Dear Sirs,
I have a kind but maybe trivial question about woofers parameteres.
I know already that the Vas is a measure of the resistance to motion of the cone, the surround, and the spider.
Something like its inertia.
The lower the Vas the higher the inertia ? (1st question)
But if I have two woofers, the first with a Qts=0.41 and the second with Qts=0.835, what does this mean in practical terms?
I mean, is the Qts a measure of how is dampened the woofer’s cone ?
For a woofer with high Qts an amp with a good damping factor is needed?
Thank you very much indeed.
Kind regards,
beppe61
I have a kind but maybe trivial question about woofers parameteres.
I know already that the Vas is a measure of the resistance to motion of the cone, the surround, and the spider.
Something like its inertia.
The lower the Vas the higher the inertia ? (1st question)
But if I have two woofers, the first with a Qts=0.41 and the second with Qts=0.835, what does this mean in practical terms?
I mean, is the Qts a measure of how is dampened the woofer’s cone ?
For a woofer with high Qts an amp with a good damping factor is needed?
Thank you very much indeed.
Kind regards,
beppe61
Pretty much. However, a speaker with a Qts of 0.83 is considered well-damped.
It should be pointed out that for decades, most sealed systems had a Qtc between 0.7 and 1.0. And they were considered well put together systems.
Just about any solid state amp, mid-fi or above, should have no problem driving a speaker of any Qts whatsoever. Damping factors in solid state amps are more than adequate for just about anything.
One thing about your speaker with a Qts = 0.83, though. If you put it in a sealed box, that Qts will rise. If you put it in a box equal in volume to it's Vas, for instance, the Qts will rise to a Qtc =1.2. Which is not horrible, just a little less tight in the bass than you might like. It will still have tighter bass than just about any ported system.
Hi kelticwizard,
Qts=0.383 is almost perfect for a B4 alignment. 0.41 is in the range unless Fs is too high making a ported box a poor choice.
-Chris
I really can't agree with you on that. A proper B4 can have tight bass, and normally does if the tuning is low enough. A woofer with a Qts=0.84 should be mounted in a wall (infinet baffle) or guitar amp. It has a small magnet for it's size.
Qts=0.383 is almost perfect for a B4 alignment. 0.41 is in the range unless Fs is too high making a ported box a poor choice.
-Chris
Chris:
Below are the step responses for selected Closed Box and Vented box alignments, from Small's papers. The colored text is added by myself.
As you can see, even in a vented alignment where the Vas/Vb ratio, (a) is 4, the bass is slightly sloppier than a Closed Box alignment where Qtc = 1.3. And that Vented alignment is a QB3 alignment, tighter than the B4 you mentioned.
A Closed Box alignment of Qtc = 1.2 will be better than Qtc = 1.3. Note how much smoother the Qtc = 1.0 alignment is.
I happen to like vented boxes, I think their advantages outweigh their disadvantages, in most cases. But the step response of most of them is not as tight as a Closed Box with a Qtc=1.2.
Below are the step responses for selected Closed Box and Vented box alignments, from Small's papers. The colored text is added by myself.
As you can see, even in a vented alignment where the Vas/Vb ratio, (a) is 4, the bass is slightly sloppier than a Closed Box alignment where Qtc = 1.3. And that Vented alignment is a QB3 alignment, tighter than the B4 you mentioned.
A Closed Box alignment of Qtc = 1.2 will be better than Qtc = 1.3. Note how much smoother the Qtc = 1.0 alignment is.
I happen to like vented boxes, I think their advantages outweigh their disadvantages, in most cases. But the step response of most of them is not as tight as a Closed Box with a Qtc=1.2.
Attachments
"I know already that the Vas is a measure of the resistance to motion of the cone, the surround, and the spider.
Something like its inertia."
No, it's related to suspension stiffness, not mass.
Also note that Qts refers to Q of the driver alone.
Qtc is Q in a closed box, and will always be higher than Qts because the air adds spring stiffness.
Well, that's true for an unfilled box; stuffing can add air friction losses that lower Q.
Something like its inertia."
No, it's related to suspension stiffness, not mass.
Also note that Qts refers to Q of the driver alone.
Qtc is Q in a closed box, and will always be higher than Qts because the air adds spring stiffness.
Well, that's true for an unfilled box; stuffing can add air friction losses that lower Q.
noah katz said:
Dear Mr. Katz,
thank you very much for your extremely kind and valuable reply.
As usual I was simplifying things too much.
Is there a parameter that can be related to the inertia of the driver?
For instance the mass of the cone?
I am asking this because at the end and IMHO it is a matter to force the cone to move and get it to stop after the impulse.
Or not?
Kind regards,
beppe61
beppe61 said:
Isn't this the Mms parameter?
Mms can be calculated with this formula:
1/((2*PI*Fs)^2*Cms)
where Fs is the frequency resonance (Hz) of the driver, PI is about 3.142 and Cms is calculated as follow:
Vas/(Po * c^2 * Sd^2)
where Vas is the equivalent air volume (m^3), Po is the density of air (1.12 kg/m^3), c is the speed of sound (344 m/s) and Sd is effective piston area (m^3).
best regards
Erwin
Hi kelticwizard,
Thanks, I stand corrected as far as impulse response is concerned. I was speaking for experience as music normally has decaying waveforms as opposed to a straight impulse. This will cover up that behaviour from the speaker unless it gets out of hand. I set my system Q around 0.7 ish for sealed or ported designs.
My decision for a ported or sealed box hinges on the low frequency cutoff and whether or not the low end is filtered or not before the amplifier. I avoid driving a speaker below it's resonant frequency if possible.
-Chris
Thanks, I stand corrected as far as impulse response is concerned. I was speaking for experience as music normally has decaying waveforms as opposed to a straight impulse. This will cover up that behaviour from the speaker unless it gets out of hand. I set my system Q around 0.7 ish for sealed or ported designs.
My decision for a ported or sealed box hinges on the low frequency cutoff and whether or not the low end is filtered or not before the amplifier. I avoid driving a speaker below it's resonant frequency if possible.
-Chris
Chris:
In addition to the the reasons you mentioned, there is also the fact that the lower the frequency, the less sensitive our hearing. So bass reflex makes sense in the bass area, but I don't see many vented mids.
In addition to certain other advantages, there is the matter that in cases where the woofer will also be carrying the midrange, the bass reflex system has less distortion due to the fact that the speaker does not have to move nearly as much to produce the bass notes as the sealed system must. the greater the excursion necessary to produce bass notes, the muddier the midrange.
In addition to the the reasons you mentioned, there is also the fact that the lower the frequency, the less sensitive our hearing. So bass reflex makes sense in the bass area, but I don't see many vented mids.
In addition to certain other advantages, there is the matter that in cases where the woofer will also be carrying the midrange, the bass reflex system has less distortion due to the fact that the speaker does not have to move nearly as much to produce the bass notes as the sealed system must. the greater the excursion necessary to produce bass notes, the muddier the midrange.
kelticwizard said:
Dear Sir,
this point is very important to me.
I have always thought that a 2 ways speaker is not a good solution just for this reason: the woofer is asked to reproduce low bass (great excursions) and the mid at the same time.
I have read that a full range speaker should be 4 ways.
Giving up to low bass (i.e. <40Hz) a 3 ways could suffice.
What is your opinion on this?
Thank you very much indeed.
Kind regards,
beppe61
e-side said:
Dear Mr. Erwin,
thank you very much for the very interesting reply.
I am completely ignorant on this topic.
Nevertheless I think that this "Mms" could be very critical, because measuring the inertia of the cone should give some indications about the power needed to drive the speaker adequately.
After all is a matter to make the woofers move fast and stop fast or am I missing something.
Maybe I am oversimplifying but to drive an high Mms woofer a very strong (i.e. high current) amp is needed.
Thank you very much indeed.
Kind regards,
beppe61
"Nevertheless I think that this "Mms" could be very critical, because measuring the inertia of the cone should give some indications about the power needed to drive the speaker adequately."
Just look at the efficiency, which accounts for the mass, motor strength, and cone area, which together determine the efficiency.
Rather than look at the mfgr's spec, which is a single number, look at the response curve with 1 W using a decent software program.
This will show how the efficiency varies with freq; often the spec is given at a midrange freq, and it is several dB less at lower freq.
WinISD Pro is a free download.
Just look at the efficiency, which accounts for the mass, motor strength, and cone area, which together determine the efficiency.
Rather than look at the mfgr's spec, which is a single number, look at the response curve with 1 W using a decent software program.
This will show how the efficiency varies with freq; often the spec is given at a midrange freq, and it is several dB less at lower freq.
WinISD Pro is a free download.
Beppe:
I should point out that Mms is usually given in the specs, along with Qts, Vas, Fs, etc.
As Noah said, Mms is just one factor. For instance, the driving force of a speaker is it's Bl factor, and that can vary. It is like with cars. One car can be heavier than the other, but still might be able to out-accelerate the other because it has a more powerful engine.
The sensitivity, (how many dB @ 1W/1M) will tell you how loud the speaker plays in the midrange and high range areas. Free software such as WinISD, BoxModel, Unibox, etc will tell you how how, when placed in a box, the speaker will play through the bass range.
I should point out that Mms is usually given in the specs, along with Qts, Vas, Fs, etc.
As Noah said, Mms is just one factor. For instance, the driving force of a speaker is it's Bl factor, and that can vary. It is like with cars. One car can be heavier than the other, but still might be able to out-accelerate the other because it has a more powerful engine.
The sensitivity, (how many dB @ 1W/1M) will tell you how loud the speaker plays in the midrange and high range areas. Free software such as WinISD, BoxModel, Unibox, etc will tell you how how, when placed in a box, the speaker will play through the bass range.
Hi kelticwizard,
It's true that a ported box reduces the excursion of the woofer. This only occurs at Fb where the resonance damps the woofer. Below this frequency the woofer becomes unloaded as the frequency drops. Well above this, the box behaves as a sealed one. There are some box designs with two peaks and broad damping over this region. There sound good too.
Hi beppe61,
There are some who believe a single full range driver sounds the best as well. Personal taste I guess. A two way speaker can sound great ( I have some). There are designs that are essentially a two way with restricted bass added to a sub section. It's a three way with a low crossover frequency between the bass / mid driver unit.
-Chris
It's true that a ported box reduces the excursion of the woofer. This only occurs at Fb where the resonance damps the woofer. Below this frequency the woofer becomes unloaded as the frequency drops. Well above this, the box behaves as a sealed one. There are some box designs with two peaks and broad damping over this region. There sound good too.
Hi beppe61,
There are some who believe a single full range driver sounds the best as well. Personal taste I guess. A two way speaker can sound great ( I have some). There are designs that are essentially a two way with restricted bass added to a sub section. It's a three way with a low crossover frequency between the bass / mid driver unit.
-Chris
"It's true that a ported box reduces the excursion of the woofer. This only occurs at Fb where the resonance damps the woofer."
The excursion reduction and output increase covers about the bottom half octave, where it does the most good in reducing distortion (because the largest excursions are at the lowest freq).
The excursion reduction and output increase covers about the bottom half octave, where it does the most good in reducing distortion (because the largest excursions are at the lowest freq).
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