To get the best frequency range possible with an accelerometer you need to ensure that you mount the accelerometer in the best possible way.  It is essential to make sure the the surface you are mounting on is clean and flat.  Ideally this will have been "spot faced".  If the accelerometer has an integral stud mount then this has to be used to get the best frequency response.  It is always recommended to apply a thin layer of silicone grease between the mounting surface and the base of the accelerometer.  You should always tighten the accelerometer to the specified torque as shown in the product manual.

Using any other mounting technique will reduce the upper frequency limit.  Further details can be seen in the following document.

http://www.pcb.com/techsupport/tech_accel.php