Simple question about loudspeaker arrangment

[hpupo]

Hi...

This is probably a simple question for most you. Lets say i have 1 8Ohm speaker and i apply 20W on it, now let's say i take two 16 Ohms in parallel (which obviously will give me 8 Ohm) and apply the same 20W. Which arrangement will sound louder? I mean i should find half the power on each of the 16 Ohm, but what about loudness?

thanks

[klampykixx]

i would also like to know this^^

[GaloDourado]

If rest os specs are the same, I understand that 2x16Ohm in paralel will be twice loudthan a single 1x8Ohm. Final impedance is the same, but twice the cone area. Better someone else will confirm.

[Ile]

It depends about drivers sensivity, if it's same for both drivers then two 16ohm would be 3db louder. Usually smaller impedance drivers are more sensitive, so there wont be that much difference.

When one 8ohm is as loud that two 16ohm, two driver have lower distortion since two cones need less movement for same level.

Two drivers could have phase issues, but can also have some positive effects like better vertical directivity that causes less floor reflection.

So it depends what you are looking for.

[18Hurts]

If the speakers are the same SPL at one watt, there is a ratio that explains how it works.

Say the driver is 8 ohms and you have one running at one watt for 85 dB.
As the amount of speakers double, output increases 3dB as long as the power stays the same. I built a line array with 12 woofers and assuming the power input is one watt no matter how many speakers there are--you get this result:

1 85dB
2 88dB
4 91dB
8 94dB
12 95.8 dB
16 97dB
32 100dB

If you add one watt to each speaker then multiply, you gain 6dB each time.

Power input works the same way. As power doubles, output increases by 3dB. If you want a 10dB increase, you need 10 times the power.

[hpupo]

The reason i asked is this, i have a guitar amplifier combo that has two channels each with one 8 ohm speaker running at 25W. I was wondering if i found a cab with four speakers (16 Ohm each) and then connected 2 in parallel if it would be louder or not, or basically the same...
I really have no idea how much 3db really means (i mean i know what it is, just dont have the perception for what it means), so in terms that i understand, how far a person would have to be in order to hear the same SPL? Assuming directionality and all other parameters the same?

Thanks

[18Hurts]

It would be 3dB louder

Basically, the loudness difference between a 25 watt amp and a 50 watt amp with the same (high powered) speaker.

Another way to think about is this, the amp will be pushed half as hard when the amount of speakers doubles at the same impedance.

For general music, 3dB is not a large gain although you can hear it. If you want enough speaker drivers so it "sounds TWICE as loud" (10dB) You'll need go from 2 speakers in two channels to around 24 spread across two channels.

If you use a 4 speaker cab instead of a 2 speaker cab, it will be a little louder at the same power. Distortion will go down since the speakers are not being driven as hard. Another option is to get more efficient speakers which is rated XXX dB at one watt/one meter.

[klampykixx]

If I may hijack briefly,

I have two 15inch subs. and will have a 2ch x 200wrms amp to run them with, theyre 8ohm subs, and the amp is capable of 4ohm operation, and is bridgeable.

will they be louder with a 200w ch each @8ohm, or louder if I connect them in parallel and bridge the amp to use the 400w @4ohm ?

[18Hurts]

Originally Posted by klampykixx

If I may hijack briefly,

I have two 15inch subs. and will have a 2ch x 200wrms amp to run them with, theyre 8ohm subs, and the amp is capable of 4ohm operation, and is bridgeable.

will they be louder with a 200w ch each @8ohm, or louder if I connect them in parallel and bridge the amp to use the 400w @4ohm ?

I would assume the amplifier is a bridgeable PA amp?

Bridging is a different concept, the two channels instead of swinging positive and negative are reconfigured for one channel to just swing positive and the other negative. The other issue is when you do this, the impedance the bridged amplifier (the load) is cut in half. If you bridge a 2 channel amplifier with a 4 ohm minimum rating per channel into an 8 ohm load--the bridged amp "sees" 4 ohms across each channel.

If you put two 8 ohm speakers in parallel for 4 ohms, the bridged amp will "see" a load of 2 ohms across each channel. If it is not rated to do so, it will put out too much current and blow the outputs/power supplies.

If the PA amp is rated 200 watts per channel into 8 ohms and 400 watts per channel into 4 ohms--it should be rated 800 watts bridged into a single 8 ohm load.

As I generally tell people, it's not the watts--it's the output. In theory, it can be easily calculated by changing watts to something called "decibel-watts" (dB/W) to make it simple. 200 watts = a gain of 23 dB over the one watt level. 400 watts = 26 dB/W and 800 watts = 29 dB/W.

All you need to do is add the dB/W rating to the speakers rating at XX dB at one watt/one meter to know how much output is available. Say a single 15" subwoofer is rated at 90 dB one watt/one meter and handles 1,000 watts. Running it at 200 watts is a 23dB/W rating so 90 + 23 = 113dB. If running at 400 watts (26dB/W) 90+26 = 116dB Finally, at 800 watts (29dB/W) You'll have 119dB.

What would be louder? When adding another subwoofer, you get a gain of 3dB at the SAME power output. If you add another subwoofer but it also gets the same power level as the other one, you gain 6dB. It would look like this.

One @ 200 watts 113dB
Two @ 200 watts each 119 dB (200 x 2)

This is the same output as one sub at 800 watts! You'll get the same output at half the power by running two. In reality, you'll be slightly higher since a single 15" will start getting "power compression" or the voice coils get hot, the impedance goes up and the power going into the coil falls which reduces output. It will also get nonlinear and most drivers are rated for power compression. In reality, two of them at 200 watts will be both louder and have better sound than one at 800 watts.

This chart will help you figure it out, the power = decibels chart!

1w 0dB
2w 3dB
4w 6dB
5w 7dB
8w 9dB
10w 10dB
100w 20dB
1,000w 30dB
10,000w 40dB
100,000w 50dB
Million W 60dB

Notice how bad it gets the higher the power you go? The same thing happens when grouping speakers together. By using the charts, you can figure out maximum output.

Qty dB gain
1 0
2 3
4 6
8 9
12 10.8
16 12
32 15

If you have two 15" subs at 400 watts total--say you want it to be twice as loud. That is a 10dB gain, if you add 2 more woofers which also drops the impedance down to 4 ohms (power doubles) The 4 woofers driven at 200 watts each give an increase of 6dB. If you have to have that extra 4dB to get "twice as loud" the amount of power required jumps or the amount of speakers requires jumps. Either 8 subs running at 500w X 2 channels or 4 subs running at 1000 watts x 2.

To counter all the kids asking me about my subwoofer, I just tell them it has a one horsepower amplifier.

[klampykixx]

wow, that was a really informative post. thanks 18hurts.