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The age-old battle between the forces of digital and analog wages on, with Sony's new MDR-NC500D noise canceling headphones claiming to out noise cancel your totally old-fashioned analog pair. Join Us For An Adventure!We live and breathe travel so follow us for some great travel inspiration and fantastic stories! In today’s hectic and noisy world, we are all searching for a little peace and quiet.
Along with noise-features, the Active Noise-Canceling Headphones let you mix in an auxiliary line-level signal from a CD or tape player.
The headphone amplifier is built around IC3-a, a third NE5532 wired as an inverting op-amp stage. This is how that feature works: One end of the potentiometer is tied to ground because we are using it as a voltage divider. A final note on using operational amplifiers as headphone amps: Most generic ones will not supply enough current to function properly. When wiring the jacks, it is a good idea to follow the audio industry standards as to which jack connection is for which stereo channel. When selecting a case for the project, be sure that it is large enough to hold the circuit board and the two 9-volt batteries comfortably. The best way to strip that type of wire is to roll a razor blade very carefully over the insulation without cutting the wire underneath. After the glue is dry, gather and bundle the wires together with several nylon tie wraps along the length of the wires.
Try this little experiment: record a person talking to you while you are wearing the headphones and have them walk around you in a circle.
Other interesting tools can be created by building different types of housings for the microphones. Microphones (Digik-Key P9967-ND or similar), headphones, PC board, case, wire, hardware, etc. The Ryckebush NC project uses a single NE5532 inverting op amp stage for line-in amplification. Ryckebush feeds the output of electret condenser microphones through a non-inverting preamp and allows switching of this output through a unity-gain inverting op-amp to select between cancelling the noise or amplifying the noise.
My first implementation of the circuit used dual 9V batteries as in the original Ryckebush circuit. All in all, kind of fun and only around three times as expensive as if I had bought something from a store ;). As you know, we were using low-quality headphones, and when we mounted the mics on the outside of the headphones, we got little beneficial effect. We don't really understand the audio alchemy explained in the press release ("the analog audio input signal is converted to a digital signal and sent through a digital equalizer to enhance the mid-range vocals and alleviate the excess bass"?) but if it means we can tune into whatever crappy movie they're playing on the plane while blocking out the roar of the jet engine and maybe even a crying infant or two, then consider our attention gotten when these things start canceling noise in February. Jack is from Australia and Jenn is from the US but together we have traveled a few parts of the world and hope to continue on doing so.
Well, you might not be able to slip off to a tranquil forest for an hour or two, but you can block out background noise with the Noise-Canceling Headphones.
The electronics consist of three op-amp circuits; each built around one half of an NE5532 dual op-amp. Besides keeping the values of R19 manageable, the 10K-ohms resistors interact with the 100K-ohm linear potentiometers.
Because the sum-ming junction of an op-amp is at a virtual ground, the 10K ohm resistor is also essentially tied to ground.
Some substitutes for the NE5532 that are known to work include the 0P275 from Analog Devices, the OPA2604 from Burr Brown, and the LM833 from National Semiconductor. There are two parts to this project: building the electronics and modifying a pair of headphones. Normal standards for stereo connections are to connect the right channel to the ring and the left channel to the tip. After the front panel is laid out and drilled, check to make sure all the controls and jacks will fit. An excellent source of thin audio cable is to buy another set of cheap headphones – the cheapest you can find. The easiest way to do that is to pre-tin the wires and melt the little dab of solder on the microphone element with the tinned wire beneath the soldering iron tip.
With the headphones complete, it is time to experiment with the Noise-Canceling Headphones.
For testing purposes, you should be in a quiet room with just a little background sound, such as a heater or air-conditioner fan.

Since we already have two microphones mounted in essentially the same place human ears are, all we have to do is send the headphone output to a tape recorder input. I started with the Ryckebusch project from this site, but I ended up making a fair number of changes.
I didn’t like the fact that the audio signal gets inverted, so I first tried changing the circuit to use a non-inverting amplifier. The inverted or non-inverted signal is then summed with the line-in signal through the final inverting amplifier. Fortunately, the Senns have removable covers over the speakers with plenty of space between the speaker and the cover. We found that we could get better results using nice headphones, but they still were not very effective. The Sony MDR-NC300D is a noise canceling in ears headphone with three different modes for Noise Canceling. This blog is to track all the adventures, misadventures, food experiments, random ramblings, interesting encounters and wild and crazy times. The project also has a phase switch that will let you keep the microphone signals in phase, thus amplifying background sound.
The phase inverter is nothing more than a second NE5532 configured as a unity-gain inverting op-amp (IC2-a).
That type of op-amp configuration can be easily modified to add a summing feature by the inclusion of R17. That affects the response of the potentiometer, As the potentiometer is rotated, there is a more pronounced increase in the output as the end of the potentiometer’s travel is reached. If you have never used an op-amp for driving headphones before, you are in for a nice surprise. Those components are available from several sources, including Digi-Key, Allied Electronics, and Jameco. If you use that type of board for the Noise-Canceling Headphones, it is best to start by spacing out the three ICs on the board so that they straddle the buses. One method for labeling the front panel is to spray the entire panel with a flat color such as white or yellow. The microphones are mounted on the earpieces of the headphones with a dab of silicone sealant. The loudness of the incoming sound, the specific frequencies involved, and the position of the sound source all play a part in how well the headphones do their job. Several interesting applications will suggest themselves that do not require any additional hardware. It sounded OK to me, but when I went to a unity-gain inverting op-amp as a first stage with an inverting amplifier as a second stage, it sounded cleaner, so that’s what I went with.
In order to both reduce higher frequency noise and to provide a secure mounting for the microphones, I cut and shaped pieces of low-density foam (squishy) to fit the inside of the cover and give the speaker a little room. It operates at 10KHz, which is smack in the middle of the audible range so ripple is a big issue. In addition, the design of the Noise-Canceling Headphones lends itself to several other interesting functions, which we will look at later. The first circuit is a non-inverting pre-amp, the second is a unity-gain phase-inverter, and the third is an inverting headphone amplifier.
All inverted sounds played back through the headphones cancel out the original sounds, leaving nothing but silence. Electret-condenser microphones need a 2- to 10-volt bias voltage for their internal FET pre-amps.
The second input comes from an auxiliary line-level input that is attenuated by potentiometer R23-a.
The NE5532 will supply a 10-volt rms signal into a 600-ohm load with very little distortion. One style of perfboard that simplifies construction is one having a pre-etched copper pattern on its solder side that connects groups of holes together.
The usual result is that the circuit will probably not work, the ICs could be damaged, and the electrolytic capacitors might explode! Keeping the wiring neat and following the layout shown here makes assembling the unit and changing the batteries easier. The headphones are modified by mounting two small electret-condenser microphones on the head-phones, one on each earpiece. After you have prepped the wire, mark the wire that is connected to the ring and the one that goes to the tip of the jack.

Using a toothpick or other suitable substitute, mold the silicone around the edges of the microphone element to smooth everything off. The two microphones capture the exact phase and timing relationships of sound as we hear it. The microphone elements used in this project feature full 20-Hz to 20-kHz frequency response.
Since the preamp is non-inverting and the final audio stage is an inverting amplifier, the output of the preamp can be fed directly (via a potentiometer) to the input of the final stage.
Though this closed the speakers off a little, the effect was not significant enough to be noticable (to me, anyway). I found that by using 22uF low-ESR tantalum caps for the reservoir capacitor and by carefully routing all wires away from this capacitor to minimize inductive coupling, the ripple was beneath the threshold of my hearing.
However, by building your own headset, you can add features not otherwise available and have fun while doing it!
Since the Noise-Canceling Headphones is a stereo device, the circuit is actualty two identical circuits side-by-side. Potentiometers with an audio taper are, of course, available, but a linear-taper unit is easier to obtain and costs less.
Be careful not to get any on the black felt surface – that is where the sound enters. Areas that can benefit include outdoor activities such as hunting or just observing nature.
It also teneded to acoustically isolate the microphones from the speaker elements which reduced the likelihood of feedback.
Note that getting the wires positioned just right was extremely important, as was putting the voltage doubler on a separate circuit board. We found that due to sound propogation delay, non-inverted output (in our case) produced better effect than inverted output.
The Sony MDR-N600D is an “over-head” pair of headphones capable of canceling 99% of noises.
A voltage-dividing network, which also decouples the bias volt-age from the power supply, is provided by Rl and Cl. Obviously, the left and right microphones should be attached to the left and right sides of the headphones, respectively. The Noise-Canceling Headphones is the perfect device for environments that have a loud ambient sound level, such as rooms with loud ventilation systems. There is also a faint but noticable hiss when the noise cancelling circuit is enabled, so I wouldn’t want to use this stage unless the environment was pretty noisy to start with. I found the best results to be when the mics were placed to one side of the foam cover, directly in front of my ear canals. We also observed that headphones were ineffectual for high frequencies, so to reduce noise produced by the circuit, the input was put through a simple RC lowpass filter with Wo=1K. That potentiometer sets the level of the microphone signal feeding the headphone amplifier.
The ground connection on an electret microphone cartridge is easily identified by the solder connection between the terminal and the mic’s case (C).
Another source of true parabolic dishes is Edmund Scientific, 101 East Glouchester Pike, Barrington, NJ 08007. It was kind of a pain, but not as bad as listening to a barely audible high-pitched whine ;).
After soldering on the microphone elements, it is good idea to test them prior to gluing them to the headphones.
With the microphones mounted at an angle between 90 degrees and 120 degrees, you will have a stereo image of the sound source too!
For some advanced experimenting, use two dishes (one for the left microphone, one for the right) and experiment with stereo reception of a distant sound.
If you adjust beyond the null, background sound will become louder as the out-of-phase signal exceeds the ambient sound level. If it sounds like you have a massive head cold and can barely hear yourself, the circuit is functioning properly.

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