Controlling tha Noise?

Quite a few submitters have asked "How do you make a quiet PC". Well, rather than tackle it from the PC standpoint, how about devices that can quiet a whole environment? Along these lines, 16977 asks: "I've been considering building an active noise control system for an area about the size of a closet. ANC today doesn't work quite as well as it did in Silence, Please (works best for low frequencies, only covers small areas, etc.), but it is still a fascinating technology. I'm wondering if anyone out there has done similar projects with either the hardware or controlling software of ANC, and what information they have to share." And since I have your attention on this subject, sammy.lost-angel.com asks: "I would like to ask the slashdot community about their recommendations for noise-cancelling headphones. Traveling in planes is very noisy, and with MP3 players becoming more and more common, I would like to hear some experiences with various different noise cancelling headphones paired up with MP3 players. How well do they work in general? What is the best and most cost-effective headphones available?"

Comments

Cost Effective Noise-Canceling Headphones (DIY)

[Mr.Mustard]

Headwise has a DIY noise-canceling headphone project. That's probably the most cost effective way to get a pair.

Noise cancelling headsets...

[nneul]

Granted, this is a bit out of the price range most people are willing to pay, and are overkill if you just want headphones, but the Lightspeed 25K ANR aviation headset is fantastic.

I tried it once in my cubicle (inside a large IBM mainframe style machine room with a couple of rackfulls of machines and 4 large air conditioners) and it almost completely silenced the ambient noise.

Keep in mind, these headsets are around 20-28dD passive, plus another 23-30 dB active noice cancellation, but they are designed around the frequencies put out by 4 cylinder piston airplane engines at around 2400 RPM.

I believe Bose X headsets are similar. I don't know if their non-aviation headsets are anywhere near as good those.

BTW, The 25K's typically go for around $450-$500.

Noise-Cancelling headphones

[the_greywolf]

Electronics Now (more recently named Poptronics) published a cover article on this very subject. It's in the September '97 issue. I'm quite certain you could find it at any library that carries magazines - our local public library doesn't destroy magazines until they're 5 years old, so you might be in luck if your public library has a similar policy.

The project is a very simple one. Microphones are mounted (with epoxy?) on the outside of the headphones, and their cable runs down along with the headphone cable. The control box has a phase adjustment knob that allows you to adjust for the distance between the microphone and speaker elements for maximum effectiveness.

I haven't built the project myself, but if you have enough of an interest in electronics, you can build it yourself quite easily with parts from the local Radio Shack.

active noise cancelation

[Perdo]

because you can never place the noise cancelation generator at the exact same place as the noise source, you will always end up with places where the noise caceling device makes the noise twice as loud. Two rocks droped in a pond create waves. some times the waves are equil amplitude and frequency but opposite polarity and cancel eachother. Other times the waves are equil frequency and aplitude but their polarity is the same. The interfearance pattern created is the basis of active noise cancelation. But since you can never get the pattern to line up perfectly, the effectiveness of noise cancelation for general white noise is horrible.

Better to dampen the source as well as possible. Liberal use of sorbothane is extremley efective in reducing noise in a computer. shock mount every fan, the motorboard, power supply, cd drive and hard drive on sorbothane risers. Use nylon screws through the sorbothane spacers with sorbothane washers. Line the inside of your case with anechoic (egg crate) foam. Bigger fans turning at lower rpm are preferable. Centrifugal fans tend to be quieter when moving a given amount of air than radial (standard) fans. 36x is about the fastest CD drive you can get that will not induce horible vibrations in addition to their noise component. fan filters made of nylon stockings reduce fan noise considerably while standard chrome fan grills actually add to the noise a fan creates.

My computer is relativly quiet (56db 12 inches from the air intake) while still moving air at 700 cfm through the case for cooling. I used 48 volt centrifugal furnace fans on sorbothane shock mounts to acomplish this.

Re:active noise cancelation

[one-egg]

There was a review of noise-cancelling headphones in the LA Times a year or two ago. Somewhat unsurprisingly, the expensive ones worked better. But the most interesting comment in the story was a social one: on airplanes, everybody talks louder than normal. With the 'phones on, the writer could clearly hear conversations 3 rows back. He found it annoying -- but not nearly as annoying as the guy just behind him who hummed "Do you know the way to San Jose" over and over throughout the flight. Without the 'phones, he was inaudible, and I'm sure he had no idea anybody could hear him. Drove the writer nuts.