Why do guitar amps never have the design considerations of hi-fi speakers?

[Dolmetscher007]

I am currently working through some tutorials on amp circuit design. Prior to looking into designing and building my own amp, I have done a fair bit of research on speaker cabinet designs, like for a home hi-fi system just to listen to music. The drivers in a nice hi-fi system almost always have drivers specifically designed in to handle specific bands of the frequency spectrum: tweeters, woofers, subs, etc. Also, these systems almost always have "cross-overs" that channel these frequencies to the drivers that were designed to handle those frequencies.

Pretty much 100% of the guitar amps that come to my mind just have 10" or 12" universal drivers that serve to reproduce all of the frequencies that amp will put out. I am still very early in my understanding of amp circuits, so I am totally sure that there is a logical reason for this. I am just wondering what it is? What do amps not have tweeters?

Possibly even more important, why do the speaker cabinets themselves never seem to have any design features to speak of. They are just wooden boxes. Sometimes they are open, and sometimes they have a sealed enclosure. But I have never seen a guitar cabinet with a ported speaker enclosure, or a passive radiator enclosure.

So to summarize, with classic guitar amps...

1. ...why no tweeters/woofers/subs?
2. ...why no crossovers?
3. ...why no enclosure design: (sealed, ported, passive radiator)?

Thanks guys!

Michael

[nosaj]

I am currently working through some tutorials on amp circuit design. Prior to looking into designing and building my own amp, I have done a fair bit of research on speaker cabinet designs, like for a home hi-fi system just to listen to music. The drivers in a nice hi-fi system almost always have drivers specifically designed in to handle specific bands of the frequency spectrum: tweeters, woofers, subs, etc. Also, these systems almost always have "cross-overs" that channel these frequencies to the drivers that were designed to handle those frequencies.

Pretty much 100% of the guitar amps that come to my mind just have 10" or 12" universal drivers that serve to reproduce all of the frequencies that amp will put out. I am still very early in my understanding of amp circuits, so I am totally sure that there is a logical reason for this. I am just wondering what it is? What do amps not have tweeters?

Possibly even more important, why do the speaker cabinets themselves never seem to have any design features to speak of. They are just wooden boxes. Sometimes they are open, and sometimes they have a sealed enclosure. But I have never seen a guitar cabinet with a ported speaker enclosure, or a passive radiator enclosure.

So to summarize, with classic guitar amps...

1. ...why no tweeters/woofers/subs?
2. ...why no crossovers?
3. ...why no enclosure design: (sealed, ported, passive radiator)?

Thanks guys!

Michael

Guitar amps don't need tweeters, in a band setting they are the treble.
No crossover on a guitar amp because the amp and speaker are designed for each other. You will find crossovers and tweeters on bass cabinets though.
Speaker cabinets with the ports and reflex are for bass frequencies and you will find these designs in bass amps.

Your problem is your looking at it all wrong. A hifi system encompasses the whole band, while a guitar amp encompasses the guitar....so on and so forth.

nosaj

[Enzo]

The most fundamental point here is that guitar amps are not hifi amps. Your stereo system has a job to do, it has to faithfully reproduce the original music signal. Ideally it adds nothing nor leaves anything out.

But a guitar amp is not there to REproduce anything, it is the fundamental creator of the sound. The amp is PART of your instrument. The guitar amp quite purposely adds things and takes things away. They WANT to have their own sound. That is why a MArshall sounds nothing like a Fender, and why musicians prefer one over the other.

A stereo hifi has to handle everything from the deepest bass to the tinkliest highs. A guitar doesn't have deep booming bass, and also lacks sparkling highs. Your basic guitar sound is rolling off in the 3k-5kHz region of sound. SO a guitar amp doesn't need subwoofers or tweeters, because that is not part of guitar sound.

Hifi speakers are designed to have a relatively smooth, flat response over their range. Guitar speakers are peaky, with that rolloff over 3kHz. To get relativley even output across a range, hifi speakers tend to be less efficient. Guitar speakers tend to be pretty efficient. More efficient means more sound for a given power input.

As to the enclosure, we see both closed back and open back cabinets. We don't see ports much because that tends to apply more to bass cabs.

[Chuck H]

To sort of encompass what both nosaj and Enzo are saying...

An electric guitar with an electric guitar amp is an instrument. You couldn't use an electric guitar by itself as an instrument effectively. The two together have a characteristic sound. Just like an oboe has a characteristic sound. And you can't play a piccolo part on an oboe or vice versa. But you CAN listen to both on a hi fi system.

[olddawg]

A few mass produced guitar amps DID incorporate horns/tweeters w/ crossovers in the late 60s and very early 70s. Some Standels, a few VOX, and Acoustics come to mind. They were fine for reproducing extreamly CLEAN guitar. For any amp clipping, fuzz, etc they were horrible. Lately, you do see them on a lot acoustic guitar amps and a few odd jazz amps for squeaky clean applications. Generally electric guitar can get PLENTY icepicky with the usual full range paper surround speakers. I played in a band (shortly) where the front man had a JCM800 combo that was “customized” by an “expert” (old TV tech). It had 2 JBL Bullets in it. It was a horrible useless abortion imho. But the guy was constantly bragging about “his tone”. But he couldn’t really play...lol. Go figure.

[Dolmetscher007]

When the ferromagnetic strings of a guitar vibrate through the magnetic flux created by a guitar pickup, the signal that is induced into the copper wire and sent to the output jack is made up of numerous frequencies ranging from 82.41 Hz to ~12 kHz, or realistically well beyond 40 kHz with all the overtones and harmonics possible.

Speakers that are designed to accurately reproduce an audio recording i.e. "Hi-Fidelity" speakers, are definitely, as you guys said, designed to represent the entire frequency spectrum in order to generate pressure waves through the air across the entire frequency spectrum audible to human ears. A piccolo will naturally produce pressure waves in the upper frequencies, where as the lowest string on a bass guitar will hang out in the lower registers.

But, unfortunately, none of that has anything to do with the fact that a metal guitar string produces frequencies between 82 Hz and 40+kHz, yet the device that we plug that guitar into, is not at all designed to accurately reproduce that signal. If there is some scientific reason for not attempting to accurately reproduce the frequencies induced by the vibrating guitar strings, that is totally cool, and I'd love to know more. But I'm wondering if it isn't more of a case of, "this is just how it has always been done."

Don't get me wrong! "This is how it has always been done" is often a perfectly fine answer. For example... 35mm film has a certain "fidelity" that was adopted by the film industry at one point, for whatever reason, and that was that. When digital cameras came along, and they began to realize that they could more accurately reproduce reflected light frequencies, beyond the "definition" of 35mm film, there was (and still is) a huge backlash of people saying that the new super-high-definition video is "too real" and now you can see every skin flaw, makeup smudge, nose hair, and taste bud on a 40 ft tall screen... saying that this new "HD" stuff doesn't look as good as the tried and true 35mm is a perfectly valid argument.

But... from the POV of an amp designer (which I clearly am NOT!!!), I think I would want to build an amp circuit that DOES reproduce the string vibrations as accurately as possible, and then send that amplified signal into a speak cabinet that WAS designed to reproduce that signal as accurately as possible. And then... use things like EQ, filters, and even intentionally designed speaker baffles to "color" the sound of my amp to sound like... well... however I want it to sound?

[The Dude]

Wow! Those JBL bullets were harsh nasty sounding hunks of crap anyway, IMO. They did "cut through the mix" in a stage monitor, but not in a good way if you care about fidelity. I can't imagine using them in a guitar amp...... of any kind.

[The Dude]

...... For example... 35mm film has a certain "fidelity" that was adopted by the film industry at one point, for whatever reason, and that was that. When digital cameras came along, and they began to realize that they could more accurately reproduce reflected light frequencies, beyond the "definition" of 35mm film, there was (and still is) a huge backlash of people saying that the new super-high-definition video is "too real" and now you can see every skin flaw, makeup smudge, nose hair, and taste bud on a 40 ft tall screen... saying that this new "HD" stuff doesn't look as good as the tried and true 35mm is a perfectly valid argument.......

I think there's a lot of validity in that comparison. Sure, guitar generates harmonics well above and below its fundamental frequencies. But it's generally accepted that a good guitar sound does not include a lot of that information. You'll be hard pressed to find a sound engineer who's boosting 15k and 40Hz on a guitar track. More often than not, anything below 200HZ is rolled off and anything above 5K is cut. In part, to leave room for other instruments and sounds.

[Dolmetscher007]

I played in a band (shortly) where the front man had a JCM800 combo that was “customized” by an “expert” (old TV tech). It had 2 JBL Bullets in it. It was a horrible useless abortion imho. But the guy was constantly bragging about “his tone”. But he couldn’t really play...lol. Go figure.

Man... don't we all know, "that guy?!" The Tone guy. He's the same guy that knows what gauge string Eric Clapton used on Lala on an early live bootleg, before Layla was released as a recording. Yet, can't actually play the main lick to Layla.

The same guy creeps into tons of endeavors.

• Skateboarding: The guy that has the ultra rare Powell-Peralta misprint Christian Hosoi deck and talks about is Independent trucks, Swiss bearings, and T-bone wheels... but can't even ollie 3 inches.
• Culinary: The guy with the handmade $6,000 Japanese chef's knife, the liquid nitrogen ice cream, and the Egyptian cotton chef's coat with abalone shell buttons... but takes 2 hours to dice 20 onions, and couldn't brunoise a carrot to save his pampered chef life.
• Graphic/Web Design: Has a wacom tablet, four color-balanced 4K monitors, the full adobe suite and every obscure boutique plugin, but still makes their living downloading stock photos and just adding text in papyrus font (barf).

[loudthud]

So to summarize, with classic guitar amps...

1. ...why no tweeters/woofers/subs?
2. ...why no crossovers?
3. ...why no enclosure design: (sealed, ported, passive radiator)?

Because it's only Rock and Roll !

[Enzo]

from the POV of an amp designer (which I clearly am NOT!!!), I think I would want to build an amp circuit that DOES reproduce the string vibrations as accurately as possible, and then send that amplified signal into a speak cabinet that WAS designed to reproduce that signal as accurately as possible.

Then you no longer have a guitar amp, you have a PA system. The electric guitar does not make sound, it makes an electrical signal. There is no "sound" to reproduce. The job of the designer is not to make a hifi. His job is to make a system that combines with the guitar to make pleasing guitar sounds.

[Chuck H]

When the ferromagnetic strings of a guitar vibrate through the magnetic flux created by a guitar pickup, the signal that is induced into the copper wire and sent to the output jack is made up of numerous frequencies ranging from 82.41 Hz to ~12 kHz, or realistically well beyond 40 kHz with all the overtones and harmonics possible.

Well... Not exactly. When you consider just the early signal path there are serious detriments to extreme HF already built in. Witness:



This is a rough model for a PAF in a guitar with 500k pots for volume and tone controls as played through a typical 20' cable into an amp. And this is the reality of what happens due to the resonant peak that results from the pickups inductance as it relates to the associated capacitances. Unless you get out of the box and use those carbon/crystal type cables or very short standard cables this is the reality of what is happening to the guitar signal before it ever even gets seen by the first gain stage in any amplifier.

[J M Fahey]

A guitar amplifier is not an amplifier but a sound processor.

There is a lot of things it does to the guitar signal, lots of non-linearities added, specially if itīs a Tube amplifier ..... and transistor amplifiers, which by definition are way more linear, have to introduce some of them artificially if they want to be liked like Musicians.
Such non linearities fit the strict definition of "distortion".

Distortion produces harmonics, always higher in frequency than original signal.

Low level harmonics are perceived as "good" , higher level ones as "buzzy annoying" so filtering them out is perceived as "good".

Guitar speakers *all* drop like a brick, 24dB/octave above a certain frequency, typically between 2000 and 3500Hz , so they naturally filter the nasty (as perceived by human ear) higher distortion harmonics.

If higher "natural" harmonics as you mention are also junked, so be it.

In any case nobody misses them because they were never heard in any case and are not part of the Music we hear, so .....

IF somebody adds tweeters to guitar speakers, cabinet will reproduce those frequencies ... but people run in horror away from them.

I remember listening to Acoustic cabinets sporting 2 x 15" (Altec?) speakers topped by a mid sized reentrant horn ... sound was brain piercing unbearable some 30 meters in front of them, canīt imagine being closer, typically wires connecting them were snapped off with cutting nippers, go figure.
Might have been useful in a Woodstock type setting, so people could listen to guitar from 1 or 2 blocks away, straight from the stage, but nowhere else.

Also remember listening to similar Kustom cabinets ... again horns were disconnected to make them usable.

And 70īs solid state Ampeg Bass amplifiers, think 240W RMS driving 2 extra bright JBL 15" speakers (which reach flat up to 8 or 10 kHz on their own) ..... sound was exactly same as tearing 2 Velcro strips apart.

So now you have a small "actual live results" sampling, personally listened at by somebody you know, and not Internet lore copypasted from "what happened to a friend of a friend of a friend" or "which I read somewhere"

I can only imagine the *horror* of adding nothing less than Bullet tweeters to a Marshall cabinet, driven by an already perceived as buzzy JCM 800 .

Brightest acceptable (and would sound very good) would have been a couple 4 x 12" filled with Greenbacks.



notice response steadily dropping above 4kHz, being incredible 20dB down at only 6500Hz !!!! ... less than one octave above!!!
10dB drop just from 6000 to 6500Hz !
It is hard to make such a steep filter electronically, go figure, and speaker has it built-in , "mechanically".

[nosaj]

Sure is a big jump after having looked through some tutorials.
nosaj

[alexradium]

A guitar amplifier is not an amplifier but a sound processor.

There is a lot of things it does to the guitar signal, lots of non-linearities added, specially if itīs a Tube amplifier ..... and transistor amplifiers, which by definition are way more linear, have to introduce some of them artificially if they want to be liked like Musicians.
Such non linearities fit the strict definition of "distortion".

Distortion produces harmonics, always higher in frequency than original signal.

Low level harmonics are perceived as "good" , higher level ones as "buzzy annoying" so filtering them out is perceived as "good".

Guitar speakers *all* drop like a brick, 24dB/octave above a certain frequency, typically between 2000 and 3500Hz , so they naturally filter the nasty (as perceived by human ear) higher distortion harmonics.

If higher "natural" harmonics as you mention are also junked, so be it.

In any case nobody misses them because they were never heard in any case and are not part of the Music we hear, so .....

IF somebody adds tweeters to guitar speakers, cabinet will reproduce those frequencies ... but people run in horror away from them.

I remember listening to Acoustic cabinets sporting 2 x 15" (Altec?) speakers topped by a mid sized reentrant horn ... sound was brain piercing unbearable some 30 meters in front of them, canīt imagine being closer, typically wires connecting them were snapped off with cutting nippers, go figure.
Might have been useful in a Woodstock type setting, so people could listen to guitar from 1 or 2 blocks away, straight from the stage, but nowhere else.

Also remember listening to similar Kustom cabinets ... again horns were disconnected to make them usable.

And 70īs solid state Ampeg Bass amplifiers, think 240W RMS driving 2 extra bright JBL 15" speakers (which reach flat up to 8 or 10 kHz on their own) ..... sound was exactly same as tearing 2 Velcro strips apart.

So now you have a small "actual live results" sampling, personally listened at by somebody you know, and not Internet lore copypasted from "what happened to a friend of a friend of a friend" or "which I read somewhere"

I can only imagine the *horror* of adding nothing less than Bullet tweeters to a Marshall cabinet, driven by an already perceived as buzzy JCM 800 .

Brightest acceptable (and would sound very good) would have been a couple 4 x 12" filled with Greenbacks.



notice response steadily dropping above 4kHz, being incredible 20dB down at only 6500Hz !!!! ... less than one octave above!!!
10dB drop just from 6000 to 6500Hz !
It is hard to make such a steep filter electronically, go figure, and speaker has it built-in , "mechanically".

keep in count that those frequency response diagrams are related to a speaker on a panel,in an anechoic chamber,driven by a solid state amp.
Fairly different story is a speaker in a closed/open guitar/bass cabinet of some sort driven by a tube amp with low or no feedback at all,the result is most of the times a boost on bass and treble due to speaker impedance resonances and rising slope on HF.