Does a REL subwoofer make the speakers' job easier?

I was amending my above post, and ran out of time before fully completing my thoughts.

As we know, a continuously-variable phase control is very uncommon on subwoofers. All the control on the Rythmik subs does is provide either no delay, or up to 16ms of delay. 16ms of delay does exactly the same thing as moving the sub 16 feet back in space (approximately; sound travels at about one foot per millisecond).

Audiophiles have long had to move their sub(s) around, searching for a location in the room where the sub and main speaker seem to best "blend", where the sub doesn’t sound separate from the loudspeaker. That effort involves two completely different issues: 1- the phase relationship between sub and speaker; and 2- the interaction of sub and room. Unfortunately, the two are often in conflict with one another; the best location for one issue is the worst for the other. That’s one reason integrating subs with speakers has always been such a hit-and-miss proposition.

The worst place to locate a sub (or speaker) is where the room is creating a "mode": either a resonant mode ("’room boom") or a null ("suck out"). What a continuously-variable phase control allows one to do is find the best location in a room in regard to the sub being in a non-mode location, and to then use the phase control to align the sub in time with the loudspeaker, rather than moving it physically (to a location where a room mode exists).

Room modes are completely a function of room dimensions, and you can see where the modes are most likely located in your room by putting its dimensions into one of the room mode calculators easily found on the ’net. Place your sub(s) where room modes are at their lowest level, then use the phase control to align the sub and speaker. An elegant solution to an old problem! ;-)

Unfortunately, it’s not that simple; the long wavelengths of low frequencies (often longer than the rooms dimensions)---upon reaching a room boundary---reflect back into the room, meeting other waves and combining with them to create an increase in response (when in phase) or a null (when out of phase) at the location where the waves meet. It can therefore be a complicated mess, one difficult to completely resolve. A continuously-variable phase control is but one tool to use in addressing the issue of sub/speaker/room integration. It's therefore no surprise that many critical audiophiles have never been fully satisfied with the results of adding subs to their loudspeakers. For them, Richard Vandersteen has done the hard work for you. Just buy his Model Seven or Kento Carbon. ;-)

@gladmo: I time after after time see and hear people laud REL for their high-level connection design. Well, Brian Ding provides both high-level AND line-level connections in the non-XLR/Standard Size versions of the plate amp of his Rythmik Audio subs (the face plates of which are clearly pictured on the company’s website)..

But he also includes a continuously-variable phase control, which he labels "DELAY". It provides from 0 milliseconds of delay (0 degrees of phase rotation) to 16 milliseconds (180 degrees of rotation), and anywhere in between. The phase switch included on other subs (providing either 0 degrees of rotation or 180 degrees)---including on all RELs’---is a complete joke, of very little practical value. And is in fact an insult to one’s intelligence.

The notion that a sub doesn't require a continuously-variable phase control because a sub is either in phase or is not is a bizarre one. If your cross-over frequency is centered at, say, 100Hz, both sub and main speaker are reproducing that frequency (the high-pass and low-pass filters creating a slope---a decline in output---of the drivers involved). If the wave from both reaches the listening position at the exact same time, their combined output creates a flat frequency response (when well designed and implemented ;-). If a 100Hz tones reaches the lp with the waves from the sub and main speaker completely out-of-phase (180 degrees of phase rotation, or delayed in time 16 milliseconds, commonly referred to as opposite polarity), the two waves will combine to create a deep null in the response. A smaller degree phase mis-alignment will create a shallower null. This is not opinion, it is a fact, one of course well known for a century by all loudspeaker designers. Speaker designers have to provide the same phase alignment between the bass woofers and midrange drivers in their full-range loudspeakers, so as to create a flat frequency response. The alignment between a sub and a loudspeaker is no different. Why WOULD it be?!

Phase can be a somewhat complex matter, but in the case of subs it is not. The phase switch on most subs gives only two options: either the signal is left as received, or it is rotated 180 degrees (the phase is flipped, i.e. reversed).

The phase control included in the Rythmik "standard size" plate amps is not a 0/180 switch, but rather a continuously-variable rotary knob control, providing from 0 degrees of phase rotation (no delay) to 180 degrees of phase rotation (16 milliseconds of delay). In 16ms sound travels approximately 16 feet (one foot per ms), so setting the Rythmik phase knob control to 180 degrees/16ms does the same thing as moving the subwoofer back 16 feet, but does it electronically instead of physically.

So the Rythmik phase control allows one to position the sub where one wants it in the room (so as to avoid locations where room modes exist---peaks or nulls, a consequence of room dimensions), the phase control then used to align the sub with the main speakers. I would not own a sub without a continuously-variable phase control. The 0/180 phase switch is a joke, far too crude to be of much value in a high performance hi-fi system. IMO.

As for the REL subs making the speakers’ job easier: as others have already said, the REL (and almost all other dubs) provides no filtering for the loudspeakers, so they and their amp(s) still "see" a full range signal. Not relieving the main amp and loudspeakers of having to reproduce low frequencies is to ignore one of the benefits of using sub(s). Bass frequencies "eat" far more of the power an amp creates than do higher frequencies; if you remove low frequencies from the signal the main amp receives, far more power will be available to the loudspeakers, and it will be lower in distortion. Removing the low bass duties from a loudspeaker will allow it to play louder, and with less distortion, especially true with planars.

As you read in an above post, Vandersteen offers a high-pass filter to remove bass from the signal sent to the main amp when using his subs; HSU does too. But you can easily install a simple 1st-order (6dB/octave) filter on the input jacks of your main amp; it consists of a single capacitor, the value of which is dependent upon the frequency at which you wish to crossover from your speakers to sub, and the input impedance of the amp. The formula to find the correct cap value may be found on the ’net.

Another route to take is to install a separate electronic crossover in your system, in-between your pre-amp and the amp for the speakers. A benefit of using a separate x/o instead of the Vandersteen or single-cap filter is that the x/o frequency is usually adjustable. If all you need is a 1st-order filter, the old Dahlquist will work okay (especially if you replace the original parts with higher quality ones), and can be found used for a coupla hundred bucks. Really good x/o’s provide adjustments for both frequency and slope (6/12/18/24dB/octave, 1st/2nd/3rd/4th-order). Pass makes a great one, but it of course ain’t cheap. Nelson Pass offered a cool little one in his First Watt line (model no. B4. Get it? ;-), but it is no longer available assembled, only as a DIY kit.

By the way, though REL is most well known for offering a high-level sub connection, the non-XLR versions of the Rythmik plate amps do as well, along with low-level (which REL does not).