Designing the AtomHorn, a 25-30 Hz tapped horn from Germany

your design looks fine.

however, you should always compare your design with a ported enclosure in order to see how much "horn effects" you are getting.

in your case, you are inputting 2.83v into 6.5 ohms, which is 1.23 watts.

1.23 watts into that driver in a ported cab is 1-2db lower in spl than your horn, so you are only getting 1-2db of horn effects.

in my opinion that is not worth the added complexity of building a horn.

+1. For the cab to have decent sensitivity the mouth area needs to be increased by a factor of six or more.


That's the result of lowered excursion compared to a VB, and lowered excursion is the product of higher sensitivity.
http://www.readresearch.co.uk/loudsp..._article_1.pdf
http://www.readresearch.co.uk/loudsp..._article_2.pdf
http://www.readresearch.co.uk/loudsp..._article_3.pdf

a good way to think about horns is to look at some brass horns...trumpets, french horns, trombones, f-tubas, concert tubas. they have increases in efficiency of the low notes as they get larger.

there is a reason why bfm built his "tuba home theater" as large as he did.

to sum up the papers that he posted, in order to hit low notes with high efficiency, you need a big horn to couple the long waves of the high impedance (strength) device at the throat to the low impedance air at the mouth. for intuition it is like fanning the air with your bare hand vs. holding a magazine/paper. the latter couples to the air better and blows more wind.

Most designers of tapped horns don't understand them, and get all excited when they get 3 or 4dB higher sensitivity than the same driver in a VB. IMO if you're not getting at least 6dB of gain from a horn it's not worth the bother. A dead giveaway that you're on the wrong track is if you see response peaks in the midbass 10dB or more higher than the low frequency response, just as is the case with your chart.


That goal is unattainable. Tapped or not horns that go low are large. If you want to go to 25-30Hz with a horn the smallest cab that's worth the effort will be about 300 liters total volume. If you must go smaller use a direct radiator or bandpass.

That's why I went ahead and built my dual Tang Band 8x12" design. I got a lot of criticism over that design because it barely had enough sensitivity to make sense. It's an undersized design, only putting real horn gain in down around the corner and top end, but not a lot in the middle. I wanted to learn, and I believe I learned a lot by going ahead and building that monster. I'm still learning, but I'm further along than I would otherwise be. All it cost me was $500... I spent more to learn less useful knowledge back in the 90's learning computer programming from a crooked technical college.

As for the design, I'd try and get more horn gain going on. As others have said, increase the mouth size a bit (and S3 as well)... that'll help. Of course, that will make it bigger - you'll have to decide how much space to trade off. Maybe move the corner up if you have to... even a couple of Hz can make a big size difference. Watch the phase graph... it's not quite lined up within 90 degrees yet in the passband.