Speaker Stories

    Choosing New Speakers: Power-Handling Considerations

    Issue 153

    In Part Two of this series (Issue 149), we examined the reality that accurate speaker sensitivity ratings have a direct bearing on how suitable the ratings may be when considering varying room sizes and the listener’s distance from the speakers. We also looked at power requirements for driving speakers sufficiently for those respective room sizes. A speaker with a higher sensitivity will produce a greater perceivable volume at a fixed distance and amount of power than one with a lower sensitivity.

    Bigger rooms may require more power to be delivered to the speakers in order to achieve the same volume, due to a greater distance to the listening area than would be necessary in a smaller room with a shorter listening distance from the speakers.

    Many audiophiles know and appreciate these facts. Some will decide that what they want are speakers with high sensitivity, regardless of room size. It’s a way to maximize the performance and value of your power amplifiers. Why so? Because it affords more headroom from our power amps, which do not have to work so hard with speakers that are more sensitive. A smaller room is also “kinder” and less demanding of a power amp when paired with high-sensitivity speakers than if the speakers are used in a larger room.

    Sometimes, when looking at buying a speaker, certain specifications are not readily made available to us, even something as seemingly fundamental as a frequency response graph. Instead, we are just provided with, for example, a frequency response spec of, say, 41 Hz – 30 kHz +/-3 dB. In its own right, this is not hugely informative about what our speaker is capable of, let alone tell us anything that is all that informative about the speaker’s sonic qualities. One could say that this spec basically states that it is a working speaker, functioning within basic parameters, and nothing more!

     

    Frequency response measurement of a woofer. Courtesy of Wikimedia Commons/Oliokia.

    Frequency response measurement of a woofer. Courtesy of Wikimedia Commons/Oliokia.

     

    Let’s make sure that we have the correct amount of amplifier power for our needs in the first place.

    Variations in power (and volume) can alter the tonal balance and frequency response of the speaker. (This is on top of the fact that different speakers will have different frequency responses and this too can be part of their tonal character.) We often see 2-way and 3-way loudspeaker designs where the frequency range is split between the bass/midrange and tweeter, or bass, midrange and tweeter drivers. As varying amounts of power are put through the drivers in a speaker, so too, the character of the sound may vary at different frequencies. The different drivers exhibit variations in their audio character as a result of their construction – driver and spider materials, magnets, voice coil/motor design, cabinet colorations and other factors.

    An example may be that of a speaker cone which physically changes its shape as it is subject to more power being put through it. As such, it may vary in its measurable frequency response for a given frequency and volume, to say nothing of intermodulation distortion, where two or more signals are played together. These types of effects are reduced and made less noticeable in speakers with good-quality crossovers, drivers and cabinets, and which integrate and time-align everything well.

    There is another advantage to mating high-sensitivity speakers with higher-powered amps: this provides more headroom, or power in reserve, that is available to feed our speakers’ demand to respond dynamically to the program material. Again, many of us may already appreciate and understand this, but just how much headroom do we actually need, and is it really that important?

    Imagine the following typical scenario: You purchase a 100-watt power amp that is able to give you a nominal/rated 100 dB sound pressure level, and connect up your stereo speakers which are rated at 85 dB sensitivity. (Typically, the manufacturer will not stipulate at what distance the power amp will deliver those 100 watts. Instead, you may get a rating of how much power it will deliver to an 8-ohm-nominal speaker at 1 meter at 2.83 volts output. Not particularly helpful.) However, for a reasonably-sized room of 6,000 cubic feet, these would effectively now have a 75 dB sensitivity at a typical listening position. Good-quality speakers will handle a peak of about 20 dB above their nominal rating, so for short bursts, the speaker should handle 105 dB output. But, what about your 100-watt power amp in such a situation? Suddenly it’s being asked to produce 5 dB more demanded of it than it can deliver, and as a result you either experience a very nasty audible distortion from the power amp clipping, or perhaps the amp switches itself off to protect its circuitry. Neither is a desirable outcome.

    If instead you now double the output of your power amp to 200 watts, you have increased your maximum SPL capability to 103dB, approximately doubling of sound intensity (though keep in mind that a 10 dB increase is necessary for the sound to be perceived as twice as loud). Even now, you are still two dB shy of being able to comfortably handle the 105 dB peak or burst. If you again double the power to 400 watts, your power amp is only now capable of outputting 106 dB, or in other words, just 1 dB of headroom when it comes to handling bursts of peak output volume.

    Need power? The Constellation Audio Hercules II monoblock amplifier can deliver 1,100 watts into 8 ohms.

    Need power? The Constellation Audio Hercules II monoblock amplifier can deliver 1,100 watts into 8 ohms.

     

    The point of the example is to illustrate the advantage of considering buying higher-sensitivity speakers that can actually deliver the peaks they may be subjected to, without subjecting the power amplifier to demands it can’t meet. When playing in larger rooms that necessitate more powerful amplification to cover larger distances to the listening position anyway, this makes consummate good sense, but perhaps your setup would benefit from a larger power amp than you may have initially considered was adequate anyway, if you wish to avoid amplifier clipping and possible damage of your equipment.

    If you are generally listening at lower volumes, then these considerations may not initially concern you at all. However, if you want to optimally set up or calibrate your system to sound its best at reference volume levels (for example 75dB), with everything in proportional balance, (and in the case of a home theater/multichannel audio system, with the correct levels and speaker distances programmed into your A/V receiver), you may then actually enjoy it far more when played at much lower volume levels.

    But hang on a moment. We may have determined that more clean power is a good thing, but is it really the case that higher-sensitivity speakers can handle more power for dynamic bursts and peaks? If we assume that the answer to that question is yes, does this really help us answer the following which is still somewhat shrouded in mystery: “How loudly are my speakers capable of playing?” And, perhaps equally significantly, “How long might my speakers survive if they are subject to frequent peaks in output?”

    These are pertinent questions, because as many of us know, actual power delivery will often be vastly reduced when we run multiple speakers in a surround system of 5.1, 7.4, or larger. Selecting adequate power for your stereo system may be all that matters to many if not most readers, but it may be of equal or greater significance for those of us who use the same power amp(s) for both stereo and home theater in the same system. However you may operate your dedicated equipment, it would be good to know just exactly what demands we are putting on our systems and what their power handling capabilities truly are. Can anything help us make more informed choices in this regard?

    In a coming article we will consider some helpful information and new software that can assist us in demystifying this clouded question.

    Header image: Kaiser Acoustics Kawero Vivace loudspeakers. From the Kaiser Acoustics website.

    14 comments on “Choosing New Speakers: Power-Handling Considerations”

    1. Russ,

      Thank You for another great article. One thing I’d like to touch on when it comes to amplifier power, one of the most common reasons for speaker failure is overdriving your amp. Hopefully a reader or two can learn from this instead of the way I (and I’m pretty certain many others) learned-the hard and much more expensive way. When you overdrive an amplifier the resulting waveform is much more like a square wave and at the top and bottom where it clips you’re actually delivering a DC (direct current) voltage to your speakers instead of the nice pretty constantly changing sine wave they’re designed for. It doesn’t take much DC to destroy a speaker, especially tweeters with their very fine voice coil windings, woofers are more tolerant because of bigger diameter coil wire but they’re certainly not immune either. The old “crank it to 10 and rip the knob off” adage from radio DJs may as well have been coined by someone trying to sell speakers, or at least replacement drivers. Don’t think that pairing a low power amp with speakers rated to handle much more power than your amp will deliver can save your speakers either. I’ve seen a great many more speaker drivers with burnt voice coils due to an amp being asked to deliver more wattage than it can and clipping than I’ve seen drivers with burnt voice coils that were subjected to an amp much too powerful for them. So, keep your amplifiers at levels where they don’t clip and distort sound. Your speakers and your ears will thank you!

      1. Dear OHT,

        Firstly, thank you for your kind comments.

        I know what you mean about learning the hard way! When I was a teenager, I blew out the first three sets of speakers from my Ford Escort Mark I. I used to listen to them so loud all the time, I didn’t realise the exhaust was blowing. Passers by must have hated me bombing past disturbing the peace in my Signal Green machine blaring out!

        On this point though, many car power amps I treied were over badged on how much power they would actually deliver and no doubt contributed to the problem further. I never loaded the car with extra subs but I had upgraded the in door and parcel shelf speakers like many of us.

        However, valuable lessons were learned about the importance of quality amplification.

    2. Thanks for this series. I have a related question about sensitivity. Why do so many speakers of all size, configuration and driver design (cones, panels, anything but horns, I guess) end up at around 87 dB or so sensitivity? My Magnepans are 86. PS Audio’s new FR30 is 87. When I was building my first speakers to pair with an 8-watt Pass diy amp, over and over again the drivers I looked at checked in at about the same narrow range of 86-88 dB. You’ve emphasized how 3 dB represents a doubling of power, so maybe I don’t fully appreciate just how much a 3dB difference in sensitivity represents.

      1. That’s a really good question. I’ll have to ask some speaker designers.

        I’ve never done an A/B comparison with high-end speakers, efficiency, and perceived loudness, but I’ve done it with guitar amp speakers, and I can tell you there’s a really big difference in volume output between a roughly 93 dB-efficient speaker and a 101 dB (approximately) speaker. In the former case I could crank the volume of a 20-watt (more or less) amp up to 10 and it wasn’t all that loud, subjectively. It sounded glorious (in tube guitar amps, distortion is a good thing), but was unusable at gig volumes. When I put the 101 dB speaker in, the amp became, for want of a technical measurement, ungodly loud. I could barely turn the amp up past about 2 before hitting ear-ringing level.

      2. Hi jfuquay,

        Thank you for taking the time to comment!

        One point of view is that 87dB will deliver far more than adequate volume for many listeners in many domestic situations where the seated listening distance is also more typical of a home seating situation. It is something of a sweet spot in output that will cater for many perfectly well. You may sit up to about 4 meters away before you lose 12dB to the room, dropping your listening volume to 75dB.

        Also, listening to music above 85dB for prolonged periods of time has been shown to greatly contribute to hearing loss.

        You may find the previous articles referred to in the series of further help from issues 147 and 149 respectively:
        https://www.psaudio.com/copper/article/choosing-new-speakers-what-information-is-helpful-part-one/
        https://www.psaudio.com/copper/article/choosing-new-speakers-sensitivity-and-room-size/

        In issue 149 we talk about handling peaks and burst output further.

    3. I had been driving a pair of Klipsch RF-82 speakers with a Sony STR-DA5400ES A/V receiver, which is rated at 120 watts per channel. I recently upgraded to a McIntosh C2700 tube preamp and MC7300 amplifier, rated at 300 watts per channel. The speakers are the same and in the same location as before, but the increase in sound quality is stunning. The sound is more balanced, there’s less distortion and there is now a large sound stage. At the time I acquired the Sony, it was considered to be the top of their line. I can’t tell you why the McIntosh system is so superior, maybe it’s the increase in power. In any case, it’s the best thing I’ve done for my system in years. I’ve started the search to find a matching amp so I can configure them as mono blocks at 600 WPC.

      1. Hi Jack,

        Thanks for your comments. It sounds like you have an excellent set-up!

        I mention in the article: Good-quality speakers will handle a peak of about 20 dB above their nominal rating, so for short bursts, the speaker should handle 105 dB output.

        May I ask what listening distance and deisred volume level you would like to listen to your speakers?

        Your Klipsch have an excellent sensitivity rating of 98dB. Sitting 11 feet from your speakers, at 85dB you still have 20dB headroom (105dB) while running your amp at approx. 60 watts.

        Speakers love power, and now that you have more than doubled (approx. 2.5x) the nominal rated power from the Sony 120 to 300, your speakers are fulfilling more of their potential with greater ease. The quality of the power transformers and output stage of the MC7300 will be far superior to the A/V unit. Adequate space for the transformer, heat sinks and amplifiers is highly competed for within A/V design as it supports more channels. Your McIntosh is a dedicated powerhouse which your speakers will thank you for, and as you have noticed, a great jump in performance for your investment.

        1. Hi Russ,

          That day was a bad eye day so I wasn’t wearing my contacts. Looks like I brain farted the switch that says meters / feet. We get numbers a little different from those today. To answer your question 9 – 11′ depending on how the Stressless is reclined / positioned. SPL of 75, efficiency of 97 dB, headroom 30 dB were my numbers. But the bust was meters, not feet. Still, despite being deaf above D8, the difference is amazing and I’m jumping in with both feet.

          My environment is a little strange. Behind the listening position and slightly to the right is a door into the kitchen. The left rear corner is a stairway, a hallway and an entrance to the dining room at a 45 degree angle, so the room sucks a lot more power than you would think. Both the stairway and the hallway have sharp slap echos that last forever, but that’s another day.

    4. This calculator is quite useful. This article was good, but kind of missed the point.
      The point is that for any system to be able to reproduce live music, it must be capable of at least 105dB peaks (85+20 headroom).

      Getting into how easy speakers are to drive is important, but most systems won’t cut it even based on speaker manufacturers quoted sensitivity!

      http://www.mh-audio.nl/Calculators/REAP.html

      1. Thanks for the calculator lrj. The MC7300 says I’m normally running 60-watts per channel just for casual listening. The calculator says that, after throwing some rough numbers at it, I need 511-watts to stay out of clipping. I’m sure that’s all approximate, but I’ll bet clipping was a big part of the problem.

      2. Hey, that is interesting. I used my dB app to learn that about 70 dB is a pretty high volume for me. So my Rogue Sphinx, at 200 watts into 4 ohms, gives me 100 dB at 114 watts, piece of cake! (I turn the Sphinx volume to 3 o’clock and use my DS DAC’s gain cell as the volume control when streaming or playing CDs. I just really need to remember to dial it back when I switch to vinyl, but that needle drop always reminds me if I haven’t.) thanks again.

    5. Right. Room reflections will help, which are not included in the calculator, so it’s not perfect. But if you have sufficient power based on the calculator you’re gold!
      Many amps will distort as they near their rated max output, which is another thing the calculator doesn’t take into account. So just because you need 1000W and your amp can deliver 1000W (at the rated impedance), doesn’t mean it is delivering 1000W without a lot of distortion. But with the room effects, it hopefully balances out?

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