How do you read a sensitivity chart?

[tylerb100]

I hope I'm in the right forum for this question.

Many speaker kits I'm looking at building don't publish their sensitivity. Some speaker manufacturers don't either, for that matter. But they nearly all publish a sensitivity chart. But as we know, the charts have highs and lows. So do I look at the high peaks, the low valleys, or take an average when coming up with a sensitivity number?

And what if it's a kit and I'm combining the charts of a tweeter, which often has a sensitivity rating in the low 90's and a midrange which has a sensitivity in the upper 80's. How do I come up with a single sensitivity rating for the entire speaker?

Also, I'm looking at building a bare bones kit and making my own cabinet. How can I estimate the sensitivity of the completed speaker if I don't know how the cabinet will affect it? Is it possible to estimate a rough number?

Thank you all for your knowledge

Ty Black

[BobEllis]

This would probably get a better response in the Missions Accomplished forum.

What you seem to be referring to are the frequency response charts. Sensitivity is frequency dependent, so to be totally accurate you'd specify the sensitivity at a particular frequency, often that is 1 kHz. For system sensitivity, you can look at 2.83V response and visually average it. It's really just a relative "do I need a high power amp or can I get away with a smaller amp?" kind of number anyway.

Usually the woofer is the least sensitive driver and limits the system sensitivity. Look in the spec sheet for sensitivity/efficiency. Start there. To estimate system sensitivity for a single woofer system, subtract 6 dB for partial baffle step compensation and crossover losses from the listed sensitivity. For dual woofer systems, determine if the woofers are connected in series or parallel. A series connection is 3 dB more sensitive than a single, so add 3 dB for that and then subtract the 6 dB for baffle step. With a parallel connection, your voltage sensitivity is 6 dB higher than a single driver, so when you've added and then subtracted 6 dB you end up with a system sensitivity about the same as a single driver. For systems designed for on/in/near wall applications (like most centers) you won't have baffle step compensation, so just subtract 1 dB from the driver(s) sensitivity.

I'm going to guess your follow on question will be how to determine much power a system can handle. A decent estimate is the total of the woofers' power handling. But, it really doesn't matter because you are less likely to damage your speakers with too much power than too little. Too little power and the amp clips when you try to play loud. That creates a lot more high frequency energy than most music and is more likely to damage the tweeter. Of course you can damage woofers with too much low frequency power but most are more forgiving than tweeters and you'll likely notice the strain and turn it down before doing permanent damage. In reality, you use a heck of a lot less average power than you might think. A watt into speaker with a sensitivity around 87 dB/2.83V is louder than most will listen for extended periods. Of course you need to have some headroom for loud crests, so you need about 100 W to give you 20 dB of clipping headroom.

Hope this helps.

[tylerb100]

Thanks for your reply, Bob. I have a Cerwin Vega center channel with a sensitivity of 94. I'm having a hard time finding front L/R kits that will match that level. Being able to read the charts would help. I can't find a frequency response chart of the CV HT-CTR, but I emailed the manufacturer and they replied that it's got a rating of 94. Since they didn't include their charts, I have no way of knowing how they are interpreting their data. I'm very new to this. I have absorbed a lot of infor in just a couple of weeks. But I'm still trying to figure it all out. It's quite complicated for a newbie outsider ;-)

[BobEllis]

That Cerwin Vega is more sensitive than most of the kits you'll find. You should be able to turn down the center up to 10 dB or so to match the L/R in your receiver's setup menu. Use the calculated sensitivity difference as a starting point. You'll want to measure the output to get the best level match.

Now the bad news - you'll notice that the center's timbre and sound quality isn't up to most of the kits you'll find at Parts Express, Madisound, Meniscus, etc. Try to budget for a matching center to make the front soundstage seamless. Some insist that the surrounds must match, too. I'm not serious enough about HT to worry there. I don't even have a center, I use phantom center mode and some small inexpensive surrounds. Give phantom center a try when you've built your L/R - see if the CV brings much to the party.

[tylerb100]

I will bring the center down and see where that gets me. Good idea. Once I finish building the L/R set, I'll start thinking about building something to replace the center. Sadly I currently have a pair of Bose Model 21's as my L/R and I can hardly hear them. So replacing those boat anchors is my priority.

[BobEllis]

Your speaker setup options don't allow you to reduce the volume of the center and/or increase the L/R? Mine allows +/-10 dB on each, which should be enough to tame the CV.

By the way, don't use that "B" word in polite company.

[Alaric]

By the way, don't use that "B" word in polite company.

:rofl: