A question about power (sorry) !!

Discussion in 'Archived Threads 2001-2004' started by Dave_Whiting, Sep 10, 2002.

  1. Dave_Whiting

    Dave_Whiting Stunt Coordinator

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    Take for example the Marantz sr4200 which is rated at 70x5. NOw it appears common knowledge that this reciever will not put out anywhere near that power with all channels driven ( lets say 30x5). The question I have is does the power to every channel drop to 30W as soon as you go to 5.1 mode. Or do they do some tricky stuff. The reason I ask is because in a movie you will probably never drive all the speakers at the same volume. I hope this makes sense.
     
  2. Jonathan M

    Jonathan M Second Unit

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    Hi Dave,

    Yes, you are correct. The 30Wx5 or so is all channels driven simultaneously to the point where they begin clipping. In general movies, this is a fairly rare occurence (And even then, 30W is still quite a bit of juice as long as your speakers are reasonably sensitive.)

    As far as I'm concerned, the speakers are the most important bit. If the receiver is setup with speakers set to Small, then very little sub 80Hz bass is going through it's amps, and so the 30W per channel will be enough for most listening levels. It'll only be in loud explosion scenes etc. that the power may get to be a problem, and only if you are listening at high levels.

    If the speakers you are using are reasonably sensitive and they are operated in "Small" mode, then 30W will be more than enough.

    What sort of speakers are you going for - planning on the DIY approach?

    Cheers
    Jonathan
     
  3. Dave_Whiting

    Dave_Whiting Stunt Coordinator

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    I am considering the Wharfedale diamonds 8.1, 8.3 and centre. Also thinking about the Harman Kardon avr 3500 as I can get it at a good price. About 20% of retail through my Dads business.
     
  4. Dave_Whiting

    Dave_Whiting Stunt Coordinator

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    This is confusing. Lets say we are watching a movie pretty loud. Say nothing is coming out of the surround channels and I have the front left and right at approx 40 watts. Now something happens in the movie and all channels are involved. So say are driven at 5x40, so does that mean I wont lose power to the front channels just every speaker will be distorted due to clipping and probably blow up. Hence if in a movie and at any stage all speakers are being driven, wouldn't the max power you want to supply any speaker 30 watts (assuming 30x5 is when clipping sets in).
     
  5. Kevin. W

    Kevin. W Screenwriter

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    Dave,

    I took a look at the website for the speakers. These speakers ar 6ohmn(thought compatable with 8ohm receiver). This will drive the amp of the receiver harder. Wattage wise:

    1watt/1m:86db
    2watt/1m:89db
    4watt/1m:92db
    8watt/1m:95db
    .
    .
    64watt/1m:104db

    From this table to get to reference levels you would have to sit 1m away from your speakers and have your receiver put out 64watts. I would make sure you have a receiver or amp that puts out what it advertises othewise clipping and distortion could become a problem.

    Kevin
     
  6. Jonathan M

    Jonathan M Second Unit

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    Hey Dave,

    While what Kevin has said is true (regarding power requirements) the 30Wx5 or whatever is CONTINUOUS power into all 5 channels simultaneously. Music, or Movie soundtracks are transient in nature, not continuous - especially the loud passages. I would personally be surprised if the sr4200 would not be up to performing the task. Sure, it may be strained (And may even start clipping) at very loud passages, but as long as it's not for long, it will not damage the speakers. Often the capacitance storage in the power supply can help here too. The short time power available will be higher (probably nearer or even exceeding the specced power). Also, most of the power content during loud passages is in the sub 100Hz region (As it needs to be much louder in order for us to hear it) and so if the speakers are set to small the actual power needed from the amp will be reduced quite a bit. Most soundtracks have 99% of content at least 15dB below the peak level, so it's probably not going to be a problem. The best thing is to take the speakers (if possible) to the store, plug them in to the receiver and listen. It would pay to do this in a room of similar size (or larger) than you plan to use them in. If it plays loud enough for you there, then you'll be fine. I suggest running something like LoTR through as a test - very loud soundtrack.

    Hope this helps. I guess the bottom line to remember is that doubling the power only gives 3dB more volume. Unless you really need the reference level sound (it's loud) I wouldn't be concerned.

    Cheers
    Jonathan
     
  7. Dave_Whiting

    Dave_Whiting Stunt Coordinator

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    THis whole refence stuff seems a bit dumb. I mean you have to double your watts to get a 3dB gain (which is only just a notiveable difference in loudness). So it ref is 105 db and you are putting out 102 dB who cares.
     
  8. John Royster

    John Royster Screenwriter

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    one last thing to ponder... at the low sensitivity of those speakers I'd be thinking at least 100W into all channels preferably 200 watts with a seperate amp unless this is a small room.

     
  9. Dave_Whiting

    Dave_Whiting Stunt Coordinator

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    Do you guys reccon the harman kardon avr3500 with 5x45 will be up to the task.
     
  10. Dave_Whiting

    Dave_Whiting Stunt Coordinator

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    Kevin,

    Forgive my lack of knowledge, this could be a stupid question. Those dB calculation before, are they for one speaker??. How does having 5 speakers effect that??.
     
  11. Jonathan M

    Jonathan M Second Unit

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    Hi Dave,
    I'm not trying to answer on Kevin's behalf, but this is how I believe it goes:
    The "reference level" for Dolby Digital is 85dB continuous from EACH speaker, allowing for a peak volume of 105dB from each speaker (20dB louder than the continuous or "average" level). This is supposed to be how movie theatres are configured, although this level is LOUD and most (at least in NZ) will likely be lower than this.
    With 32W of power you will be able to achieve 101dB one metre away from a single speaker. The peaks are what will require the extra wattage (64W for 104dB, 72W for 105dB). Most likely you will not often actually listen at reference level, so it won't matter. Also, even if you were to, it would mean that the amp may start clipping during the peaks. At this level though I would think the speakers would have more of a problem than the amp.
    As for the H/K - it will have more power than the rated 45x5, so I would think it would be enough even to reach the magical "reference" level [​IMG]
    Cheers
    Jonathan
     
  12. Kevin. W

    Kevin. W Screenwriter

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    Jonathan M
    Thanks for answering my question because I always thought Reference meant 105db and peaks above that. That could explain why my ears bleed after a good movie[​IMG]. So as long as Dave sits 1m away from his speakers he should only need about 1to2 watts of power. Keeping the volume at a moderate level should warranty no more that 32w for those intense transients.
    Dave,
    The table is for one speaker. If I remember right for every 1meter your from the speakers(eg 2m) you lose 3db and therfore have to double the wattage to regain that lose.
    Kevin
     
  13. John Royster

    John Royster Screenwriter

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  14. Dave_Whiting

    Dave_Whiting Stunt Coordinator

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    Thanks everyone. I am learning :b . Jonathan I might go into the listening post on the weekend and compare the Marantz sr4200 and the Harman Kardon avr 3500.
     

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