February 2021

It's All In The Timing
Roger Skoff writes about one seldom-discussed audio essential.
Article By Roger Skoff

  Years ago, after I had designed my first super-high-end power cable and was testing it prior to bringing it to market, I had a truly strange experience: Changing the power cord on just the amplifier driving my main speakers gave me what sounded like at least another half-octave of deep bass response from my sub-woofers, even though I had made no change at all to the amplifier driving them!

The system I was running at the time was very similar to what I'm still using as one of my systems, even today: Various signal sources were all connected through a Jeff Rowland Design Group preamp, to a Jeff Rowland amplifier driving a pair of Acoustat 1+1 electrostatic speakers running full-range down to a 6dB per octave crossover at 80Hz and a pair of separately-powered subwoofers taking over to run the rest of the way down to below 20Hz. Because the subwoofer amp had its own built-in power cord that couldn't be changed, the only amplifier power cord comparative testing I could do was with the Rowland amp, which, like most better high-end electronics, was fitted with a quick-change IEC power connector on the back of its chassis.

When I changed the Rowland's power cord from the one that I had been using to the new one that I had designed, I was pleased to hear the improvements that I had hoped and planned for. There was also something else, though, about the amplifier's sound with the new power cord that came as a complete surprise to me: Not only was there greater clarity and detail across the range of the main speakers, but the subwoofers – driven by a completely different amplifier that still had its original factory-installed zipcord rubber power cable and molded-on wall plug – sounded better, too!

Frankly, my first thought was that it was an illusion. Either that or the dread "placebo effect." You know -- where they claim you hear what you expect to hear instead of what's actually there. The problem with that, though, was that I hadn't expected to hear it. The new apparent bass increase was sufficiently interesting and sufficiently different that I called other people in to listen, just to verify that I wasn't imagining it. They heard it, too. So, what could it be?

Rise time.

The new power cord on the Rowland amplifier had improved its rise time in (at least) the frequencies that constitute the harmonics of those put out by the subwoofers. That had effectively increased the "attack" of the bass transients, and that was what had given the bass more "punch" or "slam" (like the kick of the kick-drum), and made the bass seem louder, "cleaner", and deeper, all at the same time.

Wikipedia defines "rise time" as: "In electronics, when describing a voltage or current step function, rise time is the time taken by a signal to change from a specified low value to a specified high value." A better way to describe it might be to say that rise-time is analogous to drag-strip performance, only instead of a car or a bike getting up to speed in the shortest time possible, it's a speaker diaphragm that's ultimately doing the acceleration.

And, just as how quickly a dragster can accelerate is determined by how much power is available to move how much mass, so also is, at least by analogy, the rise time of a circuit or the movement of a speaker driver. And that's where this whole issue started – with a change of AC power cord changing one amplifier's effective rise time; with that allowing the amplifier to power a set of drivers to quicker acceleration in the upper bass and into the midrange; and with that quicker acceleration making the (separately-driven) subwoofers sound cleaner and deeper. (This, incidentally, was on woofers with anechoic chamber response already measured to be down only 3dB at 15Hz.)

How can that be? Simple:

Woofers – any woofer of any kind – have to move lots of air to be able to make bass frequencies at high volume. (Or even normal listening levels.) That means that their diaphragms either have to be large or there has to be lots of woofers in the system (or both). Large drivers, regardless of what they're made of, are always going to be more massy than small drivers, so it's always going to take more power to get them moving (or to stop them, but that's a different story), and, for any given level of power, they'll always have more inertia and get moving more slowly than smaller drivers. This slower rise time can, by "softening" or actually delaying the leading edge of the musical waveform, result in "muddy" and poorly-defined bass—which, just in itself, is a reason why some speaker manufacturers cross their designs over to a smaller, faster, driver (the mid-range, or sometimes even a "mid-bass" driver) at as low a frequency as is possible.

When you add one more factor, this all starts to make sense: Any sonic frequency at all, from any thing at all (not just music) has harmonics. Those are internally generated additional frequencies at twice, three times, four times, the original (fundamental) frequency, and so on; all the way up at diminishing levels of volume, that give a sound its distinctive characteristics. (Their different harmonic structures are why, for example, a violin and a clarinet playing exactly the same note sound so completely different.)

And that's why better reproduction of the frequencies played by the main speakers, above the crossover point from the subwoofers makes the woofers sound better. Instead of relying on the woofers to reproduce the bass harmonics, crossing-over gives that job to the main speakers, which -- especially in my case, where I'm using super-quick electrostatic speakers – can handle it vastly better and more accurately, even if only because of the lesser inertia of their diaphragms.

Then, when you speed things up even more by adding a better power cord to make sure you're getting all the speed-of-response the amplifier is capable of, the entire bass tone, (fundamental plus harmonics) as reproduced by both of the speaker sets, has a more accurate leading edge; becomes better-defined and "punchier"; and sounds like it goes deeper than ever before.

It's not just better cables that will do this. The same will happen with anything at all that improves your system's ability to reproduce the "leading edge" of the signal. And the effect is not limited to just the bass frequencies. The Fulton Premier speaker (JLB version pictured above as an example) , of back in the 1980s, used a "Super-Duper-Tweeter" that crossed IN at 45 kHz and extended out all the way to 80 kHz (far, far beyond the range of human hearing) for exactly the same reason, and with apparent great success. The same was true of the Townshend supertweeter and the more recent ones from Enigma Acoustics. All of these had greatly extended frequency response, and all of them were described as adding greatly to the clarity, spatial, and imaging and soundstaging characteristics of the speakers they were used with.

Importantly, though, it wasn't their frequency range that did it – even bats might have had trouble hearing their sound at its upper limits! Instead, it was their speed. To be able to go out that far, they had to be capable of near-instantaneous rise times, and it was that lightning speed that did the trick.

So, one more high-end mystery is solved. Maybe next time, I'll tell you about the time that 75 cents-a-foot speaker cable seemed to clearly outperform the same manufacturer's $55 a foot model.

In the meantime, though, sit back, relax, close your eyes, and...

Enjoy the music!

Roger Skoff