Emulating car battery output through home power?

[sophiecentaur]

hmm

450 watts into 4 ohms is 42 volts RMS, 60peak

which means that thing must have a power supply capable of 60volts and almost 40 amps, 2.4KW.
If so , even my preposterous supply would be way undersized for Audiobahn's AT12001DJ .

What size input fuse does it have ?

If you were to use a push me pull you arrangement, you might expect 24V peak to peak swing (less the inevitable drops across the amplifying devices), which would give 576W (absolute Peak Power) into a 1Ω load. I have to wonder about the efficiency of 1Ω LS units, too. What flummoxes me about this is that diminishing returns will set in if you try to obtain high voltages for the supply, from a 12V source. Do the manufacturers use inverters to get more oomph?
It seems to me that their advertising is more high power than their amplifiers. boomboom.

 

[jim hardy]

Do the manufacturers use inverters to get more oomph?

yes. I helped son fix one, it made 40 volts DC so was capable of 80V peak to peak.
Somebody had reversed battery which wrecked the PWM IC and inverter transistors. Audio power IC's on other side of SMPS transformer were okay.

It seems to me that their advertising is more high power than their amplifiers. boomboom.

Agreed.

boomboom?
Given that a speaker has DC resistance ~ 80% of its nominal 8 or 4 ohms, it's hard to envision more than 1/5 of the power it receives actually being turned into sound.
That means hot air from both ends ?

 

[Averagesupernova]

Couple of things:
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There ARE amps out there that will produce spec'd output power.
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The 1.4 amp spec is probably in standby with no output.
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There is no such thing as RMS power although it is spec'd in the car audio world routinely. Power is always average. Even peak envelope power in an AM transmitter it is average taking the RMS volts and the RMS current at the peak of the envelope. The reason car audio equipment got into spec'ing things as RMS is because people started to realize the games that were being played.
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My guess is that the Audiobahn amp will do what it says. It is a class D amp designed only for sub-woofers. Not a very large portion of the audio spectrum.

 

[jim hardy]

There is no such thing as RMS power although it is spec'd in the car audio world routinely. Power is always average.

I always took RMS to infer average over one complete interval of the test signal as opposed to the instantaneous measurement at a transient's peak.
I tell friends who ask: "RMS is an honest measurement, don't believe any power number that's not marked RMS."
If power is energy/time , and a watt is a joule per second,
a marketeer who wants to stretch the truth can claim X microjoules per microsecond at a peak. X is RMS X crest factor^2 .
Sinewave of 8 volts RMS across 8 ohms is 8 watts
at the peak of the sinwave though it's 16 watts instantaneous.

If he can find a waveform with higher crest factor than a sine, what can he claim ?

it's limited only by his internal power supply voltage !
Red and blue traces have same RMS value but red one's peak is 3x blue one. He could claim 9X more "music power" than his honest competition's RMS for the exact same amplifier...
The worst of the abuses described in that TI paper is to calculate power using the internal power supply's highest transient voltage... liar liar pants on fire...

I agree with you on that Audiobahn amp,

 

[Averagesupernova]

The car audio world is a tricky place. Some amp manufacturers have spec'd their amps at 1 watt. In car audio competition there are various classes and amplifier size is often criteria to determine what class you get put in. db drag racing as it is known is a competition to see who makes the loudest bump. If you have an amp rated at 1 watt which is capable of delivering 1000 times that power how do you think you will fair against those who have amps that are honestly rated? I believe there is a standard 'burp' that is played over the system. It is not just a 50 mS transient. It is probably a couple seconds long.
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For those of you who think a 1500 watt amp is extreme, I did a quick google:
https://www.google.com/search?q=out...ved=0CAgQ_AUoAmoVChMIpLPQtZ30xgIVB48NCh0JRASR

 

[sophiecentaur]

Power is always average.

Average over whatever time interval you choose to specify. Rate of doing work may be very relevant, even though it only applies for a brief period.
But I am not 'forgiving' HI manufacturers. They are mostly selling snake oil. Their Peak Power may well be relevant to someone, somewhere. Loud impulsive sounds may get through where low organ notes will exhaust the power supply and make it sag.

 

[Averagesupernova]

The main reason I want to specify that power is average and not RMS is because we cannot take the instantaneous power at the crest of a sine wave and multiply it by .707 and expect a correct result which is what we typically do with the voltage and current. It should go without saying that average will be defined over a specific period of time and this time varies due to many reasons.

 

[jim hardy]

we cannot take the instantaneous power at the crest of a sine wave and multiply it by .707 and expect...

Sinewave is well behaved, its crest factor is √2.
So, for sine with resistive load peak power is twice true power.

Square wave would have crest factor of 1because peak = average.

In self defense speaker manufacturers defined a test signal for rating their speakers
http://www.jblpro.com/pub/technote/spkpwfaq.pdf

...at end of that document

clip a sinewave and it approaches a square wave with same peak, containing twice the power

 

[sophiecentaur]

The main reason I want to specify that power is average and not RMS is because we cannot take the instantaneous power at the crest of a sine wave and multiply it by .707 and expect a correct result which is what we typically do with the voltage and current. It should go without saying that average will be defined over a specific period of time and this time varies due to many reasons.

I think the rationale is that a typical audio signal mostly consists of bursts of mid range frequencies and impulsive sounds and it covers many octaves of spectrum. Mostly, it doesn't consist of long periods of single sinewave. For brief periods, in most audio programme, the Power level will be much higher than the Power Level that you would measure with a long term 'thermally' based Energy / Power meter. So it isn't altogether 'bad' to talk about peak power. Many circuits will cope with short peaks of high power without folding. More demanding programme material will sort them out, though.
Interestingly, to give a consistently 'loud' sounding audio signal, the phases of the various components can be tinkered with so that the high peaks are ironed out so the mean level can be turned up to avoid clipping. This, introduces some distortion and the process will also have to introduce some delay but it is useful when, as in AM, there is a fixed maximum that can be handled by the modulation process. this is referred to as Audio Compression.

 

[sophiecentaur]

I want to specify that power is average and not RMS i

To be precise, the RMS value, over a given interval is the Power. RMS is the Sum of the Squares of the Volts (say), divided by R, averaged over that time, whatever the waveform happens to be. If you do that sum on a set of samples of a waveform, you will get the same answer (i.e. correct value) as if you measured the power with a calorimeter. It is common to assume that 0.707 of peak applies to every waveform and many cheap and cheerful meters will do that, assuming a sinusoid, every time.