As already mentioned, all brakes will increase what we as shooters experience as muzzle blast intensity simply because the muzzle gas is redirected closer to the area we are at when the firearm is fired.
If you want a brake, great but realize your going to have to deal with increased muzzle blast. If that is something you do not want to do, then you can add weight to your rifle to ****** the recoil, use a better recoil pad or just live with it.
Also, as mentioned, a suppressor is the quietest means of reducing felt recoil. I have heard there are some out there that are as good as the better muzzle brakes at reducing felt recoil. I have shot some of the better ones and have not been impressed. Quiet, yes, reduce recoil, not so much....... Especially on the larger chamberings.
If your going to deal with the issues of a muzzle brake, why not get the most benefits of a brake. I hear this all the time, I want the quietest brake possible. My reply to them is do you want to control recoil or not???? If your going to invest the money and live with the issues a brake imposes on you and those around you, you may as well get the best return for your money in my way of thinking.
As far as what makes a muzzle brake loud or really loud??? That depends on many things.
1. The individual. I have had some customers say that a Holland QD brake put them on their knees when they shot their rifle without ear plugs. Other tell me that when they shoot at big game, they still never hear the brake, this is where I generally fall as well. So it really depends on the person, some are REALLY effected by a brake and others are not. Only one way to find out..... I always recommend hearing protection when using one however if at all possible.
2. Muzzle gas pressure. If your shooting a 308 in a 26" barrel compared to a 7mm Allen Magnum in even a 30" barrel, the big 7mm will have dramatically higher muzzle pressure then the 308. As a result, the muzzle blast will be more intensive with brake on or not.
3. caliber and velocity of the chambering. Some may say this is a load of crap but if you take a 7mm RUM and load it with a 140 gr Accubond to 3500 fps and then take a 375 RUM and load it with a 300 gr to 2850 fps, the 7mm always seems to be harder on the ears to me then the larger chambering. Again, goes back to expansion ratios and muzzle pressure levels.
SO what makes a brake louder or quieter then another brake. Generally, angle of ports and the velocity at which the muzzle gas is vented from the brakes in my testing.
With my line of Painkiller muzzle brakes, I used an aggressive 30 degree back angle on the ports but I Also made the ports with a high volume and large baring surface. This does a couple things. The back angle and large surface area really promotes recoil reduction. The high volume ports reduces gas velocity. In the end, you get high recoil control but also in a manner that is not as sharp as far as muzzle blast as other paritition style muzzle brakes.
Simply put, if your going to live with a muzzle brake, why not get one that will do what its designed to do, reduce recoil. Then protect your self from the issues of any muzzle brake.