which are similar. i bet i could do the same here:
201X%20SERIES.jpg
 
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Arouse1973

Adam
Dec 18, 2013
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LR, what inductor and resistor? It has all the looks of a high pass Sallen and key filter, probably Butterworth response.

Adam
 

flippityflop

Feb 2, 2014
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LR, what inductor and resistor? It has all the looks of a high pass Sallen and key filter, probably Butterworth response.

Adam


what?? active filters don't have inductors --- in any case... so LR, being an active, never have inductors. so you can't say that just because it doesn't have inductors, it's not LR.

btw by LR it means "Linkwitz-Riley filter"

i didn`t keep on writing "Linkwitz-Riley", because i know people will default in the type of thinking, "oh, Linkwitz is german!! so that's why he favors the design! makes sense!".

these days i keep finding myself more and more needing clarify what i mean
 
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davenn

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another option is to buys these potentiometers (categorized as trimmers in digikey, though i think they're quite big to called "trimmers"), which are similar. i bet i could do the same here

they are called trimmers because they are defined as trimpots, where they are set and forget, ie. they are not constantly adjusted
Trimpots vary in size from a few mm for surface mount ones up to ~ 1cm (10mm) as in those 2 that you showed above

Dave
 

flippityflop

Feb 2, 2014
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they are called trimmers because they are defined as trimpots, where they are set and forget, ie. they are not constantly adjusted
Trimpots vary in size from a few mm for surface mount ones up to ~ 1cm (10mm) as in those 2 that you showed above

Dave


shouldn't have said that friendly side comment... starting to say too much again....
 

bertus

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Nov 8, 2019
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Hello,

No, the site where the images where linked to, has moved on the internet.

Bertus
 

WHONOES

May 20, 2017
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I would suggest that you read Don Lancaster's book "The Active Filter Cookbook". It tells you all you could want to know about active filters and comes down on the the side of the "equal value component Sallen - Key" topology.
As for designing a practical speaker, regardless of whether you use a passive or active design you must read " The Loudspeaker Design Cookbook" by Vance Dickason.
There is much to learn before you embark upon this project.
BTW, you should not be considering overlapping filter boundaries by 25% as this will cause some considerable lumps and bumps.
 
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