Last Saturday(July 30, 2011), we conducted a simple experiment at Golden Ears. The purpose of the test was to see how much discrepancy there was between the bass frequency response of flat speakers and flat earphones.
Something that you should remember as you read this article is that the quantity of bass experienced through speakers is fundamentally different from the bass from earphones as it impacts the entire body.
A way around this when using earphones is to use an external subwoofer or to simulate this effect through bone-conduction earphones, but you might as well use full speakers if you are relying on an external subwoofer, and the poor sound quality of bone-conduction earphones make them a hardly adequate solution where things stand.
As there exists no viable workaround to the earphones lacking impact, the bass is boosted on many earphones to achieve a similar - but suboptimal - result. As you will see, bass-boosted earphones in fact sound closer to flat speakers than their counterparts with a completely flat frequency response, and the quantifiable difference (in dB) is what we are testing for today.
So, please bear in mind that the objective of this article is not to claim that a particular method / amount of bass boost is ideal, but rather to establish what is feasible given the current technology.
1. With the test subjects present, ADAM S2.5A speakers were modified to resemble the Small Room X-Curve at the listening point.
2. Using the combination of iPhone 4 and ER-4S earphones, a 500Hz sine wave (which is only affected minimally by in-ear resonance) was played so that test subjects could set the volume to their usual listening levels, after which it was fixed.
3. 500Hz sine wave signals were generated by a computer and played back through ADAM S2.5A speakers (the subjects had no access to the computer)
4. Speaker volume was adjusted by the administrator as requested until the subject considered the volumes from speakers and earphones to be identical.
5. The subject listened to a test source on an iPhone 4 and ER-4S for a set time.
6. The same test source was played back on a computer and ADAMS2.5A speakers and equalized by the administrator until the subject considered the bass frequency response to be identical.
Earphones' volume was matched individually as it tends to show much difference from person to person due to different anatomy and fit.
The source used for the testing for bass quantity comparison was the track “Kyoto”, from the album “Right of Way” by Ferry Corsten (the pattern repeats itself regularly, which makes it ideal for this comparison).
The results marked out two distinct groups:
1. -6dB discrepancy at 20Hz (5 subjects)
ER-4S earphones are rather difficult to fit properly, and for this reason, I had previously exclusively tested subjects who could achieve the right fit.
- ER-4S fits perfectly: 1 subject
- ER-4S can be fit tightly and deeply, even if unpleasant: 2 subjects
- Custom eartips: 1 subject
- Special silicone eartips: 1 subject
And subjects belonging to this group perceived a -6dB difference (with plus or minus 1 dB error) between earphones and speakers, both in the previous test and the current.
2. -10~12dB discrepancy at 20Hz (-10dB: 4 subjects -12dB: 1 subject)
The other five subjects took part only in the July 30th trial, and the wider perceived discrepancy is likely attributable to bad fit with ER-4S earphones.