Volume on Amps Dbs decibels)

Discussion in 'AV Receivers & Amplifiers' started by redcat, May 8, 2007.

  1. redcat

    redcat
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    Now this must be a stupid question but i gotta ask, on my Sony AMp when you turn the thing up the number goes down. I think it says dbs or somthing, is that decibles (sp). IF so why does this decrease the the noise increases?

    Also i have some AG Micro Ti speakers (sub on its way ) which are very quiet, the output shows 10 dbs does this seem high or is it becasue the subs missing or because they are new ?!

    cheers!
     
  2. Keiron

    Keiron
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    If I'm not mistaken, volume controls apply attenuation. In other words, when it's on full (all the way round to the right), the attenuation is 0db. The more to the left you turn it, the more attenuation is applied. So think of it as decreasing attenuation, rather than increasing the volume.

    However, the Sony 5200ES I've recently been playing with goes into positive dbs, which I don't understand at all :confused: In which case, everything I've just written could be garbage!
     
  3. redcat

    redcat
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    hmmm, ok thanks!
     
  4. KenG

    KenG
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    Zero DB is the reference point, which is normally too loud for most home environments. Go below this and the numbers are negative, above and they are positive. Typically you will see levels in the -20DB to -30DB levels for normal listening which means the amp is at that level below the reference point. For most amps the reference level is somewhere around 50% to 70% of the volume control.

    Ken
     
  5. AVdavid

    AVdavid
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    I thought the volume control increased the signal from the preamp rather than attenuate the level from the power amp I may be wrong though

    Dave
     
  6. Bogi

    Bogi
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    The 0db reference point was originally implemented for calibration purposes in home surround receivers/processors. So when calibrating your system for Reference levels (the intended level by the director and sound engineer in studios) you set the volume to 0db at which point your SPL meter (Sound Pressure Level meter) should show 75db on each chanel for Pink Noise calibration tones. You should be able to calibrate the different chanels individually with the master volume set at 0db (reference point). When all chanels show 75db on your SPL meter you're set.

    However, for practical listening in an home environment, it's unlikely you'll use Reference levels for actual listening, as this is too loud for most people. As Ken pointed out most people are in the -20 to -30 db area, occasionally going up higher, maybe -14 or similar.

    This 0db reference point calibration feature is mandatory for all THX certified processors, and are included in quite a few non-certified equipmenet as well (THX licensing is quite expensive).

    Some receivers/processors have the ability to switch between two display modes, so you can choose to use either the 0db display or a more traditional +xx db scale.

    Cheers
    :)
     
  7. Badvok

    Badvok
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    Wow, I'm even more confused now. My CA Azur 540R normally works between -45db and -60db with -45db being very loud in my room.
     
  8. sidxms

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    How high does it go on the other side?

    For example my sony 1200es goes upto +23dbs so for me the avg volume is 20-30db as mentioned.

    sid
     
  9. Badvok

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    To be honest I've never turned it fully to either end. I'll check tonight when I get home.
     
  10. Badvok

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    Finally got around to investigating further and the 540R volume range displays as
    -70db to -2db.
    It doesn't go to zero - weird eh?

    With my speaker setup -20db is about equivalent to a reading of 75db on a Radioshack SPL placed at the prime listening position using the 540Rs pink noise generator for each individual speaker. NOTE: This is far too loud for comfortable listening in my room, I couldn't measure the actual sound level with sound coming from all speakers at that amp setting unless I used ear defenders.

    I think that means the actual displayed value on the amp is pretty meaningless!
     
  11. mikel543

    mikel543
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    The amlifier in the AV receiver will have 2 stages a pre-amp stage and a power amp stage.

    The output of the power amp stage is preset at a fixed level so that when an input signal of a specific reference frequency and specific voltage level is applied the output meets the required reference output power level in W, without exceeding signal distortion limits.

    Volume control is achieved by adjusting the level of the output from the pre-amp stage. Basically Less signal in = Less power out. The pre-amp stage consists of a small amplifier, the gain control of this amplifier is connected to the volume control.

    Gain is defined as the ratio of output voltage to input voltage. The gain can also be expressed in decibles by dividing the ouput voltage by the input voltage, taking the log of the result and then multiplying this by 10.

    ie 10 log (Vout / Vin)

    Now if Vout = Vin the gain will be 0dB
    If Vout > Vin the gain will be positive + x dB
    If Vout < Vin the gain will be negative - x dB

    If the signal is fully attenuated by the input stage then the gain will be - infinity dB.

    It should be noted that the dB level on the volume control is purely the gain setting on the pre-amp and not the sound level out of the speakers.

    The volume control on some audio equipment is calibrated to the gain of the pre-amp stage, therfore they start at - infinity dB go up through 0 to perhaps say +8dB (depending on the max gain of the pre amp). You'll find this on a lot of professional PA equipment, e.g. the sliders, Sensitivity and EQ controls, on a mixing console will be labelled in that way.

    Hope this helps to explain why your volume control starts at minus infinity and goes from large -numbers towards zero.
     
  12. mikel543

    mikel543
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    In correction to my previous post, Vout and Vin should be POut and PIn as we're talking about Power here not Voltage. Thats what you get for trying to post in a hurry.
     
  13. sdb123

    sdb123
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    Definitely attenuates the signal....don't ever plug a CD Player directly into a power amp (without volume control)! :eek:
     
  14. mikel543

    mikel543
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    Your right about not plugging a CD player into a power amp, unless you want to be deafened.

    However depending on how the circuitry in the pre-amplifer stage is setup the signal can be attenuated or boosted. In most cases the signal is attenuated as we don't want to overdrive the output stage of the power amp, clip the waveform and blast the listeners out with loud distorted music, however some Amps allow the pre-amp stage to boost the signal to the power amp for extra volume (don't really know why you would want it though)

    My Denon AV receiver can be cranked up into the +db range however I have never had it up that far as I don't have any faith in 1970s construction techniques and fear my house will come crashing down around me. <LOL>
     

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