Don't suffocate in your soundproof studio!
Do you intend to soundproof your studio?
It is a pleasure to work in a soundproof studio, free from irritating outside noise, and relaxing in the knowledge that nothing you do will annoy your neighbors.
So to soundproof your room, you add mass to the walls, ceiling, floor, windows and door, exactly as you should. And you make sure that there are no leaks. Sound will find its way through even the tiniest of gaps.
But with effort and attention to detail, you can indeed have a soundproof studio. Perhaps not perfectly so, but effectively so for your purpose.
But there is now a problem. Since you have sealed all the gaps against sound penetration, you have also made your room air-tight.
Indeed, it can often be difficult to open and close the door to a soundproof room because of the air pressure.
Now, as you work in your soundproof studio, you will find that you get hot and stuffy. If there are other people in the room, it will happen more quickly. If there is a singer, he or she will feel uncomfortable first.
Some people who find that that their studio becomes hot and stuffy in use go out and buy an office-type fan. But this merely redistributes the hot and stuffy air around the room. It provides a slight subjective benefit when it is wafting in your direction, but not all that much.
For a cool, fresh working environment you need two things: ventilation and air conditioning. These are two separate processes. Ventilation does not cool the air (unless it's Alaska outside) and air conditioning does not provide fresh oxygen.
Ventilation is often perfectly adequate in itself. Although the temperature may rise, at least there is oxygen in the air. If you don't mind a hothouse environment, then ventilation from the outside world, using a large fan for quietness, may be enough.
The problem with both ventilation and aircon systems is that they create noise. A professional studio will spend a fortune on its system, installed by a specialist contractor who understands recording studios.
In smaller studios, it is usual to expect noise from the ventilation and aircon systems and simply tolerate it. You can switch them off when you are recording using microphones, and for critical listening during the mix.