Polyfusion Model 755

The 755 prevents the cause of feedback rather than just treating the symptom. By constantly shifting the audio frequency, the 755 allows your public address system to be operated at much higher gain levels without electro-acoustic feedback.

• Low noise circuitry
• Phase accurate, not a filter
• Continuous shifting, zero response time
• Proven, patented, warranted
• Since it is not a filter, it won't produce "holes" in the audio spectrum or color the sound with phase distortion.

What It Is

The Model 755 is an electronic signal processor designed to reduce, or eliminate Audio Feedback in a Public Address System. It is in fact a frequency shifter capable of continuously shifting the frequency of all signals passing through it, by as much as 6Hz. This shift is not typically audible unless it is compared to the original signal.

What It Is Not

The Model 755 is not a Filter, and is therefore unlike most Feedback Suppressors, which rely on one or more "notch" filters to attenuate a specific frequency, or frequencies. Although this approach can be effective, it is not without some serious tradeoffs. For example notch filters cause considerable phase shift to the signal in their pass-band and this is a form of distortion. Of further consequence is the situation which occurs when the System Resonant Frequency is within the vocal spectrum. In this instance, setting the notch filters to frequencies required to prevent feedback, will actually result in attenuation of the voice your are attempting to amplify, thus defeating the very purpose of the PA System!!

Why It Works

Think for a moment about the various elements which comprise a typical Public Address System. There is the microphone, which goes to the amplifier, which in turn drives the speakers. So far everything is all right, but there is little more to the story. When some of the amplified sound from the speaker gets back to the microphone, and is then once again amplified, we have a serious problem. The problem does not take long to manifest itself in the form of feedback. In fact after only a few trips around the "Loop", the entire system is howling at a high pitch, typically at the System's Resonant Frequency.

Now let us add the model 755 to the equipment line-up. By inserting this frequency shifter in the "Loop" we can prevent the re-processed sound from building on itself, because now each time it travels around the "Loop", it is at a slightly different frequency and therefore never gets the opportunity to re-enforce itself.

This patented process provides the single most effective means of dealing with audio feedback, with the least number of tradeoffs, that current technology allows. Its presence on a system is transparent to the audience, but its dynamic effectiveness is truly remarkable.