I've decided to build a pair of subs for my son's studio, likely using a pair of 18" JBL 2268HPL drivers. The goal is low THD in vented or aperiodic enclosures, to determine the best design for crossover points higher than most typical larger subs can pull off for their size.
At first we looked at dual 12s, but none of the decent reasonably priced 12s were capable of the low distortion figures the JBLs could do from way down low to way past 100hz. The SB34NRXL is the only 12 I've used with distortion numbers closer to the JBL ($400), but one of them is close to the cost of the JBL ($340). That means closer to $700 using 2 of the SBs, for the same cone surface area as the JBL. The SBs have the xmax advantage over the JBL 2268s, but that isn't relevant at higher frequencies closer to the LP cutoff.
I've heard the JBLs in various configurations and enclosures. They are likely the best 18s available under $500 for vented enclosures and open baffle based on my listening experiences. Because of this, my son has gotten ahold of a pair of the JBLs and wanted to build a pair of vented subs, but he's also open to aperiodic enclosures if they can go down into the mid 30s using little to none shelf correction.
We'll be running these off of 1000W Icepower plate amps with very light EQ, one driver per enclosure, per side. They'll mainly be used for mixing electronic pop, jazz and acoustic music. He plays drums and is very picky about low end. The bass has to be accurate and have exceptional dynamic capabilities.
I preferred the 2268s because they have an excellent reputation and sound great in the right enclosure at just about any level. This is another trait not typical with large pro audio drivers. We looked at 18 sound, B&C and Eminence, but the JBL always won due to price vs performance.
The enclosures were going to be 6 - 7 cu ft based on the preliminary specs I have on the 2268s. I'd like to hear about some of the designs others have done using JBL2268s.
At first we looked at dual 12s, but none of the decent reasonably priced 12s were capable of the low distortion figures the JBLs could do from way down low to way past 100hz. The SB34NRXL is the only 12 I've used with distortion numbers closer to the JBL ($400), but one of them is close to the cost of the JBL ($340). That means closer to $700 using 2 of the SBs, for the same cone surface area as the JBL. The SBs have the xmax advantage over the JBL 2268s, but that isn't relevant at higher frequencies closer to the LP cutoff.
I've heard the JBLs in various configurations and enclosures. They are likely the best 18s available under $500 for vented enclosures and open baffle based on my listening experiences. Because of this, my son has gotten ahold of a pair of the JBLs and wanted to build a pair of vented subs, but he's also open to aperiodic enclosures if they can go down into the mid 30s using little to none shelf correction.
We'll be running these off of 1000W Icepower plate amps with very light EQ, one driver per enclosure, per side. They'll mainly be used for mixing electronic pop, jazz and acoustic music. He plays drums and is very picky about low end. The bass has to be accurate and have exceptional dynamic capabilities.
I preferred the 2268s because they have an excellent reputation and sound great in the right enclosure at just about any level. This is another trait not typical with large pro audio drivers. We looked at 18 sound, B&C and Eminence, but the JBL always won due to price vs performance.
The enclosures were going to be 6 - 7 cu ft based on the preliminary specs I have on the 2268s. I'd like to hear about some of the designs others have done using JBL2268s.
They are not subs. They are not made for open baffle. They are woofers, made to be used in a vented enclosure. Parts express sells them and offers enclosure tips right on the same sales page. Hope this helps.
I know their intended use. JBL uses them in various applications, some being SRX series subs. The reason I like them in general is their broad banded, low THD performance. That makes them versatile, but I their strength is low distortion bass.
I've seen various suggestions for vented boxes. The .39 Qts makes them good candidates for a QB3 alignment with average QL range, placing Fs close to or at Fb. The balanced VC makes them very linear electrically speaking which lowers 3rd order HD.
I'm looking for more refined answers than generic suggestions from PE would suggest. Thats just a basic guideline. Building a higher end ported enclosure requires alot more consideration than just the alignment or tuning frequency itself.
Charlie Laub made some naked dipoles with these 2268s. He claimed distortion to be lower than most drivers in this class, which I agree with.
I've seen various suggestions for vented boxes. The .39 Qts makes them good candidates for a QB3 alignment with average QL range, placing Fs close to or at Fb. The balanced VC makes them very linear electrically speaking which lowers 3rd order HD.
I'm looking for more refined answers than generic suggestions from PE would suggest. Thats just a basic guideline. Building a higher end ported enclosure requires alot more consideration than just the alignment or tuning frequency itself.
Charlie Laub made some naked dipoles with these 2268s. He claimed distortion to be lower than most drivers in this class, which I agree with.
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What is it you wish to accomplish? How about a push-pull, slot load? I mean, I don't know what else to suggest other than what this driver is intended to be used for. What I am I missing ?
@Scott L Sorry, thought my intentions were clearer.
I'm just trying to get the most out of it and take some suggestions from others who have used this driver in the same intended way.
Yes, I'm looking to use it as a dedicated sub, but a little higher up into the midbass, roughly to about 100 - 150hz. The reason for specifically choosing this driver is its overall precision and low THD at upper cutoff for its size. That means careful enclosure design to not ruin the midbass potential, as most larger (15 ~18"+)subs sound like sloppy garbage past 100 hz.
I'm just trying to get the most out of it and take some suggestions from others who have used this driver in the same intended way.
Yes, I'm looking to use it as a dedicated sub, but a little higher up into the midbass, roughly to about 100 - 150hz. The reason for specifically choosing this driver is its overall precision and low THD at upper cutoff for its size. That means careful enclosure design to not ruin the midbass potential, as most larger (15 ~18"+)subs sound like sloppy garbage past 100 hz.
@Scott L In all sincerety, does that really matter? In my case, because it may not be classified as a "sub", it still would sound great as an extended range sub due to its cleaner than usual lower midrange for its size. Thats a large part of its allure, plus Its also very sensitive for having roughly 16mm p-p xmax. Let's put it this way - if the driver fulfills the intended task regardless of label its given, then I don't see a problem using it that way. Being that JBL uses this driver in some of their SRX subs, that's conformation enough it can do the job, despite what the subwoofer police may say. What driver would you recommend which could check more boxes than the 2268H?
My 0.5 Cent is that I have never experienced Aperiodic enclosure play bass in the same quality like closed box.
Several years ago I tried with both SB29 bass and 26W revelator (alu).
Closed played ALOT better 🙂
Thanks @Rokytheman That's the type of feedback I wanted. Sealed is definitely better for predictable results. Trying to color outside of the lines doesn't always end up being worth the risk. I do confess liking the sound of properly tuned aperiodic boxes. It really depends on the driver. Trying to choose the best arrangement for uncolored midbass.
You just don't seem to understand. You, and MANY others. A "SUB" is a device meant to be used at frequencies LOWER than what a normal woofer can cover. It's gotten to the point that the word, "SUB" is thrown at any dam thing that has a woofer in it, especially if it's in it's own box. "SUB" means beneath, like a "sub" floor. Generally designed to cover 20-80 Hz, and does not usually do very well into the mid-bass. The 2268 is a fine woofer indeed ! The 2269 is perhaps somewhat better, but that does not mean the 2268 will not work for you. It should work very well indeed, as a WOOFER. If we can assume that the published specs are correct, it's a QB3 woofer (as you have previously pointed out, correctly) and correspondingly works well into the mid-bass area. QB3 woofers are, in my opinion, a really nice compromise compared to their B4 counterparts, some of which (old school) doubled as sub-woofers (like the 2245). It's all about optimization. Just build the best dam box you can. Learn about construction techniques that lend themselves to superior sound. You can search this here DIY site for "constrained layer damping" and have thousands of pages to read. This is the end of my contributions to this discussion. If someone else has a "special flooby-dust" design to share that's better than a proper vented enclosure for this driver, then bring it.
@Scott L Now i see what you're trying to tell me. Sure its not technically a sub in the most accurate sense, but it works well in the intended application given there's room to manipulate the enclosure for best results in MY specific design. When you look at how bad some designs out there are, claiming to be a sub in its most purist form, its obvious how easy it is to spread misinformation. Im not that much a stickler for exact terminology as long as whatever is being described works as its promised. Life's too short to nit pick stuff to death.
Since they will used for mixing electronic pop, jazz and acoustic music, and your son is very picky about low end, I'd suggest a low tuning, 20Hz or slightly lower.
There is a lot of content below the 2268's Fs of 33Hz that may or may not be useful in a mix, but I've found it hard to "dial in" unless response extended down to at least 20Hz.
Using passive radiators rather than ports would allow for low tuning without port resonance or chuffing problems.
@weltersys PRs are definitely quieter around box tuning Fb. They also reduce midrange spillover not having a physical opening. I get concerned about efficiency reduction (losses) from PR mass. I'm also suspicious about PR linearity around its peak excursion. I'm not familiar with calculating PR size to avoid this.
Regarding port noise,, I usually opt for the shortest port with adequate cross section. Boundary gain should get us down flat into the mid 20s, including closer proximity to the sound source. I'd use a U shaped baffle right behind the driver to filter rear cone midrange energy.
I may be able to try some sealed alignments with a Qtc of 0.6 and work my way up to 0.66 ~ 0.7 watching for best F10 ratio.
Regarding port noise,, I usually opt for the shortest port with adequate cross section. Boundary gain should get us down flat into the mid 20s, including closer proximity to the sound source. I'd use a U shaped baffle right behind the driver to filter rear cone midrange energy.
I may be able to try some sealed alignments with a Qtc of 0.6 and work my way up to 0.66 ~ 0.7 watching for best F10 ratio.
Have you tried double flared? Less turbulence so quieter. I use a heavy fiberglass bat behind the woofer and port on the back so any bleed is not in your face so to speak. Have done side ports on my subs so I can place close to a wall if needed.
Rob 🙂
@Robh3606 Good call on the side ports. I usually do round ports with adjustable tubes. If they get too long, it appears to be more susceptible to 1/4 wave resonances along biggest side dimension of enclosure. I've experimented with perforated tubes wrapped in felt and have found a noticeable reduction in mid frequency standing wave resonances.
Tapered ports appear to work well, but haven't really needed them, using a larger diameter to stay further away from higher port velocity. The thing which keeps me from excess port lengths is larger enclosures, which inherently reduce port length for given tuning frequency.
As for passive radiators, I wish there were better models available for larger diameters. Most of the common PRs are cheaply made with non linear suspensions. I believe there's a missed market opportunity for electrically tunable PRs with variable dampening by means of a VC and smaller magnet ie. as found in cheaper, higher Q woofers. A portion of the drive signal can be used to counteract the PR dampening in the desired bandwidth. A separate crossover can be used to filter the FB signal to the PR. I know thats brain storming, but there's potential for easier tuning for greater LF extension at minimal losses.
Tapered ports appear to work well, but haven't really needed them, using a larger diameter to stay further away from higher port velocity. The thing which keeps me from excess port lengths is larger enclosures, which inherently reduce port length for given tuning frequency.
As for passive radiators, I wish there were better models available for larger diameters. Most of the common PRs are cheaply made with non linear suspensions. I believe there's a missed market opportunity for electrically tunable PRs with variable dampening by means of a VC and smaller magnet ie. as found in cheaper, higher Q woofers. A portion of the drive signal can be used to counteract the PR dampening in the desired bandwidth. A separate crossover can be used to filter the FB signal to the PR. I know thats brain storming, but there's potential for easier tuning for greater LF extension at minimal losses.
These drivers can be used as "subwoofers" but not in the usual sense. You cannot put them in a small box and EQ the response. The surrounds and cone were not designed for that. But a properly vented box (or PR) that is on the larger side volume wise can be a great match for them. The dual gap design delivers low distortion, but keep in mind that Xmax is not all that high so take note when designing the system.
The Earthquake SLAPS-M12 (Symmetrically Loaded Audio Passive System) passive radiator has an Sd of 483 sq.cm. and 4"(100mm) peak to peak excursion, which should be adequate for the 2268's 8mm Xmax.
Price is generally under $100.
The reports I've read about them indicate the double symmetrical suspension works well, can handle huge amounts of weight (not needed in your larger enclosure) with linear, non-rocking motion.
IMHO two of those JBLs, mounted in force-cancelling slot loaded W-frame open baffle, could give a capable low-frequency system. Open baffle with air load is the only way to lower the high'ish 33Hz resonance at least a bit, to make better use of the internal driver feedback. The motor of this woofer seems to be very linear for BL(x) but the suspension is certainly quite progressive to protect the driver.
The internal feedback could be further increased by negative amp output impedance, lowering apparent system Q. This very low system Q is not a penalty, quite the contrary. The frequency where the (nonlinear) suspension spring starts to dominate is shifted down.
There are downsides, of course, like excursion overdrive and it's recovery which both might be not as nice and clean as possible.
And sadly, the elephant in the room for open baffle with modern PA woofers is often chuffing noises from the forced convection cooling of the voice coils.
At any rate, I think we all would agree with @Scott L that the recommended vented cab is the only reliable way to max out the performance of this driver, overall. But no sub duty.
With anything else we're on our own...
The internal feedback could be further increased by negative amp output impedance, lowering apparent system Q. This very low system Q is not a penalty, quite the contrary. The frequency where the (nonlinear) suspension spring starts to dominate is shifted down.
There are downsides, of course, like excursion overdrive and it's recovery which both might be not as nice and clean as possible.
And sadly, the elephant in the room for open baffle with modern PA woofers is often chuffing noises from the forced convection cooling of the voice coils.
At any rate, I think we all would agree with @Scott L that the recommended vented cab is the only reliable way to max out the performance of this driver, overall. But no sub duty.
With anything else we're on our own...
@CharlieLaub The distortion specs of the 2268 are one of the main reasons I chose it over the others I considered. Its one of the most accurate 18" drivers I've listened to. Other advantages are its light weight, very smooth lower midrange and consistent specs. The split coil is a huge advantage for linearity. It can be used far higher up than other drivers costing multiple times more. The relatively small xmax doesn't bother me since its mainly used for indoor operation in a medium sized room. I'll be reaching its thermal limits.well before xmax in a large enclosure. I have about 500W to utilize which works out just fine. The 2268 is a perfect example of quality over quantity
Yes, I'm aware of the larger enclosure requirements. I usually look for drivers which can do a QB3 alignment, placing Vas=Vb and Fs=Fb. That puts the box tuning where the mechanical resonance of the driver is and has multiple advantages which reduce distortion at lower frequencies. Larger enclosures also mean better efficiency and linearity.
Smaller ported boxes suffer from many drawbacks, with port length requirements being a big one, but the main ones are the non linearity of the enclosure volume and the abrupt unloading of the driver just under the box tuning, requiring a sharp HP to avoid driver damage.
Lower box tuning keeps the upper bass mostly untouched from the majority of the resulting phase shift. That equates to cleaner upper bass and lower group delay. Alot of people who complain about ported boxes not sounding as good as sealed ones haven't tried a larger QB3 aligned sub. Our ears are less sensitive to the lowest bass in terms of detectable distortion and transient response. Often times the room itself decays much slower than the speaker, so the room defines the lowest bass time domain performance more than the speaker itself.
A sealed enclosure setup may be more accurate in general, specifically transient response wise. A well designed ported box doesn't audibly suffer from many of the claimed issues based on my own experiences. It can reduce distortion in the lowest range where its tuned thanks to reduced excursion around Fb. The only realistic drawback is the port midrange leakage and resonances, which again can be avoided with careful design.
Yes, I'm aware of the larger enclosure requirements. I usually look for drivers which can do a QB3 alignment, placing Vas=Vb and Fs=Fb. That puts the box tuning where the mechanical resonance of the driver is and has multiple advantages which reduce distortion at lower frequencies. Larger enclosures also mean better efficiency and linearity.
Smaller ported boxes suffer from many drawbacks, with port length requirements being a big one, but the main ones are the non linearity of the enclosure volume and the abrupt unloading of the driver just under the box tuning, requiring a sharp HP to avoid driver damage.
Lower box tuning keeps the upper bass mostly untouched from the majority of the resulting phase shift. That equates to cleaner upper bass and lower group delay. Alot of people who complain about ported boxes not sounding as good as sealed ones haven't tried a larger QB3 aligned sub. Our ears are less sensitive to the lowest bass in terms of detectable distortion and transient response. Often times the room itself decays much slower than the speaker, so the room defines the lowest bass time domain performance more than the speaker itself.
A sealed enclosure setup may be more accurate in general, specifically transient response wise. A well designed ported box doesn't audibly suffer from many of the claimed issues based on my own experiences. It can reduce distortion in the lowest range where its tuned thanks to reduced excursion around Fb. The only realistic drawback is the port midrange leakage and resonances, which again can be avoided with careful design.
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@KSTR I agree. I was very aware the choice of this driver pretty much required some type of ported enclosure design to get the most from it. That was definitely a consideration when I decided to use it.
As I mentioned before, a ported enclosure with the right woofer can be more of benefit than disadvantage. I'm usually a sealed or aperiodic box kind of guy, but from a practicality standpoint there will be little sacrifices made, specifically to accommodate my son's purposes and intentions being they're mainly for him. The neo motor is a huge weight benefit as well.
The practicality of a simple ported box is good for portability in case he ever wants to use these for lighter duty PA use, given he employs the required safeguards of limiting and HP filter.
The motor noise is really only a problem with OB designs as you stated. Well designed drivers won't suffer from this as much as long as the excursion is kept within reasonable limits.
As I mentioned before, a ported enclosure with the right woofer can be more of benefit than disadvantage. I'm usually a sealed or aperiodic box kind of guy, but from a practicality standpoint there will be little sacrifices made, specifically to accommodate my son's purposes and intentions being they're mainly for him. The neo motor is a huge weight benefit as well.
The practicality of a simple ported box is good for portability in case he ever wants to use these for lighter duty PA use, given he employs the required safeguards of limiting and HP filter.
The motor noise is really only a problem with OB designs as you stated. Well designed drivers won't suffer from this as much as long as the excursion is kept within reasonable limits.