The are many types of tweeters available in the market, the common one that most Swiftlet farms are using is the Piezo type. This simply tweeter doesn't has a magnet on its back and it produces sharp and clear sound especially sound of bird's chirping.
Best of all it is cheap and easily available. The Piezo tweeter that commonly use by farms come in two type. The higher end one has a copper coil and a diode at its back and it produces better sound quality than the one that has no copper coil.
( two different shapes of copper coiled tweeters " Motorola quality")
Furthermore the coiled one tends to last longer than the one without copper coil. Using the coiled type would solve your problems of changing them frequently.
The coiled type Piezo tweeter referred by many as "Motorola Tweeter' because it has the superb sound quality, Crystal clear & sharp sound similar to the original Motorola Tweeter with 1/4 of the price.
( copper coil and a diode at the back of a Piezo tweeter for long lasting use . " Motorola Quality")
Of course using the original Motorola tweeters would cost many times more than the one I had mentioned furthermore the sound produced by both is similar and the original Motorola tweeters are not easily availability.
This Piezo copper coiled tweeter comes with the frequency of 5k-20khz which is within the echolocation of the swiftlets. Its sensitivity is at 105 db.
Using it you won't have to worry about whether your tweeters are transferring the complete sounds which your amp/DVD are playing.
( a nest built on top of a Coiled Tweeter)
Placement of tweeter
Having used the above tweeters one also has to make sure the placement of the tweeters are at the correct place and all are in strategic location to have the most optimum birds attraction capability.
We can't simply place the tweeters as we want in the farm this would not attract birds to stay and to make nest.
As we all know sound and placement of tweeters are important factors that determine a successful farm.
All tweeters must be faced the entrance hole of the farm. This is because when the sound is played birds that entered the roving area ,especially new birds that entering the farm for the 1st time would fly deeper into farm especially into the nesting room.
If the tweeters are placed not facing the entrance hole chances are most birds that entered the roving would eventually fly out without entering further to the nesting room. Birds that had entered the roving area maybe confused and leave the farm immediately.
( the tweeters are facing the entrance hole)
Most failed farm shared similar problem of birds didn't fly deep into the farm to cover more areas especially nesting room. Therefore having a good tweeters and the placing them in a strategic area would helps to increase birds population.
The average recommendation of tweeters per area/farm is, 60-80 pcs of tweeters per 1400-1600sf is sufficient enough. Of course the are many who put more than this and some less.
I had came across farms that have 250 tweeters for the size of 1400sf. Well for me 60-80 pcs of tweeters are good enough.
So having good quality tweeters really makes a different as the sound transferred out by the tweeter is clear & sharp that similar to the original sound of birds.
This would make the birds feel safer and comfortable when the enter the farm for the 1st time.
So make sure your farm passes one of the most important factors of micro environment that determine a successful farm.