"Detuned" 4x12 and an 18W
Posted: Sun 06/30/19 4:19 pm
For about six years, I've had a '69 Slant 4x12 loaded with a pair of 16Ω Scumback 65W M75-PVC on top and a pair of 16Ω 65W H75-PVCs on the bottom. It is wired series parallel for 16ohms, has a phase-flip switch, and was used primarily as a reference for when I was building and testing Plexis and other amps and needed to be able to handle some power. These days, it spends much of its time in its box, quietly hoping to come back into service one day With an 18W, it sounds congested and flat, facey, and with a thumpy low end that isn't really complimentary. To me, it's not really a good match and not the sound I am going for personally.
I love the clarity and almost three dimensional quality of an 18W combo with a low wattage Greenback. It's just a stunning combination and really hard to beat. I should clarify that I don't often play these amps to where they are really distorting. I like to get them cooking to where they come alive. If the neighbors are out, I will push it a bit. I prefer to plug straight in and use the Vol and Tone pots. I have tried a bunch of speakers and to my ear the Celestion Heritage 20W is a killer speaker and perfect match. However, I find with that speaker, the combo cab does not handle the low end of the Normal channel all that well and the low midrange gets a little blurry. I love the sound of the Normal channel but I have been wanting to tighten that low end just a hair but not go to a heavier speaker as I like that blur, but just want a little bit more tightness. It's really just a very small thing.
Today, I decided to mess around with so-called "detuning" method described by Kevin O'Connor et al where a speaker(s) is removed from the cabinet and operated normally (with the appropriate change in impedance, if needed). I got out the 4x12 and tried the following:
1. Removed the bottom two H75s and wired the upper pair of M75s for 8R.
2. Paired one M75 and one H75 in upper holes.
3. Paired on M75 and one H75 diagonally.
4. Paired both M75s diagonally.
5. Pared one M75 (upper) with Celestion 20W Heritage G12M (lower) diagonally.
Here is what I found:
1. There is a huge difference in the quality of the sound between a fully loaded 4x12 and a "detuned" 4x12 where two of the four speakers are removed.
2. A phase switch on the amp or cab is very useful. You need to find the right phase.
3. The detuned sound gains breadth and air and becomes much "tighter". The low end is massive. Just huge. I play Les Pauls with underwound, unpotted pickups and let me tell you, running an 18W into this sounds like a piano. With any of the speaker combinations I tried, the low E string attack is greatly improved with more of a percussive quality. You hear the characteristic woody quality of the cab but it doesn't have the "bloated beam" low end of a fully loaded 4x12.
4. The low end that is a bit soft and blurry in the standard 1x12 combo is thick, punchy, and articulate with the detuned 4x12. The mids are clear and defined. Everything is well separated with no one frequency dominating. The Tone control on the amp becomes even more sensitive.
5. The detuned cab sound is very omnidirectional. Very satisfying. It's more of what you love. You can walk in an arc in front and experience a nice "bubble" effect that is pleasantly loud and full. You can even turn it way down to TV level and it's warm and full.
6. I much preferred the sound with the speakers mounted diagonally. I went back and forth between side-by-side mounting and diagonal mounting, and for me, diagonal was the way to go. It was more balanced and wider sounding. I can see where side-by-side in a band situation would be useful as you get that extra bit of focus aimed at your head. But for my purposes, I'm going for that super-organic-3D-reverby-sound-from-everywhere adjective soup sound.
7. Out of the combinations I tried, I ultimately preferred two M75s mounted diagonally. The H75s do that Hendrix thing; my ear picks out that "thing" they do immediately. With the M75 and H75 mix, the H75 tended to dominate the mix a little too much for me. The H75 added some more bell-like top end, but I found the lower mids to be a bit too stiff and "up front". I could see this being spectacular for a Strat though where you want that syrupy, glassy Marshall sound. There is plenty of low end with the detuned cab, even with coupling caps at 10nF! Plenty! With the M75s, there is a killer balance of tight, articulate low end and chime.
8. Detuning does a very cool thing and "works". You have to try this for yourself if you've read about it and been curious. Some might consider the sound a little too hi-fi (maybe?) for their tastes. It is a very big, honest, and revealing sound. I am also running two 65W M75s so it does take a bit more to little more to get them breathing than the 20 watter, but man, they are really, really great sounding and very close to that 20W Heritage.
So in conclusion...
EDIT: I didn't mean to imply that this was "better" than an 18W combo. Just different. After writing all this, I went back to the 1x12 combo with the 16R 20W Heritage G12M, turned it up, and man, that is a glorious, pure sound...
I love the clarity and almost three dimensional quality of an 18W combo with a low wattage Greenback. It's just a stunning combination and really hard to beat. I should clarify that I don't often play these amps to where they are really distorting. I like to get them cooking to where they come alive. If the neighbors are out, I will push it a bit. I prefer to plug straight in and use the Vol and Tone pots. I have tried a bunch of speakers and to my ear the Celestion Heritage 20W is a killer speaker and perfect match. However, I find with that speaker, the combo cab does not handle the low end of the Normal channel all that well and the low midrange gets a little blurry. I love the sound of the Normal channel but I have been wanting to tighten that low end just a hair but not go to a heavier speaker as I like that blur, but just want a little bit more tightness. It's really just a very small thing.
Today, I decided to mess around with so-called "detuning" method described by Kevin O'Connor et al where a speaker(s) is removed from the cabinet and operated normally (with the appropriate change in impedance, if needed). I got out the 4x12 and tried the following:
1. Removed the bottom two H75s and wired the upper pair of M75s for 8R.
2. Paired one M75 and one H75 in upper holes.
3. Paired on M75 and one H75 diagonally.
4. Paired both M75s diagonally.
5. Pared one M75 (upper) with Celestion 20W Heritage G12M (lower) diagonally.
Here is what I found:
1. There is a huge difference in the quality of the sound between a fully loaded 4x12 and a "detuned" 4x12 where two of the four speakers are removed.
2. A phase switch on the amp or cab is very useful. You need to find the right phase.
3. The detuned sound gains breadth and air and becomes much "tighter". The low end is massive. Just huge. I play Les Pauls with underwound, unpotted pickups and let me tell you, running an 18W into this sounds like a piano. With any of the speaker combinations I tried, the low E string attack is greatly improved with more of a percussive quality. You hear the characteristic woody quality of the cab but it doesn't have the "bloated beam" low end of a fully loaded 4x12.
4. The low end that is a bit soft and blurry in the standard 1x12 combo is thick, punchy, and articulate with the detuned 4x12. The mids are clear and defined. Everything is well separated with no one frequency dominating. The Tone control on the amp becomes even more sensitive.
5. The detuned cab sound is very omnidirectional. Very satisfying. It's more of what you love. You can walk in an arc in front and experience a nice "bubble" effect that is pleasantly loud and full. You can even turn it way down to TV level and it's warm and full.
6. I much preferred the sound with the speakers mounted diagonally. I went back and forth between side-by-side mounting and diagonal mounting, and for me, diagonal was the way to go. It was more balanced and wider sounding. I can see where side-by-side in a band situation would be useful as you get that extra bit of focus aimed at your head. But for my purposes, I'm going for that super-organic-3D-reverby-sound-from-everywhere adjective soup sound.
7. Out of the combinations I tried, I ultimately preferred two M75s mounted diagonally. The H75s do that Hendrix thing; my ear picks out that "thing" they do immediately. With the M75 and H75 mix, the H75 tended to dominate the mix a little too much for me. The H75 added some more bell-like top end, but I found the lower mids to be a bit too stiff and "up front". I could see this being spectacular for a Strat though where you want that syrupy, glassy Marshall sound. There is plenty of low end with the detuned cab, even with coupling caps at 10nF! Plenty! With the M75s, there is a killer balance of tight, articulate low end and chime.
8. Detuning does a very cool thing and "works". You have to try this for yourself if you've read about it and been curious. Some might consider the sound a little too hi-fi (maybe?) for their tastes. It is a very big, honest, and revealing sound. I am also running two 65W M75s so it does take a bit more to little more to get them breathing than the 20 watter, but man, they are really, really great sounding and very close to that 20W Heritage.
So in conclusion...
EDIT: I didn't mean to imply that this was "better" than an 18W combo. Just different. After writing all this, I went back to the 1x12 combo with the 16R 20W Heritage G12M, turned it up, and man, that is a glorious, pure sound...