Cheap and Different Sub

[Patrick Bateman]

If I'm not mistaken, I've documented more car audio tapped horns than anyone except for Peter Kulicki. Tapped horns are an interesting option. I personally believe that the stories about their incredible efficiency are exaggerated, but their sound quality is quite remarkable. I think the remarkable sound quality is because the rear wave from a tapped horn is just ninety degrees out-of-phase, wheras the rear wave in a ported box is 180 degrees out-of-phase.

IMHO, the biggest drawback with tapped horns is that they're still quite large. They're not as large as front-loaded horns, but they're definitely larger than sealed boxes, vented boxes, and bandpass boxes. A few years ago I did a box on Diyma called the "triple 8" which was designed to cram three eights into the smallest footprint possible. When I measured the sub, I noticed that the box was so undersized that it's efficiency wasn't a heck of a lot higher than a plain ol' sealed box. From that project I learned that it's probably not worth the trouble unless the tapped horn is fairly large. It will still work if it's undersized, but the output from the rear of the cone will be muted. (Because the horn is too small.)

This isn't the end of the world - in a conventional horn the response sounds like shit if the horn is too small. Tapped horns have a lot more in common with vented boxes than with front loaded horns, so when you make them too small they don't sound like a front loaded horn that's too small. (IE they don't sound like shit when they're too small, they just don't sound as efficient as they could.)

So I was impressed by this tapped horn from lilmike on avsforum. It's a neat design, and would be a great sub for a sound-quality oriented car setup:







Here's the link, with plans: http://www.avsforum.com/avs-vb/showthre ... dus&page=2

[Patrick Bateman]

The last graph shows the distortion of the tapped horn. One thing I've been harping on lately is the use of push-pull. I am using push-pull in all of my subs now. You can see in the measurements that the single-driver push pull has 2nd harmonic that's just 15-20dB below the fundamental, and that's at one watt! Distortion goes up with excursion, so you can just imagine how crazy the distortion is at fifty or a hundred watts.

Note that the Exodus is great driver too! I think that a lot of people aren't aware of how much distortion is in a sub. There are plenty of subs where the second harmonic is actually louder than the fundamental!

[Patrick Bateman]

I've made some improvement to the sub. But first, here's some plans that "radman12" at AVS came up with*:






The box above is for an Anarchy Audio woofer. I like the woofer, but all of my car amps aren't really optimal for it. For instance, my mono sub amp maxes out at two ohms, so I'd be throwing away a lot of power if I used their woofer. Also, I could use my stereo amp with a pair of the Anarchy subs, but that would take up about five cubic feet of my car. That won't work.

So what's the solution?



The Alpine 823D or 843D. Take your pick. If you want to run a stereo amplifier, buy the 823D and hook up one voice coil to each channel. Want to run a mono sub amp? Get the 843D and run the voice coils in parallel. (The 843D has slightly different parameters, shouldn't make an audible difference in the bass.)


Here's the Alpine versus the Exodus. This is modeled with 250 watts into a 2ohm load. The Alpine is belting out a solid ten decibels(!) more. This isn't due to efficiency - in fact the Exodus is more efficient! It's simply because the Alpine's 2ohm coils are a better match for a car audio amp. (The Exodus has an Re of 6.4ohm.) If anyone's curious, the reason that the smaller woofer is more efficient than the larger one is that the Exodus has a higher efficiency bandwidth product, 96 versus 69.
Please note that the Alpine is basically maxed out at 250 watts. Their spec sheet says you can give it more power, but I'd be cautious - it's exceeding xmax by a little bit. BE SURE TO USE A SUBSONIC FILTER. Subsonic filters are absolutely necessary with designs like this. I'd set it at 30hz. You won't miss anything below 30hz - there's virtually nothing there in music. (Home theater is a different story, but this is a car sub, not a HT sub.)


For comparison's sake, here's the predicted and measured output of the sub with an Anarchy woofer. As you can see, it's nice and flat and deep.

Besides putting out more SPL with a car amp, the Alpine tapped horn has a bit more output because it has about fifty percent more displacement. This only makes a difference of about 2dB, but it should be slightly noticeable.

Note that the dimensions of the Alpine tapped horn are IDENTICAL to radman12's design EXCEPT the width The Alpine tapped horn has an internal width of 8.5"; the Exodus tapped horn has an internal width of 7.25". IF YOU DON'T ADDRESS THIS THE ALPINE WON'T FIT!! Just wanted to make that clear, in case anyone realizes their sub won't fit in the box!

* here's the link, and kudos to radman12 for taking the time to model this in Sketchup http://www.avsforum.com/avs-vb/showthre ... st18387271

[Patrick Bateman]

Here's some info on the Alpine sub, from Jim Walter at Alpine:

"Here's a basic rundown of some details on the new 8" subs we are launching here in the next few weeks.

Some highlights:

Segmented Motor Structure w/ 1pc Frame and Shorting Ring
There a 6 magnets, radially segmented and aligned around the shorting ring/frame/heatsink. The shorting ring is connected to the frame via three legs that allow the entire frame to act as a heatsink. We intro'd this design with our 2010 Type R 10" and 12" and we've carried this into the new 8"s as well …. it’s a pain in the butt to tool and assembly but the results are worth it. Check out the cut-view model, you can see on the left side, the shorting ring is directly connected to the exo-skeleton of the frame with one of three radial ribs the fit through the segments in the magnets.

Result:
Great Power Handling: 350W RMS / 1000W Peak Power Handling
Super Low Inductance: 0.55mH (843D) / 0.67mH Le (823D) and its very well tamed and symmetrical with respect to both displacement and current. Graphs attached.



H.A.M.R. Surround and FEA Optimized Spider
Just about perfect progressive compliance that is light and soft enough for super fast transients, but strong enough for full-power operation while unloaded in a vented enclosure or in free-air IB.

Result:
Durability: If any of you have been able to come to our CES Roadshow trainings, you’ll see the 823D run free-air at full clip on an M6 without a hiccup.
Sound Quality: We’ve actually been running these as midbass/front subs (56-250Hz/20-250Hz) in the Camaro Demo car. The speed, accuracy and power of these guys in astounding! I’ve got an 8W3 here and an IDQ8 and they can’t hold a candle to it, especially when you get some real power into them (to my ears at least). This SQ isn’t only a function of the suspension, but during my final approvals, I found the difference in suspension materials to play quite a critical role … so I give the suspension credit here. Graphs attached.


CRC Pole Piece / High-Grade Y40 Magnets
14mm of Klippel verified Xmax (70%) stands out from the crowd not only in linear stroke, but also in symmetry. These are extremely well controlled woofers. Graphs attached.

Result:
High-Output: These aren’t Jacob’s crazy eights … but they’ll get more than plenty loud and keep their composure while doing it. I absolutely love these in 0.50cubes @35Hz … tons of output for any sane person and a pair of them will smile all day on a PDX-M12.
Small Box Requirements: In the CES Demo Camaro, we’ve got them in a plate steel enclosure roughly the size of the woofer’s magnet (0.1-0.2 cubes). For a QTC of 0.90, try a quarter cube. Essentially, they work in boxes smaller than the shipping container they come it. Ported, 0.3-0.5 cubes and keep them in the mid to upper 30s … and they’ll do it with SQ to boot in a vented enclosure.
Efficiency: They are 8s, so no 88dB numbers here, but they are 83.5dB efficient and have the excursion and power handling only to get louder from there.
"

[Patrick Bateman]

Here's the manual, with the T/S params:

http://www.alpine-usa.com/product/view/swr-823d/Specs

[subwoofery]

What happened to the Audiopulse, TC Sounds, Soundsplinter version of that tapped horn?

Kelvin

[Patrick Bateman]

I noticed that the insubnia plans disappeared. Here's some links to keep this design up-to-date.

1) here's the sub that I ended up building: http://www.diyaudio.com/forums/subwoofe ... tient.html

2) Here's the insubnia plans : http://lh4.ggpht.com/_WXjTASetbPo/S6_Zx ... layout.jpg

I am too lazy to re-read both threads, but if I recall correctly, my sub design is exactly the same as the insubnia, except the depth is deeper. So use the existing Insubnia plans, and modify the depth to accomodate the Alpine.