Setting up REW to measure MIDBASS and speaker response at +100dB. I am running in to issues?

[CustomSpeakerPods]

Hello everyone again!!! I am back at the project of measuring SPL midrange speakers for use in car audio. I have 2 main goals:
1. To determine the best possible driver to produce the most powerful midbass response when installed in my speaker pods.
2. To determine how different SPL type speakers (DS18, PRV, Sundown, etc) perform at high/rated power (100, 200W, etc.) And to determine if any of that is really necessary in a vehicle with a +150dB sub stage.

I'm not sure if I am out to disprove/prove anything, but my current 'feeling' is that you need to have the correct driver to get more midbass, and no amount of door treatment will eliminate the fact that a door is an infinite baffle. Also, even if a speaker is rated for 200 watts RMS, it will not perform well at that level, and furthermore, if you do not set up your system properly at those levels you will damage your equipment due to the limitations of the speakers at those power levels (exceeding Xmax at lower frequencies).

My current testing setup is as follows:
OUTPUT: PC connected to M-Audio M-Track SOLO > RCA to Amplifier (DS18 G1800.4D)
Measurement: UMM6 USB microphone placed 1m away from speaker face
Enclosure: ~5 cubic foot MDF box with removable speaker baffles for testing different size speakers

I have calibrated REW to match the output voltage of the amplifier: 0dBfs = 20V. Microphone input level (windows setting) 30.

Everything seems to work properly, except I am seeing a strange artifact in my distortion graph: vertical line at 65Hz, consistent in all measurements. Where do I start with troubleshooting this potential issue?
Thanks, B

 

[staticV3]

Could you show the distortion in absolute terms, not relative to the fundamental?

Like this:


Currently, it is unclear whether the rise in relative distortion stems from a rise in absolute distortion or a fall in fundamental.

 

[CustomSpeakerPods]

Could you show the distortion in absolute terms, not relative to the fundamental?

Like this:
View attachment 403207

Currently, it is unclear whether the rise in relative distortion stems from a rise in absolute distortion or a fall in fundamental.

I may have had something funny going on with my Impluse settings?
This is response and distortion of a Kicker CS65 coaxial at 2.8v

 

[staticV3]

I may have had something funny going on with my Impluse settings?

Not sure what you mean by impulse settings.

This is response and distortion of a Kicker CS65 coaxial at 2.8v

Those graphs look ok, nothing suspicious there.

 

[CustomSpeakerPods]

Not sure what you mean by impulse settings.


Those graphs look ok, nothing suspicious there.

Impulse settings are to 'reduce measured reflections'... I think. i saw it on a video at some point.

 

[staticV3]

Impulse settings are to 'reduce measured reflections'... I think. i saw it on a video at some point.
View attachment 403214

These are set to default, so again nothing wrong there.

 

[CustomSpeakerPods]

These are set to default, so again nothing wrong there.

I believe I fiddled with them when taking my previous measurements. Thank you again!

 

[Randyman...]

Regarding mobile midbass drivers:

Stereo Integrity TM8's are specifically designed for high-performance midbass in auto installs (doors). Has an integrated rain guard to boot! It's a more appropriate driver for a door/IB than a high-end 9" Morel Elate (had those in a previous install), and less than 1/2 the cost (S.I. is manufacturer direct). I think he makes a 10" now as well. These drivers are extremely high quality, and I love my TM8's! $500/pr - currently on sale for $400/pr (same as the pre-order price I got over a year ago!)

Of course you likely know about vehicle dimensions and midbass cancellations with door-mounted drivers that are very had to counter (unavoidable physics). But these TM8's are kicking with 150w and some fairly deadend/selaed doors and doorcards, and might bump them to 300wrms like I did with the Morel Elates.

TM8 – StereoIntegrity.com

stereointegrity.com