Audiophile Related - Understanding power, peak, contious and dBs - Page 1
Forum section: electronics / projects

author: DW1961
author_rank: Frequent Contributor
timestamp: August 01, 2020, 08:42:54 pm
content: My original post was all messed up. I've corrected that below--sheesh! Sorry.Lets say you a have a speaker that is 45 watts continuous/100 peak at 93dB sensitivity @ 8 ohms.(We'll fill in the other aspects as we go.)Now lets say you have two amps:Amp 1 = has 19 watts per channel continuous @ 8 ohms and 19V.Amp 2 = 30 watts per channel continuous @ 8 ohms and 24V.So you get roughly 32.5% more power on amp 1.-------------------------------------------------------------"Increasing an amplifier from 25 watts to 50 watts (double the power) increases the acoustic power by 3dB."https://geoffthegreygeek.com/amplifier-power/So you hear any difference in volume between amp 1 and amp 2.So why not go with a lower wattage amp and save money? In other words, what's the benefit having amp 2 instead of amp 1?

author: TimFox
author_rank: Super Contributor
timestamp: August 01, 2020, 09:04:12 pm
content: Wrong analysis.1. If you have two amplifiers, both rated to drive 8 ohms, with different maximum power ratings, and you connect them one at a time to an 8 ohm speaker, you can get more output from the speaker when driven at higher power.2. If you adjust the gain (volume control) to get the same power (within the maximum limit of both amplifiers), you will get the same output from the speaker.3. You do not "double the volume" with twice the power. Sound level is perceived logarithmically, and doubling the volume is not a defined concept. See the many discussions of the Weber-Fechner Law, e.g.,https://ocw.upc.edu/webs/42254/Acustica_EN/Bloc2/Fitxes/T07_02_Llei_Weber_Fechner.htm4. If amplifier 1 is not loud enough to annoy the neighbors, then amplifier 2 will give you more sound output. (Not the result you stated.)5. The speaker rating of 45 watts continuous/100 watts peak is a maximum rating: you may damage the unit if you apply more power. The amplifier ratings are the maximum output with a specified level of distortion.6. The voltages you mention for the amplifiers are not correct: 19 V rms into 8 ohms is 45 W mean power (NOT rms power, a common misnomer) and 24 V rms into 8 ohms is 72 W mean power.7. The speaker sensitivity rating is a specification of how much acoustical output you get for a given electrical input. It is defined as the indicated sound level (in dB SPL) obtained 1 meter from the speaker with 1 W electrical input. The definition of "dB SPL" is the ratio of the acoustic power divided by a very low reference level, usually 20 x 10-6pascal sound pressure, which is roughly the threshold of hearing, and defined in the ANSI S1.1-2013 spec for sound level meters.

author: DW1961
author_rank: Frequent Contributor
timestamp: August 01, 2020, 11:09:31 pm
content: Quote from: TimFox on August 01, 2020, 09:04:12 pmOf GEZUZ! I misaddressed that up. No kidding you don't double power volume by doubling power! I've now changed my question. Please comment again! Sorry!

author: TimFox
author_rank: Super Contributor
timestamp: August 01, 2020, 11:27:25 pm
content: The higher power amplifier can make more acoustic power out of the speaker than can the lower power amplifier out of the same speaker. I really don’t understand your question.If you are comparing two different amplifiers, there's a lot of "all other things being equal". An excellent 19 W amplifier putting out 15 W may have lower distortion than a crappy 30 W amplifier putting out the same power (15 W). Were all other things equal, however, if you only need 15 W to achieve the desired sound level for your application, one would expect the 30 W amplifier to have lower distortion at 15 W than does the 19 W amplifier at 15 W output. That is one reason to use the higher power amplifier. 93 dB sensitivity means that 1 W will achieve 93 dB SPL out of the speaker (1 meter from the speaker), which is enough for many applications. 500 W would drive the speaker (if it could handle it) to 120 dB SPL, which is nearly painful and may cause hearing damage. If you put the maximum peak level of 100 W into the speaker (which is 20 dB above 1 W), you will get a respectable 113 dB SPL, louder than a jackhammer and comparable to a chainsaw. The 30 W amplifier (15 dB above 1 W) will give 108 dB SPL at 1 m. Long term exposure to 85 dB SPL is considered to be harmful to hearing, and is regulated by OSHA. The sound level will fall off as you move back from the speaker; in a normal room, the fall-off is complicated by reflections from the walls, but in free space the power falls off with the square of the distance.

author: Bassman59
author_rank: Super Contributor
timestamp: August 02, 2020, 03:36:13 am
content: Quote from: DW1961 on August 01, 2020, 08:42:54 pmAmp 2 will be louder than Amp 1, all other things being equal. Significantly louder? No. Cleaner louder? Yes, assuming distortion specs are the same at the rated output.Driven into distortion, Amp 1 could be as loud as Amp 2.The spec that ultimately matters is desired SPL at a particular distortion level. If the SPL you get with Amp 1 and your speakers suffices, then you use Amp 1.

author: DW1961
author_rank: Frequent Contributor
timestamp: August 02, 2020, 05:20:22 am
content: Quote from: TimFox on August 01, 2020, 11:27:25 pmTim,Assume all things are equal except power.Good information. Thanks.So, no difference except power is power and amp distortion from having to push the amp harder is the only reasoning? (Such as a heavy bass line or equalizer hitting the bass heavy?)

author: DW1961
author_rank: Frequent Contributor
timestamp: August 02, 2020, 05:22:03 am
content: Quote from: Bassman59 on August 02, 2020, 03:36:13 amOK so power is power and like Tim said, the only concern is amp distortion?If 3dBs is the sound pin make when it hits a hard floor, and doubling power only gets you 3dBs, how is Amp 2's 32% increase going to be louder to the human ear?

author: JohanH
author_rank: Frequent Contributor
timestamp: August 02, 2020, 07:51:12 am
content: Quote from: DW1961 on August 02, 2020, 05:22:03 amEvery 1 dB change is told to be clearly perceptible to the human ear. 3 dB should be noticeable. According to listening tests you need an increase of 10 dB to perceive an actual doubling of volume, though (even if 6 dB theoretically doubles amplitude).If the speakers can stand 45W I would go with the larger amplifier. If nothing else, you have more headroom with the larger amplifier before hitting its limits (clipping). If you are sure you are not going to listen to loud music, then it is up to you; you can use as small amplifier as you want.In general, with typical listening scenarios (speaker at home in nominal room), you would rather have an amplifier with equal or more power than the speaker, to minimize the risk of clipping with a too small amplifier. Clipping is always worse for the speaker than temporarily driving it with a higher power than nominal.

author: TimFox
author_rank: Super Contributor
timestamp: August 02, 2020, 01:09:43 pm
content: There is an informal definition of the dB in acoustics:If you tell your kid to turn down the volume on the TV, he will reduce the sound by 1 dB, which is the least perceptible difference.A 3 dB change in sound level is quite audible. A factor of 1.32:1 increase in power is 1.2 dB.Do not confuse dB (which is a power ratio) with dB SPL or dBm, or any of the myriad cases where a reference level is stated in the suffix.You can say that dropping a pin is a sound of 3 dB SPL. Doubling the power is an increase of 3 dB.

author: Siwastaja
author_rank: Super Contributor
timestamp: August 02, 2020, 01:21:15 pm
content: Remember that "volume" is just a psychological concept, not a scientifically measurable number.The only way to say how many dB of power you need to add to "double the volume", is to ask volunteers to listen to different power levels and ask them about when they felt it "doubled".

author: TimFox
author_rank: Super Contributor
timestamp: August 02, 2020, 01:31:00 pm
content: It is vaguely like temperature in degrees F or C (not K): you can say that the difference between 80 and 60 degrees is twice that between 80 and 70 degrees, but you can't say that 80 degrees is twice as hot as 40 degrees. (Analogy only)

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: August 02, 2020, 02:02:49 pm
content: Loudspeaker power specs are near to worthless. If you actually fed the rated power to most speakers they'd go up in flames or at least fry the voice coils. The only number to care about is the sensitivity. From that you can predict dB output. Remember that music is an unpredictable waveform, anything but a constant power, and your speaker placement in a given room has a huge effect, so these calculated results may not predict how loud you think it sounds.

author: madires
author_rank: Super Contributor
timestamp: August 02, 2020, 02:36:45 pm
content: And there are more things to consider. The impedance of the speaker changes with frequency, it's not a flat line. Tthe power needed for an agreeably listening experience at home isn't high unless you live above a night club. Clean 10W plus a good set of speakers is totally sufficient. If you want to know more about SPL weightings regarding human sound sensitivity you can start with dB(A) (https://en.wikipedia.org/wiki/A-weighting).

author: TimFox
author_rank: Super Contributor
timestamp: August 02, 2020, 03:12:17 pm
content: A very important detail about actual audio waveforms (both music and speech) is the high peak to average ratio, compared with a continuous sine wave.A higher power amplifier also has a higher level at which it clips the waveforms. Presumably, clipping the waveform is annoying to the listener.Of course, with electric guitars and similar systems where music is being produced, rather thanreproduced, the distortion and clipping of the amplifier is part of the musical instrument, so the considerations are different from those applicable to high-fidelity reproduction of recorded sound.

author: DW1961
author_rank: Frequent Contributor
timestamp: August 02, 2020, 07:42:13 pm
content: Quote from: Siwastaja on August 02, 2020, 01:21:15 pmI'm getting that."Whatever level you perceive as twice as loud, it is not at +3dB, which is twice the power. It is normally more than +6dB (4 times the power). Historically it is considered to be around +10dB, which is 10 times the power. This following table summarizes the increases (the loudness is based on 10dB gain for double loudness).+3 dB =Loudness Change +23% <----------!!!!Sound Pressure Change 1.4Power Change x 2Double the power (+3dB) gives around 25% increase in perceived volumeFour times the power (+6dB) gives around 50% increase in perceived volume10 times the power (+10dB) gives around 100% increase in perceived volumehttps://geoffthegreygeek.com/amplifier-power/So, I am misunderstanding how 3dB is about the sound of a pin dropping, but = a 23% increase in volume.

author: TimFox
author_rank: Super Contributor
timestamp: August 02, 2020, 07:57:52 pm
content: I already explained this:3 dB SPL (note the suffix) is the sound level associated with dropping a pin.3 dB (no suffix) is a power ratio.

author: bson
author_rank: Unknown
timestamp: August 02, 2020, 08:42:53 pm
content: Quote from: DW1961 on August 01, 2020, 08:42:54 pmThat's complete nonsense. Acoustic power and electric power are linearly related by the loudspeaker's efficiency. Pa = eff * Pin. "3dB" is just a red herring since 25W to 50W is also 3dB.

author: TimFox
author_rank: Super Contributor
timestamp: August 02, 2020, 08:48:18 pm
content: Quote from: bson on August 02, 2020, 08:42:53 pmMisleading: Since the acoustic power is proportional to the electric power for a linear loudspeaker, increasing the input (electrical power) by a factor of two (3 dB) will increase the output (acoustic power) by a factor of two (3 dB). DW1961 may be confusing amplifier power rating with amplifier power output.

author: DW1961
author_rank: Frequent Contributor
timestamp: August 02, 2020, 09:13:14 pm
content: Quote from: TimFox on August 02, 2020, 08:48:18 pmOK, so the way I am understanding it now is like this:-Double the amp power, you get a 3dB increase in acoustic power.-Acoustic power causes sound pressure, which can be measured objectively.-Acoustic power does now equal loudness.Adding x2 the power adds +3dB of acoustic power, but only increases volume by 23%.Note to self:Just thought of something else I want to bring up and going to make a note of it here:PLEASE DISREGARD REPLYING TO THIS FOR NOW: Ohms and average power for any 4-8 ohms rating and any 4-8 ohms speaker. An amp rated at 100 watts at 4 ohms may give an 8 ohms speaker nearly the same power calculated at 4 ohms depending on frequency?

author: TimFox
author_rank: Super Contributor
timestamp: August 02, 2020, 09:23:15 pm
content: The physical statements are correct. (You should be more careful about the use of common terms such as "adding" and "multiplying"; "adding twice the power" means "tripling the power" in plain English, since 1 + 2 = 3. Doubling the power does add 3dB to the result).The final statement about the volume is not a physical statement, but the result of psychoacoustic experiments with the perception by human listeners, and is related to the Weber-Fechner law.

author: DW1961
author_rank: Frequent Contributor
timestamp: August 02, 2020, 11:29:12 pm
content: Quote from: TimFox on August 02, 2020, 09:23:15 pmYes, understood about terms, for sure.OK, so now about my thoughts on the power ratings for an amp, still using our TA 3116D class amp.The amp ratings are rated at 4 ohms:– 2 × 50 W Into a 4-ΩBTL Load at 21 V(TPA3116D2The two other chips are rated with different voltages and ohms.For example:Spec Sheet Source:https://www.ti.com/lit/ds/symlink/tpa3116d2.pdf?ts=1596389304658&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FTPA3116D2Note that the chips are different. This is from the same spec sheet.Then we have the spec sheet graphs which do not specify which chip, but seem to be for all (3) chips listed on the spec sheet.It seems like they are rating it at an average using the graph for 4 ohms. It looks like the power output is an average between THD of 1-10, as is indeed 100 watts total at 4 ohms @ 21V. (Graph to the right of the 8 ohms graph.If we use the 8 0hm graph, it would seem the average is 29 watts per channel or 58 watts total @ 21V. With a little fudging for graph reading inconsistencies, we could say roughly that it is putting out about half the rated power at 4 ohms as it is at 8 ohms @ 21V.I'm going to stop here to make I'm not in error.

author: TimFox
author_rank: Super Contributor
timestamp: August 02, 2020, 11:44:50 pm
content: I think you mean that the power into 8 ohms is approximately half the power into 4 ohms, which is reasonable, since the devices are close to constant-voltage sources.

author: DW1961
author_rank: Frequent Contributor
timestamp: August 03, 2020, 04:57:34 am
content: Quote from: TimFox on August 02, 2020, 11:44:50 pmYeah that's what I meant.Okay, so how can I say this?So what I am understanding is that it is good to have the amp rated at 4 ohms, since driving an 8 ohms load is easier on the amp?Also, if you connect 4 8 ohms speakers in parallel to that amp chip, then you would share 100 watts with each speaker, and the amp could power it without a problem, since it would be seeing the load as 4 ohms?If so, yes, the 4 - 8 ohm speakers would be operating at 25 watts each, whereas at 8 ohms and two speakers ( using the calculation that running at 8 ohms and 21 v = 58 watts total) would get 29 watts each.That sounds like a pretty good trade off for having twice the speakers and only losing 4 watts each speaker?Just as an aside, that little amp chip is pretty impressive given heat, power efficiency, and THD at 50% volume?

author: TimFox
author_rank: Super Contributor
timestamp: August 03, 2020, 01:18:41 pm
content: Since transistors normally operate at low voltages (compared with tubes), and 4 ohms is the lowest popular speaker nominal impedance, it is common to design the circuit and power supply with 4 ohms in mind. The amplifier may run cooler into an 8 ohm load, while delivering less power than into a 4 ohm load.Two identical 8 ohm speakers in parallel will present a nominal impedance of 4 ohms to the amplifier, and each one will receive half the total power.Four8 ohm speakers would give2 ohms, and you need to see if the amplifier is happy with that low load resistance. Re-do your arithmetic about four speakers.

author: DW1961
author_rank: Frequent Contributor
timestamp: August 03, 2020, 05:30:20 pm
content: Quote from: TimFox on August 03, 2020, 01:18:41 pmTim,Researched that and got it. (8 ohms/4 speakers = 2 ohm load)Thanks much for hanging in there with me. I appreciate it.