Is it better regarding sound quality small full range like mid tweeter with high or low Qms?
Example Alpair 5.3 has Qms=2,3, SB65WBAC25-4 Qms=6.
Example Alpair 5.3 has Qms=2,3, SB65WBAC25-4 Qms=6.
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Low Qms means high loss factor which is bad for efficiency and linearity. Why the latter? Because there are no fully linear brakes.
Qms provides precisely zero guide to sound quality: it is merely a mathematical construct representing mechanical damping at Fs. The simplistic twaddle that has been doing the rounds for the last few years implying that low mechanical damping is automatically 'superior' completely overlooks that fact that a/ it's just a mathematical representation for behaviour at & near Fs, which does not necessarily hold good anywhere else, and b/ you might actually need some mechanical damping. 😉 Wideband drive units work on the basis of controlled TL modes (resonances & bending modes in the diaphragms, along with, as relevant, progressive decoupling) in adition to regular oscillatory (front - rear) motion. So depending on cone size, materials, geometry, motor design, target resonant frequency, compliance & overall Q values, the amount of mechanical damping needs to be tailored to control these and produce the desired response.
Drivers with a very high mechanical Q can sound more open, cleaner and have a better dynamic range. This is because they have less loss. The surround is more flexible, the spider is better constructed, they have better air flow and usually have higher sensitivity. So a high mechanical Q is a very good indicator of energy storage behavior
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Well quoted, from somebody unspecified, who has utterly ignored everything I pointed out above. 😉 Given the fact that you started this thread asking a question, and have now posted an unspecified quotation in very large, bold letters, I assume you were not asking a question at all, but merely want to promote this nonsense.
I wonder if it ever occured to the original author of the above that all drive units, and particularly wideband drive units, actually require some mechanical damping to function. For instance, it would be physically impossible to make an Alpair 12P with a high Qm suspension, as it would not (could not) provide the necessary level of control over the coil & cone. The 12P is actually a rather good example of how simple assumptions can be misleading, because in addition to that general point, there is another aspect involved: in point of fact, the Alpair 12P's surround is extremely low-loss and has almost no damping effect at all: it's there primarily as an air-seal, with the spider providing over 90% of the driver's mechanical damping. However, since Qms is a lumped total, 'minor' details like this get overlooked.
I am also wondering what 'open,' 'cleaner' and 'better dynamic range' mean, since sans qualification, the above is total rubbish as it has no engineering basis whatsoever. 'Better airflow' is complete drivel -that depends on the basket, motor (magnet, polepiece & coil former) design & has no direct connection to Qms whatsoever. There is nothing to stop you making a driver with extremely low levels of mechanical damping in a basket with relatively poor airflow. 'Higher sensitivity' is also drivel sans any qualification. Higher than what?
Please. Let us stop this twaddle, and actually look at some engineering facts. Facts are usually more useful than wild, unsupported comments with zero qualification.
Thiele Small parameters, of which Qms is one, are mathematical constructs based on electrical filter theory that provide a simple model of a drive unit's behaviour around Fs, and up to the mass corner frequency Fhm.
Fhm = 2Fs/Qts
Above that point, mass dominates, and the accuracy of T/S approximation falls away.
Qms is a construct, not a 'real' value.
Qms = (2pi * Fs * Mms)/Rms
A wideband drive unit, operating under controlled TL conditions, is a resonant structure that requires damping in order to control the bending & transverse resonant modes through the substrate. Casually stating 'reducing damping is better' would render many of them instantly inoperable, with massive, uncontrolled modes because the suspension is no longer controlling the diaphagm. QED.
I wonder if it ever occured to the original author of the above that all drive units, and particularly wideband drive units, actually require some mechanical damping to function. For instance, it would be physically impossible to make an Alpair 12P with a high Qm suspension, as it would not (could not) provide the necessary level of control over the coil & cone. The 12P is actually a rather good example of how simple assumptions can be misleading, because in addition to that general point, there is another aspect involved: in point of fact, the Alpair 12P's surround is extremely low-loss and has almost no damping effect at all: it's there primarily as an air-seal, with the spider providing over 90% of the driver's mechanical damping. However, since Qms is a lumped total, 'minor' details like this get overlooked.
I am also wondering what 'open,' 'cleaner' and 'better dynamic range' mean, since sans qualification, the above is total rubbish as it has no engineering basis whatsoever. 'Better airflow' is complete drivel -that depends on the basket, motor (magnet, polepiece & coil former) design & has no direct connection to Qms whatsoever. There is nothing to stop you making a driver with extremely low levels of mechanical damping in a basket with relatively poor airflow. 'Higher sensitivity' is also drivel sans any qualification. Higher than what?
Please. Let us stop this twaddle, and actually look at some engineering facts. Facts are usually more useful than wild, unsupported comments with zero qualification.
Thiele Small parameters, of which Qms is one, are mathematical constructs based on electrical filter theory that provide a simple model of a drive unit's behaviour around Fs, and up to the mass corner frequency Fhm.
Fhm = 2Fs/Qts
Above that point, mass dominates, and the accuracy of T/S approximation falls away.
Qms is a construct, not a 'real' value.
Qms = (2pi * Fs * Mms)/Rms
A wideband drive unit, operating under controlled TL conditions, is a resonant structure that requires damping in order to control the bending & transverse resonant modes through the substrate. Casually stating 'reducing damping is better' would render many of them instantly inoperable, with massive, uncontrolled modes because the suspension is no longer controlling the diaphagm. QED.
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Interview with Joachim Gerhard of Audio Physics
Here Mr Gerhard comments that many new drivers are very heavily damped in order to give flat frequency response, something which is characterized by low Qms. He then goes on to say that many of the older drivers with much less mechanical damping and high Qms were much more dynamic.
Like Scott said, T/S mainly talks about behaviour down at the FS, the only exception may be in the LE and MMS/MMD factor, but that is for MMS and MMD largely influenced by the motor and the cabinet i think.
Le is inductance of the magnet, and works a bit as a high pass filter (to simplify it), the higher the Le, the less high frequencies are present in the response
MMS (and the linked MMD) influences the needed strentgh of the motor, but the number on it's own doesn't say that much.
I'm more looking at the cone geometry, cone material, frequency response, dispertion and distortion figures to see if a driver will be good sounding or not, not at T/S parameters. They only tell how low it can go in what kind of alignment and how big the speaker cabinet must be.
Le is inductance of the magnet, and works a bit as a high pass filter (to simplify it), the higher the Le, the less high frequencies are present in the response
MMS (and the linked MMD) influences the needed strentgh of the motor, but the number on it's own doesn't say that much.
I'm more looking at the cone geometry, cone material, frequency response, dispertion and distortion figures to see if a driver will be good sounding or not, not at T/S parameters. They only tell how low it can go in what kind of alignment and how big the speaker cabinet must be.
What is the source, and his comparative data? Otherwise, with the greatest respect to Joachim, he is simply expressing an opinion without providing basis. For instance, the above itself is telling:
'Many new drivers...' (models & types unspecified) '...are very heavily damped...' (means of classification unspecified) '...in order to give flat frequency response, something which is characterized by low Qms' (which to put it mildly is a generalisation, since many drivers with a low Qms do not have a flat response).
'...many of the older drivers' (models & types unspecified) '...with much less mechanical damping...' (means of classification unspecified) '...and high Qms were much more dynamic' (definition and comparisons unspecified).
Perhaps you can supply the missing definitions, comparisons & data, because without them, we're dealing with no more than opinion, not fact, and that opinion's value depends on the basis. In God we trust. In all others, we verify.
'Many new drivers...' (models & types unspecified) '...are very heavily damped...' (means of classification unspecified) '...in order to give flat frequency response, something which is characterized by low Qms' (which to put it mildly is a generalisation, since many drivers with a low Qms do not have a flat response).
'...many of the older drivers' (models & types unspecified) '...with much less mechanical damping...' (means of classification unspecified) '...and high Qms were much more dynamic' (definition and comparisons unspecified).
Perhaps you can supply the missing definitions, comparisons & data, because without them, we're dealing with no more than opinion, not fact, and that opinion's value depends on the basis. In God we trust. In all others, we verify.
Always watch who you are quoting. There is more total BS out there than in politics. " More dynamic" may just mean far higher distortion as the driver is uncontrolledly. Your choice.
As far as selecting a driver, wideband drivers have many compromises and each is a preference.
As far as selecting a driver, wideband drivers have many compromises and each is a preference.
Correct, assuming the driver is working under piston (oscillatory) conditions. It breaks down somewhat when TL modes come into play however.
Right, and that was what Small, and previously Thiele, Novak & Thuras created these models for. And very useful they are too, for the purpose intended. Of course, it's worth keeping in mind that many of the data we lump in with T/S parameters aren't actually T/S parameters at all -they're fundamentals (Mmd, Mms, Fs, Re etc.) which we include / incorporate with them.
Scottmoose according to you big knowledge, no matter Qms how you will describe without listening above mentioned drivers?
Fs, Qts and frequency response of what drivers? He's saying that Qms is a simplification that doesn't describe the drivers actual behavior enough to make conclusions about it's sound. So, don't you think in that case more information would be needed, other than the Qms of the driver?
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Oh thank you. I'm curious to know now too, they appear very similar except one has no spider. Very nice looking drivers!
Latter, sorry, not my language. All mechanical resistance is somewhat non linear. Drivers with low mechanical resistance can only have a small contribution to distortion from this source. The more mechanical resistance, the more non linearities from that source may manifest themselves.
Qes is no more a mathematical construct than Qms. Old timers who have done these measurements with a scope know, that you look at a point on the impedance curve that is 1/3rd lower than the maximum. This is of course arbitrary, it could have been 1/2 and nothing would change except the numbers. But the underlying physical quantities don't change. Qes is a measure of electric braking force and Qms of mechanical braking force.
As to Scottmoose's point: there is no reason to believe that drivers need friction to operate. None.
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Lose the attitude.
Describe in what way?
If you want a brief description then:
SB65WBAC25-4 is a 2 1/2in wideband drive unit in a cast alloy basket with a 1in coil, oversized dustcap and a tangentially ribbed aluminium cone to control bending / resonant modes of the substrate & a copper cap to the polepiece, and a middling to higher Q for use primarily in sealed enclosures, though QW variations are theoretically possible. Sensitivity is reasonable for a driver of its size, response linearity good on axis up to its primary cone mode, although it may have to have some form of energy storage centred on approximately 1KHz (interestingly this does not appear to show up on the impedance curve though). Off-axis isn't too bad out to 30 degrees in terms of consistency, although not as good as I would hope for given the cone size; likely a result of the roll surround & dustcap dimensions. Inferring from the on & 30 degree plot though, it should be good to at least 15 degrees off axis. Although Fs is low for a 2 1/2in driver, distortion & power handling will be limited if run unfiltered given the small size.
Alpair 5.3 is a 3in wideband drive unit with just over 28% more radiating area than the aforementioned SB. It uses a polymer basket, a 1in coil, copper cap to the polepiece, aluminium-magnesium alloy cone with a very shallow profile & small dustcap bonded to the end of the VC. Unlike the SB it is a single-suspension spiderless design where the surround does all the mechanical damping & control. Qt is middling, and can be used in sealed or variations of vented enclosures, including QW. Sensitivity is reasonable for a driver of its size, response linearity good on-axis with slightly less HF rise than the SB, but a minor cone mode @ 2.4KHz which is a transverse reflection from the duscap. Off axis plots are not provided, but the ones I have suggest it holds up as well or better than the SB despite being larger, mostly due to the cone profile, inverse surround & small cap profile. Like the SB, power handling is limited in outright terms due to the small size, but being a slightly larger unit in practice it should handle a little more LF, though all drivers this small are ultimately limited in this regard (note MA & SB do not use the same method for testing power-handling: MA assume it's unfiltered.
And that's about all you can reasonably say from the published data. Note the drivers are not even in the same size bracket so detailed comparisons are somewhat specious anyway.
Low Qms will allow for a greater possiblity of using a high Rout amplifiers. It just means you do not need the amplifier to supply as much damping as in a high Qms would require.
I have seen a whole lot of misinformation in the “hugh Qms” thread. In the end, the driver, the amplifier and the enclosure need to supply the same total amount of damping for flattish response and good tramsient behaviour.
Pigeon holing just the driver likely means the OP has only ever heard a high Rout amplifier.
The amplifier, loudspeaker, and what connects them is a system.
The Alpair 5.3 just edges out the FF85wk as my favorite 3” driver. Especially when stock, EnABLed they are much closer (i could not pick between the 2 during an extensive audition).
In trhe end “what does it sound like”.
dave
If the driver doesn’t have those losses, they then need to come from the amplifier and the box.
dave