How Much Amplifier Power is Needed to Drive My speakers? Do the Math!

shsshs Posts: 53
edited January 2 in Speakers
The question is often asked, how much amplifier do I really need; is my 80 watt per channel AVR going to drive my speakers to an appropriate listening level? One way to answer the question is to use one of the many calculators available. My favorite discussions of this and calculators are: https://www.crownaudio.com/how-much-amplifier-power Or: http://www.acousticfrontiers.com/2013322spl-calculator/

But using such a calculator may not reveal why you need a certain amount of power for a given set of circumstances. So, let’s use math to look at this question in a few simple steps. For illustration, we will use the Polk LSiM towers and bookshelf speakers that I own and use in my home theater. Polk specifies the sensitivity of the these LSiM speakers as 88dB at 1 meter and 2.83V (not 1 watt). This spec is a bit of a complication right away and that will be discussed below, but for now let’s assume that with 1 watt of power from the amplifier the LSiM speakers produce an Sound Pressure Level (SPL) of 88 dB for someone sitting 1 meter or about 3.28 feet from that speaker. That is a pretty loud level, 3 dB above the 85 dB reference level used in movie theaters, but only for someone setting 3 feet from the speaker.

Let’s move back to a more reasonable listening position, say 4 times further way, or 4 meters (13 ft). According to the inverse square law (SPL drops off with the square of the distance) every doubling of the distance drops the SPL by 6 dB, so at our 4-meter seating distance our LSiM speaker is producing at nice loud, but comfortable, 76 dB SPL with only 1 watt of power from the amplifier! (It is probably more like 2 watts, see below.)

But that is only if you like listening to a single frequency at a constant level as that is the way speaker sensitivities are typically tested. With music and movie content, we have to allow for transient or peak levels that are 10 times or 20 dB above the average or rms (root mean square) level of the music in order for the sound to be reproduced without compression or distortion. Movies are mastered with their 85 dB reference SPL 20 dB below the peak level to make sure that loud noises, special effect or loud music are accurately reproduced. If you want your system to accurately reproduce these sounds in your room, the requirement for 20 dB more SPL to handle these loud sounds actually requires 100 time more power from an amplifier. So to accurately reproduce the reasonably loud, but modest 76 dB SPL (with 96 dB peaks) at our seat 13 feet from the speaker, the required amplifier power is now 100 watts.

Now let’s say you want to show off your system to friend and show a movie at reference level for the movie theater or 85 dB SPL with 105 dB peaks. Now the math says that the additional 9 dB of SPL requires 8 times more power, or 800 watts from the amplifier, to accurately reproduce the loudest sounds in the movie or music without compression. So, it is easy to see why people want more that 100 watts per channel if they enjoy pushing their system occasionally.

So, what happens if you only have a 100 watt per channel amplifier? You can turn up the sound and it will sound louder, perhaps quite a bit louder as the transients may now be clipped or distorted and we have learned to hear that distortion as representing a loud sound level. Turning up the volume until you hear distortion is something we have all done, and a higher power amplifier may not sound as “loud” at a given average SPL as a lower power amplifier, but it will sound more like live music and be a more accurate reproduction recorded sound. (As is often pointed out as well, such distortion does send more energy to the tweeters and can result in the tweeters getting burned out.)

Let’s get back to that Polk sensitivity spec of 88 dB at 1 meter and 2.83 volts, whereas typically speakers are be specified at 1 meter with 1 watt of power from the amplifier. 2.83 V is the same a 1 watt into an 8-ohm speaker, but not for a 4-ohm speaker, where a 2.83 V signal would draw 2 watts from the amplifier. While the Polk LSiM information sheet list the speakers as “compatible w/ 8 Ohm outputs ”, the very positive Sound and Vision review of the LSiM speakers in June 2012 listed their nominal impedance as 5 ohms with a minimum impedance or 2.86 ohms at 66 Hz. So, it is reasonable to assume that when producing the specified 88 dB SPL with 2.83 volts, the LSiM’s were drawing closer to 2 watts from the amplifier rather than 1. Put another way, the LSiM’s sensitivity driven with 1 watt would be 85 dB and all the power calculations above would need to be doubled to account for the real power draw or sensitivity of the LSiM speakers. That would mean 200 watts for a modest 76 dB SPL without distortion and 1600 watts for 85 dB reference level!

Now let’s work in the other direction. In a real room, the SPL does not fall off a fast as the inverse square law would predict as reflections and reverberations reinforce the direct sound. Plus, it is not fair to assume that in most passages a single speaker has to reproduce the desired sound level and typically a subwoofer or two is providing a lot of the oomph in the loud passages relieving the load from the other speakers. Not only that, but an amplifier’s power rating is typically specified as rms or average power and most amplifiers have some ability to reproduce short-term spikes a few dB above the average power and many amplifiers will put out more power into a 4 ohm load than 8 ohms, but typically not twice as much. (Ironically, the best amplifiers with the largest and “hardest” power supplies have less dynamic headroom above their rms (average) rating than less expensive amplifiers, but they also have higher rms power ratings).

So, in reality a few hundred watts per channel is likely to do the job with the LSiM speakers and 800 watts per channel, e.g. the D-Sonic amplifier I use to drive my speakers is not totally ridiculous. It actually sounds very good and on occasion I do enjoy cranking it up and do hit reference levels with 105 dB transients!
SONY VPL-VW385ES, Da-Lite 92" 0.9 HD progressive 16x9 screen, Apple TV 4K, Oppo UDP 203, Anthem AVM 60, D-Sonic 4000 (800x3, 400x4) for bed layer, 2 Crown XLS 1002 (225x4) for Atmos; Speakers: Polk LSiM 705s, 703 front, 4 702F/X surround, 4 Polk TL3 (Atmos), Velodyne DD15 Subwoofer.
Post edited by shs on
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Comments

  • tonybtonyb Posts: 31,711
    Good info, and most of that has been posted a million times over the years. Here's the problem with that answer.....your talking Chinese to most people who want to know if their receiver is powerful enough for their speakers.

    They want a yes or no answer, not a mini series about power, ohms law, or other stuff that they simply aren't going to comprehend or put into the reality of their situation. Laymen's terms, short answers is what they are looking for. They'll ask if they need a more detailed response. Some come here just to get a question answered, then poof they are gone. Not many stick around to become contributing members or to seek further knowledge on audio. Would be nice if they did, but to each their own.

    I like giving responses to questions I know the recipient is going to understand. That is the main reason they came here anyway, to get their question answered...quickly, and without having to sift through 3 pages of back and forth. Good info none the less, thanks for posting it, but I guarantee the same question will be asked over and over again.
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  • GardenstaterGardenstater Posts: 213
    To the OP, I appreciate the writeup. The devil's in the details. Thanks.
    George / NJ

    Polk 7B main speakers (1979, orig owner)
    Martin Logan Dynamo sub
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  • shsshs Posts: 53
    The point is that while it only takes 1 or 2 watts on average to produce a nice comfortable and reasonable "loud" listening level, it takes several hundred watts of power to accurately reproduce the dynamics of the music or special effects, but that is what makes the sound sound real or live as opposed to compressed and dead. More power is not for a louder sound, but rather for a better more dynamic sound.
    SONY VPL-VW385ES, Da-Lite 92" 0.9 HD progressive 16x9 screen, Apple TV 4K, Oppo UDP 203, Anthem AVM 60, D-Sonic 4000 (800x3, 400x4) for bed layer, 2 Crown XLS 1002 (225x4) for Atmos; Speakers: Polk LSiM 705s, 703 front, 4 702F/X surround, 4 Polk TL3 (Atmos), Velodyne DD15 Subwoofer.
  • mhardy6647mhardy6647 Posts: 24,059
    edited January 2
    The converse can also be true, for those of us ;) who prefer the big, effortless dynamics and "they are here" presence of high-sensitivity loudspeakers. "Our" amplifiers spend most of their time at output levels of 1 watt or less -- often much less. And lots of amplifiers (especially the Big Bertha, high output power amplifiers) just ain't at their best under such circumstances.

    The characteristics of the load also matter a lot. Much of the 'synergy' folks invoke, I think, reflects the suitability of an amplifier with respect to the actual load it sees from the loudspeaker(s).

    Plus, some amplifiers... just... ain't... great (sounding) -- irrespective of specifications (and, sometimes, irrespective ofprice, too).
  • JazzheadJazzhead Posts: 69
    I'm driving my recapped and fully modded original RTA-12's with D-Sonic products as well - a couple of M3a-600M monoblocks (800 watts each). That amount of wattage may seem like overkill to some, but I've been told that Polks thrive on high-current amplifiers and most of all I enjoy the great presence, detail and dynamics that the D-Sonics provide at low listening volumes. They are wonderful sounding amplifiers.
    Polk Audio original RTA-12 (1980) with 12 inch Polk Stands. Acoustically/structurally/electrically modified. David Shirly rebuilt crossovers including Sonicap/Mills, Cardas rhodium binding posts, Neotech OCC internal wiring, Sonic Barrier 3-layer, Dynamat, Over-damped outer drivers.
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    Herbie's Audio Lab system isolation - Tenderfeet, Big Fat Dots, Grungebuster Dots, Little Fat Gliders
    Herbie's Audio Lab Super Black Hole CD Mat
    Dedicated 10 gauge power circuit
  • K_MK_M Posts: 1,617
    I think the bigger reality, most do not know how loud 85-90 db truly sounds.

    And the OP is grossly over estimating how much power is needed for something to sound "loud" to the average person.

    800 watts is almost never "needed"

    We have had 250 watt amps in the past, and 50-90 watts (according to the digital meters) was unbearably loud on transients.

    So maybe in theory ..but reality, maybe only in a huge room and sitting far away.
    Lsi15, Lsi9, LsiC,Rta11t,M5jr+,M4, SDA SRS 2.3TL, Rti6....Still listing stuff, a work in progress.
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  • K_MK_M Posts: 1,617
    tonyb wrote: »
    Good info, and most of that has been posted a million times over the years. Here's the problem with that answer.....your talking Chinese to most people who want to know if their receiver is powerful enough for their speakers.

    They want a yes or no answer, not a mini series about power, ohms law, or other stuff that they simply aren't going to comprehend or put into the reality of their situation. Laymen's terms, short answers is what they are looking for. They'll ask if they need a more detailed response. Some come here just to get a question answered, then poof they are gone. Not many stick around to become contributing members or to seek further knowledge on audio. Would be nice if they did, but to each their own.

    I like giving responses to questions I know the recipient is going to understand. That is the main reason they came here anyway, to get their question answered...quickly, and without having to sift through 3 pages of back and forth. Good info none the less, thanks for posting it, but I guarantee the same question will be asked over and over again.

    Something else you rarely or ever see addressed, a high current amp is better for driving low impedance speakers at certain frequencies, we all agree, but they are not magic.

    For speakers that stay mostly around 7-8 ohms a high current amp is at a disadvantage compared to one that is not considered "High current".

    A lot to get into, but by optimizing for low impedance loads, more normal impedance loads are not driven quite as well.



    Lsi15, Lsi9, LsiC,Rta11t,M5jr+,M4, SDA SRS 2.3TL, Rti6....Still listing stuff, a work in progress.
    B+W-Sold
    Electro Voice EV-SIX
    Infinity-Sold
    Advent-Now gone
    Yamaha A-S801
    Yamaha RX-V377
    Yamaha RX-A860
    Yamaha RX-A3060
    Harman Kardon Hk-350i
    Harman Kardon Hk-........
    Harman Kardon PM-665
    Harman Kardon HK-775
    Pioneer.......Stereo Receiver

  • F1nutF1nut Posts: 43,385
    85-90 dB is not very loud.
    uoe9hl1hnfdx.gif
    Political Correctness'.........defined

    "A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."


    President of Club Polk

  • mhardy6647mhardy6647 Posts: 24,059
    Well... I guess it depends on how one looks at it. I mean, yeah, compared to a jackhammer, jet engine, Apollo V liftoff at ground zero, or a Skilsaw battling its way through a piece of MDF, yeah, not so loud. Conversly, OSHA's permissible exposure limits suggest it's pretty loud to me. Empirically (and FWIW), 85 to 90 dB at my listening position is about as loud as I ever listen (at least at this point in my life).

    While I am wasting bandwidth -- I am still trying to figure out how the heck there can be any downside to a well designed and implemented high current amplifier.

    :|


    on topic -- I am a strong proponent of math (having ahem collaborated with Mrs. H on bringing a mathematician and an economist into the world!) -- but personally I am one of the four-thirds of Americans who has trouble with math, such as fractions. :#
  • audioluvraudioluvr Posts: 1,655
    Well I'm thinking 1.5 watts
    Home System:
    SDA 1C's - Full mod with the help by Dave...
    1000 Va Dreadnought- w/ WireWorld Mini-Eclipse cables
    WireWorld Mini-Eclipse 7 speaker cables
    WireWorld Silver Eclipse IC's
    Cambridge Audio Azur 851N - DAC/Streamer
    Belles 21A Tube Pre
    B&K M200 Sonata Monoblocks
    BLE-Design 16mm Power Cables
    Denon DVD 2900

    Barn system:
    SDA SRS 2.3's Full mod done by myself
    Carver C-1 pre
    Carver M1.5t
    BluDenso - Bluetooth receiver/DAC
  • BlueFoxBlueFox Posts: 12,505
    I have 1200 watts/channel. This is adequate for the living room.
    Bud - Silicon Valley

    Lumin X1
    Sony XA-5400ES SACD
    Pass XP-22 pre, X600.5 amps
    Magico S5 MKII Mcast Rose speakers, SPOD spikes

    Shunyata Triton v3/Typhon QR on preamp, Denali 2000 (2) on amps
    Shunyata Sigma XLR analog ICs, Sigma speaker cables
    Shunyata Sigma HC (2), Sigma Analog, Sigma Digital, Z Anaconda (3) power cables

    Mapleshade Samson V.3 four shelf solid maple rack, Micropoint brass footers
    Three 20 amp circuits.
  • mantismantis Posts: 15,491
    This line of thinking is something we overlook many times. We look at numbers and want the most out of them or we inside feel deprived. Even if we never use the 200-1000 watts of power in our amp sections we feel some level of comfort knowing it's there. Having the exact amount of power needed in ones system is something so hard to except and then go with especially when so many people say more is better you need 200 watts to run your speakers or you will never hear what they can do etc etc etc. I'm one of those people who has these feelings and just started a thread in this line of thinking.
    Excellent write up and I have to agree with tonyb with what most people are looking for. A few selected people in here can read what you wrote and actually talk about power room acoustics Ohms law and sensitivity.
    My next receiver upgrade I'm actually going to calculate the exact amount of power needed to achieve my needs, also going to go through the feature set and inputs and make sure I get what I need and not just jump on flagship model because thats what I have Always done to not feel left out and see IF that line of reason is the correct thinking.
    One thing that inspired me to think more logical over Manhood LOL is Dodge and its crazy amount of Horsepower they are putting on the street. I got a 2017 Dodge Durango with the 5.7L Hemi and it sparked all my old 1/4 mile race days back into my blood. It put me on this journey towards the Demon of 840 HP and going absolutely crazy. My next purchase was absolutely going to be at least a SRT Durango or Jeep GC or going crazy with a TrackHawk in 707HP.
    When you start looking how much these vehicles cost vs the R/T level 5.7L models it's a ton of money to have extreme power on the street you can't use without going to jail. For the Track go HP crazy as you can use all of it but on the street it makes no sense.
    My Son has a Audi S4 and before that a A4 and at first he was tickled pink with the amazing amount of power the 3.0 Supercharged engine has.But he also feels it's a waste on the street as he can't use it without getting a ticket or going to jail.
    Wisdom came from our conversation as I remembered my days with my 11 second Buick Grand national on the street and how having all that power in a daily driver was stupid from one point of view.
    Dan
    My personal quest is to save to world of bad audio, one thread at a time.
  • Viking64Viking64 Posts: 4,683
    mhardy6647 wrote: »

    on topic -- I am a strong proponent of math (having ahem collaborated with Mrs. H on bringing a mathematician and an economist into the world!) -- but personally I am one of the four-thirds of Americans who has trouble with math, such as fractions. :#

    Hey, Mark! Why don't you collaborate off?!?!?! :p

    And how can YOU be one third of Americans? :o

    There are 2 kinds of people:

    1) Those that never finish things they start.
  • K_MK_M Posts: 1,617
    edited January 6
    mhardy6647 wrote: »
    Well... I guess it depends on how one looks at it. I mean, yeah, compared to a jackhammer, jet engine, Apollo V liftoff at ground zero, or a Skilsaw battling its way through a piece of MDF, yeah, not so loud. Conversly, OSHA's permissible exposure limits suggest it's pretty loud to me. Empirically (and FWIW), 85 to 90 dB at my listening position is about as loud as I ever listen (at least at this point in my life).

    While I am wasting bandwidth -- I am still trying to figure out how the heck there can be any downside to a well designed and implemented high current amplifier.

    :|


    on topic -- I am a strong proponent of math (having ahem collaborated with Mrs. H on bringing a mathematician and an economist into the world!) -- but personally I am one of the four-thirds of Americans who has trouble with math, such as fractions. :#

    85-90 to me is fairly loud.

    About the "High current" amp thing, an amp can really only be designed to operate most efficiently into a small range of impedance.

    So if it is designed to work great into 4 ohms for instance, it will work less well into 8 ohms and even less well into 16 ohms for instance.

    Now very few speakers are ever 16 ohms to begin with, but many speakers will have a low impedance in one part of the range, but then rise to 6 to maybe even 12 or more ohms at higher frequencies.

    The compromises are Heat, distortion, and lower output at certain impedances or frequencies.
    So while the 4 ohm rated amp will be great at ranges where the speaker is actually around 4 ohms, (bass usually) it will not be as great where the speaker rises to 6-12 ohms higher in frequency.(higher frequencies or speakers that are NOT 4 ohms in the bass)

    In other words there is no magic or free lunch, its either good at low impedances or good at higher impedances, but can not be great at both.




    Lsi15, Lsi9, LsiC,Rta11t,M5jr+,M4, SDA SRS 2.3TL, Rti6....Still listing stuff, a work in progress.
    B+W-Sold
    Electro Voice EV-SIX
    Infinity-Sold
    Advent-Now gone
    Yamaha A-S801
    Yamaha RX-V377
    Yamaha RX-A860
    Yamaha RX-A3060
    Harman Kardon Hk-350i
    Harman Kardon Hk-........
    Harman Kardon PM-665
    Harman Kardon HK-775
    Pioneer.......Stereo Receiver

  • treitz3treitz3 Posts: 13,616
    K_M wrote: »
    In other words there is no magic or free lunch, its either good at low impedances or good at higher impedances, but can not be great at both.

    Ever heard of this funny little thing called a tube amp?

    Tom
    In search of accurate reproduction of music. Real sound is my reference and while perfection may not be attainable? If I chase it, I might just catch excellence.

    ~ The best way to enjoy digital music reproduction is to never listen to good analogue reproduction ~

    ~ When the law ends, tyranny begins ~
    ~ Not all things that can be measured can be heard and not all things heard can be measured ~
  • mhardy6647mhardy6647 Posts: 24,059
    treitz3 wrote: »
    K_M wrote: »
    In other words there is no magic or free lunch, its either good at low impedances or good at higher impedances, but can not be great at both.

    Ever heard of this funny little thing called a tube amp?

    Tom

    ... well, at least a transformer (or autoformer)-coupled tube amp -- or a transformer/autoformer coupled soiled state amp, for that matter.

    ;)

    kngnvi9z1qvb.png
    Not mine -- my MC-2100 is in a big ol' box in the basement.
  • treitz3treitz3 Posts: 13,616
    Mark, what are we gonna do with you man? First you admit that you are on a measurement based forum that has NOTHING to do with sound and now you have a great tube amp like that just sitting in a, "big ol' box in the basement".

    Damn Son, what are we to take of this? You feeling okay? Been to the Doc lately? Been eatin' them wild mushrooms growin' out in your pasture or somethin'? Takin' after the youngin's and downing Tide Pods or WHAT?

    SMH...

    Tom

    In search of accurate reproduction of music. Real sound is my reference and while perfection may not be attainable? If I chase it, I might just catch excellence.

    ~ The best way to enjoy digital music reproduction is to never listen to good analogue reproduction ~

    ~ When the law ends, tyranny begins ~
    ~ Not all things that can be measured can be heard and not all things heard can be measured ~
  • mhardy6647mhardy6647 Posts: 24,059
    edited January 6
    ZLTFUL wrote: »
    I like it when K_M posts comments...they are always good for a laugh.

    Well, here's the thing -- realizing full well that there are direct-coupled amplifiers that can't -- ahem -- "double down" (what an idiotic term... don't get me started); i.e., deliver twice their rated 8 ohm power into a 4 ohm load (due to limitations in current, usually) -- I think that most any amplifier that can deliver, say, 50 watts into 8 ohms can also deliver 50 watts into 4 ohms (half the voltage and twice the current). :)

    I am guessing what they meant was that some amplifiers are designed, in essence, to be voltage sources and some as current sources; but, power is voltage times current, and a watt's a watt. Any reasonable amp will work reasonably well into a load that varies by e.g., a factor of two in impedance as a function of frequency.

    6vg706mdz1wa.png

    The real trouble comes in when there are wild swings in load impedance and/or phase angle... and (IMO, unfortunately) that's more common nowadays than it was when the loudspeaker designer's bag of tricks was much simpler than it is today.

    One is reminded of notorious amp-killer loudspeakers like the Infinity IRS Beta, and even the somewhat less notorious (but still potentially dangerous) Quad ESL-57.

    tgm0f927uuqw.png
    Fig.1 Infinity IRS Beta, impedance magnitude of woofer tower (top above 500Hz) and midrange/treble panel (2 ohms/vertical div.).
    https://www.stereophile.com/content/infinity-irs-beta-loudspeaker-measurements

    cxl3g82e4ozp.png
    source: http://www.quadesl.com/quad_main.shtml


    The issues with these two loudspeakers aren't due to the nominal impedance per se. ;) Both of these loudspeaker designs are near-short circuits at high frequencies, which can have amusing and costly consequences with amplifiers that have any tendency towards HF instability/oscillation (due to haphazardly-implemented NFB, e.g.).






  • BlueFoxBlueFox Posts: 12,505
    This only works for DC.
    mhardy6647 wrote: »
    ZLTFUL wrote: »
    I like it when K_M posts comments...they are always good for a laugh.

    6vg706mdz1wa.png

    Bud - Silicon Valley

    Lumin X1
    Sony XA-5400ES SACD
    Pass XP-22 pre, X600.5 amps
    Magico S5 MKII Mcast Rose speakers, SPOD spikes

    Shunyata Triton v3/Typhon QR on preamp, Denali 2000 (2) on amps
    Shunyata Sigma XLR analog ICs, Sigma speaker cables
    Shunyata Sigma HC (2), Sigma Analog, Sigma Digital, Z Anaconda (3) power cables

    Mapleshade Samson V.3 four shelf solid maple rack, Micropoint brass footers
    Three 20 amp circuits.
  • Viking64Viking64 Posts: 4,683
    BlueFox wrote: »
    This only works for DC.

    Inside the Beltway?
  • mhardy6647mhardy6647 Posts: 24,059
    edited January 6
    I really don't know why you keep saying that -- it is not true.
    The difference is that Z is not constant; R is. All of the mathematical interrelationships hold for Z as they do for R. The difference is that the value of Z changes as a function of frequency.

    Thus the reference to impedance (EDIT: and phase) curves.

    This stuff is fundamental to the design of power supplies, amplfiers, filter networks (EQ) and crossovers. Electricians, too, have to deal with this stuff all of the time.
    https://www.electronics-tutorials.ws/accircuits/ac-resistance.html
  • BlueFoxBlueFox Posts: 12,505
    edited January 6
    Sorry, it’s the engineer in me. I say it because I am right. Post the AC version if you feel like it.
    Bud - Silicon Valley

    Lumin X1
    Sony XA-5400ES SACD
    Pass XP-22 pre, X600.5 amps
    Magico S5 MKII Mcast Rose speakers, SPOD spikes

    Shunyata Triton v3/Typhon QR on preamp, Denali 2000 (2) on amps
    Shunyata Sigma XLR analog ICs, Sigma speaker cables
    Shunyata Sigma HC (2), Sigma Analog, Sigma Digital, Z Anaconda (3) power cables

    Mapleshade Samson V.3 four shelf solid maple rack, Micropoint brass footers
    Three 20 amp circuits.
  • mhardy6647mhardy6647 Posts: 24,059
    edited January 6
    E(rms) = I(rms) x Z

    EDITED cause, yeah, rms.

  • K_MK_M Posts: 1,617
    mhardy6647 wrote: »
    E(rms) = I(rms) x Z

    EDITED cause, yeah, rms.

    I Pmed you with more specifics about what I am referring to.

    This is something well known to amplifier engineers, but I fully expected it to not be known to many in the forum.

    I realized you may be one of the few to understand.
    Lsi15, Lsi9, LsiC,Rta11t,M5jr+,M4, SDA SRS 2.3TL, Rti6....Still listing stuff, a work in progress.
    B+W-Sold
    Electro Voice EV-SIX
    Infinity-Sold
    Advent-Now gone
    Yamaha A-S801
    Yamaha RX-V377
    Yamaha RX-A860
    Yamaha RX-A3060
    Harman Kardon Hk-350i
    Harman Kardon Hk-........
    Harman Kardon PM-665
    Harman Kardon HK-775
    Pioneer.......Stereo Receiver

  • K_MK_M Posts: 1,617
    edited January 7

    .
    Lsi15, Lsi9, LsiC,Rta11t,M5jr+,M4, SDA SRS 2.3TL, Rti6....Still listing stuff, a work in progress.
    B+W-Sold
    Electro Voice EV-SIX
    Infinity-Sold
    Advent-Now gone
    Yamaha A-S801
    Yamaha RX-V377
    Yamaha RX-A860
    Yamaha RX-A3060
    Harman Kardon Hk-350i
    Harman Kardon Hk-........
    Harman Kardon PM-665
    Harman Kardon HK-775
    Pioneer.......Stereo Receiver

  • K_MK_M Posts: 1,617
    edited January 7
    This simply explains it....


    "There are two related but distinct limitations on the maximum instantaneous power output available from a given output-transistor configuration and load impedance. The maximum possible voltage output is determined by the amplifier's internal DC power-supply voltage, which must not be allowed to exceed the transistors' allowable maximum levels. There is also a limitation on the peak current that can be drawn by the load, which also must remain within the transistors' rated operating range. The continuous power output (the product of the voltage and current) and the heat dissipated by the transistors must also be considered, but these are related to long-term operating conditions and are normally much lower than the peak levels.

    In conventional amplifier designs, a choice has to be made between the maximum current-out-put and maximum voltage-output capabilities of the amplifier, as they relate to the load impedance. In order to develop 200 watts into an 8-ohm load, say, the maximum voltage must be 40 volts RMS combined with a current output of 5 amperes. For 200 watts into a 4-ohm load, only 28.3 volts is required, with a current of just over 7 amperes. If, however, a 40-volt maximum output is delivered into 4 ohms, the load will draw 10 amperes, corresponding to 400 watts- well beyond the amplifier's design limits and probably those of the speaker as well. On the other hand, if an amplifier designed to drive 4-ohm loads to 200 watts is terminated in an 8-ohm load, it will only be able to supply 100 watts output."
    Lsi15, Lsi9, LsiC,Rta11t,M5jr+,M4, SDA SRS 2.3TL, Rti6....Still listing stuff, a work in progress.
    B+W-Sold
    Electro Voice EV-SIX
    Infinity-Sold
    Advent-Now gone
    Yamaha A-S801
    Yamaha RX-V377
    Yamaha RX-A860
    Yamaha RX-A3060
    Harman Kardon Hk-350i
    Harman Kardon Hk-........
    Harman Kardon PM-665
    Harman Kardon HK-775
    Pioneer.......Stereo Receiver

  • ZLTFULZLTFUL Posts: 5,201
    Instead of just copying and pasting, could you *PLEASE* cite your sources with a link at the very least?
    "Some people find it easier to be conceited rather than correct."

    "Unwad those panties and have a good time man. We're all here to help each other, no matter how it might appear." DSkip
  • mhardy6647mhardy6647 Posts: 24,059
    edited January 7
    Well -- whatever the source... it is true (and pretty much a given) but the only real endpoint there is output power, which isn't the be-all and end-all of amplifier performance. The quote fails, I would opine, to support the earlier claim that an amp will "work less well" into 8 ohms as opposed to 4 ohms (see below).

    Most (direct coupled) amplifiers will "work better" into a higher impedance load in that they will run cooler, if nothing else. "Less output power" is even a little misleading, since, e.g., 2.83 VAC is 1 watt into 8 ohms, but it is 2 watts into 4 ohms (3 dB different). The difference, of course, being the amount of current flowing through the load in the two cases.
    As to distortion -- not many amplifiers anyone uses any more have audible amounts of harmonic distortion, at any rate... and any they do produce is dwarfed by the harmonic (and other) distortions produced by any conventional radiator loudspeakers. :|
    K_M wrote: »

    85-90 to me is fairly loud.

    About the "High current" amp thing, an amp can really only be designed to operate most efficiently into a small range of impedance.

    So if it is designed to work great into 4 ohms for instance, it will work less well into 8 ohms and even less well into 16 ohms for instance.

    Now very few speakers are ever 16 ohms to begin with, but many speakers will have a low impedance in one part of the range, but then rise to 6 to maybe even 12 or more ohms at higher frequencies.

    The compromises are Heat, distortion, and lower output at certain impedances or frequencies.
    So while the 4 ohm rated amp will be great at ranges where the speaker is actually around 4 ohms, (bass usually) it will not be as great where the speaker rises to 6-12 ohms higher in frequency.(higher frequencies or speakers that are NOT 4 ohms in the bass)

    In other words there is no magic or free lunch, its either good at low impedances or good at higher impedances, but can not be great at both.



  • K_MK_M Posts: 1,617
    edited January 7
    mhardy6647 wrote: »
    Well -- whatever the source... it is true (and pretty much a given) but the only real endpoint there is output power, which isn't the be-all and end-all of amplifier performance. The quote fails, I would opine, to support the earlier claim that an amp will "work less well" into 8 ohms as opposed to 4 ohms (see below).

    Most (direct coupled) amplifiers will "work better" into a higher impedance load in that they will run cooler, if nothing else. "Less output power" is even a little misleading, since, e.g., 2.83 VAC is 1 watt into 8 ohms, but it is 2 watts into 4 ohms (3 dB different). The difference, of course, being the amount of current flowing through the load in the two cases.
    As to distortion -- not many amplifiers anyone uses any more have audible amounts of harmonic distortion, at any rate... and any they do produce is dwarfed by the harmonic (and other) distortions produced by any conventional radiator loudspeakers. :|
    K_M wrote: »

    85-90 to me is fairly loud.

    About the "High current" amp thing, an amp can really only be designed to operate most efficiently into a small range of impedance.

    So if it is designed to work great into 4 ohms for instance, it will work less well into 8 ohms and even less well into 16 ohms for instance.

    Now very few speakers are ever 16 ohms to begin with, but many speakers will have a low impedance in one part of the range, but then rise to 6 to maybe even 12 or more ohms at higher frequencies.

    The compromises are Heat, distortion, and lower output at certain impedances or frequencies.
    So while the 4 ohm rated amp will be great at ranges where the speaker is actually around 4 ohms, (bass usually) it will not be as great where the speaker rises to 6-12 ohms higher in frequency.(higher frequencies or speakers that are NOT 4 ohms in the bass)

    In other words there is no magic or free lunch, its either good at low impedances or good at higher impedances, but can not be great at both.




    Nothing has unlimited current and voltage.
    Transistors have a limited voltage range they operate with also.

    So if the power supply is designed for one voltage and ideal with a certain impedance range, it can not by design be ideal for another impedance range, unless the power supply voltage is altered, either to be higher or lower.

    As someone above hinted with something similar with Tube amps, the only ideal way to have it work well with low and normal impedance loads, is to have a dual voltage power supply. (tubes do it differently of course)


    Some amps have this ability, but not common.
    Higher voltage at 8 ohm loads
    Lower voltage with 4 ohm loads.

    I never said it was the "End of the world", but on a forum, where many claim "Everything matters" ....

    Lsi15, Lsi9, LsiC,Rta11t,M5jr+,M4, SDA SRS 2.3TL, Rti6....Still listing stuff, a work in progress.
    B+W-Sold
    Electro Voice EV-SIX
    Infinity-Sold
    Advent-Now gone
    Yamaha A-S801
    Yamaha RX-V377
    Yamaha RX-A860
    Yamaha RX-A3060
    Harman Kardon Hk-350i
    Harman Kardon Hk-........
    Harman Kardon PM-665
    Harman Kardon HK-775
    Pioneer.......Stereo Receiver

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