Does anyone know the most effective and quietest way to ventilate a small isolation booth? Any suggestions will be welcome.

Bathroom Vent fans noise levels are rated by "Somes"(rhymes with "Roams"). The quieter they are, the more expensive they get.

It is better if the Fan is at the OTHER end of a long Duct that has lots of turns and isn't rigid and runs at low speed. I would try to make it PULL air out of the booth instead of Blowing in. Some fans are reversible.

jmp

years ago, I build a fan box that was about 3 feet long, with a fan at one end, an air opening at the other. In between were 3'4" plywood baffles, covered in sound insulation. This allowed air flow, but fan noise was close to zero.

There are probably plans on the internet.

good ideas already. Getting a inline fan should do the trick. This one might be too much, just look for a lower cfm.
http://www.iaqsource.com/index.php?module=product&prod_..._mfg=22&prod_id=1782

Silent bathroom type
http://www.iaqsource.com/index.php?module=product&prod_...b_cat=0&prod_id=1940

I ended up having a ventilation plenum built for me. I had ordered D.Y.I. plans to build a vocal booth. The build wasn't too difficult, nor was it expensive. When I was placing my order for the plans, the sales guy offered to have the company build and ship me the plenum promising it to be ultra quiet. I found the price to be reasonable. Once I had everything put together, my vocals were isolated and the airflow was very good. There is no fan noise and a nice cool airflow in and out.

I would recommend this company.
www.dawbox.com