Frequency Response Question

[Fife]

I'm looking to purchase a Boston Acoustics CRC7 center channel speaker. I have owned CR8 fronts for many years (I know they have a low sensitivity). The frequency response for the center channel speaker goes as low as 80hz +/- 3db. That number must represent a decibel droppoff per number of hz closer to its lowest limit. Does anyone know where the droppoff curve begins? I ask because I have the option of crossing them over at 80 or 100hz. I'm thinking 100 is better. If I did 80 would their be a sonic hole? I have my fronts crossed over at 80hz. I can't seem to get hold of a frequency response graph.
Thanks

 

[Leprkon]

I'm looking to purchase a Boston Acoustics CRC7 center channel speaker. I have owned CR8 fronts for many years (I know they have a low sensitivity). The frequency response for the center channel speaker goes as low as 80hz +/- 3db. That number must represent a decibel droppoff per number of hz closer to its lowest limit. Does anyone know where the droppoff curve begins? I ask because I have the option of crossing them over at 80 or 100hz. I'm thinking 100 is better. If I did 80 would their be a sonic hole? I have my fronts crossed over at 80hz. I can't seem to get hold of a frequency response graph.
Thanks

Hmm.. first of all.. are you talking a HT-type application or a DVD-A / SACD application ? HT is much more forgiving.

The drop-off is not really "per-decibel". It's actually a total loss of 3dB from the signal strength at the peak frequency when measured at 80. When you drop from 80 to 79, you won't lose 3 more dB. It might be a total of 3.1 dB, but it won't be 3 + 3 for a total of 6.

For an HT application, one thing that might help you decide would be the size of the drivers. If the mains have a larger driver than the center, they will probably (no guarentee here) go lower than 80 Hz. If they are the same size as the center, then a crossover of 100 would probably be a better bet.

For audio DVD or SACD, I'd set the crossover to 100 as well.

 

[Fife]

Thanks for the reply. My receiver (HK 235) allows me to cross over each speaker "pair" at different points. My fronts have a response down to 60 hz. I have them crossed over at 80 hz. I will mainly be using home theatre and CD music. I will probably not use the pure direct mode because I feel I need the subwoofer. My fronts just aren't large enough. There is a stereo mode that enables the subwoofer. I don't forsee any SACD or DVD-A use in the near future.
Thanks

 

[nm2285]

3db is not a great audible difference. there would be no gap if you chose 80. i would usually cross them over lower for music, higher for movies (because the smaller drivers usually produce more musical bass as long as it is within their limits)

 

[crashguy]

If they are rated to 80 Hz +/- 3 dB, that means that at 80 Hz, they are 3 dB down from the average of the rest of the response. It may be better described as a "lower frequency response limit" which may make it make more sense.