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[Craig Hauber]

Looking for something to go between a sub like the LAB and my mid-high boxes that struggle to go as low as 130Hz (but would rather cross them over higher)

The mid/highs are a very large dual EV DL12x loaded on a 25" long horn with a custom phase-plug slot type throat.  They get wicked-loud with very minimal power.
I can put 1 on top of 2 JBL SRX dual-18's and still run out of low end with plenty of headroom left on the tops.  -I do not have sensitivity numbers on the top boxes as we are still getting them all up and running.  
Right now I'm looking for quick-and-dirty if need be, but would like to build a matching LF box in size. (Trap, 42"high X 30" deep X 24" wide front, 18" wide back)

here's a pic of the box.

[Art Welter]

Craig,

I used to have low mid horns similar to yours with EVM 12". A pair per side kicked down to the 60-80 HZ range, on some country gigs I actually ran them without any subs.

How are the low mid horns damped?
What is the compression chamber size?
Have you tried flipping half the cabinets over (coupling the HF) to reduce the width of the stack and reduce comb filtering problems that may be causing a lack of lower low mid?

Art Welter

[Ivan Beaver]

Is it me or does the HF horn look to have a much wider pattern than the low freq side?

[Tim McCulloch]

Ivan Beaver wrote on Fri, 16 October 2009 20:14

Is it me or does the HF horn look to have a much wider pattern than the low freq side?

You beat me to it.  With that much depth to work with, a narrower horizontal coverage HF horn would be doable, I think.

A tight pack of these would be a physics lesson.

Have fun, good luck.

Tim Mc

[Craig Hauber]

Art Welter wrote on Thu, 15 October 2009 17:34

Craig, I used to have low mid horns similar to yours with EVM 12". A pair per side kicked down to the 60-80 HZ range, on some country gigs I actually ran them without any subs. How are the low mid horns damped? What is the compression chamber size? Have you tried flipping half the cabinets over (coupling the HF) to reduce the width of the stack and reduce comb filtering problems that may be causing a lack of lower low mid? Art Welter

We only have six working and mostly use 2 per side, but flipping and stacking was what I was thinking If I got up to 4 per side.

The 12" driver chamber is sealed and not very large.  It is the width of the box and the driver magnets end up an inch-or-so from the back panel.  I stuffed them with fiberglass insulation and it seemed to smooth out some  of the low-mids.

The cones are sort of "phase-plugged" with a slot type opening where you can see the dustcap and cone surface immediately above and below it.  The cone hits it if you try to get loud LF out of them.  The tightness of the cones and the sealed chamber make it difficult to accidentally do it though.
The thickness of the drivers flange gasket and the at-rest position of the cone effect how much distance between cone surface and phase-plug.  (And I've found alot of variation in what are supposedly identical drivers.)  I do not know what that spec should be and how variations in it effect the audio.

The HF horn and MF seemed fairly well matched in overall width -Quite narrow.  The sidewalls of the HF stay narrow then flair out near the end.  All 4 surfaces are curved unlike older radial type horns with 2 straight sides.

Overall they work really well and I love the efficiency.  Very hard to find a large enough space to set up and thoroughly test on my current budget.  Many of the shows we have used them on have been toss-up-and-go events.  The sound is very pleasing for live use and the customers are so amazed at how much sound comes out of such relatively small and few boxes.  -And they are absolutely dead from behind -tough to even tell they are working.

[Art Welter]

Craig,

When I asked how are the low mid horns damped, I was wondering about the actual horn, not the compression chamber.

On the fiberglass horns I made, we laminated Built-rite, a kind of wood fiber insulation material to the horn, then filled the chambers with expandable foam.

That treatment increased both the level and quality of the low end.

The DL12X is about 5 dB hotter at 400 HZ than at 100, it takes a fair amount of EQ to get them flat even in a front loaded cabinet. You may be mistaking the usual slanted horn response for a lack of 100-130 HZ.

Xmax is 4.1 MM, even without an additional "donut" if you are hitting the cone and have about 1/4" clearance you are over Xmax.
You should experiment with the rear chamber size, you may find that a smaller compression chamber will work better.

Loading styrofoam "bricks" into the compression chamber is an easy way to test, keep loading more until the LF/excursion does not improve.

Have fun!

[Craig Hauber]

Art Welter wrote on Sat, 17 October 2009 09:29

Craig, When I asked how are the low mid horns damped, I was wondering about the actual horn, not the compression chamber.

Sorry, didn't get the terminology -was thinking driver damping.  The horn walls are exceptionally rigid -like slapping the side of a 45' sailboat -they sound at around 1k (and up) when struck.

Quote:

On the fiberglass horns I made, we laminated Built-rite, a kind of wood fiber insulation material to the horn, then filled the chambers with expandable foam. That treatment increased both the level and quality of the low end.

I can't get into the space between horn and cabinet side -it doesn't open into the driver chamber.  I can holesaw into it from the driver chamber but think it is already filled with something -box side is very dead sounding when pounded on.

Quote:

The DL12X is about 5 dB hotter at 400 HZ than at 100, it takes a fair amount of EQ to get them flat even in a front loaded cabinet. You may be mistaking the usual slanted horn response for a lack of 100-130 HZ.

I love the shear loudness of that range, would rather add to the 100Hz range instead of subtracting the 400-and-up.  Right now I can get useable show volume with a 100W amp if I had to.  (Great for "green" events running off solar panels or car battery amps.
I'll pull some impedance plots and measured frequency responses for you to look at.  How do I do a 1w/1m test? (don't "watts" vary by impedance? -what voltage do I use for a 4-ohm load)

Quote:

Xmax is 4.1 MM, even without an additional "donut" if you are hitting the cone and have about 1/4" clearance you are over Xmax.

How does varying the distance effect the system?  If I'm farther back away from the plug vs being almost on it.  Been wondering what the ideal spacing is as I got all these boxes used and unloaded.  Don't know what they originally came with but tried many drivers (including vintage ones) and the EV 12" ones seem to work the best -in clarity and SPL

Quote:

You should experiment with the rear chamber size, you may find that a smaller compression chamber will work better. Loading styrofoam "bricks" into the compression chamber is an easy way to test, keep loading more until the LF/excursion does not improve.

It's really hard to measure or even see the cones, is there a procedure for this?  (They are way up a narrow horn and you just see dustcap) -Stobelight?  Laser?  High-Speed photography?
At the levels it takes to get them moving it hurts my head getting up in there for a look -even with plugs!

Quote:

Have fun!

I fully intend to!

Thanks for the advice!

[Art Welter]

Craig,

Sounds like the builder of your cabinets used a lot more fiberglass then I could afford in 1979, or did something similar to what  I did.

A 45 foot sailboat generally would have nearly an inch thickness of fiberglass below the waterline, which would make a horn like yours weigh about 150 pounds without an enclosure.

If your cabinets are relatively recent, they could use siped foam core and epoxy (like current surfboards), which was not around in the bad old days. It is very expensive to use those products.

Who is the designer / builder?

Amps delivers more power into a lower impedance, but for a nominal 4 ohm load just set the amp at 2 volts sine wave at 60 HZ, then sweep up. Most meters will be accurate at 60 HZ AC, not so much at other frequencies, so calibrate at 60 HZ.

Lay the cabinet on the side, prop it up paralell to the ground, put the mic on the ground one meter away from the center of the two cones, subtract 6dB for a equivalant LF  free space reading.

20 volts at 10 meters would be more accurate, but loud as hell.

As far as excursion, a dot on the cone is pretty easy to see move, but the depth of the horn will make it hard to get off axis enough to measure.
You could gaffer tape a Popsicle stick 4.1 mm from the cone, then slowly advance power and see what voltage is required to make it hit.

The tapping noise should be easy to hear. Start loading the styrofoam “bricks” in the compression chamber and and see what happens.

Without seeing the phase plug design I can’t say what moving the cone away from the plug will do, but for sure the plug should be farther than Xmax from the cone or you are limiting the output.

Don’t expect the cabinets to be flat, there is nothing wrong with EQ.

Art Welter

[Duane Massey]

It is not particularly difficult to build a mid-bass horn using a 15" driver, but there are very few people actually doing it. I would certainly think this would be appropriate for your situation, but such a box will not be small.

[Craig Hauber]

Art Welter wrote on Mon, 19 October 2009 14:14

Who is the designer / builder?

Not sure, the only label on them is "harbinger" and I don't know if thats a builder, owner (or both) but searching that name brings up nothing related except for a cheap chinese speaker brand.

Here's the compression chamber showing the "phase plug"  The opening above is just a tilt-handle and access into the upper portion of the box which contains the 2" and horn only.

It is roughly 2.4 cu ft (not including driver volume) and I put a batt of 3" fiberglass in there.