Subwoofer in 210 cabinets

[Jack6428-2]

Does anyone have any ideas / recommendations for turning the bottom ported area of a 210 into a subwoofer?

I would use a 3 or 4-way active crossover and have the following potential subwoofer candidates:

15 inch, 3154?s - foam surrounds
15 inch, 3156?s - accordion surrounds
15 inch, 421LF?s ? accordion surrounds
18 inch, 3182?s ? foam surrounds
18 inch, 3184?s ? accordion surrounds

Main portion of 210?s are currently original 515?s with phenolic spyders / rigid surrounds but I could switch to 515B?s.

Horns will be either 1505?s, 803?s, or 311-90?s with 299?s for a 3-way system or a 4-way system with 290?s (phenolic diaphragms) supplemented with another smaller horn with 802G?s.

Thanks - NG

[GM]

Greets!

Dual 3182s in a sealed bipolar layout located in the lower rear corners. Keep the original 515s if they are still OK or at most just need re-magging if AlNiCo. Reactance annull them. This will open up the top half of the rear chamber for more sub 'cab' Vb. Obviously, bracing in general and horn damping is key to making both the horn and sub work at peak efficiency.

GM

[Jack6428-2]

Hi GM,

Thanks for the input.

I?m glad you?re suggesting I keep the original phenolic spider 515?s, which were original to these cabinets when they were removed from the theater in Monterey CA. I heard they have the best mid-bass response. Do these type 515?s go particularly well with the 210 cabs (i.e.: would you recommend them in a similar application in an A5/828 VOTT cab with a sub in the bottom)?

When you say ?lower rear corners? do you mean mounted on the lower panel where the vents currently are, one speaker placed on left and one on right of flat panel (like: OO)?

Are you proposing the entire cabinet be sealed with no ports?

Should there be any dividing up of the interior of the cabinet to separate the horn-loaded 515?s from the subs?

Could you explain what you mean by ?reactance annulling?? Can this be done at GPA along with the remagnitizing?

Is there something special that should be done (sand, kitty litter) to the insides of the horn curves other than just adding custom formed curved ribbing?

Last question - you suggest I use two 3182?s in each cab, which call for a total of 64 cubic feet vs 32 cubic feet for the 3184?s. I realize the 3182 go down lower in frequency but will the 210 cab volume be enough to support both 3182?s and both 515?s?

Thanks again - NG

[RacerXtreme]

Hi,

I've thought about stuffing an 18 (or two) in the
bottom of my 210's for years, but never did it. What about JBL 18's ? They hit very, very hard in the right box. And just out of curiosity, what do you do about time-aligning the drivers with the 515's above ? From a side view, it would be tough to get all the woofers in the same vertical plane. There is a time-alignment feature on my Rane AC23 x-over, but I'm not sure whether it can fully compensate for the difference in displacement.

How many 210's do you have ? One thing for sure, you should read the article Jim Dickenson did on repair and renovation of the big VOTT cabinets. He even talks of making some tricky panels that basically get rid of the parallel surfaces on the sides of the horn. Ever see an RCA Ubangi ???

I'm stuffing four JBL 2225's in two of my 210's and four Altec 515's in the other two cabinets.
The system probably won't have the punch down low that 18's would, but on the other hand, eight 15" woofers should move a reasonable amount of air..... Just picked up four Peavey MB-1's that sound exceptionally good (in my opinion). I was kind of surprised. They operate from 125Hz to about 1200Hz and are very efficient.

Ultimately, unless you can find someone who has done exactly what you're thinking of and can give you some feedback on what they learned, you're heading into uncharted territory. But hey, it's a great idea. If you do it, let me know how it turns out. I might do the same thing.

[bfish]

RacerX,

Your AC23 can add up to 2ms delay to the mid and low channels, to apparrently align them with a HF driver that is physically placed up to 2-3 feet BEHIND the MF and LF drivers, as is usually the case with a HF driver on a long horn, placed on top of the stack. This may not be the case when the MF driver is also horn-loaded, and may actually be behind the HF driver. In this case, you may have to experiment with phase-reversal of the HF driver, or even relocating it, to get everything "lined up".

As to the sub, most experts agree that phase alignment of anything below 150Hz is inaudible/not required.

[GM]

Greets!

You're welcome!

They aren't the best for stock 210s AFAIK, but in theory are best for a compression loaded (reactance annulled) 210. Not having actually been able to compare them to the other 515s, it's an educated guess on my part based on what I know about them. Really, what's needed is the field coil version so it can be dialed in to each system's 'quirks'. Otherwise, the -8G is probably best for both the 210 and 825/828 cabs.

No, I mean down on the extreme lower left/right side rear in a bipolar layout. This 'kills several birds with one stone', i.e. puts them up against the floor/wall junction for close coupled 1/4 space loading, reduces the amount of bracing required, and they ~cancel out their excursion vibrations. If you install one motor side out and reverse wire it, then they will ~cancel out any even order harmonics due to non-linear excursion.

Right, the 3182s have sufficient power handling for sealed, so might as well use it.

The rear compression chamber should be configured so that there is a coupling passage to the upper air space, which is adequate in theory. My SWAG is you'll wind up needing ~1.5-2.25 ft^3 for the compression chamber since I needed 3 ft^3 for my 515Bs in slower roll off alignment. If they should be 'boomy', then aperiodic vents tuned to ~16 Hz can be added.

Reactance annulling is something you will have to do by adjusting the rear chamber's volume (Vb) such that the rear of the driver is acoustically loaded the same amount as the front of it. This can be done either by just doing an impedance measurement or a frequency plot. Basically what you're doing is raising the driver's closed box Fs (Fsb) back up to match the horn's Fc. This yields a maximally flat horn alignment and the flattest acoustic phase response in its passband with a second order roll off, so a 4th order L-R at the right point will yield a 4th on the sub and 6th order on the 210.

Since we need as much Vb as practical, bracing and coating the rear of the horn flares with sand loaded paint or equal will suffice when combined along with either 'wings' or bracing across the mouth. FWIW, I damped the rear of mine with thick rubber floor tiles like is used in hospitals. Not particularly cheap, but very effective. They became so heavy though that I wound up cutting the horns out and building separate 20 ft^3 cabs for the dual 515B 'subs'. Even then, they required two people to handle them.

GM

[GM]

Greets!

Yeah, JBL 2245s would be my choice, but he already has some 3182s, so might as well use them.

As bfish implied, our hearing acuity rolls off with decreasing frequency until we become pretty much solely pressure sensitive, so we only hear/feel amplitude and if the offset is <1/4WL, we perceive it as aligned. This equates to ~30" at 80 hz/4th order, so whichever sounds loudest either wired in phase or reverse gets you 'close enough'. If there's more gap than this, then an adjustable phase is desirable.

With all the acoustic efficiency you'll have, About all you'll need is some BPs to cover the VLF and use EQ shaping for the rest down to ~40 Hz.

GM

[bfish]

Ok, GM, I'll ask the inevitable next question;

How about bipolar 2245s, as mentioned, in annulled/damped/braced 825s as discussed before, with a 515-8GHP, 4th order active XO, plenty of power (1-9440A for each 2245). I think they've said the modified volume is nearly 8 cu ft, and I may gain a foot or two by using the area aound the 515 BC. Weight isn't an issue, obviously, as the flares are backed with 1" concrete...really. 1" dowels will be strategically speared and glued thru the walls of the sub chamber for bracing. Music only, HT not desired, and no SAF issues. Preffered alignment? Heavily stuffed? Sealed/vented/leaked? I thinking a pair of 2245s could nearly match the 515-8GHP in max SPL and sensitivity, if they could do it in such a small space.

I have all the stuff, and have been chewing over how I want to do the bottom for too long now. it's time to cut holes and go. The system is 4-way deliberate overkill, it's all about headroom.

What about a polar arrangement where both cabs on the same wall all pulled and pushed in unison (there's probably a name for it)? Would it give you a swirlie?

[GM]

Greets!

Not familiar with the -8GHP, but dual 2245s calc to ~101.7 dB/2.83V/m using published specs. An A7 optimized 515B is ~106 dB though, so I imagine you'll need (4) 2245s to ~keep up. If you want this kind of headroom down low you'll either need a huge concrete horn or (32) 2245s/channel in ~118 ft^3 excluding any room gain, so it will be somewhat less, but you'll need to measure its gain to know how much. In a nominal 8-9 ft^3 sealed, (2) should work fine though since they will only require ~4W to keep up to the horns and probably < 10W down low once room gain is factored in.

I'm not following, I mean all four drivers will need to be in acoustic phase, otherwise they will be dipolar and roll off at a higher frequency.

GM

[bfish]

Gulp...32 in 118 ft...that's even beyond my twisted imagination, not to mention budget. The truth hurts, but it's what I wanted to hear. The GHP specs say 104.5 dB at 4 ft/1W (E2/R) in a stock 828. With a 200W AES rating (vs 600W/ea continuous program/2245), the 4X power is doable (close enough for me, I'll power-limit on the XO to protect everything anyway). Lot's of trouble to try to achieve realistic dynamics with a single package, but that's what I want to do. Where does the 3dB-down point calc with the sealed bipole layout?

Dipolar's out, the swirlie thing was a (weak) joke. All drivers in-phase understood. I don't know if the 2245s have much non-linear distortion, but do like the innie/outie idea to overcome any they might have. Would a symmetrical layout ITR (outie on left of one cab, right on the other) be OK?

Now, practically and realistically, if YOU were building them, would you go with the bipole layout, or stick with a single vented, as in Roland's old recipe? I know you like your dynamics, too.