How can I force just his voice?

[motherless]

I'm having a hard time forcing his appearance due to my condition, so for now I want to focus on just his personality in my head. What should forcing look like if I don't imagine him next to me?

[Luminesce]

Mental skills should get easier with practice, visualization would hopefully become less difficult if you kept at daily practice (even if just for a few minutes, as long as it's every day)

Otherwise, focusing on the general sense of presence of your tulpa is fine, and of course if they could talk then that's enough to focus on

 

I imagine your tulpa still isn't vocal though, in which case you're probably in the group of people who accidentally prevent their tulpas from speaking, generally due to it not feeling "real enough" early on, but letting them speak at all regardless of whether they sound fully independent from you or like themselves yet is still a necessary step. Tulpas will begin to sound more like themselves and feel less like your own vocalized thoughts over time (if they do to begin with), you just need to accept that anything reasonable is them talking/learning to talk as a starting point.

To that end, some people practice parroting, which is intentionally imagining your tulpa speak as a form of early vocality forcing. The pro is that it helps get over the "It's not my tulpa, it's just me" block that some people have that prevents them from ever making vocality progress, but the con is you may not transition smoothly to feeling like it's actually your tulpa talking and so get stuck thinking you're still always talking for them, which is basically the same problem. Optimally, you give your brain a little wiggle room to imagine they are actually responding when you talk to them, and just don't doubt that it's them - if it's not that convincing, then (as long as it still makes sense as something they might choose to say) simply consider it them learning how to speak (well, because it is). Eventually, as you treat your tulpa as a separate person in your mind and put focus into anticipating their actions/speaking as independent from your own, your brain should start getting the idea and shape the experience to be more robust and fulfilling -

If it isn't from the start! There are plenty of people who do just fine from day one, mostly by simply not doubting anything at all lol (keep it within reason though), but it's plenty common for people to get kind of trapped in doubts as well. Doubt is directly counterproductive to shaping the tulpamancy/plurality experience, so really all you can (and need) to do is give them a chance regardless of how things feel at the start, and over time it should become much more obvious when they are doing/saying things of their own volition. Eventually their speaking should be unmistakable for your own, with their "mindvoice" feeling like them in addition to (hopefully, technically optional to imagine a unique voice) sounding like them