i read that the speakers Q is its damping factor, or something like that....and that low Q speakers (<.3) should be in ported boxes, and that high Q (>.7) should be in sealed enclosures...
i know when one is designing a box, he can alter the Q he wants the system to be, i hear .707 is a popular Q because it is in the middle....
since the designer gets to essentially "choose" which Q value he wants, is this the new overall damping of the system or just the damping of the enclosure? does a high Q enclosure damp the speaker more than a low Q enclosure does?
i know when one is designing a box, he can alter the Q he wants the system to be, i hear .707 is a popular Q because it is in the middle....
since the designer gets to essentially "choose" which Q value he wants, is this the new overall damping of the system or just the damping of the enclosure? does a high Q enclosure damp the speaker more than a low Q enclosure does?
There's a pile of different parameters called Q, and they all have to be kept straight. Sorry!
Basically, Q is the inverse of damping. You can get a rigorous definition of the meaning of Q in general from any physics text that covers vibrations and waves. The definitions of Qes, Qms, Qts, Qtc, Qb, Ql, and the various other members of the Q family specific to loudspeakers can be gotten out of a speaker design text; if you don't have a copy of Dickerson's Loudspeaker Design Cookbook, run right out and get it.
Basically, Q is the inverse of damping. You can get a rigorous definition of the meaning of Q in general from any physics text that covers vibrations and waves. The definitions of Qes, Qms, Qts, Qtc, Qb, Ql, and the various other members of the Q family specific to loudspeakers can be gotten out of a speaker design text; if you don't have a copy of Dickerson's Loudspeaker Design Cookbook, run right out and get it.
Q is about losses in a resonant system. The higher the Q, the lower the losses, and the higher the resonance.
Tap a good wine glass on the rim... it sings a note, one note, and keeps singing for awhile. This high Q. It has low losses, the energy just keeps "ringing" until all the energy in the glass radiates out as sound. Now this wouldn't make a good speaker because anytime the music hit that note... the speaker would wig out. In this case you want a speaker box to combine with the speaker to lower the Q.
Now tap a plastic cup up on the rim... thunk. This is low Q system, the energy you added was rapidly dissipated (lost) in the material itself. Now this could make a good speaker, but you certainly would not have to go crazy damping it with an exclosure.
Now you have a real-life-physics-based-"feel" for Q. In many things, high Q is an indicator of quality... not so simple with speakers... Q would have more to do with "flavor" or "type". Don't equate low Q with low quality... speakers are inherently low efficiency devices... 3% give or take a few.
The speaker savant's will come along now and confuse the bujeesus out of you; and save you from ramblings such as this.
Tap a good wine glass on the rim... it sings a note, one note, and keeps singing for awhile. This high Q. It has low losses, the energy just keeps "ringing" until all the energy in the glass radiates out as sound. Now this wouldn't make a good speaker because anytime the music hit that note... the speaker would wig out. In this case you want a speaker box to combine with the speaker to lower the Q.
Now tap a plastic cup up on the rim... thunk. This is low Q system, the energy you added was rapidly dissipated (lost) in the material itself. Now this could make a good speaker, but you certainly would not have to go crazy damping it with an exclosure.
Now you have a real-life-physics-based-"feel" for Q. In many things, high Q is an indicator of quality... not so simple with speakers... Q would have more to do with "flavor" or "type". Don't equate low Q with low quality... speakers are inherently low efficiency devices... 3% give or take a few.
The speaker savant's will come along now and confuse the bujeesus out of you; and save you from ramblings such as this.
I just googled this. it has an interesting table summarizing the popular alignments.
http://www.winebase.com.au/audio/avsbdm.htm
http://www.winebase.com.au/audio/avsbdm.htm
And the higher the acceleration of the cone, the greater the seeming 'mass' of the air (air in the box and in the port) that has been set in motion by the driver. Thus the importanceof the low Q driver when designing ported systems. That is a 'general' rule though, there is no reason, other than it being a general truism. I've had plenty of results that end up showing another result, as have others, I'm sure.
Now, once that has been understood, it should be noted that the resonance (q) of a port/box (both are designed as a mated set, ie the port resonance is a part of the box - as a 'design') should not be too close to the resonance ( Hz) (q) of the driver. If both are the same, then.. the woofer my end up exciting itself to death. PSB did this a while back, with the 500 series of speakers. And ended up replacing many a driver. ie, thousands. Ouch. sorry to use you as an example, Paul.
Oh yeah. The fact that air can be compressed and act like a 'spring', is what allows it to be analysed with the idea of it (in a sealed box - a ported box is similar but a bit different --in analysis), as a specific volume, in a box, to have a 'Q'. No spring---no 'Q'.
Now, once that has been understood, it should be noted that the resonance (q) of a port/box (both are designed as a mated set, ie the port resonance is a part of the box - as a 'design') should not be too close to the resonance ( Hz) (q) of the driver. If both are the same, then.. the woofer my end up exciting itself to death. PSB did this a while back, with the 500 series of speakers. And ended up replacing many a driver. ie, thousands. Ouch. sorry to use you as an example, Paul.
Oh yeah. The fact that air can be compressed and act like a 'spring', is what allows it to be analysed with the idea of it (in a sealed box - a ported box is similar but a bit different --in analysis), as a specific volume, in a box, to have a 'Q'. No spring---no 'Q'.
"it should be noted that the resonance (q) of a port/box (both are designed as a mated set, ie the port resonance is a part of the box - as a 'design') should not be too close to the resonance ( Hz) (q) of the driver. "
If you saying that Fb, the port tuning freq, shouldn't be the same as Fc, the driver/boc resonance, I disagree.
Two things - first, the driver resonance only causes an impedance peak that limits power input, the result being no excess cone movement at all at Fc, unless Q is too high.
Second, if you were to overlay the freq, the effect would be to reduce cone excursion, because that's what happens at Fb.
And if Fb = Fc, the impedance peak of the driver resonance gets combined with the impedance trough of Fb, giving a more even impedance across the range.
"No spring---no 'Q'."
Sorry, I disagree with that as well - that's like saying you can't have R without C or L.
If you saying that Fb, the port tuning freq, shouldn't be the same as Fc, the driver/boc resonance, I disagree.
Two things - first, the driver resonance only causes an impedance peak that limits power input, the result being no excess cone movement at all at Fc, unless Q is too high.
Second, if you were to overlay the freq, the effect would be to reduce cone excursion, because that's what happens at Fb.
And if Fb = Fc, the impedance peak of the driver resonance gets combined with the impedance trough of Fb, giving a more even impedance across the range.
"No spring---no 'Q'."
Sorry, I disagree with that as well - that's like saying you can't have R without C or L.
A related question:
How does the Q of a filter relate to its Fc and its corner frequencies? Most filter tables I know (and I do have Dickason's book) give only formulas for construction of a particular LP or HP filter, be it active or passive. SO you get the parameter values.
What I haven't found though is tables that give the corner frequencies of specific alignments, say, F1, F2 and F3 for a 3 pole filter down 3 dB at Fc.
Why I want to know this: often, you can use the drivers' own rolloff and associated corner frequencies to use as a filter section. So, if you know that your driver has a pole at Fx, which Fy and Fz do you have to conjugate it with to get an acoustic 3 pole Bessel filter, for example.
Any references on this?
How does the Q of a filter relate to its Fc and its corner frequencies? Most filter tables I know (and I do have Dickason's book) give only formulas for construction of a particular LP or HP filter, be it active or passive. SO you get the parameter values.
What I haven't found though is tables that give the corner frequencies of specific alignments, say, F1, F2 and F3 for a 3 pole filter down 3 dB at Fc.
Why I want to know this: often, you can use the drivers' own rolloff and associated corner frequencies to use as a filter section. So, if you know that your driver has a pole at Fx, which Fy and Fz do you have to conjugate it with to get an acoustic 3 pole Bessel filter, for example.
Any references on this?
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