subsonic filter
500 Watt CAFz'r
Joined: Oct 2004
Posts: 870
Originally posted bt DWVW
Sorry DW...I missed that post.
Ok...let's stipulate that you don't really listen to much below 30Hz.
If you are inputting a 60hx signal into a sub, you would want the output to be exactly what you put in....60 Hz.
However if the woofer is moving relative to you at any speed, the sound that will reach your ear will be changed to a degree proportional to the difference in speed between the woofer and the listener.
If you also stipulate that frequencies below your set lower limit can get to the woofer, theose tones will cause the woofer to 'move" relative to you.
As the woofer approaches you, the frequency will rise, as the woofer recedes, the tone will lower.
If this happens at 20 cycles per second, then the 60Hz tone, although still 60Hz at the woofer, will be percieved as a varying tone at the listener, varying exactly the number of times per second of the subsonic note.
The principle is the same as the siren in the ambulance, first approaching you with a higher tone , then a lower tone as it recedes.
The ambulance driver however, never hears the change of tone, as he is moving along with the ambulance, and the siren's speed, relative to the driver, is zero.
Picture that ambulance doing laps around a track, while you sit in the stands, listening.
Although the input to the siren is constant, the output that reaches your ear will vary up and down in frequency at a cycle of laps/time as he either approaches or recedes from you.
The siren, and the woofer are exactly the same....a loudspeaker...except for the frequencies they play.
I had a thought that the "Doppler effect" would actually be included in the original recording, and to remove it might be an alteration of the original, but upon further reflection, I realize that although the mic used to record the 60Hz tone may have been moved by the 20Hz signal, the velocities, and excursion of the mic diaphram would be miniscule as compared to the 1" excusion common with most subs. I'm not too sure though, so perhaps someone with an engineering background could jump in. Perhaps it is all relative.
[ September 21, 2005, 12:24 AM: Message edited by: Car Trek ]
Car Trek, I am not sure what you are doing with all that math, it is impossible to play 64 Hz oscillating at 20 cycles. The very definition of 64 Hz is the sub is moving back and forth 64 cycles per second. .
Ok...let's stipulate that you don't really listen to much below 30Hz.
If you are inputting a 60hx signal into a sub, you would want the output to be exactly what you put in....60 Hz.
However if the woofer is moving relative to you at any speed, the sound that will reach your ear will be changed to a degree proportional to the difference in speed between the woofer and the listener.
If you also stipulate that frequencies below your set lower limit can get to the woofer, theose tones will cause the woofer to 'move" relative to you.
As the woofer approaches you, the frequency will rise, as the woofer recedes, the tone will lower.
If this happens at 20 cycles per second, then the 60Hz tone, although still 60Hz at the woofer, will be percieved as a varying tone at the listener, varying exactly the number of times per second of the subsonic note.
The principle is the same as the siren in the ambulance, first approaching you with a higher tone , then a lower tone as it recedes.
The ambulance driver however, never hears the change of tone, as he is moving along with the ambulance, and the siren's speed, relative to the driver, is zero.
Picture that ambulance doing laps around a track, while you sit in the stands, listening.
Although the input to the siren is constant, the output that reaches your ear will vary up and down in frequency at a cycle of laps/time as he either approaches or recedes from you.
The siren, and the woofer are exactly the same....a loudspeaker...except for the frequencies they play.
I had a thought that the "Doppler effect" would actually be included in the original recording, and to remove it might be an alteration of the original, but upon further reflection, I realize that although the mic used to record the 60Hz tone may have been moved by the 20Hz signal, the velocities, and excursion of the mic diaphram would be miniscule as compared to the 1" excusion common with most subs. I'm not too sure though, so perhaps someone with an engineering background could jump in. Perhaps it is all relative.
[ September 21, 2005, 12:24 AM: Message edited by: Car Trek ]
500 Watt CAFz'r
Joined: Oct 2004
Posts: 870
Irrelavent to what?
Please explain if you think I've made an incorrect statement or assumption.
I've simply submitted my theory as to one reason why ported boxes sound better with a subsonic filter than without.
Let's hear your side as to why you think it makes no difference.
Comparing a filter with obvious sonic benefits, to equal wire lengths(which have none) demonstrates your lack of understanding of basic physics....would anyone else care to comment?
[ September 21, 2005, 02:19 PM: Message edited by: Car Trek ]
Please explain if you think I've made an incorrect statement or assumption.
I've simply submitted my theory as to one reason why ported boxes sound better with a subsonic filter than without.
Let's hear your side as to why you think it makes no difference.
Comparing a filter with obvious sonic benefits, to equal wire lengths(which have none) demonstrates your lack of understanding of basic physics....would anyone else care to comment?
[ September 21, 2005, 02:19 PM: Message edited by: Car Trek ]
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Posts: n/a
Friend - I've taken my fair share of physics. Thanks for the concern though.
Your desire to microanalyze the totally inaudible distortion you are talking about is totally comparable to the inaudible difference equal wire lengths offers. Both are inaudible.
Would you like a diagram or something?
Based on your loose calculations a speaker should not be able to recreate any frequency with any practical accuracy as the same 'problem' of "doppler distortion" would occur throughout the spectrum when playing anything other than a pure tone.
So explain how not having that woofer moving 1" at 20hz solves the "problem" but having it moving 1" at 30hz isn't a "problem"?
The infrasonic filter, as already explained, was developed to combat low level rumble in analogue recordings. While digital recordings reduce this greatly there may still be substantial non-musical information that exists below the audible range. While this is inaudible, it does take power to reproduce it. An infrasonic filter blocks the hash and lets your system play the audible spectrum as it was designed.
I would LOVE to sit and switch a 20hz infrasonic filter in and out on any popular music and have you tell me, by ear, when it was on or off.
And yes - many "bass amplifiers" include "subsonic filters" for marketing purposes, not sonic ones.
Your desire to microanalyze the totally inaudible distortion you are talking about is totally comparable to the inaudible difference equal wire lengths offers. Both are inaudible.
Would you like a diagram or something?
Based on your loose calculations a speaker should not be able to recreate any frequency with any practical accuracy as the same 'problem' of "doppler distortion" would occur throughout the spectrum when playing anything other than a pure tone.
So explain how not having that woofer moving 1" at 20hz solves the "problem" but having it moving 1" at 30hz isn't a "problem"?
The infrasonic filter, as already explained, was developed to combat low level rumble in analogue recordings. While digital recordings reduce this greatly there may still be substantial non-musical information that exists below the audible range. While this is inaudible, it does take power to reproduce it. An infrasonic filter blocks the hash and lets your system play the audible spectrum as it was designed.
I would LOVE to sit and switch a 20hz infrasonic filter in and out on any popular music and have you tell me, by ear, when it was on or off.
And yes - many "bass amplifiers" include "subsonic filters" for marketing purposes, not sonic ones.
500 Watt CAFz'r
Joined: Oct 2004
Posts: 870
Alrighty then.
That's a good question....I don't think it is possible to perfectly reproduce sound from a loudspeaker....very close is the best we'll do with todays present technology.
That being said,
Lets say the sub you are using is ported nice and low at 30hz.
There is almost no excursion from the sub at this frequency, and almost all the energy is being emitted from the port(s).
As the input signal drops below the tuned frequency two factors occur.
First: the excursion of a driver is inversely proportional to the frequency....the lower it goes, the more it must move to achieve the same output.
Second: the driver "unloads" as the frequency drops below the tuned frequency, consequently experiencing much more excursion than it should.
Although the "doppler" will occur to a small degree at every frequency, it is only at the bottom of the spectrum that the distortion will exceed 1%(perhaps much more, but again I haven't done the math).
Distortion occurring at audible frequencies cannot be removed without losing audible information, but that IS irrelavent to whether or not a subsonic filter works.
There are varying opinions as to how much distortion is acceptable from a speaker, but most are that over 1% is audible in a full range, and over 5% in a sub.
The ability to perceive the difference is more often than not a learned skill.
Once I've shown someone what to listen for with, and without a filter, they almost always "get it".
I'd have no problem passing your blind test, as the difference is quite noticable. To be fair tho, the filter should be set a few Hz below the box tuning to achieve the desired results.
Most of my customers, and all my installers are quite amazed in fact, and would not go back to an unfiltered ported box.
[ September 21, 2005, 05:15 PM: Message edited by: Car Trek ]
That's a good question....I don't think it is possible to perfectly reproduce sound from a loudspeaker....very close is the best we'll do with todays present technology.
That being said,
Lets say the sub you are using is ported nice and low at 30hz.
There is almost no excursion from the sub at this frequency, and almost all the energy is being emitted from the port(s).
As the input signal drops below the tuned frequency two factors occur.
First: the excursion of a driver is inversely proportional to the frequency....the lower it goes, the more it must move to achieve the same output.
Second: the driver "unloads" as the frequency drops below the tuned frequency, consequently experiencing much more excursion than it should.
Although the "doppler" will occur to a small degree at every frequency, it is only at the bottom of the spectrum that the distortion will exceed 1%(perhaps much more, but again I haven't done the math).
Distortion occurring at audible frequencies cannot be removed without losing audible information, but that IS irrelavent to whether or not a subsonic filter works.
There are varying opinions as to how much distortion is acceptable from a speaker, but most are that over 1% is audible in a full range, and over 5% in a sub.
The ability to perceive the difference is more often than not a learned skill.
Once I've shown someone what to listen for with, and without a filter, they almost always "get it".
I'd have no problem passing your blind test, as the difference is quite noticable. To be fair tho, the filter should be set a few Hz below the box tuning to achieve the desired results.
Most of my customers, and all my installers are quite amazed in fact, and would not go back to an unfiltered ported box.
[ September 21, 2005, 05:15 PM: Message edited by: Car Trek ]
Originally posted by Eli47:
</font><blockquote>quote:</font><hr />Originally posted by Miluni:
Is this any different form the infrasonic filters that come with some amps?
Is this filter a good idea to have in a SQ car?
</font><blockquote>quote:</font><hr />Originally posted by Miluni:
Is this any different form the infrasonic filters that come with some amps?
Is this filter a good idea to have in a SQ car?
The correct term is "INFRA-SONIC" .(below hearing range of humans)
I know alot of people here have been in the industry for so long, you should know better than to go with the flow, and correct people that erroneously use the term "subsonic". (write your MLA, and senators to abolish this term in our industry.) </font>[/QUOTE]Hmmm, Straight from the dictionary.
sub·son·ic (sb-snk)
adj.
1. Of less than audible frequency.
2. Having a speed less than that of sound in a designated medium.
Therefore the amp manufacturers are correct in their terminology.
500 Watt CAFz'r
Joined: Dec 2000
Posts: 952
I don't know what dictionary you used, but Miriam-Webster http://www.m-w.com/cgi-bin/dictionar...onic&x=17&y=12 , defines it as;
Pronunciation: "s&b-'sä-nik
Function: adjective
Etymology: International Scientific Vocabulary
1 : of, relating to, or being a speed less than that of sound in air
2 : moving, capable of moving, or utilizing air currents moving at a subsonic speed
3 : INFRASONIC 1
- sub·son·i·cal·ly /-ni-k(&-)lE/ adverb
Main Entry: in·fra·son·ic
Pronunciation: "in-fr&-'sä-nik, -(")frä-
Function: adjective
1 : having or relating to a frequency below the audibility range of the human ear
2 : utilizing or produced by infrasonic waves or vibrations
Pronunciation: "s&b-'sä-nik
Function: adjective
Etymology: International Scientific Vocabulary
1 : of, relating to, or being a speed less than that of sound in air
2 : moving, capable of moving, or utilizing air currents moving at a subsonic speed
3 : INFRASONIC 1
- sub·son·i·cal·ly /-ni-k(&-)lE/ adverb
Main Entry: in·fra·son·ic
Pronunciation: "in-fr&-'sä-nik, -(")frä-
Function: adjective
1 : having or relating to a frequency below the audibility range of the human ear
2 : utilizing or produced by infrasonic waves or vibrations
Guest
Posts: n/a
Most people start hearing distortion at about 10% with a full range music signal. Like Paul said, if your theories were correct we would have some pretty lousy sounding audio. I mean why not just have tweeters playing, and let the distortion added from the speaker moving in and out take care of the rest of the frequency range?
