In general, this is a bad idea.
People usually suggest this idea because they want the non-headphone wearers to have fun too. They don’t realize how much fun Silent Disco is to watch. But, here is the thing: Silent Disco is only fun to watch in silence.
When there is only silence, it is incredible to watch the people dancing to (seemingly) no music. It is a crazy fun to be NOT wearing the headphones at a silent party because it LOOKS so weird!
But it only looks weird if you can’t hear music. The silence creates cognitive dissonance that is hilarious. By having audible music playing for your non-headphone wearing guests, you are depriving them of a really good time.
Audible music coming from loudspeakers takes away from the headphone wearers because some of it bleeds through the headphones.
Don’t get me wrong; Our headphones do provide sound isolation (some call it noise cancellation) but it is only due to the headphones covering the ear. In other words it is not much.
The headphone wearers will only hear a little bit of the loudspeakers but it will be enough to diminish the experience.
Now there is nothing wrong with having a small speaker playing quiet background music while the headphones are being used.
The wearers won’t hear that and it won’t disturb them. . But if you are having a DJ with big speakers play music at any sort of volume that DJ’s usually play- that will ruin the headphone experience.
There is nothing worse than hearing two songs at the same time. -Also, remember that Big speakers used by DJ’s also provide knee shaking bass that people actually “Feel” in their body. The headphones don’t have that. So, even if the headphone wearers don’t hear the high frequencies from the big loudspeakers, they will feel the low frequencies from the big loudspeakers and again that will cause a significant decrease in any pleasure the headphone wearers are feeling.
Another important aspect of the Silence is that it motivates people to try the headphones.They want to hear what everyone else is hearing. They don’t want to miss out. And if they have their own audible music from loudspeakers, that pressure to put on the headphones is taken away.
In closing: There is nothing wrong with a regular DJ just playing loudspeakers. I do that for a living. There is nothing wrong with Silent Disco, but it does require silence.