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A resonance chamber with triple width for the LS1511-type speaker. This is the same type of the "sugar cube" speaker used in model trains by Zimo and ESU. A LS1511-speaker can be ordered at Doehler & Haass and can be used with the currently available decoders from Doehler & Haass, ESU and Zimo.
Use of this resonance chamber gives an even better representation of bass-sounds than the double resonance-box version.
The resonance box can be glued (I personally prefer kristal klear) to the speaker. Make sure you'll have an air-tight seal between the speaker and the resonance box for the best sound.