Tuesday, January 12, 2016

New Folded Corner Bass Horn: Why? It Is An Acoustic Amplifier!

Why would anyone need a bass horn?  Why not just drive the speaker directly with lots of electric power?  Simply put, the horn provides considerable gain so you can use a much smaller electrical amplifier.  Another way of putting it is that you can have a smaller electronic power amplifier because you already have a pretty large acoustic power amplifier.  The result of having this acoustic amplifier is that the speaker driver does not have to work nearly as hard while horn-loaded.  The benefit of not working so hard (as a direct radiator would have to do) is that you get cleaner, louder, more undistorted bass than you can ever get with the same driver as a direct radiator.

To get a comfortable listening level in my small listening room, I have found that all that is required is a power input of 100 microWatts.  In fact, Hornresp predicts a one-meter sound level of 70dB at 0.0234 Volts (23.4 mV) rms input.  This does indeed correspond to a power input of only 0.0001 Watt, or 100 microwatt.

In addition to working amazingly well at the microwatt level at home, it appears as if the acoustic amplifier that this horn is would work well anywhere you might need very high levels of clean, undistorted sound.  For example, the combination of the New Folded Bass Horn with Tymphany FSL-1225R02-08 driver would work especially well in a large room or outside where the average power input level could be quite a bit higher than it can in my small listening room.  For example, at the specified voice coil dc resistance of 5.5 Ohms, only 2.34 Volts rms is required to draw one Watt from the amplifier.  However, Hornresp predicts a one meter sound level of 110dB from 35Hz to 400Hz at one Watt input.  As you might imagine, a one-meter 110dB sound level would be way too loud in the home environment.

How much gain does the New Folded Corner Bass Horn provide?  Here is a way to find out.  Tymphany rates the sensitivity of the FSL-1225R02-08 at 96.3dB at one Watt input at one meter as a direct radiator.  Loaded with the New Folded Corner Bass Horn, the average one Watt one meter sensitivity predicted by Hornresp is 110dB.  At the very least, this amounts to a 13.7dB gain over the same speaker as a direct radiator.  It is more than that as well because the 13.7dB horn gain applies over a bandwidth of 35Hz to 400Hz while the non-horn-loaded rating of the manufacturer applies over a bandwidth that probably does not extend down to 35Hz or even close.

The horn gain of 13.7dB allows you to get the same acoustic sound level from an amplifier power only 4.27% as much as you would need to get the same sound level from the same speaker as a direct radiator.  This is the same as saying that the horn multiplies the electric power put to the speaker driver by a factor of about 23.4!  So, if you have a 5W amplifier and you factor in the horn gain, you will actually have a 117.2 Watt amplifier!  At even higher sound levels, to get a system amplification including bass horn gain of 1000 Watts, you will only need 42.66 Watts from your electronic power amplifier!

Note:  According to the manufacturer, the FSL-1225R02-08 has a 150Watt power handling rating.  Here is a table of predicted one-meter sound level versus power input for the New Folded Corner Horn combined with the FSL-1225R02-08:

One Meter
0.0234 0.0001 70.0
0.0740 0.0010 80.0
0.2340 0.0100 90.0
0.7400 0.0996 100.0
2.3400 0.9956 110.0
7.3997 9.9556 120.0
23.4000 99.5564 130.0

Predicted sound levels are extremely high even at modest amplifier power input levels.  It would be interesting to set a pair of these horns up outside and try them out at an input of as much as one Watt :)

Note:  The bass is overwhelmingly loud and clear through a stereo pair of these horns.  Until you hear it yourself, you will just have to take my word for it :)