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Old 13th February 2014, 08:53 PM   #11
badman is offline badman  United States
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Originally Posted by markus76 View Post
^
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).
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Old 14th February 2014, 05:17 PM   #12
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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.
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Old 14th February 2014, 05:20 PM   #13
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Originally Posted by markus76 View Post
^
Don't use ported subs. This will give unpredictable results when listening so close. Especially when the port is far away.
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.
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Old 14th February 2014, 06:14 PM   #14
badman is offline badman  United States
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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!
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Old 14th February 2014, 06:16 PM   #15
badman is offline badman  United States
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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
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Old 14th February 2014, 07:03 PM   #16
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Oh yeah that could be a little problem

Cheers to the cheap solution!
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Old 14th February 2014, 08:54 PM   #17
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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?
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Old 14th February 2014, 09:46 PM   #18
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Turn the sub sideways so that the port and the driver are equidistant to the head?
If I can get wife to give up the windowspace, I can stick them in the windowbox that way)
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Old 15th February 2014, 11:07 AM   #19
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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.
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Old 15th February 2014, 01:11 PM   #20
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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.
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