Originally Posted by
RMC
Hi Robert
You're right re 2482 compression driver, its response curve shows it is flat (± 3 db) to 5khz then drops rapidly. So 4khz x-over is about as high as you can get anyway considering the horn/lens 4khz limit you indicated.
LIKELY CORRECTION: In posts # 4 (and 14), you indicated having found the DAS spec sheet for the horn/lens (I don't have it) and that it is good for 800-4,000 hz. The upper limit seems low compared to an original 2395 horn/lens (up to about 7-8khz with 2441, good for 2405), but if indeed yours is limited to 4Khz, then you can't use the 2405 with a JBL stated x-over of 7,000 hz or higher (not lower) as I suggested initially. Therefore, the bullet 2402 remains in the race. However, you should also consider the 2404 tweeter with a x-over at 3,000 hz or higher (similar to 2402 at 2,500+ hz), but it has much wider coverage angles (100° X 100°) than the 2402 (40° conical) to probably better "match" your lens coverage. You can also look elsewhere for a proper tweeter. As for coverage of the original 2395 its rated at 140° horizontal X 45° vertical, which is quite wide horizontally (DAS lens coverage I don't have).
There's also an issue with regards to a side-effect of mutual coupling of drivers in a box (e.g. 2 X 15") that people rarely consider nor mention around here, which you should be aware of about the drivers' sound dispersion : BEAMING. This is a directional property occuring when multiple cone drivers are close to each other, such as 2 x 15" in a cab. After showing - 6 db beamwidth curves for three sizes (10", 12", 15") of dual low frequency drivers, JME adds:" The assumption is made that the drivers are arrayed in a vertical line, so that maximum coverage will be obtained horizontally." (John M. Eargle (JBL), Loudspeaker Handbook, Chapman & Hall, 1997, P. 80). No, there's no typo error in that statement. Vertical driver alignment leads to increased vertical driver beaming ("focus") and maximum horizontal coverage. Horizontal driver alignment leads to increased horizontal driver beaming and maximum vertical coverage! Further explanations of this below.
In your post # 8 you mentioned the 4350 woofers being used only to 200 hz which seems about right, since the 4350b version data sheet mentions a 250 hz x-over to a 12" 2202H up to 1.1khz. It would probably take a whole book to explain each of the Design Engineer's choices made for that complex loudspeaker. Just remember these are large control room monitors, with that environment in mind, not exactly home hi-fi speakers. But I'm pretty sure the 200-250 hz x-over to a 12" driver is in good part for reasons related to avoiding or reducing horizontal beaming effect that comes from having two 15" drivers side-by-side if they were used up to 800 hz for example. Meaning the 200-800 hz or so range might have been too directional horizontally (narrow listening window).
This is where the intended application/purpose of your boxes becomes important: Home "Hi-Fi", Sound reinforcement indoors or outdoors, Studio monitoring, Disco Club use, etc. ?? My feeling is that it may be for Home sound. Then, horizontal sound dispersion is usually priviledged in such situation, having enhanced stereo effect (that was ONE of the reasons for my initial 2405 tweeter suggestion, another one being slant plates dispersion patterns mentioned above). An exception to wide horizontal sound dispersion in home use is Multi-channels Home Theatre sound application, because of the desirable localization of some sounds (e.g. dialogue). J. Eargle wrote a small article about that (Home theatre sound) in Audio Magazine long ago, considering his vast knowledge and experience in Cinema Sound, among his many other Audio fields of expertise: Bible!
Electro-Voice also has an interesting explanation of the beaming side-effect related to the use of dual woofers in their model TL 770D data sheet of 1996 (this is a two-woofer in a vented box similar to a 4508 for example). In the section dealing with "Use in multiples": "Cone loudspeakers may be stacked for greater acoustic ouput and a narrower beamwidth. (...) This principle is already employed in the dual-woofer TL770D, and is responsible for the higher sensitivity and narrower vertical beamwidth (with the system long axis vertical) relative to similar single-woofer systems. (...) At relatively low frequencies, below about 150 hz for typical TL series dimensions, stacking produces additional acoustic output without altering dispersion." (P. 3)
The last phrase from that quote is based on the fact that low frequencies are mostly omnidirectional, so no altering of sound dispersion there. But higher than the low frequencies, beaming starts to kick-in with dual-driver boxes... Since your proposed box is NOT a duplicate or real 4350 it will be impacted, more on horizontal woofer dispersion if the box is placed longer side down as you mentioned for a 4508 type of box.
By analogy, a similar situation of beaming also happens with mid/high frequency horns combined. In his "Handbook of Sound System Design", ELAR, 1989, in section "Directional properties of combined radiators", sub-section "Techniques for narrowing coverage", John Eargle of JBL states "In-line vertical stacks of horns have long been used for producing narrower vertical coverage that can be provided by a single horn. (...) Note that the horizontal pattern of these arrays is the same as for a single horn. If horns are placed side by side, horizontal coverage will be narrowed, again at the expense of considerable lobing. (...) Note here that the vertical pattern of the horizontal array is the same as that of a single horn." (P. 90-91). Read horn = woofer.
Moral: your intended boxes (as per your indications) don't seem like a good idea sonically and you may regret their sound after all the work is done... In my view, It's better to know ahead of time to minimize the number of banana peels on your way. Its your time and money so YOU decide what YOU want to do, for me it doesn't change anything, but I hate seeing an audiophile colleague heading for the wall, then having to re-do the job afterwards... Don't build boxes because of impressive looking double woofers, just to minimize appearance of too wide a horn on a narrower cabinet or for the nice looking 2402, but rather make some that are technically sound with what you have or find within budget, for your enhanced musical enjoyment ! If you continue as is, there's good chance you'll have omnidirectional bass, then narrower double woofer coverage up to 800 hz, then slant plates wide dispersion 800-4,000 hz, and finally narrow coverage from 2402 tweeter. Sounds good ??
My suggestions: Since you already have the compression drivers/horns/slant plates with wide dispersion, then find a suitable tweeter with wide dispersion and with an acceptable x-over point for tweeter/horn . If double woofers are a must, then have the box/woofers vertically aligned for improved woofer horizontal dispersion up to 800 hz, improved stereo effect, and better match with horn/tweeter dispersion patterns. In your shoes, I would still strongly consider a pair of boxes with one E-145 in each since you already have those ("free" gear). Even used alone, the E-145 are quite capable fellows if they are in good shape (original, reconed as such or with good aftermarket kit). Their intended application such as bass, organ, LF reinforcement, plus an Xmax of 7 mm (twice that of E-140! according to JBL's spec sheet), are such that you can pump some pretty good bass output from these. Finally, I've seen a reasonably uniform frequency response for a Musical Instrument driver.
RE your post # 12: Your quote regarding "Model 4508 Bass reflex dual driver" enclosure appears to come from JBL's "Low Frequency Enclosures, 05/80. Those dimensions for 4508 have varied a little over time from 41.75 X26.5 X 18.25" to 39.75 X 26.5 X 17.25" (JBL, 1982, Pro Catalog). If you build such boxes, make sure you have correct dimensions to work with. JBL Pro Enclosure Guide also gives other box suggestions.
RE Berga 12 post # 15: 2226H may turn-out to be expensive, plus a "waste" of your E-145, and not necessarily a good idea "with a big punch". Though In sound reinforcement for Disco application it may make sense... Regards,
Richard