Big 'JBL Cinema-like' 2-way with SEOS-15

Hello to you all,

As I am planning to create a large 2-way (JBL Screen Array-like) system. The picture shows the JBL 4673, which concept I like, but I intend to better its looks and hopefully its sound.

Specs:
http://www.jblproservice.com/pdf/Theatre%20Series/4673A.pdf
and:
http://www.jblproservice.com/pdf/Theatre%20Series/4673B.pdf



I would like to share my initial thoughts on this project, which will be my first DIY loudspeaker project.

For some time now, after a lot of research, I quess this type of loudspeaker system is most suited to my preferences.
I listen to all sorts of music, but mostly electronic music and I watch movies on my fairly large screen.
My goal is to realize what I refer to as 'big sound', the sound from a high-end PA or cinema system, but without the typical horn honk or boom bass you so often experience in clubs, cinema's or open air concerts. I like to be 'part of the music' instead of just listening to music. My room is large enough and my girlfriend is of 'the bigger the better' type, so WAF is no issue.

The cabs I'll be using are professionally made (baltic birch on the inside and thick MDF panels on the outside) and quite big (192 Liters = 6.8 cu ft, 15 inch, double rear ports, tuned to 37Hz). Some mods to the cabs might be necessary, depending on the drivers that will eventually be used. For comparison, the JBL 7673 cabs are 9.1 cu ft., but my cabs are of significantly higher weight, something my back will appreciate ;D
I am pretty sure I'll use the SEOS-15 on top of this cabinet, probably mounted in an adjustable bracket. I would love to use a JBL bracket but these are hard to find here in Europe. The mounting hole is close to the top of the cab, which allow me to adjust the Waveguide to obtain a nice integration between woofer and WG.

Amongst others, I consider JBL 2226 HPL a suitable driver for this project. Crossing somewhere between 800-1200Hz seems possible, because of its gentle behaviour. The T/S parameters suggest a decent low end could also be obtained. Because my budget is limited and this project will require quality drivers, I consider buying these second hand. I guess the SEOS will be fitted with BMS, Beyma, 18Sound, JBL24.. or similar. New Celestion compression drivers and woofers are probably within my budget as well as the DNA drivers of course.

As this project is in its earliest stage (only inside my head , any comments and suggestions are more than welcome.

Cheers, Roland

 

Thanks for your reply Mike,


Iam aware of the importance of the distance between the drivers with regards to lobing and I think with the cabinets this won't be a problem as the upper side of the woofer is close to the top of the cabinet (I guess about 2-3 inches). There is (by far) not enough space left to mount a WG above the woofer (within the cabinet). A WG could be mounted directly on top of the cabínet and the spacing between the WG and the woofer will be very small (at least 4 times smaller than the spacing between horn and woofer of the JBL 4673)
The cabinets are a gift and because they are so well built, I'll definately use them.


As mentioned in my initial post my goal is to get a 'big sound'. I could also choose to use the cabinets as subs and tune them even lower, to 20-25 hz or so, but then I'll need smaller 2-way's on top of these subs (or on stands) and this will imply more work and will probably also be the more expensive option.
Sticking to the 'big 2-way'-option will give me sufficient bass anyway (30-35hz) and I am sure the SEOS-15 is a very good match (depending on the drivers of cause).


Last but not least, I like the looks of a large cab with a horn or WG on top of it, like these loudspeakers by Polish manufacturer Ancient (of which the space between the drivers is still larger than will be the case on my cabs) .


I'll keep you posted.

 

As you may notice this 'project' is certainly a long term affair, BUT it has certainly not quietly died.


After consideration on the set up; large waveguide + midwoofer vs. subwoofer with separate smaller cab (8 or 10" midrange + WG), I have decided to stick to the initial idea of a big midwoofer with a matching WG (15 or 18 inch wide). The main reasons for this decision are:
- To achieve 'Big Sound' one needs big speakers and big horns/WG's which are highly efficient (Pro drivers are mandatory)
- Less components means, less technical issues to overcome (i.e. crossover, driver matching etc.) and less effort/money to be invested.
- It seems not easy to build dedicated subwoofers capable of keeping pace with a highly efficient mid/high section. I guess most of us are familiar with the typical signature of many (most?) PA systems, where the bass seems to lumber behind the rest of the system and dominate the concerted output. Most contemporary dedicated subwoofers (the actual drivers) are designed for rather small cabinets, with the abillity to handle a lot of power (heavy suspension). In order to deliver substantial output these drivers also feature big magnets and have a long voicecoil resulting in high xMax to move a lot of air mass (despite the small cabinet). As a trade off effiency suffers, which is no big deal in professional applications, because amplifier power is cheap. I think 'musicality' (for the lack of a better word) in lower frequencies often leaves a lot to be desired in this apprach. Many shortcommings in today's PA can be adressed with advanced loudspeaker management systems. Since a living room is not a public theatre, why not develop a speaker system with the actual performance as a primary goal ?

Though I would love my speakers to extend below 20Hz, since I love the sound of a church organ every once in while, I think the extra efforts may not compensate for the results.
In conclusion, I will need a pair of efficient 15" midwoofers featuring: a light cone/supspension, more xMax than the typical midwoofer (but without the other mechanical characteristics of a dedicated subwoofer). Furthermore, a linear response from 100 up to 1000Hz and a usable frequency range which extends from (roughly) 30 up to 4000-5000Hz would be desirable.
This description seems appropriate for 'an utopian' driver, one that 'has it all' and would make a small dedicated mid conedriver or mid horn redundant. You can't fool Newton, so every solution in loudspeaker design is a trade-off; probably one of the most populair one-liners in the loudspeaker scene. I firmly believe in the optimization of a simple design concept, like a 2-way full range loudspeaker system.

After extensive research I found only a few of the numerous 15 inch drivers available in the shops with appropriate T&S parameters to match my goal. I guess this is why some old drivers (either for low- mid and high frequencies) have become sought after items for the DIY community. In the old days of PA technology the size of cabinets and horns obviously was secondary to performance goals.
The need for (audio) components with irregular specs has led to an increase in the number of small manufacturers/shops focusing on this niche. Evidentally these these specialty products are priced accordingly.
Coincidentally I came across a pair of vintage Fane Studio 15L drivers. The smaller 8 inch brother from the same Studio Range, the Studio 8M, is one of these 'sought after drivers'.
Judged from the specs, these drivers appear to be exceptionally versatile and, though not exactly a perfect match for my cabinets, with some tweaks they may work pretty well.
First of all these drivers are unusually efficient with 104 dB. Contrary to most 15" mid woofers these are able to deliver substantial output below 100 Hz, even below 50 Hz and therefore eliminate the need for seperate subs. At the same time the response from 100 to 2000 Hz is quite linear and there is usable response beyond 4kHz so a decent crossover to a large WG/horn should not cause serious problems.

A quick and dirty simulation of the drivers in my cabs yielded a (theoretically) max. output close to 150 dB!!!
Plenty of headroom, thats for sure


According to the specsheet they seem able to deliver an adequate midrange. A (relatively) low MMs (66 gms) is rarely seen in combination with a high BL (22 Tesla).
These drivers are obviously of high build quality, a different class compared to Eminence Beta or similar priced drivers.
The cabinets are a little larger than ideal for the Fane 15L's (190 Ltr whereas 140 would be better). The ports are tuned to 27 Hz while 35 or 40Hz would be more appropriate, but with dsp these issues are not difficult to overcome. Besides, unless PA-like output levels are required these drivers are unlikely to be pushed even closely to their mechanical and thermal limts in domestic conditions.


In the next update I will focus on the waveguide/ horn to be used and elaborate on compression drivers.


Comments are highly appreciated.

 

Forgot the spec. sheet 8)


Unfortunaly, due to the file size limit, I had to compress the image, as a result of which some parts are faded.