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Soundtraxx Sugar Cube speakers

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KPack:
I haven't been too impressed with the 4s speakers, which is why I ended up doing sugar cubes.  I thought those were great until I used Scale Sound System speakers (their duel CoEval) which were a night and day difference.  He stopped producing the Coeval line and now has a new speaker which I haven't tried yet.  I'm curious to see how it stacks up.  Now I'm experimenting with high-bass self enclosed speaker systems by TB Speakers.  They are huge and a pain in the rear to install, but they have by far the most bass I've heard from a speaker that can fit in HO scale.

Settings to adjust bass (an equalizer) is great and all, but the limiting factor here is the speakers.  Most speakers of this size are unable to play bass notes in any way close to what we would like.  So changing the settings to add more bass won't make a difference if the speaker can't play it.  The enclosure that the speaker is housed in, as well as the path for sound to exit, can help to some extent.  But still, a speaker that is only capable of playing notes above 200Hz will only be able to play sound above that level no matter what you do to it.  You need to find a speaker that is capable of playing sounds lower in the spectrum if you want more bass.

Lastly, some sound files are recorded with more bass, and some have less.  The 567 ULT does have bass (my TB speakers bring it out), but the exhaust is very prominent, drowning out some of the lower sounds.  Other sound files like the GE 7FDL-16 have more prominent bass within the recording itself.

-Kevin

Alan:
Kevin is spot on about speakers having limits.

The primary lower limitation is resonance frequency. Sound pressure (volume) rolls off rapidly below a speaker's resonance frequency. Resonance frequency is mostly dictated by mass which is dictated by size. All things equal, a 12" speaker will have a lower resonance frequency than a 6" speaker because it has more mass. Greater mass gives a lower resonance frequency which gives the speaker the ability to reproduce lower notes. That's why woofers are big speakers and sub-woofers are really big speakers.

A Helmholtz resonator is a method widely used to get just a little more low end out of a speaker.  Often called "tuned port" or "bass reflex" a Helmholtz resonator is a specific cabinet design that resonates at a frequency slightly below the speaker resonance. This effectively adds a little bit of volume to the bottom end. The drawback to a Helmholtz resonator is cabinet size. It is quite large compared to sealed enclosures. I suspect the big cabinets Kevin is installing may be ported enclosures.   

Here's a novel way of thinking about it... Look at the diameter of the exhaust pipes on a locomotive diesel engine. There is your minimum required diameter speaker. Exhaust pipes have resonance frequencies too! Clearly these folks have figured that out.





Sorry, expecting such tiny speakers to reproduce anything remotely close to real train sounds is tilting at windmills. However, I wish you all the luck in the world trying. Any improvement is an improvement.

KPack:
For reference, here's what I've been experimenting with.

TB Speakers T0-2008S: http://www.tb-speaker.com/products/t0-2008s

TB Speakers T1-1925S: http://www.tb-speaker.com/products/t1-1925s

The above speakers are an enclosed system with a passive radiator to effectively double the size of the speaker cone.  The smaller of the two has a bass frequency of 200 Hz, and the larger is 150 Hz.  They are difficult to install due to the size, but I have not found anything that offers as much bass as these two.  Video recording unfortunately does not do a great job at capturing how it sounds in person, but you can watch the end of this video to get a comparison between different setups:
What the camera can't accurately capture are the bass notes.  The locomotives actually vibrate when the prime mover is on.  The one thing I haven't loved about the above speakers is the sound level.  I typically have my sound low, but in a noisy place these speakers don't put out a ton of volume.  Not a huge issue for me, but others might want more volume.

-Kevin

Alan:
Lower sound level from a passive radiator system is to be expected. The passive radiator cone increases the total moving mass which lowers the system resonance. That's good. Except the magnet and voice coil hasn't increased proportionally hence the lower volume. You have more mass but it is being moved by the same original motor. Given that you are working with 1/2" diameter voice coils, you can't simply pump more current to compensate. There isn't much voice coil area to dissipate a lot of heat.

They show the system resonance (Fs) as 200Hz. That's impressive for such a small unit. I have no doubt they sound better.

I also noticed their system response is eerily close to human speech range. No wonder they recommend it for soundbars.


https://www.dpamicrophones.com/mic-university/facts-about-speech-intelligibility

KPack:
Thanks for the info Alan.  Makes sense now why the volume is lower.

I'll be experimenting with these some more.  Good quality products (made in Taiwan) and lots of options.  I may try out one of the larger sizes than what I have linked to above, if I can find a way to shoehorn it into a locomotive. 

-Kevin

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