"Of course since my receiver is THX cert, now you have me wondering if my 0db is actually 105. In otherwords, "-20 dB" on your dial will be different than "-20 dB" in someone else's room and on different equipment. How that relates to sound pressure, or loudness, in your room will depend on the amps, speakers, and room environment. It is suggesting, in your case, that at the "-20 dB", the electrical signal is attenuated. Kenstr, the reason you see -20 dB on your volume control is as explained above. and, so, have we answered Kenstr's question or confused him more? Again, being anal, that is a meaningless nothing notation of an unknown ratio, whereas 95dB SPL would be correct, and 95dB SPL at 1 meter would be more correct. "I measured my speaker's output as 95dB", for example. However, while not technically a direct unit of measure, we have used the decibel as a measure. Now that is the anal and technical definition.a notational form expressing a ratio. If we consider the human threshold of hearing to be 20 micropascals and the threshold of pain is 100 pa, this represents a ratio of 5 million.as well our response tends to be logrithmic. The decibel, then, is correctly identified as a method of notation.and a convenient one at that. It is sound pressure (SPL) that is normally measured and the square of sound pressure is proportional to acoustic power. As such, since acoustic intensity is power per unit area it is eligible to be expressed decibels. The decibel applies to power-like quantities. In any case, the bel is defined as the logarithm (base 10) of the ratio of two powers. This is confusing.how can you measure something not using a unit of measure? No, the dB was used to measure ppower loss over telephone lines, not voltage. dB is a very versatile unit, and so it's used in many ways, which can be confusing.Īnyway, since THX says that "reference level" is 105 dBa, many people try to calibrate their amps so that they play at 105 dBa when their volume control is set at 0 dB.īy the way, you might have figured out by now that, if they wanted to, amp manufacturers could calibrate their display so that 0 dB represented "the quietest sound that the amp can make" and then your volume knob would count up from zero. In this case, we are again referencing the loudness of a certain thing relative to a certain reference value, but in this case, the "reference value" is 0 dB (or, more correctly, dBa) is "the quietest thing that a human ear can hear" and everything else is measured relative to that. That's the dB unit that you hear talked about when people say that "a jet engine is XXX dB, a rock concert is XXX dB, etc.".
![negative decibel scale negative decibel scale](https://thumbs.dreamstime.com/b/decibel-scale-decibel-scale-sound-level-102089570.jpg)
The correct unit above is actually dBa, or dB "audio". Here, I'm using it to refer to the loudness of sound.
![negative decibel scale negative decibel scale](https://labster-image-manager.s3.amazonaws.com/v2/DBS/5caefcc9-4ac1-4863-8684-d6a5ece913a0/DBS_PosterDecibels.en.x1024.png)
In the previous paragraphs, I was using dB to refer to the amount of gain that your amplifier was adding to the signal. This can be confusing, since we're now actually using the term "dB" in two separate ways.
![negative decibel scale negative decibel scale](https://i.pinimg.com/736x/ee/41/7a/ee417a5de05505800a80a02bfe470aaf--decibel-sound-waves.jpg)
While that might sound good, depending on where the 0dB reference point is set, it might actually be quieter than some other amp at 0dB, if the other amp's 0dB reference point is calibrated higher than my amp's.Īs a previous poster mentioned, the THX spec says that "reference level" sound should be at 105 dB. Some amps, like my Denon 3803, can go above 0 dB-for example, in stereo mode, my Denon can go up to + 18 dB. How loud that actually is depends on where your amp's reference level is. If you're at -20 dB, then you're 20 dB below the reference level, or 1/100th the loudness of reference level. The negative dBs that you're seeing simply indicate that the amplifier is putting out sound at some level that is below its 0 dB reference level. To avoid launching into an over-mathematical description, I'll just say: It was originally used to measure voltage loss over telephone lines.
![negative decibel scale negative decibel scale](https://www.mindnlife.com/wp-content/uploads/2023/08/HHF-Noise-Level-Chart-01-1024x569.png)
For most amps, 0 dB is calibrated to be close to the loudest signal that the amp can make, so in reality, some amplification is probably going on to bring the line level input signal up to 0 dB.ĭB is a type of unit used to measure the relative strength of two things. I say, "arbitrary reference point", because the actual loudness level at 0 dB depends on many factors and will differ from amp. I'll add to what others have already correctly stated.Ġ dB is an arbitrary reference point, indicating that the amplifier is, in theory, not increasing or decreasing the sound at all.