Getting good sound quality below 200Hz

@bumpy48, I'm taking it that your listening experience is related to playing full range music but without the higher frequency drivers connnected. If that is the case, then I'm not sure that the listening experience will be that useful since the majority of bass instruments have harmonics way above the 200hz. That's precisely why there is a disjunction between what you hear when playing the bass drivers alone and then playing full range. You could get a synthesiser and play some sinewaves in the chosen frequency range but that won't be particularly educational either, I think.

Yoyoyaya  Looks like you are right about this, but it was a surprise to me and I needed a reality check.

I tend to agree. It’s as if you’re trying to fix what may not be broken. Without hearing the range of frequencies the instrument produces, it will never sound right. A bassist plucking the lowest note on the instrument cannot be reproduced if frequencies above 200 are excluded. 

The frequency response chart is from a test infinite baffle.  It is not as good an indicator as the response for the speaker in cabinets so please look at the fr in the PDF.

Having said that, the example cabinets say if you try to use this in the home you are going to need a lot of EQ to get to neutral, and that brings us back to measurements. This is a speaker with a lot of tone for stage performance.

A few things.... In general, listening to 150 to 250 hz alone sounds like mud. You are listening to the highest bass regions or more arguably the lowest midrange frequencies. Thanks to @pedroeb for posting a link to the driver. This driver has a QTS of 1.26, that alone tells you that this woofer is ideal in a huge sealed box or free air situation, but also, this very high QTS also tells a story of how this driver can react. Also, you are correct about the graph.  That spike is huge, but crossed at 200hz at 24db per octave that driver is down near 100db by the time it reaches that spike. 

So a few suggestions. Make sure that you use an amplifier with great control over your woofer, it doesn’t have to be tons of power, but most likely should be. You are after an amplifier with good current capabilities.

Placement is critical, this woofer will respond to boundries in the 200hz range like few others. Distance to the floor and rear and side walls all matter.

I suggest that you download Room EQ Wizard software. It is free and works fairly well. I’ve seen it said a few times in this forum to measure speakers very close to the driver. in this case, measure from the seating position first, then move the mic closer to the speakers up and down and side to side and look where your boundries have peaks or dips in the frequencies that you are concerned about. Also look for a hole right above 200.  You do not need a crazy expensive mic, the idea hear isn’t to get accuracy to a tenth of a db, plus or minus 1db will give you a look at what you are dealing with. I suspect that you are dealing with your room. .