If you have some free time and you are good in handicraft maybe you could DIY your own Hex tweeters.
I saw this DIY Hex Tweeter at a Swiftlet farm in Selangor. It is very unique with the wire mesh on top of the Hex to prevent other birds to perch on it.
The advantage of DIYing the Hex is that you could choose the type of tweeters you want. It can be the simple cheap Piezo tweeter to the more expensive Motorola quality type or perhaps the Metal Tweeters (NH Type).
For me I would prefer to use better quality tweeters though the price might be expensive but we only use few of them.
You could use 4-8 pcs of tweeters. Anything more than that I think it is a waste. Don’t forget to use good speaker wire (100% copper). No point of using good quality tweeters if the wire is not the copper type as it would affect the sound quality.
It is recommended the mouth of the tweeters should face horizontally to prevent rain water from entering. Having facing horizontally the sound could travel farther. The top of the Hex cover should be slightly larger so that it could prvent rain water from entering.
Look at the picture it is very easy to DiY.
Good Swiftlet farming All!