How to Improve the Sound Quality from TTS Decoders.

[RDS]

I've just fit another a4 tts decoder to hornby a1 great northern (with the small tender with separate coal bunker,which limited my ability to use a tube enclosure).

i used the standard 28mm speaker & enclosure, face down, heavily sealed with blu tack, and drilled loads of holes in the chassis and coal bunker partition, and lined out the whole lower part in 5mm lead (total weight 65g to replace the hornby metal weights). 

The sound quality and volume is twice as good as most of my other tts loco's, on standard vol 4 it is nearly as loud as vol 7 on a large bass reflex i have in another loco!

just shows what can be achieved with the standard tts speaker & enclosure, but it took alot of time! Well worth it to get such rich sounds from a small tender.

[Fishmanoz]

Good one Percy, should be useful to others. 

 

For the non-audiophiles amongst, a bass reflex speaker design is one where a port or open tube is included in the speaker box.  This device, if designed properly, improves the low frequency response and efficiency below what can be achieved with a sealed speaker cabinet, or allows the use of a smaller box for the same frequency and efficiency. Put simply (and it's not actually simple), by the time the sound has come from the back of the speaker and travelled through the box and port, it reinforces the sound coming from the front of the speaker over a range of low frequencies  

 

However, physics is certainly working against us with any speaker that will fit in a tender. If you look at the speaker Percy has used, you'll find it has a resonant frequency quoted at 330Hz plus or minus 60Hz.  In other words, it makes things better from 270-390Hz, hardly bass frequencies(down to 20-30Hz) but certainly low. Then below that range, the response will drop like a stone. 

 

But it lets not knock it, Percy reports a significant improvement over a simple design, so worth considering. 

 

PS.  CS, if you are reading this and google bass reflex, you'll find one of the pioneers in bass reflex design is almost my namesake. Not only that but he tutored me at Sydney Uni back in the 60s. Weird guy, but certainly knew his speaker design.