Receiver power and speakers, DVDs help digital SLR owners
Week of November 21, 2004
Q: I’ve been looking at a high-quality surround receiver rated at 100 watts per channel at 8 ohms between 20-20khz, with distortion below .1%. The speakers I’d like to get are Infinity Beta 50 speakers. The speakers are 8 ohms and can handle 250 watts. Will the receiver have enough power for them?
– Brian Taylor, Oak Hills, CA
A: The receiver has good specifications and will have more than enough power, but your question needs dissecting a bit to show you why. You left out the most important speaker specification that relates to your question.
In addition to power handling (given in watts) and impedance (given in ohms), speakers also have a sensitivity, or efficiency rating. This is given in decibels per watt at one meter, for example 91 db/wm. This means that when one watt is put into the speaker, 91 db of sound can be measured at one meter’s distance.
To make a 3-decibel change, you must double or halve the power. So if your speaker has a rating of 91 db/wm, to make 94 db you need two watts and 88 db requires 1/2 of a watt.
To see how drastically speaker efficiency can impact power requirements, we will compare two classic speakers: the Klipschorn, rated at 106 db/wm, and the Ohm A, rated at 76 db/wm.
To produce 100 db from a Klipschorn requires 1/4 of a watt. To produce 100 db from an Ohm A requires 256 watts! These are extreme cases, but serve well for illustration how much a speaker’s sensitivity affects power requirements.
Most speakers range from the upper 80s to the low 90s. Numbers 91 and up are considered very efficient, between 88-90 is average, and below 88 is inefficient and power-hungry.
I looked up the sensitivity rating of the Beta 50s for you. They are rated at 91db/wm, so unless your room is very large and you are going to play very loud, 100 watts should be more than you will ever need.
Q: My friend bought that fancy Digital Rebel camera and he’s having trouble with it. Do you know of any websites that could help him? He’s so excited about it, but I know he’s feeling overwhelmed!!
-Dawn Walton, Shadyside, PA
A: I do not know of any tutorial websites about the Canon Digital Rebel. If you read on, though, I know of something much better.
Your friend can take solace in the fact that he is not alone- many people have purchased digital SLR cameras and don’t know how to get the most out of them. The cameras have tremendous capabilities, and the owner’s manuals supplied with the cameras do not seem to really help people as much as they should.
Tell your friend to look for a $25 DVD called “Introduction to the Canon Digital Rebel” from Blue Crane Digital. Blue Crane Digital has produced DVDs that provide video lessons on understanding class-leading inexpensive digital SLRs from Canon and Nikon.
I have reviewed Blue Crane’s DVDs and found them to be interesting, well produced, easy to understand, and sure to be very helpful to new digital SLR owners. Even if you think you know your camera and digital photography well, you will learn something new from the DVD. If you don’t know your camera all that well, you are likely to find them a godsend. And best of all, they are fun to watch, too!
I have yet to see the Blue Crane DVDs in big stores yet, but hopefully they will be stocking them soon as they are a godsend for new digital SLR owners. If your friend would like to buy one, and online search for Blue Crane Digital is currently the easiest way to find them.
