Seismic Audio 18" cabinet

[kblackmore]

I bought a pair of 18" unloaded bass cabinets from a music store I frequent (the price was too good to pass up). I did some research and found them on the internet http://www.seismicaudiospeakers.com/...-rms/p/SAP-18S. After measuring, I found they have a 1.25 in X 19 in port at the back of the baffle. It is just the wood stopping before it joins at the back of the cabinet with the wood being 1/2 in cabinet. What effect does it give the port to locate it in the rear like that, or is a matter of manufacturer convenience? If my calculations are correct when I reverse engineered the enclosure, I found it is 3.3 cu ft. and tuned to 78 Hz. Does anybody have any suggestions for woofers to load it with? 78 Hz seems a little high a F3 for a bass cabinet (i normally try to get them to clean to at least 40 Hz). Would it be better to just seal the port off and build a new port on the front top of the cabinet and aim a little lower? Another thought would be to completely re-engineer the box by removing the existing baffle, bracing it and add a new front baffle to bring it out to approx 5 cu ft. I bought the cabinets to add some bottom and punch to my EV S-152 cabinets. Any opinions would be appreciated.

Thanks
Ken

[Chris Roemer]

Re: Seismic Audio 18" cabinet

Why not just load them w/whatever driver that is in the ad (18", 98dB, 500w RMS, 5.6 lb magnet, and 3" v.c.)? If you do, they'll reach down to 20 cycles (just like it says). ;-)

[kblackmore]

Re: Seismic Audio 18" cabinet

I think that is manufacturer hype, if the resonant frequency is 78 Hz, you'll kill a woofer trying to go that low. I have emailed Seismic and they keep promising to send the specs to the woofer, but have yet to provide them.

[kblackmore]

Re: Seismic Audio 18" cabinet

A clue on the manufacturer hype 1) pro bass cabinets don't go to 20 Hz 2) cabinets that go really low get really big. I just built a cabinet that will go to mid 30's, and it's 13 cu ft and about 250 pounds.......

[Paul O]

Re: Seismic Audio 18" cabinet

I bought a pair of 18" unloaded bass cabinets from a music store I frequent (the price was too good to pass up). I did some research and found them on the internet http://www.seismicaudiospeakers.com/...-rms/p/SAP-18S. . Any opinions would be appreciated.

Thanks
Ken

Oh those things.. hate to say it but I think you just wasted your money. This is a manifold design or at least that is what they were trying for so it doesn't model like a reflex you need to try Horn Response or something similar. EV and a few others built this style box back in the day and those too wouldn't be much of a sub by todays standards with a lowend response that falls off fast below 60hz, the drivers need to have a high EBP(FS over QTS), a stiff suspension and a long VC because the box offers no excursion control, that driver parameter combo was uncommon back in the day but amplifiers weren't very big either so it wasn't a hugh deal, but now you could easily bounce the coils off the backplate with a cheap amp. Are these boxes MDF or real plywood? If they are ply I'd suggest gutting and installing a new baffle with a front port but only if you can find a decent driver that will work reasonable well(40hz f3) in the box volume you end up with. If these are MDF I suggest you just use them to heat your shop while you build something from scratch to utilize a modern driver.. which will deliver much better performance.

[kblackmore]

Re: Seismic Audio 18" cabinet

I thought something might be interesting about the port placement. I have no experience with manifolded cabinets. I also found something interesting with the built in crossover whereas the old owner hooked the crossover up backwards (why?). It put the cap directly across the input. I think I'll just gut the cabinets, make a standard baffle on the front and find a 15 or 18 inch woofer that will be happy with that enclosure.

Thanks for the input
Ken

[Cuppa Joe]

Re: Seismic Audio 18" cabinet

With the Seismic Audio cabs covered in rat fur, the baffles are some kind of plywood while the shells are MDF. You could gain a little more Vb if you flip the driver magnet-side out, tho you'd need a new way to grill the front. Maybe it could be used as a kick box crossed at 80Hz to (perhaps) 250Hz above real subs?

[kblackmore]

Re: Seismic Audio 18" cabinet

Actually the thought was for a bass cabinet below some EV's that I have. Baffle is OSB plywood. I'm just going to load it with a pair of 18's that I have laying around for an upcoming party. Afterwards I am going to rip out the baffle, reinforce the cabinet some, and install a new baffle across the front. Due to the size of the cabinet, I haven't decided whether I am going to load it with a 15 or 18 in woofer. Whichever gets me the most dB down to about 40 Hz as cleanly as possible. Always hated starting with the box first, and looks like I really stepped in some doo doo this time.

[Brian Steele]

Re: Seismic Audio 18" cabinet

I think I'll just gut the cabinets, make a standard baffle on the front and find a 15 or 18 inch woofer that will be happy with that enclosure.

Don't gut the cabinet, i.e. don't take out any of the internal panels. Simply attach a baffle to the front. It looks like there's enough space there for an 18" driver and perhaps a shelf vent for an Fb of 35 Hz.

[kblackmore]

Re: Seismic Audio 18" cabinet

Hooked up cabinets last night for party, sound like the scoops of the older days (no bass up close, bass gets stronger throughout the rest of the room). Definitely not the coverage I was wanting. Got your idea Brian, will try fitting a new baffle without gutting the cab. Now to find a good woofer for the box......

[Paul O]

Re: Seismic Audio 18" cabinet

Hooked up cabinets last night for party, sound like the scoops of the older days (no bass up close, bass gets stronger throughout the rest of the room). Definitely not the coverage I was wanting. Got your idea Brian, will try fitting a new baffle without gutting the cab. Now to find a good woofer for the box......

That effect has more to do with the sub location in the room than the sub design itself, picking the right location inside a room for a sub is difficult.. and the smaller the room the more trouble you will have.