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Author Topic: Unused subwoofer shorting  (Read 3127 times)

Taylor Hall

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Re: Unused subwoofer shorting
« Reply #10 on: March 06, 2020, 05:17:14 pm »

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Ivan Beaver

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Re: Unused subwoofer shorting
« Reply #11 on: March 09, 2020, 07:08:38 pm »

Art is correct.

Whenever I go into a facility that has an existing system, I ask the sound guy to turn the system on (powered or unpowered cabinets), but not to run a signal into it.

Most places would frown on you disconnecting their cabinets to put a shorting plug on them.

And once you "touch" the system, YOU now OWN it.  If something doesn't work afterwards, YOU will be blamed because you touched it.
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Ivan Beaver
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Paul Miller

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Re: Unused subwoofer shorting
« Reply #12 on: March 09, 2020, 07:18:12 pm »

...

Ivan it was something you posted about years ago that led to me having an "a-ha" moment. As I recall, at a subwoofer shootout with two TH115s, you did the testing, then later discovered that one of them had actually been unplugged. So not only was the setup running at half its potential, but that unused sub's disconnected driver was partially counter-acting the working sub.
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Brian Jojade

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Re: Unused subwoofer shorting
« Reply #13 on: March 09, 2020, 07:59:15 pm »

Having never experienced this, how much impact does it REALLY have? Yeah, anything that vibrates can absorb sound.  Is the second sub actually absorbing enough to make a real difference?
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Brian Jojade

Ivan Beaver

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Re: Unused subwoofer shorting
« Reply #14 on: March 10, 2020, 12:42:35 pm »

Having never experienced this, how much impact does it REALLY have? Yeah, anything that vibrates can absorb sound.  Is the second sub actually absorbing enough to make a real difference?
It is not an "across the board" type absorption, but rather freq dependent.  You will end up with notches at different freq.

There can be a number of factors that affect this, the actual tuning freq and or resonances of the non driven speaker, the location of the driven loudspeaker in relation to the non driven one, reflective surfaces around either one, the ratio of driven to non driven loudspeakers and so forth.

The actual answer will vary a good bit.  It is easy to get an outside measurement, but indoors, all sorts of other factors become involved.

As a general rule, it is best not to do it, just in case
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Art Welter

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Re: Unused subwoofer shorting
« Reply #15 on: March 10, 2020, 01:15:11 pm »

Having never experienced this, how much impact does it REALLY have? Yeah, anything that vibrates can absorb sound.  Is the second sub actually absorbing enough to make a real difference?
The results of one test under controlled outdoor settings using a Keystone tapped horn are posted below.
With the adjacent "dummy" cabinet shorted (green trace), frequency response was basically unchanged from the the single cabinet response.
With the "dummy" cabinet not shorted (purple trace), four ranges were affected, two with +1 to 2dB gain, two with -3 to 4dB less. With "smoothing" applied, the differences only appear to be 1dB  ;).

I'd expect distance from the powered to  "drone" cabinet as well as differing Fb (Frequency of Box tuning) to affect response with different, unpredictable frequency response shapes. Probably worse than the effect on frequency response is the drum-like response of the "drone" cabinet, as it will continue to ring after excitation, as the driver has no electrical damping.

Art

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Mark Wilkinson

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Re: Unused subwoofer shorting
« Reply #16 on: March 10, 2020, 02:20:36 pm »

here's a goof i did for a laugh...

as i was indoors replacing a driver on one sub, listening to some  tunes with another sub cranking, i'm like wow...feel how much this driver is vibrating in my hands.

So I really crank the music and hook a voltmeter to the loose driver....get a full 1 volt out.
Then decide to make a transfer using it as a microphone..beautiful ain't it ? :)
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Gordon Brinton

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Re: Unused subwoofer shorting
« Reply #17 on: March 12, 2020, 07:22:21 am »

The results of one test under controlled outdoor settings using a Keystone tapped horn are posted below.
With the adjacent "dummy" cabinet shorted (green trace), frequency response was basically unchanged from the the single cabinet response.
With the "dummy" cabinet not shorted (purple trace), four ranges were affected, two with +1 to 2dB gain, two with -3 to 4dB less. With "smoothing" applied, the differences only appear to be 1dB  ;).

I'd expect distance from the powered to  "drone" cabinet as well as differing Fb (Frequency of Box tuning) to affect response with different, unpredictable frequency response shapes. Probably worse than the effect on frequency response is the drum-like response of the "drone" cabinet, as it will continue to ring after excitation, as the driver has no electrical damping.

Art

Where was the test mic in relation to the live sub? ...out where the "would-be" audience is seated?

I am thinking that we might hear less of a difference at 50 feet away than we would at 3 feet away.
« Last Edit: March 12, 2020, 08:06:47 am by Gordon Brinton »
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Ivan Beaver

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Re: Unused subwoofer shorting
« Reply #18 on: March 12, 2020, 08:41:12 am »

here's a goof i did for a laugh...

as i was indoors replacing a driver on one sub, listening to some  tunes with another sub cranking, i'm like wow...feel how much this driver is vibrating in my hands.

So I really crank the music and hook a voltmeter to the loose driver....get a full 1 volt out.
Then decide to make a transfer using it as a microphone..beautiful ain't it ? :)
Years ago Community made some cheap speakers with a built in level indicator (LEDs).

We had one in the warehouse just sitting there-nothing plugged in.

We were playing with another sub and noticed that the meters on the Community were flashing, due to the back EMF of the driver that was not being played.  That driver was actually moving a good bit with no input, which was producing that voltage.
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A complex question is easily answered by a simple-easy to understand WRONG answer!

Ivan Beaver
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Art Welter

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Re: Unused subwoofer shorting
« Reply #19 on: March 12, 2020, 11:42:44 am »

Where was the test mic in relation to the live sub? ...out where the "would-be" audience is seated?

I am thinking that we might hear less of a difference at 50 feet away than we would at 3 feet away.
The outdoor test was done with the test mic laying on a piece of plywood on the ground.
Moving out to 50 feet, the same dips and peaks (and drone...) would be heard about 24dB more quietly  ;D.
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ProSoundWeb Community

Re: Unused subwoofer shorting
« Reply #19 on: March 12, 2020, 11:42:44 am »


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