The Effect of Ear Sleeves: Etymotic Research ER-4B

Ear sleeves play very important role in IEM acoustics. With an adequate bore size and proper insertion depth, one might be able to get a potential performance of an IEM in full. The previous test result on Etymotic Research MC5 proved this.

However, MC5 is a dynamic transducer earphone. Generally, a dynamic transducer acts independently under the input load due to its low acoustic output impedance(constant-pressure driven), unless the driver's compliance has been reinforced(titanium & bio-cellulose & sapphire & etc) for certain purposes. Since most of the IEMs available in the market are made of a balanced armature transducer, which has a high acoustic output impedance, it is required to run the same test on a balanced armature earphone as well, to further verify the effect of ear sleeves.

THINGS TO CONSIDER:

1. Ear Sleeves of Shure & Etymotic Research are compatible to each other; not sure about the ones made by Westone. Somebody get me some Westone sleeves, then I will include them in this analysis as well.
2. Silicone sleeves offer better bass extension, due to the silicone's water resistant property.

3. Shorter the bore length, the more even high frequency response for MC5.
4. Wider the bore diameter, the better treble extension for MC5. 

5. A balanced armature transducer, in this case Knowles ED-9689, reacts to the input impedance more or less sensitive than a dynamic transducer, MC5; possibly due to MC5's helmholtz resonator equlization?

BOTTOM LINE:

1. Personally, I would like to choose clear sleeves among silicones, and shure olives among foams. Of course, all these can be achieved, only with proper insertion depth.