TheKman76
Well-Known Member
This will be a slightly rambling and nerdish post, fair warning.
There has been an undercurrent of fascination for all things speakers in my life and one of the things that I've always wanted to understand better is why guitarists like their 4x12 cabinets so much. Obviously it's the way they sound, but exactly what property of the sound is it? And what factors contribute to that sound? I think the MF is the ideal group to answer this question!
OK, background theory.
Beaming:
Some of you will be familiar with the principle of 'beaming' as it relates to speaker drivers, it describes how sound emanating from a speaker can be either diffuse or directional based on the surface area of the drivers and the frequency of the sound. In the context of large drivers like 12" guitar speakers, high frequencies tend to be very directional, while lower frequencies tend to be omnidirectional.
Coupling:
Many of us will be aware that every time you double to number of speaker drivers used to convert X Watts of amplifier power you'll get a +3dB gain in output. This is a slightly more tricky concept to understand and has some caveats, but in essence a 4x12 should have a +6dB advantage in output over a 1x12.
So, through experimentation I found that by adding low-end to my guitar sound I liked it considerably better. I haven't played through a 4x12 in 30 years, but I remember being awe struck by the apparently natural low-end it produced. Less obvious but equally awesome was the airy room response which seamed to be a part of the space rather than from a point source. For all this time I assumed that this originated from the fact that the speaker drivers just didn't have to work as hard, the load was spread across more drivers, they can each sounds clearer or more natural.
Recently I had a theory that there was some cabinet resonance which contributed to the low end. Anyone who has practical experience with acoustic resonance will tell you it's often not very musical, unless considerable effort has gone into it's implementation. It didn't seem reasonable to me that an unbelievably agricultural 4x12 cabinet having no particular regard for resonance should be simply awesome to listen to. That would be an unreal coincidence. Sure, the Fender Bassman combo amps may have had some design smarts built in, but the vast majority probably have no great regard for the acoustics of speaker cabinets at all.
Finally today a couple of things seemed to fall into place.
Firstly is the coupling effect. I went and re-read some of the theory around this again and one phrase kept coming up, "at frequencies below the coupling wavelength". Right, of course, a 4x12 will really only couple completely at half-wave lengths larger than the combined diameters of the closely mounted drivers, call it 600mm. In practice this is more like twice that wavelength, lets call the full-wave length 2.4m. 340/2.4=~140Hz. Ok, so you'll get +6dB below around 140Hz, tapering off a little towards 300Hz or so before you start getting cancelations. Well, there's you low-end boost, right there!
Then I started thinking about the effect of having all those speaker cones moving in symphony. The proverbial 'wall of sound' effect. It's really a worst case scenario of high-frequency response according to the Hi-Fi speaker design handbook... but is it really? In Hi-Fi we'd try to maintain a point source for any given frequency range by making the driver area smaller and keeping the coupling distances between drivers to a minimum and designing the cross-over to suite. Avoid beaming, basic best practice. And yet, lots of people love the sound of open-baffle Hi-Fi speakers where the room is part of the speaker cabinet acoustics. Even more absurd, flat panel speakers can also sound amazing, presumably by means of filling a room with such a vast array of point sources as to render the actual source transparent. Owners of ribbon speakers enthuse about these features too.
So, I'm beginning to think that the property that makes our favourite 4x12 cabinets so good is simply the vast surface area of closely coupled drivers. Sealing the cabinet makes it more bass present, but the rest of the design is largely down to practicality and has little impact on the output.
If you've made it this far... you're a nerd. Welcome.
What I'd really like to hear is experiences from player of 4x12 cabinets. Does any of this ring true? Is there something else to it?
There has been an undercurrent of fascination for all things speakers in my life and one of the things that I've always wanted to understand better is why guitarists like their 4x12 cabinets so much. Obviously it's the way they sound, but exactly what property of the sound is it? And what factors contribute to that sound? I think the MF is the ideal group to answer this question!
OK, background theory.
Beaming:
Some of you will be familiar with the principle of 'beaming' as it relates to speaker drivers, it describes how sound emanating from a speaker can be either diffuse or directional based on the surface area of the drivers and the frequency of the sound. In the context of large drivers like 12" guitar speakers, high frequencies tend to be very directional, while lower frequencies tend to be omnidirectional.
Coupling:
Many of us will be aware that every time you double to number of speaker drivers used to convert X Watts of amplifier power you'll get a +3dB gain in output. This is a slightly more tricky concept to understand and has some caveats, but in essence a 4x12 should have a +6dB advantage in output over a 1x12.
So, through experimentation I found that by adding low-end to my guitar sound I liked it considerably better. I haven't played through a 4x12 in 30 years, but I remember being awe struck by the apparently natural low-end it produced. Less obvious but equally awesome was the airy room response which seamed to be a part of the space rather than from a point source. For all this time I assumed that this originated from the fact that the speaker drivers just didn't have to work as hard, the load was spread across more drivers, they can each sounds clearer or more natural.
Recently I had a theory that there was some cabinet resonance which contributed to the low end. Anyone who has practical experience with acoustic resonance will tell you it's often not very musical, unless considerable effort has gone into it's implementation. It didn't seem reasonable to me that an unbelievably agricultural 4x12 cabinet having no particular regard for resonance should be simply awesome to listen to. That would be an unreal coincidence. Sure, the Fender Bassman combo amps may have had some design smarts built in, but the vast majority probably have no great regard for the acoustics of speaker cabinets at all.
Finally today a couple of things seemed to fall into place.
Firstly is the coupling effect. I went and re-read some of the theory around this again and one phrase kept coming up, "at frequencies below the coupling wavelength". Right, of course, a 4x12 will really only couple completely at half-wave lengths larger than the combined diameters of the closely mounted drivers, call it 600mm. In practice this is more like twice that wavelength, lets call the full-wave length 2.4m. 340/2.4=~140Hz. Ok, so you'll get +6dB below around 140Hz, tapering off a little towards 300Hz or so before you start getting cancelations. Well, there's you low-end boost, right there!
Then I started thinking about the effect of having all those speaker cones moving in symphony. The proverbial 'wall of sound' effect. It's really a worst case scenario of high-frequency response according to the Hi-Fi speaker design handbook... but is it really? In Hi-Fi we'd try to maintain a point source for any given frequency range by making the driver area smaller and keeping the coupling distances between drivers to a minimum and designing the cross-over to suite. Avoid beaming, basic best practice. And yet, lots of people love the sound of open-baffle Hi-Fi speakers where the room is part of the speaker cabinet acoustics. Even more absurd, flat panel speakers can also sound amazing, presumably by means of filling a room with such a vast array of point sources as to render the actual source transparent. Owners of ribbon speakers enthuse about these features too.
So, I'm beginning to think that the property that makes our favourite 4x12 cabinets so good is simply the vast surface area of closely coupled drivers. Sealing the cabinet makes it more bass present, but the rest of the design is largely down to practicality and has little impact on the output.
If you've made it this far... you're a nerd. Welcome.
What I'd really like to hear is experiences from player of 4x12 cabinets. Does any of this ring true? Is there something else to it?
