How do I make my Mac speakers sound like iPad 2 speakers?
Depending on your budget, I would use something like Rogue Amoeba's Audio Hijack 3 to process the sound output and model the speakers of the iPad.

If you have extra budget, you'll want to record in a acoustically quiet room some songs and test tone generators out of the actual iPad speakers (and maybe sample several devices to see how much variation is present in the iPad line). Use a high quality microphone if possible for this.

You'll have issues correcting for the Mac speakers though and should probably invest in some good powered studios monitors or headphones if you really want to hear what the iPad would sound like.

If you don't have decent audio analysis software, you might want to look at something like Spectre

p.s. FWIW - My MacBook 2015 (40% volume) sounds about the same as my iPad Air 2 (90% volume) and passing the MacBook audio through the AUBandpass filter. Configure the bandpass to be centered around 2 kHz and a width of 5000 cents.