Download the new research report here:
Meriläinen, Esa: Comparative Measurements on Loudspeaker Distortion: Current vs. Voltage Control Archives of Acoustics. Vol. 42, No. 1, pp. 71–81 (2017).
Meriläinen, Esa: Comparative Measurements on Loudspeaker Distortion: Current vs. Voltage Control Archives of Acoustics. Vol. 42, No. 1, pp. 71–81 (2017).
a question is the audibility of the distortions that are improved by current driving dynamic loudspeakers
Geddes seems to rate most small signal, smooth nonlinearities, especially those of dynamic drivers as no problem at all for audibility compared to physical acoustics of radiation, diffraction, room interactions
the only place I see even slight speculation of significant audible improvement from current drive from several experts writings would be reducing power compression of voice coil resistance rise with heating with V drive
Geddes seems to rate most small signal, smooth nonlinearities, especially those of dynamic drivers as no problem at all for audibility compared to physical acoustics of radiation, diffraction, room interactions
the only place I see even slight speculation of significant audible improvement from current drive from several experts writings would be reducing power compression of voice coil resistance rise with heating with V drive
It could be of interest for SOTA active loudspeakers though, where all of this is irrelevant and EQ is easily applied. As far as I can tell from the data, it can do little about displacement related distortion or cone breakup, and 2nd-order distortion often did not improve much or even got worse in some cases, but 3rd-order and higher IMD is tackled quite effectively. Some drivers like the 10" PA job go from thoroughly meh to superb.
Unfortunately that would also make it easier to let the magic smoke out. Another point for active concepts - active studio monitors generally ship with built-in limiters already.
I think that most of the mental inertia is on the markets. That is the major reason why I think current control will not penetrate markets first in separate amplifiers and loudspeakers. Instead I expect that some active speaker manufacturers would be first producing new speaker models with current control and not even mentioning it.
@ Nikolas Ojala
Hi, Thanx for posting the link to the PDF on Archives of Acoustics Great www, & Very interesting paper
The reductions in THD they found are very impressive indeed !
Whether the industry takes advantage of the findings, is another matter though.
Hi, Thanx for posting the link to the PDF on Archives of Acoustics Great www, & Very interesting paper
The reductions in THD they found are very impressive indeed !Whether the industry takes advantage of the findings, is another matter though.
Industry will obey demand.
I have a feeling that audio hobbyists must wake them up.
Anyway, this is diyAudio.
I have a feeling that audio hobbyists must wake them up.
Anyway, this is diyAudio.
It is not mental inertia, because the market will do anything that brings money.
But it would be stupid for a manufacturer. Firstly, he has to build up a whole new area of competence, and find people who understands this stuff. Next, if he is an amp manufacturer, he has to lock himself to just one speaker because with current drive the amp must be adapted to the speaker, or make an amp that is configurable to many different existing and coming speakers. Suicide, commercially, because it i'll cost him a fortune and he will make no money to speak off.
Jan
I have posted in a number of threads on the issue of current drive and what I believe are its audible advantages. Reductions in displacement-dependent non-linearities are not a feature that jumps to the top of the list - not least because the inevitable motional feedback required (which I assume here to include pre-calibrated compensation means as well as traditional, 'online' motional feedback) also implores substantially linear drivers to start with.
IMHO the biggest advantage is the elimination of (current-dependent) non-linearities due magnetic non-linearities in the motor structure such as those employing block steel pole pieces. Once identified this distortion is easily identified in many speakers - even in some where copper plating or other such means has been employed to reduce the effects.
I also point out that thermal compression in a single driver is inaudible as the thermal constant is relatively long. BUT what is normally overlooked is the effect of thermal compression in a multi-way system that changes the frequency balance and is audible. Current drive eliminates this distortion.
Both of these advantages will hopefully encourage others to try even if commercial implementations remain unlikely.
IMHO the biggest advantage is the elimination of (current-dependent) non-linearities due magnetic non-linearities in the motor structure such as those employing block steel pole pieces. Once identified this distortion is easily identified in many speakers - even in some where copper plating or other such means has been employed to reduce the effects.
I also point out that thermal compression in a single driver is inaudible as the thermal constant is relatively long. BUT what is normally overlooked is the effect of thermal compression in a multi-way system that changes the frequency balance and is audible. Current drive eliminates this distortion.
Both of these advantages will hopefully encourage others to try even if commercial implementations remain unlikely.
On the commercial front, it is also worth remembering that while relatively simple and highly effective means of implementing current drive in active loudspeakers are available - such as those exploiting David Birt's self-balancing bridge, such arrangements are difficult to compensate in reality because of the semi-inductive nature of most drive unit impedances, for example.
Attempts by drive unit manufacturers to compensate current-dependent non-linearities in all but two cases known to myself employ means that promote the semi-inductive behaviour. An easier design to accommodate in Birt's self-balancing bridge, for example, is one employing either diametrically cut pole pieces or non-conducting pole pieces, where classical inductive behaviour is promoted instead.
Both of the stated measures circumvent the problematic non-linearities at source, however, such that the advantage of then implementing current drive for this purpose is somewhat blunted. Moreover semi-inductive drivers will 'feature' higher sensitivities (at least at higher frequencies) and therefore might seem more attractive for manufacturers too...
Attempts by drive unit manufacturers to compensate current-dependent non-linearities in all but two cases known to myself employ means that promote the semi-inductive behaviour. An easier design to accommodate in Birt's self-balancing bridge, for example, is one employing either diametrically cut pole pieces or non-conducting pole pieces, where classical inductive behaviour is promoted instead.
Both of the stated measures circumvent the problematic non-linearities at source, however, such that the advantage of then implementing current drive for this purpose is somewhat blunted. Moreover semi-inductive drivers will 'feature' higher sensitivities (at least at higher frequencies) and therefore might seem more attractive for manufacturers too...
I see there a possibility, at least in some cases, to produce a purely current controlled speaker and a separate passive unit in which an audio transformer increases signal voltage and then a resistor increases output impedance, which is pretty much what is needed. This combination is far from ideal but could be useful with a modern and powerful solid state amplifier.
Suppose a customer has a good amplifier. He is ready to try a set of current controlled speakers. What shall he do, if he does not want to purchase a new amplifier? He needs also the passive unit between his trusted amplifier and the new speakers. If he later decides to purchase also a new amplifier, he may sell the passive unit to someone who needs it.
Suppose a customer has a good amplifier. He is ready to try a set of current controlled speakers. What shall he do, if he does not want to purchase a new amplifier? He needs also the passive unit between his trusted amplifier and the new speakers. If he later decides to purchase also a new amplifier, he may sell the passive unit to someone who needs it.
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