The Brains of the Outfit

People wonder what it is that makes our subwoofers so special; how do we obtain the startling results that we deliver? About 90% of it is good, sound, common sense engineering built on a foundation stretching back some 25 years. But then, there is that last bit, the tricky bits that elevate merely very good products into the realm of the truly special.

The brains of a great subwoofer lie in its filter bank; the crossover circuits that define the behavior of its performance. All subwoofers use 1 of 2 types of filters; they either choose to limit and roll off just the high frequencies, allowing the bass to emerge from the sub but permitting the speaker to run full range. Or they seek to roll off both the high frequencies from the sub and also bass to the main speaker. We use the former, most choose the latter.

The answer to why we chose the less invasive route is simple, we know that we were not invited to be a part of the speaker design team when they evolved their designs, in many similar to our journey, over decades of study and learning on the best ways to create the most natural sound. We choose to reveal the best and leave the rest.

But, we are told by engineers whose brains run rather farther to the left half of the brain than ours, that we must eliminate bass to the main speaker, that allowing a speaker to run full range permits bass to overdrive the speaker, that it creates Doppler distortion and other even more insidious forms of audible pollution that limits its performance. To which we say a polite, “No”, in fact, the very reason you purchased the speakers you are now adding a REL to is because you fell in love with the careful choices the speaker’s designers made. That their work most closely approximates the way YOUR ears, brain and life experiences inform you of the sound of music live. Altering this would and does—we know because we’ve developed and listened to virtually every topology of filter set over the past 30 years–destroy the delicate balance of design that talented main speaker designer made to achieve the experience you already love. We just want to help you get at the more complete, totality of that experience it. Not alter it, dry it out and process it which I can assure you, the second approach does.

Sharp versus Gradual: The second major choice we make in designing a REL crossover is choosing the primary filter set. Will it be sharp and aggressive or smooth and gradual? Without diving too far down the engineering rabbit hole of slopes and knee points, nature prefers gentle, progressive overlap to sharp harder edged transitions. Go visit a beach sometime, frequently beaches have cliffs standing adjacent to them; the sharp filter set if you will. If you could come back in a million years you would see that nature had reduced the sharp filter–the sharp-edged aggressive crossover slope of the cliffs–to resemble their gentler-sloped sandy beachy counterparts. We prefer a gentle filter slope that permits good overlap with the output from the main speaker. We make it all work seamlessly by designing filters that can extend all the way down to 20 Hz on almost every model, so that you can roll off the higher frequencies lower down and allow the REL to mate perfectly BELOW the functional limit of the main speakers. It is this ability to get down beneath the main speaker and blend seamlessly that is a big part of REL’s magic.

High Level Input Versus Low Level: Experienced REL devotees might be surprised to learn that even though we are famous for our High Level Input, which connects to the speaker terminals of the main stereo (or dual mono) amplifier(s), you are really using the filters built into our Low Level Circuit. It’s true. Whichever way you choose to connect, the ultimate crossover filter is actually built into our Low Level board, the High Level circuit is reduced in level just before this occurs so that it can use this crossover filter. So, does this mean we have hoodwinked hundreds of thousands of customers? Of course not, it means there is no point to crossing over in the High Level portion of the circuit when it will need to have its output reduced so that our power amplifiers can see a signal appropriate to their gain structure.

But it also means that our Low Level circuits enjoy exactly the same special attention to crossing over, and do just the same job of blending and making naturally better full range sound than any other subwoofer design we know of. And these days, with the slowly growing numbers of active wireless speakers, that is good news for those who either don’t have access to their amplifiers (because they are built into the speakers themselves) or use a particular style of amplifier (some Class D amps for example have unusual aspects of their designs that make it undesirable and even unstable to hook them up High Level to a REL) that cannot take advantage of our High Level Circuit. Either way, we have you covered.

Hopefully this sheds some light on what makes a REL such a special experience for its listeners. How every filter we have ever developed passes through an endless series of listening assessments evolved over decades of careful designs and that only the most natural approach to this is fit to make it into your REL. But also know that we remain hungry, always looking for that last little bit, the next performance edge that no one else has considered that will take us that much closer to the real life experience of great music and theater sound.

Enjoy the music,

John Hunter


July 12, 2017 - Posted in: System Thinking