multiple speakers and SPL

[Justin Thomas]

Because the "true" complaint about bands being "too loud" ismore related to frequency, not just volume. There are also the studies in the 60s & 70s that show that aesthetically, humans prefer LIMITED frequency range when amplification is involved. If it's an orchestra, sure, 20-20k. It's very interesting. And I doubt the human ear has "evolved" that much since then. I think the "advances" in PAs & the whole "complete even reproduction of all frequencies" is the bigger issue.

In answer to guitar/bass problems specifically, I think we only need ask two questions of that "sound engineer" (which, engineers have degrees): what am I actually drowning out? & Fo I sound like shit? If the answer to those is "nothing" and "no," then "let my rig do its job!" A real sound guy should be able to articulate what is too loud, what frequencies, & have more than just "I can't control you" in his comeback line.

If there is a specifically made piece of gear made for amplifying an instrument (GUITAR AMPLIFIER?) then it should be used before the "all purpose utility flunky amp system" is applied. And good golly bass sounds like butt-ass-crap straight through a PA. Electric gyitars sound worse.

*** I know others have sifferent opinions. If they articulate them, I won't argue. Please don't argue with mine. A simple thumb in either direction will suffice. Just not in the eye!)

Justin & Jusrin

[tedmich]

I guess besides my appetite for "knowing" I'm trying to validate myself for playing a full stack...lol. I've been on a Peavey kick and bought a Triple XXX head, triple XXX 412A cab and a 5150 412B cab..

That rig will destroy small buildings if played above half way, +1 on the XXX, I still miss mine.

Do try this, dime the gain on the Ultra channel and the have the TMB tone stack at full cut. Its active so thats -12db, then sneak up the master until you can just hear it: CAREFULLY bring up the 3 tone controls until you have the insane gain (!), this can work even better with a vol pedal or other attenuator in the FX loop; magical chaos. With some pedals I could dime the Master and the gain and then role in MONSTER gain with the tone stack...good times!

[olddawg]

Another excuse to post a picture of the Wall of Sound, in circulation some 45 years ago. It may have been "wretched excess" BUT there was a sound principle behind the design, pun INTENDED. Nothing new about it either, sound engineers 90 years ago had it all worked out, way better than you would expect.

Time was, a band would pay me a couple hun to haul my van full of gear to a venue, where they sounded terrific. Compare that to the sound you get today, a couple overdriven cheapo speakers-on-sticks that sounds like a fly fart. That's progress ... NOT. You get what you pay for, you get what you work for. The only "progress" is today's audiences are trained to accept crap audio because they listen to their plastic pocket pals with a ten buck pair of ear buds, and think that's good. IOW the "broken AM radio" sound is now the law of the land. Phooey.

MP3s... on Dollar Store earbuds... lol..
I used half stacks forever. I found them to be very focused and directional. That’s ONE reason why back in the old days you would see a stage full of them. Nowadays I get told I’m too loud with a 1x12” open back 20 watt combo. It fills you a club stage very well. One of the loudest amps I have ever heard (next to a Marshall 200 watt Pig, 200 watt Hiwatt, 200watt Sound City, or some other beast) was a thing called a “Fender Super Twin”... it was like a silver face Twin reverb but in a 4x12” open back combo form like a SR used 4x10”. Drummers I knew HATED them because of the blowback and they like an ice pick to your head.

[Justin Thomas]

That would have been a Quad Reverb (4x12) or Super Six Reverb (6x10). A Super Twin was a 2x12 w 180W & a black front panel, though it bore little resemblance to any true blackface...

Justin

[Helmholtz]

Well I can say (from experience today and historically as a matter of fact) that sitting in front of a single twelve can get rather "beamy". I think spreading the power among eight speakers has to resolve that to some degree even if SPL is improved.

It may sound surprizing, but I learned from acoustics literature that increased cone area, multiple speakers and larger baffles all increase beaming. The least beaming (constant average SPL at all angles) would be produced by an ideal point sound source.

[Helmholtz]

It's real. Not often you get something for nothing. Paper with analysis: [ATTACH]53261[/ATTACH]

Thanks for the paper. Looks as if I was wrong. I will try to contact electroacoustics professor Manfred Zollner for clarification.

[J M Fahey]

Donīt worry, the paper is wrong.

I didnīt want to get into this because I donīt have spareb time to argue Religion, and the "3 dB doubling" is just that,itīs completely contrary to my experience.

Each time the number of speakers is doubled you gain 3dB...

Sorry but this is a myth.

And FULLY agree with:

So can one just infinitely add speakers and gain volume? Why add power when one just needs speakers? Double the speakers and effectively double the power? Doubling of power gains 3dB. Therefore doubling speakers adds 3dB, infinitely?

which is Physics 101 .

To my understanding only on-axis SPL level of middle and high frequencies will increase caused by beaming - while off-center SPL should decrease accordingly. Otherwise efficiency would increase infinitely with higher speaker number.

This assumes constant amp power input for all speaker arrangements.

Yes .
There is *a little* extra increase because of crosscoupling nearby speakers, but itīs a weak effect compared to focusing.
But people hear the latter and attribute it to the former.

Sadly, some "respected people" believe or mindlessly repeat the 3dB doubling Mantra, at least at face value (once you start treading the small print it isnīt so) and to boot they are misquoted, so thatīs a hard to stop snowball.

Sadly there is *some* increase in SPL in front of a multiple speaker, but itīs caused 90% by beaming and maybe 10% by mutual coupling ... but nobody I know has set up the experiment.

The speaker motor is still a physical object that must be moved. I think there is a point where you are delivering too little power to the speaker to move it properly. So the power to spl curve for a speaker would not be linear, but fall off at low power levels.

Speakers are very linear at lower levels, what is not linear is our ears, Fletcher Munson effect, but thatīs not a speakerīs fault.
Speakers are NOT linear at high levels, both mechanically (excursion moves voice coil outside magnetic gap) and thermal (voice coil increases resistance, exact same attenuation as if you added a resistor in series with speaker) so you may say speakers are louder at lower power.

Part of the explanation why a 4 x 12 driven 100W (colder coils) is louder than a single 12" (scorching coil) again driven 100W.
And why a 18W 1 x 12" combo is "louder than you expected" compared to a 100W 1 x 12" combo.

As a practical example, run a 5W guitar amp flat out into a single small speaker (like a Champ for example), then do the same into a 4x12 of the same impedance. The power delivery in watts stays the same, the SPL is much greater.

PLEASE compare apples to apples, the cheesy 50's kitchen radio grade Champ speaker can never be compared to *one* 12" Celestion, let alone to four.
Even less the cabinet size and type.

Just one free sample of the "mutual coupling" paper horrors:

The influence of room boundary walls on the power output of a loudspeaker
has been well researched and documented. In [1], Allison shows how the
presence of a single boundary wall increases the power output of a
loudspeaker by 3dB at low frequencies, and that introducing two more
boundaries gives a net increase of 9dB.

NO NO NO NO NO NO.
Power OUTPUT stays exact same, for Godīs sake!!!!
But halving space where sound is radiated because of a wall (space goes from 4 Pi to 2 Pi) increases SPL by 3 dB inside the now halved space ... but total output (so total power) remains the same.
That alone disqualifies the paper.

Those who get it, will get it; those who donīt .... I have more pressing things to do than vacuous arguing.

Just remember that one of BASIC principles explaining the World around us is "conservation of Energy" ... which continuous "doubling" out of the blue would contradict.

One of these days Iīll setup a 1/2/4 x 12" cabinet comparison and measure pink noise injected into it with my SPL meter.

Big problem is that I "should" need to measure in an anechoic space (none available) or at least away from walls (difficult).

[Justin Thomas]

I see no way that changing room size can affect power in any way... That's just silly at best. Of course, my Bassman on 10 thru a 2x15" certainly SEEMS louder in the closet than the auditorium...

Oh, wait - SEEMS!

Justin

[glebert]

There was a thread recently with a discussion about speaker efficiency and electrical vs. acoustic power. To talk about "power" and not state which power you are talking about is just going to make this discussion even less productive.

[nickb]

@Juan. I'm not going to agree or disagree with you but the paper does have some authority. It can be found in the AES library and so I would it expect to have been peer reviewed.
http://www.aes.org/e-lib/browse.cfm?elib=7198

I know of at least one author, Vance Diskason in "Speaker Design Cookbook v7" page 12 also says it. He seems very knowledgeable.

I can't claim to have thoroughly read the paper but I have skimmed it. My understanding is that

a) in a non-reverberant space only the beaming effect exisits.

b) in a reverberant room the speakers couple which increases the efficiency and thereby increasing the output power in watts. Therefore conservation of energy is not violated.

c) As the room size increases, so the coupling must reduce since at the limit the room is the identical to an open space. This is where the infinite speakers / infinite efficiency argument goes off the rails since to accommodate that many speakers requires an open space so only beam forming applies. I don't think the paper addresses this and that is perhaps it's failing.

[Leo_Gnardo]

Speakers are very linear at lower levels, what is not linear is our ears, Fletcher Munson effect, but thatīs not a speakerīs fault.

Had that ready to post last night but for some reason it would not upload. So thanks Juan for mentioning it! Besides F-M, when you're trying to hear something relatively quiet, there's the masking effect of ambient noises in real world listening, and it gets worse with the age of the listener. Presbycusis is the fancy name for it. Plus tinnitus, which plagues many folks as age advances, masking quiet sounds from within the hearing system. WHAAAAT?



Also very true:

Speakers are NOT linear at high levels, both mechanically (excursion moves voice coil outside magnetic gap) and thermal (voice coil increases resistance, exact same attenuation as if you added a resistor in series with speaker) so you may say speakers are louder at lower power.

[Helmholtz]

People tend to confuse sound pressure (SPL), a local (position dependent) quantity, with average acoustic/sound power which requires integration over all directions/angles.

I didn't like that the paper doesn't bother to provide real measurements.

I could imagine, though, that doubling the speaker number increases power efficiency somewhat. This might happen if close placement of speakers improves acoustic impedance matching between cones and air, just like a Klipsch horn increases efficiency even at very low frequencies where there is no beaming. After all speaker efficiency is typically low because of the mismatch between the acoustic impedance of the cone and the surrounding air. Efficient power transfer requires good impedance matching. As long as there is impedance mismatch and reactive power involved, the energy conservation law doesn't need to be violated by increased efficiency.

If there is one thing I learned from reading acoustics literature, this would be that acoustics is much less intuitive than electronics.

[ultra-gain]

So, even on this forum which I find to be a great source of straight shooting no BS and objective reasoning, this topic seems to be less talked about and understood. Lots of back and forth everywhere I searched. Thinking maybe a speaker manufacture might indulge my curiosity I emailed Eminence and one of their product engineers replied that yes doubling speakers does indeed add 3dBSPL as if the power had been doubled. I think I'll ask him how that relates to power and infinitely doubling speakers.

Hopefully no love lost over this thread peeps. Got a little heated

[Chuck H]

Well first I would like to thank Juan for using "MY" post as a launch pad for his argument. Which includes the observance that otherwise knowledgeable people have been regurgitating the "double speaker +3dB" rule for ever. Well, mister smarty pants, all I can say to that is... Yeah, I did that. I got it from Enzo and others and just figured I didn't know better, so... Anyway, I'm actually glad to hear that it may be an oversimplification or even a misunderstanding of what's actually happening and/or the principals at work because my real life experience had me scratching my head the first time I read it. I always figured what I thought I was hearing was inaccurate because of typical perception failings. That or maybe I was somewhat of a dufus that couldn't know any better because of my mental limitations. I do know that perception isn't always reality. I also know it's all that really matters

[HaroldBrooks]

Not sure if anyone mentioned this, but there is also the "Size of the Sound Source".

It might be related to psychoacoustics and the way our two ears and brain works, as I believe the ear and brain can interpret not only the SPL of the sound, but the physical size of the sound source, through phase disruptions and reflections. So if sound at the exact same SPL is emanating from a single point, or if it is spread out over several square feet (as in a stack arrangement), the perception of the size of the sound source will be different. The speaker array will generally sound "Bigger", and hence might have a feeling of being louder.

My very first experience with this was at Queen concert many years ago. Brian May's guitar sound all by itself was HUGE ! I realized his stacking 9 Vox amps on the stage was no accident, and the sound men complimented his "Spread" of sound. If I closed my eyes sitting in the 40th row, I could swear his guitar amp was 80ft wide.

Big sound as a perception is often linked with loud, particularly when they appear at the same time, so one enhances the other in the mind of the listener. So it may not just be SPL we are after in using an array of speakers...

https://www.ultimate-guitar.com/stat...335771.jpg@642