What is reference level REALLY mean?

Discussion in 'Archived Threads 2001-2004' started by Vaughan, Nov 29, 2002.

  1. Vaughan

    Vaughan Agent

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    I have been reading various threads, and have read people talking about reference level and spl's that their systems can achieve and need to know is reference level 105 db peaks and subwoofer 115db or it 105db peaks for each channel. I have good knowledge of subwoofers in general but as of recently am finding it hard to believe what one person says, as people often contradict themselves with different answers which complicates things. Can somebody please help me on this, and is THX reference level the same as dolby reference level?
     
  2. Edward J M

    Edward J M Cinematographer

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    Acording to Dolby Labs:

    105 dB peaks from any surround channel and 115 dB peaks from the LFE channel.

    If the speaks are set to small, this becomes 121 dB peaks from the LFE channel.

    All measured at the listening position in your room.

    If I'm wrong, I'm sure other posters will correct me.

    Based on your other post, you've hit real reference levels on AOTC with your SVS Ultra subs.

    Most enthusiasts listen at 10-15 dB under reference. Bass peaks of 110-113 dB are common at these "saner" listening levels.

    Hope this helps..............please solicit other opinions to confirm.

    Ed
     
  3. Dustin B

    Dustin B Producer

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    Edward nailed it.

    THX is a standard, that's it. Not a sound format. The reference level we speak of is defined for Dolby Digital. Then we just trust that DTS will be close to it (I keep seeing that DTS is recorded 4dB louder than DD most of the time, take that for what it's worth).
     
  4. LanceJ

    LanceJ Producer

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    Sooooo.......what exactly is "reference level" good for?
    LJ
     
  5. Dustin B

    Dustin B Producer

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    Exactly what it's name says. A defined level everyone can refer to.

    The two main uses I can think of are:

    1) Use it to get a very good idea of what levels someone is experiencing when listening to their system without being there.

    2) Use it to make sure you are hearing exactly what the sound engineers wanted you to. Personally I think reference level is too loud. Mind you I've never heard it on a system that can do reference level cleanly. Might change my mind when I have a system that can do it cleanly, but I doubt it. Don't think I'll ever go past 5dB under reference except for an occational demo session.
     
  6. Bill Kane

    Bill Kane Screenwriter

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    In the world of Dolby Digital encoding, the sound engineers devised the 105dB level of main speakers and 115dB for the sub as the optimum level for movie theaters. This has been adapted to HT environments.
    In this instance, reference level is an actual standard. The point often made is that after calibrating to reference level, most people actually LISTEN at a lower volume which is much more comfortable in smaller rooms.
    Here's another thread: Look for the post(s) by audio writer John Kotches
    I agree HTF ought to cover this subject in Beginners Questions & FAQs tutorials.
     
  7. Vaughan

    Vaughan Agent

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    Sorry if some read my other post regarding the Servo 15(I had a servo 15 for three years now prior to getting the svs ultra package).I was convinced to buy a duel package for even more power.I am considering using the servo for ultimate low frequencies.Just think, I will have one servo 15 and duel svs ultra subwoofers and I will definitely give a full review of my system with all three subwoofers very soon.Now the servo15 has been considered one if not the best subwoofer in terms of output in the subsonic range.Now i know that some will disagree because it is servo controlled meaning restricted output to 10THD.Maximum output at 10THD was 111 at 20herz which is quite amazing(keep in mind that my room is 6m by 6m and the sub is corner loaded)This is not maximum output as I can bypass the limiter and crank almost 5 db without distortion.This subwoofer can reach a nominal 14 herz and I measured 10herz(although very little).In fact I highly doubt a single svs if any that can match the servo 15 in max output at very low frequencies.However my duel svs ultra subwoofers can destroy a single servo 15 if my benchmarks are any indication, which I am extremely happy with.Thanks for all the feedback, and a special thanks to Ron , these subwoofers are probably the most cost effective way to achieving cinema bass.I must just say that I live in South Africa and found it hard to get these svs subs shipped(I had to choose Israel as the country closeset, which in no doubt added greatly to my cost), but the sheer performance was good enough for me to forget.
     
  8. Dustin B

    Dustin B Producer

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    Also remember the Servo15 is an acoustic suspension (sealed) design and the SVS is a bass reflex (ported). Sealed subs will start to drop in output sooner (usually up around 40-50hz), but will fall off at 12dB/octave. Ported subs, because of what the port does won't start to drop off as soon. When they will start depends on the tuning point and a few other things. When they do start to drop off though it's at 24dB/octave.

    So below tuning there will be a point at which a sealed sub will be louder than the ported one. However the level will be very reduced compared to the input signal and there is very very little source material out there with significant content under 16hz. Besides all you could do is feel it and I don't think a Servo15 can play it loud enough that you will really feel it.
     
  9. Michael R Price

    Michael R Price Screenwriter

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    While I've never listened to a movie at reference level, I believe that levels up to around 110db are reasonably comfortable to our ears, if your system is not distorting at all and your room is not causing any adverse effect on the sound. That's a big if though... there's a difference between playing to reference level without clipping/bottoming, and playing to reference level without significant distortion. Even in a small room, I think only a few of the larger speakers/subwoofers would be capable of this. I think reference level is not a realistic goal for most reasonably priced home theater systems.
     
  10. Bill Kane

    Bill Kane Screenwriter

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    I think reference level is not a realistic goal for most reasonably priced home theater systems.

    Are you suggesting that the common 100wpc AVRs people are using, coupled with speakers rated, say, 40-150watts, are susceptible to distortion when calibrated and played to Reference Level? This is my opinion, and I accept your "big IFs," but I wouldn't think so. The mainstream AVR amplifier makers publish their THD numbers and realize full well what sound-engineered media the units are being asked to reproduce.

    Here's another point about Reference Level -- the 105dB for main channels and the 115dB for LFE/Bass -- are PEAKS, or transient loudness (as Edward noted). Not 105/115dB all the time.

    For example, soundtrack dialog, which is 90 percent of DVDs,
    plays back in the low 70dB range when the AVR volume control is set to the value that has been calibrated at 85dB on Avia/S&V or 75dB with VideoEssentials.
     
  11. Dustin B

    Dustin B Producer

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    Dialog will more than likely still be clean on most systems. What Michael is talking about is the action/special effects sequences that contain the peaks that will push you system up to the 105 and 115dB levels.
    Power handling isn't the issue with receivers. Speaker sensitivity is. Take a look at this page:
    http://www.myhometheater.homestead.c...alculator.html
    Plug in your speakers sensitivity rating, enter your receivers per channel power rating (to be realistic you should probably knock 10% or more off this rating; a few are actually accurate though), your listening distance, one speaker and select the second radio button. Press calculate and that is a very good guess at how loud your speaker can play with the available power.
    This doesn't take into account whether it can do this level with low distortion (most won't) though.
    To do reference level cleanily there are two ways to approach it (with some that will be in the middle). Very capable speakers in the 90dB/W/m range that can take a lot of power and amps that can dish out that much clean power (I'm talking 300-400W). Or higher sensitivity speakers (96dB/W/m or higher). The higher sensitivity speakers won't need a lot of power to reach the highest peaks asked by DD.
     
  12. Dan Hine

    Dan Hine Screenwriter

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  13. Michael R Price

    Michael R Price Screenwriter

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    I don't mean 110db constant volume, but rather peaks. I am fine with continuous levels in the 100db range when I sit closer to my speakers [to reduce any distortion]. I am currently underpowering my system though and hope to soon learn more about what a distorting or compressing speaker sounds like. I have a hunch that most speakers still sound reasonably clear when driven hard but some sort of distortion causes us to think it's "too loud" for our ears when it's really not. The variety of sound levels we experience in nature, as well as live music, leads me to believe this.
     
  14. Seth_L

    Seth_L Screenwriter

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    I play movies at reference volume all the time. I have a 110WPC Sony DA5ES and "average" sensativity Infinity Interlude speakers. I have no problem hitting reference cleanly in my room.

    Seth
     
  15. Vince Maskeeper

    Vince Maskeeper Producer

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    Much of what was said here has been part of the document for 6 months.
    -V
     
  16. Bill Kane

    Bill Kane Screenwriter

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    Vince, I'm terribly embarrassed; but I did look first...doh!

    bill
     
  17. Vaughan

    Vaughan Agent

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    Vince, can a reasonably cheap speaker system be capable of reference level? Do not count distorion in as there will NO DOUBT be a heck of distorion, I belief.But can a cheap system at least attain reference level, for better or worse.Doesn't amplifier power come into play here, and speaker sensitivity or can anyone achieve this level(remember, just the volume, as reaching this volume cleanly is a whole new discussion, one that I would love to start).
     
  18. John Kotches

    John Kotches Cinematographer

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    Vaughan,

    There is no definitive answer to your latest question.

    The ability for a speaker/receiver (or amp) combination to hit reference level is a function of:

    Speaker Sensitivity
    Speaker Impedance
    Available Amplifier power
    Distance from the speakers

    Without all of this info, one cannot give a solid answer to the question posed.

    If a speaker (or any other component) is massively distorting, you won't want to listen to it for long.

    Regards,
     
  19. Seth_L

    Seth_L Screenwriter

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    Vaughan,

    Sure if you're speakers have a sensativity of at least 86dB and you sit no more than 2m away from any of them and you have at least 100WPC you can do it. You may be able to pull it off with slightly less power or slightly less efficient speakers due to room interactions.

    Seth
     
  20. Michael R Price

    Michael R Price Screenwriter

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    Oops, nevermind. I didn't read Vaughan's question. Seth and John are right, but I do have doubts about taking *x* sensitivity and *y* power and then saying a system can do reference level.
     

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