Isobarik with uneven signals - diyAudio
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Old 30th May 2006, 02:55 AM   #1
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Default Isobarik with uneven signals

I know that you would never do it intentionally (at least I think not) but if you accidentally fed a different signal to each driver (say left channel to one and right to the other) what would be the result? Possible damage?

The reason I ask is that I am considering using this type of setup but bringing both drivers signal lines out the terminals so that two channels of a stereo amp (fed the same signal on both channels) could be used. My concern is what might happen if someone misused it by applying the regular stereo signal to it instead of the dual mono intended.

mike
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Old 30th May 2006, 04:00 AM   #2
Volenti is offline Volenti  Australia
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There's no chance of uneven signals causing damage (short of simply too much power, which would cause damage with even signals anyway)

The majority of bass is recorded in mono anyway, any stereo bass components would be mechanically summed mono by the coupling of the two drivers, I've set up iso subs like this before and had no issues.
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Old 30th May 2006, 06:26 AM   #3
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Quote:
any stereo bass components would be mechanically summed mono by the coupling of the two drivers
Im not quite sure this is accurate, the two woofers isobarically mounted will work together if the signals are in phase with the same amplitude. If the signal is not then one woofer will be pushing the other one, if the stereo bass signal is out of phase then the woofers will be pushing into each other, this has potential for cone/surround tearing.

As for mono signals, anything with a ".1" will be mono, ie. most movies. However, any music recorded with two microphones is almost guaranteed to have at least phase variance between the two, and different amplitudes.

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I am considering using this type of setup but bringing both drivers signal lines out the terminals so that two channels of a stereo amp (fed the same signal on both channels)
Quote:
...applying the regular stereo signal to it instead of the dual mono intended.
Which are you going to do? Could you elaborate on the amps you are going to use, wiring layout (y-adapter?), stereo/mono switch, sub pre-out to stereo amp... etc.
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Old 30th May 2006, 01:02 PM   #4
chops is offline chops  United States
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Quote:
My concern is what might happen if someone misused it by applying the regular stereo signal to it instead of the dual mono intended.
Well, the simple solution to that is not to let anyone screw with your equipment.

Also, if you're using a non-bridgable amplifier like me, just use a Y-adapter for both channels of the amp.

Are you using a receiver or preamp that has a dedicated subwoofer "LFE" output? If so, just use that.

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If the signal is not then one woofer will be pushing the other one, if the stereo bass signal is out of phase then the woofers will be pushing into each other, this has potential for cone/surround tearing.
I would also think that the voice coils would heat up rather quickly this way, causing possible damage there as well. (little or no cone movement + more power = little or no VC ventilation, a lot of heat build-up and burnt up VCs)

"Honey!... The biscuits are burnin'!!"
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Old 30th May 2006, 01:50 PM   #5
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The application is automotive. A stereo power amp would be used but the plan is to use an opamp based lowpass/mixer/pad for combining two speaker level outputs. The mixer would have to be carefully designed of course to avoid common grounds on the two inputs. Of course one could just use one channel of the PA but that seems like a waste.

mike
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Old 30th May 2006, 02:14 PM   #6
Volenti is offline Volenti  Australia
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Quote:
Originally posted by nunayafb

Im not quite sure this is accurate, the two woofers isobarically mounted will work together if the signals are in phase with the same amplitude. If the signal is not then one woofer will be pushing the other one, if the stereo bass signal is out of phase then the woofers will be pushing into each other, this has potential for cone/surround tearing.

show me any music that has stereo low frequency components that are both out of phase with a high enough signal level and sustained for long enough to matter.

At most you'll get one channel doing something while the other one isn't, and with 2 drivers properly coupled together with a small air gap you get mechanical coupling with a bit of extra damping from the driver that isn't getting a signal.

At "normal" power levels playing music there's absolutely nothing to worry about.
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Old 30th May 2006, 08:47 PM   #7
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show me any music that has stereo low frequency components that are both out of phase with a high enough signal level and sustained for long enough to matter.
Ok, a drum on one side of the stage and a bass guitar on the other with stereo mics. two different signals, with different phases and different amplitudes. "for long enough to matter" any difference between the woofer signals is a problem and therefore matters.
The fundamental principal of isobaric operation is that two identical woofers with identicals signals are used.
If im understaning your opinion correctly you are referring to music that is mixed in the studio and all of the bass is mixed mono, this is not always the case with all music im just trying to illustrate that.


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At most you'll get one channel doing something while the other one isn't, and with 2 drivers properly coupled together with a small air gap you get mechanical coupling with a bit of extra damping from the driver that isn't getting a signal.
With isobaric you cannot have this situation. To be properly coupled you need the signals to be identical. Remember when properly set up an isobaric config. halves Vas, this is due to the combined suspension stiffness acting against the same airload, with two motors. Driving one woofer in a box designed for isobaric is not good, especially with a stagnant woofer "dampening" the sound.
Just out of curiosity I unplugged the outer woofer in my isobaric setup and ran a sine sweep(20-300hz), it was heavily damped and muddy sounding. I built custom O-rings to seal the two together so I know that my air gap is well sealed. IMO, its never good in reference to isobaric to damp one of the woofers, there are already enough losses and noises/distortion induced in the system when properly configured



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Of course one could just use one channel of the PA but that seems like a waste.
Depends on the ohms of the woofer and the rating of the amp, if 4ohm woofers and 2ohm stable amp, parallel the woofers and use one channel, and you wont need the mixer circuit.
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