Measuring BC thresholds at high frequency

[carolinemasamba]

The BSA protocol recommends that when testing BC thresholds at high frequencies the test ear should be covered.
I am intrested in finding out what methods you employ, head phones or ear plugs or anything else.. and why ?? not the other

[Brimstoneandfire]

On my placements I've used headphones, inserts (when already using them to test anyway) and foam ear plugs.

I've got a feeling that correctly positioned foam ear plugs or inserts might be better at occluding the test ear than a correctly positioned headphone. I'm just speculating this upon the basis that you'd perhaps get a better acoustic seal from the foam in the EAM than the relatively hard rubber transducer provides around the pinna (lots of contours, afterall). I'm assuming this argument would hold more water if we could test BC at higher presentation levels; without vibrotactile responses being an issue!

... I think the ear plugs might be handy for patient comfort, but then there's the cost/budget implications of bringing in earplugs?

[AcousticS]

Basically, I measure the bone conductor is positioned with a bone conduction receiver on the mastoid. On the other side head phones or ear plugs should not occlude the ear canal. This gives both sides an additional closed pipe. It is my opinion, to circumvent the osteotympanaler bones sound. This is the sound that is emitted from the skull. This is taken from the tympanic membrane, strengthened by leveraging the auditory canal ossicles chain and land transformation and delivered to the cochlea. Our results are then distorted.

[galls83]

similarly i agreed also to this way. placing the BC on the test ear and Masking on the non-test ear and making sure not to occlude the test ear. but as predicted with this method, BC thresholds if exceeding a high value will result in vibrotactile responses or eventually over masking for some thresholds

[Guy]

AcousticS is referring to what I know as the "occlusion effect". This is important only below 2kHz so below 2kHz (where air borne radiation from the case of the BC is not a problem) it is important not to cover (occlude) the test ear and to occlude the non-test ear only when delivering masking noise.

At frequencies above 2kHz the occlusion effect is negligible but air borne radiation (i.e. sound) from the BC is a problem and to ensure that we are actually testing by BC and not AC radiated from the case of the vibrator we must cover the test ear, either with a headphone or an ear plug (which has a greater attenuation). An ER3A plug is fine for this. In general the higher the BC frequency the greater the problem. See my paper on this: Bone conduction errors at high frequencies: implications for clinical and medico-legal practice. J Laryngol Otol, 1993, 107, 305-308.

Why not cover the non-test ear? The head shadow effect helps but I reckon the non-test ear will be covered for masking purposes already.

[AcousticS]

Originally Posted by Guy

[...] See my paper on this: Bone conduction errors at high frequencies: implications for clinical and medico-legal practice. J Laryngol Otol, 1993, 107, 305-308. [...]

Perfect !

I then googled:
http://www.thebsa.org.uk/docs/RecPro/PTA.pdf

This occlusion effect is also in the hearing aid supply with an secret ear known as "insersation lost".
What this means is: destruction of natural ear canal resonance (OEG).

Remedy for this is the hollow channel secreat ear (to German: "Hohlkanal Otoplastik").


Picture by www.Pahl-Otoplasik.de