Is there any voltage limit to a loudspeaker driver unit (traditional cone ones, not electrostatic)? If the driver has a power handling of 100 watts, can it be any combination of voltage and current?
I assume not; surely the voltage required is within certain limits due to it being the bit that causes the excursion of the cone?
I cannot find any current or voltage details in the blurb for retailers online. I might just be crap at searching for things.
Am I correct in thinking that better amplifiers have better current delivery capability?
No. You're varying the voltage level to the speaker which has a fixed impedance. The current will automatically vary along with the applied voltage. You just need to ensure you have sufficient current available from your amp.
Yes, but there are other additional criteria to be met in those better amps.
Its not quite as simple as that. The impedance varies with frequency and will be inductive at some frequencies and capacitive at others. There will be a small number of frequencies where it is actually resistive and it might even match the rated impedance occasionally. However, things will have been tweaked so that with a constant voltage drive the frequency response will be as flat as reasonably possible.
A loudspeaker responds to current, not voltage. When a voltage is impressed across the voicecoil, a current flows that is directly related to the impedance at that frequency, and it is the current flow that creates the voicecoil movement. A moving coil loudspeaker will generate a back-EMF whenever the impedance is inductive, seen as impedance rising with increasing frequency.
Because the speaker also has an impedance which is fixed. For 8 ohms and 100 watts:
Current (I) = 3.5 A Voltage (V) = 28.2 V
If you increase the voltage then the current will also increase, and so will the power.
You could use a constant-current supply to deliver the same power with an increased voltage, but at some point the voltage would exceed the voltage rating for the speaker coil and the insulation would start breaking down.
Current drive (or at least a modified form thereof) is used to drive spring reverb units, and various other transducers where a constant current is either preferable or essential, and where voltage drive is inappropriate.
Most HiFi amps had a lot of negative feedback, giving a very low output impedance, effectively damping mechanical and electrical resonances in the speaker unit.
Usually the power specification, will be "into a certain load".
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550W into 2 ohm 350W into 4 ohm 215W into 8 ohm # per channel
How they rate a speaker, is shown here.
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In old style amplifiers, the shielded transformer might develop 60 volts for the rails on the power stage (classic transformer, bridge rectifier, large caps for filtering, PSRR for hum reduction). And that is the most that the output transistors could use.
I haven't spotted any trend to using solid state power supplies, regulated ones (like a wall wart or the equivalent of an ATX supply). The DC for the power stage was unregulated and in proportion to mains. If your mains was 5% higher than normal, the rails inside the amplifier would be 5% higher than normal. This is a weakness of old amplifiers, and if there is any sort of sustained transient on mains (enough of a transient to blow your surge suppressors to bits), it could ruin the amp.
The class of amps, is covered here, but the list still isn't complete. Presumably only "common" classes receive articles, instead of the "made up" classes. One of the benefits (and from a consumer point of view the disadvantages) of things like Class D, is they're efficient enough to be stuffed inside the Sub. Which is a mistake, when you see the cooked mess that results after 3-5 years. Amplifiers belong in their own cabinet, not stuffed into a speaker.
Remember that voltage is the first important parameter, because without a voltage potential, current cannot flow. If the max RMS power rating of the speaker is of a known value, then the RMS driver voltage will determine the RMS power P = V²/R where R is the equivalent to the speaker impedance at 1kHz.
No, because the voice coil has a specific resistance
No, it is the current times the number of turns that defines the applied force.
That may be proportional to the voltage, but it is not the prime mover except in an electrostatic loudspeaker.
You deduce that from the power and the voice coil nominal impedance.
E.g a 10W loudspeaker of nominal 4ohm impedance will take an average current of SQRT*(10/4) or a shade over 1.5A RMS at full power at require an applied voltage of SQRT(10 x 4) or around 6.3V RMS to do it.
All HiFi amplifiers, but not Brian May's favourite VOX AC30s, which have
*no feedback whatsoever* giving them around 80 ohms output impedance, allowing the 'sound' of the ultra thin loudspeaker cones and the bass resonance of the cabinet to dominate the 'colour' of the sound.
No spring reverb I have ever come across was driven by a current amplifier. Not in any Marshall or Fender or indeed any of my own designs.
Loudspeakers however, yes. The happy accident of Vox, was copied initially by myself and subsequently nearly all guitar amplifier manufacturers to increase the output impedance of transistor guitar amplifiers to get a more 'valve sound'.
Then you haven't looked in the right place. I have a late model Fender guitar amplifier that is nearly 100% 'digital'.
The audio signal is buffered and turned into digital samples amd passed to a digital sound processing chip, whose code is controlled by an arduino style chip that monitors all the control and switch positions. And sends a digital stream to the DSP, where all teh sound crunching is done.
Then that output goes back to the input digitiser chip which also has a DAC in it, to feed the analogue pre-amp output. That is then fed to a class D pulse width modulated power amplifier to generate 100W of screaming guitar power and the whole shebang is powered by a switched mode power supply of about 200W capabiility
Its very light and best of all doesn't push hum into the guitar pickups.
It is also cheap. No spring reverb, No array of audio signal ICs. No scratchy pots. All done in software.
Lots of things could blow amps. We generally designed them with at lest
10% overload on voltage, and with output current and SOAR limiting and with some kind of thermal cutout circuit..
If we didn't, the custromes sent them back with e.g. turds inside them (true story from deep purple's roadies and their Marshall cabinets)
*shrug* that's simply bigotry. You can stuff amps wherever they can get power and stay cool
That might be in a big 19" rack for a 10kW P.A.a rig, on a shelf in your living room or inside a loudspeaker cabinet for the guitarists, or indeed a sub bass room thumper
It's the unnecessary exposure to bass at high energy, plus the usage of a certain glue between eletrolytic capacitors to "stiffen them" against the noisy environment they're in.
You don't need to do that for home equipment. A separate cabinet could be used instead, and the lifetime of the equipment would be "normal" as a result.
One guy in another group, his collection of Class D channels mounted inside the sub, they failed. He found a guy in his own country, who was doing nothing but fixing those. I warned him, that the nature of the glue that was breaking down chemically (due to the temperatures inside the sub), that material wasn't going anywhere, and the unit would only fail again. And, it did... There would be no point sending it for a repair a second time. The problem is, the glue went all over the place (onto the PCB in places) and it just does not come off easily. If there was a good solvent to remove it, maybe it wouldn't have been so bad. When the glue decomposed, it was conductive.
Bad design does not invalidate the principle. Back in the day no Marshall 'top' could be found with the fragile 200mA HT fuse still in place. Usually it was replaced with foil from a cigarette packet. That wouldnt shake itself to pieces during heavy use of bass notes.
That doesn't mean we shouldn't put fuses in amplifiers.
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