Quantum HB Speakers
In our continuing effort to provide the best model railroading sound options we have been searching for and evaluating speakers in the HO size realm to find units that would produce more bass response - and we succeeded. These are now in stock at our primary distributor, American Hobby Distributors. Have your favorite dealer contact them.
Pictures
Review of QSI Solutions New Small High Bass Speakers for HO Sound Applications
by Larry Maier
8-23-07
Today’s sound decoders use digital technology similar to that found in CD players to store and reproduce the sounds associated with our favorite engines. The original recordings are usually reasonably well done, and the digital technology allows the recordings to be stored and played with a quality that is very close to the original sound. Indeed, listening to the output of one of today’s top sound decoders through a good set of headphones can be just like standing inside the engine compartment of a classic or modern diesel (standing inside the steam chest of a steam engine is probably not a good idea).
While the quality of the sound at the output of the decoder is quite good, it must somehow be coupled into the surrounding air to create the sounds waves that we hear. There is the weak link in the system: the speaker. Unless you operate one of the larger gauge models, there is probably only room for maybe a 1” speaker (or smaller) in your model. In speaker theory, there is a frequency, designated Fs, that is the free air natural resonance frequency of the speaker. The critical information related to Fs is that the speaker is physically unable to reproduce any frequency significantly lower that Fs. Thus, the lower Fs, the lower the minimum frequency that the speaker can reproduce and the more bass. Fs is determined primarily by the moving mass of the cone and the stiffness of the suspension. Small speakers have a small cone, and therefore a small cone mass, and normally have a relatively stiff suspension so that the speaker cone does not move too far and damage the cone. The net result of this design is that most of the speakers used in model train sound reproduction have a relatively high Fs and are therefore are unable to reproduce the low sounds associated with “diesel rumble” or the throaty sounds of a steam chuff. Even worse for the model sound enthusiast is that when you place a speaker in an enclosed baffle (such as an engine car body or other small enclosed space), the value of Fs increases due to the stiffness of the air trapped behind the speaker (note that you do need the baffle, because if it is not present, the sound behind the speaker will simply flow around the edge of the speaker and cancel the sound in front).
QSI Solutions has found a speaker that significantly improves on the existing situation. It is shown in the picture below:
Notice that the speaker has a very thick, rolled section supporting the cone, and that the cone is metalized. The rolled suspension results in a very “floppy” cone suspension system. The metalized cone increases the cone mass and keeps the cone stiff enough to reproduce high frequencies. The result of these two design features is that the Fs of this speaker is much lower than conventional model sound speakers. In addition, the “floppy” suspension allows more cone movement which means it can move a larger volume of air at low frequencies than conventional speakers. For the user, these features translate into louder reproduction at lower frequencies than with conventional speakers, assuming the same speaker installation for both speakers.
The response of the new speaker is shown below:
The response curve shows that the Fs is at 310 Hz, so the speaker has full output at this frequency and a useful output to about 150 Hz (-10 dB). For comparison, the curves for a 1" and 1.1" standard speaker are shown below:
For both of these speakers, Fs is in the 520-560 Hz range with useful output to about 275 Hz (-10 dB). In other words, the new speaker gives you an additional octave of output at the low frequencies for the same mounting and baffle configuration. While this does not count as the “deep bass” you see in advertisements for sub-woofers, it does add considerable depth to the sound of your favorite locomotive.
A further benefit is that the new speaker is rated at 2 watts continuous and 4 watts peak. Standard 1” speakers are typically rated for .2 to 1 watt. Since most of the energy in locomotive sounds is in the lower frequencies, this means that you can drive the new speaker harder without distortion, again producing more useful output in the low frequencies.
OK, so what is the down side to all of this. The new speaker is thicker than standard units to allow more magnetic structure and more cone movement. It measures about 0.45 inches thick compared to about 0.21 inches for other units. In some installations, this extra space may be a problem. If you have the space, however, the new speaker will definitely improve the sound of your locomotive.
My first use of this unit was to add sound to a Walthers, Proto 2000 PA1. I was very pleased with the sound of the finished locomotive. There is a definite low frequency thump of the piston moving exhaust gases out of the cylinder. And there is a clear click of the characteristic diesel fuel ignition.
