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What Does Watts Per Channel Actual Mean?

Discussion in 'Audio Hardware' started by AcidPunk15, Aug 7, 2017.

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  1. AcidPunk15

    AcidPunk15 Forum Resident Thread Starter

    New Brunswick, NJ
    On the manual for my Denon DRA- 425 Says it supplies 50 watts per channel. Does this mean that mean each tweeter/woofer/Mid gets 50 watts or the entire speakers get 50 Watts of Power? I am confused. Also sorry if this is such a noobish question.

    If anyone else can explain impedance, Crossover frequency, nominal impedance, and sensitivity this would be greatly appreciated.

    All comments are welcomed!!!
    Myke likes this.
  2. Morbius

    Morbius Forum Resident

    Brookline, MA
    50 watts is the maximum power the amplifier is capable of producing, for instance the loudest sound on a recording. Impedance is the same as resistance also ohms i.e. an 8 ohm speaker. Nominal impedance is the lowest resistance for a given frequency ( anywhere between 20hz and say 250hz) a speaker presents to an amplifier. Sensitivity is the loudness of a speaker in decibels (db) for a 1 watt input. You might say an insensitive speaker produces 76db at 1 watt where as a more sensitive one will produce 89db at 1 watt. Frequency is another way of saying vibrations per second or hertz (hz) where 20 hz is 20 vibrations per second and 20,000 hz or 20 kilohertz (kHz) is 20,000 vibrations per second. So happens the range of human hearing is 20hz - 20khz. Since woofers reproduce bass and tweeters treble the crossover point is where the low frequencies are filtered out so only high frequencies reach the tweeter since low frequencies will damage a tweeter.

    You can certainly find more detailed info by searching the web or related topics on this site. Have fun!
  3. Cooly McDuck

    Cooly McDuck Well-Known Member

    Seattle, WA
    My super basic understanding:
    - Watts per channel - amp capable of sending up to x (in your case, 50) watts per channel to each speaker, depending on the volume. So if the volume was all the way up, it'd be sending 50 watts per channel to the left speaker, and 50 to the right speaker.
    - Impedance - look it up for more detail, but it's a measure of the resistance the speakers will push back on any signal sent to it
    - Crossover Freq - the point in a sound wave where your speakers decide to send the sound through the woofers or tweeters (or whatever combination there of, depending on number of woofers/tweeters)
    - Nominal Impedance - the average impedance of a speaker, because it's not a constant thing. For example, a speaker could be 8 ohms at a certain frequency, and 3 at another... nominal is just the spec from the manufacturer of what the average impedance is.
    - Sensitivity - how responsive your speakers are to the power sent in... low sensitivity will mean a speaker requires more power to create more noise, high sensitivity means it doesn't require a lot of power to create a lot of noise. When people talk about speaker efficiency, this is what they're referring to.

    But don't take my word for it! There are a ton of websites with better explanations out there.. do some searching. It's confusing stuff.
    AcidPunk15 and Blue Gecko like this.
  4. Thorensman

    Thorensman Forum Resident

    If output is specified as RMS
    This is the fairest measurement.
    It's the ammount of power the amplifier
    Will supply at full power when driven correctly by the preamp .
    Loudspeakers Are rated by. Nominal impedance . This is opposition to the power the amplifier feeds into it, 4 ohms being quite low and therefore cause the amplifier to work higher.
    This in turn will cause it to draw more power from its powersupply, thus with smplifier rating you may see 50 Watts at 8 ohms and 70 watts into 4 ohms
    As this extra drawing of power from powersupply will cause the amplifier to produce more power. The actual
    Ammount dependant on how good the amplifier power supply is.
    Not all amplifiers are equal.
    A 20 watter like the old Nad 3020 ( i think) has masses of current, so will drive a demanding loudspeaker like the
    Old Linn Isobarik when many 50 watter s

    will trip out on thermal limiting as it cannot supply enough current.
    As I say there is more to amplifier/ speaker matching than best buy ratings.
    This is a measurement of how efficient
    The loudspeaker is.
    85 to 90 DB per watt/metre being quite good. In a nutshell an efficient loudspeaker will go loud with a few watts. A 10 watter coupled to a 90 db/ m will go louder than a 50 watter into 80db/ m
    To double power from 10 watts you need probably 70 watts it more,
    In essence the best way of knowing if an Amp/ speaker works is to couple them up and try them out,
    Last edited: Aug 7, 2017
  5. KT88

    KT88 Forum Resident

    I'll add that the speaker system is what receives the power from the amp in watts. So, that power is divided by the crossover and distributed to the individual drivers in the speaker system. The lower frequencies have more power and the woofers require it to deliver deep bass at the same level as the higher frequencies. So power is not divided equally. If you have 50w sent to the speaker system, relatively full range, as an example, then the woofer is probably receiving around 30 of the watts, with the midrange taking 15 and the tweeter 5 watts. There are also losses in the crossover, so the amplifier would need to deliver an additional couple of watts to compensate for that. Since music is dynamic and the signal has many possible frequency and amplitude combinations, this situation is never really played out all at the same time. Rather the power is broken down as required by the speakers to produce whatever level you set it at of only the frequencies sent to it in any instant. You'll use maybe 10 watts much of the time, then a passage with strong bass may demand 25w peaks for a few seconds each.
    Blue Gecko and Thorensman like this.
  6. Blue Gecko

    Blue Gecko Forum Resident

    Wow.... just wow... some awesome responses. I intially started to reply to a couple of the responses, but please accept my thanks with a simple like to your post... I'm sure it's barely enough. I used to work at a engineering university and could always get technical questions answered. Thankfully Hoffman Forum participants are on the ball.
    AcidPunk15 likes this.
  7. lance b

    lance b Forum Resident

    Sydney, Australia
    The power required to drive each individual speaker in a 3 way speaker is dependent on what music is being delivered and what the crossover points are. Generally, it takes much more power to drive the woofers simply because they need to move more air than the midrange and the tweeter for a similar volume of music across the frequency range. As a possible example, if an amp was delivering full power to the speakers, a woofer may be using 35 Watts of that power, the mid using say 10 Watts and the tweeters using 5 Watts. This is dependent on the crossover frequency split up as well as that will determine how much frequency range each driver needs to reproduce and what power those frequencies are made up of.

    Impedance is similar to resistance in that it is the load the the amplifier "sees". Theory is that the amp is supposed to deliver 50 Watts RMS per channel into 8 ohms both channels driven at a particular maximum total harmonic distortion. 8 ohms is the usual impedance that is used to determine the power that an amp can deliver and makes it a little easier to judge power delivery across different amplifiers. Into a 4 ohm load, the amp should deliver twice the power, but that is dependent on a number of other factors like the power supply limitations of the amp in question. This doubling of power into half the load is rarely if ever achieved. A good power supply needs large transformers with lots of copper and large capacity capacitors, big power transistors (or whatever) etc, etc and this all costs money.

    Sensitivity of a speaker is simply how efficient the speakers are at converting the amp's power into sound. A high efficiency speaker will sound louder for the same power than a low efficiency speaker. The figures generally used are quoted in dB with 1 Watt input at 1 meter and are measured with a sound pressure meter on the speaker axis. High efficiency speakers are generally about 90 dB at 1 Watt at 1 meter, low efficiency could be considered to be under 85 dB at 1 meter. As an example, it would take about twice the power to drive am 87 dB speaker to the same sound pressure levels as a 90 dB speaker.
  8. Bathory

    Bathory 30 yr Single Malt, not just for breakfast anymore

    as to not get technical. its a simple formula.

    more is better.

    i have NEVER had less than 165W/channel RMS (RMS) is the key word.........oops, sorry, I did have (still do) an older only tx-890 (125 rms W) but its in basement guard duty now. otherwise, thats it.

    i now have 650W into 8ohm RMS, and well over 1000W into 4.

    go big,... or just don't bother.

    those 100W and similar amps, are GREAT, if they have a lot of current, if the current delivery is wee, skip em. speakers NEED to be driven, and they NEED constant current/or voltage, depending on if you have standard magnetic drivers, or Electrostats ( thats another discussion in itself)

    either way, listen to a lot of amps, and let the goosebumps make the decision for you. thats what i did. i JUST KNEW, as soon as i heard my amps, and the hair on my arms stood up like my first view at playboy as a wee mite, then i said, THATS IT..... I NEED THOSE ! i saved, and saved, and i bought them. I have not looked back since, and each time i play some good tunes, and sometimes, the hair still stands, you just know.

    enjoy the ride, its wondrous !!

    oh, also, do not be cheap. no money does not mean quality, but to does mean a lot, when your into the mid to higher fi setups.
    Let the moths out of your wallet before they eat your money :)

    happy listening !
    AcidPunk15 likes this.
  9. samurai

    samurai Step right up! See the glory, of the royal scam.

    How about tube watts vs. solid state watts?
  10. Cockroach

    Cockroach Well-Known Member

    Visalia, CA
    There are basically two kinds of watts per channel: There's RMS, or root-mean squared, which is the truest way to measure AC power. It is a method of averaging the power, and the fairest way to measure an amplifier's output capacity. Then there's peak power, which is how much power an amp can possibly push, distortion-be-damned. Many cheap amplifiers advertise high watts-per-channel, but in fine print somewhere, disclose that it's peak power. Knowing peak power is useful as an indication of the amp's capacity to handle a transient burst of musical energy, but only in relation to its RMS output.

    I've had a few hard sodas, so I hope that makes sense. :eek:
    AcidPunk15 and Sneaky Pete like this.
  11. head_unit

    head_unit Forum Resident

    Los Angeles CA USA
    Simple: watts per channel means how many watts are in each channel. You're welcome.
    timind likes this.
  12. head_unit

    head_unit Forum Resident

    Los Angeles CA USA
    Of course you are confused, it is confusing! :mudscrying:

    Yes, the entire speaker gets the power. But not 50 watts all the time, as others noted it depends on the volume setting and how loud the input source is and the impedance of the speakers. Most of the time you are probably not even using one watt. But hearing is logarithmic, and a small 3 decibel step requires doubling the power. Then another step doubling again to 4X, then 8X, and very quickly the power has gone way up when you are partying on the patio!

    The crossover has parts like capacitors, inductors, and sometimes resistors to divide that power between woofer, midrange, tweeter (and also sometimes to adjust the frequency response). Most of the power goes to the woofer, some to the midrange, little to the tweeter.

    The crossover frequency is just the frequency at which the handoff takes place. For example a 2 kHz crossover means that for the woofer, frequencies more and more ABOVE 2 kHz are reduced more and more. For the tweeter, frequencies more and more BELOW 2 kHz are reduced more and more. It's not an all-or-nothing, instantaneous cutoff. How sharp depends on the crossover. Some people think slower (like 6 decibels per octave) is better, whereas some brands tout "infinite slope" (very steep like 48 dB/octave) as better. Take my word as a loudspeaker design engineer, neither is correct. There is NO "always better" there are just design tradeoffs. One of the things more money gets you in a more expensive speakers is usually a more sophisticated crossover with better quality parts, which can give a better sound to the better quality woofer/tweeter and hopefully better cabinet.

    The impedance of a speaker is basically how resistant it is to current flow. This varies widely at different frequencies, so the nominal impedance *should* be a kind of sort of minimum, to let you determine if your amp will get too stressed at full crank. For instance, connecting a 1 ohm car sub to a 4 ohm rated amp and turning it way up will probably break the amp after a while. Why? Because at a given volume setting, a lower impedance will draw more electrical current out of the amp, until the amp gets in trouble. By the way, sorry but speaker power handling ratings are pretty much all meaningless, useless nonsense even if they say RMS or CEA or all kinds of other qualifiers. However, so long as you TURN IT DOWN if things start to sound bad, you cannot have "too big" of an amplifier.

    Sensitivity is just how loud a speaker plays for a given amount of power. A more sensitive speaker like a horn can play very loud from, say, a low powered triode tube amp. An insensitive speaker needs a lot more power to play loud. Tiny speakers are all insensitive due to "Hoffman's Iron Law" and the physics of real speaker parts...plus all tiny speakers to me seem often somehow lacking some kind of liveliness.

    Unfortunately, many manufacturers b@ll**** their sensitivity specifications, so they are pretty useless as well. Even when they say something like "1 watt @ 1 meter" the spec is still useless, and certainly not comparable between different brands. Too bad, because it makes a BIG difference. A speaker with an actual 85 dB sensitivity might need a 1000 watt amp to play at rock concert levels (assuming it could). A speaker with 95 dB sensitivity would only need a 100 watt amp!
    AcidPunk15 and Dennis0675 like this.
  13. Methodical

    Methodical Forum Resident

    How do these wattages differ from those 20 or 30 watt tube amps.

    I myself have 500w amps, but have always wondered about those tube amps and their lower watt rating.
  14. Vinyl Addict

    Vinyl Addict Forum Resident


    Well written.
  15. Claude Benshaul

    Claude Benshaul Forum Resident

    That's actually a very good question but lets look at it from another direction. When stripping the magic of music from the equation the inescapable conclusion is that loudspeakers are just machines. You provide them with electrical power and they turn it into mechanical motion and like every other machine the work they produce can't exceed the energy they received.

    The energy is measured in watt and the work is measured in dB. The efficiency of a loudspeaker is measured by how much dB can a loudspeaker produce if provided with 1 watt. Obviously the higher the dB the more efficient the speaker is.

    So what's with the 500W RMS? Well, do you seriously believe that a simple machine like a typical loudspeaker really need the same electrical energy as an air conditioner? Of course it doesn't and in much of its operation it needs only a fraction of this power and this is why it is possible to "drive" them with low output valve amplifiers. The extra watts provides headroom, that should you hit a peak when this power is really needed, it will be there to be used. With valve amplifiers it is usually advised to connect efficient speakers because they don't have the extra energy reserve to drive the speakers during peak demands.

    This explanation is really basic and I know that I mixed apples to oranges because you can't really compare watts to dB, but I think it will do for now.
  16. Bathory

    Bathory 30 yr Single Malt, not just for breakfast anymore


    Honestly, i pray someone in here answers this. I myself have always wanted a nice tube amp, just to get the feeling they are supposed to deliver.

    only closest sound is the carver sunfire with the current taps with going through a %1 resistor???( correct if wrong)
    that does eliminate the damping factor, so its a little softer and boomy, but NEVER poor sounding, I really enjoy it.

    Soon, I will try some nice tube amps, as soon as we move, ill get saving for the tube amp(s)
  17. Methodical

    Methodical Forum Resident

    Thanks for your response.

    Here's how I interpret your explanation in a nut shell. The higher wattage amps provide headroom, which I am familiar with, for less efficient speakers and less efficient speakers need more power.

    With tube amps rated at 20-30 watt amps for example, you're best served using high efficient speakers, assuming 95 or higher, because those amps provide no headroom for peak action because higher efficient speakers don't need much power to run loud (i.e. less or no headroom needed).

    My speaker efficiency rating is 88, so those lower wattage tube amps would not be a good fit for my speakers, based on the suggestion that high efficient speakers be used with those tube amps, correct.
    Last edited: Aug 8, 2017
  18. chervokas

    chervokas Forum Resident

    With tube amps, it's really more important to look at the impedance curve of the speaker than the efficiency alone. Tube amps will deliver maximum power into the reflected impedance load the output stage is expecting to see, so if you're connecting an 8 ohm speaker to the 8 ohm tap of the tube amp, the amp will be able to deliver maximum power. But as the speaker load moves away from 8 ohms in either direction -- higher or lower -- the amp's ability to deliver the power demanded will decline. Also, tube amps will be very limited in their ability to deliver current into a highly capacitive load. So what you really want with a tube amp is a resistive load -- a relatively flat impedance curve, and ideally a relatively high impedance, with phase angles that never get too steep and especially not in a capacitive direction. In particular you don't want a speaker that has an impedance that drops with a phase angle that turns sharply capacitive in the bass, upper bass or lower midrange -- areas were there's a lot of musical energy and where larger speaker cones demand more current to move.

    If you had an 88 dB/m/w speaker with an impedance that never dropped below 8 ohms with relatively benign phase angles in a smallish room, a 30 watt tube amp might be perfectly fine.

    The problem is that today, in the era of cheap high power solid state amplification, most speakers aren't made with consideration for the kind of gentle loads that tube amps do best with.

    In terms of peak power and headroom, again, with the tube amps, to some degree it will depend on the impedance of the load at certain frequencies, the output impedance of the amp (tube amps have higher output impedances than solid state amps generally, but some sorts of tube circuits have considerably higher output impedances than others), and the nature of the tube amp's power supply.

    This is I think a useful read on the subject of tube-friendly speaker loads -- DHTRob - Tubefriendly loudspeakers?
    Tim Müller likes this.
  19. chervokas

    chervokas Forum Resident

    Just a note about nominal impedance ratings on hifi speakers. They tend to be kinda all over the place. Nominal impedance has never been lowest impedance along the speaker's curve, nor really a mathematical average of the highest and lowest impedances. There was an old formula for nominal impedance that was minimum impedance X 1.15, but that doesn't really hold up in the marketplace any more. Plenty of speakers with impedances that dip to 4 ohms or so at a certain frequency that aren't marked as 4 or 5 ohm nominal speakers, as they should be under the 1.15X formula. Some might be marked as 6 ohm nominal, which is in the ballpark at least, depending on the curve. Others might be market "compatible with 8 ohms" in order not to scare potential buyers away, but they might be better thought of as 4 ohm speakers. You really need to look at the speaker's impedance curve -- if the impedance is 4 ohms or so at frequencies were there's a lot of current demanded and a lot of energy in the music -- like bass and lower midrange frequencies -- it may be better to think of those as 4 ohm speakers for the purposes of matching them to a driving amplifer. If the impedance dips like that but up at 10kHz or above or something, where there's very little current demanded and very little musical information, but it stays a 8 ohms or above elsewhere, that's a speaker that is probably a lot easier to drive and one you might really think of as an 8 ohm speaker despite the minimum impedance reaching a lot lower at some frequencies.
  20. Gibsonian

    Gibsonian Forum Resident

    Iowa, USA
    Never running out of power, never clipping is a beautiful thing.

    Of course never clipping with a poor sounding system is torture. Quality first, power requirements met, second.
  21. Tim Müller

    Tim Müller Forum Resident


    I'd like to add to your excellent explanation.
    You pointed out that the impedance curve of the speaker depends on frequency. That is, there is a minimum impedance at a certain frequency, and also a maximum impedance at a different frequency.

    It is also true, that tube amps deliver the most power when impedances of amp and speaker are matched.

    Because of the dependence of impedance on frequency, the speaker receives more or less power from the receiver, depending on the frequency. That means, the produced sound pressure is also dependent on the frequency dependance of the impedance of the speaker and amp.
    Generally, this is not good, because the sound depends on the combination of amp and speaker, in an unpredictable way for the non-technically minded user. Some speaker-amp combinations will sound somewhat dull, but with a different speaker impedance curve (different speaker) may sound agressive, or so.

    On the other hand, most semiconductor amps (transistors or ICs) have very low output impedances, much less than an Ohm. Therefor such amps "don't care" for speaker impedance.

    Therefore, it's a good idea to combine a tube stage with a semiconductor output buffer stage (emitter follower) to reduce the output impedance of the amp. You get the sound colouration of the tube, but not the disadvantages of the need to use "tube-friendly" speakers, or the like.

    Best regards
    Morbius likes this.
  22. AcidPunk15

    AcidPunk15 Forum Resident Thread Starter

    New Brunswick, NJ
    Wow, these responses have been great. Keep them coming if you feel you have something to add. I have never gotten so many in depth and knowledgeable responses. Usual they are vague short and snobby, but these responses are why I joined this forum. Once I have the money I will buy modern Integrated Amp worth $300-500 tons of wattage. This set up is my first "Hi-Fi" Analogue Setup. I spent $15 on my Technics SL-BD20, $75 on my Denon DRA-425 $60 on my Nakamichi LX-3 and $10 on Nakamichi Sound Space 8. I will be purchasing 1 Elac Debut F6 once I have moved to Austin in 2 weeks. Thx again guys keep them coming. Add or alter the topic of this thread I don't care.!!!!!! I haven't been sleeping well sorry for the poor grammar.
  23. rockin_since_58

    rockin_since_58 Forum Resident

    Simi Valley, CA
    If I remember correctly from way back...RMS is derived from the peak to peak value of the sine wave. You take the total amplitude of the sine wave and multiply by .707 to get RMS. RMS is more of an average of the peak to peak signal. Okay technical experts, correct me if I am wrong :)
    Cockroach and AcidPunk15 like this.
  24. BayouTiger

    BayouTiger Forum Resident

    New Orleans
    An interesting article that goes into the topic of volume level rather than output power.

    FWIW, a Watt is a watt. Tube vs SS have nothing to do with it. Many believe the difference is that tubes distort very differently than SS when pushed beyond their limits. thus the perceived difference in wattage. You need to double the wattage to appreciably change the perceived volume so there is not as much of a difference in 100 vs 150W as you would think. I always find it kind of silly that most manufacturers historically offer amps in, say, 20W increments when it makes more sense to offer a 75, 150, and 300W version.
  25. RiCat

    RiCat Forum Resident

    CT, USA
    Many good responses as to what's watts. Always a caveat however. Watts/chn is meaningless unless: The testing method is stated (as in RMS or peak power or ??); The resistance load the measurement was done at (8 Ohm or 4 ohm or ??); The frequency spread for the stated watts (as in 20-20k, @1k or ??); and The measured distortion for the stated power (typically shown as a % THD ). Lastly even with additional information the number is only good as a rough comparison between models and tells you nothing about how the unit sounds. Watts alone is a voodoo number without the additional specs.
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