Hello ppl,
This is my first post since july.
Skipped two jobs n now on my own again for some time to do all the DIYing I was supposed to do long back.
Now,
I am reading this bible by Vance Dickanson, n you ppl are gonna teach me a lot of technical stuff now. I will be quoting him n asking you ppl what it is. Please cooperate 🙂
A> "Closed boxes exhibit a fairly shallow rolloff of abt 12 db/octave whereas passive radiator designs have a 24 db/octave rolloff".
B> What is minus three decibel half-power frequency "f3".
These are for starters, more to come (tat depends). Hope no one gets bugged.
This is my first post since july.
Skipped two jobs n now on my own again for some time to do all the DIYing I was supposed to do long back.
Now,
I am reading this bible by Vance Dickanson, n you ppl are gonna teach me a lot of technical stuff now. I will be quoting him n asking you ppl what it is. Please cooperate 🙂
A> "Closed boxes exhibit a fairly shallow rolloff of abt 12 db/octave whereas passive radiator designs have a 24 db/octave rolloff".
B> What is minus three decibel half-power frequency "f3".
These are for starters, more to come (tat depends). Hope no one gets bugged.
Well, for question A. The rollof states how the speaker acts as the frequency changes. As it reaches the limit of the design, it 'rolls off' as the output gets weaker because the cabinet and driver don't work out of their range. How fast it rolls off is defined by the enclosure and sub parameters. In the sealed, 12db per octave means that by the time the frequency becomes half of the design rolloff, it'll be weaker by 12 decibels, which is a lot, being that 3db is a double in intensity. That 12db is four doubles in intensity, or halves. So in that 24db per octave box, you know that the working frequency of the speaker will cut off faster and more sharply.
Onto question B. Yes, the f3 point of the system, be it an amplifier, crossover, speaker, whatever. What this means is the frequency in the range of any system where the effective output is decreased by half.
An example, say I have an amplifier with a bandwith up to 200khz (I do actually have one of these) and say that its power output for the same input level is decreased by half when the input frequency is 160khz. This 160khz would then be the f3 point of the amplifer. Actually, it has two f3 points. There's one on the high end, and one on the low. Most amplifiers have a low end limit as well, to prevent DC from passing through. Say a common household amp has a low end f3 of 15hz or 20hz, therefore, the output would be half if the frequency became that low as well.
Actually, your ears have f3 points as well😉
Onto question B. Yes, the f3 point of the system, be it an amplifier, crossover, speaker, whatever. What this means is the frequency in the range of any system where the effective output is decreased by half.
An example, say I have an amplifier with a bandwith up to 200khz (I do actually have one of these) and say that its power output for the same input level is decreased by half when the input frequency is 160khz. This 160khz would then be the f3 point of the amplifer. Actually, it has two f3 points. There's one on the high end, and one on the low. Most amplifiers have a low end limit as well, to prevent DC from passing through. Say a common household amp has a low end f3 of 15hz or 20hz, therefore, the output would be half if the frequency became that low as well.
Actually, your ears have f3 points as well😉
A>> Roll off
So if say, I tune a closed box system to 20 Hz then the intensity will decrease by 12 db at what frequency?? [I'm sorry, did not understand that part properly]
Also I infer from what you explain that, wrt a particular decibel level if the intensity is say A then if the decibel level is increased by 3 db then the intensity doubles - Is that right.
B>> f3
I infer that we can talk about f3 wrt power output only right?
The frequency at which the power output decreases by half right??
But if you have a 250 watts amplifier with a 200 KHz bandwidth, then it will be amplifying any signal within that bandwidth to 250 watts right?? Then why will it fall down to 125 watts at say 160 KHz which will be considered as f3 of that amplifier. [Did not get this part either]
Please clarify 🙂
So if say, I tune a closed box system to 20 Hz then the intensity will decrease by 12 db at what frequency?? [I'm sorry, did not understand that part properly]
Also I infer from what you explain that, wrt a particular decibel level if the intensity is say A then if the decibel level is increased by 3 db then the intensity doubles - Is that right.
B>> f3
I infer that we can talk about f3 wrt power output only right?
The frequency at which the power output decreases by half right??
But if you have a 250 watts amplifier with a 200 KHz bandwidth, then it will be amplifying any signal within that bandwidth to 250 watts right?? Then why will it fall down to 125 watts at say 160 KHz which will be considered as f3 of that amplifier. [Did not get this part either]
Please clarify 🙂
First. Let's you tune it to 20hz and it is 12db per octave.
First thing to remember, an octave is a double in frequency, or a half in frequency. The octave below 20hz is 10 hz. The octave above 20hz is 40hz. This is also what occurs in a piano when you move up or down by 12 semitones (eight whole notes).
Anyway, onto the speaker enclosure. At 12db per octave and 20hz tuning, you then know that by the dropping of the frequency by the octave, you get 12db less output.
As far as the f3 point, that generally means power. It could mean the output of sound from the speaker, or the rolloff on a microphone as well. It just means the point at which the output drops by half during the extension of frequency. In the mic, this means the point at which its sensitivity decreases by half. See what I mean here?
About the amplifier, actually, I should have said frequency range, or response, not bandwidth.
Most amplifiers have a frequency responce range that is greater than the power bandwidth. Say it's range is up to 200khz. It will operate to that frequency, but will probably reduce in output siginificantly before the frequency reaches that 200khz mark. Therefore, we state an f3 point to give the user an idea of how the response acts. If it is down by 3db at 160khz, then we know it's going to be very weak by the time we reach 200khz.
I hope this helps you. 😉
First thing to remember, an octave is a double in frequency, or a half in frequency. The octave below 20hz is 10 hz. The octave above 20hz is 40hz. This is also what occurs in a piano when you move up or down by 12 semitones (eight whole notes).
Anyway, onto the speaker enclosure. At 12db per octave and 20hz tuning, you then know that by the dropping of the frequency by the octave, you get 12db less output.
As far as the f3 point, that generally means power. It could mean the output of sound from the speaker, or the rolloff on a microphone as well. It just means the point at which the output drops by half during the extension of frequency. In the mic, this means the point at which its sensitivity decreases by half. See what I mean here?
About the amplifier, actually, I should have said frequency range, or response, not bandwidth.
Most amplifiers have a frequency responce range that is greater than the power bandwidth. Say it's range is up to 200khz. It will operate to that frequency, but will probably reduce in output siginificantly before the frequency reaches that 200khz mark. Therefore, we state an f3 point to give the user an idea of how the response acts. If it is down by 3db at 160khz, then we know it's going to be very weak by the time we reach 200khz.
I hope this helps you. 😉
Given all those box volume calculators, if I fixup the volume of my closed enclosure to tune the system to say 22 Hz then..........
My system will play the 22 Hz signal at some decible point 'x' db, so what it means is at 44 hz it will play this signal at 'x-12' db right??
The same way, the passive radiator will play the 44Hz signal at 'x-24' db right?
I got this "sealed.xls" box caluculator from "diysubwoofers.org" and when I entered the t/s parameters for the AdireAudio DPL12 the frequency response shows a flat line along the 0 db level after 76 Hz but below 76Hz it falls to -3 db at 28 Hz and -12 db at 15 hz. What does the curve mean?
Also f3 n fb the system resonance frequency were both 28.8Hz (qtc = .707)
What does the above mean?
I do not know how to attach a file (excel file) otherwise you could have seen the data n the graph for yourself.
My system will play the 22 Hz signal at some decible point 'x' db, so what it means is at 44 hz it will play this signal at 'x-12' db right??
The same way, the passive radiator will play the 44Hz signal at 'x-24' db right?
I got this "sealed.xls" box caluculator from "diysubwoofers.org" and when I entered the t/s parameters for the AdireAudio DPL12 the frequency response shows a flat line along the 0 db level after 76 Hz but below 76Hz it falls to -3 db at 28 Hz and -12 db at 15 hz. What does the curve mean?
Also f3 n fb the system resonance frequency were both 28.8Hz (qtc = .707)
What does the above mean?
I do not know how to attach a file (excel file) otherwise you could have seen the data n the graph for yourself.
You sound quite confused. Closed box systems exibit a shallow rolloff of 12db/octave as frequency DECREASES. The roloff will occur below the F3 which is the point where sensitivity decreases by 50%. A vented or passive radiator system rolls off at 24db/octave below the tuning of the system. Passive radiators and vented systems utilize the rear wave to increase output, or lower f3 (depending on the alignment). Q is a dampening factor. Lower Q means lower dampening and higher Q means higher dampening. The dampening desribes how the airspring of the enclosure stops the speaker from resonating. I dont think you're quite ready to start reading something as technical as vance dickasons loudspeaker cookbook. You need to get the basics down before you can dive into the technical jargon. www.diysubwoofers.org has pretty basic explinations of the enclosure types and should give you some idea of how they work.
For clarity sake ....Duo said:
a 3dB increase is double the power .... a 10dB increase is generally considered to sound twice as loud. It's one of the reasons that all else being equal, there's very little difference between an 80W amplifier and a 100W amplifier.....
I know you already know this stuff Duo but I'm posting for the benefit of SSsai.
ssSai: You almost have it... let me clarify the details.
Frequency range: Can play down to certain low notes and up to certain high notes. For example, many manufacturers will state this as 40Hz - 20kHz. This is not a useful speaker measurement because it does not tell you the actual performance between the low and the high.
Frequency response: A specification for frequency range that also includes the perfomance between the high and low notes. For example, 40Hz - 20kHz +/- 1.5dB. Notice that this tells you the graph is very flat.
Frequency response graph: A chart showing the SPL output of the speaker over the audio band from 20Hz to 20kHz. Many extreme performance speakers, like subs and super tweeters, will show a graph from 0Hz to 50kHz. It is never perfectly flat.
Corner frequency: The high or low point of a frequency response graph that shows when the SPL output of the speaker begins to roll off from a normal near-flat response.
Roll off: A measurement of the slope of the frequency response graph after the corner frequency. States as dB/octave and is often multiples of 6dB/octave (6, 12, 18, 24, etc.). Different types of enclosure designs create different roll off rates.
f3 point: The frequency when the roll off is enough to drop the SPL output to -3dB from normal near flat response. If this is the low f3 point, then any lower will be even less output and the frequency response graph will be dropping at the roll off rate.
All audio components have these characteristics, but some specs are most often used to describe specific pieces. For example, because good amplifiers are usually very linear, you really only need to know the frequency range and the two f3 points. Speakers are much less linear so a frequency response graph is the better spec. From it you can see corner frequency, flatness, f3 points and roll off rates.
🙂ensen.
Edit: Spelling
Frequency range: Can play down to certain low notes and up to certain high notes. For example, many manufacturers will state this as 40Hz - 20kHz. This is not a useful speaker measurement because it does not tell you the actual performance between the low and the high.
Frequency response: A specification for frequency range that also includes the perfomance between the high and low notes. For example, 40Hz - 20kHz +/- 1.5dB. Notice that this tells you the graph is very flat.
Frequency response graph: A chart showing the SPL output of the speaker over the audio band from 20Hz to 20kHz. Many extreme performance speakers, like subs and super tweeters, will show a graph from 0Hz to 50kHz. It is never perfectly flat.
Corner frequency: The high or low point of a frequency response graph that shows when the SPL output of the speaker begins to roll off from a normal near-flat response.
Roll off: A measurement of the slope of the frequency response graph after the corner frequency. States as dB/octave and is often multiples of 6dB/octave (6, 12, 18, 24, etc.). Different types of enclosure designs create different roll off rates.
f3 point: The frequency when the roll off is enough to drop the SPL output to -3dB from normal near flat response. If this is the low f3 point, then any lower will be even less output and the frequency response graph will be dropping at the roll off rate.
All audio components have these characteristics, but some specs are most often used to describe specific pieces. For example, because good amplifiers are usually very linear, you really only need to know the frequency range and the two f3 points. Speakers are much less linear so a frequency response graph is the better spec. From it you can see corner frequency, flatness, f3 points and roll off rates.
🙂ensen.
Edit: Spelling
These posts clearly define what I started out to say. Good of us to have many people with this common knowledge. 😀
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