I'm no expert -- can't really even follow the discussion of derivatives -- but it seems to me that with the exception of the comments about comparing drivers in free air, and that about echoes and reverb, no one is addressing the fact that we rarely use woofers without some sort of enclosure, and the enclosure and its inevitable resonances and reflections seem to me to be what makes bass sound slow. Certainly if a woofer can accurately reproduce a sine wave at the highest frequency it is audible at (and how many db down does it have to be for it to be inaudible?), and it doesn't interact electrically with the other drivers, you would expect it to sound fast. But are these conditions actually met? Certainly once the driver is in an enclosure they are not close to being met.
1 - Derivatives are real easy: it is the rate of the change. If you go with a constant speed, the rate of change is zero: the first derivative of your speed is zero. If you increase your speed with 10m/sec every second, you have a derivative of 10m/sec/sec.
The nice thing of the sine wave, as noted above, is that it's rate of change is, well, a sine wave. So it's derivative is also a sine.
2 - I still don't understand the meaning of "bass sound slow". Do you mean that there is a lack of transients? That would be normal for a woofer, it is way too heavy to reproduce those high-frequency parts of the spectrum. And it is futile to search for a "fast woofer" because ALL respectable woofers are too heavy to reproduce the hi freqs. If they were not, they would be less good as woofers.
Now the speaker SYSTEM may sound as if it lacks transients, and one could call it "slow", but it is not the woofer's fault, and you cannot solve it by searching for a fast woofer. You solve it by getting an optimal xover and making sure your midrange/tweeter are in balance with the woofer and each other.
Your point about the enclosure is well taken, because if properly damped it is another element that will prevent the woofer to sound "fast".
Jan Didden
The nice thing of the sine wave, as noted above, is that it's rate of change is, well, a sine wave. So it's derivative is also a sine.
2 - I still don't understand the meaning of "bass sound slow". Do you mean that there is a lack of transients? That would be normal for a woofer, it is way too heavy to reproduce those high-frequency parts of the spectrum. And it is futile to search for a "fast woofer" because ALL respectable woofers are too heavy to reproduce the hi freqs. If they were not, they would be less good as woofers.
Now the speaker SYSTEM may sound as if it lacks transients, and one could call it "slow", but it is not the woofer's fault, and you cannot solve it by searching for a fast woofer. You solve it by getting an optimal xover and making sure your midrange/tweeter are in balance with the woofer and each other.
Your point about the enclosure is well taken, because if properly damped it is another element that will prevent the woofer to sound "fast".
Jan Didden
Here's my input regarding "fast bass":
Last summer i read the great article on bi-amping by Rod Elliot, and I got totally sold on the idea of not just bi-amping, but tri-amping. I started out by building his 3-way active filter, with LR-characteristics. After that, I built a 6-ch amp based on an Elektor design named the "HEXFET amplifier". I also built me some
sealed enclosure speakers (approx 150 l), with VIFA D25-AG-35-06 tweeters, Peerless CDC165C as midrange, and some "noname" $30 10" Woofers.
So, what about bass? Well, when I first powered up the system to listen to it (an exiting moment, I can tell you), my first impression was that the bass was so incredibly tight; everything was just "there". The sound of drums and bass was just fantastic, and after some longer period of listening I figured the "tightness" came from the ability to hear the transients from the drums and the fingers touching and releasing the strings of the bass guitar.
AFAIK the "attack" sounds I'm referring to has nothing to do in the frequency range of the woofers, rather in the mid-to-high-range.
I was rather surprised initially that my cheap woofers sounded so good, but after thinking it through I now give all the "bass credit" to the midrange and the tweeter.
For anyone longing for "tight bass" I would highly recommend at least bi-amping - it has done wonders to the musical reproduction in my home.
BTW, I use 300 Hz and 3500 Hz as crossover frequencies, 24 dB/octave.
Just my 2 cents worth
Last summer i read the great article on bi-amping by Rod Elliot, and I got totally sold on the idea of not just bi-amping, but tri-amping. I started out by building his 3-way active filter, with LR-characteristics. After that, I built a 6-ch amp based on an Elektor design named the "HEXFET amplifier". I also built me some
sealed enclosure speakers (approx 150 l), with VIFA D25-AG-35-06 tweeters, Peerless CDC165C as midrange, and some "noname" $30 10" Woofers.
So, what about bass? Well, when I first powered up the system to listen to it (an exiting moment, I can tell you), my first impression was that the bass was so incredibly tight; everything was just "there". The sound of drums and bass was just fantastic, and after some longer period of listening I figured the "tightness" came from the ability to hear the transients from the drums and the fingers touching and releasing the strings of the bass guitar.
AFAIK the "attack" sounds I'm referring to has nothing to do in the frequency range of the woofers, rather in the mid-to-high-range.
I was rather surprised initially that my cheap woofers sounded so good, but after thinking it through I now give all the "bass credit" to the midrange and the tweeter.
For anyone longing for "tight bass" I would highly recommend at least bi-amping - it has done wonders to the musical reproduction in my home.
BTW, I use 300 Hz and 3500 Hz as crossover frequencies, 24 dB/octave.
Just my 2 cents worth
Yes, Pelle, it seems your speakers are well integrated into an excellent SYSTEM. As you say, finger plucking sounds may come from the bass guitar, but that doesn't mean it's a bass sound; it isn't. The strings may vibrate in a lot of overtone modes generating hf transients, those go to the mid/high drivers. The string vibrations also exite the guitar body to vibrate in IT'S resonance mode, being in the low freq range. That sound is directed to the woofer. (I know there is overlap, just for simplicity, OK?).
If all those component sounds reach your ears in the right balance (level and phase-wise, although the requirement for correct phase is debated), it all seems to fall together and you get the impression of tight and quick start-stop bass. Another occasion that your brain is fooled, but at least this one is so obvious that we can clearly understand and accept it.
Jan Didden
If all those component sounds reach your ears in the right balance (level and phase-wise, although the requirement for correct phase is debated), it all seems to fall together and you get the impression of tight and quick start-stop bass. Another occasion that your brain is fooled, but at least this one is so obvious that we can clearly understand and accept it.
Jan Didden
Fascinating reading... the parts I can understand at least
In fact it makes me think twice about tweaking my subwoofer more to make it sound tighter. Mind you, increasing reservoir capacitance and wiring the (dual)VC in parallel rather than just wiring one gave noticable improvements - the bass *was* slow before!! btw what's wrong with saying slow? - I am only talking about 20-50hz reproduction - and bass got much tighter using both coils, is this purely because of resistance?
It seems almost impossible to achieve "good" bass, but I think the listening room is the number one factor. Impossible to get around the bloody room modes in a normal room
With respect to frequency range I am finding this increasingly true - if I turn my sub off the overall bass (bass guitar, drums etc.) becomes tighter and more defined, but with no warmth or existence of low notes. Further evidence: several friends have much cheaper speakers than me, yet generally their bass sounds pretty tight, but with no real lows...
Sorry this post isn't especially relevant, I just wanted to contribute in some way
-Simon
ps, there's the monster nearly finished, made before I joined this forum sadly (it's larger than a washing machine):
In fact it makes me think twice about tweaking my subwoofer more to make it sound tighter. Mind you, increasing reservoir capacitance and wiring the (dual)VC in parallel rather than just wiring one gave noticable improvements - the bass *was* slow before!! btw what's wrong with saying slow? - I am only talking about 20-50hz reproduction - and bass got much tighter using both coils, is this purely because of resistance?
It seems almost impossible to achieve "good" bass, but I think the listening room is the number one factor. Impossible to get around the bloody room modes in a normal room
With respect to frequency range I am finding this increasingly true - if I turn my sub off the overall bass (bass guitar, drums etc.) becomes tighter and more defined, but with no warmth or existence of low notes. Further evidence: several friends have much cheaper speakers than me, yet generally their bass sounds pretty tight, but with no real lows...
Sorry this post isn't especially relevant, I just wanted to contribute in some way
-Simon
ps, there's the monster nearly finished, made before I joined this forum sadly (it's larger than a washing machine):
Attachments
Don't forget the enclosure which tunes the acoustic highpass behavior of the woofer. In a sense, you could call it part of the crossover network. It's all about resonance and group delay. Critically damped, low Q alignments will tend to be called "fast" (ugh, I hate that word
) while the ringing of high Q alignments will make them be called "slow." Same with rooms. A room with a high Q ringing in the bass frequencies will give a perception of "slow" bass. IMHO these effects are more prominent than any second order HF effects from the other drivers. You can hear the difference even if the woofer is lowpassed very low and no other drivers are playing.
SimontY said:[snip]It seems almost impossible to achieve "good" bass, but I think the listening room is the number one factor. Impossible to get around the bloody room modes in a normal room
[snip]
Sorry this post isn't especially relevant, I just wanted to contribute in some way
-Simon
ps, there's the monster nearly finished, made before I joined this forum sadly (it's larger than a washing machine):
Room modes: Bingo! You got it. Very relevant post.
Jan Didden
janneman said:
Yes, and room modes have been mentioned a few time on this thread. Rooms are one of the main factors for the speed of the bass.
I'm interested in having a discussion on bass, rooms, positioning, one sub or two, etc.
What do you all think, should we do it on this thread or start a new thread?
Steve
Keep it all in one place.
Hi Steve,
Maybe it is a good idea to keep all these bass matters in one place. After all we are trying to reproduce great bass in a room. The room is and extension to this thread. Driver - box - room. Amp? Possibly power supply and output device discussion. With the focus on bass performance of course.
Cheers.
Hi Steve,
Maybe it is a good idea to keep all these bass matters in one place. After all we are trying to reproduce great bass in a room. The room is and extension to this thread. Driver - box - room. Amp? Possibly power supply and output device discussion. With the focus on bass performance of course.
Cheers.
in fact, bad positioning of loudspeakers (layout of radiation planes of woofer-mid-tweeter), bad positioning of the baffle as a whole and miscalculation (or wiring) of x-over have mostly the same outcome: opposed phase and dips or spikes in freq-plot.
Time-allignement i think it is called.
But this has nothing to do with the dynamic capabilities of the drivers...
Time-allignement i think it is called.
But this has nothing to do with the dynamic capabilities of the drivers...
Hmm..............
Yes Lieven,
You are right. It has been mentioned earlier in this thread - a bit differently. Lots of good thoughts in this thread. Read it through.
Have you used any 'room modes' software? It will be interesting to know what results were obtained and how useful they were.
Anyone?
Cheers.
Yes Lieven,
You are right. It has been mentioned earlier in this thread - a bit differently. Lots of good thoughts in this thread. Read it through.
Have you used any 'room modes' software? It will be interesting to know what results were obtained and how useful they were.
Anyone?
Cheers.
How Woofers Work
Maybe a quick review of how a woofer actually works would be appropriate here. To paraphrase Tom Danley and others:
The mass of the woofer has nothing to do with "fast bass" directly. It does effect efficiency, however.
Take a woofer and suspend it in space on an infinite baffle. Feed it a signal that starts low in frequency, then gradually increase frequency with velocity kept constant and the woofer will display a 6 dB increase in output/octave as its radiation efficiency increases from the acoustic load. To make a woofer "flat" in response, one has to weaken the motor, or reduce voltage, to reduce velocity which will then correspond/offset with the increase in radiation efficiency. The result is equivalent to adding an RC circuit to the woofer, with a -90 degree phase shift. Flat response is delayed reponse, relative to the ideal. Once the slope is set at 6dB, the moving mass only sets the start point of the slope. This is true for all woofers with flat response.
While it is possible by increasing motor strength or reducing moving mass one may create an overdamped response which more closely mirrors the the 6 dB/octave slope, it is at the expense of flat response - Amplitude is rolling off 6 dB.
For those more sensitive to time/phase shifts this may be the preferred sound, where others may favor the flat amplitude model and not mind the delay. Enclosures are another ballgame.
Group delay/transient response are better in a sealed box than a ported enclosure. One may opt for a ported enclosure for various reasons such as increased effeciency or lower response, but a sealed box will, with some planning, subjectively sound very good and yield lower group delay. As the roll off in a sealed box is 12 dB/octave, the room lift may, to some extent at least, offset the roll off to yield nearly flat response quite deep. A perfectly sealed room will provide a 12 dB lift, if you can find one.
As a ported enclosure roll off at 24 dB, room lift can help, but not to the same extent.
The other extreme would be tuning a peak in response just before roll off in a ported enclosure with a "Q" near 1 or more. This causes the greatest group delay, and will sound strange to those listening for, or sensitive to, over or underdamped bass.
Btw, the terms underdamped/overdamped arose from filter theory. As a general rule, a vented box Q of .5 may sound a bit dry to some, .6 - .7 nearly optimum for those of the tight bass camp, and above .8 leaning toward the underdamped.
To further complicate this delay issue, use a perfect woofer fed signals of equal amplitude at 100, 50 and 20 Hz, all mid band in the perfect woofer, and the delay will be ~ 2.5, 5, and 10 miliseconds from terminals to output just from going lower in frequency. So, the delay added by the individual electrical characteristics of brand x woofer must be added to this fixed delay.
Tim Moorman
Maybe a quick review of how a woofer actually works would be appropriate here. To paraphrase Tom Danley and others:
The mass of the woofer has nothing to do with "fast bass" directly. It does effect efficiency, however.
Take a woofer and suspend it in space on an infinite baffle. Feed it a signal that starts low in frequency, then gradually increase frequency with velocity kept constant and the woofer will display a 6 dB increase in output/octave as its radiation efficiency increases from the acoustic load. To make a woofer "flat" in response, one has to weaken the motor, or reduce voltage, to reduce velocity which will then correspond/offset with the increase in radiation efficiency. The result is equivalent to adding an RC circuit to the woofer, with a -90 degree phase shift. Flat response is delayed reponse, relative to the ideal. Once the slope is set at 6dB, the moving mass only sets the start point of the slope. This is true for all woofers with flat response.
While it is possible by increasing motor strength or reducing moving mass one may create an overdamped response which more closely mirrors the the 6 dB/octave slope, it is at the expense of flat response - Amplitude is rolling off 6 dB.
For those more sensitive to time/phase shifts this may be the preferred sound, where others may favor the flat amplitude model and not mind the delay. Enclosures are another ballgame.
Group delay/transient response are better in a sealed box than a ported enclosure. One may opt for a ported enclosure for various reasons such as increased effeciency or lower response, but a sealed box will, with some planning, subjectively sound very good and yield lower group delay. As the roll off in a sealed box is 12 dB/octave, the room lift may, to some extent at least, offset the roll off to yield nearly flat response quite deep. A perfectly sealed room will provide a 12 dB lift, if you can find one.
As a ported enclosure roll off at 24 dB, room lift can help, but not to the same extent.
The other extreme would be tuning a peak in response just before roll off in a ported enclosure with a "Q" near 1 or more. This causes the greatest group delay, and will sound strange to those listening for, or sensitive to, over or underdamped bass.
Btw, the terms underdamped/overdamped arose from filter theory. As a general rule, a vented box Q of .5 may sound a bit dry to some, .6 - .7 nearly optimum for those of the tight bass camp, and above .8 leaning toward the underdamped.
To further complicate this delay issue, use a perfect woofer fed signals of equal amplitude at 100, 50 and 20 Hz, all mid band in the perfect woofer, and the delay will be ~ 2.5, 5, and 10 miliseconds from terminals to output just from going lower in frequency. So, the delay added by the individual electrical characteristics of brand x woofer must be added to this fixed delay.
Tim Moorman
dear all,
I hope I am doing this right, since it is the first time I take part in a forum. I am an amature speaker builder. I will comment on some of the topics in this thread.
A low Qms will help to dampen a woofer which is nice around Fs or Fc. For higher frequencies this low Qms will work as a handbrake.
The relation between radiation efficiency and frequency of a loudspeaker is not linear. For the lowest frequencies it climbs exponentially. besides, the bigger the conus, the higher the resistance at a certain frequency. So bigger speakers produce more bass and with less effort, even if the total displacementvolume is the same of that of a smaller cone.
I feel that bigger cones give tighter bass, if all the rest is more or less the same.
Room influences are indeed crucial. Low frequencies will have a radiation pattern between a halve sphere if placed in the middle of the room or even of 1/8th sphere if placed in a corner. that means that 7/8th of the soundpressure will join the 1/8th of the direct sound more or less in phase.
I have learned from this that a flat response in an anaechoïc room is not an advantage. you can have perfect results with speakers that slowly decrease their spl fom 100 Hz down, especially with the smooth decrease of sealed enclosures.
I feel that a lack of fast bass is therefore often just too much bass.
A question for Ashok: did you get the TS parameters of the dovedale speakers? I am very much interested since I have a pair of my own.
Jan.
I hope I am doing this right, since it is the first time I take part in a forum. I am an amature speaker builder. I will comment on some of the topics in this thread.
A low Qms will help to dampen a woofer which is nice around Fs or Fc. For higher frequencies this low Qms will work as a handbrake.
The relation between radiation efficiency and frequency of a loudspeaker is not linear. For the lowest frequencies it climbs exponentially. besides, the bigger the conus, the higher the resistance at a certain frequency. So bigger speakers produce more bass and with less effort, even if the total displacementvolume is the same of that of a smaller cone.
I feel that bigger cones give tighter bass, if all the rest is more or less the same.
Room influences are indeed crucial. Low frequencies will have a radiation pattern between a halve sphere if placed in the middle of the room or even of 1/8th sphere if placed in a corner. that means that 7/8th of the soundpressure will join the 1/8th of the direct sound more or less in phase.
I have learned from this that a flat response in an anaechoïc room is not an advantage. you can have perfect results with speakers that slowly decrease their spl fom 100 Hz down, especially with the smooth decrease of sealed enclosures.
I feel that a lack of fast bass is therefore often just too much bass.
A question for Ashok: did you get the TS parameters of the dovedale speakers? I am very much interested since I have a pair of my own.
Jan.
Fast Bass
I looked through data for woofers and calculated;-
Acceleration = Bl/mms
for several units. These parameters are given in the TS parameter list. See if you think it ties in with those units that give fast bass, and those that don't. The Audax aerogel units came out as the fastest in this test, out of the ones I tried that is.
I'm not sure how much of this concept is the fault of Journalists, but having built and tried out a few bass speakers, I can see what they mean.
I looked through data for woofers and calculated;-
Acceleration = Bl/mms
for several units. These parameters are given in the TS parameter list. See if you think it ties in with those units that give fast bass, and those that don't. The Audax aerogel units came out as the fastest in this test, out of the ones I tried that is.
I'm not sure how much of this concept is the fault of Journalists, but having built and tried out a few bass speakers, I can see what they mean.
Inductance
Mass has nothing to do with speed of the woofer, or fast bass.
Current provides the "speed" and is altered by inductance.
Acceleration is basically SPL.
http://www.adireaudio.com/tech_papers/woofer_speed.htm
There are other delays based on driver construction, and increasing delay with lower frequency, but keeping inductance low is critical.
Tim
Mass has nothing to do with speed of the woofer, or fast bass.
Current provides the "speed" and is altered by inductance.
Acceleration is basically SPL.
http://www.adireaudio.com/tech_papers/woofer_speed.htm
There are other delays based on driver construction, and increasing delay with lower frequency, but keeping inductance low is critical.
Tim
Re: Inductance
We're talking here about the acceleration and deceleration of speaker cones.
Adire Audio starts with Newton's law:
force = mass x acceleration (eq 1)
Next they translate this for speakers:
drive unit motor force x current = mass x acceleration (eq 2)
So far, so good.
From this, they go to: "So, let's rewrite equation 2, and replace the time-invariant parameters with a simple 'C' to indicate a constant (a parameter that does not change with time):
Ci = Ca (eq 3) or i :: a (eq 4)"
Excuse me?
In other words they say that acceleration is proportional to current. And, for a fixed motor force and moving mass ("time-invariant") this is true. However, in reality we CAN vary the cone mass or the motor force and when we do this we're out of the world of "eq 4" and back into the world of physics.
I'd be grateful if someone could explain this to me if I'm wrong.
I don't think so, Tim. Because Adire Audio says something, it doesn't make it so.Tim Moorman said:
We're talking here about the acceleration and deceleration of speaker cones.
Adire Audio starts with Newton's law:
force = mass x acceleration (eq 1)
Next they translate this for speakers:
drive unit motor force x current = mass x acceleration (eq 2)
So far, so good.
From this, they go to: "So, let's rewrite equation 2, and replace the time-invariant parameters with a simple 'C' to indicate a constant (a parameter that does not change with time):
Ci = Ca (eq 3) or i :: a (eq 4)"
Excuse me?
In other words they say that acceleration is proportional to current. And, for a fixed motor force and moving mass ("time-invariant") this is true. However, in reality we CAN vary the cone mass or the motor force and when we do this we're out of the world of "eq 4" and back into the world of physics.
I'd be grateful if someone could explain this to me if I'm wrong.
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