Play this video clip and have a look at the power of using hexagonal tweeters paying a powerful external sound.
I always prescribed the use of hexagonal tweeters at every BH that I visited or constructed.
This powerful tool will triple the number of birds to your BH rooftop if you used and located it properly.
One of its strong benefit is to push your external sound played at 360* angle.
Yes your external sound will be pushed 360 degrees angle and will attract more birds from what ever location they are flying closed to your BH.
Every birds that flew around your BH is a kind of asset to your BH.
If they can be invited over your BH and flew inside the entrance hole you will stand a higher chance of getting them to be your permanent tenant.
Usually if you play a good and powerful external sounds those birds will in fact come to kiss your hexagonal tweeters.
They will try to land on your tweeter and might stays there for some short seconds or a few minutes.
My best recommendation to any BH owner is to fix this powerful gadget as closed as possible to your main entrance hole.
Remember the right location plus the right height will force them to enter your main entrance window.
If you choose the wrong location plus too high above the roof surfaces you have lesser chances to draw them into your BH.
Let those birds come to the hexagonal tweeters and quickly forced them to enter your entrance hole.
Make sure all that responded (100%) will eventually enter your BH.
Try this idea and I am almost certain that your nests population will suddenly shot up within the next few months.
I assumed that your BH internals are proper.
If they entered and not a single one stays, you need to ask for help.
Call 017 7551318.