Making a landline phone ring on stage
It’s much better to have a landline home or office phone actually ring on stage. The sound is obviously more localised to the source, and the sound is correct for the look of the phone.
Many professional theatres have stage management desks with phone-ring functions built in.
Some theatre supply companies have specialist phone ringers available to hire.
Sparks Theatrical Hire in London, UK have a video of their ringer operating:
Companies such as Tele-Q offer phone ringers for sale.
Making a Mobile / Cellphone Ring on Stage
Mobile phones are an exception to this as it’s risky to have a mobile phone ringer on during the show. Mobile phone ringtones can be recorded and replayed through a speaker behind where the phone will ring on stage.
New software from StageCaller enables you to make an iPhone or Android phone ring on stage via a wifi network, rather than using the cell network, making the call more reliable, and removing the possibility of an incoming call ruining the show
Making a phone ring without a ringer
If you don’t have access to an SM desk with a ringer, you can usually get a ring out of a modern phone by applying 48V AC across the ringer terminals. As the supply voltage is (in the UK at least) at 50Hz frequency, the frequency is too high to simulate a phone ring accurately, as the frequency of the ringer voltage on a phone line is around 20Hz. However, it will be acceptable in many circumstances.
An electronic engineer will be able to recommend a solution which can lower the frequency of the voltage.
Do not attempt this without referring to a suitably qualified electrician first.
An older phone with bells inside it may need a higher voltage, but you could always use a standard domestic doorbell as a ringer, which operates on a much lower (and safer) voltage.
It’s always good to have the phone cut out (as in reality) when the handset is picked up, so try to incorporate this if you’re able to rewire the phone.
How to make a voice recording sound like it’s on a phone
Open the digital file of the original recording in your favourite sound software. Use the EQUALISATION function (use the Help system if it’s not obvious) to adjust the tonal quality of the sound. Most equalisation controls have at least three ‘bands’ of audio frequencies that can be adjusted, and they’re usually called high, middle (or just mid) and low. To replicate the sound of a phone call, you need to boost / raise the middle frequencies (which are the audio frequencies responsible for the clarity of the human voice) and lower the others (high and low).
How to make a live microphone offstage sound like it’s coming from a phone call
The audio quality of a phone call is much lower than sound captured by a microphone, so again, we need to make use of equalisation controls (EQ) on a sound desk to achieve the right sound.
Connect the microphone into the sound desk as usual. Use equalisation controls on the mixing desk input channel to reduce the high and low frequencies, and boost the level of the mid frequencies.