3012HO/LF in a wedge

[kartiste]

Due to the ravages of age, I find myself casting about for a more portable rig without sacrificing too much performance. I have a Crown XLS1500 on the way, with which I plan to bi-amp a box leftover from a stillborn project from long ago, but with different drivers than it was designed for. Originally, I was going to put two K110’s in a wedge for a vocal floor monitor, but halted the project when the K110’s were needed elsewhere. The box (pictured) is built except that the baffleboard was never cut nor the vent shelf glued in.

I think I can put a 12” and a 6” in this box, and use it either upright in the backline or as foldback in rehearsal or when DI’d to FOH. I’ve narrowed the drivers down to a 3012HO or 3012LF, and an LA6-CBMR or Alpha-6CBMR (all Eminence). The reason for the latter choices is that I won’t need to expend extra volume for a sub-enclosure. I might also add a pair of Motorola/CTS KSN1005’s, with crossover.

I have an Audioarts 2100A crossover and a 4100 4-band parametic EQ, and I’ll be using a Tech21 RBI pre-amp.

I’ve been looking at the 3012HO and 3012LF with the Jeff Bagby spreadsheet, but I’ve been having a heck of a time ironing out the group delay and the vent air velocity. The main problem I’m having is optimizing the vent design so it will a) produce the “right” Fb, b) be quiet and c) fit in the box without interfering with the drivers. And, of course, d) the vent(s) must be experimentally tunable during assembly.

My idea at present is to cut a new shelf which will go all the way to the back and seal off the main volume, which would then be 44.25 liters gross. I would install two 3” dia. or four 2” dia. straight vent pipes into that shelf, running parallel to the baffle, with the flared ends facing into that rectangular cavity. Here’s where it gets sticky, since using end flares to allow a higher, yet quiet, vent velocity means the pipes must be closer to the drivers (to accommodate the flare flanges), but without the flares (and thus bigger and longer required tubes) there is a question of whether their other ends will be too close to the opposite wall at the correct length.

So I have some questions, if this is not too tedious:
1) How close do calculated vent lengths come to actual lengths when using end flares? Some of the commercial flare/tube kits I have seen are just shy of calculated lengths, but my experience with other builds (long ago) was that the vent tunes at a shorter actual length than predicted. I surmised this was due to end losses making the vent effectively longer (I never used flares).
2) What effect, if any, will the exit cavity shown have on tuned length and duct noise? It measures 21” x 2.5” x 5” (avg) deep.
3) Which would work better in this box, the 3012HO or the 3012LF?
4) What would be the ”right” Fb for an HO in this box? Higher eases the vent length problem, but with 300W available from the XLS1500 I don’t want to exceed xmax at 41.2 Hz (I only play 4-string).
5) Which of the 6” drivers is a better match? I’m thinking maybe the LA6, due to its higher thermal dissipation limit.
6) What’s a good crossover design for adding a couple of KSN1005’s (in series) across the 6”? I’ve seen some circuits, but I’m not sure about the crossover frequency that will be most compatible with these 6” drivers.
7) Is there a detail drawing available somewhere that shows exact dimensions in profile of the 3012’s (needed to determine duct clearance)?
8) What is the intrusion volume of each of these four drivers?
Any help/suggestions appreciated.

http://i900.photobucket.com/albums/a...g?t=1362496409

http://i900.photobucket.com/albums/a...g?t=1362496699

http://i900.photobucket.com/albums/a...g?t=1362496646

[Sundogue]

Check out this link to a fEARless 112.

Not pimping the cab, but it might help give you some ideas.

F112

[BogeyBass]

Originally Posted by kartiste

1) How close do calculated vent lengths come to actual lengths when using end flares? Some of the commercial flare/tube kits I have seen are just shy of calculated lengths, but my experience with other builds (long ago) was that the vent tunes at a shorter actual length than predicted. I surmised this was due to end losses making the vent effectively longer (I never used flares).

Depends on which program you model with. My experience WinIsd seems to show a longer length compared to other programs. Error factors will be actual box volume being calculated by user to be smaller or bigger. And other programs have compensation for port location and damping material and tend to show a shorter length

2) What effect, if any, will the exit cavity shown have on tuned length and duct noise? It measures 21” x 2.5” x 5” (avg) deep.

The angled back will most likely introduce error factors to the tuned length. How much is unknown. I would estimate its effect would be similar to having a shorter length.
If your shelf is only 5"? i believe the port tuning would be way to high around 80hz though. Exit velocity is the concern dont wanna be to high. those dimensions at full power would be around 15ms. Which is close to ideal around 15 to 20ms.
Some systems are much higher around 35 to 40ms as long as its a large mouth or flared, chuffing is usually not audible if the system is under 500 watts.

3) Which would work better in this box, the 3012HO or the 3012LF?

The 3012ho most likely would do better in a small box. the power handling between the 2 is not much more than 50 watts in a small box. Im guessing your around 1.5 to 2 cubic feet.
The real factor is Max SPL and the higher sensitivity of 3012ho is much higher. Even though the 3012ho would handle 50 watts less power its max SPL is higher than the 3012lf. In a smaller box the 3012lf would have more bass response. And the resonant frequency is much lower. So the Fb could be tuned much lower than the 3012ho and would keep smearing and inaccuracy of a reflex cabinet further away from the bass guitars 44hz fundamental. many would argue im sure the 3012lf's power handling is much higher than 450watts, but compared at 400 watts for the ho and 450watts for the Lf. the higher sensitivity of the HO seems more ideal

4) What would be the ”right” Fb for an HO in this box? Higher eases the vent length problem, but with 300W available from the XLS1500 I don’t want to exceed xmax at 41.2 Hz (I only play 4-string).

I would keep it close to a BB4 alignment or basically keep the tuning freq at the Fs of the driver. Trying to keep the Fb at or below bass guitar fundamental. In this case Fs of the 3012ho is around 51 hz. and i would keep Fb at 51hz or 2 to 3 hz below it

5) Which of the 6” drivers is a better match? I’m thinking maybe the LA6, due to its higher thermal dissipation limit.

opinions vary with closed back drivers, the can have odd peaks and more distortion if crossed over low. since it is a 12" driver crossover frequency can be higher to stay away from lowend distortion. otherwise depends on your ears and the sensitivity of the driver. If its equal to the LF driver or if if its higher than the LF driver you will need to play around with padding the mid if to loud. because of limited airspace and the volume a mid enclosure would take up. sealed back seems easier, only drawback is higher spl and a wild impedance curve which makes crossover design a little more challenging.

6) What’s a good crossover design for adding a couple of KSN1005’s (in series) across the 6”? I’ve seen some circuits, but I’m not sure about the crossover frequency that will be most compatible with these 6” drivers.

Piezo tweeters dont need crossovers because their impedance curve is much different than a standard driver. With the motorola drivers i believe the expected highpass response starts around 5K. to get a real idea whats happening you would need a frequency analyzer to see whats really going on. Depending on the response you could experiment with overlapping the crossover frequency of the 6" mid. again good starting point is around 5K for the upper frequency of the bandpass used for the 6"

7) Is there a detail drawing available somewhere that shows exact dimensions in profile of the 3012’s (needed to determine duct clearance)?

You might have to contact eminence tech support. response is usually really quick. Otherwise the given depth on the datasheet is probably more than enough

8) What is the intrusion volume of each of these four drivers?
Any help/suggestions appreciated.

you must be trying to figure out the total volume of the drivers for your calculations. I have used this calculator before how accurate it is i dont know. there is a guide for everything here

otherwise i have used a generic .12 cubic for drivers and in your case with a closed back and some tweetors expect a total of .2 to .3 of driver volume.

.

[::::BASSIST::::]

Answer: 3012ho