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Subwoofer Design like Fan without Sound
Subwoofer Design like Fan without Sound
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Old 5th December 2017, 06:09 AM   #1
Anahtar is offline Anahtar
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Default Subwoofer Design like Fan without Sound

Hi everyone,
I have an idea but I would like to ask you for not having technical knowledge, it is enough for me that this idea can be theoretically possible..

I would like to design ported subwoofer with 2 air holes with two air check valves. One hole is for air input to subwoofer, another one is for out.
Check valves will block reverse air flow.

Subwoofer input will be given around 1000 watts for air transfer but subwoofer sensitivity will be very low.Input will be a sinusoidal signal at 30 Hz with high Vrms (1000 watt). Because low sensitivity output, SPL will be less than 70 dB and the human ear is not sensitive to low frequencies, your ear can not sense anything but because of air flow, subwoofer will work like a fan

Diaphram of woofer will move very fast and air flow will be very fast because of power output but very low sensitivity provides no sound to hear.
I mean, subwoofer will turn into a silent fan


My questions are:

1- Is it possible theoretically? I dont care it's efficient or not.
2- For low sensitivity, how the subwoofer should be? Size,holes, etc.. Please give me some parameters for low sensitivity.


Note 1: I calculated SPL --> 70 db with that website, if sensitivity will be around 40 ,it will be okey.


Peak SPL Calculator


Note2: Human ear can not hear, for 30Hz sound at 70 dB.


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Last edited by Anahtar; 5th December 2017 at 06:43 AM.
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Old 5th December 2017, 07:37 AM   #2
TNT is offline TNT  Sweden
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Sound is not a steady flow of air in one direction. Sound is air pressure variations (back and forth). You seem to have designed a pump. It will only be good for DC, given your room is airtight - DC (constant over? pressure) is really boring to listen to - it only give you a lock in the ear

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Old 5th December 2017, 07:41 AM   #3
Anahtar is offline Anahtar
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Exactly what I want to design a pump but it is not possible with AC sinusoidal input with low frequency ? I know, Airflow will not be continuous but it should work, shouldnt?
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Old 5th December 2017, 09:41 AM   #4
chris661 is offline chris661  United Kingdom
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If you want DC airflow, then yes, with some valves it can work.

You could improve things by putting valves on both sides of the driver, so both the front and rear of the cone can vent to the outside world. That'll double your airflow.

Chris
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Old 5th December 2017, 10:01 AM   #5
Anahtar is offline Anahtar
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thanks for your answer, my question is, how? how can I decrease sensitivity? How should be the design?
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Old 5th December 2017, 10:39 AM   #6
goldyrathore is offline goldyrathore  India
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Quote:
Originally Posted by Anahtar View Post
how can I decrease sensitivity?
You should increase sensitivity. Why do you want to decrease sensitivity?
BTW, some fish tank pumps use 50/60hz in similar fashion.

A sub-woofer driver is very inefficient for a pump task. A pump with motor is more efficient.

Whats your goal?
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Old 5th December 2017, 10:41 AM   #7
Anahtar is offline Anahtar
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I want to have a fan without noise, high power provides more diaphram movement but less sensitivity provides less SPL. So I get less sound but more air. Thats my goal
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Old 5th December 2017, 10:49 AM   #8
goldyrathore is offline goldyrathore  India
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Other things being equal, diaphragm movement = Air flow=SPL.
Irrespective of sensitivity. Higher sensitivity will get it with low power
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Old 5th December 2017, 11:32 AM   #9
scottjoplin is offline scottjoplin  Wales
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Quote:
Originally Posted by chris661 View Post
You could improve things by putting valves on both sides of the driver, so both the front and rear of the cone can vent to the outside world. That'll double your airflow.
Wouldn't that cancel everything out? I think the only way it might work is like a 2 stroke engine, one piston and two valves ducted so they vent 180 degrees apart
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Last edited by scottjoplin; 5th December 2017 at 11:35 AM.
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Old 5th December 2017, 11:39 AM   #10
Ron E is offline Ron E  United States
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Quote:
Originally Posted by Anahtar View Post
I want to have a fan without noise, high power provides more diaphram movement but less sensitivity provides less SPL. So I get less sound but more air. Thats my goal
Where do you think the power that goes into the driver will go? It heats up the air in the box. Your "silent" fan will blow hot air, and not very much of it. This is why you want high efficiency and not low.

A diaphragm pump will make small amounts of high pressure air. What you seem to expect is lots of low pressure air.

To play along with your silly notions: to make a driver have low sensitivity, you minimize
Bl*Sd/(Mms*Re)

That means weak magnet, low # of turns, small area, high mass and high DC resistance all work to reduce efficiency/sensitivity.

To make a propeller fan quiet, you make it larger and turn it slower. This is the best approach to have a "silent" fan.
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