Comment by shrx
5 days ago
We have a similarly converted rotary phone at my local astronomy club's observatory, used to receive visitors. It's driven by an arduino if I remember correctly. The main issue is that the sound quality of its built-in speaker is quite poor, especially compared to modern cell phone speakers we're used to nowadays, with a narrow frequency window and frequent echoes.
In contrast, I've been messing around with some old analog phones and VOIP stuff recently, and I've been blown away with how good the quality is over what I was expecting. The audio bandwidth is low yes (it's G.711u, so 8 KHz), but the actual quality is great, with no hyper-compression artifacts or over-applied background noise filters. And yes this is on the original 60's carbon microphones.
The regular phone calls I normally make on my cell still all sound like they are underwater for some reason, except for those rare times when the better connection is actually working.
I've seen projects that swap out the rotary phone speaker with a speaker from a pair of on-ear headphones.
The Secret Life of Machines TV show has a fun demo of how the speakers in old telephones produce sound https://youtu.be/MCgCSMq5Xpo?si=CT5aOGttBpPk9tEM&t=458
Interesting. I remember voice clarity being exceptional on old handsets and being really subpar on gsm and later. Only now we FaceTime voice and discord the quality seems to be coming back.
How can that be if the speakers in phones ubiquitously were so bad?
My understanding is that at some point the audio of phone calls ended up being compressed multiple times on its way to the receiver as it went through different voip setups and such.
Prior to that, uncompressed or compressed once calls weren't so bad on bad speakers.
Could be that it wasn’t bad but has gotten bad because of aging of the speaker, capacitors, resistors, etc.