Help Me Mod My Cab

[The WideBody]

Blew a speaker in my bassman 50's 2x15 cabinet yesterday. Measured the internal volume and intend to do some speaker shopping. The internal volume is about 3.75 cu ft. Much too small for the 2x15 that it was. I want to do a single 15 lfc and at least a smaller mid bass driver. I dont want to do to much deconstruction or reconstruction and need to use an off the shelf passive crossover. I hope to either find a suitable sealed back mid driver or convert the vacant 15" opening to a small sealed area for the mid driver but that would eat up about a full cubic foot.

My budget is $200 so i am considering the eminence alpha line. I figure the crossover to be $50 so the remainder will have to be split between the drivers.

Please suggest the following:

Driver combo

Tuning freq

Lfc port diameter and length

Thanks for your input.

[will33]

Look at the emi. Legend CB158 or Beta 15A, with the Beta8A or la6cbmr.

off the shelf crossover should be the 800hz 2-way. It'll play a lot better with the beta8 than it will with the closedback.....impedance curves.

The mid only needs to be in a little sealed box. .1 - .15 cu.ft.

Box tuning 45-50 hz.

My .02 as far as cheap but effective.

I'd let a few more folks throw some ideas out there before you go buying anything.

[billfitzmaurice]

What amp? That's just as much part of the equation as the rest. With low power a ported cab is usually not the best idea.

[The WideBody]

Originally Posted by billfitzmaurice

What amp?

Bassman 50 - by all accounts a low powered amp. So ports are out?

[chadds]

Sell it and get something else. I had one with JBLs. The design is very poor. By the time you take out the baffle you could have bought something else.
There are many single 12"s now that will spank it.

[billfitzmaurice]

Originally Posted by The WideBody

Bassman 50 - by all accounts a low powered amp. So ports are out?

Vented isn't worth the effort. You also want a 4 ohm load. I'd use a pair of Beta 12, using reducer plates to adapt the 15 holes. Be sure to beef up the cab bracing and line it with polyester batting. Forget the mid driver.

[The WideBody]

Originally Posted by billfitzmaurice

I'd use a pair of Beta 12, using reducer plates to adapt the 15 holes.

Great! Where do i find these reducer plates?

[Arjank]

Originally Posted by billfitzmaurice

With low power a ported cab is usually not the best idea.

What are your arguments?

[will33]

You'd make them out of a piece of 3/4" plywood. Basically fill in the current speaker cutouts, then re-cut them for 12" drivers.

And yeah, better to have a 4ohm load for your bassman.

[The WideBody]

Originally Posted by chadds

Sell it and get something else.

Unfortunate (for me) story. I had a buyer lined up. The night before the buyer was to come i thought that i would fire it up one last time. I must have burnt out the speaker at that time cuz when the buyer showed up - the only tunes that would come out of the cab were early sabbath stuff!

[Arjank]

Originally Posted by The WideBody

the only tunes that would come out of the cab were early sabbath stuff!

great sense of humor!

[The WideBody]

Originally Posted by will33

You'd make them out of a piece of 3/4" plywood. Basically fill in the current speaker cutouts, then re-cut them for 12" drivers.

And yeah, better to have a 4ohm load for your bassman.

Please point me at a tutorial or something so that i don't have to reinvent the wheel.

Wouldn't a single fifteen and a smaller mid bass driver add up to the 4ohm load. Missed that day in math class when they showed us how to figure impedance.

[will33]

Originally Posted by The WideBody

Please point me at a tutorial or something so that i don't have to reinvent the wheel.

Wouldn't a single fifteen and a smaller mid bass driver add up to the 4ohm load. Missed that day in math class when they showed us how to figure impedance.

No, it'd be 8ohms on both sides of the crossover. I didn't think ahead to ask you what amp you're using.

I'll see if I can dig up a pic of an adapter ring. Basically, cut circles the size of your 15" holes, cut circles in those to mount the 12" drivers and glue them in.

[will33]

It'll look sort of like a donut, 15" ring with a 12" hole in it.

[will33]

Have you looked into getting your JbL's reconed rather than all this modding? They might be worth more out of the box than they are in it.

[BassmanPaul]

Put your 15" driver onto a piece of ply. Draw around it with a pencil and then mark the eight mounting holes. Cut around the outside of the circle and drill out the holes. If you draw lines connecting each hole with its opposite you'll find the centre. Mark and cut the appropriate sized hole for the 12" driver. Drill and mount T nuts 10x32 for the 12" driver. You can mount the ring into the cabinet using the original hardware. attach some weather stripping to act as a gasket. Repeat for the other driver. 1/2" ply should be fine for this.

[The WideBody]

Originally Posted by will33

Have you looked into getting your JbL's reconed rather than all this modding? They might be worth more out of the box than they are in it.

Pulled one out. I don't know what make it is. It has a fender sticker on the back. I will try to upload pics.

[billfitzmaurice]

Originally Posted by The WideBody

Great! Where do i find these reducer plates?

At your local lumber yard, disguised as sheets of plywood. All you need to do is to remove the excess.

[1n3]

So, not a JBL. Eminence or CTS, I would guess. If you're pretty sure it's only one speaker, I'd try to repair it. Should be cheaper than replacing two speakers, and easier than modding a cab. And the cab might be more valuable if left original, though I don't know that.

I'm a little skeptical that it's blown. The storyline doesn't fit well - 50w head, hasn't been used much... an inspection would be in order. Look for cone tears, loose surrounds or spiders, voice coil leads touching the cone, etc.

[billfitzmaurice]

Originally Posted by 1n3

I'm a little skeptical that it's blown. The storyline doesn't fit well - 50w head, hasn't been used much... an inspection would be in order. Look for cone tears, loose surrounds or spiders, voice coil leads touching the cone, etc.

Back in the day I blew Fender 'special design' drivers regularly with a 50 watt Bassman. The only thing 'special' about those drivers was the sticker, and until at least the mid 70s Fender used guitar drivers for both guitar and bass on standard versions. Unless JBL or EV they're not worth reconing.