Speaker Cabinet Advice (w/Ampeg B25)

[labman]

I have a Ampeg B25b (1972) and it has just spent months in the tech's shop getting all fixed up. While I was waiting for it I bought another B25 rig (1969) that included the 2x15 cabinet to fill the void. I had it listed here for sale (the full rig) and I think it is spoken for locally so it is heading out. But I got to try the refurbished B25 head with the 2x15 cabinet and a newer 4x10 Ampeg Classic cabinet I have. I re-wired the 4x10 in series so to run it at 16 Ohms. Very easy by the way.

I prefer the sound of the 15s. I like the older motown kind of tones. But I am only playing at home for fun and I would like to get a single 15 cabinet. So I need to decide what to do. I am a very experienced furniture maker with a shop and could easily make a cabinet and buy a speaker. But I have read some articles about the cab needing to be tuned properly and what not. I am not an electronic techie person. My eyes glaze over like when I am trying to do my own taxes. But building a cabinet still interests me. I could order matching tolex, grill cloth and hardware from Fliptops and make it a good match to the B25. There doesn't appear to be too much science involved in the old 2x15 but I could be wrong.

So the question(s):

Are there basic plans that this tuning is not really such a big deal?

If I were to build a cabinet what would be a good speaker? Vintage warm and a good match for this 50 watt amp.

Am I better off buying a cabinet from someone? I don't see many 16 Ohms 1x15 cabs.

What would be a good brand/model to buy?

Since the repair of the amp went WAY over budget (fried PT and new tubes and on and on and on) I would like to make this a small investment, sell the SVT410 Classic and and have a couple bucks left.

thx!

Ken

[craig.p]

If you take an unused phone plug (no cable attached to it) and stick it into the extension speaker jack, then the output transformer will run at 8 ohms and you'll be able to use whatever 8 ohm driver you want.

On the cab, since this is just for personal practice, my advice is to keep it simple: build a "large-ish" infinite baffle box, which will eliminate the need to fool with porting. (Not that porting's a really big deal, but it's just one less thing to have to do where there'd be little payoff in a personal-practice situation.)

For example, you could put a Peavey PRO 15 ($60 at Parts Express) into a sealed 6 cu ft box (3x2x1) and wind up with a cab that's only 3 dB down at 60 Hz and will "EQ up" at the bottom end very nicely. Make it 4 cu ft (2x2x1) and it's still down only 3 dB at 62 Hz. Line the inside surfaces with sound absorbent material (also from Parts Express) and you're good to go. Simple!

Just one of many ways to go.

FWIW, one of my practice boxes is a 2.6 cu ft sealed cab with a PRO 15, and it sounds great. Down only 3 dB at 65 Hz.

[JimmyM]

one of those old ev tl606 designs would probably do you right if you don't get a fliptops replica.

[labman]

Thanks Jimmy. That is one I was reading about. The fliptops would be great but with shipping I was hoping to spend less. Do you like the EV speaker as well? I know they are new into the bass market but I am a big fan of Weber speakers with my guitar amps. hey are now offering a 15 for bass. Anyone know much about them.

I need warm and Motown goodness spilling on the floor.

[JimmyM]

i do like the old ev design but it's been years since i heard one. i don't know much about weber speakers for bass, sorry, but i am impressed with their dedication to keeping old designs you never see anymore alive, even if their price tags are very high.

[labman]

Maybe a bit more expensive $125 for a 15" ceramic, 175 watts/2" voice coil. I do like supporting smaller family business.

Would that cabinet design be ok with this speaker perhaps?

THX

[JimmyM]

very hard to say since i'm not familiar, but if weber thinks it would be, it probably will.

[craig.p]

Oh, boy...

Have Weber email you the Thiele-Small parameters for that driver. If you get a deer-in-the-headlights reaction from them, then look elsewhere, unless you enjoy shooting craps. I'm not saying the driver isn't worth the price of admission, just that a) it damn well better be at that price point and with that feature set, and b) it ought to be provable.

[ericope]

Hi Labman - I've had my old B25 rig since 1975, and it had already seen a ton of down-and-nasty gig use by then. Due to economics when I was a teen, it had to double for both bass (high school jazz band) and guitar (loud garage rock with my using an Electroharmonex Muff Fuzz - the tiny little box, not the Big Muff stomp box). It worked fine for both applications and has served me very well over all of these years. I believe it was around '98 that I found a small SVT-15E 1 x 15" 200 watt cabinet up at the pawn shop in absolute perfect condition, for $200. I also did the 8 ohm trick craig p. states and found immediate improvement with this cab. over the bulky stock 2 x 15" cabinet. I feel it has been an extremely good match for this head, and has elevated it's competency as a warm, compact lower-wattage bass rig very nicely. Funny, it makes for a pretty darn nice compact keyboard rig too! Guitar? Well, let's say it's, uh, BEEFY!

I bought a near-matching Eminence 15" driver to construct an eventual "twin" of the SVT-15E (will leave it unbranded, of course) for stacking the two cabs and creating a type of really compact "full stack" effect, and will use this with the Hartke HA3500 head I've had for a couple of years, reuniting the B25 with it's original cab for a semi-retired relic and back-up rig. I fully believe that this "SVT-15 stack" could be readily used with the B25, returning it to 16 ohm mode and cabling these 8 ohm cabs in series.

I find that copying the SVT-15E cab shouldn't be all that big of a deal for my project. In my mind, and ear, it just seemed to "fit" the B25 head considerably better than the stock dual 15" cab does! Of 3/4" high grade plywood, the dimensions are: 23.75" wide; 21.5" tall; 15.75" deep, and it has two PVC-type baffles in the lower front corners of the cab. These "tubes" are 2.75" in diameter, and go 5" deep into the cab from the front surface of the baffle/driver mounting board. If procuring the flange rings is of issue, I'm thinking a good epoxy would work.

I'm not "Mr Tech" in terms of Q-factors, etc., but this type of compact yet beefy cab/Eminence driver has worked very well with this particular head. One would think it should work reasonably well using other driver brands of similar specs, compatable with such a ported enclosure. However, I've always thought it would be pretty cool to experiment with making a folded horn or basing it on other designs such as the EV, too. Thanks for letting me share, and good luck with your project.

[labman]

Thanks ericope. I sent an email to Weber just before Xmas but I am still waiting to hear back from them. I have considered the SVT-15E cab. There have been a couple for sale locally that last few months. One still is but they are asking 300 but I think they would come down to 250.

One complication with the head is the speaker outputs. I had the tech make some mods. He also recommended quite a few after reading up on the amp. But as it is set up now there is only one speaker out (and tapped from the OT) and that is 16 Ohms. So I can not use the extra 1/4 plug trick. If I was to pick up the SVT-15E I would need to swap out the speaker with a 16 Ohm.

I am not very techy either on this stuff (electronics) but I am with woodworking. Still hoping to build a great box and putting a killer speaker in it if I can get the right cab design. I have seen the mentions of some type of modeling software for speaker cabs but I wouldn't know what the hell I was doing and I am a Mac user and those appear to be PC based software.

I have a cabinet plan drawn up that is an alteration of the EV TL606 design. I have it re-sized do the exterior dimensions are widened out to fit well, under the B25 head (width). I adjusted the height to make it lower and brought in the depth a couple inches. This would keep the same cubic volume (3.2 ft.) in the cabinet. The final exterior dimensions are closer to the SVT-15E. 24" wide x 24" high by 14" deep. The width is what I wanted to match to the head but the height and depth could still vary.

It is only drawn up yet. Nothing has been cut. I just seek someone that has the proper knowledge (maybe Weber) to give me a nod of approval.

thx!

[craig.p]

If that B25B cab is gone, then you'll probably have no further need for the 16 ohm tap on the output transformer. Have your tech move the speaker jack connection from the transformer's 16 ohm tap to its 8 ohm tap. It's a trivial bit of work that will release you from this 16-ohm driver bondage.

[labman]

Probably a great idea. He had the amp for months and I was hoping to not send it back again. Cost me way too much money. It had a blown PT. He felt it was because the wiring on the original XLR speaker cable had shorted out. Anyway he was sick of working on it as much as I was in waiting for it. Maybe a different tech in town. I wish it were something I could do (change the tap).

8 Ohms would be much more practical for sure.

[craig.p]

See if there's an electronics tech school in the area, and bring it there. Any first-semester student can do the job for you in five minutes if you bring in the unboxed+detubed chassis. All that's required is a soldering iron and an ohmmeter.