I'm not going out to buy a Marshall half stack any time soon but I've had some questions in my mind for awhile about number of speakers, sound, and “presence.†Ok, let's run some scenarios. I did not include ohms because I don't know what is “normal.â€
#1 You have a 100-watt amp head. You TWO half stacks that have 12†speakers. So you have two identical cabinets that have four 12†speakers for a total of 8 speakers.
#2 You have a 100-watt amp head. You ONE half stack that has 12†speakers. So you have four 12†speakers.
#3 You have a 50-watt amp head. You TWO half stacks that have 12†speakers. So you have two identical cabinets that have four 12†speakers for a total of 8 speakers.
#4 You have a 50-watt amp head. You ONE half stack that has 12†speakers. So you have four 12†speakers.
These other scenarios are bonuses:
#5 You have a 100 watt combo amp with only one 12†speaker
#6 You have a 50 watt combo amp with only one 12†speaker
Down to business. How would these amp configurations sound compared to one another? One sound fuller? Louder? Tighter? Also, as this question, too, has rattled my brain for awhile. What if you put into the equation of all the above but with 10†speakers? What if they were all 15†speakers, what difference would it make.
Okay amp doctors there are the questions. Hopefully you'll be able to give some good explanations! J
"Nothing...can take the place of persistence. Talent will not; nothing is more common than unsuccessful men with talent. Genius will not; unrewarded genius is almost a proverb. Education will not; the world is full of educated derelicts."
Corbind, Tough questions. I am not an expert in any way on this stuff. What little I know is from studying PA systems. But I can answer a few questions.
Sound is measured in Decibels. Every increase of about 12 Decibels would be perceived as doubling the volume (twice as loud).
You can actually figure out how loud a speaker is by knowing it's SPL (Sound Pressure Level or efficiency) rating. This is one of the most important things to know about a speaker.
Whenever you double the wattage to a speaker, you get a 3 Decibel increase in volume.
Whenever you put 2 similar speakers side by side you get a 3 Decibel increase in volume.
Let's say that all the speakers you mentioned are rated 100dB 1W/ @ 1/M. This is a very good rating for a speaker. There are speakers like this, some even rated as high as 102 or 105. Â 100dB 1/W @ 1/M means this speaker will produce 100 decibels volume with 1 Watt applied at a distance of one meter. Wow! one Watt?, Yes, one Watt. BUT, you have to double the watts to get a 3 dB increase in volume. To play in small clubs, it is recommended that your system produce 120dB at one meter. For large clubs you want maybe 126-130 decibels. Levels over that are dangerous to humans.
OK, lets compare your 50W amp to the 100W amp into one 12" speaker with an SPL of 100dB 1/W @ 1/M
Watts applied         Decibels of volume produced
     1                     100
     2                     103
     4                     106
     8                     109
     16                     112
    32                     115
     64                     118
   128                     121
So a 50W amp would get you around 117dB's, the 100W amp would get you around 120dB's volume.
Now if you have 2 X 12" cabinets you'll get a 3dB increase (you are pushing more air). So the 50W amp would put out 120db's the 100W amp around 123dB.
Now, I am treading on ground that I'm not entirely sure of. But I would guess, if you double your speakers to 4 X 12" you would get another 3dB gain in volume. And then if you doubled that to 8 X 12" you would get an additional increase of 3dB. But I may be wrong on this last paragraph. I have some friends who really know this stuff, I'll ask them and get back to you.
What will probably surprise you, is that most people think a 100W amp is twice as loud as a 50W amp. Not so. It would take about a 500W amp to be twice as loud as a 50W!!
Speaker efficiency is very important. You will see speakers rated 90dB 1/W @ 1/M. Going by the chart above, this speaker would only produce 111dB's with 128 Watts applied. So check specs carefully when looking for speaker cabinets.
Also, speakers in parallel share the Watts. So a 100W 1 X 12 combo, the speaker gets 100 Watts. If its a 2 X 12 combo, each speaker only gets 50 Watts.
There is also the matter of impedence or resistance. You will see amps rated 100W @ 4 Ohms, 80W @ 8 Ohms. Ohms is a measurement of resistance. Â When you combine speakers in parallel you reduce resistance.
2 16 Ohms Speakers in parallel = 8 Ohms load
2 Â 8 Ohms Speakers in parallel = 4 Ohms load.
That's enough for now. I think you can see this is a very complicated subject. There is much more to know. Try visiting Peavey's and Yorkville's websites. They have tons of information on the subject of sound.
Wes Â
If you know something better than Rock and Roll, I'd like to hear it - Jerry Lee Lewis
Nice post Wes. I think the one thing that intrigues me the most is the difference in sound from having one spearker, 2, 4, or 8. So it looks like volume actually does increase slightly by adding a second speaker.
"Nothing...can take the place of persistence. Talent will not; nothing is more common than unsuccessful men with talent. Genius will not; unrewarded genius is almost a proverb. Education will not; the world is full of educated derelicts."
Those in the know say 3dB. But it has to be a similar speaker, and a certain distance apart.
Eminence Speakers has a great website that explains a lot of this.
http://editweb.iglou.com/eminence/eminence/pages/resources02/sensitivity.htm
If you know something better than Rock and Roll, I'd like to hear it - Jerry Lee Lewis
There's a point at which a speaker can't go louder without putting lots more power into it, and adding another speaker can really give the system a boost then.
