Exactly, blue; you just described it much better than I did. 

Jurgen, I knew you were really saying the same thing but thought I would clarify in case there were others that didn't know.

Interesting.  If any audio engineer/modellers are out there, maybe they can answer that one.  I would imagine that if there were merit to the idea Soundtraxx or QSI would be looking into it.

The biggest stumbling block for model locos is literally wavelength.  The length of a soundwave produced by the bass rumble of a diesel prime mover is several times larger than the largest speaker we can put into a loco model; the best we can get out of a model is a "chopped" partial bass wave; that's why it's never deep or intense enough.  We need some Star Trek technology to invent a virtual speaker that can be bigger than our models.  Well, I suppose if we were able to produce a realistic rumble, it would just shake our trains right off the track anyway...

Rio Grande Dan, worked for Infinity I think.  Perhaps he can shed some light on the subject as well.

That first paragraph of the wiki info is spot on the money I think.

I red the wiki post and it actually doesn't apply to the little speakers in Model Trains. alot of what they're talking about is for large room or car stereo speakers and sub-woofers and looking for that heavy THUMP THUMP you achieve with the Big speakers. In a 2 in speaker it's basically imposable to move that much air. So in order to achieve the lowest Independence on a 1-1/2 inch to 2-1/2 in speaker it's needed to be done by isolating the movement of air and lower the Independence with capacitance response. This is part of the secret to Bose Speakers and their ability to achieve symphonic sound with 4 inch tuned enclosed and face to face baffles where they have two speakers in opposite response one pushing and the other pulling and working together to produce the Big sound with small speakers. I've seen a couple of the new DCC sound systems like soundtrax is designed this way but use only one speaker in an unclosed air tight in the back non ported speaker box to try to get the best base response they can with what they have to work with. In the late 1970's I worked for Infinity Systems and that's one thing we did in the Lab was play with resistant sound and ended up building the Quantum Tweeter a speaker with ultra high frequency sound with no baffle or moving parts and those sucker screamed, They still own that patent. Now Bose went the opposite way and went with the Mini woofer system and found you don't need a 16 inch woofer to get the big sound by using reverse reflect and tuned Paper tubing with 4 inch woofers and as they increased the capacitance they decreased the frequency to produce very low frequency speaker enclosures and achieved BIG DEEP sound with little speakers. If you want a deeper bass sound you need to play with the enclosures and increase or decrease the Capacitor size and Micro-Ferrite value to achieve the Deep Bass. But remember your still only using a 2-1/2 inch speaker or smaller to try to get the sound from and in my opinion until you can move a sufficient amount of air your not going to get a deep Diesel Motor or horn sound. But you may come close to at least what will satisfy you somewhat.

Dan

One last thing about Bass reflect is,- The best speaker box would be made of solid concrete and the space behind where the speaker is attached would be exactly twice the volume of what the speaker cone would travel. so if you have a speaker box around your speaker stuff some cotton balls in side it before adding the speaker and put it in you engine and see if it doesn't help the reflect sound. Don't stuff it solid or pack it just put two or three in the box and then put your speaker back in and run the train see the difference or listen to the difference if you like the deeper sound leave them in.

Dan

An interesting feature of small speakers attempting to produce large volume levels of sound at low frequencies is that when the diameter of the speaker becomes small related to the wavelength of audio frequence being produced, the volume level becomes proportional to the velocity at which the speaker throws rather than the travel of the speaker code. As frequencies get lower (like for a major prime mover) the throw of the speaker cone get get pretty horrendous. Even with larger speakers than anythng that can be shoehorned into HO equipment you may find speakers trying to move their cones back and forth up to an inch at the lowest frequencies! Yikes that's a long distance and seriously impractical in a 1" speaker...

Another thing comes into play when speakers are in amplitude is proportional to peak cone velocity is doppler effect. This is especially prevalent in single speaker design where all frequencies are covered by a single speaker cone. The large excursions of the cone to provide volume at low frequencies are moving the source of the higher frequencies (the cone) closer and further away from you the listener. This causes the high frequencies to change apparent pitch through the doppler effect (the thing that makes a hi-speed train seem to drop in pitch as it passes a fixed, track size observer.  The doppler effects can generate a substantial amount of undesirable frequency (shift) resulting in a high degree of distortion. Unlike harmonic distortion where the distortion frequencies match up with the original frequencies, the doppler generated frequency sidebands are unrelated frequency-wise. This produces a sort of audio mud.  The only ways around this are to use different speakers to cover different parts of the frequency spectrum (another reason why hi-fi speaker systems often have 2 or 3 or more speakers in them) or to use a big enough speaker to minimize the speaker cone velocity needed to generate the desired amplitude. Neither of these are practical in HO equipment.

And we wonder why HO locos sound 'tinny' compared to the prototype!

FWIW

Charlie

... Steve, let us know how those CV tweaks, etc, worked out for you.

The CV tweaks did help get some of the actual "sounds" I was looking for, but it appears there's no help for the 'tinny' sound Charlie mentioned.

Dan mentioned sub-woofers.  In the TV Surround Sound world, a sub-woofer can sit in a corner of a room to handle all the bass.  It's not directional; it can be heard (and felt on occasion) no matter where you are.  If DCC had a sub-woofer output, to fill the room with the very low end sounds while the locos provided the treble, I'll bet the combination could be awesome.  Maybe it wouldn't work so well if many locos are working at once... but then again maybe it would!

We have decoders for locomotive, turnouts, and other accessories, now I'd like someone to pursue a sub-woofer decoder so we can check it out!!

While reading Charlies post I had the same sort of thought.

What if a decoder could send a wireless audio signal to a receiver/sub woofer located under the layout?  Now, if there are multiple Locos operating maybe that doesn't work...but maybe it could work too?

Could you just consist the under-table decoder (for the sub-woofer) with your loco(s)?