Loudspeakers and voltage & current

[David Paste]

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?

Thanks in advance.

[Rod Speed]

David Paste <paste...@gmail.invalid> wrote

> 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?

Its actually the current that produces the magnetic field
that moves the coil in the magnetic field from the magnet.

> I cannot find any current or voltage details in the blurb for retailers
> online. I might just be crap at searching for things.

The spec normally specifies the impedance.

> Am I correct in thinking that better amplifiers have better current
> delivery capability?

It is much more complicated than that.

> Thanks in advance.

[Cursitor Doom]

On Sun, 18 Feb 2024 22:14:58 -0000 (UTC), David Paste
<paste...@gmail.invalid> wrote:

>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?

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.

>
>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?

Yes, but there are other additional criteria to be met in those better
amps.

[David Paste]

On Mon, 19 Feb 2024 09:34:29 +1100, Rod Speed wrote:

> It is much more complicated than that.

I should've known!

[John Walliker]

On Sunday 18 February 2024 at 22:46:36 UTC, Cursitor Doom wrote:
> On Sun, 18 Feb 2024 22:14:58 -0000 (UTC), David Paste
> <paste...@gmail.invalid> wrote:
>
> >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?
> 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.

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.

John

[Owain Lastname]

On Sunday 18 February 2024 at 22:15:02 UTC, David Paste wrote:
> 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?

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.

https://sound-au.com/articles/current-drive.htm

Owain

[me9]

John Walliker <jrwal...@gmail.com> wrote:

> 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.
>

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.

--
braind

[Paul]

Usually the power specification, will be "into a certain load".

https://geoffthegreygeek.com/speaker-impedance-changes-amplifier-power/

550W into 2 ohm 350W into 4 ohm 215W into 8 ohm # per channel

How they rate a speaker, is shown here.

https://dynaudio.com/magazine/2023/july/impedance-ask-the-expert

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.

https://en.wikipedia.org/wiki/Category:Electronic_amplifiers

Paul

[Sid]

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.

[Peeler]

On Mon, 19 Feb 2024 09:34:29 +1100, cantankerous trolling geezer Rodent
Speed, the auto-contradicting senile sociopath, blabbered, again:

<FLUSH the abnormal trolling senile cretin's latest trollshit unread>

--
williamwright addressing Rodent Speed:
"This is getting beyond ridiculous now. You're trying to prove black's
white. You're arguing with someone who has been involved with the issues all
his working life when you clearly have no knowledge at all. I think you're
just being a pillock for the sake of it. You clearly don't actually believe
your own words. You must have a very empty life, and a sad embittered soul.
MID: <j08o6b...@mid.individual.net>

[The Natural Philosopher]

On 18/02/2024 22:14, David Paste wrote:
> 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?
>

No, because the voice coil has a specific resistance

> I assume not; surely the voltage required is within certain limits due to
> it being the bit that causes the excursion of the cone?
>

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.

> I cannot find any current or voltage details in the blurb for retailers
> online. I might just be crap at searching for things.
>

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.

Note that 6.3VRMS is around 20V peak to peak.

> Am I correct in thinking that better amplifiers have better current
> delivery capability?
>

Louder ones, certainly. :-)



> Thanks in advance.

--
The urge to save humanity is almost always a false front for the urge to
rule.
– H. L. Mencken, American journalist, 1880-1956

[The Natural Philosopher]

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.

It saved the cost of a whole valve...

--
“Ideas are inherently conservative. They yield not to the attack of
other ideas but to the massive onslaught of circumstance"

- John K Galbraith

[The Natural Philosopher]

On 18/02/2024 23:13, Owain Lastname wrote:
> 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.

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'.




--
"Corbyn talks about equality, justice, opportunity, health care, peace,
community, compassion, investment, security, housing...."
"What kind of person is not interested in those things?"

"Jeremy Corbyn?"

[The Natural Philosopher]

On 19/02/2024 04:32, Paul wrote:
> On 2/18/2024 5:14 PM, David Paste wrote:
>> 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?
>>
>> Thanks in advance.
>>
>
> Usually the power specification, will be "into a certain load".
>
> https://geoffthegreygeek.com/speaker-impedance-changes-amplifier-power/
>
> 550W into 2 ohm 350W into 4 ohm 215W into 8 ohm # per channel
>
> How they rate a speaker, is shown here.
>
> https://dynaudio.com/magazine/2023/july/impedance-ask-the-expert
>
> 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.
>

Oh, we were up to 100+ volts by the 80s easily.

> 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).

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.

> 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.
>

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)

> 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.
>

*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


--
"The most difficult subjects can be explained to the most slow witted
man if he has not formed any idea of them already; but the simplest
thing cannot be made clear to the most intelligent man if he is firmly
persuaded that he knows already, without a shadow of doubt, what is laid
before him."

- Leo Tolstoy

[Paul]

On 2/19/2024 4:40 AM, The Natural Philosopher wrote:

> *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.

Paul

[The Natural Philosopher]

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.


> Paul
>
>

--
“But what a weak barrier is truth when it stands in the way of an
hypothesis!”

Mary Wollstonecraft