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[Dante]

I've been really happy with this little stack (pic below). The two 1x12s get the job done without breaking my back and sounded great at an outside gig a couple weeks ago (one on each side of the stage). That said, if anything, the rig has a bright tone. Not 'white noise on top' bright, but not dark at all....kinda like the highs are fine, but the hi-mids may be too strong. Whatever, again, it sounds great and I can get girth with the amp.

FFWD to a jam at my buddy's house the other day: I played through my H&K Switchblade 50 combo and it sounded massive. I thought it was the room (we were in a basement) but it sounds the same today in my bedroom. I did upgrade the speaker in that thing to a WGS that is supposed to be a V30 clone with a smoother top end. I'd say that's an accurate description, none of the brittle tops of the v30 that I don't like. (pic below)

Just for kicks, I fashioned a speaker cable (male to female) to use the combo as a speaker cab with my head. The results were the same, sounds massive. Sounds way better, and much closer to what I'm used to. So....is it the speaker, or is it the cabinet?

I guess the only way to know is to yank the speaker out of the combo (not fun, you gotta take it all apart to get there), and put it into one of my Yamaha cabs. Or, I could just lug around the combo (it's HEAVY) as a speaker cab and have a backup amp already in place.

I'm leaning towards just lugging around the beast, always have a backup 

[Harley Hexxe]

Hey Dante,

    I'm going to go out on a limb here and guess the combo is open-back, and the Yamaha cabs are closed-back?

    If so, can you remove the back on the cabs and try it? You may be getting the ambient speaker sound reflecting off the walls creating that difference you're hearing.

    That would be where I'd start.

Harley

[Dante]

Harley - Yup. The combo has a panel on the back that doesn't close it off completely and the little cabs are sealed tight. I wonder if that'll do it, I'll try taking the back off one today to see. Thanks 

[rnolan]

Hey Dante, that the combo has a panel that doesn't close off completely it's kind of a "tuned port" so you may find that taking the back of your Yamaha sealed cabs is too much  and you may need to just provide a slit similar to the combo to achieve a similar affect.  The size of the opening/slit is usually tuned to the speakers resonant frequency.  Of course the WGS may just be a speaker more to you taste regardless. 

So typically there are 3 main cab designs: 
Open back 
Tuned/Ported   
Sealed 

The speaker surround (where it attaches to the frame) is generally different (stiffer and more robust for open back situations as there is no air suspension for the cone).  The surround can be less stiff and thus slightly more responsive for sealed and ported cabs as both provide air suspension for the cone. 

However, I wouldn't be surprised if you discover it's mostly the speaker difference.  I had a Yamaha quad box a while ago and I was never particularly enamoured with the speakers.  I put a couple of really old Plesey 12U 50's in it and they sounded much better.

[Dante]

I am familiar with the partial back design - and I'm assuming that taking the whole back off will be too bright, or not boomy enough (for lack of a better term)

My plan is to try it just cracked, see how it sounds, then try it completely off, then cut a bit of wood to make a partial back and see how I do

[Dante]

Well, I took all the screws out of the back except one on top to hold it in place. Played a chord, undid that screw and listened again.

To my amazement, it did sound more resonant (boomier) with the back off. I expected the exact opposite effect, but I've learned to try things before discounting them and I'm glad I tried this trick.

The cab is built pretty nice (pic below). It's plywood, got an Eminence Legend 1218 (150w/8ohms) speaker. I had a piece of 1/2" plywood in the garage that was almost the perfect size. Just a bit wide and slightly short. I cut 1" off one side and centered it with about 1" gap at the bottom and 1" at the top. Sounds noticeably bigger than the sealed one.

Pic below of the new back panel, maybe I'll cover it with tolex, maybe I'll leave it as it is, nobody else sees it

My drummer will love this, he has a hard time hearing me onstage and my cabs are on either side of him.

[Harley Hexxe]

Dante,

   I'm glad that worked. If you're happy with how it sounds now, then leave it that way, but I would probably go for a top and bottom board going across the back, and leave about a 3"-4" opening across the middle. That should give enough of a balanced output front and back.

   From the pic, I'm guesstimating the cab is approximately 14-15 inches tall. That's where I'm getting my estimate from for the opening

[Dante]

It's definitely better, but I will cut my slab o'wood in half (longwise) to do exactly what you're recommending. Cabs are 14" tall, outside dimension...good guesstimate

Thanks very much for recommending that, it's got a bit more girth. Still not as much as the combo, but I suspect that's the speaker at work. I looked up the Eminence 1218 and it's supposed to be a slightly brighter speaker. I may look into the WGS for the open back and leave the closed one alone, or I may open that one too...who knows?

[Harley Hexxe]

Dante,

   It's my pleasure man.  We're all here to share our knowledge and experience.

   You're getting a bit more girth from the combo because it has a bit more cubic feet in the interior of the open cab, so the ambient speaker sound produces more reflections before it escapes out the back of the amp. That's something the Yamaha cabs can't physically do because it's too small. It looks to have close to one cubic foot of enclosure space there.

   Your combo on the other hand looks to be approximately the same size as my Fender Cyber-Deluxe combo and that's just slightly over two cubic feet. I read in an electronics course book a long time ago that the ideal enclosure space for a 12" speaker is three cubic feet. Of course that's for a closed-back cab. You can definitely get more of a full bodied sound with the open back of the Yamahas but it won't match the combo.
    The only reason I suggested the top and bottom boards across the back is to give the sound some more surface to reflect off of before it escapes out the back. You could even make a 5" board across the bottom of the back of that cab and let the sound escape through the top half. Possibly, that might bring out more of the girth if the cab is on the floor.

   Experimentation is the way to the destination.

[rnolan]

Hey Dante, seems the Yamaha cabs also have a small opening top and bottom to the front, maybe tuned to the Eminence's resonant freq  .  Cubic capacity in a box is tied to the lowest note you want to reproduce. So 8 cubic feet boxes go down to 32Hz (1/4 wave length) and are popular sizes for HiFi (before the sub craze).  So 4 cubic feet <> 64Hz so what Harley is recalling, 3 cubic feet would be good down to the guitar low E @ 82Hz which makes sense for an "ideal enclosure" (unless you like a lot of drop D or tuning down). 
Interesting there is no sound absorption material, then often guitar cabs don't have any.  Main reason for it is to lesson standing waves in the box as all the surfaces are parallel.  But from what Harley is saying, maybe you want reflections (ambient speaker sound) and standing waves, particularly low freq ones.

[Dante]

I will try the idea of putting the board all the way down, allowing the opening to be on top. That should project well.

The combo cab is wide, it's as big as my ol' Boogie....why I figured the cab has a lot to do with it. It definitely fills a room, which is what I'm looking for. I know I'll never get those tiny cabs to sound that big, but this helps. Thanks again!

Let me tinker and i'll report my findings. I still may try mixing the WGS with the Eminence - that may be pretty nice too. Don't know till ya try

[Dante]

Hey Dante, seems the Yamaha cabs also have a small opening top and bottom to the front, maybe tuned to the Eminence's resonant freq  . 

I think what you're seeing is the speaker box frame is cut away on top/bottom to allow the speaker to fit. Then, there's a piece of the grillcloth showing (it's wrapped around the front baffle) that looks like a hole going through...that's not the case, it's solid wood there. You can see a bit more in the upper right corner, that's where the Yamaha badge is.

[Harley Hexxe]

Dante,

    I'm not sure if you're looking for more bass response, or more midrange response from your cabs. The suggestion of the board across the bottom should, (in theory), give you more of a lower midrange boost and more reflections in the higher range.

   Likewise, placing the board across the top of the cab opening and leaving 3-4" open across the bottom will allow the bass reflections to bounce off the corner of the floor and wall it's facing.

    I think there's been a lot of experiments like this already, which is why amp manufacturers decided to leave the openings in the center of the combo amps.

    From all the reading I've done of the different cab designs, I've come to the conclusion that it really isn't the frequencies that matter as much as the slight delay that is produced when the ambient speaker sound tries to catch up with the front of the speaker projection. It isn't nearly enough of a delay to produce any kind of echo or even a reverberation. It's just enough to make the sound bigger, and it does do that quite well.
   I'm very curious to hear what your take is with your experiments.

[Harley Hexxe]

Richard,

     What I was reading back then, was some generic electronics instruction series that I couldn't recall who published it even if I wanted to. I think it was originally published in the mid to late 60s. I know it was in the early 70s when I was getting into this. If you recall, at that point in time speakers weren't nearly as powerful as they are today. Back then, if you had 25 watt Celestions, you had the cream of the crop! But that manual was referring in general terms for speaker enclosures for HiFi applications, and if I remember correctly, that was about building studio monitors.

    I did build a cab with 4x12" Celestion 25 watt speakers out of plywood and lots of coats of paint and wax to seal it. It was a monster. I remember it made my dad laugh out loud sometimes watching my scrawny teenage ass trying to move that thing around. I think it weighed more than I did. If it didn't at first, it certainly did after I experimented with it later on.

    The cab was roughly the same size as the Fender Dual Showman Reverb TFL5000 cab, but it was 3" deeper so I could have a 12 cubic foot enclosure. The speakers were not placed on top of each other or side by side, but rather they were staggered from top to bottom. The top was mounted on the left side of the cab, and the next one down was mounted on the right side, and I repeated that with the bottom half of the cab too. I did this to find out if the cab would sound better with all four speakers resonating in a large enclosure like that, but left my self the option of putting baffles in between each speaker, which I did after a few months. After that, I decided it could sound better if I added a reflex baffle, and opened a port for each speaker. So, I added a couple of 90 degree baffles in each cab, and opened a 6" hole on the opposite side of each speaker. If you haven't visualized it at this point, that cab I was hauling around was essentially four 1x12" cabs in a single big box. All that added wood by this time made this thing so heavy, it was ridiculous, I had to put casters on it. I did like the sound of this thing by this time, but it was not the easiest thing to take to a gig. Small clubs and going upstairs was out of the question, but large auditoriums and outdoor gigs it was great.

    The amp I was using was a home built thing that wasn't a copy of a Fender of Marshall amp. In fact I don't know what kind of circuit it was. It came from a book titled Electronic Diagrams. and it was an 80 watt guitar amp design. The parts were all sourced from various electronics parts stores that were all over the place at the time, I remember the transformers were made by Philips, and the tubes were RCAs. All that stuff was dirt cheap back then.

     The whole point of me doing that was to build a bigger, and better amp than the Vox 2x12 combo I had at the time. After about two years of experimenting with it, I came to realize that the Vox could still keep up with that amp and sounded a little bit better. So I ended up selling that rig, and started getting into Fender amps for something different. I never looked back after that.

[Dante]

@Harley; that's a great story. I had a similar experience with a Carvin 4x12 cab, when I decided to put a 3/4" plywood wall inside to make it a true stereo cab. The cab was already too heavy, then I added that wall. I could barely lift it

Back to the little Yamahas: I cut my rear panel in half and took about an inch off, ended up with about a 4" gap. The open cab seems louder, maybe because it's on top...I'll switch that to test it. Definitely better, louder, and yes Richard, more in the lower mids.

Pic below. I know the input jack is off center, it's covering a big knot in the wood...it may not be staying there permanently, but it works for now