Speaker sensitivity when running as "small". (1 Viewer)

[Lanny Hoff]

Trying to come up with a one-line summation of a question or comment is tough. I hope this one gets some lookers.

I've been thinking about getting new speakers, and as I look the possibilities for replacement one of the specs that I'm interested in is speaker sensitivity. At first glance it seems that the more sensitive, the better, but I started thinking about it in more detail, and I wonder if it's that important in a system that will be used primarily for HT, with a receiver which will be crossing over at 80hz. Then I came up with my question:

How does eliminating all sub-80hz material from a speakers load affect it's apparent sensitivity?

It appears to me that the low frequencies are the ones that have the most to do with overall sensitivity as it's reported by manufacturers, and if we take that burden away from the speaker, that it's effective sensitivity must go up. The question is: how much does it affect the usable headroom?

Has anyone given this much thought?

 

[DanaA]

I definitely could be all wrong here as I don't understand the technical side at all as well as some here do, but my impression would be that the lows place the biggest demand on the amp and, as a result, freeing the amp from the burdon of having to send power at the lower frequencies would enable more clean power to be directed to the 80Hz and above frequencies.

 

[Lanny Hoff]

I agree, but the thrust of my question is what effect this crossover frequency will have on the speaker. I think you are right, the amp will have effectively more power, and I guess that this is related to what I'm asking.

To simplify: if we take a speaker that is designed to operate + or - 3db from 38hz-20,000 hz at 89db/w efficiency, and eliminate the frequency range below 80hz, what net effect will this have on the speaker's efficiency, ignoring the amplifier in question? I think it would go up, but would it?

This may be splitting it too fine, but I'm curious to know if anyone has any information on this topic.

 

[Michael R Price]

The sensitivity should not change if you set the speaker to small. What happens when you set a speaker to small is that the heavy bass load is removed from the speaker, the speaker will have less stress on it and thus less distortion. In other words it will just sound better, especially at high volumes. Of course, if you don't have a very good subwoofer you may not like the bass quality.

You will be able to play a little louder before the amp/speaker distorts.

 

[Erich S]

If sensitivity is the sound level measured at one meter when given one Watt of input signal, should this be frequency dependant or is this one Watt of pink noise? How does sensitivity relate to the speakers impedance? The impedance of the Paradigm Studio/20 hits its minimum at 200Hz, well above an 80Hz cross-over.

 

[Lanny Hoff]

Now we are getting to the nitty gritty.

The big question is this: does a speaker's sensitivity change if the effective bandwidth is is asked to reproduce changes?

If we take a given speaker that develops 89db with one watt of pink noise (is that how they are really measured?) over it's operating range, which, for the sake of discussion we shall specify as 40hz-20,000hz, how much sound does it develop with that same one watt of power if we limit the signal to 80hz and up?

 

[Michael R Price]

About the same sound because the 40-80hz component of the pink noise (which is 40-20000 Hz) will be greatly reduced but to have *1 watt* of power means increasing the volume of the rest of the spectrum. But it doesn't matter since you have a subwoofer making up the difference. So if you want to be real technical about it then your mains sensitivity increases. Bottom line, it doesn't matter at all.

 

[Lanny Hoff]

That sounds fairly convincing, thanks.

 

[Doug Drake]

In response to Erich's question, sensitivity as reported by manufacturers is typically measured at 1khz. A speaker will have different sensitivities at every point of the frequency spectrum. You'd have to measure it all across the spectrum, and graph it, to get a meaningful picture, IMHO.

I think the key role that sensitivity plays in your speaker selection is the potential impact on your amp. My speakers have a sensitivity of 101db/watt/meter at 1khz. That means it requires about 1/8th the power to reproduce a 1khz sound at the same volume as a speaker with a 91db sensitivity.

Many solid state amps are at their "cleanest" at their higher power output levels. A high sensitivity speaker will sound best with amps that are also clean at their low power output levels, because they will not take much current to power them.

There are some great lower-sensitivity speakers (below 90db for example) but they require lots of good clean power to drive them, something many amps can't do until you get into the higher priced units.

Forgive my ramblings...

Doug