Tapped Horn behavior
Disclaimer: If I had 24 grand, I'd have already bought 6 th-115's.
Out of Necessity and an empty bank account, I'm playing with a portable tapped horn. If I fail to find a usefull solution I can reluctantly convert the boxes to dual 15 3015lf subs.
The goal is a single driver box that puts out at least the same spl as an average double 18 can so I can run 3 on one side of an amp. Tapped horns also allow lower frequency reproduction.
The one I am playing with does have much better output below 60 hz than my (now sold) double 18 EV (very effecient). It beats my double 18 by 8-10 db below 60. Above 60 is another matter.
If I'm reading Tom Danley's white paper correctly: It would seem that two cabinets of the same physical size with the exact same driver, one a vented box, one a tapped horn, will both have about the same spl level at 1w at about 100hz. The differences seem to be in power handling and maximum spl wheras the tapped horn will put out 10-15 db higher output at maximum.
Am I understanding this correctly?
I would have thought that the tapped horn would be 3-6 db hotter at 100hz, I.E. equal output to a double cab.
:smash: Please help this idiot understand this. I got me a chainsaw, some wood, and a bunch o drivers and I needs me subs that do 40hz and will fit in the trailer.
I have a few DIY sub plans I purchased but I'm not seeing adequate results. So I'm trying a different approach. If I could get close to the th115 in output at 100hz, then I should be fine untill I can actually buy some.
While I'm at it, has anyone compared the TH-115 to the Titan48?
No, same box size, but each driver's specs is optimized for the different alignments, i.e. as he notes, the driver specs for a tapped horn are different from one optimized for the same BW/box size in a vented alignment.
Anyway, since I don't know the details of either the EVs or TH designs you're comparing I can only assume it's an apples n' oranges one, i.e. you don't have the right driver/TH combo to compete with the EV to get all of the claimed TH performance increases over them and for all I know it will take a custom driver.
WRT the 3015 competing with whatever driver is in the TH-115, how do you figure a relatively low Xmax/low power handling driver is going to come anywhere near matching its output, especially in a similar bulk?
The reference speaker was a 3015lf in an oversized vented box against a couple of variations of the TH115 style cabinet someone else had attemped to theorize. Th-115_style.PDF
This cabinet had the 3015. I also compared the two with JBL2225 moded drivers and my results were consistent.
Variations included longer path length (resulted in steeper cutoff and 3 db lower horn output), The original design, Original with various mouth and reflector options tweaked with test gear running. The next will be the original with the DT20 V style throat.
It seems to me my problem is in dealing with the back of the driver. I am either not getting enough horn gain in the mouth area
or too much cancellation.
Of interest I'm seeing 117db at 50hz with 1w just prior to the tap point. I can move the DB meter from the tap point to the mouth and see the cancellation of about 7-8 db where the horn and driver rear interreact. I wonder if the driver needs to be closer or farther from the throat or if I need some sort of partial shielding to block part of the in-phase signal re-entering the horn.
"WRT the 3015 competing with whatever driver is in the TH-115"
The B&C looks like 6.5mm coil overhang plus 25% of gap is 9.5mm, at 9.6mm the Eminence is stated in a similar fashion.
A similar 9mm ceramic driver from Eminence.
The 4015FL is about half the price of the B&C, and has over twice the warranty.
The power on the 3015LF may seem low, but if tuned low it's x-max limited (so it does it really matter?).
A similar sized box, two high x-max 18s vs one high x-max 15. The power at 80V to the double 18 box is 3dB higher as it is 4R. Both play about 133dB at 100hz in sims, but the TH has over 4dB more output at 40hz.
Note: the 18s modeled here have substantially more output than the EV 18s you mentioned.
I found myself in a similar situation not long ago.. 3015lf's on hand, and trying to get the most out of them. My quick and easy solution was this:
However, I'm sure that this can be improved upon GREATLY, by people smarter than I.
So, I think what may help screamers out, is if people post some hornresp/akabak sims with various cabinet designs SPECIFICALLY FOR the 3015lf that tries to satisfy the following goals:
1. It's a PA sub, 40-120hz is the powerband.
2. +- 3db at MOST within that band. (Ideally, MUCH flatter -- no one note wonders please)
3. PA cabs can be big, but not enormous, probably about 600liters, not much more.
4. Most area under the curve. (IE most overall spl)
5. something that's buildable
6. Design that is power limited, not displacement limited within this powerband (at least not displacement limited up to about 40 volts or so)
7. These will be used in groups, probably 4 at minimum, up to 8.
So, any thoughts?
I also think that one is not limited to an upright box you can lay on it's side. I'm starting to think that a Lay down stackable box might be just as usefull.
Instead of just a roughly 4 foot tall box with a 24" horn opening at the bottom face (roughly), one may want to consider a 28x24 (roughly) horn at the END of a box that is 3-4 feet deep.
This might make for easier horn slopes and tapered horn walls to avoid parallel walls and possibly limit standing waves. Since finding 4 feet depth next to a stage is common enough for some of us, it may make sense. I've found that finding 4 feet of width is harder in many small clubs if you need to stack em..
Stacking two or three of these per side in places where placing anysub in front of the stage is impossible.
You can generally find about 4 foot depth under mobile stages as well for center clustered subs.
One could create a "Mouth" adapter to drop a single cabinet into
for upright use.
I'm trying to get a feel for horn resp.
Lots of smarter guys than me already have contributed, but I figured I might be able to add a bit. I worked a lot with jbell on his 3015 TH project and have simmed a lot of 3015 TH alignments. Once you've figured out hornresp (read the entire help file....I am still learning things), you'll realize that Mr. McBean has done nearly all of the heavy lifting for us.
Thanks for the wonderful software David!!!
My limited experience suggests that a typical tapped horn will provide about 2 octaves of smooth bandwidth. With 40 as a low, you'll be seeing things get ugly above 160. With the 3015LF, it behaves a little better (can be good till 250 or so if done right, lots of pro-sound drivers are like this, but typical pro-sound drivers usually have limited Xmax). If you want louder - you've got to give up lower and vice-versa.
Unlike a lot of drivers used in THs, the 3015LF really likes a BIG cabinet. A simple single-driver cabinet can exceed 103 dB in 2 pi, 2.83V from 40-200 Hz, but it is BIG - over 550 L. With the 3015LF you can add also a series inductor and smooth the response a bit. To get a high efficiency (+3 dB over direct) with this driver requires a large enclosure. You'll run out of Xmax around 300 watts. At 300 watts, a single (550 Liter) cabinet will make 127 dB.
Realistically - if you confine yourself to roughly 12 cubic feet (1.5X2X4 feet), and an 18X18 mouth, you're looking at 101 dB (+1 dB over direct) at 2.83V from 40 Hz and about 122 dB at 200 watts when you run out of Xmax (but still well within xlim).
....Which is pretty much a smaller version of what Jim came up with. If you've got the drivers already and can handle the pack space, build Jim's box, it does work well. If you want ruler-flat response, add a series inductor of 4 mH - it flattens the lower frequency ripples right out (though I doubt I'd hear the +/- 2 dB, and I am sure the room I put them in would do more damage to the response than that...).
The beauty of designing a TH in hornresp is that you can change the response curve (within reason) to meet your needs. If you want a rising response, play with the TH wizard and adjust things. Adding an additional segment can really open up more tuning possibilities, but makes things a little harder to fold up and build. For example, adding a short segment with a faster flare near the mouth of the horn (L45) can increase the 100-140 Hz output by 3 or 4 dB relative to 40 Hz at the expense of bandwidth above 140 Hz.
Anyhow - I'm sure that I have raised more questions than I have answered. Danley certainly does better with his drivers and designs, but he's smarter than I am.
Rest assured - there is no free lunch to be had. No magic here, just math and physics.
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