Welcome to our forum.
The problem is getting a recorder with a microphone sensitive enough for the low volume and low frequency inside the house.
Quote from: whariwharangi on May 12, 2014, 10:31:32 pm The problem is getting a recorder with a microphone sensitive enough for the low volume and low frequency inside the house. ThIS, this right here is what is waking you up? You can't find a recorder sensitive enough but it wakes you up. whewww. Sweet dreams.
I find it hard to believe it's a hot tub sending out this vibration, but then these things can change in pitch and amplitude depending on what they are in contact with. Now... a refrigeration compressor of some kind (window a/c, heat pump, central air....) is quite capable of making the low frequency hum you're complaining of. The compressors in fact sit on rubber bushings to try and block the vibration and even with that it can be heard/felt a fair distance away. And if the bushings are shot it gets pretty loud.People also tend to turn their a/c units on at night for comfort as they sleep.I would look for an A/C unit in contact with wood. Maybe a central air unit sitting on a large wood deck.