Axiom Home Page Forums General Discussion Home Theater Double Blind Test

Founder of the Bas Pro Shop, he discovered that lakes are flat.

Yeah, Adrian; I heard that he also claimed to be a descendant of St. Columba.

Adrian, driver size wasn't part of the discussion, so no "counter-intuitive" factor in that respect should have been suspected. The point was equal power used with a given speaker when playing a note within its designed capability at a given sound level, regardless of frequency. It's entire possible that a 12" driver would be less sensitive than a 4" mid-range(or a 1" tweeter). If that was the case and those drivers were used in the same speaker, the more sensitive drivers would have to have their output attenuated so that the speaker would have level response over its designed frequency limits. This can be done with an attenuation network at the end of the crossover consisting of a resistor in series with the more sensitive driver and another resistor in parallel(so that the impedance of the driver isn't changed).

Sound power is a given quantity which doesn't vary with frequency. For example, an acoustic(not electrical)watt of sound power output by a speaker results in about a 112dB sound pressure level at the standard 1 meter measuring distance. Frequency isn't a factor. If the particular speaker used 1 watt of electrical power and the measurement at 1 meter was 92dB, since this was 20dB down from the full 112dB, the efficiency of that speaker in converting electrical power into acoustic power is about 1%. Typical speakers with sensitivity ratings in the upper 80s of dBs are another 3dB down and are therefore about 1/2% efficient.

Hey Zimm. All you horse flogging has caused me to take a closer look at what I was posting. Johnk is, of course, correct (big surprise). I promise to stop making generic low = more power statements.


Design both of the driver and the box does have a lot to do with how efficiently the sub delivers its bass. All the really big drivers I have seen used in the DIY world seem to need a lot of power for the really low notes. I think it has to do with needing a big motor assembly to reach the high excursion needed to produce those sub 20Hz notes and still maintain linearity as the driver approaches it maximum extension. The big pro drivers seem to trade off low end extension for efficiency and headroom higher up.

Sealed designs rely on eq boost and room gain to maintain linearity. That can take a lot of power. Horn loaded designs seem to rely on gain from the box to increase efficiency.

That's all true. I'm guess I'm just confused by the real world seating position sound versus the math. If it requires big motors, and big boxes, and if room effects dampen bass after the one meter measure, etc., etc., then the math seems off in application. But I don't presume to know the whys, just the purchasing needed to get the sound to the seat. I've had very nice sounding 30w speakers. But, in my experience, when you want to get realistic bass, and mid-bass, you "need" amps with more power, even if the driver stays the exact same.

All B.S. (mine ) aside, I'd love to find out that a good 50 watt amp could drive my home or car system to reference levels (loudish). I get that most sound can be made with under 100 watts (hell, tweeters scream with 20) but that whole bass thing just throws me off.

Not unlike the farmer who walked his "flat" field a million times and had trouble believed he was walking up hill his whole life, I guess.