Right in principle, but the maths is wrong. From my previous post...
"The "electromechanical force coupling factor" is normally written as (B.L)^2/Rc, where L is the length of the conductor in the magnetic field of mean flux density B and Rc is its electrical resistance. The coil resistance Rc can also be expressed as Q.L/Sc, where Q is the coil resistivity and Sc is its cross-sectional area. Substituting then allows the electromechanical force factor to be rewritten as B^2.Vc/Q, where Vc is the volume of the coil in the magnetic field defined by B.
The coil resistance Rc and length L therefore make no difference to the sensitivity - that is, the sensitivity properly measured with constant power input. It is instead the VOLUME of the conductor in the field B that is the important factor, which will also likely be a non-negligible part of the total mass in the "mechanoacoustic force coupling factor" too.
That being said, there are secondary effects that are effected by Rc even when the power input is constant. As an example, the 4Ohm driver will require a current that is sqrt(2) times larger than the current in the 8Ohm driver for identical power input (and a voltage sqrt(2) times smaller to compensate). As a result, the 4Ohm driver will produce a relatively larger output of current dependent non-linearities."
Also to add is that, strictly speaking, if changing the coil resistance does alter a parameter such as coil height then you have a different driver. Manufacturers might number them the same for their convenience, but they will measure differently. A discussion of the effects of coil resistance (on drivers and amplifiers) needs to be one of comparing apples to apples and using amplifiers with loads for which they are designed.
During my little adventure designing an amplifier on these forums, it increasingly become evident, low impedance outputs often mean more distortion. The reason for this can readily be understood, because low impedance means larger currents for the same output power, if we compare with a higher impedance. Transistors, and today, most amplifiers are based on transistors, become more pronouncingly non-linear at high currents. Furthermore, to counteract this non-linearity in output stage transistors, global negative feedback requires a higher voltage difference at the input stage. To understand this, let us imagine the voltage difference is the sum of two voltages: the driving voltage, which is Vo/A, where Vo is the instantaneous voltage at the output and A the open loop gain, and another voltage that increases non-linearly to make the output transistors behave as linearly as possible with increasing current demand. To put it simply, at higher output currents there is more stress on the input stage to compensate for non-linearities, which results in more distortion.
agreed. Generally you cannot change impedance without sacrificing parameters like copper mass of coil, its dimensions etc. Have a look at Jensen speaker datasheets to find out different data with 4/8/16R drivers.
But there are some rare exceptions. You can build equivalent drivers using 2 or 4 layers of copper wire respectively. With a turns ratio of 1:4 the resulting impedance ratio was 1:16 - not a very promising result.
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This is one half of the truth. The other half: Increasing speaker impedance requires higher voltage delivered by the amp for same output power. This requires more voltage gain for same input sensity - resulting in reduced neg feedback resulting in increased THD.
Otherwise you compare apples with pears.
My point relies on the very fact high current power transistors are notoriously non-linear at high current outputs. If the design of an amplifier requires more gain, aim at a higher open loop gain, and use more agressive local negative feedback. This results in much higher circuit complexity, but that is a price one has to pay.bucks bunny said:
My reply is not an exhaustive treatise about amplifier non-linearity: there are very good reference books for that.
Returning to professional JBL drivers: JBL chose flattened copper or aluminium wire with almost rectangular cross section area. The voice coils are edgewound (don't ask me how this is done 🙄). By altering the ratio of the (almost) rectangle's longer and shorter sides they could alter the cross section without necessarily affecting the voice coil gap width.
Yes, that's it. Thanks a lot 🙂! It's rather helpful to backup my arguments 😀.
Best regards!
Higher ohm system = lower THD....I don't even think I have to argue this one, you can look this up in the specs of the amp?
I thought this was Amplifier 101??? and I don't even build amps....
One creates more heat than the other. Who wants more heat, raise their hands
And to make sure there is balance, I have never felt that lower ohm speakers sounded better, I felt the opposite. I think in the larger scheme of things, its probably not the largest issue but I do feel like higher ohm subwoofers always sounded better in the area of transients. Seemed like they were more instantaneous, or powerful, compared to same watt, lower ohms...Lower ohms seemed more wimpy. I can't say this scientifically though, A lot of variables unmonitored in there..
I thought this was Amplifier 101??? and I don't even build amps....
One creates more heat than the other. Who wants more heat, raise their hands
And to make sure there is balance, I have never felt that lower ohm speakers sounded better, I felt the opposite. I think in the larger scheme of things, its probably not the largest issue but I do feel like higher ohm subwoofers always sounded better in the area of transients. Seemed like they were more instantaneous, or powerful, compared to same watt, lower ohms...Lower ohms seemed more wimpy. I can't say this scientifically though, A lot of variables unmonitored in there..
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Isn't this a double edge sword? Electro-mechanical relationship. Resistance in the acoustical realm results in a tighter sound...The DF specs reach crazy high numbers as it is, I thought, and finally, low inductance is a factor in dampening as well.
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It depends on using the right amplifier for the right load.
This is incorrect. For the same power input, the same heat will be dissipated. As I wrote previously, in going from an 8Ohm to a 4Ohm driver, the current may increase by a factor of sqrt(2), but the voltage will decrease by a factor of sqrt(2) if the power input is the same. The net result is that the power dissipated by the coil resistance will be the same also.
A properly engineered louspeaker and amplifier system will be properly matched. The coil resistance will therefore not be an issue unless the system has not been designed competently.
In a competently designed system, the nominal coil resistance should be an irrelevance since it will have been considered in the design process when the low-frequency alignment was selected. What you appear to be talking about is the variation of Qts by interchanging one driver for another and hence ending up with a different alignment, which is a different topic.
Although off-topic too, it is worth mentioning that the heating of the voice coil can result in the coil resistance increasing by as much as a factor of two. This is one reason for the superiority of current drive over a conventional voltage-drive amplifier, because in current drive, the nominally infinite amplifier output resistance means the coil resistance does not significantly affect the alignment. But it's a different topic...
I don't get the double edged bit.
I was referring to electrical resistance, of course acoustic resistance helps with damping.
I think the crazy numbers have come from the marketing men who have grabbed at the big numbers as though they are directly representative.
Definitely not my area of expertise lol...but I used to be under the impression that higher ohm systems were used in PA for the reasons of less heat. That might be an old wise tale or something.
Otherwise I guess it holds true that higher ohm systems produce less THD.
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When you have stopped laughing, I would add that this is completely true. In a conventional voltage driven loudspeaker, the coil resistance should by definition dwarf the amplifier output resistance. The pursuance of irrelevant numbers such as high damping factors and channel separation (and even large volume control knobs) is indeed the plague of the "ad men".
You may find it laughable but I think there is more to it. If inductance affects the acoustical outcome then so does resistance. Because of the relationship between inductance and resistance, this has to be true. If you are such a master of this discussion... what is the affect of resistance on the final acoustical signal? A hint for you...the right answer isn't "nothing"
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This has no reason to be true if an amplifier has been designed competently for a given loudspeaker.
Where there is a difference is in the possibility of higher current-dependent non-linearities in the lower resistance driver generated in or reflected from the driver's magnetic circuit - due to the higher current and due to the offending inductive components being relatively higher than the coil resistance. Use current drive and it too is an irrelevance, however.
I was referring to my agreement being laughable.
Yes higher voltages are used to minimise losses, notably in power transmission across the country.
I have a lot to learn, so please, laugh at my expense, I'll laugh with you.
break this down then...
My guess is that the same signal to heat relationship is being experienced in the voice coil...I also am proposing that electrical resistance manifest itself as acoustical resistance (just like electrical inductance slurs acoustical transients)....but I am theorizing.
break this down then...
My guess is that the same signal to heat relationship is being experienced in the voice coil...I also am proposing that electrical resistance manifest itself as acoustical resistance (just like electrical inductance slurs acoustical transients)....but I am theorizing.
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