MXR 10 band EQ problem UPDATE- It's working

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boogietone

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I recently bought a used MXR M-108 10 band EQ. I didn't have much time
to mess with it at first and it sounded good they it was set when it arrived.
When I finally got around to adjusting it a few weeks later I discovered the
far left EQ sliders for the 31.25 hz and 62.5 hz sliders are not working. The
volume slider on that side works great though. Can it be just the sliders need a
cleaning? Can I just take it apart and fix it pretty easily? Anyone have any issues
with there's?
Any help would be greatly appreciated.
Thanks in advance!
 
If I remember correctly those two sliders didn't do much on mine either, I think those frequencies are mainly for people playing bass.
 
The low E string on an in-tune guitar is 82.4 Hz. Any information below that is only registered as noise/distortion by the speaker. Turned up loud enough, it can be felt, but it won't be heard as part of the audible tone. Studio engineers routinely chop off those frequencies in mixing for that very reason.
 
Good to know! Thanks! I'm obviously not too familiar with EQ's except the onboard
EQ's on Mesa amps. Always something to learn.
 
Sorry i have to disagree with most of what's been posted so far. I been using an MXR M-108 ten band EQ in the loop of my Mark IV as well as many other amps and the ONLY two sliders I do use are the two lowest ones for some low end punch and they make a BIG difference. If your not hearing a very noticeable difference my guess is either your speakers are very weak in the low end or maybe there is something wrong with the EQ. Every amp I have used the MXR EQ with has a very noticeable jump in the bass when using those controls. Besides the pedal was designed just for the guitar why would they put in useless controls. Believe me there is plenty of sound below the E string fundamental. If your not hearing it something is wrong.
 
t0aj15 said:
Sorry i have to disagree with most of what's been posted so far. I been using an MXR M-108 ten band EQ in the loop of my Mark IV as well as many other amps and the ONLY two sliders I do use are the two lowest ones for some low end punch and they make a BIG difference. If your not hearing a very noticeable difference my guess is either your speakers are very weak in the low end or maybe there is something wrong with the EQ. Every amp I have used the MXR EQ with has a very noticeable jump in the bass when using those controls. Besides the pedal was designed just for the guitar why would they put in useless controls. Believe me there is plenty of sound below the E string fundamental. If your not hearing it something is wrong.
It's also dependent on how you EQ the amp as well as how the amp is voiced. I was never able to get much out of those sliders with how I personally set up my amp.
As for the pedal being designed specifically for guitar, I don't think that's completely the case. My thoughts are that MXR designed it around the guitar players needs but also wanted the pedal to be flexible enough for bass players as well.
 
http://www.ultrawavestudios.co.uk/Guitar_Tuner/Help/guitar_tunings.htm

Might offer some help on the freqs according to tuning
 
Hmm, I guess I'll open it up and take a look inside.
It is being used with a VHT/Fryette Amplification 50/12
2X12 combo with EL34's. It is the Fryette PE50 speakers
that are custom made to VHT by Eminence. I'll try the MXR
with my DC-5 tomorrow when I get home. Maybe I'll hear
those freq's then. That amp has the stock C90. Thanks for
all the replies!
 
t0aj15,

What you're describing isn't in disagreement with what I posted. Sonic information below the fundamental tone can be heard by the human ear as low as, on average, 20Hz. It just isn't heard as music. Just as with a guitar speaker (which has even less dynamic range than the human ear), such information is registered as noise/harmonic distortion. In this case, the "harmonic" part comes from information that is known as resonant undertones.

If the sound pressure levels are high enough and the frequency response of the source signal is low enough, you can feel resonant undertones all the way down to single digit Hertz levels (though no guitar cabinet can generate such frequencies), even though below 20Hz, you're no longer technically hearing them. That's why the sub-fundamental sliders on an EQ can still make a noticeable difference. The problem is, the difference they're making is no longer musical, per se, but rather is more influential on the amount of bass response the audience (and the player and the other members of the band, for that matter) feels rather than hears.

It can still be fun to have so much sub-bass response that your audience feels every single palm mute and chug in their rib cages, but it needs to be understood that it comes at a risk. The guitar speakers in a typical cabinet do not have the dynamic range to be able to reproduce such frequencies without the risk of damaging themselves. Now, the damage risk doesn't operate like a high-pass filter, with a precise threshold below which the speaker will automatically blow. The risk isn't digital that way, but neither is it linear. As the frequencies produced drop below the low end of the speaker's dynamic range, the risk increases logarithmically the lower they go.

That means that, with frequencies below the fundamental of the guitar string but above the speaker's lower threshold, the information is registered as noise/distortion, adding some percussive thump to the sound, but at no real risk to the speaker. For information below the speaker's dynamic range, though, there is a risk that resonant undertones will create destructive harmonic resonance within the structure and fabric of the speaker itself. Even slightly lower-than-threshold frequencies will cause minute damage that will gradually build up over time. If they are played loud enough over that time period, the damage increases at a faster rate. With frequencies sufficiently below the speaker's threshold and with sufficient sound pressure levels, a single instance of reproduction may be all it takes to destroy the speaker.

This is why, in a professional studio, no engineer will ever allow you to crank up the bass of your signal below his speakers' dynamic threshold, not even if he intends to remove those frequencies in the mix. Cumulative damage to extremely expensive studio monitors occurs very quickly with typical sound pressure levels used in recording. Now, if, knowing all that, you still want to crank up the sub-fundamental bass on your rig because you enjoy what it does to your signal, go right ahead. I just wanted to make you and the other readers aware of exactly what the risks are.
 
Chris McKinley said:
t0aj15, What you're describing isn't in disagreement with what I posted. Sonic information below the fundamental tone can be heard by the human ear as low as, on average, 20Hz. It just isn't heard as music, such information is registered as noise/harmonic distortion.
I have no idea where you got this bit of info but in nearly fifty years of working with sound systems & speaker cabs of all types that's the first time I've ever heard it, and to be quite honest I don't buy a word of it.
 
t0aj15,

I believe I got it from my days as a neurophysiologist, but I also believe you can find it in pretty much any high school physiology textbook. As a matter of fact, I believe you can probably find it in the paperwork that comes with almost any pair of quality earphones when you buy them. On average, the human ear's hearing range is from 20 - 20,000 Hz, or 20Hz to 20kHz. People vary, but that's the average range.

Now, while you can hear sounds down to 20Hz, you can feel them down into the single digits. However, just because your ear is capable of hearing a given sound as low as 20Hz, it doesn't automatically mean your guitar string is capable of generating sounds as low as that. On a standard-tuned guitar, the low E string, as I mentioned previously, produces a fundamental tone of right around 82.4Hz. That's the lowest tone it is physically capable of generating. By definition, anything below that is considered a resonant undertone, a/k/a a harmonic undertone. Resonant undertones can certainly be felt by a human being all the way down to single digits, as also previously mentioned.

However, in order for a resonant undertone to be perceived as actual sound instead of just a felt vibration, a few things have to be in place. First, the mass of the item generating the originating fundamental tone has to be sufficiently large such that any undertones generated are of sufficient amplitude to be perceived by the human ear. Vibrating guitar strings, unamplified, do not have sufficient mass for this.

Second, the power transformer and speakers must both have sufficient dynamic range such that the undertones in question are capable of being generated as sound without dipping below the low threshold of the dynamic range. This is almost never a factor with the power transformers used in guitar amps, but is regularly an issue with typical guitar cabinet speakers. If the undertone is lower than the speaker's low threshold, it will be manifested by the speaker as destructive vibration, damaging or even destroying the speaker, especially over time. If the undertone is above that threshold, it will be generated as sound. If the natural unaltered amplitude (i.e., volume) of the undertone is too small, as it typically is in a guitar string, the amp's tone circuitry and power transformer must "step in" to boost that undertone's amplitude to a level where it can be heard by the human ear. This is something almost all amps do quite well.

Third, and regardless of the other factors, the undertone generated by the combination of the guitar string, power transformer and speakers must have a frequency greater than the low threshold of 20Hz, on average, of the human ear. Otherwise, and even if is above the low threshold of a given speaker, it will be perceived as a felt vibration rather than as sound by the human listener.

If the undertone is higher than the human ear's low threshold but lower than the speaker's low threshold, then even though the human ear is still capable of hearing it, it will be experienced as noise/harmonic distortion because the speaker itself is not capable of generating that frequency as an actual tone. Such an undertone will also cause varying degrees of damage to the speaker.

Guitar speakers' dynamic ranges vary from type to type, but typical 12 inch speakers naturally emphasize the guitar's midrange of frequencies due to their size. Though usually technically a full-range speaker, the size of the transformer and cone and the cone's materials naturally favor about a three-octave range situated in the middle of the spectrum. If you want high-fidelity reproduction of tones lower than the aforementioned 82.4Hz, you are more likely to succeed if you use a dedicated woofer or sub-woofer designed to handle such frequencies without being damaged.

Doing so doesn't automatically guarantee that you will be able to actually hear specific undertones in the signal, though. The undertones still have to be above 20Hz (the human ear's lower threshold) and they have to have sufficient amplitude. The amplitude is almost never a problem, since as mentioned, the power transformer of a typical guitar amp is more than capable of providing sufficient signal strength.

It should be noted, however, that even with a sub-woofer capable of safely reproduding it, and even with a transformer capable of generating sufficient amplitude, the insufficient mass of the guitar string itself means that most of the amplitude of that undertone relative to the fundamental tone will be "artificially" provided by the amp's tone circuitry and the power transformer, meaning an unavoidable introduction of at least a minimal level of added harmonic distortion. There's a good chance that absolute purity of the undertone won't be a significant criterion, but some distortion is unavoidable.

Well....that's it. As for "buy[ing] a word of it", I don't suggest you buy it from me. Verify for yourself every single little point I've made by checking it out on your own. Since you're already not accepting what I'm writing in this thread, and this post is only more of my writing, I suggest you verify anything and everything you care to through independent sources. Cheers. :)
 
A string cannot sustain on its own frequencies that are below the fundamental, however, they may be created by manually moving the string, such as with picking. It is usually assumed that picking creates fast transients, as the string is snapped by the pick, but very low frequencies are created by the pick moving the string before it is released. These show up in the "chugging" created by slow rhythmic movement, and are enhanced by palm muting, as high frequency tones are reduced.

The Human ear is more sensitive to tones in the 1kHz-4kHz range, so very low frequencies must be boosted heavily in order to hear them. They are also processed as touch, especially very low frequencies. The music equipment itself (amps and speakers) also tends to reduce harmonic content below 50-100Hz.

Whether or not low frequencies are construed as music or noise by the brain is debatable, but there is no question that they can be produced and perceived. I consider them to be percussive (in effect, noise), as they are NOT related to the fundamental at all since they are produced artificially. The musician is, however, capable of moving the strings at a rate that IS related to the fundamental, or at least to some tone in the music, so may produce related tones by modulating the picking rate.

Wow - that sounds like a boring science paper.
 
All of that great information aside, did you get your MXR unit working right? I don't think they would dedicate two sliders to a frequency an amp would not normally reproduce for an ear that could not hear it. Just marketing and common sense. Please don't provide any additional arguments. I am still all in a fluster over finding out Al Gore was lying and global warming has dumped 50 inches of snow on my aunts house.

I want to get one of those 10 band GEQ stomp boxes as well. Need to have another tone shaping tool in the box. Have you used a parametric EQ? I see many of those along with the graphic EQ in many racks.
 
I haven't had a chance to mess with it yet. Hopefully sometime this week.
I had a parametric EQ a while back but sold it. It was a Rane PE15 I think.
I don't really want a rack so I got rid of it. The 10 band will suit me fine.
Even if those two sliders aren't working it has really helped my VHT.
Thanks for all the input everyone.
 
Couldn't it be that the audible effect of the two lowest sliders (talking about a standard tuned guitar) is caused more by the tails of the filters influencing higher frequencies rather than that issue about undertones? In every way, I believe those two sliders shouldn't have a great impact on the guitar tone. Depending on the whole equipment, one could hear their effect more and another one could not feel it at all.
 
I will repeat what I said in my first post before all this WAY off topic techno-babble started, the MXR M-108 10 band GEQ that I have in my possession DOES FOR A FACT have very useable controls below the 82.41 hz open E string. Both the 31.25 hz & the 62.5 hz controls are very useful and produce sound (not noise) that is easily perceived by anyone other then perhaps the hearing impaired. Before arguing this point I suggest you try one for yourself. I wouldn't have bought it if it came with two non-functioning controls on it.
 
You have to be careful with boosting frequencies any speaker can't handle. A typical guitar speaker doesn't handle much lower than 70Hz. So if you are boosting 31.25Hz and 62.5Hz you are just jeopardizing your speakers. We all know you don't plug a bass into a guitar amp because it will mess up the amp. Why? Because the speakers can't handle the frequencies the bass puts out. So if you are boosting bass frequencies into a guitar speaker that it can't handle you aren't doing anything good for your sound or for the speaker.
 
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