BillFitzmaurice.info

Thinking of a possible Simplexx 18 powered Sub concept. More of a Segway speaker at best to utilize resources.

All theory at this point, just spit balling for input. Please feel free to indulge.

The driver:
JBL 2268H from SRX700 and 900 series subs.

Thiele-Small Parameters
Resonant Frequency (\(F_{s}\)): 33 Hz
DC Resistance (\(R_{e}\)): 5.3 Ω
Voice Coil Inductance (\(L_{e}\)): 1.85 mH
Mechanical Q (\(Q_{ms}\)): 3.8
Electrical Q (\(Q_{es}\)): 0.39
Total Q (\(Q_{ts}\)): 0.36
Compliance Equivalent Vol. (\(V_{as}\)): 11.58 ft³ / 328 liters
Max Linear Excursion (\(X_{max}\)): 8 mm
Physical & Handling Specs
Nominal Diameter: 18 inches
Voice Coil Diameter: 3 inches (Dual coil)
Power Handling (RMS): 800 Watts
Power Handling (Max): 1600 Watts
(The Xmas is debated online, JBL allegedly listed it at like 23 incorrectly, admitted it and never corrected it, some say it could be the total xlimit not the one way xmax and could be as much as 11mm possibly. I have no idea this is over my head and shouldn’t make a difference for this idea)

Here’s my thinking. I have 2 SRX728 cabs. They are renowned as a great legacy cab. However, they don’t go for much on the used market, require huge amps to push them, and these boxes are a bit rough. Shipping is not an option. I’m not doing big enough shows to justify dragging them out, and actually couldn’t do it alone. Hate to sink the money into 3,000-5000 watt amps to drive them appropriately.

Specs seem good for Simplexx 18.

I happen to have a couple cheap Chinese subs that have 700w amps, with appropriate crossovers. The Chinese woofers get nasty with any amount of juice. My thought is if the JBLs handle the amps better than the cheap cones I could have a couple solid powered subs much easier to move and utilize to my needs. If they work good, that would be worth more as 2 stand alone units than then SRXs are in a dual road rash, rusted cabinet. I could keep the other as a match with the 715 tops.

I can pull the plate amps and run them into the SRX boxes now and see how they sound without having anything at stake. I am in these all for super cheap, so I’m really not out anything as far as hardware.

I’m just weighing the idea to try and sell the SRX and buy another rig vs repurposing the drivers functionally until I get into horns. Possibly have solid cabs to sell to a small facility that couldn’t handle a dual cabinet. I do have a request out to sell them to a used vendor and will wait until they reply. I do not expect any flattering offer.

Anyway, thats the long and the short of it. Is this a terrible idea?

The JBL woofers being Neo are seemingly somewhat lighter than the recommended woofers and are worth about twice as much.
Around $500 per woofer if you can find them, and I’ve seen the SRX728s for sale at $500 locally. Idk, maybe just a muse, but it’s got me thinking of functionally usable gear. I’ve got my eye on a couple BFM rigs that if the right offer comes along I’ll just go that way as I also have the SRX715 tops to pair with them.

Thanks all, look forward to hearing your thoughts.
-Zippie

How about parting them out? Those drivers have gotta be worth something on the open market. More so than in some old nasty cabinet that’s impossible to ship, I’d gather.

No horn subwoofer worth anything is going to manifest out of thin air unfortunately. Hence, why many of us end up building what we want.

Agreed, the woofers could sell, as well as the input panels. Again, there’s a shipping liability for bare woofer concern and cost. I do know these aren’t for horns. Hence the option of the Simplexx. It just gets me making dust now because I have an itch to build. I used to build more, it’s been a few years.

Looks like they list about $350 used online, parts express still sells them new for $525…

I plan to purchase my first BFM rig and be able to get tuning and listening first, then go from there. Building these Simplexx maybe and the WH6s and T18s I’ve mentioned in other posts would be a good slow start in my mind. Still a long way off as I’m down in my back probably for another couple months waiting surgery unless there’s some physical therapy miracle. Being at home trolling forums and parts express deals isn’t helping either, lol. Thanks for the suggestion. I do think that’s a very doable option if it comes down to it.

8mm xmax isn't anything special. You're better off with a T48 or T60.

I fully intend to get into BFM horn boxes. My thinking is can I utilize these reflex speakers in an updated enclosure thats more practical for smaller use? It would make them easier for me to unload(sell) and get some return on my investment while also making them more manageable to physically load in and out. I’m not trying or planning to avoid using a horn cab. Just pacing my time and experience to allow me to get back into building and still have some functional gear until the BFM rig or opportunity to build shows up. I was just curious of thoughts on the specific application of this speaker based on t/s parameters and requirements to make it suitable in a Simplexx enclosure? I’m not comparing it to a horn. I fully intend to acquire or build horns. This is just where I am at the moment on the journey. Any reservation to building a Simplexx box with this driver would be appreciated.

You can load S18s with 2268s. The specs are OK. They weren't a recommended driver because they weren't cost effective.

Zippie wrote: ↑Tue Jul 07, 2026 7:33 pm I happen to have a couple cheap Chinese subs that have 700w amps, with appropriate crossovers.

Just a warning....99.999999% of amp manufacturers lie about the power. They give you peak power and often that's at 4 ohms. Driving an 8 ohm speaker like the JBL will most likely be anemic.

Only way to make sure is to use a volt meter and a test tone to see what it will put out before clipping. Use this https://sengpielaudio.com/calculator-ohm.htm to convert the voltage to wattage ratings.

I did this years ago on a Behringer powered mixer. Only way I could get the advertised RMS rating was to put the test tone through a channel on the mixer, driving it into the hard read, then hitting the master fader into hard red.....then it got close.

Agreed. First step is pull the amp and measure voltage into clipping. It is rated at 8 ohm and the current woofer is 8 ohm. It’s sold as a 2,000 watt cab, so I think the 700w is more realistic. Looks like data shows up to a 2,400 watt peak which would have ridiculous THD I’m sure. Trying to do my homework and take it one step at a time, no rush for sure. I’ll do some voltage tests soon and report back. I’ve found some alternative plate amps online that I like that I think would be a reasonable option if this doesn’t work out just right. I’m terrible at getting way ahead of myself in my head with things that potentially will never happen. Trying to be realistic. I know this isn’t maybe an ideal setup, but I can build a solid passive pro cab complete, then add the box with the plate amp to it so worst case it can be removed and the cab still functional and clean as a passive option with traditional amp.

Bill Fitzmaurice wrote: ↑Wed Jul 08, 2026 7:28 am You can load S18s with 2268s. The specs are OK. They weren't a recommended driver because they weren't cost effective.

Thank you Bill. This was my initial concern that it would just match specs and be suitable. Having the woofers already and the fact that they were a gift puts me at a zero cost for the 4 I have.

If it were me, in your shoes, I'd sell the bare drivers out of the SRX subs, cut the cabinets up and put the pieces in the spare plywood stack, then build a couple T39's with the recommended premium drivers. All-in-all, it wouldn't be much out of pocket and you'd have usable cabs that you can easily transport and deploy on your own. Paired with a couple SLA Pro's, which take about the same power as the T39's and are a quick and easy build... your whole system could be powered by a single amp, two subs on one channel, SLA Pro's on the other channel.

Thank you Seth.

I appreciate the advice. Maybe I’m not stating something clearly. I understand the difference between what I’m asking concerning proper t/s parameters of a woofer for a Simplexx build and an ideal top of the line horn driven PA setup from the BFM lineup.

I am not shooting for an A rig right now. My interest is to begin a journey that starts from where I am at currently with a low cost of entry but yields productive experience, building, testing, and moves me towards something long term. My interest is the total experience and the process.

My goal is to consider becoming a BFM dealer eventually. So, to clarify my experience with a Simplexx system, a small underwhelming WH6L and T18 practice system, or any other system on the way to a benchmark SLA Pro, Otop12, DR200 with T39s is all part of the process and will allow me an education to the BFM systems across the board to make suggestions to application as a dealer down the road. I think I will have a lot of indoor permanent systems that will not need the full max SPL necessity of the outdoor Pro PA setups.

With all due respect to everyone here, I created this Simplexx 18 thread in the Simplexx board to have a conversation about a conceptual Simplexx system. I gladly join in and enjoy conversation about any BFM speaker and do so as appropriate in other places.

I have what I believe is an appropriate driver for the build and would like to continue the conversation that direction. I will get to T39s, I will.
I am considering purchasing a complete BFM flagship rig if the opportunity arises and the stars align. I’m just biding my time as I do not have any rush or pressing need for a specific system. This is laying groundwork for a bigger opportunity for me long term. It is also just a shot at diligent research and understanding of a cabinet and hardware before I attempt a build.

For now I’m at Simplexx. In the event that I sell my cabs in a pinch and move ahead I will shift gears as needed at any time.

I was able to check my plate amplifier quickly. With a test tone at 50hz it is pushing the amp into clip right around the 78-79 volt mark.
I did feel like with compressed music I was getting an OL reading on my meter without hitting clip. This seems to be plenty of headroom for the 2268h if I am understanding the specs and recommendations correctly. Does this seem appropriate in terms of driver needs and proper power given the specs listed above?

Clip around 80v seems like about 800w at 8 ohms. Would that suggest thats the peak of the amp and not the RMS?

I also think I had it getting my meter OL with music content and not clipping, didn’t pay close attention as I was just running some tests for signal, does this suggest there’s some freq dependent things as well?

Lots of info online suggests pushing these woofers with closer to 1250-2000watts ea for headroom because they can handle it without distorting(1600 program, 3200 peak).
I don’t have that much experience with them to know. I have pushed a single 728 with about 1,400w and it is pretty impressive outside with no boundaries.

A standard multimeter can only accurately measure singular frequencies. Any voltage measurement while music is playing is not useful at all.

Volts x Volts ÷ Ohms = Watts

The only thing I can think of that really changes with frequency, that would effect power demand on an amplifier is the impedance of the driver, which varies with frequency. The ohm rating is only a mean figure or average of the impedance. The IEC (International Electrotechnical Commission) sets the standards for speakers. They specify that a driver's impedance must never drop below 80% of its nominal rating across its frequency range. So, an 8-ohm driver is allowed to measure as little as 6.4 Ohms at some point within it's designed frequency range. If you measure the DC resistance of a driver at rest, it's just the resistance of the wire that makes up the coil. Once the cone starts moving, that motion of the connected coil in the magnetic field creates reactance which increases the impedance the amplifier sees. The square root of (DC resistance squared + Reactance squared) = Impedance. the frequencies where the cone has the greatest travel will also have the highest reactance and therefore the highest impedance. At the tuning frequency of a ported cab, the cone moves very little and the impedance will be much closer to it's DC Resistance. It's actually quite a bit more complex than that, but that's the nuts and bolts of it.

Sorry about that... all this just to say the actual load on the amplifier and the actual power (watts) it delivers is frequency dependent, as you so keenly picked up on.

As far as clipping, the voltage it occurs at, and whether that's RMS or peak, we generally use that number as the RMS value. It's not necessarily so in all cases, but usually pans out as such, as long as the amp is able to maintain that voltage under the rated load without overheating. Which is typically the case most of the time.

This is DIY, I absolutely stand for you building whatever you say suits you. My apologies if you felt my previous suggestion didn't fit the indented direction of your conversation. The only times most of the guys here would ever consider a simplex subwoofer build is if there was a space or simplicity (time) requirement. Since simplicity seems to be valuable to you in making this choice, it's a good pick, especially since you have drivers on-hand. However, the WH6L is not an underwhelming build. Build it well and your chops will be up for any build in the catalog. I look forward to witnessing your journey unfold!

Thanks Seth! That helps a lot. No apologies needed my friend. Just didn’t want to get too far into the weeds considering my best possible options knowing thats not the immediate goal. I hope I didn’t come across too short about it. My apologies as well for that matter.
As stated I am learning a lot and trying to sponge as much as I can. I have some basic shade tree experience with electrical but zero formal education. I have never looked at volts when considering speaker / amp relationship before reading it here. It has always been watts and ohms. That was even working for a commercial production company with installs as much as $100k JBL Vertec rig hanging in arrays. Just wasn’t in the vocabulary. Manufacturers tend to market watts and thats the lingo for most people. I definitely have a lot to learn.
I am excited about the WH6Ls as I think they will be really good sleepers for me. I know I have a long way to go, just trying to take it one step at a time. I’m really beginning to think this Simplexx thing will be a cool project. I have some amps I can setup to run them in a pinch if the plates don’t pan out. Might even just grab some cheaper plywood to build them with just to keep cost down. They won’t be making any world stage debut for any celebrity artists. lol. I kinda think I’d enjoy having them for my use for awhile. I honestly think the Simplexx 15 tops could be fit with the srx715 woofers and horns just to complete to build as a DIY rig.
Just to clarify I was running a 50 hz sine when I measured the 78-79 volts at clip. I just had the meter set to max hold messing with it and it went OL on me running some music so I didn’t have a good gauge of the context around it. Excited to join the club here and see what kinda mess I can make of things. All part of the plan more or less, right?

Right.

I say, go for it, Zippie. Put that woofer in a Simplexx box and gain some experience. Give us a review after you have tested it in the wild. Later, down the road, you can always sell those woofers anyway, if you want to. Nothing lost, experience gained.