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Old 30th April 2011, 08:17 AM   #11
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John, back emf is a jolly good thing! Your ampīs damping factor = ampīs output impedance divided by the driver impedance, and that damping keeps the cone from overswinging. By adding resistance to the driver impedance you get less damping - akin to a car with completely knackered shock absorbers. Feels like more bass, but in reality all you get is some muddy booming without any control. Run a formula and see how much one or two additional ohms will raise the Qtc.
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Old 30th April 2011, 08:23 AM   #12
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Quote:
Originally Posted by Pit Hinder View Post
but in reality all you get is some muddy booming without any control.
Not at all true Pit. How much electrical damping is needed depends on the mechanical Q of the system. Wih some drivers it is too easy to overdamp the system, ending up with anemic bass.

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Old 30th April 2011, 09:03 AM   #13
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Dave - horses for courses, as usual. With the drivers we use for horns a bit of fine tuning can be beneficial, drivers with Qtc off the scale used to imitate bass in tiny boomboxes (I hate them) become sheer horror.
And as to using solid core (CAT5 or the wunderwaffe Scott and I use when nobody is looking - humble doorbell wire)...the effect is not in bass. Itīs some magic somewhere in the highs, nobody has yet been able to find an explanation about the why and how. But with a very good recording and when you have had a quiet day that hasnīt overstressed your hearing - something is there. Somewhere.
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Old 30th April 2011, 03:48 PM   #14
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FWIW, assuming we don't want the wire to act as some kind of filter, we need to ensure L&C are controlled to sensible levels, and voltage drop is minimised. Internal wire runs are generally quite short, so voltage drop is usually something of a non-issue. Using the FE126En's published spec. as a baseline, & assuming a 6ft total run (3ft each leg) you're looking at a fraction over 0.3V drop in a 24ga conductor, translating into roughly 0.36dB loss. Not something to loose a great deal of sleep over; we're well into reasonable zones there, the maximum acceptable loss generally being assumed as 1v (if you're happy with that, then a 27ga conductor should be sufficient).

Last edited by Scottmoose; 30th April 2011 at 03:55 PM.
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Old 30th April 2011, 05:31 PM   #15
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And as to using solid core ...the effect is not in bass.


You won't get an arguement from me. I usually don't voice that opinion (cable wars are a bore) instead just encouraging/tricking people to try it.

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Old 30th April 2011, 05:34 PM   #16
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back emf is a jolly good thing!
The argument for current amps is that it is not a good thing. If the back EMF gets into the feedback loop and can end up getting into the signal and creating an infinite regress kind of thing. Using ohm's law, back emf drops to zero when the amp's output impedance is infinite.

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Old 1st May 2011, 09:19 AM   #17
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May I question this, Pit?

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Originally Posted by Pit Hinder View Post
ampīs damping factor = ampīs output impedance divided by the driver impedance, and that damping keeps the cone from overswinging. By adding resistance to the driver impedance you get less damping
Are you sure? Wikipedia has it the other way round: Damping factor - Wikipedia, the free encyclopedia It also states that the additional impedance of cabling is part of the source's (amplifier's) output impedance, not part of the load, which sounds more likely to me.

On this basis, increasing cable resistance will decrease the damping factor, which will decrease the accuracy of control of the voice coil. Which is why it is interesting that some speaker/amp combinations seem to benefit from thinner cables. It remains a mystery.
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Old 1st May 2011, 09:28 AM   #18
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Come on, Dave.

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Using ohm's law, back emf drops to zero when the amp's output impedance is infinite.
Have you never tried connecting a relay or some other coil across a battery and then felt the electric shock as you disconnect it? If the source impedance is infinite, the back emf will try to be infinite (hence the electric shock).

Pit, I can't see how back emf can be a good thing - it would be much easier to drive a straightforward resistive load.
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Old 1st May 2011, 09:41 AM   #19
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voltage drop is usually something of a non-issue
I couldn't agree more. The question is more about using additional resistance to tailor the damping factor to suit the speaker/amp combination. If, as some people claim, the damping factor can be too high (I still have doubts) then it could easily by reduced by inserting a small resistor in series with the speaker. It possibly only need be of the order of 0.05ohm. Consider an amp with o/p impedance of 0.01ohm (quite reasonable for a good, high-feedback design), this would change the damping factor from 800 to 160.
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Old 1st May 2011, 11:33 AM   #20
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More accurately, that would change the damping factor from 800 to 133 (8ohms divided by 0.05+0.01). It is certainly a huge change, and do you know what I reckon? I seriously doubt if anyone would be able to hear a difference. Of course if you try it and you can, please do let me know!
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