CHOOSING THE RIGHT SOFTWARE FOR SPEAKER MEASUREMENTS

An integrated loudspeaker measurement system is one thing and measurement software is another. Companies that sell lab equipment for loudspeaker measurements offer a complete set of devices that -in most cases- do not cooperate with other -commercially available- hardware.

Such integrated measurement systems today are PC-based and apart from a calibrated microphone they include an audio interface, an amplification unit, cables, a software controlled rotating base (for off axis directivity measurements) and software for current OS (operating systems). In most cases several purchasing options are given allowing for different hardware configurations or units to be sold.

The advantages of such a measurement system is the increased quality in terms of measurement noise, system endurance, system upgrade-ability, repair-ability, technical support and printed documentation.

On the other hand companies that offer a loudspeaker measurement software allow for:

Obviously the overall quality of such a measurement system can easily be compromised by the following factors:


If a DIYer or any other speaker designer wants to built his/her own measurement system with a separately purchased measurement software, it would be a nice idea to check for a low-cost microphone and amplification unit, paying attention to the following six issues:

  1. The microphone should be calibrated (stated sensitivity value, SPL response stored in a file) and its data should be easily imported to measurement system's software. Microphone's connection to the rest of the measurement system should be realized through very-low-noise cabling and plugs with proper ground shielding.
  2. The amplification unit should meet the standards specified by the software manufacturer in terms of delivered power, cutoff frequencies, minimum gain, gain flatness (sometimes not mandatory), maximum total harmonic distortion and noise level.
  3. The best sound cards are those that operate under most OSs available today and deliver the maximum number of accuracy bits and frequency range. The number of 'measurement accuracy bits' actually determines the 'digital' noise level expected to contaminate measurements. Therefore it is desired to have 24 or 32bits of accuracy and 48kHz true-measurement frequency range.
  4. Loudpeaker measurements simultaneously engage one output and two input channels:
    • one output channel for the original stimulus delivered to the amplification unit,
    • one input (recording) channel for stimulus reference and
    • one input (recording) channel for DUT's (ie. device-under-test) response.
    • The sound card, its software driver and the OS must all ensure the continuous operation of these three channels. Current OSs often re-schedule priorities of running processes raising significant problems to measurement integrity.

  5. Current speaker measurement software manufacturers offer both types of measurement: MLS and SineSweeps (or Chirps).

Both techniques have their advantages and disadvantages in the field of acoustical (SPL and phase responses, harmonic distortion) and electrical measurements (impedance, harmonic distortion). They should both be available by such a system without direct or indirect limitation.

6. Operating systems evolve in time and within a few years could make the PC you use along with your measurement software become outdated. For example a measurement software based on Microsoft Windows XP may work fine but attaching a newly-bought printer to the associated PC may prove impossible: most currently available printers are not accompanied by Microsoft Windows XP drivers. Installing current software to such a PC could also prove impossible.

It would be nice to have your measurement software manufacturer clearly define a number of years for which upgrades would be available so that a modern PC could replace the outdated one. Unfortunately a manufacturer can not promise future OS compatibility with current hardware or software. It is the client's responsibility to plan future steps concerning the PC used along with a measurement system.


For all these reasons a speaker designer should carefully investigate what exactly is offered by a software manufacturer. Other hardware availability and pricing should also be checked before any other step.