A 1kHz sine figure is specmanship?
The people who made my amps give a number of output figures: 1k sine and fullrange signal with crest factors of 9, 14 and 18dB (all continuous).
The 1k figure is the lowest.
The people who made my amps give a number of output figures: 1k sine and fullrange signal with crest factors of 9, 14 and 18dB (all continuous).
The 1k figure is the lowest.
There he is, in hyde park, standing on a soapbox....good grief. It's kind of like a student asking why the sky is blue and another student saying, "it's not blue, dummy, it's gray because its cloudy..."
Yes on the second part, I don't know what you mean in the first part. Since the vast majority of audio amps are a voltage source, voltage isn't too load dependent, at least above a few ohms. Measure the voltage with 8 ohm speakers attached and then no load, there will be little to no difference.
Sure, but is that what I meant? No. When I see amplifier rated in volts (like a pro amp), it is usually given into 8 ohm, 4 ohm, and some lower impedance. From those numbers it's easy to see the power supply sag. Since the maximum voltage into a load is given at a fixed THD, it's easy to compare. At least easier than with watts.
Voltage IS a better metric because it's quicker and easier to compare than power ratings. The information might be the same, the perception of it probably isn't.
The FTC isn't enforcing rules for power ratings. I see many cheap amps rated pmpo (peak music power out) which was outlawed in '74. Also music power, same thing. Home theater amps are tested with one channel, no way the power supply could keep that up with 5 or 7 channels. Also, saw a sony sub that was 1.5 ohms, cheaper theater rigs have the sub amp in the receiver. The other speakers are often 3 ohms (home theater in a box) and yet have 18 gauge lamp cord to the outlet. Smoke and mirrors! 1,000 watts my...
Sent from my ASUS MeMO Pad 7 using Tapatalk
Sent from my ASUS MeMO Pad 7 using Tapatalk
I've probably said this before, but here's one way to get really good specs for power output: fire up the amp, and short the power supply with an ammeter. Measure the instantaneous current (the PSU doesn't have to survive this test), multiply by the rail voltage and that's the maximum power that your amplifier can give out.
Chris
Chris
> short the power supply with an ammeter.
It won't give idle V times shorted A; max is 1/4 of that figure.
100V no-load, 100r internal impedance. 1A into a short. *ALL* this 100W power is lost in internal impedance, NOT available to a load.
The max *load* power will be at 100r load. 50V 0.5V out, 25W in load, 25W in internal impedance.
It won't give idle V times shorted A; max is 1/4 of that figure.
100V no-load, 100r internal impedance. 1A into a short. *ALL* this 100W power is lost in internal impedance, NOT available to a load.
The max *load* power will be at 100r load. 50V 0.5V out, 25W in load, 25W in internal impedance.
I just do a short term peak into the rated load. Sample the RMS power for 10, or 50mS and calculate the power based on reference impedance (load). That will yield the maximum power before the power supply sags.
When I was looking for a home theater receiver, most of the receivers were rated with two channels driven such as the Onkyo TX-NR838 -
All channels: 130 watts minimum continuous power per channel,
8 ohm loads, 2 channels driven from 20 Hz to 20 kHz, with a
maximum total harmonic distortion of 0.08% (FTC)
(North American)
Considering that the primary two channels are going to be the loudest, and the surround speakers (which are almost universally smaller and of less power handling capability) will not be driven as hared, I don't see the problem with the rating.
All channels: 130 watts minimum continuous power per channel,
8 ohm loads, 2 channels driven from 20 Hz to 20 kHz, with a
maximum total harmonic distortion of 0.08% (FTC)
(North American)
Considering that the primary two channels are going to be the loudest, and the surround speakers (which are almost universally smaller and of less power handling capability) will not be driven as hared, I don't see the problem with the rating.
These 7.1 channel amplifiers in a 4RU box are a nightmare for heat dissipation. Many of them run at alarming temperatures with just moderate signal load. Cramming 8 200-watt amplifiers 1/4" apart is a recipe for a short service life. Maybe 5-7 years at best. Not going to see 50 year service like we did with the old amplifiers from the 1960s.
Hi All, I'm fairly new to these forums although I have lurked over the years. I have a bit of a different perspective than many of you since I sit on the CTA (nee CEA) working groups that write the power standards for home and car audio (actually co-chair the latter). I have also had a few meals about 10 years ago with the guy at the FTC that is in charge of enforcement of 16 CFR 432.
In a nutshell, anyone can advertise anything these days. The FTC got involved in '69-'74 when people had amps failing with catastrophic consequences. There was a fraud issue to contend with. These days amps mostly self protect and although they don't give you the power you expect, the amp lives to see another day and no one's house burns down. Back in late '08 when I met the fellow from the FTC, it had been almost 10 years since he had received a complaint about falsified specs. As you know, the govt doesn't take action unless voters are complaining.
BTW: You might find my presentation from Rocky Mountain 2015 interesting. Google "RMAF15: What the Specs Don't Tell You and Why."
In a nutshell, anyone can advertise anything these days. The FTC got involved in '69-'74 when people had amps failing with catastrophic consequences. There was a fraud issue to contend with. These days amps mostly self protect and although they don't give you the power you expect, the amp lives to see another day and no one's house burns down. Back in late '08 when I met the fellow from the FTC, it had been almost 10 years since he had received a complaint about falsified specs. As you know, the govt doesn't take action unless voters are complaining.
BTW: You might find my presentation from Rocky Mountain 2015 interesting. Google "RMAF15: What the Specs Don't Tell You and Why."
Of course at the rate at which number of surround channels to be stuffed into the chassis continues to increase (with Atmos, now as much as 12?) , by the end of a 5-7 yr life span, the machine is likely to be a couple of generations out of date anyway. 🙄
They often don't even bother with that. Just take the unloaded rail voltage, square it, and divide by two ohms. Then claim that's the RMS power into 8 ohms.
One reason I hate powered speakers. That kind of specmanship runs more rampant than with amplifiers. Of course they claim SPL based on that, and real world ends up being -20dB.
- Status
- Not open for further replies.