Equivilant Db Levels on Integrated Amps

Discussion in 'Hi-Fi Stereo Systems & Separates' started by scorpion88, Jul 29, 2012.

  1. scorpion88

    scorpion88
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    Possibly an obvious question which I have but forgive me nonetheless.

    I have 2 amps: 1. CA 640v2 2. HK980

    The CA sounds pretty loud i.e. wall shaking at about 11.00.

    The HK sounds the same at about -Db 20.

    I have researched this but can find no definitive correlation between the 2 different measures of volume.

    Any 'Boffin' out there who can answer this.

    Cheers

    Steve
     
  2. Badger0-0

    Badger0-0
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    It's down to output levels from the source and how the amp handles the same.

    Some amps just require more input to output the same volume.

    Something that if it was standardised, would much better show similarities/differences in equipment, imo.
     
  3. scorpion88

    scorpion88
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    Thanks Badger, long time no hear:) I think I understand you but still a bit of a conundrum: i.e. I have an ancient Battleship Akai amp that punches out a 'mere' 50w but sounds much louder than both the CA and HK at similar levels on dial.

    BTW look forward to the London Claret and Blues hammering you in the first game next season with our world cup winning pedigree.:D:D
     
  4. Badger0-0

    Badger0-0
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    Oh, so you're talking about the same source?

    I read things wrong, in that case :suicide:
    Either way, the answer's easy.

    Some companies tell taller stories than others, simple as.

    Specs and real world are two totally different things as you've seen.


    As for West Ham, good luck on that one mate :D

    And good luck with James Collins returning too ;)
     
  5. scorpion88

    scorpion88
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    Thanks mate, that confirms my suspicions.

    Good luck also to the Villa not sure about JC though. Not excactly Bobby Moore.:)

    Cheers:D
     
  6. BlueWizard

    BlueWizard
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    Here is something I posted previously, this was just an FYI post, and serves no real purpose beyond random discussion -

    http://www.avforums.com/forums/hi-fi-systems-separates/1561542-what-its-worth-lp-vs-cd-spl.html

    But is does illustrate rough volume levels for various Volume Control settings on a stereo.

    Several things can effect how loud an amp is, the level of the source. In the case above, excess level from my source was the problem I was trying to solve. By inserting some 12DB attenuators in the line, I brought the level down to a level equivalent to my Turntable.

    Next to source level, is the Gain of the Amp. A high gain amp, requires less of a turn of the volume control, but is likely to go into clipping much sooner.

    On a lower powered amp, clipping itself can help create the illusion of loudness by acting as audio compression. The clipping limits the peak levels, but still allows the average levels to be raised higher and higher.

    Also, to a lesser degree, speakers can have a degree of audio compression. When a speaker reaches the limits of its excursion ability, that is the limits of how far it is mechanically able to move, you get this sense of compression as you go above that. The peaks are limited by the mechanical limits of the speaker, yet you keep pushing the average level higher and higher.

    This compression effect is also why commercials on TV seem exceptionally loud. They are restricted as to how loud the peak levels can be. So they limit the peaks, but push up the average level, making the commercials annoyingly loud.

    Next the speakers, high efficiency speaker, that is speaker with a high Sensitivity specification, put out more sound for a given amount of input. In the link above that I posted, those measured level are only relevant to my specific speakers. Different speakers equal different perceived or measure sound levels.

    Next the room, put giant speakers in a small room and it gets loud pretty fast, but put small speakers in a large room, and they get weak pretty fast.

    Then there is always a degree of Psycho-Acoustics. Not necessarily loudness but the perception of loudness.

    The only way to really know is to use an SPL (Sound Pressure Level) or Loudness Meter to get a true sense of how loud any given system is under any given circumstance.

    Steve/bluewizard
     
  7. scorpion88

    scorpion88
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    Thanks Steve but my main question what is the difference between my CA 640v2 and HK 980 at say -20 Db. They sound virtually the same but - 20 Db equals what in ACTUAL DB levels.

    Please forgive me if I am being 'thick'

    Cheers

    Steve
     
  8. Mark.Yudkin

    Mark.Yudkin
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    Neither of the amplifiers in the OP's question have calibrated volume controls.

    A THX certified controller, for example, mandatorily has such as volume control. So once the levels have been correctly calibrated using the internal test tones, a THX certified controller's volume control will accurately represent the real SPL measured for a digital source or a calibrated analogue source - one whose voltage level has also been calibrated.

    The volume control on the HK is logarithmic and measured in dB, but the 0 point is purely arbitrary in terms of real SPL, since the HK offers no means of calibration. In the case of a normal analogue amplifier it frequently represents the point where the HK's preamplifier is operating "flat", neither attenuating (that's what 0dB means), nor amplifying.

    Calibration is important since the sensitivity (and impedance) of the speakers affects the SPL of the "0dB" voltage level (calculators here and here), as does the listening distance (and room reflections). -20dB on the HK means that the volume at that point is 20dB lower than when the volume control is at 0dB - but says nothing about what that means in terms of what an SPL meter will read when you measure it. However, if you measure the actual 0dB SPL at your listening position, you could apply simple arithmetic to determine what the 0dB value means.

    The CA has makes no such pretences. The position of the volume control is purely arbitrary, and the volume control is not necessarily even logarithmic. The only thing the position of the volume control indicator says is that the volume is louder for a point further clockwise, prior to clipping.

    Steve's CD vs LP reference also addresses the problem that even if the amps volume control is an accurate reflection of reality, the sources also have to play ball, but analogue sources usually don't. Questions such as the excessive volume of commercials are different - this is a deliberate attention-grabbing ploy where the volume is supposed to be louder.
     
    Last edited: Jul 30, 2012
  9. scorpion88

    scorpion88
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    So therefore I need to buy an SPL meter to reach a definitive answer to my original question?
     
  10. BlueWizard

    BlueWizard
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    WHAT MARK SAID!

    There are standard Reference Levels tied to an AV Surround amp. Once the amp is calibrated, unless I am mistaken, 0 db is about 105db absolute. That is, at 0db, you should measure an average of about 105db with a well calibrated AV system. Because it actually measures the sound level using a microphone, it takes into account variations in speakers. But since it produces its own test tones, it can't actually allow for variation in sources. Your CD Player might be louder than say your BluRay Player. But, it likely comes pretty close.

    As Mark points out, there is no calibration process for a stereo amp. In some stereo amps, 0 db might simply be the point where Clipping starts to occur assuming a standard level input signal. Everything in the MINUS DB range under-drives the amp, meaning the amp is in its standard working range. Anything in the PLUS DB range is over-driving the amp, though again, that depends on input signal.

    Keep in mind, in this sense, DB is not a fixed thing, there are about a half dozen variations of DB rating. In some senses, dB is a power ratio. There is dBm, dBu, dBa, and I think dBf. It all depends on the application and what is being compared to what.

    When we are talking about volume or loudness, I typically refer to this as dB absolute. That is, this is the real sound level as measured in a room. In most other cases it is a ratio, the relative difference between something and something else. In some cases the reference something is a fixed and known measurement or level.

    So, I suspect the dB reading on the amp's volume control, is output relative to a fixed standard level input.

    Again, the only way to know the real volume or loudness in a given room with a given set of equipment is to use the same source content, and measure the true SPL level in the room.

    Part of the problem is, we don't know how they calibrated the Volume Control Read Out. Without knowing what is being compared to what, the numbers are all relative.

    Steve/bluewizard
     
    Last edited: Jul 30, 2012
  11. Mark.Yudkin

    Mark.Yudkin
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    When you calibrate a THX amp, you calibrate 0 on the volume control to THX reference level, which is -20 dBFS. Since the full peak swing on a DVD / BD is 105dB, this works out to 85 dB SPL (with a 20 dB headroom).

    For the LFE channel, the full peak swing is 115 dB - there's a +10 dB adjustment in the controller. Also, since 85 dB is quite loud and would induce deafness in professional calibrators, the test tones are actually -30 dbFS (75dB).
     
  12. daytona600

    daytona600
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    buy a cheap SPL meter or apps to measure sound pressure
    power output of the amp does not matter speaker effciency is the key
    a pair of efficient Horn speakers with a flea-watt valve amp
    will sound louded than a in-efficient spekers with a 1000watt amp
    i use 102db effciency full range horns and 2watts is enough for my neighbours to call the police
     
  13. Alan Mac

    Alan Mac
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    When the calibrated system is set to read 0 dB, the PEAK sound pressure level at the listening position should be 105 dB SPL

    (that is 105 dB relative to an rms sound pressure of 20 μPa)


    The average sound pressure at the listening position will depend on the recording but could reasonably be expected to be be somewhere in the region of 85 dB SPL ie. 20 dB below the peak level.


    Alan
     
  14. Andy8421

    Andy8421
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    What seems to have been lost in some of the comments above is that the measure 'dB' on its own is meaningless, it is simply a logarithmic ratio.

    It is not like a volts or amps, it needs to be a ratio relative to something to make sense.

    In the case of sound level, it is usually relative to a pressure of 20 micro Pascals, (the generally accepted limit of human hearing).

    In the case of audio signal levels, it could be relative to 1 milliwatt (dBm), or relative to 0.775 volts RMS (dBu). To make matters more complicated, it may not be linear across frequency range, but could have a frequency weighting (dBa).

    Quoting dB without the appropriate basis (unless it is very clear from the context) is a pointless exercise.

    dB on an attenuator, dBu as an audio level and an SPL of 95dB relative to 20 micro pascals in isolation have no relation to each other.
     
  15. larkone

    larkone
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    ...and there was me thinking the loudest you could turn an amp up to was 11 :cool:
     
  16. daytona600

    daytona600
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    Mine goes to 12
     
  17. BlueWizard

    BlueWizard
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    Thanks to Mark and Alan for the clarification on the THX 0dB Reference levels.

    The central point being, that on a calibrated AV/Surround amp 0dB has real meaning in the acoustical world. Not so with Stereo amp, where the dB references are relative.

    Steve/bluewizard
     
  18. BlueWizard

    BlueWizard
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    Off on a tangent, this comes from Marshall Brand guitar amps which really do go up to 11. But there is a catch. Most guitar amps go from ZERO to 10. Marshall amps go from ONE to eleven.

    If you get a chance to look at a Marshall amp, see if I'm right.

    Just FYI.

    Steve/bluewizard
     
  19. larkone

    larkone
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    Though originally from Spinal Tap:

    Nigel Tufnel: The numbers all go to eleven. Look, right across the board, eleven, eleven, eleven and...
    Marty DiBergi: Oh, I see. And most amps go up to ten?
    Nigel Tufnel: Exactly.
    Marty DiBergi: Does that mean it's louder? Is it any louder?
    Nigel Tufnel: Well, it's one louder, isn't it? It's not ten. You see, most blokes, you know, will be playing at ten. You're on ten here, all the way up, all the way up, all the way up, you're on ten on your guitar. Where can you go from there? Where?
    Marty DiBergi: I don't know.
    Nigel Tufnel: Nowhere. Exactly. What we do is, if we need that extra push over the cliff, you know what we do?
    Marty DiBergi: Put it up to eleven.
    Nigel Tufnel: Eleven. Exactly. One louder.
    Marty DiBergi: Why don't you just make ten louder and make ten be the top number and make that a little louder?
    Nigel Tufnel: [pause] These go to eleven.

    Marshall introduced these as a result of this.
     
    Last edited: Aug 1, 2012
  20. Mark.Yudkin

    Mark.Yudkin
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    That too is being rather optimistic. It has a real meaning for THX-certified A/V controllers (when used in conjunction with THX power amplification, of course). The volume indication may have a "real meaning" for non-THX controllers, but typically does not.
     
  21. BlueWizard

    BlueWizard
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    Mark, I was under the impression that all AV Receivers at least try to calibrate themselves to Reference Levels. Which means the Volume Control should be reasonably calibrated to actual sound levels in the room.

    I'm not sure if you object to what I said in general, or if you simply object to the certainty I implied. Perhaps I should have said a calibrated AV amp's volume reading has more meaning in the acoustical world than the read out on a non-calibrated stereo amp?

    Still, thanks for the input.

    Steve/bluewizard
     
  22. Mark.Yudkin

    Mark.Yudkin
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    Most A/V controllers implement some form of reference level calibration, but whilst THX controllers must have "Gain Tracking of the Master Gain Control" (see previous link), non-THX products typically don't both with this reqirement and hence my remark that the volume indication may have a "real meaning" for non-THX controllers, but typically does not.
     
  23. robertseymour

    robertseymour
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    Simple answer is that there is no correlation. The volume could go from 0 to 100, 0 to 10, -50dB to 0, -80dB to 0 or -156 to 0 It really does not matter, its just numbers on a scale between no output and maximum output. That however may mean something different in THX certified HT Amps, I have no idea really on that front.
     
  24. BlueWizard

    BlueWizard
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    Actually, there are few SPL meters that can come close to the Radio Shack Meters for the money.

    The Radio Shack come in two versions -

    1.) Has a meter/dial read out, priced at a modest £30

    2.) Has an LCD Digital Read-Out, this is the type I have. Priced at £40.

    Radioshack : Sound Level Meters : Catalog

    Wide frequency response, and it is possible to get Calibration Charts for them so you can adjust the reading to flat outside the normal working range.

    Very handy, among other things, you can play a series of test tone and map the frequency response of your speaker in your room and see if there are any aberrations that need correcting. There are many things you can see on a graph, that you simply can not hear with your ears.

    For those far more serious about room and speaker measurements, a company called Dayton Audio makes a complete computerize speaker/acoustic measurement system. And considering what you get, pretty reasonably priced -

    Dayton Audio OmniMic V2 Precision Audio Measurement System 390-792

    Dayton Audio Dayton Audio OmniMic V2

    NOTE: Parts Express is a USA company.

    Dayton Audio Speakers are available in the EU/UK so I would suspect someone somewhere has the OmniMic V2 Precision Measurement System available. (US$300, currency conversion=£193)

    Also, since it is PC based Software and a USB microphone, it should work anywhere in the world.

    Just a few thoughts.

    Steve/bluewizard
     
    Last edited: Aug 4, 2012

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