4ohm or more efficient 8ohm speaker

[ddpaulbell]

I have an Acoustic B2C Combo: 220 watts at 4ohms. It's the late eighties one with the Karlson speaker cabinet. I wish to replace the original 15" with a 4ohm 15" to get the full power from the amp. I would also like more below 60hz.Notes below A on fourth string are too thin. I need more volume period. WinSD doesn't help. I found these recommended on a Karlson speaker forum: Emininence Delta-15A, Kappa-15A, and Legend-CB15. I know the Kappa and Legend come in 4ohm. I'm also thinking about MCM, Fane, Peavey Pro.

Would an efficent 8ohm, say 98 or 100db sensitivity work also?

[B-string]

Yes

[billfitzmaurice]

Originally Posted by ddpaulbell

WinSD doesn't help.

Modeling is the only way to know what any driver will deliver from a given cab. Karlsons aren't easy to model, being 6th order series tuned bandpass, but it can be done. Unfortunately, not with WinISD. As for going lower, probably not. That's more cab than driver related.

I wish to replace the original 15" with a 4ohm 15" to get the full power from the amp

More often than not that's a wasted effort. Chances are the problem isn't power, it's sensitivity, and one fifteen may not cut it. You may need the ability to drive two 8 ohm cabs.

[ddpaulbell]

Originally Posted by billfitzmaurice

It's the only way to know what any driver will deliver from a given cab. Karlsons aren't easy to model, being 6th order series tuned bandpass, but it can be done.
More often than not that's a wasted effort. Chances are the problem isn't power, it's sensitivity, and one fifteen may not cut it.

I may be better off adding an 8ohm 15 in a separate cabinet?

[billfitzmaurice]

Originally Posted by ddpaulbell

I may be better off adding an 8ohm 15 in a separate cabinet?

Probably.

[ddpaulbell]

Originally Posted by billfitzmaurice

Probably.

What I really like is the sound of a Bag End D12-D. I used a '65 Fender Bassman with 2 12's for a long time. I researched and ran 12" specs in WinSD. On the cheap end 2 MCM Electronics 55-2952 12" 8ohm in a 2.15cf cabinet. Tuned to 40hz. 100 watt input 111db @40hz, 117db above 60hz. They are rated 175 watts continuous and 97db sensitivity. If I'd be better off spending more money than $24 a speaker I will.

[freddyi]

assuming the original 15" = white painted aluminum dustcap CTS, more motor well help with impact and sensitivity as the 54oz square slug motor is somewhat feeble. Z-minimum on that cabinet occurs at ~53Hz so some boost could be applied at 50-60Hz to get it more solid sounding. There's only about 2 cubic foot rear chamber in BC2 so you're up against that little volume vs parameters to limit LF. You could build a larger Karlson-coupler as an extension cabinet or maybe an 8 ohm tapped horn with F3 around 40Hz (F10~30Hz) to put in parallel. It would take a sheet of plywood. For free plans look at THAM15 and Jim Bell's single sheet 15" tapped horn over at Diyaudio.
fwiw I made a simple inverse taper transflex-type folded pipe with one sheet of wood with Fb~30, Fc~40 - as there were no offsets in the paths, there was an upper bass hole.