[CanadianMaestro]

That's why, ironically, ear plugs are highly recommended when wanting to enjoy a live concert. Serious permanent damage can occur very quickly at those levels, and may not show up right away.

http://www.noisehelp.com/noise-dose.html


Maximum Recommended Noise Dose
Exposure Levels
Noise Level (dBA) Maximum Exposure Time per 24 Hours
85 8 hours
88 4 hours
91 2 hours
94 1 hour
97 30 minutes
100 15 minutes
103 7.5 minutes
106 3.7 minutes
109 112 seconds
112 56 seconds
115 28 seconds
118 14 seconds
121 7 seconds
124 3 seconds
127 1 second
130–140 less than 1 second
140 NO EXPOSURE

These measurements were done on a hapless human or animal? 

 

[madwolfa]

That's why, ironically, ear plugs are highly recommended when wanting to enjoy a live concert. Serious permanent damage can occur very quickly at those levels, and may not show up right away.

 
I went to Mastodon's live show last year and tried using some quality ear plugs. It really sucked and I threw them away after half an hour.

 

[x RELIC x]

These measurements were done on a hapless human or animal?  :eek:

They aren't too far off from most recommended listening exposure times in a 24 hour period. Keep in mind they mention damage may occur, and may not be immediately perceivable, at the lower levels.

They key is that this is a play now pay later kind of scenario. Personally I like to keep it on the safe side. Anyone listening at 120db (which is twice as loud as 110db due to the logarithmic nature of the decibel scale) should feel very uncomfortable. If not there is already hearing damage.

 

[chillaxing]

   
I went to Mastodon's live show last year and tried using some quality ear plugs. It really sucked and I threw them away after half an hour.

 
 
yup, been to many concerts and show, across many genres.  Loudness was never a problem, till this last show.  Ask all my friends if they thought the same, and consensus was it was way to loud.

 

[x RELIC x]

Back to the amps for the LCD-2, the overall point is that many of these specs for peak power output are mostly for headroom on transient notes and amplifier clipping. If pushing the amp to run continuously at max spec you won't be in Head Fi very long.

 

[tomb]

A few things:
 
1. Gain and power are two different things.  It matters little where your volume knob is positioned relative to power.  Volume travel is not an indication of power - at all.  It's totally a function of the gain setting on the amp and the efficiency of your headphones.  An amp could be rated for 1W at 32 ohms and produce that power at 1/4 volume setting with one pair of  headphones and at 1/2 volume setting with another.  Impedance of the load plays a factor, but only in the respect that the amplifier will tend to produce different power levels at different load impedances.  This is because every amplifier design makes choices (compromises?) between how it amplifies voltage vs. current.  The load impedance dictates how much of each is needed - voltage vs current.  The amp may be very good at supplying one, but maybe not another.
 
2. Tests for power are not done at high gain and technically, they are not done at max volume setting, either.  Although the volume control is often shorted out anyway.  Power is tested with a load at a specified resistance.  Then usually, the source signal is varied (increased) until the signal output from the amplifier begins to clip.  It is very easy to see when the signal sine wave begins to clip on an oscilloscope.  Sometimes, the measurement is set to register 1% THD (or some other THD value) as the threshold to define the clipping point.  Voltage is then measured across the load and as referenced in an earlier post, P = (V^2)/R.  This also assumes the metering is registering RMS voltage for that "V."
 
3. The interesting thing about #2 above is that this is often done at one frequency - typically 1K, unless the power is quoted as from 20 - 20Khz.  If the frequency range is not specified, you can bet it was done at 1K.  RMS power from 20-20Khz is the most stringent specification, because that shows the mfr has actually tested the entire range of frequencies.  Important: if this is not specified, the amp may produce less power at the lower frequencies (or at some other frequency) than at 1K.  It's a reason for the common understanding that lack of power may be noticed in the bass frequencies, first.  Good amps should be ruler flat in their frequency response, but that response may be measured using a different method than max power at different frequencies, although they should be closely similar.
 
It is still very important to make measurements and if not useful as absolutes, they are certainly worthy to use for comparisons between products/designs.  Realize however, that the playing field is not always the same.  The measurements are also not all-encompassing.  Like a lot of things, they paint a good picture, but not the whole picture.  Your ears determine the final ruling.
 
EDIT: I typed too much.  Maybe I'll repeat some of what I deleted at another time.

 

[jodgey4]

  3. The interesting thing about #2 above is that this is often done at one frequency - typically 1K, unless the power is quoted as from 20 - 20Khz.  If the frequency range is not specified, you can bet it was done at 1K.  RMS power from 20-20Khz is the most stringent specification, because that shows the mfr has actually tested the entire range of frequencies.  Important: if this is not specified, the amp may produce less power at the lower frequencies (or at some other frequency) than at 1K.  It's a reason for the common understanding that lack of power may be noticed in the bass frequencies, first.  Good amps should be ruler flat in their frequency response, but that response may be measured using a different method than max power at different frequencies, although they should be closely similar.

Can you show an example of an amp that isn't ruler flat at all volumes?

 

[tomb]

 

  3. The interesting thing about #2 above is that this is often done at one frequency - typically 1K, unless the power is quoted as from 20 - 20Khz.  If the frequency range is not specified, you can bet it was done at 1K.  RMS power from 20-20Khz is the most stringent specification, because that shows the mfr has actually tested the entire range of frequencies.  Important: if this is not specified, the amp may produce less power at the lower frequencies (or at some other frequency) than at 1K.  It's a reason for the common understanding that lack of power may be noticed in the bass frequencies, first.  Good amps should be ruler flat in their frequency response, but that response may be measured using a different method than max power at different frequencies, although they should be closely similar.

Can you show an example of an amp that isn't ruler flat at all volumes?

 
I thought that might confuse some folks and debated leaving it in my post.  Frequency response is often conducted at a given power level, not the max power level.  Many amps can produce more power before they clip at 1K than they can at 20 Hz.  It doesn't mean they don't have a ruler-flat frequency response at lower power outputs.  Would you accept that distortion can vary according to frequency, or is that contrary to your beliefs, too? 

 
Maybe this quote from Wikipedia can help:
 
Quote (Wikipedia article on Audio Power):

In its 1974 Amplifier Rule meant to combat the unrealistic power claims made by many hi-fi amplifier manufacturers, theFederal Trade Commission prescribed continuous power measurements performed with sine wave signals on advertising and specification citations for amplifiers sold in the US. Typically, an amplifier's power specifications are calculated by measuring its RMS output voltage, with a continuous sine wave signal, at the onset of clipping—defined arbitrarily as a stated percentage of total harmonic distortion (THD)—into specified load resistances. Typical loads used are 8 and 4 ohms per channel; many amplifiers used in professional audio are also specified at 2 ohms.

Continuous power measurements do not actually describe the highly varied signals found in audio equipment (which could vary from high crest factor instrument recordings down to 0 dB crest factor square waves) but are widely regarded as a reasonable way of describing an amplifier's maximum output capability. Most amplifiers are capable of higher power if driven further into clipping, with corresponding increases in harmonic distortion, so the continuous power output rating cited for an amplifier should be understood to be the maximum power (at or below a particular acceptable amount of harmonic distortion) in the frequency band of interest. For audio equipment, this is nearly always the nominal frequency range of human hearing, 20 Hz to 20 kHz.

 
Again, my initial post clearly stated, "... they should be closely similar." 

 

[jodgey4]

Originally Posted by tomb /img/forum/go_quote.gif
 
Would you accept that distortion can vary according to frequency, or is that contrary to your beliefs, too? 

Lol, I think you're quite confused about what I've said on these forums. Also, amps clipping at lower frequencies sooner than higher ones? Clipping just has to do with max output, frequency should have no bearing on that. I'm assuming you're saying that once you take in to account that most recorded tracks have stronger low frequencies stored, this is the case? You're not being very clear, and this information is quite misleading.

 

[chillaxing]

Is there a is way to put a o-scope on a headphone amp and measure?
 
I'm a man of actual facts and its killing me not knowing if what i claim, is right.

 

[tomb]

  Power is V^/R, independent of frequency. Bass shouldn't be any different.

Just to be clear, this glosses over a huge issue in many portable amps, portable players, and phones.  Bass can vary - quite a bit.
 
Less sophisticated amplifiers often have DC blocking capacitors in the signal path.  Combined with the headphone resistance, these form an RC circuit.  The RC circuit creates a high-bandpass filter that can limit low-frequency response.  A -3dB characteristic of the RC circuit could very easily impinge on the lower part of the 20-20Khz audio band.  So, practically speaking, the amplifier's power is going to be severely limited, depending on the load.
 
Let's just take a common amplifier - a very famous one - typically used for Sennheiser HD580/600/650 headphones, the Bottlehead Crack.  It uses 100uf output coupling capacitors.  If we look at a chart, we can see the results of this with headphones other than 300 ohm Sennheisers:

 
The above chart is generated using the governing equation for an RC circuit with different load impedances.  The "C" in the RC circuit equation forms the basis of the chart and is 100uf, the value used for the output coupling capacitors in the Bottlehead Crack.  Note the different load impedances, especially for 16 (IEMs), 32 (Grados and most portable headphones), and 60 ohms (AKG K701 family).  The -3dB point is bad enough, but note that the -1dB point is all the way up into the high-bass for the lowest impedances.
 
This is not a criticism of the Bottlehead Crack.  It's simply to point out that there could be a lot more going on with an amplifier than just quoting frequency response or power level at a given impedance.
 
Yeah, many people know better these days than to pair an OTL amplifier with a low impedance headphone.  Yet, maybe they don't know exactly why other than some output impedance vs. load impedance rule-of-thumb that they've heard about. 

 

 

[jodgey4]

@chillaxing Yeah, you can absolutely do that. Take an old unused cheap 3.5mm cable, chop off one end, put the scope on one or both channels with resistors in series to simulate a load... and go to town. Take a track, analyze the frequencies recorded, and use that to run single test tones through that are easy to evaluate. Here's a recording I ripped off of YouTube (https://www.youtube.com/watch?v=AQYV_v2Fo1U) of Steve Jordan and Bernie Worrell (240p)... you can see the energy laid out over a 15 second sample or so near the height of the song.
 

 

[tomb]

 

Originally Posted by tomb /img/forum/go_quote.gif
 
Would you accept that distortion can vary according to frequency, or is that contrary to your beliefs, too? 

Lol, I think you're quite confused about what I've said on these forums. Also, amps clipping at lower frequencies sooner than higher ones? Clipping just has to do with max output, frequency should have no bearing on that. I'm assuming you're saying that once you take in to account that most recorded tracks have stronger low frequencies stored, this is the case? You're not being very clear, and this information is quite misleading.

OK - see my previous post if I'm confused about what you said. No offense. 

 

[jodgey4]

  >['Me: power = V^2/R, no frequency involved']
 
Just to be clear, this glosses over a huge issue in many portable amps, portable players, and phones.  Bass can vary - quite a bit.
 
This is not a criticism of the Bottlehead Crack.  It's simply to point out that there could be a lot more going on with an amplifier than just quoting frequency response or power level at a given impedance.
 
Yeah, many people know better these days than to pair an OTL amplifier with a low impedance headphone.  Yet, maybe they don't know exactly why other than some output impedance vs. load impedance rule-of-thumb that they've heard about. 

 

Still doesn't address how bass can change with power, and you cherry-picked an amp with some of the most unique properties on the market - not dismissing that most people don't know much about amps, but I think we're either talking past each other or coming from a different understood premise.

 

[tomb]

 

  >['Me: power = V^2/R, no frequency involved']
 
Just to be clear, this glosses over a huge issue in many portable amps, portable players, and phones.  Bass can vary - quite a bit.
 
This is not a criticism of the Bottlehead Crack.  It's simply to point out that there could be a lot more going on with an amplifier than just quoting frequency response or power level at a given impedance.
 
Yeah, many people know better these days than to pair an OTL amplifier with a low impedance headphone.  Yet, maybe they don't know exactly why other than some output impedance vs. load impedance rule-of-thumb that they've heard about. 

 

Still doesn't address how bass can change with power, and you cherry-picked an amp with some of the most unique properties on the market - not dismissing that most people don't know much about amps, but I think we're either talking past each other or coming from a different understood premise.

The Bottlehead Crack has no different properties than most any other OTL amp, which are relatively common.
 
But you're right - we are obviously talking past each other and this is pointless to continue.