The Rule of 10
If we cannot hear above 20kHz why do engineers insist on building amplifiers with ever higher bandwidths?
While I can’t tell you why designers other than our own like to extend amplifier bandwidth into the ultrasonic regions I can explain why we do. It’s called the Rule of 10.
The rule of 10 is a lofty engineering goal that simply states we should strive to build products with 10 times the required average use case. So, for example, if we want to make sure we can deliver flat frequency response out to 20kHz then we should try and extend the amp’s bandwidth by a factor of 10, or 200kHz. In the same vein if we want to be flat to 20Hz we’d make certain to extend that by a factor of 10, to 2Hz.
We don’t always get what we want nor do we use the Rule of 10 as a strict formula, only a guide. The reasons for this are simple. By stretching the parameters beyond requirements we gain headroom, staying within the comfortable bounds of an amp’s abilities. Taken too far in any one direction this goal can actually make things worse. For instance, demanding too much ultrasonic performance can require design changes that have negative impacts elsewhere.
The Rule of 10 is valuable advice if it is kept in balance and harmony with the rest of the design.
The poet Robert Frost wrote, “good fences make good neighbors”. If you’d never read his poem, Mending Wall, you might think he liked fences. You would be wrong. The poem is actually about the opposite.
One of the dichotomies of product design is about fences. It’s a problem faced by companies as big as Microsoft and Apple (Apple likes fences, Microsoft not so much), and as small as PS Audio (we’re on the fence about it to make a pun).
Interface fences are needed. Boundaries and standards are set to ensure the proper interface of equipment with the outside world. As in any neighborhood, we all have to agree on some level or sources would not interface with preamps and amps.
One of my readers cried out when I suggested an end-to-end system approach to building our new loudspeakers. “But I like to mix and match equipment. It’s part of the fun of our hobby.” Indeed, our customers run the gamut from tear-the-walls-down tweakers to folks who like their fences.
There’s no way to keep everyone happy. This we know. I think the secret to great products lies in the notion of maintaining outside accessibility of equipment while, at the same time, offering a PS-specific connection scheme. It’s an idea that’s been bubbling in me for some time. Not fully formed yet, but slowly creeping in.
Good fences make good neighbors as long as they aren’t impenetrable walls.