Good match for a 2x15'' cab(good speaker to use with a 158b)

[Skippy]

I own a 215 Sunn cab with a stock 158b transducer, which is fine by me, but it's the other speaker that I would like to change.

Can anyone please help me choose a 15'' speaker that will work to it's maximum capacity in there? (IE what would be a good match, and why)

The cabs' speakers are wired in parallel, and both have to be 8 ohm, so they match my amp's impedance(4 ohm). Also the cab as a closed back.

Keep in mind I use this rig for guitar.

Thanks in advance!

[Skippy]

So I red about JBL bass speakers, and the D140 and K140 seem really tempting to me.

However, I haven't found anything, anywhere about how they compare for guitar playing.

Anyone have experienced both?

Still wanna hear about all interesting options

[EdBass]

The 140 series drivers were meant for bass; they might sound great for guitar, but the 130 series (D130F, K130) were generally the JBL's used for guitar.

[Skippy]

Yeah, tought about using a 130, they would be a very nice choice I think.
But I don't plan to replace my 158b. Adding a 130 would mean a guitar speaker + a bass speaker; Can they cohabit in the same cab?

[Isaac]

I'm not a fan of mixing drivers in a cabinet. The interactions are pretty much impossible to predict. Might sound good, might sound bad. That goes as much for bass drivers of different kinds as for bass drivers and guitar drivers. Admittedly, this is more of a problem for bass applications than for guitar. In the guitar frequencies, it's much less likely to be a problem.

The question is, what kind of guitar sound are you looking to get with this setup? The old JBLs are very smooth, very clean, and a lot of guitar players like to have an elevated breakup region in their speakers, which the JBLs do not have. Check out the frequency response graphs on the Eminence guitar drivers to see what I mean.

Here's an example: http://www.eminence.com/pdf/Ramrod.pdf
See the response peak at about 3.5K Hz? That gives a brightness to the sound. Most JBLs won't have that.

[Skippy]

Thanks Isaac and EdBass for the useful info!
My amp is Fender Twin-esque, so obviously it's a very clear, glassy sound. I like my clean sound pristine, but powerful too. Matching it with the Sunn cab proved to be a revelation: the sparkling highs of the amp were lifted by the booming lows of the sunn 158B driver, making for a very full, round sound that was very well defined and tight as hell!
(BTW, I recommend to anyone who never tried a good clean sounding guitar amp through a bass 2x15 cab to do so, you will be pleasently surprised. )

Back to topic... here is what I use my rig for:  
Instrumental indie rock, heartbreaking and epic at the same time
Doom Metal (ence the abusive amount of low end needed!) and when I add my Dwarfcraft Shiva fuzz in there, believe me, it destroys.

Now about the mix and match of speakers, I certainly don't want to buy one only to realise it won't fit with the 158B.  I guess I'll have to either get another one of those, or take it out and put two other(of the same) bass speakers in there, which I might do after all.
Any suggestions of good bass speakers to use with guitar ?