Power amps with & without controls…..what gives!

How do power amps work that have no volume controls on them?

Actually no amplifiers have “volume” controls. The power amp it self is fixed at a given output, let’s say 100W for example. If the amp does have a “volume knob” it is actually a control associated with the pre-amp stage of the unit. When turning that knob you are actually adjusting the input sensitivity. So in a scenario where you have a separate pre-amp and amplifier the pre-amp will take the signal from the source component and allow you to manipulate the signal with the use of maybe tone controls, attenuation, etc. The signal then is passed along to the amplifier, which is once again fixed at a given output. So controlling the amount of attenuation on the pre-amp will have a direct effect on the amplitude of the signal at the input of the amplifier. So the amp will amplify whatever signal is at it’s input by the same amount regardless of amplitude.

So simply put the amplifier is only capable of 100W of amplification. How “loud” it plays (or the resulting amplitude at the output) depends on the level of the signal you present to it at the input stage. Fort the units that do have attenuation controls you have the luxury of controlling it sensitivity to the input signal.

by Jason Levert

How to properly set delay speakers

When configuring a sound system how do you properly set the delays?

The ultimate goal when setting up delay speakers is for the listener to not even notice the delay speakers are there. Yes, as silly as it sounds it’s true. A properly configured delay will give the illusion that the sound is still coming from the source and not the delay itself. There are several ways to go about a proper setup for your delays. Believe it or not you can actually configure a delay very precisely with a tape measure and not expensive test equipment. Just remember one very simple rule, sound travels 1130 feet per second (at sea level with 70% relative humidity at 72 degrees). In other words sound will travel 1.13 feet every millisecond. So if your delay speaker is 35 feet away from you primary speakers a delay of 31 milliseconds would be right on the money. Of course there are several sophisticated and expensive electronics to do the same thing. They use a calibrated microphone to compare the arrival times of a reference signal from the main speakers and the delay speakers as it arrives at the microphone. This difference in arrival times is obviously your delay time.

However there is also a phenomenon known as the HAAS effect which is too in depth to discuss in one post but what’s important to know is how it relates to settings delay times. In the study of psychoacoustics it is found that often times delaying the “delays” even further behind the arrival time of the primary speakers actually enforces the perception that the sound is originating solely from the primary speakers. This is because the secondary arrival is suppressed due to “involuntary sensory inhibition” which correlates to the human ear’s ability to localize sounds.

by Jason Levert

My system doesn’t sound like it did in the store. Should I buy an EQ?

My system doesn’t sound like it did in the store. Should I buy an EQ?

NO! EQ’s are probably the worst addition to any system you could make. The acoustical characteristics of your room affect the sound of your system as much as any other component in the chain. EQ’s can be used successfully when you have the proper equipment to calibrate them. Most EQ’s available on the consumer market are poorly designed and are more detrimental to you sound quality than they are helpful. Now the units manufactured for pro audio use are far superior and can help you achieve the results you need without inducing unwanted phasing and harmonics. Most if not all pro audio installations required the use of one or more EQ’s because every installation is so drastically different. The majority of the time in a residential situation you will have more success tuning the room itself. Simply pay attention to system placement, furnishings, flooring, window coverings, etc.

by Jason Levert