I’ve been doing a lot of research on sound in model railroading lately, since watching these Tang Band speaker videos. I’ve been measuring frequency responses of different speakers, models, and scales - including the prototypes. Obviously we know that it is very difficult to get true low bass frequencies due to the small relative size of our models, but what does “bass” really mean?
I’ve analyzed the low frequencies of several prototype diesels and steam engines. In general most diesel prime movers have a low rumble right around 40-50 Hz. This is true bass that you can feel as well as hear when you are standing near the engine. Steam engines also have many different sounds that drop below 80Hz.
So what does this mean for our models? In general terms I have found a large discrepancy between “average” and “best” in the different scales. Example, it seems that most casual listeners make comments about “good low end” when they hear tones ~500Hz.
The interesting point about that is 1. 500Hz is obviously far off from what the prototypes are doing and 2. 500Hz is actually achievable from O all the way down to N. Factory speakers in O will get to ~400Hz pretty commonly. Factory HO speakers like Intermountain uses with LokSound decoders get to ~500Hz then roll off. Factory N scale cell phone type speakers, believe it or not, are not far off of HO in the 500-600Hz range.
What about “best” type install? I have been able to get down to and below ~100hz with Tang Band speaker modules in O scale, as have others. This is significantly better bass than many aftermarket installers are getting with “high bass” speakers. The best HO installs I’ve found have good response down to ~300Hz which is close to factory O installs. Those installs tend to use cell phone type speakers, which happens to be what the best N scale installs use as well. So I guess it shouldn’t be a surprise that the best N scale installs I found use two cell speakers and get down to ~350-400 Hz.
So what does this all mean? I think it shows that there is a lot of room for improvement in bass response in all scales over the factory speakers. It also means that if you can basically “move up a scale” by upgrading. I was most impressed by O with Tang Band and N with cell speakers. N can really be made to sound about as good as HO. Of course if you want the best relative sound O scale wins. There is a big difference between sub 100Hz and 300Hz on the low end.
I’m working hard to see how close to 50 Hz I can get