After leading wedding bands for over a decade, the single biggest request I still get from clients is "Please! don't play loud at my Simcha". So why is it that so many people walk away from a Simcha complaining that the music is too loud? In order to answer this question you need to understand that there are many different reasons for this, and sometimes it's a combination of a few different reasons. I will try to explain one at a time.
First we need to determine; "How loud should a band be?" That depends at what part of a Simcha. During a Smorgasbord, Chuppah and dinner the volume should be soft, however during the dance sets the volume has to be loud enough to cut through the crowd so that the people singing and dancing know what part of the song and rhythm they are up to, otherwise the dancing may be become uncoordinated. Lets call this volume "Necessary volume"
Now that's where the first issue comes in. Some catering halls have echoing acoustics because of hard surfaces in the room like glass, mirrors, hard walls etc. (like a gym). The sound of the band at "Necessary volume" will now bounce all over the room creating a boomy noise. If the band plays lower then "Necessary volume" you may not hear the music clearly and the singing & dancing will become uncoordinated. Some Halls have excellent acoustics with carpeting, drapes and acoustic ceiling tiles to absorb sound.
The second reason is, the PA system needs to be powerful enough for the job. In order to hear amplified music clearly in a large room full of people, you need powerful amplifiers and large speakers that contain heavy magnets so they can move a lot of air. Some band leaders will bring smaller lighter PA systems since it is not easy schlepping a big heavy one. When they need more volume than the PA can handle, the system can overdrive and you will hear distortion. Just like turning a home boom boxs volume to 10, you hear distortion.
The third issue is generation gap. The young folks want is louder, their parents want it lower. When we are younger our ears have a strong tolerance level to the volume of music. As we age that tolerance level goes down (or away). Band leaders decide who is responsible for hiring them at the next Simcha. If it is mostly the young friends of the Choson and Kallah the band has to satisfy them in order to book the next wedding.
The fourth reason is as follows: If the musicians of a band play together on a regular basis under the direction of the same leader, there is a certain familiarity and understanding between them. If the musicians don't work together regularly, or the band leader is unfamiliar with them, one musician can cause the entire band volume to increase.
Here's a scenario;
The band starts a dance set at "Necessary volume". OK everything is good. Now the drummer really wants to get into it. So, he hits the drums a little harder (playing louder). Now the keyboardist or bass player can't hear himself so he increases his own amplifier. The guitarist now feels left out so he cranks the volume on his amp. The horn players can't hear themselves so they ask the band leader to make them louder in the main PA. Now the entire band is at twice the "Necessary volume". Having a good sound technician bring a PA system with stage monitors to a Simcha may be an expense, but it can help out this situation since he controls everyone volume.
When all is said and done, a client at his own Simcha is usually too busy physically, mentally and emotionally to notice anything, and usually gets a surge of adrenaline which make his ears more tolerant to music just like in his youth. While some of his friends are complaining that the band was too loud he is delighted and thinks the band volume at his Simcha was just perfect. The next client says, "Please! don't play loud at my Simcha!" so the story repeats itself, and in the end he will be satisfied too.