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Old 22nd November 2005, 09:13 PM   #1
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Default Filter Questions/Suggestions for a Bi/Tri-amped System

Hello

I have been searching and simulating for a while on active filters, especailly those Linkwitz-riley and bessel, I was surfing in www.linkwitzlab.com and www.sound.au.com. I think its time to crystallize my thoughts now..

Any way, I have two 12" loudspeakers which are best dedicated for midrange audio spectrum, and two 4 Ohm tweeters, those types which have a coil, means no peizo, cuz I don't like the way it sounds. I will buy th subwoofer later on, while discussing this system on the forum..

If I want to build 4th order LR HP filters based on Rod's formulas, and use a cut-off frequency of 250Hz, or 310Hz. And build a 4th order LR LP filter which sums the L & R channels, and has variable gain circuit based on an opamp like that described in linkwitzlab, also will have a cut-off frequency which is the same as that of LR HP filter. I am aware of the fact that I will have to use Linkwitz transform circuit if I use a closed box for the sub, and may be the sub controller in Rod's pages, so I will not use the 4th order LR LP filter with the later configuration.

Now, the sub will have its own enclosure, but I still don't know which to use, clsed or veted box, and the two 12" speaker + tweeters will be fitted in separate closed enclusures, each closed enclusure will contain a 12"speaker and a tweeter.

I was wondering if I use a 2nd order passive LR HP filter for the tweeters at 4Khz or 6Khz, because I am still afraid that tweeters may be at risk when I have the cutoff frequency of the LR HP active filters at 250Hz or 310Hz . Would that bring problems to my new Bi-amped system if I use passive filters with the LR active crossovers.

I already have 10s of amplifiers ready to pump, ranging from 20 watt to 200 watt, but I only want to apply Bi-amping to my new audio system, although I could use three-way active filters, but this will increase the wiring work, don't care about the cost though, I don't know, may be there is somebody who can bring a better idea justifying that a Tri-amped system is much better, and has more details in the sound.

Also I need a calculator software to make the 2nd order LR passive filter.

Another thing, I saw that Linkwitz uses delays in his crossover circuits, especially at the HP LR filters, shall I worry about that too, in case I go to Tri-amped system, and shall I worry about it if I am still going for Bi-amped system . Also can you guys suggest something practical about power distribution in both Bi-amped, and Tri-amped systems. I am still doubted about the sut-off frequency in deed, though I feel its ok, but deeply, I don't feel its ok.

Thanks in advance
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Old 22nd November 2005, 09:44 PM   #2
Keld is offline Keld  Sweden
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Hi
Have you considered buying a digital xo like the DCX2496 ?, then you can try out various orders, gain, delay and xo frequencies.
after trying out the best configration you can build a "supercircuit".
and if you dont want the DCX after that you can allways sell it (cheap)to me. I want one more
DVC Keld
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Old 22nd November 2005, 10:04 PM   #3
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Hi

Simply NO, cuz I don't know where to get that digi thingy from, if you want more filters, I can sell them to you readily assembled on vero boards, but without opamps

I still have the option to experiment using a breadboaord...

Any way, I have tinned and green masked vero boards which are more useful and trustable than the ordinary non-tinned. They cost me 2.75$ each

I think I like this one , as it seems alot impressive to me in deed, but won't build them as I don't know how to make it two-way, also linkwitz seems to have optimized this three-way crossover for a specific speaker system.

I will post my schematics later
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Old 23rd November 2005, 08:16 PM   #4
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Hi

Where are the audio monsters ??
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Old 24th November 2005, 12:07 PM   #5
sreten is offline sreten  United Kingdom
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Default Re: Filter Questions/Suggestions for a Bi/Tri-amped System

Quote:
Originally posted by metal

I was wondering if I use a 2nd order passive LR HP filter for the tweeters at 4Khz or 6Khz, because I am still afraid that tweeters may be at risk when I have the cutoff frequency of the LR HP active filters at 250Hz or 310Hz . Would that bring problems to my new Bi-amped system if I use passive filters with the LR active crossovers.
Thanks in advance
They most certainly would be at risk without the passive crossover,
which should not affect the operation of the active crossover.

Quote:
Originally posted by metal

IAlso I need a calculator software to make the 2nd order LR passive filter.
Thanks in advance
http://www.mhsoft.nl/spk_calc.asp

Though reality is a little more complicated ........
Its highly unlikely a standard LR c/o will suit your drivers.

Quote:
Originally posted by metal

Another thing, I saw that Linkwitz uses delays in his crossover circuits, especially at the HP LR filters, shall I worry about that too, in case I go to Tri-amped system, and shall I worry about it if I am still going for Bi-amped system . Also can you guys suggest something practical about power distribution in both Bi-amped, and Tri-amped systems. I am still doubted about the sut-off frequency in deed, though I feel its ok, but deeply, I don't feel its ok.
Thanks in advance
More advanced c/o design that the above link takes into account
driver amplitude response, phase response, and mounting effects.

The power distribution depends somewhat on the relative efficiencies
of the sections you are driving, but for c/o points of 300 and 3kHz i'd
say ~50% bass, ~30% midrange, ~20% treble.

/Sreten.
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Old 24th November 2005, 11:13 PM   #6
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Default Re: Re: Filter Questions/Suggestions for a Bi/Tri-amped System

Quote:
Originally posted by sreten


They most certainly would be at risk without the passive crossover,
which should not affect the operation of the active crossover.
Thats good news but...

Quote:
Originally posted by sreten


Though reality is a little more complicated ........
Its highly unlikely a standard LR c/o will suit your drivers.
Could you explain more please...I don't get it, is it better to go Tri-amped instead of Bi-amped and using 2nd or 4th order HP passive LR filter..also did you mean I have to make advanced measurements for the drivers to find out which c/o frequency to use...

Quote:
Originally posted by sreten

More advanced c/o design that the above link takes into account
driver amplitude response, phase response, and mounting effects.
I found that to be the case while I was reading the explainations about that crossover network, the guy did really hard work, then I will have to measure alot here and there...to find my speakers Fs, Qts, and Vas.......also may have to use TrueRta to measure responses, unless there is a better software

Quote:
Originally posted by sreten

The power distribution depends somewhat on the relative efficiencies
of the sections you are driving, but for c/o points of 300 and 3kHz i'd
say ~50% bass, ~30% midrange, ~20% treble.

/Sreten.
That seems reasonable and logical, thanks
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Old 25th November 2005, 08:48 AM   #7
sreten is offline sreten  United Kingdom
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Default Re: Re: Re: Filter Questions/Suggestions for a Bi/Tri-amped System

Quote:
Originally posted by metal

Could you explain more please...I don't get it, is it better to go Tri-amped instead of Bi-amped and using 2nd or 4th order HP passive LR filter..also did you mean I have to make advanced measurements for the drivers to find out which c/o frequency to use...
Hi,

hard to say which is better - depends on circumstances.

Regarding c/o design - say your target is 4th order L/R
acoustic response for the mid/treble crossover.

This cannot be implemented by an off the shelf c/o, to achieve
this design goal the c/o must be exactly matched to the drivers
when they are mounted in the final enclosure - not easy.

/Sreten.
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Old 25th November 2005, 09:05 AM   #8
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I'd also add that a summed sub channel going as high as 300Hz is going to not be good for the stereo image. You want a summed channel to be 100Hz or lower really. If you must cross that high then use stereo subs.

I also question why you are trying to use 12 inch speakers as mids, but also crossing them far too high for high fidelity. Are you building a PA system?
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Old 25th November 2005, 10:45 PM   #9
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Hello All

In deed, I was amazed this morning, I used STK4191V @-/+ 36 Volts, and wanted to test the two 12" speakers to see where to choose the cut-off frequency. I used TrueRTA, I started from the lower end @ 20Hz, and put a 1K resistor in series with one of the speakers, and started measuring the voltage drop across that resistor to see where I get the highest voltage drop at the first lowest frequecy while sweeping, I got that at 565Hz, but I still can find that there are dips and peaks in the speaker response at many different frequencies, any way, that will not work.

Thanks to David B. Weems book "Great Sound Stero Speakers", I saw that he explained how to measure Fs, Qtc, and Vas of a speaker, I will apply these tests to the two 12" speakers, and start designing a closed box for them, may be not !!

I also read in another book that its best to have two bass woofers, and be able to sum their inputs to have a mono bass output which means you can have stereo or mono bass output, thats because if you are watching a movie, then you switch to mono, saying that the results are much more thundering rather than a stereo when listening to horses or gun shots, while for music, you beter switch it to stereo. And as richie said, that filter was far below 100Hz, it was tuned at 70Hz, thats correct richie, thank you

Any way, returning to the 12" speakers, I removed the 1K resistor, and started listening, what the hell I was trying to do man, it seems If I use these speakers, I will end up with a PA system, the sound was too loud, and I had to close my ears, becasue I could not stand both the High-end bass, neither the mids I concluded that I have high SPL speakers, any way, that STK was barely hot, even whan I drove the speakers very loud, till I really could not stand it, and got out of the room to listen.

In deed I am almost lost now, I think I will have to go for 8/10" speakers, put them in a closed box, and use 12" subwoofer @ cut-off frequency @ 100Hz as richie said, as I don't need a PA system in my room, so at last, I will be kicked out, as was gonna happen today, when police came asking who is the hell was playing too loud, neighbours were just sick of it Also I will use STK4191V for the sub, bring two other STk4161V/4141V for the speakers and tweeters respectivelty. I don't know, may be you guys have some thing else to say


Quote:
This cannot be implemented by an off the shelf c/o, to achieve
this design goal the c/o must be exactly matched to the drivers
when they are mounted in the final enclosure - not easy.

/Sreten.
That seems to demand lots work and measurement, but does it really worth the try Streten, I don't know, it seems I am too lazy to do that
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Old 26th November 2005, 08:55 AM   #10
AndrewT is offline AndrewT  Scotland
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Hi,
I agree with the other poster.
That gap between the tweeter and 10inch mid needs to be filled in with a more appropriate mid. Maybe in the range 4inch to 6inch.

This then makes it a 4 way system, allowing you to dedicate the sub to real sub duty say up to about 120Hz.

Can I suggest you build the system as active initially using a DCX2496 to select all the parameters, then sell it on and use the data to generate the active or passive crossovers.

If you go the passive route then also consider using an amplifier dedicated to each driver and its crossover section. (bi-amping or tri-amping in the UK)
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