Does anyone know the ideal enclosure volume and port dimensions for the JBL 2012H Midrange/Mid-Bass Transducer?
JBL's product sheet recommends 10-30 liters and an example of 8.5 liters tuned to 75 Hz.
What would the size of a 75 Hz port be?
I happen to be building a version of Daniel's Ancient Audiophile's quest for the Ultimate Home System.
So, any advice would be welcome.
Well, it has been several months now, and 60 people have chosen to view this thread.
But, unfortunately, no one has offered me any advice on the 2012 transducer. Since, I have about $500 tied up in a pair of these drivers. I have been forced to search else where for some sort of a workable solution.
Whenever, I have tried using an internet speaker enclosure calculator program, the resulting enclosure dimensions appeared to be way out of line with JBL’s recommendations. In both Bass reflex and Acoustic Suspension enclosure designs the internal volume appeared to be way too small. This has only added to my confusion about what to do with these drivers.
Unfortunately, it would appear that this web site does not offer a lot advice on the 2012. But, I did come across a very helpful piece of advice when I widen my search to include “Dog Boxes”. Long time member “Giskard”, was helping someone with an enclosure question about the 2202H drive, when he stated the following:
Yes, but you might prefer the overall sound of ported instead of sealed. It's a preference and you should give both a listen to see which you prefer. The Qts of the 2202H is intentionally low so that any reasonable size enclosure (1.5 to 2.0 cubic feet) you put it in that is sealed will result in maximum transient response. That's what the JBL midrange transducers are designed for - maximum transient response in sealed enclosures. You might want to look on the Internet and read about Acoustic Suspension versus Infinite Baffle. The 2202H in a 1.5 to 2.0 cubic foot sealed volume behaves like an Infinite Baffle design whereas a transducer such as the LE10H in the same size volume behaves like an Acoustic Suspension design. Most JBL midrange transducers are intentionally designed to operate in sealed enclosures as Infinite Baffle systems to maximize transient response.
You can also play around with BB6P and see how different sized sealed volumes affect power handling, efficiency, response, group delay, etc. A Qtc of ~ 0.5 is critically damped, anything below that enters the realm of an Infinite Baffle design (the transducer begins to act as if it were in "free air" and the enclosure volume begins to have diminishing effect on the transducer). A Qtc of 0.577 is a Bessel response and a Qtc of 0.707 is a Butterworth response. It's probably best to stay away from anything higher than 0.707 in general.
Quote:
Originally posted by maxwedge
Is there a minimum depth that I need to be aware of that could cause problems?
Sure, your internal physical dimensions for any midrange enclosure should follow the "golden ratio" as midrange is the most critical and you want to avoid reinforcing internal standing waves like the black plague. There have been several discussions on this forum about the topic and numerous solutions worthy of investigation. Sonotubes, non-parallel sides, non-parallel baffle and back, etc.
I've really come to love those beasts.
Well, thanks to Giskard, I finally have an understanding of just how unusual the 2012 driver is. And that the ideal enclosure for this driver can be either an Infinite Baffle of 10 to 30 liters or a Bass Reflex enclosure of 8.5 liters tuned to 75 Hz. Since, mid-bass drivers are generally operated one to two octaves higher than their resonance, any differences in the frequency response between the enclosures shouldn’t be noticeable.
Currently, I have a pair of these drivers temporarily housed in Infinite Baffle enclosures with a net internal volume of 11 liters. But, I do plan on converting one of my test enclosures to a Bass Reflex design for a direct comparison.
Also, I may have found a simple solution for the 2012’s rising frequency response. If a 1.5mH coil is wired is series with the driver, the added reactance appears to flatten the response over the 400 to 1000 Hz range. Unfortunately, this simple solution will only work if you are using an active crossover and a separate amplifier for the 2012 drivers.
Hopefully, I will be testing 1.5mH coil equallizer and base reflex design soon.
And will let you know what the results are.
Baron 030
'Sorry I missed this. An 8.5 liter box tuned to 75 hz requires a 3" dia port 9.1" long. Since port velocity will probably not be a factor, you could also use a port of 5 sq.in. and 6" length for the same response.
John
Baron, at what frequency are you trying to cross over? I also am trying to optimize these drivers, and in fact I'm in the process of building a pair of ported enclosures for them right now. I have found that in a sealed enclosure of about 30 liters, the response is down about 4 or 5 db at my crossover frequency of 300 Hz. Although I am also concerned about transient resonse, I'm hoping that reflex loading these drivers will flatten them at least at the crossover frequency. I have chosen to use a program suggested Vb of 8.8 liters tuned to 93 Hz. The higher tuning frequency should yield a flatter resopnse at 300 hz verses more extension at low frequencies. I should have them up and running by the end of this weekend. I'll let you know what I think then.
Hi John
Here is what I am going to be trying soon.
An enclosure with a net internal volume of 8.5 liters (0.3 cu’), works out to be about 9.5” x 12 7/8” x 6.25” is size. This is taking into account for the driver, 2 ports, and ¾” x ¾” cleats running along each inside edge. For the 2 ports, I am going to use 1 ½” Schedule 40 PCV pipe. The pipe has an inside diameter of 1.578125” and if my calculations are correct the correct length should be 4.9782” for 75 Hz. Oh, and as part of my calculation, I am assuming a 1 ¼” thick front panel. Hopefully, this should keep the port opening from coming too close to the rear panel. And believe me, It really is all a tight fit is such a small box.
I know this is going to sound strange. But the JBL Venue system uses a metal enclosure for this driver. It is to reduce power compression by dissipating heat out of the enclosure.
So, if I decide to go ahead with a bass reflex design, I am planning on using 2 ports.
One port will be mounted near the top and the other near the bottom of the enclosure. This will allow for a cooling convection current to flow through the enclosure.
And since, I will be using a Crown K1 to drive these 2012s with 350 watts per channel, heating may be come an issue.
Yeah, with the slightly rising response this driver exhibits (not to the degree of the 2123, but in the same realm), a higher-Q sealed enclosure (ie smaller) could definitely be used to "prop up" the bottom end response of the driver, to make it easier to crossover. It's quite easy to expect 300 Hz to be slightly raised, with an enclosure with a Q of 1 or so, compared to one with the traditional sealed enclosure Q=.707. It'll model showing a peak in the box-modelling programs, but IRL, once you add the effect of the rising natural driver response, it'll be much closer to flat...
As for vented- unless you're going to use it in such a way as to need serious bottom-end excursion out of the driver (ie, a 100 Hz crossover point, or something similarly low), I'd shy away from vented enclosures. It's always harder to passively cross-over a vented enclosure as a high-pass, than it is a sealed enclosure. That second impedence peak above box resonance is a PITA to deal with, using a passive highpass crossover in a ported midrange system...
Regards,
Gordon.
I'm using active crossovers. Do you think a vented enclosure would be a problem in that case? Maybe my sealed box is just too large (it's about 1 cubic foot).Originally Posted by GordonW
Over the years many people have made reference to a Drew Daniels based or inspired system.... I always shake my head and wonder why. I would hazard to guess that virtually everyone who has made this statement never actually heard the Daniel's System. To pull off a system of that mass and magnitude and not have it sound significantly worse than the sum of it's parts is quite feat. A feat that Daniels was able to accomplish through significant effort aided by his significant skill.
I suppose some people are drawn to it by it's sheer mass.... but today's array PA systems are significantly superior to the Grateful Dead "Wall of Sound" and have a much more cohesive sound. To build a version of the Daniels System and not end up with a smeared wall of sound is almost impossible. I have heard that Daniels himself recommends that people buy LSRs and subwoofers over attempting the "Daniels System."
I am not saying that a scaled down system using some of Daniels' ideas isn't quite possibly a good idea, but to follow it part way without really knowing what you are doing, while quite possibly a real kick in the pants, be prepared to lower your audio expectations.
Widget
This is the big shortcoming in Drew Daniels's system--no response tailoring information whatever. The early versions prescribe a pair of UREI 525 crossovers, but the later system uses some BGW amps with custom contour cards for the various drivers. Go figure. And he does not share the contour information with the reader. I looked at this myself before deciding that it was nothing but a small scale PA, probably a pretty good one, but I doubt it would be at all satisfactory for in-home use, as Widget says. Remember, his target audience is the dedicated crowd that has been listening to D130's with N2400's and 075's since 1957 and now have the leisure to spend some of their children's inheritance on a balls-out system. Drew's to be commended for recommending the LSR32. In fact he was fairly adamant about it; if I find the reference I will post it, but I confirm Widget--it's out there. If you want to make a home-brew large format JBL, study the studio monitor series, including the K2's, and pick one you can get the parts for and copy crossover information. Anything else is fraught with difficulties.
David
I must admit that I got into building my own speaker systems as a result of reading Drew Daniels' articles, and in fact, I did borrow some of his design ideas for the speakers I finally built. I read about his systems years before I made my first box primarily because I didn't feel I had the skills necessary to make it sound good. What changed for me was my acquisition of a digital speaker controller. This unit made it possible for me to mix and match speaker elements, crossing them over with virtually any type of slope, and tailoring their responses with a flexible parametric EQ. There is also no need to physically time align the drivers, that function is accomplished by a built in digital delay. I know some people don't care for the sound of these units, but after playing around extensively with high quality film caps and air core coil passive crossovers, I will never go back to them.
Yes, with digital system controllers, for SR, I believe we've been there for awhile. With upsampling at 24/192 digital processors may have reached a threshold where many more people will find them a better option even for home hi fi. But as Giskard points out, there is the cost. For awhile at least, I think there will still be people willing to struggle with the old technology of passive and active analogue filters, especially if we can keep the network wizards around to help us.
Despite my having the LSR32's to listen to I share your interest in the larger systems. I am, though, a little puzzled by using a 2012 for hi fi. Though out of production it is still possible to put together a 2122, a 10" mid/bass that was purpose designed for monitor applications. If you want a current production model, I think the 2051 neodymium 10", which is used in the 4348, would be worth a look.
David
OK, I'm game! Where the heck do I get a couple of 2051s? I thought the 4348 was just available in Japan, but can you buy them (and parts) from JBL in the US?
I did a quick plot of the 2251J against the 2123H, and they look like virtually the same driver. I would think that they would each be equally suitable for use in a studio monitor. What do you think?
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