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Knowing how many watts a speaker needs to sound it's best?

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  • Knowing how many watts a speaker needs to sound it's best?

    I read a lot of threads where one would say "to get the most out of this speaker, it takes a good amount of power to drive it" or "it dosen't take much to drive this speaker'. What specs do I need to look at to determine how many watts I should provide a given speaker?

  • #2
    Sensitivity.
    "I just use off the shelf textbook filters designed for a resistor of 8 ohms with
    exactly a Fc 3K for both drivers, anybody can do it." -Xmax

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    • #3
      Mastering engineers (typically) set their meters so 81db from a single monitor is 0db at their console. So basically the loudest passage on a track is going to play at 81db on a single one of their monitors. Up to 84db because they’re mostly mixing two channel.

      With many speakers, you can achieve this with about a watt.

      Twice as loud would take about 10 watts.

      Much louder than that and you’re really limiting listening time as hearing damage happens much faster.

      81-84db is fairly loud and you can listen all day without hurting your ears.

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      • #4
        "Watts" It's often surprising how little you usually need if the amp is of good quality (good power supply). Small inefficient (low sensitivity) speakers usually can't take much power before running out of xmax. The most power hungry would be big inefficient speakers used at a good distance from the listening position because SPL drops quite a bit over distance.

        If the impedance drops low, especially in the lower frequencies, that's when you need an amp with a good power supply.

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        • #5
          When they say a certain speaker needs a good amount of power ask them to explain with further context. At present, I have 86db speakers next to me with 60 watt power ratings. They are connected to a 25 watt Class-D amp. I used a voltmeter to measure as I turned the amp down below maximum 25 watt power. The speakers are loud to my ear. Context: I don't like loud music and I'm sitting close to the speaker. I have different speakers with the same ratings except a larger cone diameter. They aren't as loud on the same amp. Context: I'm playing the larger speakers at a lower frequency without an enclosure.

          Without context, a lot of those general statements you've read are not helpful because your goals and equipment might be totally different from their goals and equipment. For example, people who prefer low power tube amps, linear power sources, and like to listen at live concert loudness levels are very concerned with speaker sensitivity. They only have a little bit of power and they're trying to listen to loud music so they need high efficiency (high sensitivity) speakers. In contrast, pro-audio people might have high powered amps but still need high sensitivity speakers because they're trying to supply a certain style of sound to a large event area.

          The key is to know your goals might be different from the goals of other people posting speaker comments. And, honestly, some people say things because they're repeating what they've heard from other people. If you ask for context you might find out they don't understand why they said what they said. Which is great because both of you get to learn something new in that case.

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          • #6
            Ii wasn't really speaking of loudness, or how loud a certain speaker will go with a certain amp. I was asking why such and such speaker sounds better driven by a 100 watt amp vs a 25 watt amp, but at the same volume level. Example: My Harmon Kardon 30 watt receiver driving my 8" 2 ways did not sound nearly as good (or punchy) as with my Realistic 100 watt amp. Now I have a Old Sony 65 watt receiver from 1972 and it sounds great still, but the HK, just didn't have it, even though it was a good receiver.

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            • #7
              Your old amplifying equipment could be very problematic. Do you have any new amps?

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              • #8
                Watts on all amps are not always equal .When I was much younger I had a pair of Altec Lansing voice of the theaters in my bedroom . I was driving them with a Marantz 1060 amp ( actual power output about 35 watts per channel . These speakers could be driven by a boom box to ear splitting levels .I could get all the volume I wanted out of them . Then a friend brought over a McIntosh 100 watt per channel tube amp and hooked it up . What a difference in sonic quality .even though I didn't need any more power than I had before the sound was more detailed especially on the bass . I think it was the larger surplus of power and a higher quality amp makes a difference . .

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                • #9
                  Originally posted by breadfan View Post
                  I was asking why such and such speaker sounds better driven by a 100 watt amp vs a 25 watt amp.
                  Dynamic headroom.

                  www.billfitzmaurice.com
                  www.billfitzmaurice.info/forum

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                  • #10
                    Originally posted by djg View Post
                    Your old amplifying equipment could be very problematic. Do you have any new amps?
                    All of my old equipment is in very good shape. Like I said, the Realistic 100 watt and the Sony 65 watt pushed my 2-ways fine, it's the 30 watt I HK that had the problem. My reason for the question is mainly because I want to be able to drive my new speakers in my car, so I an debating on what head unit, watts, if I'll need a couple of amps, ect. ect. I was only using the example of my other receivers because that's all I have to compare. My other receivers are not the issue, they work fine, sound fine.

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                    • #11
                      Originally posted by billfitzmaurice View Post
                      Dynamic headroom.
                      Thank you. Makes a lot of sense. So to be safe, just go with as much power as the speakers will handle.

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                      • #12
                        It takes double the amplifier power to play +3dB more. Being a logarithmic scale, you can see how this quickly eats up available watts. double the volume is +10dB and this is 10 times the power.

                        Dynamic headroom is about having enough watts to hit peaks without clipping. +10dB headroom is often quoted as a minimum - but this really depends on the music content.

                        So here is a practical example. Say you have a speaker with 86dB average sensitivity per 1 watt of input. If you like to listen at an average of 92dB - you need 4 watts of power. Now, say this music contains peaks at 102dB - you need 40 watts of power to play this cleanly without clipping and risking damage.

                        So more efficient speakers will require less power to drive them to the same SPL.

                        Lower resistance speakers (4 ohm nominal) typically are more sensitive, but they draw more current. This is sometimes referred to as "hard to drive" - due to low load.

                        The above only focusses on thermal power handling. Excursion power handling is another consideration.

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                        • #13
                          Originally posted by breadfan View Post

                          Thank you. Makes a lot of sense. So to be safe, just go with as much power as the speakers will handle.
                          and then multiply x 4 especially if you like to turn up that bass "knob". Loud bass reproduction consumes a lot of power. That is why I use 4 Peavey CS-800X amplifiers to drive my bookshelf speakers.

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                          • #14


                            Maybe head units have changed from my days of car-audio, but a 50 watt per channel rated head unit has little on a 'good' 50 watt amp. I say 'good' 50' watt amp because a lot of companies like to stretch their ratings. As an example of both extremes; the last Pioneer ($500+) head unit in my old truck output a claimed 50 watts x 4, the speaker wires originating from the unit's pigtail were absolutely tiny as was the input power + and - wires. Instead of using the head unit, a 50 watt, (or was it 25?) Orion hcca 225 was used to drive the front mains (250hcca for the subs), the speaker out wires (yes it had wires) were around 12 gauge and I think the the + and - power input wires were closer to 8 gauge.

                            No comparison.

                            This is just an extreme example as I would guess the head might output maybe 15 real watts (way overrated) while the orion hcca 225 is known to output around [email protected] ohm (or was it 1 ohm) with a huge amp draw (way underrated).

                            Look really close at the ratings and even then take them with a grain of salt.



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                            • #15
                              It's been forever since I looked for a car stereo. Today, I think I'd buy an amp and a 3.5 mm jack. And a DSP + bluetooth input if I still had budget.

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