what to add on to Stack

Get some old ampeg 115's preferably with shiny voice coil caps with the tin badges on:

"Badges! We don't need no stinking badges"

 

Your going to have to bi-amp and add something designed to act as a sub. If it were me, I would add a Bill Fitzmaurice Tuba 24.

 

an 18?

 

2x15 is probably your best bet though.

maybe an emperor 4x15?

 

hi. ill suggest getting more of the same speakers. why? anytime you mix speakers that are reproducing the same frequencies, you get some crap as well as the good stuff you want. the crap is that the speakers wont start or stop at the same time, if they are ported, its even worse as the sound coming from the port is out of phase with the speaker... so, take 2 different speakers with different ports, and you have 4 different things makin sound at different frequencies, 4different phases within where all the ports and spks overlap. you will get peaks, dips, and it will sound different depending on where you stand, as all that crap will change timing/phase from a different location. i had to chime in as you mentioned serious low end, i assume you are serious. ive had the ampeg 8x10's with double 18 evx in ampeg pro cabs, modified for me by ampeg. (pro cabs are deeper, but the same size front, its a shame they stopped making them.) even with a crossover and dfifferent slopes/xover frequencies, the crap was still there. i say try more of the same cabs. if you like your cabs sound, more of the same will increase the efficiency, power handling. your cones will only have to move 1/2 the distance they move now to get the same sound level. then you will have headroom to boost that 28-40 hz region we lust for. to me, it seems going from one cabinet to two cabs you would think it would be twice as loud. ive always noticed it to be almost 2.5 times as loud. additive effect. but if you mix speakers, you get the crap. try everything everyone suggests, but see if you notice what ive mentioned. nowadays im running 4- 18's full range, (youd be suprised at the nice mids) and jbl horns. if you see us on tour, the two 8x10 are not plugged in , just for looks lol , happy speaker hunting ! johnny a

 

+1 to the above, (johnny a). Plus, aren't those HLF cabs kinda heavy on the low end already? I know the 410 version is, and I believe the 610 is similar, but with a portion sealed. Same huge porting on the bottom though, seems like it would give you all the lows you could stand. Anyway, just another 2 cents.

 

I do that too for some real clean stuff in studio but I stick a couple of twelves in it to make it three way and cross in and out at 18dB:

The 408 is better crossed out at 250 hz in this room corner.
But sometimes a stack of 10's and 15's running full range from two separate tube heads sounds kind of raw and brutal and good and then nothing else will quite do. If you stop them disturbing each other with the different back EMF of the speakers by driving and eq'ing them separately that is. We usually have a little labs phase tool somewhere just in case we hit snags reamping.