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
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....
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
"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?
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
This last info was very helpful. With all those extra speakers, I can see now why you are being so careful. I think I have a solution for you that won't cost that much money. You'll want the amp that has the best sound quality on your B&W's, so the Anthem will definitely power them. The real question is what you are going to power your rear and surround speakers with. For them, you need a good quality amp with power, but it doesn't have to be anything overly expensive.

I'm currently testing an amp made by QSC (Model GX3). Its a 2 channel pro audio amp that sells for $300. I don't think I would recommend you use it on you 802D's. Power wise, it would be OK, but they demand a better sounding amp like your P5. But for sides, rear, unpowered subs and maybe a center channel, this amp should be more than up to the task. Its got separate gain controls for both channels, balanced, SE and 1/4in connections, its bridgeable and has some crossover features for a sub. It also looks nice and its built like a tank. I don't see where you can go wrong. For your application, its perfect. Also, thats their entry level amp. They make ones that have more power, but I really doubt you would need it. They sell them at Guitar Center, and they have a very good return policy if you don't like it.

There's also something else you can do with your 802D's to make them sound better. If you got more than 1 amp like the QSC I mention above, you can free up some channels on your P5, and use 4 channels on your 802's instead of 2. The 5th channel can go to your HTM. It's not just a power upgrade, it will improve sound quality as well. Its just an idea, and you can always test it at any time because you already have the equipment.

Hope this info helps. If you do something similar to the above, you'll have no issues at all being underpowered.