They never really explained how the Goa'uld's voices sound like that either(or they did and I missed it). But there actually could have been something to change the voice. During the merger maybe an extra organ could've been added to the vocal cords to produce a booming, threatening tone.
But oh well, what's done is done. I still await the next one.
(I could potentially watch it now, but as you know I traditionally watch it with my mom and dad and it's pretty much impossible for them to watch it more often than once a week.
)