2x15" Bass Cabinet

[Isaac]

I'm not sure. I've never been able to find any specs on the JBL D140 drivers. I'm pretty sure they were rated at either 75 or 150 watts each, so the cabinet could reasonably be expected to handle 150 or 300 watts. That makes sense, because a similar cabinet was used with the 2000S, which put out 120 watts RMS.

[Soundmasterg]

That cabinet is the 200S cabinet and they sound really nice with a Sunn amp. They sound good with other amps too, and can really put out the volume, but you won't notice the volume until you are at least 15 feet away because of the type of cabinet it is. As long as those JBL D140 speakers are working ok, then it should sound very nice! I believe the D140 was rated at 150 watts, but Ted Weber says they are more like a 100 watt speaker if I recall correctly. The Sunn 200S that your cabinet would have come with was a 60 watt bass amp, so if they were rated at 100 watts each, that would be plenty.

You got a steal on that thing at that price. It would cost you more than that to build a cabinet, and the JBL speakers sell for lots of money on ebay. Take a look at watch some auctions and you'll see. I'd be interested in your cabinet myself if the price was right and it didn't have to ship too far. I like the sounds those can make, especially when coupled with a Sunn head.

[EdBass]

Are you near Toledo? I'm pretty close, and I'll buy it if you want to sell it. Give me an idea of what you want for it, and we can negotiate based on condition when I get there. Or send me some jpegs and I'll lock on a price via email.

[Guest]

Ed, do you know someone named Will Midge?

[Guest]

So is the aforementioned Ampeg amp too powerful for the speaker cabinet?

[EdBass]

Nope, don't know a Will Midge. I guess you're keeping the cab. I doubt you would hurt the D140's with that solid state Ampeg. If they are 8ohm speakers, you have a 4ohm cab, and if you dimed the Ampeg I guess you would cook them eventually, but from harsh & nasty transistorized distortion, not from brute force. If you need that kind of sound pressure level, you need more rig anyway! Get a healthy tube amp, you'll be amazed at the volume & richness of sound you get out of that old cab.

[Soundmasterg]

The cabinet could be wired as a 16 ohm cabinet too, in which case, putting a 4 ohm load on it wouldn't be a good idea.

[EdBass]

The cabinet could be wired as a 16 ohm cabinet too, in which case, putting a 4 ohm load on it wouldn't be a good idea.

Hmmmm...I hadn't though of that. How would you go about putting a load on a speaker cabinet? Why wouldn't running this cabinet at 16 ohms be a good idea? Under what conditions would someone wire a 2X15 bass guitar cab @ 16ohms?  Could it damage something, if so what?  

The angled boards behind the speakers actually LOAD the back of the speaker in such a way that it makes the cabinet louder than it would be otherwise.

Man, I'm confused, how does this work? Do you have a lot of experience with speaker cabinets? I always like to learn something new, and your expert opinions are certainly new to me!

Hey "Guest", hook up your Ampeg and wail away, you should be fine! Get a tube amp as soon as possible. D140's and tubes are a great match.
PS, A good 4X10 is probably the best match for your solid state Ampeg, and it just so happens I have a few of them lying around...

[Isaac]

I'm not entirely sure what Soundmasterg meant, but, if the bass cabinet is wired for 16 ohms, adding a second cabinet at 4 ohms would take pretty much all the power from it. If it is 16 ohms, and the head running it is solid state, then there won't be much power available. Let's say the amp is rated at 150 watts at 4 ohms. That will give you about 80 watts at 8 ohms, and 40, 45, maybe 50 at 16 ohms. It would probably be better to wire it for 4 ohms, and get the full power out into the cabinet.

You ask, "Under what conditions would someone wire a 2X15 bass guitar cab @ 16ohms? Could it damage something, if so what?" You'd want to wire it for 16 ohms if you planned on using several of them. One head could run four 16 ohm cabinets, and only see a 4 ohm load. Nothing would be damaged. Solid state amps are voltage sources, and tend to be damaged only when they are asked for more current than they can provide, as when the load impedance is too low. Tube amps are different, and should have the impedance more closely matched.

Finally (for now!), the port in a cabinet sets up an acoustic resonant circuit called a Helmholtz resonator, which increases the output within its resonating band. It generally adds half an octave to an octave on the bottom end, at the expense of a much steeper rolloff below the cutoff frequency. If you want to learn more, I suggest starting with "The Loudspeaker Design Cookbook" by Vance Dickason. It's aimed at home stereo speakers, but there's a lot of good information there.

[Soundmasterg]

Sorry Edbass, I meant to say that putting a 4 ohm SOURCE on a 16 ohm load wouldn't be a good idea. With two 8 ohm speakers, you could wire them in series for a 16 ohm load, or in parallel for a 4 ohm load. With solid state, you just get a different power ouput and volume depending on what load you hook them up to, as long as you don't go too low. With tube amps, you should match them up to whichever load they want to see to get the best sound and volume. So if you have a Sunn tube amp head with an 8 ohm and a 16 ohm load, then you want to hook it up to a cabinet or cabinets with the same load or your sound will suffer, and in extreme cases, the amp will suffer damage.

The other thing about the cabinets is that those angled boards behind the speaker basically reflect the sound down towards the port. They also provide resistance to the speaker cone when it is going back because of sound pressure waves hitting the angled boards. Both of these effects make the cabinet much louder than it would be if it was just empty inside, but they also serve to make the cabinet a lot louder fifteen feet away than it is right on stage. Some people like this effect, and others don't. The ones who didn't designed other type of cabinets like the SVT cabinet which is very loud and punchy and gives an even response right up close and far away too.

[Anonymous]

Actually Soundmasterg, this time you are sort of correct. All amps are going to respond in kind depending on the load they are driving, regardless of being tube or SS. Tube amps are more sensitive in their response to a specific load and generally will have varied output trans taps to maximize their performance with a given load. Solid state is vastly more sophisticated, as the only real danger is running it at load levels below where they are designed to be stable, generally 4ohms is safe, and some are stable to 2ohms. Some commercial power amps are even stable down to <1ohm. Too little of a load is the amp wrecker, too much load is more forgiving, even with a tube dinosaur.
Speaker cabs come in many configurations for either specific response characteristics, or as in the case of musical instrument cabs to attempt to reproduce a wide range of frequencies evenly and efficiently, while being "flavored" for the particular instrument being reproduced. This subject is way too involved to get deeply into in this forum, so I'll try to specifically address horn loaded bass guitar enclosures, and keep it VERY basic. The "angled boards behind the speaker" are actually an attempt to emulate a much larger vented enclosure by "folding" one up inside the box. As a rule of thumb, the larger the enclosure the better the low frequency response. A speaker has two sides to its cone; the purpose of venting the enclosure is to take advantage of the back side by using it to supplement the sound pressure emanating from the front side. Only lower frequencies can be enhanced by a folded horn enclosure, because higher frequencies don't turn corners so good. The higher the frequency, the more directional the sound pressure, and visa versa. By varying the size and depth of the vent, you can fine tune it towards a particular frequency range. The horn loaded vent does extend the "throw" of a cab because it takes a few, or even sometimes several feet for the vented pressure to get a good "bite" on the ambient air molecules, which of course are the medium we are dealing with in the first place.
Kind of basic, to be sure, but I hopefully this pretty much sums up what's going on in our little 2X15 Sunn enclosure dilemma. Keep the info coming guys; this is a great source for all of us to learn more!

[EdBass]

Ummm, that last post (or maybe dissertation is more accurate) from "Guest" was actually from me. I guess I kinda forgot to sign in  before I responded to the fresh, inovative, yet slightly misguided revelations on transducer theory from Soundmasterg.
EdBass

[Isaac]

Yeah, I figured it was you.

[Soundmasterg]

Thanks for the background info Edbass. I was just giving a very basic amount of info, and probably was too basic to really tell him what was going on with his cabinet, so your post gave the info he needed I'm sure.