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Why do subs in free air make mechanical noise?
Why do subs in free air make mechanical noise?
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Old 8th November 2017, 05:02 PM   #1
kcducttaper is offline kcducttaper  United States
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Default Why do subs in free air make mechanical noise?

Basically just as the title states. I've had a couple drivers now (mostly Daytons and Tang Bands) that I'll break in for a couple hours in free air. I don't send silly wattage to them and generally only run at around 1/2 of their xmax, so excursion isn't the deal. I'm just wondering why I start to get some mechanical noises on most all of them around 1/2 xmax in free air. Interestingly, when I stuff them in the box they're going to live in, the noises vanish up until they're either overpowered, or hit excursion limits. I'm not really worried about it, but I am curious what causes the noise in free air. Thoughts?
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Old 8th November 2017, 05:50 PM   #2
boswald is offline boswald  United States
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Why do subs in free air make mechanical noise?
The suspension is tuned for more resistance from the air in your enclosure. Any noise like you have means that the voice coil is wobbling and rubbing. Have you noticed any change with differing orientation whille running unbaffled? If you cannot eliminate the noise, break them in in a box.
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Old 8th November 2017, 06:17 PM   #3
scottjoplin is offline scottjoplin  Wales
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What is the noise can you locate it?
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Old 8th November 2017, 06:56 PM   #4
chris661 is offline chris661  United Kingdom
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Thing to remember is that free-air operation gives you a 6dB/octave acoustic highpass filter. Any little bit of HF that the driver produces is given huge advantage over the low end when it comes to hearing it.

When loaded into an enclosure, the low end is restored and might be 40dB above the HF noises. ie, the HF noises will be virtually inaudible.

PS - add in wind noise from the motor structure, tinsel leads slapping the cone etc etc. When mounted cone-out, those noises remain inside the box, more-or-less.

Chris
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Old 8th November 2017, 07:26 PM   #5
lcsaszar is online now lcsaszar  Hungary
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I also noticed that some drivers generate squeeking noise in free air. It' s probably due to the spider.
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Old 9th November 2017, 11:12 AM   #6
wolf_teeth is offline wolf_teeth  United States
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Port turbulence of the vented pole piece is one major contributor. The spider will give and break-in and not 'creak' so much when exercised enough.

Wolf
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