Particle board cab vs solid and/or ply....your thioughts?

[Mike Sulzer]

Oh, I have commercially made flight friendy PA cabinets ,specially for: https://en.wikipedia.org/wiki/Les_Luthiers
Mind you, they are very hard to amplify because they use wild self made instruments:a cello made out of an oil drum, violins made out of Danish Ham cans, a trumpet made out of a water heater, Pan pipes made out of Lab test tubes, a marimba made out of hollowed coconuts, their keyboard is literally a keyboard: a typewriter where hammer-letters hit water filled test tubes and so on.
https://youtu.be/LyCDY5accVU?list=PL...sfi7n3eu-Wd4D1

Since they constantly fly all over the world they needed the lightest cabinets possible, I made them out of 9-10mm (3/8") plywood and JBL speakercomponents, which made them heavy anyway, but less so, a pound saved is a pound saved, no matter where.
Today I would have used Neodymium all over the place.
Knocking on any panel of course was like hitting a drum skin, or so it seemed, but by adding diagonal reinforcements and front to back braces they ended up being quite dead.
Then carpet covering on the outside (for protection more than anything else) also helped.

So you have already done it, at least the first part. I am not surprised!

[Mike Sulzer]

Ah!!! But with either the Strad or Martin the vibration is additive, but with the guitar cab it's subtractive (for the most part). In that case you'd have to tune the cabinets resonance to that end. Intentionally subtracting frequencies. This with the added element of amplification at variable volume and distortion character. I, for one, am overwhelmed by the prospect. I've been lucky a few times building resonant cabinets. Unlucky on two occasions and (I suppose) neutral at other times. It's absolutely a crap shoot. On the other hand, I've never gotten unpredictable results with MDF (and never outstanding either).

Well, there is a way to make to make a colored sound from a speaker cabinet increases the sound level. It is called a folded horn, and you would "mis"-design it to get the coloration you want, if you knew how. A folded horn is usually used for subwoofers, but there is no reason in principle it cannot be done for guitar speakers. An interesting way to start would be to see if you could take a single 10" guitar speaker and get as much volume out of it as normally with 2x12" speakers. Forget about trying to control the coloration on the first attempt. Undoubtedly the first attempt will be colored anyway, but not the way you want!

Of course this might be totally incompatible with making something easy to carry around, but it is a project that not many people have done.

[Chuck H]

Well, there is a way to make to make a colored sound from a speaker cabinet increases the sound level. It is called a folded horn, and you would "mis"-design it to get the coloration you want, if you knew how. A folded horn is usually used for subwoofers, but there is no reason in principle it cannot be done for guitar speakers. An interesting way to start would be to see if you could take a single 10" guitar speaker and get as much volume out of it as normally with 2x12" speakers. Forget about trying to control the coloration on the first attempt. Undoubtedly the first attempt will be colored anyway, but not the way you want!

Of course this might be totally incompatible with making something easy to carry around, but it is a project that not many people have done.

A stellar idea. One I've kicked around on a few occasions but never actually acted on it. I was thinking of something on the order of a 2X10 cab with one speaker dedicated to the folded horn. In that instance you could probably make it smaller than a 4X12 and get similar frequency response. Keeping in mind that the folded horn design (for guitar) wouldn't need to get down to 30Hz. And you're surely right. There would be a couple of prototypes before any satisfactory results.

But in this case is it really the cabinets resonance? or are we qualifying that the cabinets internal design volume has a resonant frequency? What we were discussing was the actual effect of cabinet wood vibrations. Which I thought was a different (but certainly related) subject.

[Richard]

I think it's hemholz resonance. Same as blowing across a bottle. The air acts as a spring and the speaker hardly moves at the right frequency, sort of like if you have a telephone cord (if you can remember those) you can wiggle one end very little and the cord can have quite an amplitude with very little input, in terms of motion.

Just read a bit, I guess horns help the speaker transfer the energy to the air more efficiently.

[J M Fahey]

Folded horns in guitar cabs?
If midrange ones qualify (not tweeters), then we have at least two winners.
1) the mighty (and unbearable) Acoustic 201
loaded with 2 15" Altec speakers and a County Fair/School Gym approved folded "voice" horn, SPL was high enough to melt brains many yards away:


not to be outdone, Kustom made what looked like a 3 x 15" cabinet, where the top one was an even larger round "voice" folded horn.

Both examples with horns covering most of the guitar range,except the lowest octaves.

Sound was unbearable, everybody snipped them off and just left the cone speakers.

[Mike Sulzer]

A stellar idea. One I've kicked around on a few occasions but never actually acted on it. I was thinking of something on the order of a 2X10 cab with one speaker dedicated to the folded horn. In that instance you could probably make it smaller than a 4X12 and get similar frequency response. Keeping in mind that the folded horn design (for guitar) wouldn't need to get down to 30Hz. And you're surely right. There would be a couple of prototypes before any satisfactory results.

But in this case is it really the cabinets resonance? or are we qualifying that the cabinets internal design volume has a resonant frequency? What we were discussing was the actual effect of cabinet wood vibrations. Which I thought was a different (but certainly related) subject.

I think the goals of the 2x10" that you describe could be met with a single 10" driver with the horn back loading the driver, such as described here:The Frugal-Horns Site -- High Performance, Low Cost DIY Horn Designs. However, you do not need the bass they are after and so the horn would not need to be as big relative to the driver size. (You could start with an 8" or even a 6" guitar speaker just to get some understanding of how it would work.)

What I am thinking of is a primitive front loading folded horn, sort of a Cerwin-Vega sub woofer made small. Horn action could deteriorate below 150 Hz and so it really does not need to be all that big. The problem comes in achieving the full range out to about 5 KHz. I am concerned about the higher frequencies not getting out of the box, and if they do, beings too directed.

The resonant cabinet aspect comes after you get the basic horn working. The pressure varies along the length of the horn, and so you have ample opportunity to introduce panel resonances with various characteristics, and make it lighter at the same time.

The ultimate goal, no doubt totally impossible, would be something that weighs only somewhat more than a standard single 10" cab, but with a sound output approaching 2x12", and a designable resonant sound. And it would only take an 18W to drive it.

[ric]

You could add a sound reflective surface or two to a combo amp by having protective front panels fold open. A folding horn.

A high school buddy n I did some school dances with Fazier Dixielander theater speakers he rented. I want to recreate them someday as a small shop spkr. They were a boxed 10" woofer pointing back in a bigger box open at the front. With a 18"-2' wide horn on top. 4 ply slats on each side of the inner box holding it centered in the outer. Simple and effective.

How about bass reflex? Properly tuned an 8" Radio Shack wizzerconed front facing and small horn in big boxes gave my slide mounted car stereo something to do indoors.

[rjb]

I have an acoustic with dead spots, what goes on there then?

You have a rattling truss rod, which absorbs energy at its vibration frequencies.
Remove the truss rod cover (if you have one) and pour some glue down the channel.

- Acoustic Guru Man, AKA SGM II

EDIT- Or possibly a loose brace.

[teemuk]

For example, here is the spectrum of an open low E string, bridge pickup:

That tells just part of the truth: The harmonic patterns of "attack" and "decay" of the plucked note are different too. Add to that, how you pluck the string has huge overall effect on what harmonics are created during attack of the note.

Case in point: "pinch harmonics".

...But yes, overall the "fundamental" harmonic of the note isn't usually the one with highest amplitude. Guitar doesn't sound like sine wave, and it isn't even supposed to.

[teemuk]

Those E string harmonics go way up, but note the real high ones are 40db down, and wouldn;t be heard much at all. Also, the guitar, which I thought was the context, cares little for upper harmonics, otherwise we'd have tweeters.

If distorted tones wouldn't be so common most amps actually would have them. All "acoustic" amps seem to be more or less "full-range". Those upper frequencies give instruments their character. The resonant peak at upper frequencies is huge part of tone of different pickups, for example. Acoustic guitars and alike sound dead and bland through usual "guitar" cabs.

...But the tweeter won't produce a pleasant tone when we have distortion pumping up the amplitude of those upper harmonics above sane levels.

...Then again "clean" and "dirty" tones need different kind of approach due to different amounts of IM and upper frequency content. Cleans have very little IM and the upper frequencies aren't disturbing at all. You can reproduce the sound at full-range and the result is just that it sounds more "natural" than bandwidth-limited reproduction.

Dirty tones need different approach because they have/create plenty of IM, the upper harmonics are disturbing if not attenuated, and in addition its customary to hi-pass even as high as 1 kHz simply to minimize IM because it sounds like nasty farting at lower frequencies.

[Chuck H]

Well, depending on the goal of the pickup, the resonant peak isn't always aiming for where you want your final guitar frequencies at the amps output. Humbuckers generally have a resonant peak in the upper mids and higher output, but less HF than single coils. Single coils are generally preferred for clean and semi clean tones and humbuckers are generally preferred for distortion. STRAT NECK SC WITH HIGH GAIN OR JAZZ NECK HB CLEAN NOT WITHSTANDIDNG. My point is just that some pickups (many actually) are designed specifically to "set up" the frequencies that will ultimately be clipped (and very often re EQ'd). Things shouldn't be considered out of context. It's confusing and makes problem solving impossible.

[Mike Sulzer]

That tells just part of the truth: The harmonic patterns of "attack" and "decay" of the plucked note are different too. Add to that, how you pluck the string has huge overall effect on what harmonics are created during attack of the note.

Case in point: "pinch harmonics".

...But yes, overall the "fundamental" harmonic of the note isn't usually the one with highest amplitude. Guitar doesn't sound like sine wave, and it isn't even supposed to.

When a string is stretched and suddenly released, there is a broadband excitation. Displacement travels in both directions along the string and reflects. Within a few round trip times, positive reinforcement results in the growth of harmonics, and the suppression of other frequencies. One does not expect the growth times of all harmonics to be the same, and certainly each harmonic then decays at its own rate. This is very different from saying that the patterns of harmonics are different during attack and decay. The relative level of harmonics is continuously evolving.

[Mike Sulzer]

I think the only possible way to increase the efficiency of a guitar speaker using horns is to use two, one backloaded, and the other front loaded. The backloaded one would handle the "bass" (not so low for guitar) and as high in frequency as it works. Thus the opening would need to be in front, and some designs allow this. (Although the designs at Frugal horn open at the back because the purpose is to extend the low bass response of a small driver only.) The front loading horn would be short and handle just the frequencies above where the backloaded one fails. Interesting design project: can you put the two together without losing something at the transition?

[ric]

I think the only possible way to increase the efficiency of a guitar speaker using horns is to use two, one backloaded, and the other front loaded. The backloaded one would handle the "bass" (not so low for guitar) and as high in frequency as it works. Thus the opening would need to be in front, and some designs allow this. (Although the designs at Frugal horn open at the back because the purpose is to extend the low bass response of a small driver only.) The front loading horn would be short and handle just the frequencies above where the backloaded one fails. Interesting design project: can you put the two together without losing something at the transition?

For the sake of discussion, anytime a spkr is working next to a sound reflective surface, it's "loaded". Setting a cabinet in the corner of a room "horn loads" it with ceiling, floor n wall corner.

Cutting the bottom out of a coffee cup and setting it over my phone's spkr gives higher volume at the expense of a tinny sound. As you say, the devil's in the details to get a sound that many might like.

On the subject of low tech sound enhancement, read somewhere of a guitarist who set his amp on a chair and stood in front of it, then stepped aside for solos.

[Richard]

For the sake of discussion, anytime a spkr is working next to a sound reflective surface, it's "loaded". Setting a cabinet in the corner of a room "horn loads" it with ceiling, floor n wall corner.

Cutting the bottom out of a coffee cup and setting it over my phone's spkr gives higher volume at the expense of a tinny sound. As you say, the devil's in the details to get a sound that many might like.

On the subject of low tech sound enhancement, read somewhere of a guitarist who set his amp on a chair and stood in front of it, then stepped aside for solos.

I've seen that before, also the vocal mic picked up a bit of guitar amp, it worked really well.