BPI-M3 Can you tell me will this synthesizer work?

I’ve attached an image of the schematic for a synth I’m designing. The basic principle is that I have three 555 timers, each generating a square wave whose frequency is controlled by the resistors R1, R9, and R13. Each timer’s output can optionally be converted to a sin wave or left as a square wave based on a switch on the output of each timer. The three different timer outputs now are summed together at U2, but are weighted according to R5, 6, and 7. The resultant waveform is then sent through the speaker at the bottom. The whole thing is powered by a 9V DC jack.

I have two main questions: Are the 555 timers wired up correctly? This is my first time using them like this. Will there be a problem with audio impedance at the speaker? I have little understanding of impedance in this context. Thank you in advance!