The different projects

9/16/12

Horns in the home "Kuben" (Klipsch LaScala bass bin)

I got these very  solidly built speakers build according to the article below. Very skilled carpenter but less experienced as a loudspeaker the builder was. The 12" bass driver was mounted flush on the backwall of the chamber (as per the drawings). For this particular driver it meant that the driver or surround would hit the MDF at the slightest cone motion. This was sorted out by adding a subbaffle with a cicular cutout of 270mm now the cone can move 12mm. I also added some crossbraces for the sidewalls of the horn opening that vibrated quite a bit. I also added corner reflectors in the corners and in front of the driver.

As I have a selection of 12" drivers at home I decided to try them all out. First out was Beyma G320 a 10 kg monster of pro driver.  Built for midbass hit has very low Qes and quite high Fr.
The beyma has quite drooping bass but very good midrange exension, this blue trace is shown in all the other graphs as reference. Measurements were made using XTZ Room Analyzer II, microphone at 80 cm distance on axis and with the horn propped up on a 50 cm high table (to reduce early reflections)

Next up is the Fane Crescendo 80W, an other pro element but with a higher Qes.  Notise the incease in bass output
 This is a vintage bulgarian Gamma LA-1231, low Fr mid Qes and very large Vas. Much lower sensitivity than the pro drivers. More extended bass but also a hump at cutoff.  Midrange output is way beyond what you expect  with a calculated mass roll off  below 200 Hz
 Isophon 30/37A a vintage alnico driver and a classical horn driver shows a very flat response from below 250 Hz to 1250 Hz
 MGR30P40 a new budget driver does surprisingly well with good output from below 63 Hz to 500 Hz or so. Calculated mass roll off is 156 Hz, usable range is much higher.
 Finaly the old Seas 30FA, this is a 15 Ohm driver so the sensitivity is really 3dB higher. It is very similar to the Fane driver

I have 10" bass drivers with what I thought was good slam, but horns are something else.  Now I am thinking about building a pair. With some twist and turns of course. Just the basshorn is 40 kg adding top and driver the Klipsch La Scala is 78 kg, this is way to much in my taste. Replacing the MDF with 12mm plywood would cut the weight in half but it would also be to flimsy, a lighter structure either require a very different layout or fancy material that is both light and stiff.

I am sure that the midrange output can be affected a lot but changes in throat geometry, subbaffle thickness and so on. But I think some general conclusions can be made.  For maximum over all output PA drivers are what you need. However, in a domestic setting were the demand for output is far less HiFi drivers might be better. The PA drivers tend to fall of in the low range.

The low pass frequency is way higher than the mass roll off that LP=2 x Fr/Qes. This does not mean that it will sound good to 1 kHz just beacuse it has output to that range. Other have found that simulation of drivers with modest BL work really well in this horn http://www.linnaraudio.com/simuleringar/kuben/index.htm

One way to tame a horn driver with to low Qes for the particular application is to add some series resistance.
Adding 0.7 Ohm as in an average crossover does not change much

 Adding 2.2 Ohm as in a really budget crossover, will supress the 100-500 Hz range a bit, in effect bringing up the bass peak a little bit
 3.3 Ohm more of the same
 4.7 Ohm still more of the same
 8.0  Ohm now it looks more like the Gamma driver.  I would prefer to use equilizing to lift an overdamped prodriver, but connecting a series resistor and try it out is easy.

These Thiele-Small parameters suggest a closed box in the 60-100 range, marginal for bass reflex and absolutly not a classical horn driver.


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