speaker excursion..."mo power"..and bass..Sean


I'd be interested in everyone's thoughts, but hopefully Sean will chime in...

Some reading I've been doing & the "is 22 watts enough" discussion has raised a question in my mind. I'll use the Linkwitz Orions as the example, but the real questions will (should?) apply to powering most any driver.

I've been reading Linkwitz's site on the Orions, some of the theory, what it takes to build them, suggested power..etc...and I remember some post that I read in the A-gon or AA archives stating that the 60 watts Siegfred suggests isn't enough to give significant bass. I read on the SL site that he likes the 60 watts as the amp will clip just before the speaker can reach full excursion & thereby the driver will not sustain damage. He continues to state that the higher power amp he suggests (a larger ATI) will result in the driver reaching full excursion prior to the amp bottoming out & thus driver damage may result.

>Proponents of "lower is plenty" might be, at least conceptually, in line with the needed power to reach a driver's maximum excursion (almost by defintion) being all the power necessary.

>Then comes the "more power, preferrably gobs more clean power" crowd that says more power is the best in most applications.

So my question(s):

>Is the difference between these two camps just "time"(instantaneous versus continuous power)? i.e Lots of mostly unused power sitting "idle" as a reserve for the couple millisecond demand of those dynamic peaks?

>From what I've read the SL Orions do very, to exceptionally, well on bass even with the 60 watts. How would 200 watts instead of his 60 improve the bass if the drivers bottom out at a little over 60 watts? Is it again just the millisecond peak demand for power that would be available or is there another reason?
fishboat

Showing 1 response by drew_eckhardt

The clipping of a low wattage amplifier frying tweeters is a myth. A square wave is the sum of a sine wave plus all of its harmonics with amplitude 1/n. The third harmonic has barely 1/10th the power of the fundamental. Real world numbers are even better. Music has a disproportionate amount of power in the bass range so those notes clip first. With a low tweeter cross-over like 1440Hz as used in the Orion the tweeter won't see anything from a clipped 200Hz tone until the 7th harmonic which is 17dB down from the fundamental. More typical cross-over points will result in even less energy reaching the tweeter.

When you're clipping bass notes increasing the volume setting can't make them any louder. Unfortunately this does increase the high frequency energy to far beyond what you have with music. Speakers designed with some level of power handling for music can handle a lot less when all of the energy is at high frequencies. You won't have problems if you don't act like a drunken teen ager who insists on turning up the volume on a distorting system.

The SPL from a speaker is a simple function of the air it displaces, which is a function of excursion, which is proportional to the drive voltage. When you increase sensitivity you move more air with less voltage. When you're limited by excursion more power isn't going to get you any more peak output.

I built and own a pair of Orions.

Since they're active speakers and don't need to pad down higher sensitivity frequency ranges to match the least sensitive, sensitivity can vary with frequency.

The variation is radical as a consequence of driver count differences (two low frequency drivers get you a 6dB sensitivity increase), radiation space changes (there's a full to half space transition from 200 - 100Hz which gets you another 6dB at 100Hz and below), dipole roll-off at 6dB/octave, and the extremely low Q woofers (about .2 before equalization, loosing 14dB at their resonance arround 20Hz). Dipoles also don't need baffle step compensation which can cost a conventional monopole designed for free space placement 5dB in sensitivity.

At 80Hz woofer sensitivity is about 97dB/2.83V/1 meter. If you drive them with amps producing 60W into 8 ohms on the verge of clipping you'll get 114dB out of them. A 150W amp would get you to 118dB, although midrange excursion/power is going to limit how loud you can play without loosing hi-fi distortion characteristics.

Things would be different on paper with most passive speakers. At a not atypical 87dB/2.83V/1 meter you'd need 600W for the same bass output and a more sensitive 90dB/2.83V/1 meter would take 300W. But you don't need the same volume - a 60W amp would still get you 105 and 108dB from such speakers. Solid state amplifiers give you enough wattage that power isn't a problem in most domestic situations.

Orion sensitivity and maximum output are low in the last octave although that doesn't matter because there's little musical content and the the equalization is 6dB down at 20Hz.