Audio out - amplifier for ear buds

Question

I am nearly deaf, using the computer audio out 3.5 mm plug for earbuds I often can not hear the audio while attempting to watch a youtube video. Many persons do not carefully record their audio nor use closed caption.

I need to use earbuds rather than playing the sound through a speaker because I have to have the volume up so loud no-one can stand to be in the house. I turn the computer volume to the max, and the video playback to the max and can barely hear audio. It would be nice to have some range that I can turn up or down.

I have looked for circuits that will actually amplify the sound without blowing the little earbuds to pieces. I do not know the impedance of the earbuds but figure they are far lower than the 8 ohms for a regular speaker. I do wear blue tooth enabled hearing aids but the computer does not send the audio signal via blue tooth. They use blue tooth for the keyboard or mouse.

If I did have a device that could connect to my hearing aids through blue tooth, I would still need a way to control the sound level to make up for the wide variation in sound recording levels. I could write a list of ideal specifications like...

1. Simple

2. just plug into the 3.5 mm jack on the standard device such as phones, computers, etc.

3. A volume control knob

4. An automatic gain control that could level out all signal levels to a standard level so the volume control would simply be for controlling the level.

5. A bypass connection to go to an external speaker when watching a movie with someone (it would be nice to still have the ability to use my earbuds at the same time.

Issues:

1. The quality of the sound does not make much difference to me, I cannot distinguish the high fidelity nuances of music any longer. But the tone level can be very critical. When thinking of an equalizer the higher frequencies are completely gone, as are much of the lower frequencies. My hearing aids are tuned to optimize the level for my hearing. There is still the problem that the audiologist is not able to give enough volume to frequencies I am lacking because of the hearing devices feedback causing a squealing sound. I can't hear the squealing but people run out of the room when it happens. So they set the level as high as they can.

2. Headphones are uncomfortable to wear for long periods of time. The light ones seem to easily get dislodged, the expensive ones have a pressure that pushes against the head causes an ache in the head.

3. Blue tooth is wonderful, more than a few times I have gotten up forgetting I have the earbuds in and the cable yanks them out of my head.

4. I did not lose my hearing until I was an adult and a bit to close to a bomb going off. (A lot of soldiers have this problem)

5, I know there are commercial devices but I am not certain they will do what I am trying to do.

6. I originally thought an ic amp that ran on 5 volts with a volume level control that I could pug into the USB to get the power, the audio jack to get the signal, and an output jack to plug in the earbuds. Seems simple but would like some guidance. I am not sure where to find that guidance.

Appreciate any pointers,

Mike

beacon_dave · Answer

You may find that an audio compressor will help you. This would allow you to reduce the dynamic range of the audio. Basically you set a threshold and any audio above that threshold starts to get reduced. This will initially make things quieter, but then you apply 'make-up gain' to lift the overall level of the audio back up to where the peaks were. The result is that the loud sounds remain at the same level, but the quieter sounds now are boosted. It is normal to find compressors in the preamp stages of AFILS inductive loop systems. They often compress the audio down to about a 30dB dynamic range. Combined with some EQ then you can control what gets compressed. You may want to roll off the frequencies that you know you can't hear and concentrate more on the 200Hz - 2kHz range for speech.

mgillett · Answer

Thank you, This is what I figured in terms of earbuds are simply piezoelectric devices. Small input amplitude causing the thin wafer to "buzz" like crazy creating the sound wave. These have limited ability to drive simply due to the nature of their construction. Distortion becomes an issue quickly.

I do not know if other materials have been used to seek to increase this effect in an earbud configuration. Thinking thin wafer of crystal, limited ability to take much voltage, Different types of plastic bonded to a piezoelectric element? Titanium? Not much value in doing that type of research unless making an ultrasonic cutter, etc.

I agree with configuring the computer correctly, or a device that does take the audio out and send it into a Bluetooth audio signal (It would be very nice to control it with a simple twist of a knob. Rather than fumbling around for the little slider on a computer screen.

You are also correct in the concern for the "varying" crest factors of content.

DSP? Digital Signal Processing? Seems that this would be very difficult to do, the circuit would have to be able to determine some maximum level, it would then clip anything beyond this to that set max level. And possibly just bring all of the signals up to that max level, producing straight garbage. But without a max level, it would seem to be a mind-blowing experience at times. The hearing aids do have an auto "clipping" circuit that instantly clips things shut as a gunshot. You would not want to amplify that signal from its already 140-190 dB up an additional 100 dB gain if a tiny little piezo device could withstand the signal it would even be "mind-blowing" even if I couldn't hear it. It really is odd to have sound pumping into your ear and fell it through the vibration of your skull with your fingertips but barely be able to hear the sound. I am exceedingly grateful for the researches that have developed these compact, sensitive instruments that I can run on a tiny little battery.

I believe your answer is absolutely correct, I should focus on getting the computer signal sent directly to the Bluetooth enabled device.

The follow-up question is then how do I do this? I can do it with my cell phone, and many other devices but not my computer at work, at home, or the TV. (Maybe newer TV's have it built in?) (Maybe some computers have this built in as well?)