Thorn F1, my learning experiance with a Tapped Horn

Thorn F1, a DIY Open Source Project

This is a thread about my attempts to build and better understand Tapped Horn loudspeakers. I started out with a simple build and want to share my ideas and hopefully get some feedback on my thoughts.

Anders Martinsson often emphasis the strength in collaboration and the open source atmosphere.   What I have learned so far about DIY hifi is all thanks to that attitude and the people who share that belief. I hope to start a thread that can contribute to that DIY collaboration thought and mutual learning.

OK, loudspeakers for bass!

I want bass in my home and I want it to be clean, loud and accurate. I have looked at different options to reproduce bass mostly variations on Transmission Lines and Mass Loaded Transmission Lines but finally decided to go with Tapper Horn, for now.

My design goals are:

  • Bass with high quality and ability to play loud
  • Extension downwards to be able to reproduce the lowest note of a normal electric bass guitar (about 41 Hz I think).
  • Cabin depth of max 50 cm
  • I do want as much “kick” as possible without sacrificing the bass around 40-50 Hz.
  • Possibility to cross over as high as 150 Hz
  • High efficiency with max SPL at X-max of at least 125 db at 1m in 1 pi
  • Manageable size for domestic use.

I am a great fan of Anders Martinsson and his THAM designs which have been a significant source of inspiration in this build. I have also got a lot of help and feedback on this design on HiFiForum.nu from many, espessially Circlomanen, petterpersson and Martinsson just to mention a few.

I am very appealed of the robustness of PA elements and I really do like Eighteensounds products. When I did get the opportunity to buy a new pair to a heavy discount I couldn’t resist the temptation. The element of choice is Eighteensound 12LW800. I think it is very suitable for tapped horns with high BL, high fs, low Qts and fairly long excursion. Other elements that is suitable in this design without any adjustments are Beyma 12LX60, EighteenSound 12LW1400. Thanks to their longer X-max (9 mm) they will provide even higher max SPL.

Speaking of robustness; I think one can use the 12LW800 to support a car when changing tires without damaging it. The basket is built like a tank.

Internal with: 42 cm inclusive bracing.

The cabinet is just for trying out the concept. I have therefore used the cheapest particle board available and not gone for Baltic Birch Plywood or something similar at this stage.

Maybe I didn’t meet all my goals but quite a few I think. 🙂

/Forsman

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