Near field subs

Thank you for posting. Looks like another chance to do some experimenting!

A pair of 18 inchers near the listening seat seems extreme to me, kind of bass-headish. This guy must really like bass. Thankfully, when using multiple subs, one has a lot of flexibility with placement. 

In the 1960’s the most popular subwoofer being mated with the QUAD ESL was the 24" Hartley. The rationale for the use of a larger woofer cone is not to produce more bass, but cleaner bass.

A 24" woofer cone does not have to move as far as does an 18" to produce a given SPL, one benefit being the woofer’s voice coil will therefore better stay within the magnet’s maximum field strength. Lower excursion results in less distortion. The same for an 18" vs. a 15", a 15" vs. a 12", etc. Of course that presumes all else is equal, which is not necessarily the case.

Rythmik Audio offers subs with woofer cones of 12, 15, and 18 inches. They are all servo-feedback controlled, and sound more alike than different (except for the utterly unique OB/Dipole Sub, each of which contains two 12" servo-woofers mounted in an open baffle frame. It is VERY different from sealed and ported subs).

I'm not sure near field is the right term. Far field is multiple wavelengths away. A 50 hz wavelength is around 22 feet long and lower frequencies are longer yet. So you are always in the near field with subwoofer. Maybe just near placement but not near field. 

I think near field is the correct term. While it is common that far field will be multiple wavelengths away in the treble frequencies, this isn’t a defining rule. The primary requirement is that direct sound be highly dominant over the reflected ambient sounds in the room. In the bass region it’s possible to transition from near field to far field while still being less than a wavelength away, but it depends on the number and size of drivers used to create the bass. If the woofer is large enough and/or there are a lot of them it can be difficult to get close enough to prevent the room from still being dominant since so much bass is entering the room from other locations than where your ears are. Smaller woofers will have a faster falloff rate than larger ones, and if placed close to the ears can produce bass that falls off very rapidly as you move your ear away. I’ve done this with time delayed and attenuated 6" woofers off to the sides near my ears. At the listening position the bass was smooth and full, like a room with no mode issues at all. Anywhere else in the room the bass was barely audible. This produced a great sounding bass, but was tricky because even moving my head side to side a little would make the bass louder in one ear than the other. A single 10" woofer behind the head would be easier. A couple 18" woofers would need a bigger room I think to maintain a near field effect, but would be more comfortable because you wouldn’t hear drastic changes with small head movements.

@bdp24 nails it as far as woofer size and how that should be thought of.  An 18 inch driver will move very little as compared to a 10" driver producing the same output.  I'm using 18's in my system and they barely move for most playback levels.  I'm not saying everyone should cram 18" drivers into large cabinets into their living room, but larger drivers, if chosen correctly and placed in the correct cabinets, can be very musical and accurate.

I have two REL subs in my system. One in the right front corner. The other is directly left of my listening position hiding under a modern side table made out of slats of wood. So the subs are diagonal to each other and the result is absolutely incredible once I got the levels and crossovers set. 

I agree 100% with @bdp24 and @jheppe815. I’m also using 18’’subwoofers in my 2 channel audio system @105 dB SPL the subwoofer cones barely move.

Mike