Konnichiwa,
Well, the relative loss of SPL (assuming you use a competently engineered driver and a sufficiently large baffle) at low frequencies is much smaller than often assumed, so yes, it increases some forms of distortion, but this increase can usually be offset mostly by doubling up drivers and on the plus side, a dipole shows the least distortion of a step waveform of any given enclosure.
Well, in an asolute sense ANY box resonance is "bad". However, we are dealing with acoustics and reproduction for human consumption. If the resonances fall fairly low they fall into areas where they will tend to be MUCH LESS AUDIBLE, despite being present.
Well, an "ideal golden section" box of 100l will show the lowest resonance at 231Hz and a 50L one at 288Hz. All else being equal the 230Hz will be less audible. A really large Tannoy Corner York will have even lower resonance points.
Again, the smaller enclosures will shift the enclosure resonances up in frequency, making them more audible.
Act as a wideband point source, in a 2-Way speaker, especially if arranged as a coaxial driver? Avoid comb filtering from mutiple sound sources?
Sayonara
CeramicMan said:
Well, the relative loss of SPL (assuming you use a competently engineered driver and a sufficiently large baffle) at low frequencies is much smaller than often assumed, so yes, it increases some forms of distortion, but this increase can usually be offset mostly by doubling up drivers and on the plus side, a dipole shows the least distortion of a step waveform of any given enclosure.
CeramicMan said:
Well, in an asolute sense ANY box resonance is "bad". However, we are dealing with acoustics and reproduction for human consumption. If the resonances fall fairly low they fall into areas where they will tend to be MUCH LESS AUDIBLE, despite being present.
CeramicMan said:
Well, an "ideal golden section" box of 100l will show the lowest resonance at 231Hz and a 50L one at 288Hz. All else being equal the 230Hz will be less audible. A really large Tannoy Corner York will have even lower resonance points.
CeramicMan said:
Again, the smaller enclosures will shift the enclosure resonances up in frequency, making them more audible.
CeramicMan said:
Act as a wideband point source, in a 2-Way speaker, especially if arranged as a coaxial driver? Avoid comb filtering from mutiple sound sources?
Sayonara
I just thought I'd throw a spanner in the works and say that you can have problems reproducing frequencies below the lowest resonant mode.
However, this relies on the coefficient of reflection at these frequencies being very close to unity (ie ~100% of sound at these frequencies is reflected). The effects can be enough to offset or even cancel out room gain. If the coefficient is much lower, then it is not a factor and room gain promotes the intensity of these low frequencies.
This phenomena usually occurs in rooms with very thick stone walls.
However, this relies on the coefficient of reflection at these frequencies being very close to unity (ie ~100% of sound at these frequencies is reflected). The effects can be enough to offset or even cancel out room gain. If the coefficient is much lower, then it is not a factor and room gain promotes the intensity of these low frequencies.
This phenomena usually occurs in rooms with very thick stone walls.
Kuei Yang Wang said:
Scroll to the bottom of this link for raw vs added mass vs added inductance measurements with regards to impulse response which is what I think you mean when you say step response. A true step would be DC as you know.
http://www.adireaudio.com/tech_papers/woofer_speed.htm
The impulse is shown going negative first due to an inverting mic pre amp.
Kuei Yang Wang said:
Fourier analysis is valid for any signal that can be represented as repeating. If the time markers are set such that the signal has settled back down to zero that is suffecient, as the argument can be mathematically made the the signal could in fact repeat.
Any system that has a known frequency response with both amplitude and phase can be transformed into the time domain in response to any input signal. This is the basis of speaker measurement. Input an impulse and measure the time response, then transform it into a Frequency response.
Yes, I was mixing my thoughts again. Filters with a system be it 2 or 3 way (of any order). The "high frequency response" part was aimed at a raw driver.Kuei Yang Wang said:
Kuei Yang Wang said:
I would maintain that it is. The attack part of the transient is the higher frequency componet of the sound wave. If it is missing, or suppressed, the sound is almost always described as slow bass. I think it applies the same in the initial attack in the kick drum and in the pluck of the upright bass.
Russ
Konnichiwa,
Interesting, from the measurements it appears that the "added masse" was well decoupled from the voicecoil/inner cone (by intent or accident), making it less than ideal in the context to illustrate the point (look carefully - there is an indication in the impulse response that the added mass responds delayed to the stimulus - maybe it was attached with bluetack?).
It will do fine for measurements of static low frequency parameters where the cone behaves as piston, but makes it's influence on the impulse and higher frequency response rather less clear. It is true that many drivers also decouple parts of their cone with rising frequency, but this effect is hard to replicate. Using a fieldcoil driver and altering "B" will be a better measure of the effect, IMHO as it actually evaluates the Mass/BL quotient "theory" as effect.
Adjusting the Mass/BL quotient by adjusting fieldstrength would elimiate the non-ideal mecanical issues. I would recommend carrying out the test that way around.
Yes, this may be made mathematically. However, it may be equally argued practically that your signal will only be absolute zero after an infinite timewindow.
Yet measuring the speaker by methodes other than a windowed impulse (even in an anechonic chamber) gives results that tend to deviate from those using windowed impulses. I recently had a case of a driver measured using "modern" methodes that nearly 20 Years ago I had been sample testing other exemplars of in production for conformance with target parameters in an anechonic chamber.
The results from the "modern" measurement deviated drastically from that made earlier using a classic pen & moving paper response analyser with a clabriated Mike & Mike Amp. Either the drivers degraded a lot in the meantime or one measurement gave WRONG results. Now I know that the original drivers do sound quite balanced sonically and the "old" measurements showed them as quite balanced. The modern measurement shows them as having a not particulary well balanced response.
It is hard in such cases to separate the exact cause, however I find modern ipluse based pseudo anechonic measurements usually quite discongruent with percieved tonality of many a given (and according to this methode badly measuring) speaker.
Input an impulse and measure the time response, then transform it into a Frequency response.
Yes and no. It is sometmes interesting to experiment with an equaliser and different speakers. I find that even after equalising them to a given reference curve comparing speakers using drivers covering the LF with a comparably low mass/bl quotient tend to provide a "faster" subjective "bass", than drivers with a high mass/BL quotient. Averaged frequency response (steady state) can be excluded as this equalised. Resonances can be mostly excluded for the same reason.
Given the appearance of an audible difference despite no apparent material measurable difference (if impulse response indeed transforms into REAL PERCEIEVED frequency response and not just mathematically), what reason for these differences do you propose?
Sayonara
russbryant said:
Interesting, from the measurements it appears that the "added masse" was well decoupled from the voicecoil/inner cone (by intent or accident), making it less than ideal in the context to illustrate the point (look carefully - there is an indication in the impulse response that the added mass responds delayed to the stimulus - maybe it was attached with bluetack?).
It will do fine for measurements of static low frequency parameters where the cone behaves as piston, but makes it's influence on the impulse and higher frequency response rather less clear. It is true that many drivers also decouple parts of their cone with rising frequency, but this effect is hard to replicate. Using a fieldcoil driver and altering "B" will be a better measure of the effect, IMHO as it actually evaluates the Mass/BL quotient "theory" as effect.
Adjusting the Mass/BL quotient by adjusting fieldstrength would elimiate the non-ideal mecanical issues. I would recommend carrying out the test that way around.
russbryant said:
Yes, this may be made mathematically. However, it may be equally argued practically that your signal will only be absolute zero after an infinite timewindow.
russbryant said:
Yet measuring the speaker by methodes other than a windowed impulse (even in an anechonic chamber) gives results that tend to deviate from those using windowed impulses. I recently had a case of a driver measured using "modern" methodes that nearly 20 Years ago I had been sample testing other exemplars of in production for conformance with target parameters in an anechonic chamber.
The results from the "modern" measurement deviated drastically from that made earlier using a classic pen & moving paper response analyser with a clabriated Mike & Mike Amp. Either the drivers degraded a lot in the meantime or one measurement gave WRONG results. Now I know that the original drivers do sound quite balanced sonically and the "old" measurements showed them as quite balanced. The modern measurement shows them as having a not particulary well balanced response.
It is hard in such cases to separate the exact cause, however I find modern ipluse based pseudo anechonic measurements usually quite discongruent with percieved tonality of many a given (and according to this methode badly measuring) speaker.
Input an impulse and measure the time response, then transform it into a Frequency response.
russbryant said:
Yes and no. It is sometmes interesting to experiment with an equaliser and different speakers. I find that even after equalising them to a given reference curve comparing speakers using drivers covering the LF with a comparably low mass/bl quotient tend to provide a "faster" subjective "bass", than drivers with a high mass/BL quotient. Averaged frequency response (steady state) can be excluded as this equalised. Resonances can be mostly excluded for the same reason.
Given the appearance of an audible difference despite no apparent material measurable difference (if impulse response indeed transforms into REAL PERCEIEVED frequency response and not just mathematically), what reason for these differences do you propose?
Sayonara
i would like to state that im not an expert,
but i have 6 cerwin vega 712's a 706c center and a ht-s15 sub, and the only advantage the sub has in music is when its tuned down to about 40hz crossover, otherwise its very boomy and out of place witht the rest of the sound, in my opinion 15's are made to clean up the very bottom end. in movies however, they do provide more in terms of special effects, ya know the bangs thumps and shoowshes.
i dont find a 15 as something that adds swignificantly to music.
but i have 6 cerwin vega 712's a 706c center and a ht-s15 sub, and the only advantage the sub has in music is when its tuned down to about 40hz crossover, otherwise its very boomy and out of place witht the rest of the sound, in my opinion 15's are made to clean up the very bottom end. in movies however, they do provide more in terms of special effects, ya know the bangs thumps and shoowshes.
i dont find a 15 as something that adds swignificantly to music.
vicioussinclair said:
Neither am I an expert on sound systems (though some here are). But I do know something about logic. The logic followed in your statement can be shortened to this: "The 15" speaker in my system sounds poor when played above about 40 hz, therefore 15" speakers are only good below 40hz."
That's quite a remarkable conclusion. Perhaps if you read the contents of the thread, you might reconsider whether your system represents all possible outcomes.
Sheldon
vicioussinclair said:
Not true. It all depends on the enclosure design and application you intend to use. Mine is a dipole design and crossed over at 90Hz @ 24dB per octave. They are the most musical subs you could ever listen to.
My DIY Dipole Thread
Kuei Yang Wang
Instead of taking about low frequency sine waves, which in reality have little to do with what you can hear. I was trying to point out the trouble with low frequencies in the average size room and the issues with the acoustics design and it's components, the cabinet being one.
So I use this example, for all frequencies below 200 Hz or so all of the "dominant "sound waves in a room exist as standing waves, room modes, or resonances (all three mean exactly the same thing). The lowest mode is when 1/2 wavelength fits in the room, not 1 wavelength. At lower frequencies, or any frequencies away from a resonance, the sound still exists; it is just a lot lower in amplitude. Essentially, there is still a wave bouncing back and forth, but the reflections do not reinforce each other as they do for a resonance. Whether the human ear can "hear" the sound is another question, but the sound is there as far as physics is concerned.
As for as the amplifier is concerned the damping of the enclosures along with Q and air pressure do to output or the acoustic force will change the impedances the amp sees as frequencies change. One of the issues for that amp is the damping factor as impedances does not remain constant so we get back emf. In addition without decent damping factor, control of the woofer will suffer leading to loss of detail in the bass. As I was trying to point out the mass and compliance the driver also has an effect.
I was not talking about sound reinforcement equipment but vented or sealed boxes.
Instead of taking about low frequency sine waves, which in reality have little to do with what you can hear. I was trying to point out the trouble with low frequencies in the average size room and the issues with the acoustics design and it's components, the cabinet being one.
So I use this example, for all frequencies below 200 Hz or so all of the "dominant "sound waves in a room exist as standing waves, room modes, or resonances (all three mean exactly the same thing). The lowest mode is when 1/2 wavelength fits in the room, not 1 wavelength. At lower frequencies, or any frequencies away from a resonance, the sound still exists; it is just a lot lower in amplitude. Essentially, there is still a wave bouncing back and forth, but the reflections do not reinforce each other as they do for a resonance. Whether the human ear can "hear" the sound is another question, but the sound is there as far as physics is concerned.
As for as the amplifier is concerned the damping of the enclosures along with Q and air pressure do to output or the acoustic force will change the impedances the amp sees as frequencies change. One of the issues for that amp is the damping factor as impedances does not remain constant so we get back emf. In addition without decent damping factor, control of the woofer will suffer leading to loss of detail in the bass. As I was trying to point out the mass and compliance the driver also has an effect.
I was not talking about sound reinforcement equipment but vented or sealed boxes.
Konnichiwa,
No offence, but I never referred as such to sinewaves, you actyually did by insisting "wavelength" came into this in a material fashion.
Well, I hate to tell you, the only reason why "room acoustics" are an issue is because most speakers are designed in a manner that is not conductive to using them in small enclosed spaces. Making the main driver smaller actually makes the problems worse, BTW. The problem is perfectly wellunderstood and soplutions are documented, of course everyone ignores this and insteads spouts all sort of unspeakable (to avoid the moderator getting all hot and bothered) stuff.
I pointed all of this out extensively in my various posts. And I think you are wrong, with most rooms not being very high the upper boundary is closer to 300Hz+
And of course, at these room modes the sound is either severely boosted or attenuated from a supposedly "flat" response, depending where in the room with relations to the boundaries you and your speakers are. Deviations in the +/-20db region from "flat" are not uncommon with "room modes".
Actually, below room modes the sound is again proportional, without "organpipe" type acoustical "amplification", it is NOT lower in amplitude. Again, I covered this in more than some detail - so your point is?
With incompetently designed drivers and LF loads - of course.
You make the mistake of taking a particular design feature that is common to modern drivers due to a misapplication of design to be inherent to the nature of electrodynamic speaker. That is not so. Again, with suitable speaker design even an amplifier that is a near perfect current source (damping factor closely approaches zero) will not result in anything untowards.
As have many other factors.
Would you mind explaining in exactly what points "sound re-inforcement" is exclusive of sealed or sealed boxes? Moreover, you home stereo in the literal sense of the word provides also "sound reinforcement".
Why not simply accept that you are the victim of a certain fashion mixed with prejudices and a few wrongly picked up pieces of pseudo-theory?
Sayonara
jewilson said:
No offence, but I never referred as such to sinewaves, you actyually did by insisting "wavelength" came into this in a material fashion.
jewilson said:
Well, I hate to tell you, the only reason why "room acoustics" are an issue is because most speakers are designed in a manner that is not conductive to using them in small enclosed spaces. Making the main driver smaller actually makes the problems worse, BTW. The problem is perfectly wellunderstood and soplutions are documented, of course everyone ignores this and insteads spouts all sort of unspeakable (to avoid the moderator getting all hot and bothered) stuff.
jewilson said:
I pointed all of this out extensively in my various posts. And I think you are wrong, with most rooms not being very high the upper boundary is closer to 300Hz+
And of course, at these room modes the sound is either severely boosted or attenuated from a supposedly "flat" response, depending where in the room with relations to the boundaries you and your speakers are. Deviations in the +/-20db region from "flat" are not uncommon with "room modes".
jewilson said:
Actually, below room modes the sound is again proportional, without "organpipe" type acoustical "amplification", it is NOT lower in amplitude. Again, I covered this in more than some detail - so your point is?
jewilson said:
With incompetently designed drivers and LF loads - of course.
jewilson said:
You make the mistake of taking a particular design feature that is common to modern drivers due to a misapplication of design to be inherent to the nature of electrodynamic speaker. That is not so. Again, with suitable speaker design even an amplifier that is a near perfect current source (damping factor closely approaches zero) will not result in anything untowards.
jewilson said:
As have many other factors.
jewilson said:
Would you mind explaining in exactly what points "sound re-inforcement" is exclusive of sealed or sealed boxes? Moreover, you home stereo in the literal sense of the word provides also "sound reinforcement".
Why not simply accept that you are the victim of a certain fashion mixed with prejudices and a few wrongly picked up pieces of pseudo-theory?
Sayonara
Konnichiwa,
You know, WRONG AGAIN. If you compare a normal 15" loaded 2-Way "PA Speaker" and a 6.5" or 8" loaded 2-Way "HiFi Speaker" (both reflex) you find the resonance tuned around 40-50 in most cases and a similar system Q. You will the typhical Qt of the driver between 0.3-0.5 and a resonance of driver and helmholz tuning approximatly at the same frequency and similar ratios between Vas and Vb. And yes, the anechonic responses are similar as well at low frequencies only the Sensitivity and maximum SPL handling differ markedly, as does btw the distortion and compression for any given SPL Level.
Of course, non of this is surprising, as the "target application" are similar and physical laws identical, only size differs....
Sayonara
jewilson said:
You know, WRONG AGAIN. If you compare a normal 15" loaded 2-Way "PA Speaker" and a 6.5" or 8" loaded 2-Way "HiFi Speaker" (both reflex) you find the resonance tuned around 40-50 in most cases and a similar system Q. You will the typhical Qt of the driver between 0.3-0.5 and a resonance of driver and helmholz tuning approximatly at the same frequency and similar ratios between Vas and Vb. And yes, the anechonic responses are similar as well at low frequencies only the Sensitivity and maximum SPL handling differ markedly, as does btw the distortion and compression for any given SPL Level.
Of course, non of this is surprising, as the "target application" are similar and physical laws identical, only size differs....
Sayonara
Konnichiwa,
This is getting silly....
First of all, you suggested that tuning (Vas/Vb ratio and enclosure tuning) was substantially different for PA Reflex cabinets and those used in "HiFi" Applications. The fact is that they are very similar, so I felt it pruddent to disabuse you of this rather errant notion.
Now you bring in damping. Well, I CAN damp any speaker any way I like, actually. I know enough domestic "HiFi" Speakers with very little damping material and fairly thin cabinet walls.
So, would you mind being SPECIFIC as to in what sense a "Sound Reinfocement" 2-Way 15" LF Driver reflex box tuning differs materially from the tuning of a 2-Way 6.5" LF Driver "HiFi" Box and in which particular sense you cannot achieve the same "damping" in the first that you get in the latter?
Sayonara
This is getting silly....
jewilson said:
First of all, you suggested that tuning (Vas/Vb ratio and enclosure tuning) was substantially different for PA Reflex cabinets and those used in "HiFi" Applications. The fact is that they are very similar, so I felt it pruddent to disabuse you of this rather errant notion.
Now you bring in damping. Well, I CAN damp any speaker any way I like, actually. I know enough domestic "HiFi" Speakers with very little damping material and fairly thin cabinet walls.
So, would you mind being SPECIFIC as to in what sense a "Sound Reinfocement" 2-Way 15" LF Driver reflex box tuning differs materially from the tuning of a 2-Way 6.5" LF Driver "HiFi" Box and in which particular sense you cannot achieve the same "damping" in the first that you get in the latter?
Sayonara
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