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everyone,

I've an Sony SRS-D8 Active Speaker System one and half year old. It produces an constant hum or hiss whatever it is called as whenever it is turned on & whether it is connected to Dell Studio 15 laptop or to an Sony Walkman or just left disconnected without any input source & kept on. I don't know whether it used to produce that hum or hiss when it was brand new or not but yesterday I took my ears very close to the speakers found that all the speakers including subwoofers & tweaters produce hum or hiss noise.

Is it normal for an Active an Speaker System to produce this audible hum or hiss when it is idle? Or is it due to the constant fluctuation in power? Or Is something broken in speakers?

Note: It has 2 pin power plug & When the speakers are on laptop will be in sleep mode with power switch in Off position. Hum or hiss doesn't vary with volume & it is constant through out.

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No analog signal is ever perfectly clean. This is where the term signal to noise ratio comes in. The relative clarity of a signal is measured in the relationship between the signal and the noise. The noise floor is the level below which signal and noise become indistinguishable. The higher the quality the audio setup, the better it is at keeping the noise floor low, and thus, the quieter the signal it can reproduce.

Since the noise is still there when you have no signal running to the speakers, what you are hearing is the noise floor of the speaker. It isn't particularly uncommon for cheaper audio setups to have a very high noise floor that can be audible when no signal is being run. The noise floor can be raised in a number of places. If it is a digital signal coming in, then the Digital to Analog converter could be noisy. Since they are active speakers, it is also quite possible that the amp itself is noisy. The amp is probably the most common cause of the noise floor increasing.

Amps also tend to output a constant power level unless you adjust the power of the amp directly. If the volume control is adjusting the signal strength rather than the amp's power level, then the noise would remain constant as the noise doesn't come from the signal, but is inherent to the amplification process itself.

  • Oh! I see. Thanks for the help buddy greatly appreciated. I thought that there is some problem with the speakers. Another question: Is there any way that I can reduce the noise floor? – K.K.Vinay Kumar Jan 21 '14 at 16:38
  • @K.K.VinayKumar - if it is internal to the speaker, no, you can't. It is the fault of the quality of construction of the speaker. A higher end speaker would have a lower noise floor, but you can't improve it without a higher end amplifier. – AJ Henderson Jan 21 '14 at 18:18
  • Ok, thank you very much for clarifying my doubts. :-) – K.K.Vinay Kumar Jan 21 '14 at 22:39

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