<p><strong>Short answer</strong><br />
Occlusion of the middle ear increases sound pressure levels at the tympanic membrane.</p>
<p><strong>Background</strong><br />
The <strong><a href="https://hkincus.com/blogs/blogs/the-occlusion-effect?srsltid=AfmBOooDNosVutJ9SGbo5u40-t0rz8TbhOK1QO4Dg9eO_B9vwR19gMwZ" rel="nofollow noreferrer">occlusion effect</a></strong> is defined as the increase in sound pressure in front of the tympanic membrane when a <strong><a href="https://www.bose.com/stories/air-conduction-vs-bone-conduction" rel="nofollow noreferrer">bone-conducted</a></strong> signal is administered while the ear canal is occluded. Sound levels increase particularly at low acoustic frequencies (up to 1 kHz) and bone conduction hearing thresholds improve at these frequencies. The cause of this is complicated, but results from changes in the resonant properties of the ear canal when it is occluded and changes in the inertial motions of the middle ear bones (ossicles) that together result in the occlusion effect <a href="https://journals.lww.com/ear-hearing/fulltext/2011/11000/maturation_of_the_occlusion_effect__a_bone.4.aspx" rel="nofollow noreferrer">(Small &amp; Hu, 2011)</a>.</p>
<p>The occlusion effect can be as high as 25 dB at low frequencies (125 - 250 Hz) <a href="https://pubs.aip.org/asa/jasa/article/14/4/207/716598/Bone-Conduction-Threshold-Measurements-Effects-of" rel="nofollow noreferrer">(Watson &amp; Gales, 1943)</a>, which is a substantial increase in sound pressure level. The vibration frequency of an electric toothbrush is around <a href="https://en.wikipedia.org/wiki/Electric_toothbrush#:%7E:text=Most%20modern%20rechargeable%20electric%20toothbrushes,24%2C000%E2%80%9348%2C000%20movements%20per%20minute." rel="nofollow noreferrer">200 - 400 Hz</a>, which is the sweet spot for the occlusion effect to occur. I couldn't find what the <strong><a href="https://www.bose.com/stories/air-conduction-vs-bone-conduction" rel="nofollow noreferrer">bone-conducted</a></strong> sound level range is of an electric toothbrush, but <strong><a href="https://www.bose.com/stories/air-conduction-vs-bone-conduction" rel="nofollow noreferrer">air-conducted</a></strong> sound levels are <a href="https://www.audicus.com/noise-levels-of-everyday-sounds/" rel="nofollow noreferrer">around 60 dB</a>. Let's assume this is the correct ballpark also for the bone-conducted component, then adding 25 dB yields 85 dB. For comparison, 60 dB SPL is approximately <a href="https://rnid.org.uk/information-and-support/ear-health/protect-your-hearing/how-loud-is-too-loud/#:%7E:text=40dB%3A%20a%20quiet%20library,88dB%3A%20heavy%20traffic" rel="nofollow noreferrer">normal speech level</a>, whereas 85 dB SPL approximates the sound level of a <a href="https://rnid.org.uk/information-and-support/ear-health/protect-your-hearing/how-loud-is-too-loud/#:%7E:text=40dB%3A%20a%20quiet%20library,88dB%3A%20heavy%20traffic" rel="nofollow noreferrer">food blender</a>. While I don't regard 85 dB as '<em>deafeningly loud</em>', I can imagine it comes as a surprise when wearing ear plugs and you're unprepared for the occlusion effect to come into play.</p>
<p><sub><strong>References</strong><br />
<strong>-</strong> <a href="https://journals.lww.com/ear-hearing/fulltext/2011/11000/maturation_of_the_occlusion_effect__a_bone.4.aspx" rel="nofollow noreferrer">Small &amp; Hu, <em>Ear Hear</em> (2011); <strong>32</strong>(<em>6</em>): 708-19</a><br />
<strong>-</strong> <a href="https://pubs.aip.org/asa/jasa/article/14/4/207/716598/Bone-Conduction-Threshold-Measurements-Effects-of" rel="nofollow noreferrer">Watson &amp; Gales, <em>JASA</em> (1943); <strong>14</strong>: 207–15</a></sub></p>

CC BY-SA 4.0
2024-11-06T16:00:28.317Z
2024-11-07T07:47:37.353Z
2024-11-07T07:47:37.353Z
AliceD
<p>I was outside using some power tools on a DIY project and was wearing little foam earplugs as PPE. I came indoors to finish off some tea I made earlier and had put into an insulated mug, and since it had a generous spoonful of honey in it, I went into the bathroom afterwards to brush my teeth.  The &quot;intracranial&quot; sound was deafeningly loud. The sound of the bristles against my teeth, the sound of swishing of water as I rinsed out.  What is it about having those foam plugs blocking sound from the outside that makes the intracranial vibratory sound seem so loud?</p>

<perception><sensation><hearing><sensory-perception>
Why does brushing your teeth with sound-muffling foam ear plugs inserted sound so deafeningly loud?
Tim
# Why does brushing your teeth with sound-muffling foam ear plugs inserted sound so deafeningly loud?

(Asked by: username_0 on 2024-10-31)

I was outside using some power tools on a DIY project and was wearing little foam earplugs as PPE. I came indoors to finish off some tea I made earlier and had put into an insulated mug, and since it had a generous spoonful of honey in it, I went into the bathroom afterwards to brush my teeth. The "intracranial" sound was deafeningly loud. The sound of the bristles against my teeth, the sound of swishing of water as I rinsed out. What is it about having those foam plugs blocking sound from the outside that makes the intracranial vibratory sound seem so loud?

**Tags:** perception, sensation, hearing, sensory-perception


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## 1 answers

### Answer by username_1 on 2024-11-06. Score: 6 | Accepted answer

**Short answer**  
Occlusion of the middle ear increases sound pressure levels at the tympanic membrane.

**Background**  
The **[occlusion effect](https://hkincus.com/blogs/blogs/the-occlusion-effect?srsltid=AfmBOooDNosVutJ9SGbo5u40-t0rz8TbhOK1QO4Dg9eO_B9vwR19gMwZ)** is defined as the increase in sound pressure in front of the tympanic membrane when a **[bone-conducted](https://www.bose.com/stories/air-conduction-vs-bone-conduction)** signal is administered while the ear canal is occluded. Sound levels increase particularly at low acoustic frequencies (up to 1 kHz) and bone conduction hearing thresholds improve at these frequencies. The cause of this is complicated, but results from changes in the resonant properties of the ear canal when it is occluded and changes in the inertial motions of the middle ear bones (ossicles) that together result in the occlusion effect [(Small & Hu, 2011)](https://journals.lww.com/ear-hearing/fulltext/2011/11000/maturation_of_the_occlusion_effect__a_bone.4.aspx).

The occlusion effect can be as high as 25 dB at low frequencies (125 - 250 Hz) [(Watson & Gales, 1943)](https://pubs.aip.org/asa/jasa/article/14/4/207/716598/Bone-Conduction-Threshold-Measurements-Effects-of), which is a substantial increase in sound pressure level. The vibration frequency of an electric toothbrush is around [200 - 400 Hz](https://en.wikipedia.org/wiki/Electric_toothbrush#:%7E:text=Most%20modern%20rechargeable%20electric%20toothbrushes,24%2C000%E2%80%9348%2C000%20movements%20per%20minute.), which is the sweet spot for the occlusion effect to occur. I couldn't find what the **[bone-conducted](https://www.bose.com/stories/air-conduction-vs-bone-conduction)** sound level range is of an electric toothbrush, but **[air-conducted](https://www.bose.com/stories/air-conduction-vs-bone-conduction)** sound levels are [around 60 dB](https://www.audicus.com/noise-levels-of-everyday-sounds/). Let's assume this is the correct ballpark also for the bone-conducted component, then adding 25 dB yields 85 dB. For comparison, 60 dB SPL is approximately [normal speech level](https://rnid.org.uk/information-and-support/ear-health/protect-your-hearing/how-loud-is-too-loud/#:%7E:text=40dB%3A%20a%20quiet%20library,88dB%3A%20heavy%20traffic), whereas 85 dB SPL approximates the sound level of a [food blender](https://rnid.org.uk/information-and-support/ear-health/protect-your-hearing/how-loud-is-too-loud/#:%7E:text=40dB%3A%20a%20quiet%20library,88dB%3A%20heavy%20traffic). While I don't regard 85 dB as '*deafeningly loud*', I can imagine it comes as a surprise when wearing ear plugs and you're unprepared for the occlusion effect to come into play.

**References**  
**-** [Small & Hu, *Ear Hear* (2011); **32**(*6*): 708-19](https://journals.lww.com/ear-hearing/fulltext/2011/11000/maturation_of_the_occlusion_effect__a_bone.4.aspx)  
**-** [Watson & Gales, *JASA* (1943); **14**: 207–15](https://pubs.aip.org/asa/jasa/article/14/4/207/716598/Bone-Conduction-Threshold-Measurements-Effects-of)


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