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In a lot of gigs I've played, I have noticed that they have placed the amplifier speaker cab (usually just the bass amp) on top of a chair or a stool or something, so as not to be on the ground.

What is the benefit of something like that?

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I'm guessing you mean combo-amps and/or speaker cabs not amp heads? You can put the amp anywhere you like it will make very little practical difference to the sound, where you put the speaker cab is important. –  gingerbreadboy Jan 13 at 14:54
    
A lot of gigs I've played, there is just a simple amp, and sometimes the place didn't have a speaker cab –  Shevliaskovic Jan 13 at 15:05
    
What is a simple amp? This is an amp head (no speaker) > dolphinmusic.co.uk/shop_image/product/… This is a combo (amp and speaker cab combined) > americanmusical.com/Item--i-MAR-JVM410C-LIST –  gingerbreadboy Jan 13 at 15:18
    
I was mentioning the second one –  Shevliaskovic Jan 13 at 15:19
    
It makes a big difference to your question so you need to be specific. –  gingerbreadboy Jan 13 at 15:20
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3 Answers

up vote 9 down vote accepted

It is so the speaker is pointed more towards your head than your feet and so you can hear yourself better. If a small combo-amp is on the ground, the sound has to bounce quite a bit to actually get to your ears and if you are at a band practice or a gig it may mean bandmates can hear you better than you can hear yourself. If your speaker is pointed at your head you can usually cut down on a lot of volume and still hear yourself just as good then if it was louder and pointed away from your head.

Another trick some people use is they tilt the combo-amp back so they can leave it on the ground and still have the sound from the amp directly pointed at their head. If everyone in the band with an combo-amp does one of these tricks it can seriously reduce stage volume.

In all my experience as a sound technician the number one issue is and will always be stage volume being to loud. It leads to many, many problems including:

  • Feedback (High and Low)
  • Signal Distortion
  • "Bleeding" sounds
  • Musician not being able to hear themselves and others
  • Musician's hearing being damaged
  • Damage/Excessive Vibrating due to a material's Fundamental Frequency

Any one of these is a serious issue and have to be dealt with for live sound. The bass being on the low end of the frequency range has to be kept even more in check because of feedback and issues with Fundamental Frequencies. The less intense (loud) the sound is the less problems it causes. Also bassist will turn up if they can't hear themselves and every speaker I've ever seen is louder if you point it at your ears because that is how they are designed to work.

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Not to be nitpicky -- OK, this is nitpicky -- that only applies to amp-speaker combo boxes. Strictly speaking, the "amp" is just the electronics. OTOH, I can see mounting combo bass amps off the stage to avoid ugly bass resonances occurring. –  Carl Witthoft Jan 12 at 17:17
    
I'm with Carl, can we stop reinforcing the idea that an amp is a speaker in a big box. It really isn't. –  gingerbreadboy Jan 13 at 14:57
    
Well if it was just an amp and not a combo amp then the placement of the amp wouldn't matter. Most (if not all) giging local musicians use a combo amp so they don't have to cart speakers with them. –  Dom Jan 13 at 15:26
    
But saying combo-amp when that is what you mean clarifies the question and answer and means we don't have to have this conversation in the first place. –  gingerbreadboy Jan 13 at 15:40
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I see that you noticed this happens usually with the bass amp, and I don't see an answer addressing bass in particular.

I can think of some reasons:

Mechanical Coupling

Bass amps are isolated from the floor to avoid mechanical coupling.

Depending on the venue (stage design, materials, acoustics, etc) floor vibration can cause an array of problems, like triggering the snare and inducing movement noise on mics. This can be specially bad and nasty if a particularly strong resonance occurs, not only for the noise it will cause, but for the added potential of feedback.

Sound Design

Another possibility for that specific amp placement is sound-design. If microphones are being used, the timbre of the instrument and amp combo will be different depending on the placement of both the mic and the amp.

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The bass from the amp would not be as relevant as the bass from the house subs which are much more powerful and contain all the low frequencies on stage. If the stage is vibrating from just a bass amp then the house subs will definitely cause a worse problems because in most venues they are sitting right on the stage. –  Dom Jan 12 at 19:21
    
@Dom That depends on the speaker system used and the system placement/design. House subs can be directional and/or have their own isolation dynamic or placement. Even if this is not the case, there is no need to add additional mechanical coupling if it can be avoided; FOH sound doesn't kill the amps and monitor sound, on the contrary, it interacts with it. –  JCPedroza Jan 12 at 19:28
    
All I'm saying is that if the frequency is the problem than any subs will have the same problem. Btw I do work as a sound technician for wedding bands and mechanical coupling is an issue, but volume plays a much bigger role than the frequency itself. Also all sound waves are directional. –  Dom Jan 12 at 19:51
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@Dom Of course all subs have the same problem, it's not exclusive to bass amps! That's not relevant to my answer, though. Also, not all sound waves are directional, you got that backwards! In fact, sound waves of all frequencies are naturally omnidirectional (the total opposite)! It's the sound source characteristics and the wave length what carves the directionality. As we go lower in frequency, and the wavelength becomes larger than the sound source, the sound waves become less directional and more omnidirectional (inverse relationship). Low frequencies are the opposite of directional. –  JCPedroza Jan 12 at 20:35
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"I see another answer explains that the positioning is to "hear yourself better", but this will be hardly the case for bass amps, since those wavelengths are not very directional. Bass amp isolation from the floor will make little to no difference; low frequencies, the ones produced by the bass, are omnidirectional (unless a special system is used, which is not the case of bass amps)."

  • That's not strictly true (sorry!). It's in degrees : The lower end of the bass range is less directional, and will "fill the room", but middle-top end of bass definitely is directional and that's where the detail is. Our bassist always stands his amp on the drummer's floor tom case (as it's not being used)- it's about the right height and quite sturdy. The reason is so that he can hear himself without having to turn up, as Dom suggests.

Bottom line is you don't have ears in your knees, so you need to point the amp at your head a little bit so you can catch some of the sound being played.

Worst case of NOT doing this I've experiences was a keyboard player who put his amp under the keyboard (in front of knees), pointing forward. He could hardly hear himself, but to the audience he was blisteringly loud. Turned it up more to hear himself .. it didn't end well.

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Brain fart: wasn't thinking about the highest harmonics. Removed that part from my answer. –  JCPedroza Jan 13 at 14:16
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