calculate db spl from pure tone generation

[my8os]

I searched and found some threads (e.g. http://forums.ni.com/ni/board/message?board.id=170&message.id=394409&query.id=21969#M394409) but couldn't really figure out what to do. I have a pure tone generator from Labview and want to calculate the db SPL produced at my headphones using Labview. How do I go about it? 

[johnsold]

You need to know the transfer function for the headphones from voltage input (or power input) to SPL out. The sensitivity of different models of earphones vary so there is no single way calculate the SPL without specific knowledge of the phones you are using.   The SPL may depend on the mechanical environment of the headphone: Is it in free space or is it constrained as in an ear canal?

Lynn 

[Coq_Rouge]

The Sound and Vibration Toolkit has some sound measurements VIs. It offers A,B,C weighed measurements utility. But the biggest problem for the hobbyist is calibration, of the whole measurement system. I once did the measurements you are talking about. But not with labview. I did was done in a lab for hearing aids. The headphones was put on a quite expensive artificial human head with integrated measurements equipment. 

[my8os]

I don't have the transfer function of my headphones, but let's assume we can ignore it.  Then how do I calculate SPL? I'm not sure what the implications are for free space or constrained in the ear canal as you put it.

I also don't have the toolkit mentioned.

[johnsold]

How can you ignore it?  That is the whole point of the calculation.  The function of the headphone is to convert electrical energy into mechanical (acoustic) energy.  The efficiency with which it does this varies with frequency, applied power (which can lead to distortion or damage if too large), and loading (free space or ear canal).

You do not get a free lunch.  If you do not have some data (sensitivity, for example) or access to some kind of acoustic measurement equipment, you would only be guessing.  And the guesses would not be very meaningful.

Lynn