Amp power for beginner

Discussion in 'Archived Threads 2001-2004' started by Greg Br, Apr 4, 2002.

  1. Greg Br

    Greg Br Second Unit

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    ok not quite a beginner but as someone who is unfamilar with amps I have a question. I was reading The Absolute Sound and they had a few amp reviews of some moderately priced amps but I noticed that most were 50 watts power. That sure does not sound like much but in the review it raved about the sound quality. I guess I am confused how such little power could be used for say tower speakers.
     
  2. Aslam Imran

    Aslam Imran Second Unit

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    It doesnt matter if they are tower or book shelf speakers. If their sensitivity spec says that they can achieve an SPL of 90 db/watt/meter then they can achieve an SPL of 90 db for a watt of input (from the amp), at a distance of one meter from the speaker. It also means that they can achieve 93 db at 2 W input and every doubling of power there after will get the SPL up by 3db. So you can see you could drive these speakers to about 107 db at 50 W from this amp. And 107 db is pretty darn loud.
     
  3. Greg Br

    Greg Br Second Unit

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    Thank you very much, I think I need Amps for dummies. No wonder why I have been reading many articles that give you that particular spec of db/watt/meter. I guess my question would be why would anyone need 200 watts per channel if a high end 50 watt channel would give you extreme loudness already?
     
  4. Saurav

    Saurav Cinematographer

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  5. Greg Br

    Greg Br Second Unit

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    So is the db/watt/meter the best spec to look for regarding speaker efficiency?

    I was reading an article in the Absolute Sound that gave their opinions on three amps that all were rated at 50 watts of power. These were all budget amp that whent for about $1000. I had been thinking I would need these massive power amps for my speakers but I guess I have not been looking at all the right data.

    The real question is a $1000 audiophile type 2 channel amp at 50 watts going to outperform a $1000 Adcom amp that produces 250 watts per channel.
     
  6. Saurav

    Saurav Cinematographer

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  7. Greg Br

    Greg Br Second Unit

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    Great post,

    what is the general opinion on the question of amp power, is higher end low power better than good high power output?
     
  8. Aslam Imran

    Aslam Imran Second Unit

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  9. Joe Casey

    Joe Casey Stunt Coordinator

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  10. Saurav

    Saurav Cinematographer

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    Aslam, that's a very good way to put it.

    Joe, you have a point, if you want planars, flea-powered amps aren't going to cut it. Which takes you back to an even more fundamental question - what do you want from your system? If I were to generalize a little, people who prefer planars place more importance to the reproduction of a smooth and liquid midrange, than accurate rendition of explosive transients. Usually, their tastes in music tie into this too.

    So, basically, you need to start from "what do I want my system to do".
     
  11. Andrew Pratt

    Andrew Pratt Producer

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    I would have to agree that speaker senstivity and amp choice go hand in hand but lets not confuse speaker senstivity with good sounding speakers...I've heard some horrible speaker that were very efficient and some that weren't so effiecent...choose speakers based on how they sound with the amp you intend to drive them with not soley on their sensitivity. For example lets assume that you have a Denon 3300 receiver as your amp and it can put out an honest 80 watts per channel. Now when you start auditioning speakers you might want to start by looking at those that are a little on the more effiecent side (87 db/w/m or higher) but if you plan on using a more powerful receiver or seperate amp you can start looking at more inefficient speakers. Now obviously this is a very broad generalization and a dB here or there isn't going to make or break anything but it is something to keep in mind. After all a speaker that's 3 dB more efficient is the same thing as adding a dedicated amp thats twice as powerful.
     
  12. Greg Br

    Greg Br Second Unit

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    Andrew,

    Good stuff, I have noticed when looking at Speaker sensitivity that all the mid-high end speakers, Klispch, B&W, Paradigm are all in the 90's when you compare sensitivity. I had to go down to bookshelf speakers to get below 90 db/w/m. It just does not seem that with quality speakers that 150 watts is really needed, are am I out in left field on this one.
     
  13. Saurav

    Saurav Cinematographer

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    Depends on how loud you're playing. Didn't somebody mention 20dB peaks over dialog level? So let's see, say you're watching a movie at a fairly loud volume of around 90dB at your listening position, which is 10' (3 meters) from the speakers. Your speakers are 90dB efficient. Does SPL fall 3dB per meter, or 9dB per meter? Let's assume it's the first, to get a best case scenario.

    So... 90dB at listening position = 99dB at the speakers. So, your speakers are drawing 8W from your amps (every 3dB means double the power). Now, along comes this transient that's 20dB louder. How much is 20dB in terms of power? Every 3dB is double, and 20dB has about 6 3dB "steps", so that means double 6 times, or, 64 times. To accurately reproduce this transient, you need 8 * 64, which is 512W.

    How many 150W amps can do a 500W transient?

    I think this is unrealistic, because no one listens at volume levels where dialog is playing at 90dB. Or do they? Someone better acquainted with HT can probably help us out here. Also, if your room is bigger, the difference in volume from the speaker to the listening position will be greater.
     
  14. Greg Br

    Greg Br Second Unit

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    Dialog would be around 85db in normal reference level movie listening with a peak here or there, but the peak that would jump up 20db would be low end bass, not sure how many typical peaks go to 20db. If amp specs are continuous power rated but amps can handle a spike in wattage needed, then do they spec that out when looking for a amp?
     
  15. Saurav

    Saurav Cinematographer

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    I don't know, IMO not usually. Look for ratings like Dynamic Headroom, or Dynamic Power. My NAD integrated amp had something called "IHF Dynamic Power" - no idea what IHF stands for, but it sounds like something official [​IMG]
    Of course, IMO no amp has 20dB dynamic headroom. 3dB is considered very good, unless I'm completely mistaken.
     
  16. Andrew Pratt

    Andrew Pratt Producer

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    One of the reasons lager more expensive speakers might have a higher sensetivity is that they often have more drivers then a smaller bookshelf speaker....the more drivers the more efficient it could be. Still I'm a maggie fan so I live with speakers that are only 84db/1watt ....but the nice thing about maggies is that since the panels are so large they don't drop off as fast as cone based speakers...by that I mean if you provide 1 watt into a say a paradigm studio 40 you'll get something like 90 db SPL at 1 meter and 84 dB at 2 meters etc (give or take a bit)...the maggies on the other hand will be 84 dB at 1 meter and 81 dB at 2 meters (or something similar I think)
     
  17. Saurav

    Saurav Cinematographer

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    That's true, planars drop off at a different rate than cone speakers. Which means my assumed 3dB/m for cone speakers is probably incorrect, it's probably higher than that.
     
  18. Lee-c

    Lee-c Second Unit

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    IIRC, the standard formula for volume is that you lose 6db for every doubling of the distance

    from the speakers past 1 yard.

    May be a little different for planar speakers, but those are much less common.

    Reaching reference volume and being able to handle the occasional huge spike in sound

    takes either lots of power or a very sensitive speaker or some combination in the middle (a pretty

    sensitive speaker with a good deal of power will also do the trick). The only problem with

    some of the horn speakers (very efficient) seems to be that many have reported the sound

    they produce at high volumes to be bright, etched and fatiguing to listen to for long periods

    of time. But I've never had the chance to listen to one.

    Can any of you folks that own sets of good horn speakers comment on that? How do horn

    speakers sound when trying to play a movie at reference levels and there is a sudden

    explosion or other loud event in a movie? Do they handle it cleanly without getting harsh sounding?
     
  19. Saurav

    Saurav Cinematographer

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    I'm sure horns (or any extremely high sensitivity speaker) would reveal flaws of upstream components more. I've only heard that one system that's horn based, and that was pretty unique - a $20K system that's completely DIY. I have no idea how much it would cost in retail dollars to set up something like that.... for instance, he built his speakers for about $4K, I've seen pre-built versions online for $12K. So, using that as a rough yardstick, I listened to a $50K - $60K system. And that wasn't bright or harsh in the least. The sheer power of the music literally took my breath away.
     
  20. Lee-c

    Lee-c Second Unit

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    Saurav: Thanks for the info. [​IMG] The only problem with your example is that you were listening
    to a super high quality set of speakers. Which, unless one has some very good wood-working skills and
    shop space to work in, few will ever own. So that can hardly be considered representative of what
    your typical set of well-made horn speakers sound like. But I sure would love to hear that system
    you had the chance to listen to. [​IMG]
    I'm wondering how a more reasonable set of well-made horn speakers might sound. Say, something
    like Klipsch RF-7's? Anyone who has any experience with something like that, feel free to
    jump in. [​IMG]
     

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