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Headphone Buying Guide

A few months ago, a couple of students in my class asked me to help them repair the wire to their ear bud headphones. I looked at them with a puzzled look, thinking why would they want to do that? So I told them the time it takes to fix a good connection between the wire and the headphones or the jack, would not be worth their time. Of course, being the frugal person I am, I thought these may have been $20 headphones from a department store. I was WRONG. They wanted help repairing Beats by Dr. Dre Tour headphones which apparently retail for more than $120 and whose successor retails for $180.

I wanted to know what they are paying for; I proceeded to the Beats by Dre website. I searched and searched for the technical specs, but I found nothing! I visited a number of distributor sites and again nothing. I watched a number of YouTube videos that claim to discuss the technical specs, only to be disappointed as they talked about things like color, the composition, carrying case, and the like. Side Note: PEOPLE, there is nothing technical about the color, ability to fold, and the carrying case, and the shape of the wire! I then decided to view other headphone manufacturer’s website and found the same thing for almost all others. No Tech Specs! Why would anyone buy expensive headphones without knowing what they are paying for? I would not purchase a car without knowing how many cylinders the engine has, how much horsepower, is there anti-lock brakes or isn’t there, the number of wheel drive, etc. Hopefully we are not buying cars because a car because the paint is shiny, red, the seller decides to throw in a car cover, and because the doors open and close.

Is it possible that we are just caught up in brand names and celebrities, or is it possible we do not know what to look for? If you are buying expensive headphones because you are serious about your music, then you should be interested in the tech specs. Here are the things you need to know when you are purchasing headphones. Use this article as your buying guide.

First and foremost, I say if any manufacture is unwilling to tell you what they are selling (tech specs), do not purchase their headphones unless they are cheap ($0-$20). If you are able to find the technical specs for a given manufacture headphones, then here are the specs that should be of interest: frequency response, sensitivity, impedance, noise isolation, noise cancellation,  tip composition and durability. Let us look at each of them separately and describe their significant to you as a consumer and music lover.

Frequency response:

  • Spec. Information – Let us take each word separately. Frequency is the defined as the number of cycles or completed
    Speaker

    Figure 1. Speaker

    alternations per unit time of a wave or oscillation [Dictionary.com]. When a speaker or a set of headphones are being driven by an MP3 player, for example, the speaker’s cone moves in and out from equilibrium (normal un-driven position). The rapid movements create sound waves. In turn, the sound waves generated by a speaker (headphones) cause vibration in the human ear that allows us to hear. Humans with excellent hearing can hear frequencies (vibrations or alternations) between 20Hz (1 Hertz {abbreviated Hz}=1 full vibration per second) and 20,000Hz. However the younger the music listener, the more likely it is that they can hear frequencies as low as 16Hz and frequencies slightly above 20,000Hz. That is right; frequency range tends to decrease with age. For example, by the time we reach 20 years of age we are closer to 16,000 Hz at the upper end of our range. By age 60, the upper frequency limit, on average, has been reduced to around 8,000 Hz [Campbell].

  • What To Look For – When purchasing headphones keep in mind your age. Purchase headphones that at minimum has a frequency repsonse that includes your hearing range.

To find your hearing range, see your doctor for a hearing test. Alternatively, you can estimate your range by using the information above or by doing the following:

  1. Use your portable music device (example iPod), that has an estimated output 20Hz to 20,000Hz output range.
  2. Obtain a cheap set of headphones that has frequency response between 20Hz to 20,000Hz.
  3. Play the appropriate hearing test file on that device (download here: .wav, .cda, .mp3). Use the test file to find the approximate limits of your hearing.

Note: In the file, a new frequency (16Hz, 32Hz, 64Hz, 128Hz, 256Hz, 512Hz, 1024Hz, 2048Hz, 5120Hz, 10240Hz, 20480Hz) is produced every 5 seconds. Also, for the lower and higher frequencies, you may need to increase the volume. While for the frequencies between 1024Hz and 5120Hz, you may need to lower the volume down.

Human Hearing Sensitivity: Humans ability to perceive sound varies with frequency. For example, the average human’s ears are more sensitive to sound between 1000Hz – 5000Hz [Gelfand]. Even more important is human’s ability to detect sound pressure levels (SPL). Sound pressure levels are determined by the following equation

SPL db= 20 log (P / Pref)

 

where P is the sound pressure and Pref is just audible sound. SPL is measured in decibels (db) and varies with frequency. When P is equal to Pref,  SPL is equal to 0db.  This occurs at approximately 1000 Hz for most people [Campbell]. Because of all of these factors the next two characteristics will be evaluated at 1000 Hz.

Bose HeadphonesSensitivity (1000Hz):

  • Spec. Information – Sensitivity is the measure of a speaker to produce SPL; in the case of headphones, 1mW (milliWatts {abbreviated mW} is a measurement of power). Sensitivity is measured in db/mW by many headphone manufactures.
  • What To Look For – The higher the sensitivity is the better the headphones are, in this respect. Keep this in mind when you are determining which headphones are best for you.

Impedance (1000Hz):

  • Spec. Information – In order to have the maximum output power from your mp3 player, iphone, ipod, cd player or any other portable device; it is important to have the impedance of your portable device match the impedance of your headphones. When they are not matched, the portable device will not deliver the maximum amount of power to your headphones. That means you may find it necessary to increase the volume setting on your portable device to get the same level (amplitude) of sound from your headsets, as you would for a set of headsets that are perfectly matched.
  • What To Look For– It is in your best interest to match the output impedance of your audio player as closely as possible to the input impedance of the headphones you are purchasing. See your portable audio player owner’s manual for the output impedance information. If this information is not available to you, you can find it yourself with a bit of technology know how and a few pieces of test equipment.

**Easy method (not precise)**

You will need: your audio player, replacement headphone plug, and a multimeter that measures ohms. Replacement headphone plugs and multimeters and voltmeters are available here.

  1. Turn your audio player off.
  2. Then use a replacement stereo headphone plug and a multimeter (set to measure ohms) to check the impedance. See Figure 2.
  3. The resistance you receive from the multimeter will be the approximate value you need to match to ensure impedance matching for maximum output power from the audio player. Use this value to shop for your next set of headphones.

Figure 2. Testing Impedance Using A Multimeter and Replacement Plug

**Alternative Method**

Impedance is frequency dependent. This becomes important only if frequency filtering occurs after the amplification stage of the audio player. There is no real way to know unless you obtain the schematics for your player or you open the device and can follow the circuitry. Let us assume it does.

You will need: 1000Hz signal produced by the audio device {download here: .wav, .cda, .mp3), a multimeter that measures AC current, and a multimeter that measures AC voltage and a replacement headphone plug. Replacement headphone plugs and multimeters are available here.

  1. Use a replacement stereo headphone plug and a multimeter to check the maximum voltage output (Vrms). See Figure 3.
  2. Turn your audio player on and set it to the maximum volume. Play the 1000Hz audio signal Note: Signal last for 2 minutes. You will have to restart it if it ends.
  3. Read the AC voltage from the multimeter.
  4. Change the settings on the multimeter to measure AC current. See Figure 4. Check the AC current (Irms) output.
  5. You can determine your audio player’s impedance (Z) by using the equation Vrms / Irms = Z. Use this value to shop for your next set of headphones.
How To Test The Thevenin Voltage From An Audio Player

Figure 3. Testing The AC Voltage Using A Multimeter and Replacement Plug

How To Test AC Current From An Audio Player

Figure 4. Testing AC Current Using A Multimeter and Replacement Plug

Noise Isolation (sometimes called noise attenuation):

  • Spec. Information – Noise Isolation is a headphones ability to passively attenuate outside noise. In laymen’s terms, noise isolation simply blocks outside noise. All headphones do some noise isolation. Ear buds block noise when inserted into the ear canal. Headphones block outside noise by covering the entire ear making it difficult for outside noise to reach the ear and ear canal. Many manufactures have found that they can eliminate outside noise with innovative shaped ear buds and headphones. However the innovation only works to the maximum potential if your ear and ear canal is a perfect match.
  • What To Look For – This is technical spec is subjective. Nonetheless, the higher the maximum noise isolation value (measured in db) the better as it pertains to your music pleasure. Note: Too much external noise isolation means it will be harder for you to hear sounds that indicate impending danger.

Noise Cancellation:

  • Spec. Information – Noise Cancellation is an active form of noise attenuation. Headphones with noise cancellation tries to adaptively eliminate external noise by producing anti-noise (laymen’s terms) signals. Simply stated, the headphones try to eliminate the external noises by generating an opposing noise that causes the sum of the two noises (natural and generated) to be equal to 0 (non-existent).
  • What To Look For – Measuring this is tough. If this is a feature you desire, I suggest you leave this spec as the last you compare  before purchasing. Furthermore, to get a good idea of how the headphone perform, you will have to test them. Note: Having this feature will cost significantly.

Tip (Plug) Composition:

  • Spec. Information – You may see many manufactures using gold plated plug tips for their headphones. The reason for this is mainly due to corrosion. Because the plug is exposed to the air, there is a possibility that over time it will corrode. Because corroded metal does not function as a good conductor of electricity, the corrosion will reduce signal quality.
  • What To Look For – Unless your plug is in a region with year round humidity I would not be highly concerned with corrosion, especially when you consider how fast technology changes. In addition, gold is a ridiculously expensive metal right now. If you add this to your required technical specs; you could be adding unnecessary cost.

 

Durability:

  • Spec. Information – It is tough to gauge durability; however, if you have ever had headphones in your life, you know one of the first things to fail is the cord. More often than not, especially if you travel with your headphones, your headphones will develop a short (or rather an open). Many times this renders your headphones useless.
  • What To Look For – Some headphone manufactures allow you to easily replace the entire cord. If you know you are a bit rough on your headphones or if your headphones are traveling headphones consider purchasing headphones that allow you to easily replace the cord, especially if you want to purchase quality headphones.

Use this information to choose the right headphones for you and your audio player. Purchase based on your needs not based on brand name or based on the name attached to the headphones. Make an informed decision. Also if a manufacture tells you that we all hear different and that the tech specs are not important, do not believe them. It is true that we hear differently, but the tech specs do matter. Unless they are customizing headphones for your ears, then consider the general tech specs discussed above when purchasing.

Additional References:

Gelfand, S A., 1990. Hearing: An introduction to psychological and physiological acoustics. 2nd edition. New York and Basel: Marcel Dekker, Inc.

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