Who has experience with the C34 back loaded horn? I am considering building a pair.

I have given up on finding a pair of big vintage JBL's to pair with my recently overhauled Fisher X202B. So I'd like to do the next best thing and build 'em myself. I'm currently running a pair of restored KLH Model Fives and it's really a sublime rig, but I want to move some air with some big two-way horns. My general strategy is to build a 'bass bin' and try to match it with a 1.4" throated horn. I plan to manage it with a Behringer 3400 active crossover and once I have settled on crossover point I'll build a passive crossover. I'd like to go with all 16 ohm components. I can build pretty much any cabinet, but I would prefer not to have to turn it into a dog house later because I picked the wrong design.

I'm not really moved by anything more than a raw sort of intuition so bear with me or maybe tell me why I'm wasting my time.

Here's how I got to this point. A friend of mine has Altec Model 19's he bought in 1978. I have always enjoyed them, but cloning them seems like it's just going to end up being expensive to do properly. I have a pair of Cornwalls in my other home which I like very much, but I feel like I want some bigger horns out here in Montana. I have looked at the Humble HiFi Calpamos, but again I'm struck by the expense involved with the Faital drivers. There's Wayne Parham's 4PI, but there's less flexibility with the drivers than I'd like. The DIY Audio Group Fusion 15 looks like a too small box. Back loaded horns seem like they are a little more forgiving than bass reflex cabinets. A BLH seems like it would allow me to start with a an Eminence woofer and drop in a JBL 2226 at a later date. As I understand 2226's are sometimes available inexpensively when a theater is remodeled.

Am I just another dude trying to square the circle or bake a diet cookie? Anyhow the C34 cabinet is the object of my obsessive speculation right now. Who has experience with them and can give me some direction?

I miss Zilch, he probably had this one sorted out in four dimensions.

There apparently is no practical way to avoid the wave cancelling phase reversal that happens between 100 and 200 hz with this design. Even the five figure Living Voice 'Air Scout' offers a subwoofer as an accessory. Bass reflex it is.

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Originally Posted by pete1729

I miss Zilch, he probably had this one sorted out in four dimensions.

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I miss him too! Just think about the Quick and Dirty M2 projects that he would have conjured up!


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Hi;

How low do they have to go and how big can they be?

Barry.

Hi pete,

RE "... can give me some direction?"

The plans for the C34 are in the library here http://www.lansingheritage.org/html/jbl/plans/C34.htm

The C34 is an ancestor of the 4530 Pro cabinet. They're similar cabs with the former being an older home version and the latter a somewhat more recent Pro version. Dimensions wise the main difference is the 4530 is about 10" taller, giving it a little longer horn, which may explain the C34 horn said to have an effective length of 6' compared to 7' for the 4530. Fane Acoustics also had similar horn cab plans, dimensions are about those of the C34.

LF drivers specified by JBL for horn loading duty usually have one thing in common: a low Qts parameter number, which the 2226 doesn't really have (0.31). Moreover, i've never seen the 2226 being specified by JBL for horn loading. Cone driver Qts parameter is a key number in choosing a woofer for horn loading suitability, normally in the 0.15 - 0.25 range, with the middle of that range or lower being more frequent.

The original woofer in C34 was the 130A which has a low Qts (0.18), and the plans doc above also mentions the general purpose D130 woofer with a somewhat higher Qts (0.25).

Not sure though you could easily find a pair of those in good condition. In order to increase your chances for an optimal design, i'd probably look for a more recent than 130A/D130 and a better suited than 2226 woofer for your project, such as: 2205H, 2220H, (2225H), 2227H, E140/K140, depending on what you want to achieve. Qts, as well as other relevant parameters, apply to the temporary Eminence woofer also.

The 2225 is sort of an exception that confirms the rule. Its also specified by JBL for horn loading duty but having a higher than usual Qts for this (0.28). However, lets not forget at the time its Vas parameter was almost cut in half vs the 2205 it replaced, then increasing its suitability for smaller volumes. Lower Qts drivers are more "at ease" in smaller volumes than larger ones. Plus, the higher the Qts number is the more box size tends to increase.

I've calculated before the back cavity volume only behind the drivers of a rear-loaded folded horn, based on plans provided by JBL's former Technical Director George Augspurger, and as i recall it was about 1.8 cu.ft. for two 15" woofers or 0.9 cu.ft. for a single one, which is a pretty small volume.

For more info on folded horns and 4530 cabinet see the attached PDF file. Hopefully the above gives you some useful info for your project. Regards,

Richard

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