HT (Hospital Theater) acoustic evaluation

"at 2 Hz "


"I'm not concerned with low frequencies"



Obviously there is a problem in your specification - 2Hz is a extremely low frequency inaudible unless insanely high dB levels. And a starting pistol is great for an impulse generator as it is a broadband noise.


I suggest you hire a commercial acoustic engineer - who would waste money paying an installer to learn acoustics and research materials on their dime?


There is large HT contingent of DIY - because they have more time than money. Last I looked at the cost of health insurance - hospitals have a lot of money - especially if they can afford specialized machines that we cannot even imagine the price of installation.

I believe DMF and rynberg are correct, you need ear protection. Absorptive paneling might reduce "ringing" that exists in the room, and might reduce fatigue a little though. The acoustic power in the impulse in a highly reflective room will take a long time to decay, and absorptive material would probably be a big help.


It would be useful to record the spectrum of the sound in the room while the lithotripter is in operation. This would tell you where the room ringing modes are, and might be a guide in selecting attenuation materials for the walls and the ceiling.


Would it be possible to carry a portable DAT or other digital recorder in the room and record it? That way you could 'post process' it by playing back the recorded sound through the RTA away from the room.


If you found a peak in the spectrum (which should be the point at which the room is ringing at), you could use this information to find which material would give the best RT60 attenuation. I'm sure the panels and roof tiles you are using probably have this information available. This way, you could get an idea of where to start.


I doubt you need attenuation at low frequencies (walls on alternate studs, etc.) Most of your problems will be at much higher frequencies. The spectrum of this type of pulse is very wide, and the energy at the low end of the spectrum (100 Hz) is a small percentage of the total spectrum (probably 10 KHz or so). It is the 'room peaking' caused by ringing that you are hearing.


Hope this gives a few ideas,


Bob Smith

If indeed it is as loud as a starter pistol - there is a reason you always see the race starter wearing headphones. They are painfully loud. No treatment in the world will mitigate the direct sound that is destroying peoples ears - it will only remove the annoying ringing after the impulse. You could build an anechoic chamber - and the pistol sound will initially be just as loud. Surely the hospital can afford to set out some disposable ear plugs right by the disposable gloves.


Problem solved.


While you certainly can treat the room after the earplugs to remove the further annoying decay sounds - you really do need a acoustical consultant that works worldwide. You need someone that knows the materials available in your country approved for use in hospitals (for example acoustical tiles do not work because of the porous surface that can hide germs that cannot be cleaned). Even if you think there is something that might work based on the use of the rooms - there will be commercial healthcare codes - and the whole bidding and procedural acquistion processes that must be followed.. Many of the large acoustical engineering firms do work worldwide - and you can probably find one that has even a portfolio in the hospital market. They might be able to work remotely if you are capable of taking measures they need. - but would probably prefer to fly in with their own gear - maybe even cheaper than paying their consultant fee to go back and forth remotely teaching you how to take measures needed. Interestingly a high voltage spark is the same thing used as a broadband impulse tester by some acousticians - rather than using a starter pistol!


But any consultant that works on the room without addressing the hearing protection issue that remains is not worth the money. I would suspect in the US there would likely be a OSHA violation here for repeated sound exposure - even if the peak is not beyond the threshold of pain and just into the annoying threshold - there are rules that limit how much per day an operator is allowed to hear.


Asking this forum is going to get answers about woodstud and gypsum construction and fiberglass - which I doubt is used at all in your country - and certainly not in commercial construction and not at all in hospitals!

Quote:
Hi Leigh,


I think Kevin is right.


Here's a firm in Kuala Lumpur, Malasia that has done acoustic wall insulation for a Lithotripsy room at Pantai Medical Center.

ISTIQ


Good luck.


Larry

Thanks for the link Larry - don't know how I missed it.


In response to some other posts:

- The lithotripter manufacturer is quite clueless about room treatments - surprisingly. I have been to their R&D center and they have a small room for testing the machines with open foam triangles glued to the walls. Dark, ugly and dirty.

- We have a budget for the treatment room that is a fraction of what some of you guys spend on your Home Theaters... This is not the US. Lithotripsy costs $50 vs. $7,000 in the US.

- We use ear protection. Ear plugs work best but are tough to wear all day. Also, we have to communicate within the room so we have to take off the protection some of the time.

- I am installing a perforated gypsum wall next week at one center. The product is called gyptone and has a "Practical absorbtion coefficient" of 60 - 80% at higher frequencies.

- I will do some before and after tests using the lithotripter as a sound source. I am planning to use a laptop, USB soundcard and soundmeter for the measurement.


Any suggestions on (cheap) software to do spectral analysis and to compute a RT60 value from an external impulse or recorded .wav file?