frequency response error - hidden high pass?

I have a problem trying to get the frequency response of a diy sub that I built. No matter what I try graph looks like I have a 50hz 24db/oct hi pass on it. I know the sub is flat to 45hz and about 3db down at 40hz - using the sign generator and RTA shows me that, plus I can hear quite well it goes much lower than 50hz.

Testing out doors - tried different mics - different positions - different distances - different drive levels - even other subs. Played with all the settings I could think of.

The data above 50hz looks normal and changes with the variables as one would expect

FYI, I have used REW successfully to tune multi way diy mid-hi boxes - worked out great.

Ah, thank you so much for reply. As soon as I can I will (later today).

John Mulcahy said:

Can you post an mdat file?

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Ok, my apologies, I jumped the gun. Something in my method or hardware is giving me inconsistent results.

I am starting over on measuring this diy sub. I will post when I have a clearer question.

Thanks.

ddude003 said:

Hi justthisguy, It would be helpful if you were to describe your DYI sub... Make and model of driver(s), sealed or ported, active or passive... Dimensions of enclosure and if active make and model of Plate Amplifier/DSP device...

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Yes, thanks. I must be more methodical. I will post the requested details asap.