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Saturday, December 7, 2013

Understanding The Frequency Response Term Of Today's Wireless Loudspeakers

By Michelle Finger


The frequency response is the most commonly found parameter to characterize cordless loudspeakers. Even so, it may regularly be deceptive and might not always offer a good sign of the sound quality. You might not completely understand exactly how the frequency response is calculated. I will discuss what specifically this phrase means. Hopefully you will be able to make a much more well informed buying decision.

A large frequency response does not always mean the wireless loudspeakers have great audio quality. As an example a set of wireless loudspeakers with a frequency response between 30 Hz and 15 kHz may sound much better than another set having a response between 10 Hz and 30 kHz. In addition, each manufacturer, it seems, uses a different procedure for specifying the minimum and highest frequency of their cordless speakers. Generally, the frequency response displays the standard working range of the wireless speakers. Inside this range, the sound pressure level is largely constant. At the lower and upper cutoff frequencies the gain will decrease by no more than 3 decibels.

In reality, a set of wireless speakers which has a frequency response from 10 Hz to 30 kHz may actually have much poorer audio quality than a set which offers a frequency response from 20 Hz to 15 kHz. Different suppliers apparently employ different methods to determine frequency response. The normal convention is to show the frequency range inside of which the sound pressure level of the loudspeakers will drop at most 3 dB from the nominal level.

To better understand the frequency response behavior of a specific model, you should try to figure out under which conditions the response was calculated. You may find these details in the data sheet of the wireless loudspeakers. Then again, many makers will not publish those in which case you may need to make contact with the maker directly. One condition that may affect the frequency response is the impedance of the loudspeaker driver built into the cordless speakers. Typical speaker driver impedances vary from 2 to 16 Ohms. The lower the speaker driver impedance the greater the strain for the internal amp.

To better comprehend the frequency response behavior of a certain type, you should try to determine under which conditions the response was measured. You'll find this data in the data sheet of the cordless speakers. However, a lot of manufacturers will not publish those in which case you should make contact with the manufacturer directly. In fact amps may have different frequency responses depending on the speaker driver element which is built in. This change is most obvious with many cordless loudspeakers that use digital amplifiers, also known as Class-D amps. Class-D amps use a lowpass filter in their output in order to reduce the switching components which are created through the internal power FETs. The lowpass filter characteristic, on the other hand, heavily depends upon the connected speaker load.

A few amplifier topologies offer a method to compensate for variations in the amplifier gain with different loudspeaker loads. One of these techniques uses feedback. The amplifier output signal following the internal lowpass is input to the amplifier input for comparison. If not developed correctly, this approach might result in instability of the amplifier however. One more approach utilizes audio transformers between the power stage of the amp and several outputs. Every output is designed to connect a different speaker load. This method makes sure that the amplifier will be loaded equally and in addition enhances amplifier power efficiency.




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