Nearfield sub response

"Nearfield" has a very specific definition from (IIRC) JBL's Mark Gander, a quite nice guy who wrote the paper describing the concept.

"Nearfield" means you are so close to the subwoofer that the environment is not affecting the sound pressure.* As a corollary, if you moved a measurement microphone back and forth a tiny amount, the sound pressure would not change. It means you are almost touching the woofer cone.

Bill Basore at Q-Logic once did a demo at CES where they had a subwoofer right smack behind a car seat. You didn't hear much in the room, but sitting in the seat you had firm smooth bass.

So if you could put the subwoofer next to your head, you could get amazing results. Once your ears get some little distance away, you're not in the near field, and "your mileage may vary."


*Well, the environment's loading can affect the raw response of the woofer. But "near field" implies the sound has not had any chance to spread out, so neither room modes nor dispersion are not changing the raw SPL the woofer emits.
 
Hi,

Near or far field has no real effect on interaction with room modes.

The shape of the room, the listening position and placement of
the subs affects the perceived response, its probably fair to
say there is no such thing as nearfield and farfield for subs.

rgds, sreten.

Get out your measuring gear. You'll find that in the near field there's virtually no room interaction.
 
I implemented nearfield subs last night- they're monopoles placed immediately behind either end of the sofa, with the 12" about 12" from the back of the heads on either end of the sofa. The passive radiators (14Hz tuning) are at floor level.

So far I like it but there's more tuning to do. I had to run 50ft cables and use isolation transformers to kill grounding buzz from the subamp being on a different outlet than the main system.

I will say that it does seem quieter for a given SPL (at listening position), and seems more intelligible than previous setups.
 
^
Don't use ported subs. This will give unpredictable results when listening so close. Especially when the port is far away.

I see why you'd be concerned, but with the tuning SO low, I suspect it's probably okay. A little more messing with it and I can get a better feel for that though. The passive is immediately below the 12", and so is maybe 3ft from ears (but only 12-18" from body).
 
I implemented nearfield subs last night- they're monopoles placed immediately behind either end of the sofa, with the 12" about 12" from the back of the heads on either end of the sofa. The passive radiators (14Hz tuning) are at floor level.

So far I like it but there's more tuning to do. I had to run 50ft cables and use isolation transformers to kill grounding buzz from the subamp being on a different outlet than the main system.

I will say that it does seem quieter for a given SPL (at listening position), and seems more intelligible than previous setups.

Check your electrical box and retest earth ground. Balanced input helps solve this issue with a high common mode rejection ratio.
 
Check your electrical box and retest earth ground. Balanced input helps solve this issue with a high common mode rejection ratio.

None of my subamps have balanced in- the 50 ft cables are the input wiring to the subamp- the power cable is off a local outlet, on a different circuit. It's a low level induced buzz, but through my 400WPC on 101dB speakers, even a tiny little induced grounding buzz from different branches/circuits comes through quite handily.

So I threw some ratshack line isolators at the issue- working just fine now!
 
Unless the port is located more than 1/4 wavelength of the tuning frequency "away" then the port and driver will be acoustically close enough.

Close enough for summation, but I'm betting his concern is more related to amplitude, as the port/passive could potentially be 2-3x as far from the listener as the woofer and thus would be expected to have a lower amplitude.

I'll figure it all out when I run some noise at it :)
 
Close enough for summation, but I'm betting his concern is more related to amplitude, as the port/passive could potentially be 2-3x as far from the listener as the woofer and thus would be expected to have a lower amplitude.

I'll figure it all out when I run some noise at it :)
Turn the sub sideways so that the port and the driver are equidistant to the head?
 
It's a good thing I saw this thread because I was just about to spam the board with another question. Yesterday I was shifting my sub around and testing the frequency response, but had some sharp and nasty nulls. When I played the null freq, I noticed that (as usual) there was lots of sound elsewhere, except where I was sitting. "But it's loud right in front of the sub!" Then I realized, why not put the sub closer to me?

So I did that, and now those nulls were gone. I also played around with the sub's orientation to make another null "less bad". I assume this has to do with the driver exciting room modes in certain directions.
 
Unless the port is located more than 1/4 wavelength of the tuning frequency "away" then the port and driver will be acoustically close enough.

This doesn't hold true when listening very close to the source. I've never tested ported subs for direct field listening but would think it creates more problems than it solves. Closed box and dipole subs work well though.