Sound Reinforcement - Forums for Live Sound Professionals - Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums > The Basement
Sealed loudspeaker design experts?
Doug Chapman:
Hello,
Long time lurker especially of Danley and JTR threads
Today I have a question, that has nothing to do with Live Sound in the traditional sense, but has everything to do with Loudspeaker design.
In a single driver, small, sealed loudspeaker, thick plastic reinforced with some metal, about the size of a large man's Hand, how do leaks to the sealed enclosure normally affect sound?
I have a device that is not yet released on the market, which has a problem (I did not design it)
It has a very tiny GORE style membrane on the rear, which allows for some pressure in and out (commonly found on car headlights). Other than that, it is pretty well sealed (IP68)
At high outputs, audio artifacts are emitted out of this rear GORE membrane, but not by the membrane itself rattling. Putting a finger over the vent area improves sound quality to an extent
It seems the driver itself is rattling / buzzing at high output as if it had a bunch of metallic dirt on it, or as if the membrane was touching something it shouldn't be.
If you remove the rear cover of the enclosure, the rattling / buzzing of the driver beings happening at much lower levels so I was starting to think that the driver is just designed assuming a perfectly sealed enclosure.
In a speaker driver designed for use exclusively in a sealed enclosure, what else would cause a buzzing / rattling / flapping sound to occur? Am I right in thinking that an insufficiently sealed enclosure could cause this?
What do you think is making contact with what inside the driver to cause these undesirable artifacts to occur?
I have 99.99% confirmed that the undesired artifacts are occurring within the driver itself somewhere somehow, but visually watching the clear membrane as the artifacts occur doesn't reveal the answer to a beginner like myself.
Scott Helmke:
In any enclosure that puts out some bass, a small hole (like a missing screw hole) will cause some noise from the turbulence of the air. It might sound like distortion or even whistling.
David Morison:
In a sealed box, the fixed volume of air in the enclosure helps to control how much the loudspeaker cone is able to move forwards and backwards from its rest position.
If the enclosure is imperfectly sealed, then there will be less effective control of the cone motion.
That means increased distortion as you increase the SPL.
Doug Chapman:
--- Quote from: David Morison on February 18, 2023, 10:30:52 AM ---In a sealed box, the fixed volume of air in the enclosure helps to control how much the loudspeaker cone is able to move forwards and backwards from its rest position.
If the enclosure is imperfectly sealed, then there will be less effective control of the cone motion.
That means increased distortion as you increase the SPL.
--- End quote ---
Thank you, the membrane in this case is a translucent plastic, and I can't determine by watching the membrane with the naked eye what is actually happening, but it sounds as if it is touching something it shouldn't be at high SPL causing the buzzing / fuzz
If I seal up the box completely, including the gore pressure vent port, these undesired artifacts go away 99% even at max volume
The driver is a custom designed driver by Harman actually
Can drivers be designed to help account for a less-than-perfectly sealed enclosure? I.e. provide more space so that the membrane doesn't do something it shouldn't?
I guess my main question is can anything be done to the driver design, while keeping the same foot print, to assume / account for a less than perfectly sealed enclosure
Tim McCulloch:
--- Quote from: Doug Chapman on February 18, 2023, 12:44:30 PM ---Thank you, the membrane in this case is a translucent plastic, and I can't determine by watching the membrane with the naked eye what is actually happening, but it sounds as if it is touching something it shouldn't be at high SPL causing the buzzing / fuzz
If I seal up the box completely, including the gore pressure vent port, these undesired artifacts go away 99% even at max volume
The driver is a custom designed driver by Harman actually
Can drivers be designed to help account for a less-than-perfectly sealed enclosure? I.e. provide more space so that the membrane doesn't do something it shouldn't?
I guess my main question is can anything be done to the driver design, while keeping the same foot print, to assume / account for a less than perfectly sealed enclosure
--- End quote ---
The quick answer to the last question is "probably not" because what it would take to 'fix' at one frequency might not be right for another freq/velocity, etc. If the problem is the enclosure, fix the enclosure.
Reminds of a discussion between General Motors and Michelin. Seems GM was unable to make round wheels; the result was an unbalance-able tire/wheel assembly. GM ask Michelin to make out-of-round tires to compensate. Michelin said no, learn how to make round wheels.
Navigation
[0] Message Index
[#] Next page
Go to full version