How Much Current Capacity do we Need from our Amplifiers?

[NTK]

and how does one tell when "SPL does not follow linearly to the amplifiers output" ??

Usually in 2 ways. You can test for compression. For example if I increase the output by 3 dB, does the SPL increase by 3 dB? The second method is harmonic distortions.

Those are usually the criteria to tell when you speaker has gone "non-linear", and what its usable max SPL is.

 

[SSS]

Wait, you mean amplifiers don't have to "double down" all the way to 0.02 ohms to be proper, manly amplifiers?

Of course the amplifier needs not.

 

[Thighsofsteel]

Wait, you mean amplifiers don't have to "double down" all the way to 0.02 ohms to be proper, manly amplifiers?

Where can I get one of those manly amps?

 

[Ropeburn]

Wait, you mean amplifiers don't have to "double down" all the way to 0.02 ohms to be proper, manly amplifiers?

Indeed not. Doubling down to 0.8 Ohm is enough, for driving the legendary Kappa 9 heh

 

[Dialectic]

Where can I get one of those manly amps?

Get a vintage Krell, and cook it.

Cook that Krell

I was all worried that one channel of my FPB 300 was running hotter than the other. I shouldn't have been, my Krell, which was sitting in ...

audioinvestigations.blogspot.com

Indeed not. Doubling down to 0.8 Ohm is enough, for driving the legendary Kappa 9 heh

What about my 1985 Apogee Testarossas with their acoustic synergy ribbon system that plummets to -2 ohms at 40 Hz?

I'm being facetious.

 

[john61ct]

Speakers respond to voltage.

OK, but my reading of comments from members I respect here is that

speakers like my OG LS50s need power amplifiers that are capable of putting out more current than most.

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

In my mobile use case I need more efficient DC-powered power amplifiers, I assume Class D "chip amps"

So, starting with 3e A7 Mono, I want to objectively (and safely) verify the latter type can drive the LS50s just as well as the GFA-555.

"Well" as in, just as close to max safe SPL.

This process will hopefully also allow me to set up gear that will physically limit the chain to stay well below that point

so the partying teens with unsupervised access to my system can't blow out the drivers.

I would be willing to buy and learn to use a reasonably priced multi meter / ammeter if that helps, but I suspect an oscilloscope would be beyond me.

 

[CDMC]

PV = nRT

Wrong forum.

 

[wwenze]

Where can I get one of those manly amps?

 

[john61ct]

Usually in 2 ways. You can test for compression. For example if I increase the output by 3 dB, does the SPL increase by 3 dB? The second method is harmonic distortions.

Those are usually the criteria to tell when you speaker has gone "non-linear", and what its usable max SPL is.

Thanks much, off to google "compression". I assume I can (learn how to) do all this in REW?

 

[Ropeburn]

OK, but my reading of comments from members I respect here is that

speakers like my OG LS50s need power amplifiers that are capable of putting out more current than most.

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

In my mobile use case I need more efficient DC-powered power amplifiers, I assume Class D "chip amps"

So, starting with 3e A7 Mono, I want to objectively (and safely) verify the latter type can drive the LS50s just as well as the GFA-555.

"Well" as in, just as close to max safe SPL.

This process will hopefully also allow me to set up gear that will physically limit the chain to stay well below that point

so the partying teens with unsupervised access to my system can't blow out the drivers.

I would be willing to buy and learn to use a reasonably priced multi meter / ammeter if that helps, but I suspect an oscilloscope would be beyond me.

Alright mate, let's try and do some simple number crunching for a good estimation.

First, max "safe" SPL: manufacturer specs the LS50 at 106dB max. Let's see how much power that is:

85dB rated sensitivity. They're silly and give that at 8 Ohm which they aren't, so let's say 3 less, 82dB. Means 1W makes them do those 82dB, every 3dB more doubles the power, so it looks like this:

82dB - 1W
85dB - 2W
88dB - 4W
91dB - 8W
94dB - 16W
97dB - 32W
100dB - 64W (this is the point where safety is more about your ears than the speakers)
103dB - 128W (they'll be compressing and distorting badly here)
106dB - 256W (destruction)

They also spec them at "amp power 25-100W". If those 100W are maximum, which is about right for a single small coax driver, you won't even reach those 106dB without destroying them (and your ears).

Look above: 90dB and more is PLENTY loud, but let's say you really want 103 for peaks so it's "safe".

EDPR is 1.7 Ohm, right. Now Ohm's law: Current = squareroot (power / resistance). Makes sqrt(128/1.7) = 4.28 Ampere.

There you have a good estimation of your needed current. The calculation isn't exact but good enough for the purpose: you now know you need not worry at all. If that 3E amp can do 30A peaks, that's super overkill and it'll be able to destroy these speakers without breaking a sweat.

You don't wanna turn them up too much anyway for two reasons: your precious ears, and their drivers are infamous for blowing up under heavy bass load. The membranes crack and all. Don't do it, listen at safe levels

 

[Hiten]

In the forum we have good number of amplifier and speaker impedance data. We only need sound pressure level at which one listens to, which we can increase to be an extreme case. Plus also peaks in average music.
For layman if anyone can do this calculations it would be good to understand.
Thanks.

 

[EERecordist]

There might be a call for higher current in subwoofers, especially outdoors. Dave Rat is a stadium/outdoor specialist in big bass with a big budget for readers interested.

For instance the JBL 2269H is an unvented 18" driver that has been around for many years. It has about 95dB SPL for 1 Watt at 1 meter sensitivity. It has a dual voice coil and very high excursion.

It has an aluminum frame with fins for cooling. It has 1000/2000/8000 Watt ratings, continuous AES, continuous program, and instantaneous max, respectively. 8000W is 40 Amps. Common speaker connectors are rated at 30A. You are not going to want to run at the instantaneous max because that is the area where the driver fails physically, thermally or mechanically.

For the cabinet, with multiple speakers, then multiple cabinets, the designer and PA engineer will make series and parallel wiring decisions.

I think there have been some reviews of professional PA amplifiers on ASR. They will be built for reliability, power, and efficiency, not peak fidelity. As many have said, high current to the speakers is not needed at home.

The point is that in professional subwoofer systems you need to do some engineering, but even then your instantaneous peak absolute max verging-on-destruction is going to be around half of 60A for a single driver. It would be very unusual to find a driver motor equivalent to a professional driver in a home and you would never drive it to stadium levels, WAF and all.

 

[Ropeburn]

you would never drive it to stadium levels, WAF and all.

Nevermind the wife, at that point you need to worry about police helicopters and army tanks arriving at your house...

 

[john61ct]

Alright mate, let's try and do some simple number crunching for a good estimation.

Thanks much!

> 100dB - 64W (this is the point where safety is more about your ears than the speakers)

Presumably not 20m away outdoors...


> 103dB - 128W (they'll be compressing and distorting badly here)

I believe you, but how did you figure that fact out?
(and destruction?)

> They also spec them at "amp power 25-100W". If those 100W are maximum

If so, shouldn't I just measure that directly (multimeter/ammeter?) and stop there?

> The membranes crack and all. Don't do it, listen at safe levels

The whole point of my interest in the topic, is pushing up close to a specific number, but ensuring the kids (good kids, obedient and respectful, but...) cannot exceed it.

Will Watts and/or Amperes and acoustic SPL at 1m all be equivalent benchmarks, or should my limiting efforts (tbd) be based only on the latter?

 

[EERecordist]

Nevermind the wife, at that point you need to worry about police helicopters and army tanks arriving at your house...

(humor)
Maybe you could drive them away with sound... or, in the famous Kate Bush song Experiment IV, your 60 Amp speaker might cause madness...

 

[Ropeburn]

(humor)
Maybe you could drive them away with sound... or, in the famous Kate Bush song Experiment IV, your 60 Amp speaker might cause madness...

Yeah well I don't think you're going to compete with the peak SPL of a tank cannon... even a pistol is louder than any speakers

 

[Hiten]

In estimating current requirement, Should one consider crest factor of typical music ? It is said to be 10 dB to 20 dB above average levels. So if an amplifier (well made class ab with number of output transistors) and speaker (multiway to cover full range which handles large spl) are capable, more current would be required. Isn't it ?

 

[john61ct]

90dB and more is PLENTY loud, but let's say you really want 103 for peaks so it's "safe"

I do not want "plenty loud" I want to figure max safe that OG LS50 are **capable** of producing, playing M-Noise I guess (music genres being so variable).

That then gives me the target to match with the other dozen+ speakers, likely DIY one-driver-per-box, target getting right down to 20Hz within a 12x12" baffle form factor.

One question not yet answered: Will a HPF on the LS50, say 170Hz or a bit higher, increase the "max safe" SPL?

Related, will it increase the SPL produced from a given Watts/Amperes output?


> you now know you need not worry at all. If that 3E amp can do 30A peaks, that's super overkill

Maybe I can get away with a cheaper TPA3255, not have to pay the 3e premium?

 

[john61ct]

In estimating current requirement, Should one consider crest factor of typical music ? It is said to be 10 dB to 20 dB above average levels. So if an amplifier (well made class ab with number of output transistors) and speaker (multiway to cover full range which handles large spl) are capable, more current would be required. Isn't it ?

When I googled M-Noise, this issue seems to be exactly why it was adopted by the AES75 standard

 

[Ropeburn]

In estimating current requirement, Should one consider crest factor of typical music ? It is said to be 10 dB to 20 dB above average levels. So if an amplifier (well made class ab with number of output transistors) and speaker (multiway to cover full range which handles large spl) are capable, more current would be required. Isn't it ?

All above calculations are for peaks. Meaning those 10-20dB are less for the average, not more. Err.

The real current requirement for music is less, not more.