F20 meets T20! A tale of two bass horns! - AVS Forum
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post #1 of 15 Old 02-04-2012, 03:40 AM - Thread Starter
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Gentlemen, meet T20!

T20 is a 20 Hz tapped horn designed for dual Rythmik 12" subs.



F20 left ... T20 right

F20 is lilmike's design, modified to fit dual AE PB10 drivers. It's a bit more efficient in terms of material vs volume, my T20 using 3 sheets of ply with some left over. It's also actually smaller in terms of gross volume, since it is more slender. With these drivers, it has more output (due to the swept volume of the drivers ... dual 10" drivers with 10mm xmax vs dual 12" with 18mm). I'm using Rythmik DS12 drivers, an older version. F20 with these drivers needs an estimated 80w to achieve the max SPL shown.

T20 is about 93 db while F20 more like 95 db.



Do keep in mind I'm talking about sims of F20 with these drivers only.

As a team effort, Antripodean and I cut up 7 sheets of ply for these two bass horns as well as some bass bins for TD18" woofers which we started building. It's been a busy day!

Bass bins:
http://redspade-audio.blogspot.com.a...e-woofers.html

Bass horns progress:
http://redspade-audio.blogspot.com.a...-progress.html

No effort to make these pretty. T20 will live under my floor. Antripodean seems to be doing F20 for the fun of it.
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post #2 of 15 Old 02-04-2012, 01:17 PM
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Quote:
Originally Posted by paulspencer View Post

Antripodean seems to be doing F20 for the fun of it.

Amd what better reason could there be for building a bass horn that can hit 115 dB at 25Hz with less than 100W of power? All this talk of 14Kw amps is causing global warming

Of course, I always like the thump of FLHs when enjoying live music so this gets me there with a cabinet no larger than a small car!

explore the music
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post #3 of 15 Old 02-04-2012, 02:28 PM - Thread Starter
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No need to convince me! If you can build these things so quick and cheap, I say "why the heck not?!" You could run yours off a chip amp! Well, probably not the best idea, but just about anything would do the trick.
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post #4 of 15 Old 02-04-2012, 05:30 PM
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I think horns are pretty bad-ass. I don't have the space for big monsters like these - wish i did.

What's the story with "Chinese form ply"? Have you used it before? Lighter and stiffer than MDF? Sounds too good to be true.
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post #5 of 15 Old 02-04-2012, 10:22 PM - Thread Starter
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Ply usually is lighter and stronger than MDF - just hold up a panel lying flat and you will see. It depends on the ply - some is made from hardwood and is very heavy, some is very light. Cost is the issue, and voids. I wouldn't use this form ply for most speaker boxes, but with this one under the house I'm not worried. (I don't have the space either)
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post #6 of 15 Old 02-05-2012, 01:02 PM
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Another bonus is formply is "prefinished" in black, which is perfect for home theater and those on a budget

explore the music
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post #7 of 15 Old 02-05-2012, 02:13 PM - Thread Starter
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Starting to come together:





My initial impression is that these really could use a fair amount of bracing, there are quite large unbraced spans otherwise. This is 17mm formply and it's fortunately very light, quite a bit lighter than MDF, very happy about that!
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post #8 of 15 Old 02-08-2012, 07:12 AM - Thread Starter
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post #9 of 15 Old 02-11-2012, 01:09 AM - Thread Starter
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post #10 of 15 Old 02-11-2012, 11:03 AM
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lookin' good. excited to see the results of the tapped horn!


Matt

"The main reason Santa is so jolly is because he knows where all the bad girls live." - George Carlin
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post #11 of 15 Old 02-12-2012, 03:49 AM - Thread Starter
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Well I've had a little time with F20 and I've now formed an impression. It's a beast! Initial impression was a very pro sub kind of bass. Then I took some measurements to see what was going on. I've placed it in a spot in the middle of the room and it doesn't care. It brings with a certain brute force that says "I don't care if I'm upside down balancing on my pinkie finger, I'm still going to kick your arse!"

I set it up with a bit of a room curve like I would normally use, then I tweaked it by ear til I liked the result. Interesting! I like this thing running at least 15 db hot if not more. I get a good result with it running up to 60 Hz, then my 18" woofers above that. The bass is meaty with great punch and "rockiness." It has a tactile quality.

A quick look at group delay suggests this is not a strength. I wonder if the group delay is part of the sound. It's certainly great for rock, electronic music and home theatre. I haven't tested it out with acoustic double bass which is another kind of test.

One thing I'm not so keen on is not seeing the drivers so I can monitor excursion. Ultimately I'd like to set up my system to be "indestructable." More specifically, configured so that drivers can't exceed xmax. The right selection of amp power, box design, filters and limiters can mean it won't ever happen. With my T20 I'll be able to monitor excursion. Setting it up this way means being able to sit back and know I've figured out they are safe. So when crazy bass hits in a movie, I'm not worried. I don't jump out of my seat to check the subs are ok.
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post #12 of 15 Old 02-12-2012, 04:47 AM
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15dB hot!

I did almost the same thing w/ my first horn sub, but it was a 6dB hot thing. The distortion is so low, you almost keep turning it up until it 'matches' what you are used to hearing from direct radiators.....

Highpass, compression and distortion measurements should be your guide for power to it....

JSS
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post #13 of 15 Old 02-19-2012, 04:56 PM - Thread Starter
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T20 lives!

Bracing


Drivers


Temporary location


No chance to integrate properly or have a good listen, but I will say they do pack a punch!

One person commented that the bass balance in my system at one time sounded like their system which is calibrated flat. I had the bass probably 10 - 15 db hot at the time. Even as direct radiators, they are clean in a room that is heavily treated with bass traps, so highly damped with very low modal ringing.
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post #14 of 15 Old 06-05-2012, 01:29 AM
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Hi Paul, the F20 and T20 look really good. I just wonder if it is better to focus on one spot in the room or rather to distribute the subwoofers, as Wayne Parham suggested. What is your opinion ? regards
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post #15 of 15 Old 06-07-2012, 10:57 PM - Thread Starter
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Quote:
Hi Paul, the F20 and T20 look really good. I just wonder if it is better to focus on one spot in the room or rather to distribute the subwoofers, as Wayne Parham suggested. What is your opinion ? regards

One sub is best? You wallet thinks so and your wife thinks so, but the laws of Physics are often inconvenient!

A room in which one sub performs as well as multiples, is an unusually lossy room and quite rare. 99% of the time, multiple subs are better if well optimised. Of course, having subs this big doesn't help. This one is intended to run below 40 Hz where brute force rather than multiple subs is needed. I have sealed 18" woofers for 40 Hz and up. I suggest people invest in having measurments done, then you can see it for yourself.
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