Mobile Device In A Cup

I have always had a passion for sound. Whether it was producing a sound from a musical instrument or from a loudspeaker, I wanted a person’s perception of the sound to be pleasant and enjoyable.

Given the proliferation of mobile devices including tablets and phones, it is truly amazing that these devices produce very poor sound. Of course the sound can be improved by using an extra device, headphones or Bluetooth speakers, requiring wires and power. Many work very well.

I was recently at a friend’s house and knowing that I am interested in acoustics, he excitedly placed his phone in a cup and asked me how I liked the improved sound. I have heard of many people doing this and tried it once myself. I have also heard of people placing their phone in a bucket.

It really amazes me that people will spend $500-$1000 for a mobile device that has such poor sound quality that they have to put it in a plastic cup to make it sound better.

So what is going on acoustically that make people perceive a better sound from their mobile device by placing it in a cup? Could it be the resonances of the cylindrical cup enclosure or something else?

If I look at the majority of mobile devices they have the speaker on the edge or on the back. I have found that as part of their claim to have a “stereo” device Apple uses the bottom edge speaker for the left output and the earpiece speaker as the right output for the iPhone 7 and 7+. You would not know this by looking at the bottom edge which has two small speaker grills indicating maybe a left and right stereo output, but the left grill where the headphone jack used to be is closed off. Sound is only coming out of the right grill same place as older models and most Samsung models.

Back to the cup.

Any sound energy coming from a mobile device speaker located on the edge or the back transmits sound spherically away from the listener. As the sound wave propagates away from the listener it gets absorbed and decays 6dB for every doubling of distance. If there are no hard surfaces close by for the sound wave to reflect off and direct the wave back towards the user’s ears, the listener can’t hear the device. This is why, unfortunately, we can observe many people holding their device with the edge up to their ear while driving or walking in a noisy environment. Using most phones to conduct a conference call with multiple listeners is almost impossible.

By placing a mobile device in the right position in a cup allows for the spherical sound waves to reflect off of the hard surface of the cup and emanate from the open end of the cup. The sound source in the cup can excite cylindrical radial resonances of the cup but for an average size small cup these resonances might be in the 5kHz-10kHz range. The cup can also act like a closed/open pipe but again these resonances are high.

So the main benefit of the cup is capturing the spherical sound wave energy and directing it towards the listener assuming the listener is close to the opening of the cup. There is no real amplification of sound although many listeners perceive this and are proud of their inexpensive acoustic accomplishment. In addition the sound energy bounces around in the cup before coming out canceling some frequencies thus making the sound muffled and with a perceived echoed.

In the case of the iphone 7, while the left channel sound energy is being directed away from the listener the right channel is being directed towards the listener. Unless Apple built in some phase compensation, there can be some added distortion due to phase differences between the two channels.

So what else can be done to improve the overall sound of a mobile device? What if the sound could be directed towards the listener at all times?

As we are increasing using the mobile device to watch more and more video content wouldn’t it be beneficial to also have improved sound to go with the video content. The video is directed towards our eyes so why shouldn’t the sound be directed towards our ears?

This can easily be solved and I invite you to check out our Coming Soon page for the introduction of a new mobile device case that directs all sound energy towards the listener.

– There are many benefits and uses for this type of case –

Talking on the phone in the car

Louder phone alerts; alarms, sound messaging icons

Using the phone for calls and multiple participant conference calling

Outdoors while walking, running, playing golf or boating

Watching video content; movies, instructional videos, YouTube video content

Stay tuned for future blogs describing the technical passive acoustics used to design the product.