Low-wattage 15" speaker

Sticking a bigger speaker in a cab designed for a smaller speaker is a recipe for ruining your cab.

 

Putting a larger speaker in a small cab designed for a smaller speaker can cause reduced performance, like poor low end response, early onset of distortion (and not the good kind), and lower volume capability. And the Musicmaster is an open-backed bass practice cab attached to a low wattage tube amp, and open backed cabs already suffer from poor performance for bass enough without trying to force it to do something it was never intended to do. You're best either to run the speaker connections to a proper bass cab or just enjoy it for what it is.

 

Maybe a guitar speaker, I don't know. But you're really not going to get any more appreciable low end out of it no matter what you do. Even if you seal it up and port it more like today's bass cabs, it's still a very small cab. It's a small cab even for a 12". Fender just couldn't build an efficient bass cab until the 90's IMHO, and their earlier bass rigs are a testament to how much you can throttle a great sounding tube amp with a cab designed like guitar cabs.

 

You might find a vintage 15" with that low of a power rating, modern current production I seriously doubt.
Might I suggest going the other way and using a 8" or 10" speaker.

 

If preserving what you already have is important, why change anything?

 

A much better idea if you ask me. That cab might work well with a 10".

 

An excellent question. If you're able to re-design the cab properly with a closed back, a speaker more suited to putting out low end, and a port that makes the most of what you have, it's more possible to get deeper low end than with a bigger speaker. I wouldn't expect miracles, but it's possible.

But that's where my expertise on the subject ends. I'd have no idea how to go about it. Fortunately, a lot of speaker folks hang out here, so maybe you'll be able to get some more detailed help.

 

I'd just try some different low watt vintage 12" speakers in there. Don't modify the cabinet, that will just trash an amp that has some true resale value. If the amp has a removable speaker baffle, you could build a new one for another size speaker and save the original..or just build another cabinet that houses the amp chassis (I've seen this done). I've heard some tele players using this model, it's sorta sought after for it's unique tone these days. There are a lot of possibilities if you aren't hung on a speaker being a brand strictly associated with guitar/bass amps..think vintage lo fi- hi-fi, organs, radios, ect. Or just try another low watt reissue Jensen. Some of the distortion you are hearing may be because of the open back..that's a good thing with that kind of low power amp. Much more power and you's be blowing speakers right and left.

 

Let it alone for guitar and add an extension cab for bass.

 

Is the Musicmaster designed to be used with a speaker load other than the internal speaker? I'd be careful about adding any extension speakers..at least without disconnection the on board one, or being absolutely sure the amp is designed to work with anything but a 8 ohm load.

 

you must never have played through a bassman 100 into the paired 4x12

 

First, you have a wonderful vintage bass amp - all tube, with beautiful vintage tone... at low volumes. That's all it was ever meant to do. According to your posts, you would like more low end, but would prefer to keep the modest volume capability.

Your proposed solution to install a larger (15") driver with the same low power rating as the stock 12", in the same cab will not result in a better low end. Power rating is not a measure of driver efficiency, or an indication of low end capability. A 100w 15" driver is not necessarily more efficient than 10w 15" driver. Further, driver size (nominal diameter) is not a measure or an indication of low end capability.

I suggest that you abandon the driver replacement plan. If you have some diy capability, consider building a cab (people here will be glad to help with driver selection and cab design). If not, purchase a used or new cab with the same impedance as the stock 12" and run the cab off the 12w amp (alone). Most commercial cabs are at least as efficient as the stock 12", so you will have a huge selection from which to choose. A cost effective solution is to acquire a beater cab used, and post here on TB, asking for recommendations for an appropriate driver (if the cab's driver is blown).

 

Watt ratings are meaningless, so disregard it and look for a speaker that will do what you want.