February 23, 2012

How does the sensitivity of tapped horns compare?

Here is a simulation to illustrate. This is based on a Hornresp simulation that has been exported into REW for comparison:


In light blue you can see dual Rythmik 12" servo subs in a sealed box with 1w input. Around 88 dB nominal sensitivity which drops to 80 dB at 20 Hz. The black line shows T20, a 20 Hz tapped horn with around 500L volume. The nominal sensitivity at 100 Hz can't be compared, however it is 89 dB at 20 Hz. 

The dark blue line shows the excursion limited maximum output. Around 370w shared between the two drivers has the driver reach excursion limits. 106 dB max SPL at 20 Hz. The tapped horn increases sensitivity and controls excursion more so that the full 740w can be used and excursion limits are reached around that point. The output is 118 dB, which is a 12 dB increase in output. 

So the result is that two 12" drivers with 370 watts each can achieve the same output as eight with twice as much power. Since drivers and amps are much more expensive than a few sheets of cheap ply, this works out as a cost effective choice.


  1. 90db from 1W over 20-60 Hz. Excellent.

    Bye bye power compression. What sort of excursion do you see at 1w?

  2. It's more like 93 dB. The slight drop around 20 Hz will often be raised by room gain. Excursion peaks at around 29 Hz at 0.7mm. By contrast the sealed version has 1mm before EQ - 9 db is needed to get it up to 89 dB to match the tapped horn. 8w is needed to get the response up at 20 Hz and then the excursion is 2.7mm. So about four times the excursion!

  3. "29 Hz at 0.7mm"

    Awesome. A much better way that just adding more power and excursion. :-D

  4. To get 89 db from the Exodus Maelstrom 18" in a 250L sealed box you need 6w or just over 1w in a 500L vented box. The sealed box needs 2 kW to achieve 114 dB and so you need 4 kW and two drivers to match the tapped horn. It takes up the same space and you are using more than FIVE times as much power. With a vented version you can match the tapped horn with just under 2 kW and a box around the same size. You get the advantage of a wider bandwidth although the driver is no longer available.

    In a conventional system, it ends up being cheaper overall to get a driver like Maelstrom and use a lot of power, say some of those Sanyway Lab Gruppen clones. Cheaper because you don't have to add another amp and two more woofers. However I like to separate bass and sub bass, using brute force for the bottom octave and high sensitivity woofers. The SGR Illuminator is startling in its dynamic output capability and a big part of that is having each set of drivers cover a narrow bandwidth. They are low sensitivity drivers.

    This kind of setup is ideal for a horn system and for the "musical bass range" above 40 Hz, my system is sealed yet with no EQ boost.

    One thing that is remarkable about this tapped horn is the lack of box vibration due to the dual opposed mounting. The surrounding walls vibrate much more than the box itself, due do the cancellation of mechanical vibration. This is critical for an installed subwoofer. You can test this out by turning off one driver - the output drops by 6 dB but the vibration increases.


All comments are moderated.