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Hi all,
I have my dad's old custom cabinets with 12TRX's installed. There is no modeling to the cabs, they are simply oak boxes. I've been looking at the Karlsen K15 and the Electro Voice Aristocrat patterns to build new cabs from. What is the general opinion about these cabs with the EV drivers?
Also, I'm a neophyte to how to read driver specifications in a way that helps define a cab design, as well as cab construction itself, so I may need some extra explanation for the more technical details.
I'd appreciate any help y'all can offer!
Follow Ups:
You're welcome, Brandt, Paul! Here's another one I have that 'bgrim' has kindly posted:
GM
Loud is Beautiful if it's Clean! As always though, the usual disclaimers apply to this post's contents.
Thanks for all the replies! I appreciate the suggestions.
IG, is the K15 as hard to build as it looks? I keep reading that it's the way to go, but it may be beyond what I can do with a skill saw and router.
Paul, what is meant by "3 dB down point @ 43 Hz"? I
I've looked over some open baffle designs, and they seem easier to construct than the K15. Unless I am misunderstanding your comment about rear-firing horns, the TRX doesn't have a horn, just the coaxial cones. Again, this might simply be my misunderstanding of terms. I'll definitely check out the baffle step formulas.
GM, thanks for the enclosure PDF! That's helpful.
I'm going to measure the volume of the massive oak cabinets my dad put them in and see how close it is to the EV spec. I know the cabs are larger than what the drivers originally came in.
The K15 can be built with only a skilsaw and router, just make sure you have good and consistent measuring/cutting practices. :) It's no harder to build than many BLH or folded pipes that are en vogue today.
Which version is your driver anyway? Others seem to be talking about the weak motor version and open baffles, which is a good way to go in this case. If you have the 12TRX non-suffixed version with the big potted motor, it'll do better in a vented box or K15.
IG
This is the big driver with the heavy motor.
What will drive it? A high output impedance tube or Class A SS amp will effectively 'weaken' its strong motor to be closer Qts spec wise to the later versions.
GM
Loud is Beautiful if it's Clean! As always though, the usual disclaimers apply to this post's contents.
The TRX's will be driven by a Nikko NR-715, which is an SS amp. I may use it as a preamp and pick up a power amp with higher output, but will start with the Nikko.
Brandt
The 3dB down point spec was EV's attempt to define the realistic lower limit of the bass response of the driver in a specified vented box volume. This particular one was from the "How to Build an Electro-Voice Component Speaker System. From the ground up." booklet from the early 70's which featured the 12TRXC. EV was aware of the fact that they were then competing with other manufacturers who spec'd everything as "20 to 20K Hz" response. What this meant, in most cases back then, was that if you put your ear against the woofer with a 20 Hz signal playing at maximum power, then you may be able to detect some sound coming out of the woofer. EV was notable for trying to put specifications in a realistic perspective.
Open baffles are indeed easy to build, as you just need to cut a hole in a piece of plywood. BTW the 3dB down point for a flat baffle can be approximated as follows: F=4560/W, where W= the baffle width in inches and F= the 3 dB down point. This is simple enough if you use a square or round baffle, but the art of it comes into placing the driver in an asymmetric position on a rectangular baffle for instance, where several -3dB down points have to be integrated. This is not my department (I'm a horn guy), but I've heard some very surprisingly good open baffle designs. Anecdotal experiences from others can help you here. However, for really low bass the open baffle starts to get really big quickly as the above calculations will indicate: an 8 ft. square baffle will get you a -3 dB point at 47 Hz. A box is a much more space efficient way to go for most people.
The 12TRXC is a coaxial driver with a T35 horn tweeter mounted in the middle of an SP12C woofer. There are 2 kinds of box speakers: 1. The closed, or sealed, box where the acoustic springiness of the air confined inside the box is a major factor in complimenting the bass performance of the driver; 2. The vented, or ported, or bass reflex box where a vent, or tube, or rectangular tunnel is introduced into the box to resonate with the box volume at a frequency which extends the bass response lower than it would be in free air. In former times these two types became associated with (1.) an "east coast" sound (which was typified by closed box speakers which some considered had "tighter" bass which was considered better for classical music), and (2.) the bass reflex "west coast/JBL" sound which others felt had more powerful bass in the region which complimented the electric bass guitar, but was "looser", and had a steeper bass roll off even though it may have gone lower. In the present time this has all become a bit vague, and the choice of the cab type is more an issue of the intent of the designer limited by the box size. Anyway, to evaluate a driver for an optimal application, the following factor is useful: Effective Bandwidth Product (EBP). So Fs/Qes=EBP in Hz. A result of around 50 suggests a sealed box is appropriate; a result around 100 suggests a bass reflex box; results above 120+ suggest a horn application. Some drivers overlap these regions of course.
The EV Aristocrat is a rear loaded folded horn, in that the front of the woofer is a direct radiator, but the rear of the woofer (which is not enclosed in a box as the above examples) is actually a folded horn inside of a box which is intended to exhaust into a corner which will complete it's mouth, as the corner can act as a large horn mouth. A horn presents an acoustically resistant "load" to the driver. This is all much in the same way as if you cut the last 1/4 or so off of the length of a straight horn, and point it into a corner. An Aristocrat cab will certainly work if it's not in a corner position, but the bass will roll off at a higher frequency. Closed box and bass reflex configurations can also have their bass response affected by their proximity to a corner too, for better or worse.
For the 12TRXC EV recommended a box with a minimum of 2.93 cu. ft. (with a 57 Hz -3dB down point) up to a maximum of 23.3 cu. ft. (for a 23 Hz -3 dB), with a 5.85 cu ft. cab having the flattest response overall (all of these cabs having their appropriate tuned vent dimensions of course). So evaluate your Dad's cabs with this in mind. If you have minimal woodworking tools you may get by just modifying them. At least try them and see how they sound.
Good luck from the Electro-Voice Brotherhood
Paul
12TRX with the strong motor should do well in the 12" Karlson. Might also work in the 15", which is less troublesome overall. 15TRX was one of the recommended drivers for K15 and Karlsons were really made to work with coaxial speakers, so it should be dandy! :)
IG
Brandt
EV recommended a 5.85 cu. ft. box for the 12TRXC, with a 30.4 sq. in. vent area and a 3.4 in. vent length, which should get you a 3 dB down point @ 43 Hz. The Aristocrat cab is another alternative, but it really needs a corner placement to complete loading of the rear firing horn mouth. There are various online calculators where you can design your own box, but check them with each other and the EV optimal cab above. Terry G. (who sometimes posts here) has a website (see link) with a lot of 12TRX info, however it was'nt responding when I just checked it, but it may be back up later. Add an 1823M compression driver with an 8HD horn, and you'll have a classic EV rig. Hi-E regular Freddyi is Kaptain of the Karlson Krew and he may have some K advice for the 12TRX.
Good luck.
Paul
...It looks like Terry's website has been down for awhile, and as I recall there were T.S. specs for the 12TRX there. For reverse engineering in the meantime, EV listed the same size recommended box for the SP12C as the 12TRXC, and there are T.S. specs for the SP12C:
Fs= 45 Hz; Vas= 0.1671; Qes=0.75; Qts= 0.6654. There are various websites which have explanations of the significance of the Theile Small perameters. Beware mixing metric and inch/feet specs, which can result in nonsensical results, as well as using the wrong conversion formula to convert one to the other.
If you're not into a faith based initiative, then you can measure the drivers in question yourself. Room EQ Wizard (REW) can be downloaded from the Home Theater Shack website (both mac and pc versions are available) and it features a T.S. measuring procedure (with which you need to construct a simple test box to use) and the headphone output from a good laptop (macbook at least) should be fine to drive it. I have'nt tried it yet myself though.
I've never heard a Karlson, so I'm outa the loop there. For an open baffle design, do a search here for the "baffle step" formula, which you can use to predict the 3 dB down point of a baffle.
Paul
Archived site below. Fortunately, the BR cab design PDF can be downloaded:
http://web.archive.org/web/20101025120346/http://archives.telex.com/archives/EV/Builders%20Plans/Bulletin10A.pdf
GM
Loud is Beautiful if it's Clean! As always though, the usual disclaimers apply to this post's contents.
...I forgot about the Wayback! It's interesting that Terry found some variations in the TS specs on some individual drivers from the published ideals from EV. You never really know unless you measure em.
Paul
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