Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

An acoustics/music question

  1. Jul 28, 2014 #1
    So I play the guitar, and I cannot use the same amp I use to gig with, because in my home basement, it's too sharp and trebly; the high frequencies sound way too apparent. Guitarists refer to this sound as an "icepick rammed into both ears". In the two venues I used to play at most often, I could NEVER get a sound that was too sharp. Furthermore, my amp sounded much louder in those venues compared to my basement.

    I used to think it was because the those rooms were huge compared to the rooms in my house. But now I think it has a lot to do with the shape of the venues as well; the venues were both rectangular/square shaped. My basement is in the shape of one of those composite figures; if you can imagine, it's basically a rectangle, with another rectangle jutting out of the longer side of the first rectangle.

    So now I think about it this way: 1) my basement is tiny, and 2) it is not in the shape of a professional venue/room. Therefore, the reflections of the sound coming from the amp, bouncing back from the walls, makes it so that my guitar is not very pleasing to the ears.

    Am I thinking wrong? Can someone give me a detailed scientific explanation as to why it is how it is?
    Last edited: Jul 28, 2014
  2. jcsd
  3. Jul 28, 2014 #2
    You could try putting a cloth over the amp (i.e. so it covers the speaker drivers, but not touching them, of course). It should cut off high frequencies. Experiment with different cloths/thickness and you may be able to get a sound you are more pleased with.

    We discussed similar things in this thread:

    "If you put your two hands over two ears while listening to music...."
    See my reply in post #7 for some info and links.

    EDIT: Oops, I forgot this :tongue:: if there is an equalizer on your amp, you should of course try this first, by lowering the treble (and maybe some midrange).
  4. Jul 28, 2014 #3
    Although you didn't mention it, I will venture a guess that your amp settings, especially your "volume" control are not the same in both venues. It is likely that your "volume" control on your amp is much lower in your bedroom and that your actual Sound Pressure Level is considerably less than at a gig.

    This is important because of the physics of sound and how our ears hear. For many reasons, both electrical and acoustic, as your volume goes down the bass response drops off much more rapidly than treble response. This is why it is common even in very high fidelity music systems (home stereos) to have a "Loudness" switch or a compensated "volume" control so that the bass response doesn't drop off so rapidly.

    I can cite you the physics but it is actually an extremely complex interaction between electronic effects (not the same as "pedals") sound source, listening environment and human ears. Unless you really want to get in deep, it is easier to cite examples and state known variables.

    Some guitar amplifiers (Laney is one) have a Bass Boost switch that behaves much like a stereo's "Loudness" switch. If yours has one of these it can help a great deal at practice levels. Any sort of EQ, as others have mentioned can help, but this too is quite complex to work out by trial and error since room acoustics are not flat and certain, often extremely narrow, ranges get amplified while others are reduced.

    If you'd like to see this, a Pink Noise Generator and Spectrum analyzer will show you in graphic form which frequencies are boosted and which are diminished. I knew a very exacting, technical musician who at setup would use a PNG and Analyzer so he could set his controls for flat response to start off, so that he had a reference point to work from regardless of the room shape, size and composition, and then he would add or subtract on his rigs EQ to get back to "His Sound". He always sounded great.

    Regarding citations, you may have already experienced that when major pro musicians publish their settings in music magazine it is very common that Bass controls will be set at or close to "0". If you try that at home it will sound awful. However get on a big stage and "turn your volume to eleven" and what you get is powerful but very tight and crisp Bass Response with no "woofiness" and the high mids overdrive just right.

    It is good that you have asked this question since for electric guitar players, amplifiers are NOT just sound reinforcement devices. They are instruments (with voices) in their own right and part of the chain that starts in your brain and is communicated to anothers brain(s). So you are actually making steps to learn your instrument. Kudos.
  5. Jul 28, 2014 #4
    Long time guitarist... some things to consider about this.

    1] The tone controls on old HiFi systems were generally designed to have a place in the middle of the knob that neither added nor subtracted frequencies... a "flat" position in the middle. Setting all the tones to their middle position approximated a "flat response".
    The tone controls on musical instrument amplifiers do not work that way at all! They use a circuit called a tone stack, because of the way the circuit sends the signal through each control in a "stacked" arrangement, like the steps of a ladder.
    First, the signal is reduced, and then recovered by turning up the tone controls. They only "add" back up to the level prior to the reduction before the tone stack.
    For a tone stack with a treble, middle, and bass tone control, the treble and bass controls only work in the "add" direction. Their flat position is when they are set to their minimum position.
    The middle tone control is actually not a tone control but an insertion loss compensation - it raises the whole frequency response curve up and down, and its "neutral" position is going to be at about "8" for the typical knob marked "1-10".
    Now, a lot of guitarists assume that the "flat" setting is to set all the tone knobs to their halfway up middle positions, but this is incorrect. Doing that will boost the high end and the low end and dip the middle... this is called a "scooped" curve, as in the middle has been scooped out.
    The middle range is where all the good tone is on the guitar, so this is a very bad but common error in general, and why so many guitarists have a bassy muddy and tinny antagonizing sound without the richness and depth that comes from projecting the middle range voice.
    So, the first thing of all is to start with the treble and bass tones all the way down and the middle up near full - then adjust as needed from there based on the venue acoustics.

    2] The sound you hear on stage is different from the sound heard out front by the audience. If you set the tones so that it "sounds right" from where you stand on stage to play, it will just microwave the audience with punishing high end. If you take a long cable and stand out front during sound check and set the tone just right, it will sound muffled and damped from where you stand on stage to play... you have to learn how to hear and accept that sound for the sake of your audience, or use a stage monitor.

    3] Amp placement is critical. Putting amps on stands, chairs, or otherwise elevating them only acts to increase their projection of high frequencies. This helps the guitarist on stage hear his amp but kills the audience. It also reduces the bass level because the floor is not close enough to serve as a reinforcing barrier. This causes guitarists to increase the bass level at the amp's tone control, with labors the amp unnecessarily, and tends to make the sound boomy with a strong amp, and flabby or bloated with a weaker amp.
    Much better is to place the amp on the floor and let that reinforce the bass response without using the bass tone control - the sound will be more naturally conducted to the venue space.
    You don't want much low end anyway; it will overlap the bass player's range and make things sound muddy.

    4] Size and shape of the venue space make a difference, but the major contributor is going to be the absorption or reflection from the composition of the barriers (floor, walls, ceiling, windows)... concrete, tile, metal, wood, glass, carpeting, etc. The number of people also makes a difference, as they absorb sound as well.

    You say your basement is tiny, so maybe all your listening there is "near field", that can sound very "hot" in the high end. So, I would suggest, first; make sure your home amp is on the floor and knock the tones down. If that is not enough, do some room treatments to decrease high end reflections. Add more furniture, more complex surfaces, hang some rugs, carpet the floor, try to place some curved surfaces around any bare spots on the walls, etc.

    The venue with the well behaved amp may just have a more enlightened management that has taken some steps to improve the acoustical space, or the amp may just be a darker voiced amp.

    In general, use the tone controls on your guitar to make your amp sound right when the amp tones are set to "flat" (treble and bass down, middle up). Do this at low volume to minimize room effects and use that as your basis. Then use your amp tones to make the amp sound right when you take it to various venues with different acoustic spaces.

    Anyway, give some of these things a try and see if it helps.
  6. Jul 28, 2014 #5
    Hi, thanks for the good explanations!

    To address some points you all have made:

    DennisN, i tried something similar;i put tape over the center of the speaker when i found that the tone i get at home is unbearable. And thanks for the thread link!

    Enorbet, when i play at home, i use the middle pickup almost exclusively for my more trebly rat overdrive, and i switch to the bridge when i use my fuzz for solos. (I have a telecaster.) when i used to practice with my live rig at home, i set the treble and mid controls to full. This might make me look weird, but see, the middle pickup of the tele is never harsh at home. The bridge and neck pickup, otoh, were too sharp or too bassy; always one or the other. And in fact, i do use the same settings as i use when i play out, except when i play out, i am free to switch to the bridge and neck pickups since the venues sound better. And the pink noise generator sounds cool - i will learn more about them later.

    Bahamagreen - thanks for the practical advice. I do in fact use an amp stand. A long time ago, i thought that when i put my amp on the floor, it sounds bassier because the floor muffles the sound in a way. But i was advised to use a stand because you get to hear what the audience hears! That way you can control the frequencies to make a more pleasing tone.
  7. Jul 28, 2014 #6
    Putting the amp on the floor does not muffle the sound; it reinforces bass response - it is your indication to turn the bass control down and let proximity to the floor make the bass. Doing so leaves more power for the midrange.

    Please, no matter what you have been told, put the amp on the floor. Putting it on the stand does not let you hear it like the audience. You are on stage hearing stage volume where your most obnoxious frequencies are being masked by the other instruments. You cannot hear what the audience hears when you are on stage; continuing to believe otherwise is causing your audience to suffer being cooked with high frequency.

    Have you ever heard a live guitarist on stage and though to yourself, "He could use a little more high end..."? No, you will have wondered why every guitarist on stage is allowing such a shrill, brittle, tinny, horrible tone to be emitted from the stage... the reason is that to him on stage it sounds just right.

    About one out of every hundred guitarists has figured this out - be one of us, please. :)
  8. Jul 28, 2014 #7
    Cool, thanks for the help bahama.

    Is it possible to sound a bit too dark on stage (and therefore good in the audience) and cut through enough for your amp to act as a monitor?

    A more physics-oriented question. Why is it that a human voice that is heard from about 5 feet away, sounds basically the same like 30 feet away, while a guitar amp that sounds one way 5 feet in front of it sounds much different 30 ft away?

    I have forgotten a lot about frequencies/physics of sound since grade eleven, so i do not have much of a clue haha.

    EDIT: One more question, I promise. Bahama, you told me that what sounds fine on-stage will sound overly bright and harsh in the audience. What about in the situation where you mic your amp with a directional mic? Obviously you don't mic from where the audience is, you mic it from around your position on the stage! So in the scenario where you mic, the tone that sounds good on-stage will surely be pleasing as it comes out of the PA towards the audience's ears, right?

    Or is there something about waves/frequencies/acoustics that I don't know about?
    Last edited: Jul 28, 2014
  9. Jul 28, 2014 #8
    One cannot assume the above to be true simply because different brand/models were/are made differently. Even "back in the day" while Fender and it's multitude of copycats used "cut" controls, most Ampegs used feedback tone controls that both boosted and cut depending on setting, though midway was not very accurate for flat.

    ## incidentally, Ampeg borrowed that design from among other places, Dynaco kit stero preamps like the PAS-3 and Pat-4. Those had the center detente which effectively pulls the controls out of the circuit but only a very few stereo preamps and no guitar amps had or have this.

    Furthermore setting ones' tone controls for flat response in the amp is a guarantee of absolutely nothing since the resulting room sound is further colored by speakers, placement, and room acoustics including variables such as how many people are in it.

    IMHO the issues of getting "Your Tone" and faithfully reproducing that for the audience are two different problems with different solutions. Those solutions depend to a great degree upon the seriousness and commitment of the band.

    While it is by no means wise, the age old setup of PA strictly for vocals, fire it up and let 'er rip and let the chips fall where they may is still viable if it's just for casual fun.

    OTOH, if your band is serious and willing and able to go for professional sound that sounds as close to the same everywhere this requires instrument reinforcement as well as for vocals. There is a huge advantage to the guitar player in such a setup because his amp becomes essentially his own instrument stage monitor. I prefer the old Fender Tilt-Back legs and setting my amp up facing me from in front of me so everywhere I go my amp is at the same distance and angle, just 6-8 feet from my ears giving me very close to the same exact sound no matter what stage I'm on. Since it is aimed towards me and away from the crowd there is vastly reduced high end perceivable by the audience from my amp. That gets corrected by mic'ing my amp and adjusting for a balanced band sound in the PA.

    As for finding "your sound" while you may have had success by the "0-5-0" initial setup this is not universal for all players or all amps. Most just play around till it sounds good to them but I do agree it is valuable to understand how your tone controls (all of them, amp and guitar) work.

    Even within a brand, tone controls can be extremely different. For example Fender Black Face and subsequent designs have the tone controls BEFORE the volume control. This was done in an effort to make amps sound more similar at different volume settings. That makes it possible (sort of) to have one amp that was useful in a variety of venue sizes. However it also sacrifices tonal dynamics.

    Fender Tweed, Classic Marshall, Vox AC30 and all of that ilk have the tone controls in a low impedance circuit AFTER the volume control and at least one amplification device apart. On Tube/Valve amps this tone section was (and still is on some brand/models) driven by a Direct-Coupled, Cathode Follower, which because it has a maximum gain of Unity, acts as a limiter at higher volume settings. This creates "driven tone controls" which can have an immense effect on overdrive harmonics and thus the way you set your amp or can and should set your amp.

    There is a distinct, and to many players, important advantage to this last arrangement in that tone color can change just from how hard you pick strings. This creates a very dynamic, vocal quality adding considerable variety and emotion to lead playing and even some rhythm playing, with the latter also depending a lot on musical genre.

    Add to this, that some guitars have what in effect is a "brightness" bypass capacitor on the guitar's volume control (highly recommended you try this if you haven't already) which has the effect of substantially increasing bass content as one turns up at the guitar. The theory behind this, especially for a band with a single guitar player covering both rhythm and lead, is that when playing chords (multiple strings having higher output) which are commonly meant to be behind a vocal, all you commonly need is a little clarity of tone to fill in effectively while not "stepping on vocals and other players. However when it is time for a lead, commonly one or two strings (having reduced output as well as less bottom from the common use of higher strings and frets) can be given great power when the bass is added incrementally with volume on the guitar. I can go from a crisp, clean whisper to a thunderous scream just from my guitar volume alone. Furthermore when at higher settings if I pick lightly I get a beautiful tentative but barely restrained sound that changes to a growl when I hit harder. This arrangement is extremely versatile and dynamic, and most importantly, simple and intuitive while playing.

    Or, as noted above, separate stage sound from audience sound as much as is possible.

    Very good points! I too prefer guitar amps be on the floor, just tilted to face me.

    I agree with much of the first part of this last comment but strongly disagree with the part I emboldened. Certainly it is worth a try, but this kind of setup is based on the "amp as sound reinforcement" concept, rather than "amp as instrument" concept, and in either case is extremely limiting. It essentially demands your amp "be dumb" and contribute little or nothing to your sound. This may be fine for acoustic guitars but even those generally are better served by mic'ing through the PA or by contact mic's built into the bridge/nut.

    When we are talking about an electric guitar, and given that the OP is employing a Rat distortion device, I am certain he is not looking for an acoustic tone which makes the emboldened section minimally valuable at best.

    As in most threads, it is much easier to give specific advice when we are given information about the environment, equipment, and desired function than when left to guess-timate. There are more different kinds of guitar players than there are even different kinds of guitars. Throw in strings, pickups, amps, pedals/rack effects, speakers, etc and we have a very wide and complex situation.
    Last edited: Jul 28, 2014
  10. Jul 28, 2014 #9

    All good points... it is very complex as you indicate, and much of it remains somewhat of a black art.

    I play mostly jazz and blues... clean style, as you suspected. And you are right - when you use the amp as an instrument to vocalize subtlties in one's technique and style of play, lots of things change.

    My suggestions were simple starting points... sometimes they address the most likely issues, but sometimes not.


    About mic placement; the "ice pick" projects in a line straight out from the center of the cone. Some people tilt the speaker back to point it up over the audience as enorbet mentions, or they face the speaker to the back of the stage, or place a guitar case opened like a "V" and set up on end with the open part facing the speaker, in front of it... various techniques to keep the "beam" off the audience.
    Likewise, if you observe how tech people place the mic you will never see them place it directly in front of the middle of the speaker pointing stright in; they will set it off to the side close to the edge of the speaker and off axis, pointing in at an angle to the plane of the motoer board (baffle the speaker is mounted on)... to keep the mic out of the "beam".
  11. Jul 29, 2014 #10
    So true! However the reason for this is that there are so few technicians and sound engineers that are also artists, and vice versa. Those that are tend to be innovators and extremely important to the understanding of what constitutes "good sound" but it is a bit sad how few get it even after the fact.

    Two such men are Les Barcus and Tom Scholtz both of whom have very different backgrounds. Les Barcus (of Barcus-Berry fame) was a "simple" Hi Fi and TV repairman yet somehow he understood that virtually all reproduction devices distort, that is to say, add harmonics. What was the key to his understanding, and I submit this whole field of "good sound", was that some harmonics mix well and produce even choral effects. This led to his superb design of the very first pickups, peizo in nature, that were able to help in the amplification of delicate instruments like piano and flute. He discovered this largely through his affiliation with Berry who was/is a violin player and we are all familiar with how "screechy" some violins can sound. In working to understand why Stradivarius violins sound so wonderful and why so many others sound so bad, he discovered a great deal about harmonic content, how we perceive it, and how to emphasize those "sweet" ones.

    Tom Scholtz holds a Masters from MIT in Engineering and though I know less about his process I do know he came to the same conclusion from studying organs and synthesizers and learning, for example, what harmonics make a flute sound different from a saxophone. One of the developments that resulted from this is his famous "Rockman" preamp which is a bit unfortunately named since despite it's sweet overdrive and chorus effects, it's biggest breakthrough is a gorgeous "clean" sound. The fascinating thing is that this beautiful "clean sound" is not actually "clean" in that it too, like all devices adds harmonic content. It just adds the right ones.

    Les Barcus, in affiliation with Bob Crooks, developed a fascinating device called the Barcus-Berry Enhancer. They noted that in all electronic circuitry, and especially those with negative feedback, there is a phase lag that increases with frequency, so the more devices/stages, the more lag resulting in a muddier and muddier sound as the phase angle causes high-end smear. This is part of what is responsible for decreased clarity in early tape over-dubbing and of course in overly complex guitar amps. The BBE device seeks to rectify this phase discrepancy and is adjustable as to how and at what trip point it begins to activate. It is truly amazing how superbly this device functions whether the actual physical unit that connects to instruments and/or amps, but also the digital version for PC recording DAWs.

    It is worthy of note that "all devices distort" applies even to those we don't normally think of. Example - Django and Charlie Christian were not undistorted but we perceive their sound as clean largely because.... yep, you guessed it, harmonic bias, and in those cases it came largely from the even ordered bias of triodes and/or simple Class A design over AB or especially B.

    It took me a long time to figure out why so many Jazz players love Polytone amps since I found them to be hard and cold sounding. Once I understood that they are biased toward odd harmonics but held in to very low orders, it began to make sense. The only remaining problem for me was "if Jazz players like stark, cold, hard sound then why do they also like, for example, the Roland Jazz Chorus amps? Then I realized that it has to do with blend and that few designers/manufacturers understand or cater to creating tightly reigned harmonics with a pleasing blend of low-order odds and wide evens. This area is still very undeveloped but speaker choice (such as certain Celestion speakers that have had harmonic bias researched and designed through Laser Doppler Interferometer technology) helps as does that amazing BBE device or even the Scholtz Rockman used as either a preamp or in-line as simply an effect - ALL of which "wrangle the angle" back towards the original, unaltered state but also in doing so do it in a manner that reduces high order and especially high order odd harmonics. If we have to accept some coloration (and we do... there is essentially no choice in this), then let it be the right kind.

    Understood and as I mentioned certainly worth a try as is almost anything. A bass player once told me "I don't care about specs. If I have to put a 10 inch speaker in a 55 Gallon drum to get the sound I want, then so be it". He didn't understand how specs could help him, at the very least to narrow down the field of things to try, but, at the time, I didn't give just credit to "amps as instruments" and subsequently I learned they all are to some degree or another.

    I am willing to bet that your sound, though you consider it "clean" is not an exact representation of how your instrument sounds unamplified, only louder. Once we determine or accept that it is colored, we can choose the right hues and "right" by your own definition. Baskin-Robbins would likely be less successful if they only had 3 flavors instead of 32 :biggrin: though it is doubtful they would be well-served to offer 300.

    To reiterate for exact on-topic... Airbusman - Isolation, as much as you can manage, is the first step in control. An example I am betting you can feel is the adage that -

    The Drummer is the Volume Control for the Band, because he basically hasn't one.

    This is why, in the studio, and even some live setups, we have baffles surrounding the drummer to reduce uncontrolled "bleed". The most common cause of runaway volume is simply "I can't hear myself". Please yourself first so that you will play at your best, but isolate yourself so you don't step on anyone else.
    Last edited: Jul 29, 2014
  12. Jul 30, 2014 #11
    And now, precisely On Topic....

    I find this perplexing and illogical unless your definition of "louder" has more to do with frequency peaks than actual sound pressure levels. Also, are you saying that at the exact same settings your amp sounded louder in a big room than in a small one?

    Yes shape matters a lot as does composition. A hard flat surface is highly reflective compared to a soft surface and especially if that surface is not flat. Anechoic chambers in which your amp wide open as loud as you can set it, will sound like the faintest of whispers as if the sound were being sucked away, have walls covered with soft wedges in non patterned arrangements but with the apex points facing the center of the room. Some people find such rooms rather disturbing since all sonic cues essentially disappear.

    Basically this is correct. It is probably still commonplace for bands to glue egg cartons to walls in an attempt to reduce reflections even though the modern plastic ones are not as absorbent as the old cardboard fiber ones, and even those were only moderately effective.

    The cheapest ways I know of to minimize reflections, especially in those harsh areas, are to make a coulage, a sort of checkerboard but better if it has no repeating pattern, of out-of -date carpet samples (often free for the asking), cork, and other such materials. It is most effective if you reduce flatness, such as by putting foam behind some of the samples so that they bulge and irregular is better. This is even more effective if you can construct a panel, perhaps on wheels, that can be easily moved so you can experiment with location and angle.

    The reason I mention angle is because of the phenomenon known as Standing Waves. This occurs, for example, when sound bounces back and forth between parallel walls. Without getting into the concept of time and wave propagation and combination, suffice it to say that anything you can do to eliminate parallel, flat, hard surfaces will considerably improve the sound in any room.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Similar Discussions: An acoustics/music question