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Speaker Sensitivity Question...

I was doing the calculation for desired output of a speaker at a distance and the total watts that would be required to get you there. The 1 watt at 1 meter to efficiency to the speakers in db one.

The calculation adjust for the distance of your listening position as a variable.

But what about when you crossover the speakers to a dedicated subwoofer? Isn't the lower frequencies where the majority of you amp wattage gets used up?

So it would stand to reason if you eliminate the lower frequencies from your speaker (from crossing them over to a dedicated sub) that would "free up" those watts and your speakers would not need as many watts to play a desired level.

Is there a calculation for this adjustment?
Am I wrong in assuming this?

Thank you,
Bill
baranowski
ngjockey
1,042 posts
 
Most powered subs don't have an active high pass for the main speakers although they do have an active low pass for the subs. That means that the main speakers still get the full range signal and the sub supplements the low frequencies.

If you do add an active high pass for the main speakers the benefit has more to do with intermodulation and other distortions. End result... you'll be able to play louder with less distortion. Without the high pass and just a sub, some of those distortions get masked.
elevick
2,638 posts
 
Adding a sub will help with power needs, especially if you use the sub crossover.
Keep in mind that doubling the amp's power will only get you 3db increase. You need to increase db by 10db to get a perceived doubling in volume. ie 1 watt=90db, 2 watts get you 93db, 4 watts=96db,8 watts=99db and so on. It gets tough when you have 84 db Maggies and need to go from 200wpc to 400 wpc just to gain 3db volume....
baranowski OP
240 posts
 
So, I take it that even though my processor is crossing over at 80hz to the powered subs, I gain nothing as far as watts that I would still need for a given db level.

I was hoping it would help.

On a side note. For rear speakers is surround sound... do I need to follow the same amp needs as a front speaker? Or can I get away with a lower watt amp for them?

Bill
zd542
5,339 posts
 
"08-02-14: Baranowski
So, I take it that even though my processor is crossing over at 80hz to the powered subs, I gain nothing as far as watts that I would still need for a given db level."

There's more than 1 way to do this. Can you list your system? Also, about how much are you looking to spend on an amp for the surrounds?
baranowski OP
240 posts
 
I currently run...

B&W 802d fronts.
Htm1 center
802n rears.

Anthem statement p5 amp
Marantz 8801 processor

I am looking to add
B&W 804's
And a pair of monitor 600 series.

So I was making sure that...

1. My anthem amp can make the 105 db for thx specs.
2. What kind of head room do I want to try and acheive.
3. What amp do I need for the 6,7,8,9, channels... I eventually only want to use 804 speakers for the remainder of the system.

Thanks
Bill
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