Tapped Horns

Tapped Horns

Postby scooter » Fri Dec 28, 2007 12:13 am

Does anybody have any experience with "tapped" horns? I've read Tom Danley's web site about them and the theory is just not clicking for me. The delay talked about from the front of the speaker vs the non delay at the back side of the driver at the port meeting at the mouth and augmenting one another seems backwards to my understanding of the dynamics involved.
Scott Newkirk
KS Sound and Speaker Repair
Kent, WA
scooter
 
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Location: Kent, WA USA

Re: Tapped Horns

Postby gt4702e » Fri Dec 28, 2007 1:34 am

The tapped on "unity" horn isn't too hard to understand, it's just difficult to implement well.

As far as the tweeter is concerned, it's just a regular horn. So far, so good.

The mids and woofers live in a more complicated space. First off, the air space in front of the cone and the tap hole into the horn act just like a bandpass subwoofer. It's a bit tricky finding a driver that works well given the extremely small front chamber and the small port size, but there are some good options out there. Some need a chamber on the back; others will be fine without.

With a traditional bandpass system, the port would be radiating into free space, but in this design we will horn load it a bit. So long as the entry holes are less than a quarter wavelength from the tweeter, the complete system will act like a point source. You want to crossover low and steep to aid in this, but that's aided by the fact that your mid is already in a bandpass providing a 4th order slope. To put things in perspective, a 1kHz crossover would necessitate about 3 1/4" or less between the mid range tap holes and the tweeter. From there, the point where the tap holes enter is essentially the throat of the midrange horn and it's low cutoff will just be a function of its size. If you add woofers and make it a 3 way design, all of the same principles apply.

On the whole, it's nothing really magical. It is a very complicated system and I would bet the mathematics behind an accurate model are pretty painful to construct from the constituent parts. However, in the age of cheap digital crossovers with ample amount of delay and EQ, and inexpensive measurement equipment, it's pretty easy to make a perfectly decent unity horn so long as your mids are loaded reasonably in their bandpass and the tap hole to tweeter spacing is sufficiently small for your chosen crossover point.
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Re: Tapped Horns

Postby scooter » Thu Jan 03, 2008 6:20 pm

Thank you for the explanation. I was trying to figure out the interaction between the front and rear pressure waves. That answered my question.

You also gave me a use for an 18 that I built that the Q came out way off from what I'd planned on.
Scott Newkirk
KS Sound and Speaker Repair
Kent, WA
scooter
 
Posts: 35
Joined: Fri Oct 26, 2007 4:03 pm
Location: Kent, WA USA


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