Electronics > Projects, Designs, and Technical Stuff
Yet another Audiophile Question.
tooki:
--- Quote from: DW1961 on August 07, 2020, 01:58:24 am ---Another interesting fact about the 3116D class D amp is that it's distortion is 10% max.
If you look at my graphic above and the sound level, it's so loud at 1% THD that it would never need to be louder, and that's at 50% power at 19V. If I pushed it to max power and THD 10%, at 19V, I could get 95dB out of it at 10'.
Isn't 95dB at 10% THD considered pretty decent?
The point is that even if I push it to max at 19V, the dBs don't change. (24 watts to 28 watts)
At 10'.
More interesting is that:
if I push the watts up from 19V at 1% THD: 23 watts = 94Db
if I push the watts up from 24V at 1% THD: 33 watts = 96Db
--- End quote ---
The maximum distortion can go almost unlimited on any amp — it just depends on how much you overload it.
An amp power rating is so many watts at a chosen THD. Companies will advertise using a power level at what I consider absurd THD (like 10%) because it’s a bigger number. But some advertise at less THD, and ultimately the data sheet tells you more. Bear in mind that for a given THD, the maximum output power is dependent on the amp’s design, on the supply voltage, and on the load characteristics.
As for what’s decent or not: is 10% THD acceptable to you? (It’s not for me.) And is 95dB enough? Well are you playing in a bedroom or a stadium? Cause a TPA3116 isn’t going to fill a stadium.
TimFox:
I suspect that the manufacturer was specifying power at 10% THD as a measure of the clipping level. This is "eyballed" on a CRO be noting the flattening on the crests of the sine wave, and the THD increases rapidly above that power level, as no more voltage can be supplied by the amplifier. This is well below a square wave output, which has about 46% THD, based on the fundamental waveform included in the Fourier series of the square wave.
Have you considered my suggestion on how to quantitatively estimate the power you actually need for your purposes? I assume the point of this thread is that you are interested in a particular chipset to make an amplifier for your existing speakers, and you want to determine how much power is required for your application.
DW1961:
--- Quote from: tooki on August 07, 2020, 12:45:14 pm ---
--- Quote from: DW1961 on August 07, 2020, 01:58:24 am ---Another interesting fact about the 3116D class D amp is that it's distortion is 10% max.
If you look at my graphic above and the sound level, it's so loud at 1% THD that it would never need to be louder, and that's at 50% power at 19V. If I pushed it to max power and THD 10%, at 19V, I could get 95dB out of it at 10'.
Isn't 95dB at 10% THD considered pretty decent?
The point is that even if I push it to max at 19V, the dBs don't change. (24 watts to 28 watts)
At 10'.
More interesting is that:
if I push the watts up from 19V at 1% THD: 23 watts = 94Db
if I push the watts up from 24V at 1% THD: 33 watts = 96Db
--- End quote ---
The maximum distortion can go almost unlimited on any amp — it just depends on how much you overload it.
An amp power rating is so many watts at a chosen THD. Companies will advertise using a power level at what I consider absurd THD (like 10%) because it’s a bigger number. But some advertise at less THD, and ultimately the data sheet tells you more. Bear in mind that for a given THD, the maximum output power is dependent on the amp’s design, on the supply voltage, and on the load characteristics.
As for what’s decent or not: is 10% THD acceptable to you? (It’s not for me.) And is 95dB enough? Well are you playing in a bedroom or a stadium? Cause a TPA3116 isn’t going to fill a stadium.
--- End quote ---
The amp isn't meant to fill stadiums. I live in a small house, 1200 sq ft, and I could never listen to it at 50 power with the Klipsch R-51M bookshelf speakers. Way, way too loud. I can hear it fine all over the house at a few watts power. The living room is 20x20 and PLENTY of volume at a few watts.
Now, they do offer an amp with TWO 3116D chips in it. I had one of those. I sent it back. No need to blow the windows in the house. At Way too much power for my needs.
Bassman59:
--- Quote from: robca on August 06, 2020, 09:21:02 pm ---
--- Quote from: Bassman59 on August 05, 2020, 09:42:05 pm ---But the most common mechanism for driver failure is thermal overload. Too much power. Area under the curve.
It's common to think about audio power amplifiers as being "power" devices, because their outputs are given in watts and all of it. But they are really voltage amplifiers that can source or sink a lot of current.
This means that there's an upper limit to an amplifier's output, which is the supply rail. Hit the rail and you clip, we all know that, right?
What happens when you clip a signal? The simple answer is that the output stays at the rail for the duration of the time that the input voltage times the gain wants to exceed the rail (plus, perhaps, an overload recovery time).
And all of the time sitting at the rail means you're just dumping current, in a DC sense, into the voice coil and you're baking it.
The amplifier with the higher voltage rails ("more power") would allow a higher-level output to go through unclipped, and because real music waveforms don't sit at a peak for very long, a peak doesn't damage the driver because it's not generating enough heat to do so. The amplifier with the lower voltage rails ("less power") clips and stays at the rail and thus a constant voltage level, generating more heat in the voice coil and eventually the driver dies.
Area under the curve.
As for the Klipsch minimum-power recommendation, it's silly. As long as the amplifier output is clean, not clipped, a 5 W amplifier won't damage the speakers.
--- End quote ---
I'm confused, sorry. I do understand that a long duration DC signal will fry a tweeter. I'm just confused on why the exact same amplifier with, say, a +-12V rail can damage a tweeter more than the twin with a +-24V rail, assuming the output signals are identical amplitude (hence the 12V one is clipped)
I created two horrible Paint JPGs, showing what I mean. Same signal overall amplitude, in one case clipped at an arbitrary height we can call 12V, another full swing. In both cases, the area under the curve is in red. And in the clipped version, the area under the curve is smaller. More complex waveforms will look similar, unless the recovery time from clipping exceeds the highest audio frequency. But even at 44KHz, that would mean a recovery slower than 22 micro seconds
--- End quote ---
Again: area under the curve.
Your picture does show clipping and its effects, but it doesn't show units. Driver destruction is a function of heating. You can clip all you want, but as long as the total heat dissipated in the voice coil remains below "danger" levels, the driver is fine. For example, look at guitar amps -- their outputs are highly distorted but drivers don't die because generally the speakers installed are rated properly.
Remember that coil heating is integration. The driver might survive a minute of clipped inputs at/above its ratings, but will it survive the DJ night at your local club?
I think that for the low amplifier power levels relative to the rating of the drivers being discussed here, driver destruction is not a concern.
Bassman59:
--- Quote from: robca on August 07, 2020, 12:19:54 am ---Which is exactly why I was confused by the statement that a higher voltage rail will not cause problems. The contrary is true: assuming two identical ideal amplifiers with the same input and amplification factor, one with 12V rail one with 24V rail, the one with 24V rail will blow the tweeter faster.
--- End quote ---
If the gain of your two amplifiers is the same, then the output for any given input is the same, if you are not clipping. The "larger" amplifier will not blow the tweeter faster. The output level (volume) will be identical.
When you get into clipping then all bets are off, of course. The point is that the 12 V amplifier will clip before the 24 V amp, and you have to look at the specific conditions when clipping is occurring. How much clipping? What is the waveform being clipped? Lopping off the peak of a snare drum hit is very different from clipping a sine wave.
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