I'm impressed. I started mine about 15 months ago.
I'm retired. It's raining in New England. Can't play tennis. Too wet to take the Ferrari out. By buddy's Catalina 30 blew out a main sail so sailing in the rain is out. What else is there to do but cut wood?
Nicest minime would be the slot handing it to a long enough ribbon. But acoustics will not deter the FR near field wood cutter from trying I suspect.
Tang Band W23-1287SI 2"x3" Driver 4 Ohm
Nicest minime would be the slot handing it to a long enough ribbon. But acoustics will not deter the
FR near field wood cutter from trying I suspect.
Hi,
Not really, its a sort of reverse issue. Treble line arrays maintain efficiency
and cylindrical dispersion down to ~ wavelength = line array length.
Below that it becomes hemispherical and efficiency drops off drastically.
A bass slot is an entirely different matter, its hemispherical up to a point,
and IMO like my speakers would never match well to a line treble array.
rgds, sreten.
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Hi,
I agree with the first point but not the second.
A smaller version will transit to farfield at much smaller distances,
no-one is saying so far it must be used in nearfield conditions.
The advantage of the mini model approach is its far easier to
ascertain the real far field effect, and any near field effect.
rgds, sreten.
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Beyond a handy research model, if seen as a pet OB slot loudspeaker project, what it does up to 1-1.5m will be of more interest to a mini speaker enthusiast I meant. If used for a PC system in a small space, DSP programs will be easily on hand to assist it lower, or drive and cross actively with T amps, many ideas.
John K..,
Following your experiment with much interest.
Are you in a position to measure harmonics? As I posted before, there might be a mechanism at work that produces even harmonics, because the outward stroke will have a different acoustic coupling than the inward stroke. Nelson doesn't think so, but I am not convinced.
vac
Following your experiment with much interest.
Are you in a position to measure harmonics? As I posted before, there might be a mechanism at work that produces even harmonics, because the outward stroke will have a different acoustic coupling than the inward stroke. Nelson doesn't think so, but I am not convinced.
vac
In the end we may end up with two models: Nelson's one, and
John's smaller version. While John's OB will seem to enjoy the
nickname "MiniMe", then I'd call Nelson's OB "Big Bang". Oh no,
that one has already been taken...
Hi.
No. that is not the case. JK knows his onions, and knows what he is doing.
It is not about a mini practical version, it is about practical measurements.
rgds, Sreten.
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Sawdust and measurements…….. ummm good.
Vacuphile asks “As I posted before, there might be a mechanism at work that produces even harmonics”
Normally, this arrangement will actually produce less harmonic distortion that the direct radiating case.
The reason is one has added an acoustic low pass filter comprised of a trapped air volume and mass of air in the port, in addition the port will have “organ pipe” resonances.
At the very low end, the mass in the ports adds to the driver and will lower the Fs or fb relative to an open mounting .
Circlomanen has modeled something similar in post 41, if you examine it, you can see the details.
Note the general low pass slope around 200Hz and that it is approximately a 2nd order slope as one would expect from a two element filter like this.
At some point, the series inductance makes the slope steeper as it become a third order roll off.
Generally this prediction program as well as AKABAK will over state the Q of the peaks shown, the measured result normally has a lower Q.
If one made the port longer, the peaks and dips move down in frequency, if you make the area larger as well, the Q of the peaks and dips goes down as the radiation resistance damps them.
If you make the trapped air volume smaller, the low pass filter frequency moves up. If you make the driver strength as reflected through the motor and driver compression ratio “right”, one can damp the resonances into extinction and then one has a proper horn.
In both cases, a proper horn or inadvertent horn, the low pass acoustic filter attenuates the harmonics the driver naturally produces when they fall in the range where the filter has roll off. In the horns we sell at work, all of them have an air volume and port between the driver and the horn passageway for the same reasons, it reduces the distortion, same for a band pass subwoofer.
Best,
Tom Danley
Danley Sound Labs
Vacuphile asks “As I posted before, there might be a mechanism at work that produces even harmonics”
Normally, this arrangement will actually produce less harmonic distortion that the direct radiating case.
The reason is one has added an acoustic low pass filter comprised of a trapped air volume and mass of air in the port, in addition the port will have “organ pipe” resonances.
At the very low end, the mass in the ports adds to the driver and will lower the Fs or fb relative to an open mounting .
Circlomanen has modeled something similar in post 41, if you examine it, you can see the details.
Note the general low pass slope around 200Hz and that it is approximately a 2nd order slope as one would expect from a two element filter like this.
At some point, the series inductance makes the slope steeper as it become a third order roll off.
Generally this prediction program as well as AKABAK will over state the Q of the peaks shown, the measured result normally has a lower Q.
If one made the port longer, the peaks and dips move down in frequency, if you make the area larger as well, the Q of the peaks and dips goes down as the radiation resistance damps them.
If you make the trapped air volume smaller, the low pass filter frequency moves up. If you make the driver strength as reflected through the motor and driver compression ratio “right”, one can damp the resonances into extinction and then one has a proper horn.
In both cases, a proper horn or inadvertent horn, the low pass acoustic filter attenuates the harmonics the driver naturally produces when they fall in the range where the filter has roll off. In the horns we sell at work, all of them have an air volume and port between the driver and the horn passageway for the same reasons, it reduces the distortion, same for a band pass subwoofer.
Best,
Tom Danley
Danley Sound Labs
Hehe... I kept thinking of bass horn throats when I built mine.
I'm not saying my mockup baffle is a proper horn. Far from it of course. But there're indeed some characters in sound quality in common, especially in low SPL. Clean, firmly gripped, gentle but forceful when quiet. Maybe the reasons mentioned above.
I'm not saying my mockup baffle is a proper horn. Far from it of course. But there're indeed some characters in sound quality in common, especially in low SPL. Clean, firmly gripped, gentle but forceful when quiet. Maybe the reasons mentioned above.
Tom, I understand what you saying, but there is only one way to know: to measure the same driver in this setup and on a normal open baffle, and to compare distortion figures. I hope John K.. has the time and the gear to do this. It is all very theoretical now and only a good experiment can tell.
I looked at the sim in post 42 and I cannot deduce much from it. Plus, it's a sim, not much good for predicting distortion of speakers in an enclosure for which the sim was not developed.
A horn is a very different animal from this loaded slut setup. A horn is an impedance transformer that changes high velocity @ small area into low velocity @ large area. The slot loading works in an opposite direction; it changes low velocity @ large area (speaker surface) into higher velocity @ smaller area (the slot). Because of different acoustic loading on the inward and outward stroke, we may get the classical sort of assymetry which predicts generation of even order distortion products.
This is an independant distortion mechanism from the ones in the driver itself. I do agree with you that, under circumstances, the distortion products generated by the driver may be attenuated when coupled through an acoustic low pass filter. However, that is not what I was pointing at.
regards,
vac
I looked at the sim in post 42 and I cannot deduce much from it. Plus, it's a sim, not much good for predicting distortion of speakers in an enclosure for which the sim was not developed.
A horn is a very different animal from this loaded slut setup. A horn is an impedance transformer that changes high velocity @ small area into low velocity @ large area. The slot loading works in an opposite direction; it changes low velocity @ large area (speaker surface) into higher velocity @ smaller area (the slot). Because of different acoustic loading on the inward and outward stroke, we may get the classical sort of assymetry which predicts generation of even order distortion products.
This is an independant distortion mechanism from the ones in the driver itself. I do agree with you that, under circumstances, the distortion products generated by the driver may be attenuated when coupled through an acoustic low pass filter. However, that is not what I was pointing at.
regards,
vac
The asymmetry that you are talking of is the same one as some reflex ports can have (and that are sometimes leading to some rectification effect on woofers with very soft suspensions).
I think it can be significantly reduced by rounding the corners a bit or by using a short pseudo-horn.
Regards
Charles
I think it can be significantly reduced by rounding the corners a bit or by using a short pseudo-horn.
Regards
Charles
Seems to me that at the limit, this condition exists in all dynamic drivers. The open, unobstructed area on the front would provide a different loading than the rear that is obstructed to some degree by the motor, spider and frame. Maybe inconsequential due to magnitude, but the same condition nevertheless.
Dave
Dave
@Phase_accurate: my source of inspiration for my posts was indeed partially the behaviour of reflex ports. Flairing the edges is certainly a good idea to reduce air noise. However, there is a major difference. The air in a reflex port behaves like the mass in a spring-mass coupled system. It thus operates symmetrically on its momentum in both inward and outward cone movements. And even in that case, some assymetry in pipe behavour can lead to the results you describe.
@DLR
I am not talking about differences between loading on the rear and the front, but about differences in acoustic loading between inward and outward cone movement on the front side of the cone, driving the slot.
Let measurements deposit all the egg on my face I deserve,
Vac.
@DLR
I am not talking about differences between loading on the rear and the front, but about differences in acoustic loading between inward and outward cone movement on the front side of the cone, driving the slot.
Let measurements deposit all the egg on my face I deserve,
Vac.
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