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

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Comments

  • mhardy6647
    mhardy6647 Posts: 32,929
    edited January 2020
    heh... some of us use impedance matching devices. :)

    67zt4gril9du.png


    ...besides...

    Since very, very few loudspeakers present flat and unvarying impedance loads (as a function of frequency) to an amplifier (Some Magneplanars* have been pretty close) -- close enough... is close enough. Corollary: The perfect is the enemy of the good.


    * The Magneplanar MG1.6/QR illustrates this.
    https://www.stereophile.com/content/magnepan-magneplanar-mg16qr-loudspeaker-measurements

    7osjvro9c9hc.png
    Its impedance (fig.1) is basically that of a 4.5 ohm resistor, modified by the crossover, which results in the peak at 600Hz. Any good 4-ohm-rated amplifier should be able to drive the Maggie without difficulty. There are no cabinet resonances—the MG1.6/QR doesn't have a cabinet.
  • mhardy6647
    mhardy6647 Posts: 32,929
    ... here's a more perfect example of a resistor-style load in the real world of loudspeakers (also a Magnepan product)...

    wfdtkwszrwqe.png

    https://www.stereophile.com/content/magnepan-lrs-loudspeaker-measurements

    ... but most loudspeakers feel more like this to the poor amplifier...

    5976eg2avrai.png

    https://www.stereophile.com/content/polk-lsiiim703-loudspeaker-measurements
    The electrical impedance (fig.1, solid trace) remained between 4 and 7 ohms over most of the audioband, but dropped to 3 ohms at 125Hz. There is also an awkward combination of 4 ohms and –47° phase angle at 90Hz, a frequency where music can have considerable energy. Polk specifies the LSiM703 as being "compatible with 8 ohm outputs," but I suggest that a good 4 ohm–rated amplifier or receiver would work best with this speaker.
  • maxward
    maxward Posts: 1,491
    Late to this thread, but it’s a good one. I’m a little reminded of a button one of my former coworkers would occasionally wear: We have charts and graphs to back us up, so f*** off. And speaking of math, remember this wise quote, “Fifty percent of the game is half mental.” (Y. Berra)
  • shs
    shs Posts: 105
    Would someone want to comment on Class D amplifiers in these respects? There is much less power "wasted" in the transistors in those amps.
    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.
  • mhardy6647
    mhardy6647 Posts: 32,929
    edited January 2020
    Class D (pulse width modulation) amplifiers (which aren't a new thing at all, BTW) are extremely electrically efficient. Basically, they use transistors as what they are good for -- switches. The "problem" with them is that they generate large amount of high frequency (as in ultrasonic, all the way into radio frequency) noise, which must be dealt with by
    filtering of various kinds... and which can cause interference with other (analog) signals.

    This being said, even the really cheap ones today sound pretty good, and the better ones can sound quite good.

    They probably are the future of hifi as more and more territories demand ever-more energy-efficient electronic components.

    7promj7we4u9.png
    https://www.maximintegrated.com/en/design/technical-documents/app-notes/3/3977.html
  • mhardy6647
    mhardy6647 Posts: 32,929
    edited January 2020
    Early PWM audio amp (ca. 1965) offered as a kit by Sir (eventually!) Clive Sinclair :)

    38n9ulxjcx9q.png

    http://www.vk6fh.com/vk6fh/sinclair x10.htm

    EDIT: and the X-20 in 1967 :)

    5fk5ujnj8z7o.png

    source: r28usxb85fn6.png
    (page 72 of the magazine, which is page 64 of the PDF)

    Post edited by mhardy6647 on
  • mhardy6647
    mhardy6647 Posts: 32,929
    anonymouse wrote: »
    Clive Sinclair was like the Elon Musk of his time.

    Yeah... kinda... he aimed a lot lower, though.

    Remember the Timex/Sinclair $99 computer?
    I do.

    se0poq9k36of.png
  • daddyjt
    daddyjt Posts: 2,307
    I remember when I used to worship at the altar of stats...

    To illustrate my point on why stats don’t tell anywhere near the whole story, take the photo below. The amp on the left is rated at 380wpc @ 8Ω. The one on the right is rated at 100wpc @ 8Ω. Guess which one sounds better...?

    yuzpvbl6i65y.jpeg
    "Conservative Libertarians love the country, progressive leftists love the government." - Andrew Wilkow


    “Human beings are born with different capacities. If they are free, they are not equal. And if they are equal, they are not free.”
    ― Aleksandr Solzhenitsyn

  • gp4jesus
    gp4jesus Posts: 1,969
    Reminded me of a NAD*/Rotel** THX shootout, both ~$600 (Stereophile Nov ‘92).
    100 WPC vs 120 WPC RMS.
    NAD’s dynamics’ specs 370WPC/8ohms in stereo
    Rotel’s 😢.

    I don’t have the all reviewers “sound” notes, missing the NAD’s entirely. I’m not anti-NAD - all my first system was NAD. I still have a working 3020.

    When it came to the bottom line (sound quality): IIRC their strong points were
    NAD - grace under pressure*, but never great
    Rotel - finesse until just past its spec’s limits
    *never too fussy regardless of load

    Something to think about. Tony

    PS: If you find the above article on-line, feel free to correct me
    Samsung 60" UN60ES6100 LED Outlaw Audio 976 Pre/Pro Samsung BDP, Amazon Firestick, Phillips CD Changer Canare 14 ga - LCR tweeters inside*; Ctr Ch outside BJC 10 ga - LCR mids, inside* & out 8 ga Powerline: LR woofers, inside* & out *soldered LR: Tri-amped RTi A7 w/Rotels. Woofers - 980BX; Tweets & “Plugged*” Mids - 981, connected w/MP Premiere ICs Ctr Ch: Rotel RB981 -> Bi-amped CSi A6 Surrounds: Premiere ICs ->Rotel 981 -> AR 12 ga -> RTi A3. 5 Subs: Sunfire True SW Signature -> LFE & Ctr Ch; 4 Audio Pro Evidence @ the “Corners”. Power Conditioning & Distribution: 4 dedicated 20A feeds; APC H15; 5 Furman Miniport 20s *Xschop's handy work