Replacing 8ohm speaker with 4ohm in my SWR WM combo

[Beebs99]

Hey everyone. First post here!

I recently had my WM 15 speaker give out on my and am looking to replace it. I've been running simulations in winISD and it looks like an eminence legend cb15 or ca154 is going to be perfect for me. The speaker that is currently blown is 8ohm, however, you can also run an 8ohm extension cab with the amp to increase the wattage from 120w to 160w. I would like to know if I can just use a 4ohm speaker in the combo amp since I don't plan on ever using an extension cab to take advantage of the extra headroom (also the ca154 is cheaper). Will that work?

FWIW and for future reference for SWR WM 15 owners that are replacing speakers and don't know what to use (I looked through countless threads), winisd is a good place to start. The cab volume is right around 3 cubic feet and is tuned to 63hz (port is 18.5"x1.5" and is 1.75" deep). I plan to also add 4 inches to that port depth to take the tuning frequency down to around 50.

Cliffnotes: Want to replace 8ohm internal speaker with 4ohm and never use 8ohm extension cab. Can it be done?

[Electricblue]

I doubt you will hear any difference in volume because of the Ohm match.

120w/160w is hardly an audible difference. Surface area will be more beneficial than an extra 40w.

It can be done though, just make sure your guitarist doesn't attempt to attach another cab

[RickenBoogie]

+1 the difference between 120 and 160 watts is almost nothing, and because of that, I'd go with an 8 ohm replacement so you CAN add an ext cab and actually get louder with it.

[Beebs99]

Good thanks! I don't doubt there will be much volume difference, but the difference in price ($84 vs $120) is a big plus especially since this combo would probably only cost around $150-200 to replace entirely. This is kind of an emergency replacement. When I do get a cab, I will be getting a decent head along with it.

[billfitzmaurice]

Originally Posted by Beebs99

Want to replace 8ohm internal speaker with 4ohm and never use 8ohm extension cab. Can it be done?

It can, but the difference in volume will be slim to none, and Slim just left town.
If you ever do need more volume the way to get it is via running a second identical speaker, which will give you an additional 6dB. Using a 4 ohm driver now removes that option from later consideration.

[Beebs99]

Definitely good points to consider. I am going to go with the 4ohm though since I don't have much money. An extension cab and replacement speaker is out of the question until I get my tax return. Thanks for the help!

[Electricblue]

Just be aware that a 4 ohm driver will eliminate any hope of adding another cab. Give it some thinking time. A few extra funds will give you a whole bunch of possibilities.

[Beebs99]

I guess I can always watch ebay like a hawk and see if any cb15s show up

Wonder why the ca15 is almost 2/3 of the price? They seem to be very similar

[billfitzmaurice]

Originally Posted by Beebs99

They seem to be very similar

Aside from both being fifteens there's very little about them that's similar, from the frame to the magnet to the T/S specs.

[MarkBG]

The volume difference may not be that audible but at 4 ohms the amp will be operating at its optimum,and will give you more headroom before reaching clip. As long as you are sure you have no intention of wanting that second cab, 4 ohms is a good idea.

[billfitzmaurice]

Originally Posted by MarkBG

The volume difference may not be that audible but at 4 ohms the amp will be operating at its optimum,and will give you more headroom before reaching clip. As long as you are sure you have no intention of wanting that second cab, 4 ohms is a good idea.

The additional headroom won't amount to squat, while the amp actually works harder into a 4 ohm load than it does into 8.

[Jim Carr]

IME, adding a second cabinet to the WM 15 is a great way to move to a modular rig in 7 stages (while buying used):

1) buy second 8 ohm cab (any kind you like and can afford).
2) use it with WM 15 until more funds are saved.
3) buy new head (with saved funds) to use with second cab.
4) sell WM 15 and save a little more.
5) buy another cab, perhaps a 4 ohm, depending on your amp.
6) never ever ever be stuck with a heavy awkward impossible to EQ combo again.
7) miller time.

So, is saving $36 dollars and lowering the resale value of the WM 15 while making moving to a modular rig (IMHO) harder, really worth it?

[MarkBG]

Originally Posted by billfitzmaurice

The additional headroom won't amount to squat, while the amp actually works harder into a 4 ohm load than it does into 8.

OK...So...Are you saying that considering he never intends to attach a second external speaker,as he has said he does not want to do ,that replacing it with a 4ohm, on an amp that is rated for maximum (safe) output into a 4 ohm load is a BAD idea?????

[billfitzmaurice]

Originally Posted by MarkBG

OK...So...Are you saying that considering he never intends to attach a second external speaker,as he has said he does not want to do ,that replacing it with a 4ohm, on an amp that is rated for maximum (safe) output into a 4 ohm load is a BAD idea?????

I never run my amps at their lowest rated load. The higher current draw creates added heat, heat shortens component life, and if there's nothing to be gained it's just not something I'm going to do or recommend.

[Jim Carr]

To the OP (Beebs99):

Welcome to Talkbass, where engineers, rockers, retirees, teens, teachers, pros, and G.A.S.-suffers mud-wrestle for the love of bass.

[Avezzano]

Just do it: there's absolutely nothing wrong with that, since 4 ohm is allowed by the manufacturer; amp will work just fine and you'll also have an increased amount of power under your fingers. It might also be a surprising "different" overall response from the amp. It will depend on the speaker's own characteristics checked against the original one.

Only thing is: should you sell the amp, just remember to write somewhere these things on a paper attached to the amp, for the next user's benefit.

[Oobly]

I don't see any reason not to get the 4 ohm. The amp will be just a little louder, you haven't paid too much and you get to hear your bass signal.

As Avezzano mentioned, if you ever do sell it make sure the buyer knows the deal, that you can't add another cab to it since it has a 4 ohm driver.

[Zooberwerx]

Stick with the original 8 ohm configuration...there's a reason they're engineered that way in the first place as pointed out by Bill, electricblue, Dr. Jim and others.

Riis

[Avezzano]

yes, and the reason is... that you may want to add a second cab! So if you DON'T do that, the 4 ohm option is prefectly viable...

You could also, in addition:

1) bypass the external speaker output, so to prevent any possible damage from people not aware of the mod. (Better: remove the output jack completely)

2) leave the additional speaker parallel speaker output jack, but insert a fuse on one wire that protects the amp from excessive current request. For a 150w 4 ohm it should be around 6 A. Add a prudential factor of 0,7 taking into account the delay of the fuse to get burned; so a 4 A fuse would do great. (This way you could actually run two 4 ohm cabs but max 80 w each, protected by the fuse!)

3) wire the additional speaker output jack "in series" (My Nemesis works like this), so that you can later on add a 4 ohm speaker for a total of 100 w at 8 ohm, but with a wider dispersion anyway...

lots of options, if you want to have some real fun and gain some knowledge on the DIY side...

[MuthaFunk]

I say go with the 4 ohm. It not only suits your budget better, it suits your use better because you don't plan on buying an extension cab. I wouldn't worry about resale on SWR gear as it's terrible for holding it's value anyways. The used resale difference will be neglidgable IMO.