Emerald Physics BOM Bass Manager

Works excellent if you need to improve bass response.  Unit shows no sign of wear. 

Will ship for free to lower 48 contiguous states and cover paypal fees.

From website:

The Bass Optimization Manager (BOM) is a very high quality fully adjustable 4-pole Linkwitz Transform Function analog bass 

equalizer. It is designed to tailor the bass response of any speaker by adding 

an addition 10-20Hz of low bass and tailor the amount of bass from the speaker 

to match your rooms acoustics. You use two of the pots to enter the 

"Q" and "Fs" resonance (more or less the -3dB point) of 

your speaker. Then, you use the other two pots to dial in your target 

additional bass (Q) and output (expressed as boost). The EQ changes 

the woofer output from your actual curve to the target curve.

It can go between your amp and preamp, in a tape loop or between a source, like a DAC, and your integrated amp. 

The BOM works with any speaker and can add an extra 10-20Hz of low bass and offers level adjustment of that bass. Use it with Emerald speakers or any other brand for improved bass performance.