Acoustic Amp?? Why do you need one?

Hello everyone

I've read several threads on amps and I am confused on what an acoustic amp is vs. a regular amp? It seems like acoustic amps tend to be more expensive and when people talk of amps, they don't distinguish them.

Does that mean that an electric guitar or ukulele will not sound as good on an acoustic amp? Very confused

Thank you

As a general rule of thumb, electric instruments sound better on instruments made fo them and acoustic instruments sound better on acoustic amps which tend to produce the true "acoustic sound" of the uke much better. The better the uke sounds, the greater benefit from having an amp that will make sound as good plugged in as it can.

thanks Phil

Amps made for electric guitars are different from acoustic guitar amps in several ways, the two main ones are:
1) The equalization is totally different. The acoustic amp will try to be as linear as possible, while the electric guitar amp will e.g. have a boosted mid range.
2) The acoustic amp will have as little distortion as possible, while the electric amp will often use distortion as part of the sound itself. Even the 'clean' channel on an electric amp will let you overdrive the signal (=create distortion). This would be unwanted in an acoustic amp.

Another way to look at it is that an amp for an electric string instrument will try be part of the sound while an amp for an acoustic instrument will try to not affect the sound at all - i.e. be as transparent as possible.

-Tor

And besides, it just sounds cool to say, "I have an acoustic amp." It just kinda rolls off the tongue.

Simply put,....an acoustic amp is much like a portable PA System. (Public Address System) Often traveling acoustic performers will plug into a venue's PA system rather than use a separate amp. The house unit is often higher powered, and wired to the house speakers often placed to best advantage in that setting. (not always though )

You want clean amplication generally for best vocal presentation, and the same for acoustic instruments, although at times some effects are added to an acoustic performance.

The strictly electric instrument type amp colors the output, so never the best choice for vocals or acoustic instruments.

Its worth noting that many acoustic amps have feedback detection to eliminate feedback

Very interesting...I would think for a uke, you would want the cleanest sound but lots of positive comments about amps w/ effects and the ones with a mic input. It's good to know that if there is a good PA system, you don't need an acoustic amp. I am getting a pickup in my uke and don't plan on playing in public but want to be ready just in case.

Thanks everyone

Tor said:

1) The equalization is totally different. The acoustic amp will try to be as linear as possible, while the electric guitar amp will e.g. have a boosted mid range...

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Actually, that's a common misconception. If you actually graph the response of most electric guitar amps you will find that they have a fairly pronounced mid scoop. Obviously it varies somewhat from model to model but in general "Marshal type" amps the scoop is a little deeper than on most "Fender type" amps.

I used to design and build tube amps for guitars and I honestly can't tell you whether the scoop was originally intentional or was simply the result of the first amps being designed by people who were anything but electronics experts (most of the early designs were lifted straight out of the RCA and other tube manufacturers manuals). There are four factors that determine the amplitude of the signal from a magnetic pickup. Two of them - the size of the ferrous element being vibrated and the speed at which it vibrates - end up being frequency dependent. The result of all that mess is that the signal actually has a hump in the middle range. At the low frequencies you have large strings but they are vibrating very slowly. In the high range you have much faster vibration but the strings are smaller. Across the guitar's midrange you have a "perferct storm" where the string size and vibrating frequency result in a stronger signal.

Obviously, exactly how much depends on way to many factors to predict with precision - but basically it's safe to say that an electric guitar with magnetic pickups is going to have some natural "mid boost."

If anybody really cares that much I can post graphs of typical Marshal and typical Fender tone stack response... I kind of suspect, however, that I've already exceeded most folks' interest in the topic. LOL

John

I'd be stoked to see the graphs.

Acoustic amps are designed to produce cleaner, wider bandwith and a more natural sound. A passive piezoelectric pickup works better if an outboard device, like an LR Baggs Paracoustic DI is used before plugging in. The speakers on an acoustic amp are structured more like those in a home entertainment system. They usually have foam surrounds and stiff cones. Acoustic amps generally have a tweeter, coaxial tweeter or a whizzer cone to expand the bandwidth of the frequency response. This accommodates a more natural movement of the cone.

Electric guitar amps are built to amplify the frequency range and overtones of magnetic pickup/active electronics in a narrower frequency bandwidth for more efficency and acoustical output. The speakers, from companies like Eminence and Celestion, have more slop in the cones. The cone and the surround are one piece and of the same material. The surround is usually coated with a rubbery substance for more strength to prevent tearing at the cone edges.

Acoustic amps are generally closed back. This creates a flatter response as the output is quasicomplementary - push push.

Electric guitar amps are generally open backed. This boosts the acoustical midrange, as the acoustical output is a slightly out of phase - push pull - push comes out of the front of the amp and pull comes out of the back of the amp. This phasing delta cancels some of the bass and treble.

Electric guitar amps are designed for mor midrange. Play your uke through an electric guitar amp and then through an acoustic guitar amp. It sounds more natural through an acoustic guitar amp.

I can explain input biasing, if anyone is interested. Ric

Hippie Guy said:

I'd be stoked to see the graphs.

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Google Eminence Speakers or Celestion Speakers and look at the speaker graphs, Hippie Guy. Ric

I currently use the LR Baggs Paracoustic DI straight through the PA for gigs. I am in the process of shopping for an amp and was curious what you guys thought about running through a tube amp vs acoustic as well. Hippie Guy, I've read your article on the Roland AC-90 and was highly considering that but I was told by a couple people that I would be better off going through a tube because the acoustic DI was already taking care of whatever the acoustic amp would've done for the sound. Hopefully that makes sense, any advice on this would be much appreciated. I am playing with a six piece band with acoustic and electrics guitars, bass, and drums so I need a good amount of sound if that makes any difference. I also use multiple effects pedals. Thanks for your input!

Haha..I just bought the Baggs Para DI as well without knowing how it works. Someone recommended it as I am getting K&K Twinspots. The next step is buying an affordable acoustic amp.

Mealfrog41, I second the Roland AC-90. It's a powerhouse that can be used by itself as a personal P.A. and also as a personal monitor to hear yourself on stage. I use my LR Baggs Paracoustic DI with my Roland Acoustic Chorus series amps to broaden tonal control and reduce feedback like a fine art. Ric

Wow! This thread is great. I have several amps (guitar and acoustic) and never knew the physics behind the different amps. I'd appreciate anything you 'experts' have to say--definitely not boring.

I'm fairly new at this, but it takes a LOT of tinkering with tone controls and strumming 'technique' to get a uke to sound truly 'live' and 'acoustic'. It's easier to get the tone I like at home but those settings don't always apply to other playing environments. i.e. playing in a larger and acoustically lively room is always disappointing. Keeping the uke sounding live while playing with other instruments is very challenging.

Nongdam, what price do you consider affordable for an acoustic amp? Ric

I would prefer not to spend more than $200 and willing to go up $300 if it's that much of a difference in quality. Since I haven't been to a store yet, I don't know the sizes of these amps but prefer a small one as it's mostly for home use.

Here's my Roland AC-33 Acoustic Chorus amp. Notice the foam surround around the speaker cone. Also look at the smaller cone in the middle of each speaker. That's called a "whizzer cone" and it's purpose and function is to extend the high frequency range:



Following that is my Acoustic AG30. It also has a foam surround around the speaker cone. You'll also see two braided wires coming from the speaker cone into a coaxial mounted tweeter, which also exxtends the high frequency range:



In this third photo is my Vox DA20 electric guitar amp. The speaker cone and the surround are one piece. The surround is rubbery coated to prevent tearing at the edge of the cone. It has no high frequency device, just a domed dust cap:

ricdoug said:

Mealfrog41, I second the Roland AC-90. It's a powerhouse that can be used by itself as a personal P.A. and also as a personal monitor to hear yourself on stage. I use my LR Baggs Paracoustic DI with my Roland Acoustic Chorus series amps to broaden tonal control and reduce feedback like a fine art. Ric

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Thanks a lot Ric, really appreciate it. Can you think of any benefit in using a tube amp? The person that recommended it over the acoustic amp is a very accomplished producer and I respect his opinion greatly. I am completely open to either option though, and I'll probably try both out. Just curious if there might be pros and cons you might be able to point out. Thanks again!