HELP - replacement speaker for Laney K50B combo

[gastric]

I just acquired an ancient Laney K50B combo amp and '81 Ibanez Blazer from the original owner who hauled it from the UK years ago. Overall the amp is in good visual and functional condition.

Issues include - missing the original handle and has a DIY replacement installed, input 1 on the amp doesn't work, and the original speaker is totally dead.

However, if I connect the amp to my Mesa cabinet it cranks out good sounding, though slightly hissy/noisy, bass. It actually sounds pretty good, very punchy, and you can dial in tons of high end bite or dial it down for smooth low end.

So the original speaker needs to be replaced or reconed. The speaker lacks any technical details at all. Just a sticker on the back indicating "McKenzie Professional Series". From the research I've done the company is well out of business so I'm guessing finding a matched recone kit would be the most difficult plan of action.

Can someone recommend me a replacement speaker that will match well with the combo cabinet size and current mounting scheme? I'm hoping I can find an inexpensive used speaker to drop in there and walk away with a decent practice combo.

I'll do my best to provide as much technical information as possible, and can answer questions and take more photos.

• 15.5" diameter from edge-to-edge of frame
• Hole in cab is 12.75" in diameter
• Speaker is rear loaded
• 8 mounting screws 15" on center across from each other
• Dimensions of the SEALED cabinet portion 17" H x 19.25" W x 9.5" D The baffle is on a very slight slant so the actual internal volume will be slightly less than a standard box.

I have no idea what the impedence of the original speaker is, and no way to measure it as far as I know as the multimeter reads infinite resistance when set to ohm. There's also no output specs on the back of the amp itself, nor am I able to find any documented online anywhere. But it's driving my 8ohm Mesa PowerHouse 2x12 without breaking a sweat or generating much heat.


Here is a 5MB ZIP containing a bunch of photos of the parts of the combo.

I'm a real cheap ass so I'm not looking to spend $100 on a speaker for this thing. I'd hope to be able to find a used speaker for $30 that I can drop in it. Maybe $50 tops. Otherwise I'll simply sell it to someone else, though I have no idea what the monetary value would be.

[rpsands]

If the hole in the cab is 12.75" in diameter you're going to be widening it up to fit any modern day drivers (or setting up a baffle spacer). Most modern 15's have a 14" hole, and 12's are around 11".

With about 1 cubic foot of internal space I would suggest you go with a Basslite S2010 and a baffle adapter if you want a smooth bottom end.

If you want an insanely midbass heavy for maximum volume, enlarge the hole and stick a Beta 15 in there.

You might find some cheap drivers on parts express (Dayton stuff) too.

[BassmanPaul]

You'll not find a re-cone or a new 15 for $30, or even $50, that's actually any good.

Paul

[gastric]

Originally Posted by rpsands

...I would suggest you go with a Basslite S2010 and a baffle adapter if you want a smooth bottom end...

Seems like a reasonable solution for using a modern driver. $75 shipped plus some wood and time making a baffle adapter.

Worse comes to worse I sell the speaker for $45 shipped used and hope to sell the empty combo amp for the rest of my money back. Empty cab would even make a decent shell for a short 10" or less 2U rack head and speaker.

[rpsands]

Just bear in mind it'll be -3db @ 112hz in a sealed box like that. You might actually want to consider a port. Tuning it to 47hz or so would move your -3db point down to 75hz or so, -6db @ 55hz.

[gastric]

I happened to find a used 10" Basslite cheap and started prepping the cabinet for a baffle adapter. However, the existing baffle is easily removed so it looks like I can simply construct a totally new baffle VS constructing a baffle adapter.

Do any of the cabinet experts want to give some suggestions for:

• mounting the 10" Basslite
• porting the baffle properly
• dampening if that's suggested for a tiny little cab like this

[rpsands]

Recex screws from speakerhardware are the bomb for mounting neo woofers. Pre drill them with a 1/16" drillbit or so and then go to town.

[rpsands]

Also, move the speaker cutout up and to the left, then put a ~3.5" diameter port tube in the bottom right. I don't know how long it will be til I get a look at winisd but probably around 6-8" or so.

[gastric]

rpsands - Thanks for all of your help thus far. I wouldn't have even considered this project with your assistance.

I'm comfortable with the wood work involved, and my neighbor is a Locktite salesman and can give me some sealer for cab. What I'm not familiar with, and am having trouble quickly finding info on is how to physically mount the speaker - I was going to re-use the existing mounting screws for the old speaker though it was rear mounted, or go to Ace Hardware for some bolts, lock washers, and nuts for front mounting the speaker. And where to purchase the port and what the exact size it would need to be. Batting seems easy to find locally and was easy to research, assuming it's recommended for a tiny cab like this.

[BassmanPaul]

#10-32 bolts into rear mounted T-nuts. Four will do the job but all eight is better.

Paul

EDIT: Lining the cabinet is always best. You can use a mattress topper from Wallmart for this. Spray on glue makes this easy.

Paul

[gastric]

Cut my new baffle, speaker mounts great. I still need to paint it and reinstall the original mesh grill and trim, and seal and dampen the cab. Before I do that I'd like to install a port.

I used WinISD to specify the port for the Basslite 10" and a 1 cubic foot cabinet tuned to 47hz as you suggested. It seems easier and less expensive to purchase smaller diameter ports VS larger diameter ports. Here's what WinISD came back with:

4" port, 12" length
3" port, 6.25" length
2" port, 2.28" length

Does that seem accurate? The larger the diameter the longer the length of the tube? Is there a reason I would choose one over the other? The 2" port would be cheaper to purchase.

[rpsands]

Hmm, that sounds pretty close to what I got.

The big reason to choose one port over another is the surface area -- more surface area == less port air speed.

With the Basslite, I believe a single 3" port would be OK. Look at the 'port air speed' chart in winISD to see for sure. I believe 3.5" would be for sure OK, but that's a lot bigger than 3 in terms of surface area.

A 4" port is probably going to be too long. You might want to see what two 3" ports would look like if the air speed is too high.

Use the signal tab to put 50 watts through it for simulating the air speed.

In terms of depth vs. port area I think 3.5" would come out the best..should be available at the hardware store I think.

[gastric]

Very educational. You're correct, 3" gives me red in the "vent mach" 3.5" x 8.9" port puts me into the green with a single port and that will JUST fit into my cabinet. Two 3" ports gives me a 14.7" port length which won't fit if that's specifying 14.7" per port.

I've seen a couple pages on using PVC for a port tube, though most show some routing skills that I do not currently have. And I'm not able to find a reseller carrying 3.5" ports, it's apparently an odd size. So that might force me into busting out the router and having a go at it.

Or I can skip the port and go with it as is. But I have room for 1-2 ports in the bottom corners. Heh.

[gastric]

New baffle photo:

[rpsands]

You could try a triangle port in the corner. I am not sure how long it would have to be though, or how to calculate end correction on something that only shares two walls of the cabinet.

Using ABS should be easy. The way I have done it is just use a jig saw to cut to approximate size, wedge the pipe in there and then coat both sides of the hole with ABS glue. PL Premium should work too to fill the gaps but I have never tried that.

[gastric]

Thanks again for all your help. It's been very specific and extremely educational.

Like most DIY it's cost a lot more than I planned. $50 driver. Then the wood. And the screws. And paint. And... Haha. But so far so good! We'll see how it sounds when I'm done.

[rpsands]

You're very welcome

I haven't found anything conclusive on triangle ports yet, but it might be the best way to go in this circumstance if you can get someone who knows what they're doing with triangle ports to weigh in.

End correction is the term that defines it but no one can seem to give a clear explanation of how it works.

It is *probable* that is' just the same "divide by 1.5" end correction as for square ports. So you could just divide the length the round port gives you by 1.5.

The nice thing is you could probably make the triangle port easily adjustable by screwing the port shelf in through the front of the baffle.

[gastric]

Bah, I can't find anyplace that carries pipe with a 3.5" inner diameter. Comes in 3" or 4". I think I need a BOSE Waveguide. You can bend that maze into whatever length you want.

Back to WinISD it appears I can use two 2" ports that are 6" long each and come out with a really low vent mach of 0.09 at 50-100W.

Unrelated it's scary how much the Basslite physically moves. It might even be slapping my grill mesh once I install it, I'll have to check on that. I think the mesh is just about going to touch the front speaker gasket so I was likely to remove that... unless the cone actually travels as far as the front of the gasket. Then I'm back to the drawing board for bumping the grill out more. It's already 1mm or so past the front edge of the cabinet itself at the very bottom since it's slanted.

Fun times! haha

[rpsands]

Just put some rubber stoppers (1" or so) around the speaker to push the grill out

I'm not sure why two 2" ports has a lower vent mach than the one 3" port --

What I'm going to suggest, since you can remove/add the baffle, is that you do a triangular port 5" (right triangle, in the bottom right corner; just cut off a section from the corner of the baffle).

Then get a piece of wood from scrap and miter it down to deepen the triangle.

Model it as a square port in winisd (whatever comes out to a 12.5" square inch area square, probably around 3.54 x 3.54) -- take whatever depth it gives you and then divide it by 1.5 for how long to make the port.

It'll save you some money on the tube supplies, and if it doesn't sound right it's easy to plug the baffle back up. You can also cut the length down or make a longer port easily.

Tube ports get annoying to do when you have limited baffle real estate