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| Re: Some Questions Regarding This PA Subwoofer [message #45791 is a reply to message #45779] |
Sun, 14 November 2004 20:20   |
Elliot Thompson
Messages: 5
Registered: May 2009
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Esquire |
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Thanks. So, how have you concluded that the second speaker facing the
back the first speaker won't rip it apart under High SPL use? Or is this is meant to get 400 watts? What kind of cones, works bests such a design? Is the first
driver reinforced to handle the amount of air pressure being
subjected under high SPL use? Thanks! Elliot
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| Distortionss [message #45793 is a reply to message #45792] |
Sun, 14 November 2004 22:41 |
Mike.e
Messages: 471
Registered: May 2009
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Illuminati (1st Degree) |
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Hi wayne quoting
"Commercial loudspeakers generally have a force function containing both square and cubic terms,the second harmonic being predominant at medium levels,and the third harmonic increasing with increasing amplitude.."
-Loudspeaker and headphone handbook - John Borwick. I think the push pull arrangement will sound pretty good  Question-when the loudspeaker is used ABOVE resonance,what are the distortion factors - is it only BL nonlinearity? definately below Fs the stiffness is providing linearity. Book Also shows flux distribution with flush/extended pole piece(above top plate) showing reduced 2nd harmoncis by ~10db with extended pole piece The book also goes into
-Cone modes,w
-what the concentric corrugations on cones are for,
-nodal circle overtones(non harmonic!)
-also some boring derivation of point source/flat piston at the beginning :P
-HUGE! section on electrostatics
-Sizable section on room acoustics,
-enclosures and baffle resonance measurement,
-measurements and evaluation,
-hardly anything on horns though! I would buy this if it was cheap enough. Also 'high performance loudspeakers by martin colloms' is pretty good. SOme derivations,its abit more balanced, ie : normal amount of info on electrostatics :P Problem is that online descriptions of books tend to hardly even tell you chapter titles! ridiculous!Im thinking of Aes anthology on CD or something... Regards
Mike.e
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| Re: Distortions [message #45794 is a reply to message #45793] |
Mon, 15 November 2004 00:00 |
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Wayne Parham
Messages: 18792
Registered: January 2001
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Illuminati (33rd Degree) |
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The second harmonic is caused by asymmetry. Anything that causes asymmetry will cause even order harmonic distortion.The main thing that causes asymmetry in a loudspeaker is the magnet, not the suspension or pneumatic loading. Those are both much more linear than magnetic flux. What causes magnetic flux to be asymmetrical is modulation from the voice coil. When the voice coil flux is in the same polarity as the fixed magnet, then total flux is the sum of the two. But when voice coil flux is in opposite polarity, then the total flux is the difference of the two. So a loudspeaker literally pushes more in one direction than the other, even if only by a very small amount. This is the main cause of harmonic distortion in loudspeakers. See the link: Magnetic StructuresUsing a shorting ring really helps reduce harmonic distortion. It works by acting as a shorted secondary that counteracts flux modulation. When the voice coil is energized, it creates a magnetic field that interacts with the fixed magnet. This moves the voice coil and it also induces current in the shorting ring, which creates a magnetic field of its own. The magnetic field of the shorting ring is the opposite of that from the voice coil, and it serves to reduce flux modulation. It doesn't interact enough to cancel movement, just a small amount, enough to counter flux modulation. The idea is to make movement symmetrical, and it does this very well. It reduces harmonic distortion. The push-pull arrangement cancels harmonic distortion too. It does it in a different way. Instead of reducing asymmetry in the motor, it uses two of them and drives them in opposite directions. The idea is that one will be slightly stronger than the other on each half-cycle, and the opposite is true on the other half-cycle. A balance is struck because each half-cycle has a "strong" driver and a "weak" driver. 
A horn reduces distortion simply by reducing excursion. That's good, but it doesn't do anything to increase symmetry. And in the case of basshorns, the system may be driven below the frequency where the horn is effective. So my thoughts are that improved symmetry is always good. Horn loaded or not, folded or not, reduced distortion motors are desireable. In the horn's passband, improved symmetry serves to reduce distortion even more than the horn's reduced excursion provides. And in the case of a basshorn driven very low, the system reverts to being that of a direct radiator, so whatever linearity is built-in to the motor system is all you've got. Some have said that horn folding and front chambers reduce harmonics by attenuation. That is true. But what always troubled me with this reasoning is that the subsystems are used for more than an octave, so harmonics are presented within the passband. Sure, some of the higher frequency harmonics are attenuated by the front chamber and folds, but a lot of harmonics aren't. It just never made any sense to me to ignore the motor's distortion products. It seems obvious to me that the system is improved by employing symmetry-enhancing technologies. Honestly, for fidelity's sake, I think I'd rather have direct radiators with shorting rings or a push-pull arrangement than a horn-loaded subwoofer using ferrite magnet woofers without shorting rings. Unless the horn can be made huge, it's going to have an excursion jump down low. That's where the flux stabilized or push-pull arrangement can help, and where the horn really can't. If I have no design limits, the horn can be made huge and the drivers high quality with symmetrical movement. But in the real world with its real world design constraints, I think I'd take symmetry control over excursion control if high-fidelity were the goal. So to me, the decision to go with flux stabilization or push-pull plenums is very attractive. Horn loading is too, but again, it's only as good as size will allow. Symmetry doesn't require size.
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| Very true [message #45795 is a reply to message #45794] |
Mon, 15 November 2004 00:50 |
Mike.e
Messages: 471
Registered: May 2009
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Illuminati (1st Degree) |
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I agree with all this. A scoop style basshorn will have this 2nd harmonics then.I knew they were nonlinear-but didnt see how it affected the output.
So many say they like the sound of B*ssmaxx scoops,but I cant see how. The only PRO basshorn ive heard is the martin WSX,which i thoroughly enjoy pants flapping SPLS everyweek almost -down at the closest club with 2 of them!-too bad the muddled midrange ruins the sound!
Have you seen TCsounds '46mm Xmax' driver?it has ultimately flat BL curve!
The BL curve looks like some one has clicked 'linearise' on computer and theyve managed to produce a reality of this!!!
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| Re: Very true [message #45796 is a reply to message #45795] |
Mon, 15 November 2004 01:02 |
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Wayne Parham
Messages: 18792
Registered: January 2001
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Illuminati (33rd Degree) |
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I love basshorns; I love horns of all kinds.But the first time I heard a high-quality woofer with a shorting ring, I was even more impressed than the first time I heard a good high-quality horn. Put 'em both together and you have the ultimate sound system, in my opinion. From the midrange up, horn size isn't a problem so I can't see any reason to forego them. Bass is a different story. If you have the room, go horns. If not, don't. But either way, if you have the money to go with a technology that improves symmetry, all the better. It measures better and it sounds better.
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| Remember my 35hz plans? [message #45797 is a reply to message #45796] |
Mon, 15 November 2004 03:54 |
Mike.e
Messages: 471
Registered: May 2009
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Illuminati (1st Degree) |
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Well currently my 2226 is in 175litres 33hz tuned with +6db boost at 35hz(inbuilt plate amp which i cant be bothered removing)Although it definately is loud enough,why not have more SPL headroom for pants flapping stuff with less resonant behaviour and more fidelity! FINALLY the $$$ is coming through that i was missing - so im keen to cut MOST of the horn myself with skillsaw and a guide. I can use woodglue/silicon sealant incase i get it slightly wrong;-)
Exterior will probably be just paint - I was thinking of a dark blue rather than boring black.I can always change it! This way i save alot of money that wouldve been spent on the joiner! the only part he might do,is the throat baffle,because it costs heaps to rent a router.My horn only has the ONE critical 2 mitre angles on the baffle,he could do that one + wont cost much. Ive been having a serious think about horns,and I can only have 1pi loading. 35hz i think is a good compromise,i wont notice a couple of hz,and it keeps the basshorn abit smaller.I dont want to build a 50hz horn then want a lower cutoff!! Unfortunately alot of the horn volume is Vrc..But as an example 2 12"s on the same horn requires about the same. All set to go! Just wondering about speaker terminal connector now.. Regards
Mike.e
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