How Much Current Capacity do we Need from our Amplifiers?

[Guerilla]

Again



The system (or parts of it) will be to some extent portable, mobile.

There is no "usual" room type, in fact not designed for ANY "room",

cabin of a boat, back of a box truck, converted skoolie are examples.

Plus outdoors. Whether these speakers are "appropriate" for a given space is not the issue. I am learning how to make sure to use them appropriately.

You can play much louder if you high pass them at 120~ and leave bass for a bass bin. Don't look for subs going lower than 40hz. 40hz flat is plenty deep for normal music. Find second hand 15-18" PA driver and start building. Ask help in subwoofer section of diyaudio.com -Friendliest people who tend to go of topic, but very knowledgeable and not judgemental to noobs. I know cause I've been a noob over there for 20 years

 

[Guerilla]

For the LS get an amp that can drive them to 90db with half its power. Then there will be power to spare. If high passed it's woofer will hardly move at that loudness

 

[Hiten]

Vintage audio magazine quite often used to publish maximum power vs distortion (Specially at 20khz) measurements. Comprehensive speaker measurements too. Very usefull in assessing ones requirements. It is good to have capable hifi system and use it at moderate volume levels.

Reading all these years, a general objective consensus it seems is to have a powerfull, low load capable, sufficiently low distortion amplifier and a three way speaker system.

 

[wwenze]

For the LS get an amp that can drive them to 90db with half its power. Then there will be power to spare. If high passed it's woofer will hardly move at that loudness

Half power @ 90dB = full power at 93dB

That's not a lot of power

For a sensitivity of 85dB/1W that's like 6.3W of power at 93dB

 

[john61ct]

You can play much louder if you high pass them at 120~

As stated ~170Hz or higher

> Don't look for subs going lower than 40hz. 40hz flat is plenty deep for normal music.

Films use case, and nightclub style / EDM rave / dancefloor genres also.

I will likely have four boxen in both L/R stacks besides the MBM couplers, the two truesub below 80Hz likely xover at 40-50Hz, rumble filter 10-15Hz.

But yes lower one later / optional.

Center front maybe only 3 boxen. Might test a rear center also

 

[Guerilla]

You can do that but then you need basscabs beneath each since bass becomes localizable so high

 

[Guerilla]

Half power @ 90dB = full power at 93dB

That's not a lot of power

For a sensitivity of 85dB/1W that's like 6.3W of power at 93dB

Yes I knew I was too tired when I wrote it

 

[john61ct]

You can do that but then you need basscabs beneath each since bass becomes localizable so high

All the stack is stereo co-located, MBM as "basstands" if that's what you mean.

Nothing bigger than 12x12" baffle

 

[terryforsythe]

In "theory" they should double the watts for each halving of the Ohms: "under perfect conditions". Which almost never happens in the real world. So it is not that it normally happens in reality.

That assumes the amplifier reaches its voltage limit before reaching its current limit at all of the tested load impedances. Going from the comments I see, many people seem prefer that. Personally, I don't care whether an amplfier reaches its voltage limit first or its current limit first so long as the amplifier has enough power on tap to drive my speakers to the maximum SPL I desire without audible distortion and without the amplifier overheating or self destructing. Every use case is different.

 

[rjp]

How much current do we need from our amps? exactly enough to maintain the target output voltage.
This is simply I = V/R(f), where R(f) is the frequency dependent impedance of the speaker. The output voltage V will always be just a constant times the input voltage unless there is distortion.

If you want to specify an equal power for all frequencies you could write Imax = max over f of sqrt(P/R(f)).

The amp will only use Imax when R(f) is at its lowest. It's not an all-the-time thing. The current is merely what it needs to be to keep the voltage proportional to the input.

 

[solderdude]

There is also a phase component when driving speakers where as I = V/R is only about resisitive loads.

An amplifier seeing a capacitve or reactive load must be able to supply a current that is out of phase with the output voltage.
Amir has a load that can actually test for this but rarely seems to do this test (time consuming).

 

[CDMC]

In "theory" they should double the watts for each halving of the Ohms: "under perfect conditions". Which almost never happens in the real world. So it is not that it normally happens in reality.
There are many nuances involved. But, like shotguns and hand grenades, coming very close: counts.
Here is another (interesting to me [because I own one {as well as 6 NAD 2200's and 2 NAD 2100's}) amp dyno test for a PROTON D1200 which seems to show some good responses to 4 ohm and 2 ohm loads VS the 8 ohm load:

I wish people would stop posting photos and videos of the D1200 amps. I wanted one so bad in the 80s and they still make me jealous. The D1150 tested better than the D1200, hitting 9db of headroom over its rated 50w/ch!

 

[solderdude]

Hence my GFA-555 as a benchmark at over 20A.

LS50 is designed to be used with amplifiers between 40W and 100W ratings (8ohm)

GFA-555 is 200W. (400W in 3.7ohm)
3e A7 Mono is 200W (320W in 4ohm)

It would be fine using those with some restraint, certainly when high-passed.
The LS50 are hifi speakers not PA speakers.

Measuring output power levels with one of those swinging needle/LED displays could be an indicator to check on how much power goes in,

The problem here is ... parties and usage when you are not around by irresponsible individuals (kids).

Even with a 40W amp you can blow the speaker (tweeter) when someone cranks it all up and does not care if the sound is distorted. Chances of failure increases with higher power amps and higher SPL and the same amount of being 'careless' for other other peoples properties.

A limiter used before the power amp can prevent this but has to be set properly... per used amp.

How to use the speakers with any amp.... stop increasing the volume when the sound becomes distorted.
The suggested amps are too powerful for this speaker, yes even when high-passed.

No speaker measurement is going to be of help. Restraint will when using these amps. Kids and parties are a no-go with these combinations.

 

[Roland68]

By the way, here is what can happen if you try to push the LS50 too hard.

This is the typical result seen with inexperienced (or advice-resistant) users who use the LS50 for movies without a subsonic or high-pass filter—or, even worse, use it with a subwoofer but still without such a subsonic or high-pass filter. In the latter case, there is simply no way to hear when the speaker is reaching its excursion limits.

No matter how good the measurements and reviews for the LS50 are, you cannot bend the laws of physics; it remains a small bookshelf speaker with a 5.25-inch (13 cm) bass driver.

 

[Roland68]

Worst I have ever seen advertised is the 50 W 8 ohm rated Denon PMA-SX1 limited 2Ch integrated amp, 240 A instantaneous. For that amp to push 240 A, even instantaneous peak, the load would have to dip to fractional ohms.

I keep reading about these “60‑amp peak current” amplifiers, and honestly… that belongs more in a welding workshop than in a living room.
Let’s stay grounded in real loudspeaker physics for a moment.
Take something as simple as a Monacor 3.9 mH inductor — its saturation current is 7.9 A.
That’s it. Not 20, not 40, and definitely not 60.
So unless someone is testing amplifiers with a pure resistor just to justify the price tag, those huge current numbers are mostly marketing aerobics.
And loudspeaker drivers aren’t any more magical.
A typical 12-inch chassis with a 77 mm voice coil defines the maximum current long before any “60 A peak” fantasy becomes relevant.
Sure, you can claim “1000 W”, but that’s music power, not a continuous sine wave.
In the real world, I have yet to see a voice coil that can survive a true 1000 W thermal load.
To build a coil that actually handles that continuously, you’d need so much copper that it starts looking less like a speaker part and more like a commodity investment.
At that point you’re not buying a driver — you’re buying a small futures contract in Cu.
So yes, 60 A peak current sounds impressive on paper…
But in practice, the loudspeaker will tap out long before the amplifier ever gets the chance.
Just a friendly reminder that physics doesn’t read marketing brochures.

These are nonsensical theoretical figures that never actually reach the amplifier's speaker terminals, nor can they be measured there.
I own several NAD 2200 units, and the current reaching the speaker terminals never exceeds 16–20 amperes. The frequently cited 60A figure represents the maximum theoretical current rating of the transistors themselves, not that of the NAD 2200 as a whole.
The 240A figure likely refers to the theoretical short-circuit current of the power supply capacitors; in reality, the transistors, emitter resistors, and output coils used can probably handle only about 5% of that value.

 

[JakeK]

The problem here is ... parties and usage when you are not around by irresponsible individuals (kids).

Even with a 40W amp you can blow the speaker (tweeter) when someone cranks it all up and does not care if the sound is distorted. Chances of failure increases with higher power amps and higher SPL and the same amount of being 'careless' for other other peoples properties.

A limiter used before the power amp can prevent this but has to be set properly... per used amp.

How to use the speakers with any amp.... stop increasing the volume when the sound becomes distorted.
The suggested amps are too powerful for this speaker, yes even when high-passed.

No speaker measurement is going to be of help. Restraint will when using these amps. Kids and parties are a no-go with these combinations.

Exactly. This is the danger with hi-fi and parties and unsupervised kids. Someone will turn it up too loud and speakers will die and I can say this from my own experience with both. It's the tweeters that will suffer from clipping distortion and this will cause their coils to melt. A high pass filter won't protect them from that.

A bluetooth party speaker will be safe from such harms as they are usually made to withstand being turned all the way up for long periods of time. Plus they can be well suited to travel and off grid use which LS50s aren't. Either that or accept that your main speakers may get melted at some point and have some replacements on hand in case that happens, maybe some cheap and robust outdoor speakers.

 

[Mnyb]

lets poke a hole in another myth "doubling down" is not really needed it does not affect the amps performance within its limits .

Some less informed seems to think an amp that does not double down loses dynamics or compress dynamically or is nonlinear within its useful envelope .

There basically a current limit a voltage limit and a thermal limit untill you "hit" a limitation the amp is linear and works fine .

You can run around like crazy in your room untill you hit a wall the non doubling down amp moves some of the walls a bit closer .

But if your amp is powerful enough anyways you wont suffer any consequence .

IMO is the usual marketing scheme when you take a kernel of truth and stretch it beyond its applicability .
yes i do like when an amp mfg shows me that they have selected robust transistors and have a reasonably stiff power supply and good thermal margins , but at some point its getting excessive tech p0rn .

personally i would overdesign a bit , I would go for a slightly more powerful amp than i actually need and less distorsion and noise than i actually need etc etc . But i would not loose sleep over it.

 

[Sokel]

A complicated, modular and untested for environment system makes zero sense for outdoors and travel.
The problem is both at high power where the needs for outdoors are enormous an low power as the environmental noise can dwarf any hi-fi ambitions.

Headphones are much better choice.

 

[hreith]

https://www.hypex.nl/media/ed/cf/4a/1682341903/The%20engineers%20survival%20guide.pdf?ts=1769181202

page 146 ff
"Power demand of reactive load
• Maximum current pulse = 2x peak current in DC
resistance!"

 

[wwenze]

The transistors of 2200 are 15A x 2 in parallel so god knows where the 60A / 240A even come from.