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[Kim]

I've been toying with the idea of building a different speaker cab for quite some time and I finally did it.  Well, not exactly building the whole thing but just modifying an existing one.   See, I've wanted to try 15" guitar speakers instead of the standard 12", but the only ones I heard of were those Randall ones they made for Dimebag Darrell and they are not that easy or cheap to find.  So I had those in mind somewhat when I thought about making my own. 

First, I needed to acquire a decent 4x12 cab with the straight front, not the angled front.  That finally happened when I found one on a local sale ad that was affordable to me, well-built, in great condition, and not beat to hell.  It was also an empty cab, hence the much better price.   I have the tools and the skills, so here we go!   

I removed the front 4x12 baffle (5/8" plywood) from the cab and installed a new 2x15 front baffle (also 5/8" plywood) that I made.  Stained the front of the wood black then glued, screwed, and seal caulked it all in.  I reused the T nuts and bolts for fastening the speakers and cut a piece of expanded metal for the grill (matches the one I made for my Carvin 4x12 cab)  Sold a few pedals to buy a pair of Celestion Fullback 8 ohm speakers, and installed them wired for 16 ohms mono.  The 4x12 cabs usually have a single post in the center to tie the front baffle to the rear panel for reinforcement, but this 2x15 arrangement wouldn't allow a single post to be located in the center.  I made two support posts instead to be located as close to center as I could and buttoned it all up.





The real question though is "how does it sound?"  The answer is YES.    lol
There's definitely a shift to a slightly lower tonal register and a bit more "girth" when compared to my matching 4x12.  I have to say I like that a lot better, but of course more testing is needed.   Stacking them in the traditional configuration isn't an accurate comparison, IMO.  They both need to be at the same height relative to your ears so a side-by-side is preferred. Even better if they are side-by-side up at ear height instead of knee height.

Yeah. There's 2 full stacks in the music/gear room in my house right now.....Goals, right?   

[rnolan]

Hey Kim, nice work  what a great idea, really like what you've done there.  I've got a pair of new (my dad bought them ages ago) Altec 15"s in the garage which I've wondered what to do with.  Been toying in my mind various options.  Keen to hear how the testing progresses.

[Dante]

Nice job, man. That looks great

I like the sound of a 15" speaker too - ever since I played through a Peavey 1x15 combo. Two of them must sound massive 

[Harley Hexxe]

Hey Kim,

    Good job there Now you've got the full range guitar tone at that stack.

    I used to own a pair of Fender Dual Showman Reverb stacks that had 2x15 JBL loaded cabs, so I have a pretty good idea what you're getting out of those. They sounded awesome, they were just a pain in the A$$ to load around to gigs.

    Rock on bro

Harley

[Kim]

Thanks! 

I've been able to do some more playing with this setup, and even took it all over to the studio for an afternoon of some crankin' and some mic'in.  (The drummer who was supposed to also be there for full-band comparisons never turned up.  Apparently, he stayed up way too late partying the night before and spent the entire next day as a  in his bed.)     Oh well.

One of a few things we found were that the 2x15 wasn't quite as loud as the 4x12.  The Sensitivity specs are fairly close, but there's only 2 15"s compared to 4 12"s.

Celestion Fullback 15"             Celestion Seventy/80  12"
100 watts each  (x2)                          80 watts each   (x4)
99 dB                                               98 dB
65-4000Hz                                        80-5000Hz

It could be the actual surface area of the cones that come into consideration as well.  Assuming the cones are flat (of course they are not) and actually 12" or 15" in diameter simply just for ease of math formulas and comparisons reveals another side of the experiment.  Using the formula Area = π x r2 for each speaker multiplied by number of speakers means:
The 4x12 has approx. 452 sq in. of speaker cone to transmit sound.
The 2x15 has approx. 353 sq in. of speaker cone to transmit sound.
How much this comparison actually impacts the overall loudness could be debatable, but it must mean something and probably should be considered if planning your own speaker cab build.  Don't know about everyone else, but I'll pick sound Quality over sound Quantity at this point in my journey.

The difference in the sound level between the 2 cabs wasn't enormous, but was definitely noticeable that the 2x15 wasn't quite as loud as the 4x12.  I felt this to be an advantage, actually.  It meant that if you were using an amp that had to be turned up a bit more than what is practical to get into a "sweet spot" you could do so easier without overpowering the room and everyone in it. 

For mic testing, we achieved optimum mic levels at a very reasonable and manageable volume; higher than "bedroom" volume and lower than "earplugs mandatory" volume (provided of course that you weren't standing directly in line with the speakers).  My guitar used here had B Standard tuning.  Both cabs were side-by-side on the floor plugged into my Peavey JSX head, and a sound barrier was placed between the cabs.  One sm57 was used at each cab, and a single tube mic captured the room; each mic had it's own Track.  The Playback results were interesting, as you could definitely hear the volume difference.  Solo'ing each track made me think both cabs sound great by themselves, but together sounded absolutely KILLER once the Levels were more evenly matched!  I was very very pleased with the results, and the studio operator was getting a kick out of it too.  The Dry Clean sounds continued to be just as killer as I ever wanted them to be.  After the mic tests, I ran the amp up quite a bit louder and even changed to a Drop A tuning but everything stayed solid and true without much fuss.  I could get a bit of "growl" from the 15"s if I wanted but without damaging anything.  The 12"s didn't want to "growl" btw, they just "screamed" more.  I didn't use my MP-2 in this session because since I've already decided that my ADA stuff will stay home from now on, I didn't see a point in bringing it for this session.  But believe me, I'll still use it at home because I'm always experimenting with stuff there.
Everyone has their own idea of what sounds best to them, and I am hesitant to say this one is "best" for me because while it sure is now, that could change next week, next month, next year... Such is Life.

I should also mention that this 2x15 cab feels slightly lighter in weight than my 4x12.  I didn't have a scale to weigh them on for an exact number, but I can note that each Fullback 15" speaker weighs 10.6 lbs (4.8kg) according to Celestion's website, while each Seventy 80 12" speaker weighs 6.8 lbs (3.1 kg).  Ugh.  More math.  So the 2x15 cab then has 21.2 lbs (9.6 kg) of driver weight inside it while the 4x12 cab has 27.2 lbs (12.4 kg) of drivers in it to keep it from floating away.     Again, not a huge difference but a noticeable one. 

So there you have it.  I'm really happy I finally got the chance to do this, and am very pleased with the results.  I believe these are the cabs I will keep.  The other 2 4x12 cabs are getting sold, as I do not need 2 full stacks    in my house!  Looks cool though, right?  lol  If I ever get back to playing out again, and only need one cab for that I'll more than likely bring the 2x15.   
Would I trade my 2x15 for another 4x12?  No. 
Would I trade my 4x12 to build another 2x15?  I definitely "might" do that. 

[Dante]

EXCELLENT! Thanks so much for doing all that grunt work so I don't have to

I think I would totally find the same results, given the opportunity. It's a bunch of work to figure out, but really cool knowing what works/where, etc. Kudos man, thanks for going down that rabbit hole for the rest of us, it's a good amount of work and I certainly appreciate it.

[rnolan]

EXCELLENT! Thanks so much for doing all that grunt work so I don't have to

I think I would totally find the same results, given the opportunity. It's a bunch of work to figure out, but really cool knowing what works/where, etc. Kudos man, thanks for going down that rabbit hole for the rest of us, it's a good amount of work and I certainly appreciate it.

+1 

[Harley Hexxe]

Hey Kim,

     Thanks for doing all that homework! It saves everyone a lot of time and research here, I'm sure of that.

     I know if it were me, I would want to get a bit more volume out of the 2x15" cab, have you thought about porting it? I'm sure that would bring out more bottom end, but not sure about more volume. I think if I recall correctly, 45 degree baffles in the cab would help project more sound out the front.

     Just like you liked the results from balancing the levels of the two cab mics in the studio, I know that would be my preference live.

Harley

[Kim]

I know if it were me, I would want to get a bit more volume out of the 2x15" cab, have you thought about porting it? I'm sure that would bring out more bottom end, but not sure about more volume. I think if I recall correctly, 45 degree baffles in the cab would help project more sound out the front.

     Just like you liked the results from balancing the levels of the two cab mics in the studio, I know that would be my preference live.

Thanks for the feedback, much appreciated!  But I'm not interested in porting this cab for a few reasons, the main one being "I'm happy with it as is".   

These Fullbacks are indeed "guitar" speakers and as such they simply do not have the cone excursion to "move air" in the manner that woofers and subwoofers are designed to do. That said, I believe porting the cab for "guitar" speakers will have a negligible effect on the perceived volume, but could help "tune' the cab somewhat if that was desired.  To do that correctly would require more math to use the speaker specs and box cubic volume together to get the proper size and length of port. I'm willing to bet there are apps online that will do that for you; just plug in the numbers they ask for.  But there are (as always) trade-offs and I see no reason to compromise what I now have and go through more work in an attempt to get something I may not like, then have to reverse it all and still have a good looking cab afterwards. 

I definitely won't need both cabs at a gig anyway, should I ever get back to that. 

[Harley Hexxe]

Point taken.

    Rock on Bro

Harley