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X1 Highpass Filter |
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matttcattt 
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Joined: 21 April 2004 Location: United Kingdom Status: Offline Points: 106 |
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 Topic: X1 Highpass FilterPosted: 20 September 2004 at 9:38pm |
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I know the X1 design should be crossed over at 80Hz, but does it require a high pass filter (at 30Hz for example) to protect the driver from really, really low bass that could cause the driver to (forgotten the proper technical word) "go too far" and damage itself?
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(and my own bit) If it is broke, fix it. (and more) If you can't fix it, take it apart and see how it "worked". |
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whitehousejamie
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Joined: 08 March 2004 Location: United Kingdom Status: Offline Points: 1485 |
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Posted: 20 September 2004 at 9:56pm |
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Ideally, yes.
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JD01
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Joined: 23 August 2004 Status: Offline Points: 819 |
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Posted: 21 September 2004 at 11:38pm |
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But don't use TOO high slopes for the high pass. High slope filters at that low frequencies will give tremendous group delay.... |
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matttcattt
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Posted: 22 September 2004 at 12:08am |
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What would the ideal frequency/slope be? I would think, as the response of the X1 stops at 30Hz, somewhere between 20 and 30Hz and a slope of 6 or 12 db/octave?
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If it aint broke, don't fix it.
(and my own bit) If it is broke, fix it. (and more) If you can't fix it, take it apart and see how it "worked". |
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loophole
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Posted: 22 September 2004 at 12:13am |
does this apply on digital LSM systems too? if you applied different slopes to the bass and subbass hi and low passes would there be an effect to the g.d. of one band relative to the other |
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Dom
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Joined: 25 February 2004 Location: United Kingdom Status: Offline Points: 1700 |
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Posted: 22 September 2004 at 8:29am |
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Yes... You have to remember that every 6db of crossover you add moves the phase back 90 degrees... If you have say 24 high pass on your subs and an 18db low pass on your bass, they will be 90 degrees out of phase at the crossover frequency... You can correct for this on an LMS though... |
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JD01
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Posted: 25 September 2004 at 12:21am |
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You can correct the 'phase pushing' electronically, but you can't undo the delay the crossover introduced. Asymmetrical filters are 'no good'. Filters should always be acoustically symmetrical. If not you can't get flat response around the crossover frequency. Symmetrical means that if you have a 24dB LR highpass for your mids you should have an according 24dB LR lowpass for your subs. If your top does a 12dB/oct. roll off at 120Hz and you want to cross over at 120Hz it would be a good idea to use a 120Hz 12dB Butterworth highpass for that top and a 120Hz 24dB LR lowpass for the subs (just as a starting point). You can of course set a 12dB hp at 30Hz and a say 24dB lowpass at 80Hz for your subs. The lowpass and the highpass for the same band do not need to be of the same slope and chracteristic. Crossing over below 80Hz to another sub, like X1 from 30 to 60Hz and HD15 from 60Hz up I also would recommend to stick to lower slopes like 18dB or even 12dB. 12dB LR could be a good thing then. Every filter will introduce more delay..... the higher the slope, the more.... |
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Timber_MG
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Posted: 25 September 2004 at 9:50pm |
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One has to considder the acoustical slopes of the cabs and see the
final filter as an addition of the electrical and acoustic components.
asymetrical filters have their place and not all filter stages have to
have the same frequency (though not many controllers allow for this)
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matttcattt
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Posted: 26 September 2004 at 9:02pm |
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Ahhhhh! I just typed in this post and it lost it all and told me I needed to log in! I'll try again... My planned system includes 2 X1's and 2 X15's per side. I am currently thinking about the crossovers. I am planning to build my own crossovers rather than buy a controller. If I have an 80Hz lowpass and a 30Hz highpass filter for the X1's, a 2kHz lowpass and a 80Hz highpass filter for the SN 15 MB, all at 12db/oct and a 2kHz highpass filter for the SD 740 N at 24db/oct, will all the drivers be in phase and have the same delay? |
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If it aint broke, don't fix it.
(and my own bit) If it is broke, fix it. (and more) If you can't fix it, take it apart and see how it "worked". |
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Dom
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Posted: 26 September 2004 at 10:24pm |
No is the simple answer.... You will get a delay around the ports on the X1. You will need to delay the SN15MB to get it in time at the crossover point. You will then need to delay the SD 740N by the same amount +/- the distance behind/in front the compression driver is than the mid cone. Obviously this will depend on which horn you've used... Because you've used a 12db low pass on the mids and a 24db highpass on the tops, they will be 180 degrees out of phase at the crossover point.
Best bet is either use some test tones at your crossover points and set the delays by ear or download smaart from siasoft and let your computer do all the hard work for you... |
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matttcattt
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Posted: 27 September 2004 at 12:04am |
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How much will I need to delay the SN15MB's? I havent actually built anything yet, but I am planning on using the horn. How do I work out how much to delay the SD 740N's by? I havent actuall used anything yet. Wont the two 12db/oct filters in series have the same effect as the one 24/oct filter? |
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If it aint broke, don't fix it.
(and my own bit) If it is broke, fix it. (and more) If you can't fix it, take it apart and see how it "worked". |
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JD01
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Posted: 29 September 2004 at 2:47am |
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@ Timber_MG: That's why I said 'have to be ACOUSTICALLY symmetrical'. That does not necessarily mean 'electronically symmetrical and at the same frequency'.... @ Matttcattt: Even if you leave out the group delay each speaker produces, the answer would be no. That's because you have a highpass and a lowpass on each band (except the HF output which doesn't need a lowpass), but the delay caused by the highpass for the subs won't affect the MF output. So if you have 15ms group delay for the subs highpass and 8ms for the subs lowpass this adds up to 23ms, but a symmetrical highpass for the MF would only show the 8ms...... The only REALLY WORKING way would be to measure the delays. Calculating those values is too complicated by far.... But at least in the bass range a good guess can do better than running without setting delays at all.... |
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JD01 wrote: