Dynamic range and amplifier power

Discussion in 'Archived Threads 2001-2004' started by DaleR, Feb 8, 2002.

  1. DaleR

    DaleR Stunt Coordinator

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    i'm unclear on the concepts of dynamic range and an amplifier's ability to reproduce transients. i THINK that dynamic range is a term used to describe the difference between the noise floor of a signal and the loudest signal possible at a given amplifier gain setting. my confusion arises thus: does every increase in amplifier gain result in a foreshortening of an amplifiers ability to reproduce power hungry transients, such as a snare drum "snap"?
     
  2. Jon Hancock

    Jon Hancock Stunt Coordinator

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    Dynamic range, in a basic sense, is nothing more than the difference between the residual output noise of an amplifier, and it's maixmum unclipped output power.

    Gain, technically speaking, doesn't enter into it, except that it determines what signal level you need to drive it to full output.

    For example, many pro amps will require 2V RMS for full rated output power, whereas a lot of "consumer" power amps may only need 1 VRMS, or 1.5 VRMS. The gain is the multiplication of the input voltage- for example, with a voltage gain of 40, 1 VRMS will produce 40VRMS at the output (200W @ 8 ohms).

    A factor often left out of these discussions, and a very relevant one, is the sensitivity of the speaker. Standard home speaers are typically in the range of 83 to 86 dB output for 2.83 VRMS input (1 [email protected] 8 ohms). Some are a little less than that, some quite a bit more (example: Wilson X1 SLAMM is about 93 dB/watt). Why is that important? 3 dB difference in sensitivity is double or half the amplifier power required for the same loudness. 10 dB difference in sensitivity is a factor of 10 to 1! For example, my homemade X1 clones will play louder with a good 50-60 watt amplifier than most home speakers do with 250 watts/channel. But do you need the ability to hit 115 dB peaks? Probably not, in most cases. Remember, even your CD or SACD source material is limited in dynamic range (unfortunately). But it's reasonable to expect that with average SPL's of 90 dB, you'll have peaks to 100 to 105. So, going for a minimum capability of 105 dB seems prudent. If your speaker is honestly rated at 86 dB sensitivity, you'll need about 100 watts per channel for 105 dB peaks.

    Regards,

    Jon
     
  3. Ron Shaw

    Ron Shaw Stunt Coordinator

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    Dynamic range is the ratio of the noise floor of the amp vs. maximum voltage swing at clipping. Clipping is when the amplifier tries to put out a signal that exceeds the voltage output capability (usually close to the power supply voltage rails). The gain of the amplifier section is fixed. It means that for a given voltage level input, it will put out a given (higher) voltage level. Most amplifiers are designed to put out maximum rated power (or really, voltage) with about a 1 to 1.5V input (from the preamp section). The volume control in the preamp section controls the voltage level fed to the amplifier. Now you come to the dynamic range of your source material. Dynamic range is the ratio of the lowest signal level to the highest signal level. The dynamic range of a full symphony orchestra is about 80 db (from 20db to 100db above the threshold of hearing. The lowest level will be affected by the ambient noise level of the auditorium. A symphony orchestra can reach peak levels of around 130db). To accurately reproduce the uncompressed sound of this orchestra, you would need at least an 80db dynamic range. Take an example. If you are using an amplifier rated at 200 watts, an 80 db range is the difference between .000002 watts to 200 watts! (every 10db increase is 10x the power). Needless to say, not many (if any) systems can produce this dynamic range (the low side is likely to be below the noise floor of the electronics). Because of this, most source material has been compressed, to lower the dynamic range. Even heavily compressed material still has an average to peak range of 20 db or so. So, using the same 200 watt amp, your average output cant exceed 2 watts to prevent clipping on the peaks.
     

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