Two 18 watters as loud as one 36 watter?

E-rex · Post by **E-rex** » Mon 03/24/08 11:54 pm

If I were to run two 18 watters each into their own 1x12 cab would it be as loud as one 36 watter into a 2x12?

leslie · Post by **leslie** » Tue 03/25/08 12:08 am

loudness->sound pressure=dB
power=watt
So...it really depends on the dB ratings of speakers.
http://en.wikipedia.org/wiki/Loudness

E-rex · Post by **E-rex** » Tue 03/25/08 12:11 am

leslie wrote:loudness->sound pressure=dB
power=watt
So...it really depends on the dB ratings of speakers.
http://en.wikipedia.org/wiki/Loudness

consider all the speakers as being equal....apples to apples

leslie · Post by **leslie** » Tue 03/25/08 12:21 am

E-rex wrote:
leslie wrote:loudness->sound pressure=dB
power=watt
So...it really depends on the dB ratings of speakers.
http://en.wikipedia.org/wiki/Loudness
consider all the speakers as being equal....apples to apples

Then I would bet on 36,two 18 would be nice for spreaded sound.
Also you will have more headroom/loudness before breakup with 36.
This is good news or bad one,depends on the playing situation.
But,if you don't know how loud 36w(2x12"@100dB) can be, you can imagine Vox ac 30.

Francis_Vaughan wrote:A reminder about speaker cabs. The apparent efficiency of different cabs varies extraordinarily. Any multiple speaker cab acts as a phased array at close distances (where close is a few times the width of the cab - or pretty much anywhere in the area the band will play.) This is a beaming effect. The font lobe beam from a twin can add an extra 3dB, from a quad, 6dB. Also the effect of the floor and walls is important. A reflecting surface creates a virtual mirror image of the speakers, and that will act as a partner speaker nearly as well as a real one - also providing forward gain out of the cab. There is no free lunch, the power conversion efficiency has not changed, the sound is simply concentrated - and at a sufficient distance - out into the audience, where the reverbarent sound starts to be important - the effect is mostly lost. The effect is less for open backed cabs, simply because there is diffused sound from the rear.

Adding extra speakers doesn't actually allow the amp to create any additional sound, any perceived change to sound level is due to the above phased array effects, for any area of concentrated sound there is a compensating area with less sound. Impeadance mismatches also don't actually make much of a difference in power output either. This is especially true for the classic 18 Watter (without feedback). The output impedance of the amp is quite a bit higher than the desired speaker impedance, and so the power transfer quite a bit less than optimal no matter what. Counter intuitively, because the output impedance is higher than the expected speaker impedance, using a speaker impedance that is greater is what will get you better power transfer. This is the opposite of most people's intuition and experience with SS amps (where the output impedance is close to zero). But doing so takes the output stage away from the designed load line, so is not a good thing.

1950 · Post by **1950** » Tue 03/25/08 2:51 am

I have always been a freak on this idea, so i got a decibel meter way back, tested lotsa friends amps at 1 meter on a measured central speaker axes, or multiples.
The EVJ almost breaks the mould producing almost 3 times more sound than it should at 5 watts (would 5 of these equal a 30 watter).
I have a german 180 watter that has so little decibell output at full power that it gets regular write ups about its problem, a vacuum cleaner kills it dead!.
My 18 watter when fed through a doule 12" box is equal to my 30 watt head when fed through the same double 12" box.
Back in a room well away from the amps speaker is a totally unpredictable story, walls finish, floor carpet or hard, room temperature ec, change sound so much. Always wear ear protection when doing this sorta stuff.

E-rex · Post by **E-rex** » Tue 03/25/08 10:30 pm

I'm thinking two 18s will be very close to one 36...roughly 3dB louder, maybe more. I was hoping someone had actually tried this and would report on the results.

Should be the same deal as two trumpet players vs one...regardless of what room they are in or which way the wind is blowing?

I've had a decibel meter for a few years now...all kinds of experiments. For example, the combination of my 18w and my 5F2A is louder than just the 18w.

When I get my second 18w going (waiting on parts) I'll let you know how it went.

1950 · Post by **1950** » Wed 03/26/08 4:28 am

Please let us know what your outcome is on this Rex.
The loudest amp I ever heard gigged without feedback problems was a twin 12, solid state Roland, but the power was in the unusualy hard tone which seemd to "cut" through anything, including traffic noise? close up to the Roland was only sorta loud???
The Roland will never sound as sweet as our self customised 18 watters, which can be too loud in certain circumstances.
Good luck with your new build Rex.

leslie · Post by **leslie** » Wed 03/26/08 4:45 am

Loudness measuring at 1m(SPL) is one thing,loudness measured at 15m is another,and measuring diferent amps at different freqv. at 10-15m is completely another story....instrument only measures peaks and that tells us nothing,or tell us peaks of some freq.
Trumpet.

P.S. I had some books on acoustics materia on some CD ,I'll try to find if you are interested...

Chubsman · Post by **Chubsman** » Wed 03/26/08 1:32 pm

Result: the 36w is louder. You it's cleaner and less compressed at hogher volume settings. It will cut through the mix more.

If you need any kind of "cleaner" sound at 4 piece band settings, you need a 36w.

If your drummer plays with brooms... you can "maybe" get away with a 36w.... Outdoor concert... 36w is needed for sure...

lovedat800 · Post by **lovedat800** » Fri 03/28/08 9:10 pm

How about this.......how would the 36 compare to my peavey classic 30 when it comes to how loud they can get for a given degree of clean-ness? In other words, on my C30 i can turn the guitar vol pot down to clean up and i get as clean as i need at any stage volume situation i normally had to deal with. Will the 36 keep up with it in that regard? I though my 18 would, but i'm now having serious doubts. No, not just doubts, i'm very sure. The poower amp begins to distort enough so i can't clean up with the guitar and still have enough volume for a live setting. If i had to guess, i'd say it's a good 30% lower in volume than the 30 at the point where i can still clean up just enough.

I really want to build one, but if i can't gig with it then i can't use it since i already have an 18 for home.

rickdog · Post by **rickdog** » Sat 03/29/08 8:59 pm

I have built and sold several 36watters and a few 18 watters. Sometimes to the same person. For gigging, its the 36 watter. All around better performance, more headroom for cleans, more power for bigger spaces, and not much more in weight or size. It will power 4-12 cabs into a pretty loud display where an 18 watter will top out and just not get the same kind of punch. I notice the 36 watter's power over 18 Watts very much, YMMV, but from the gigging musicians that have used my amps, it's a concensus that the 36W is the way to go.

lovedat800 · Post by **lovedat800** » Sat 03/29/08 9:41 pm

You just sold me rickdog. I'm building another 18 for a friend, but once i'm done i'm starting a 36'r for myself.

Amped · Post by **Amped** » Sat 03/29/08 10:35 pm

rickdog, is the 36watter loud as a 50 watt plexi non master volume amp though? cuz that is LOUD, and not practical for most bars...

lovedat800 · Post by **lovedat800** » Sun 03/30/08 12:34 am

I can assure you it isn't. i've had my share of amps with a quartet or EL84's and i've also had a truckload of 50 watt marshalls. On average the EL34 50 watt marshalls are far louder. EL84's compress much sooner and 34's just keep getting louder and louder till they start to compress, but by that time you're deaf. So i don't know how the 36 watters are as loudness goes, but i never had a amp that had a quartet of 84's that was nearly that loud. I can't wait to build one, and i have a gut feeling it's going to be the ultimate bar amp. I never owned a marshall 50 that hit a sweet spot before the bartender's "it's too loud" cutoff point. they just started to sound good when it was at the point where it was borderline too loud. I had one that was sofriggin loud i regularly got told to turn down with the master on 2 !

leslie · Post by **leslie** » Sun 03/30/08 1:20 am

Be very carefull with watts versus efficiency.
Vox ac 30 with 2xbulldogs (100db) is VERY comparable with 50w marshall loaded with 4x12 greenbacks.
Also Vox better cuts thru mix and have much upper midd. harmonics content,which can cause headache club's soundman.
But tastefull guitarist will manage situation,as allways
http://www.youtube.com/watch?v=zXZrveuMP4Q

sub · Post by **sub** » Sun 03/30/08 10:18 am

Loudness vs. watt sometimes is a "freaky" thing.
I'd a 50W plexi (every soundguy's nightmare, few soundguy hate my 18W too.....

... what a @#***@#) and i compared with a JCM900 100W and a JCM800 100W. 900was little louder and my plexi was louder than 800

(all tried on same speaker cab: Marshall 4x12).

dartanion · Post by **dartanion** » Sun 03/30/08 12:11 pm

Since the human ear works in a non linear fashion, the perceived loudness changes require about a 10 fold increase/decrease in output power.

Twice as loud as 5W would be 50W
Twice as loud as 18W would be 180W

The overall output levels of say an 18, 36, 50 watt amps will be pretty close. The way the amp behaves is different as the power sections will stay clean longer on the higher wattage amps.

You can make any amp considerably louder by swapping in high efficiency speakers like a Celestion Blue (or it's clones) as these are about 103 db @ 1W/1M, which is a 7 db increase over say a greenback.

Post by **zaphod_phil** » Sun 03/30/08 1:56 pm

sub wrote:Loudness vs. watt sometimes is a "freaky" thing.
I'd a 50W plexi (every soundguy's nightmare, few soundguy hate my 18W too..... ... what a @#***@#) and i compared with a JCM900 100W and a JCM800 100W. 900was little louder and my plexi was louder than 800 (all tried on same speaker cab: Marshall 4x12).

I think this may be related to how higher gain amps tend to limit the signal. I once helped a guy take the clipping diodes out of his JCM900. He was thrilled by how much more touch-sensitive the amp became - and louder.

sub · Post by **sub** » Sun 03/30/08 2:37 pm

zaphod_phil wrote:I once helped a guy take the clipping diodes out of his JCM900.

good work

Gabel · Post by **Gabel** » Sun 03/30/08 5:18 pm

But I'd also like to add that two amps with the smae watt can differ A LOT in volume. Our other guiatrist have a Laney TT50 with a 4x12 Marshall 1960 loaded with 4 G12-75Ts. He has all the voluems set midway, while I have my 30W Rocker 30 set to volume at ahfl and then using an attenuator with volume set at about 3!

Donations

Links

Welcome

Two 18 watters as loud as one 36 watter?

Two 18 watters as loud as one 36 watter?

messing around.

Please.