I'm hoping this thread is relevant for novice speaker builders like myself.
I've built a 5.8 ft3/96 liter box (35" x 16" x 15") well stuffed box for a 12" Acoustic Elegance Td12h-4 woofer mounted center top and a 4" diameter x 8" long port placed center around 5" from the bottom.
sub box
My close mic measurements from the woofer are fine and from the port, what you'd expect. Together they would suggest a fine response curve.
response curves
At 1 meter, I'm seeing something fairly catastrophic. Blocking the port does not change the response.
The speaker is 10' from the back-wall, and projects into an open floor plan around 50' long. Me and my pocket clio are around 2 meters from the source.
I'm looking for general theories that explain what I'm seeing. Could I have made any novice design mistakes?
Thanks so much.
I've built a 5.8 ft3/96 liter box (35" x 16" x 15") well stuffed box for a 12" Acoustic Elegance Td12h-4 woofer mounted center top and a 4" diameter x 8" long port placed center around 5" from the bottom.
sub box
My close mic measurements from the woofer are fine and from the port, what you'd expect. Together they would suggest a fine response curve.
response curves
At 1 meter, I'm seeing something fairly catastrophic. Blocking the port does not change the response.
The speaker is 10' from the back-wall, and projects into an open floor plan around 50' long. Me and my pocket clio are around 2 meters from the source.
I'm looking for general theories that explain what I'm seeing. Could I have made any novice design mistakes?
Thanks so much.
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At low frequencies it isn't possible to gate the Clio measurements to remove reflections in the room, particularly close ones like the floor and ceiling. You are probably seeing the destructive interference of the subwoofer with its virtual image in the floor. Imagine the floor is a mirror; where you see the reflection of the loudspeaker under test, there is a virtual source (the reflection) which is time delayed to the microphone and sums destructively with the direct sound. If all of the walls and floor and ceiling were mirrors you would see a huge number of virtual sources that contribute to the SPL additively or subtractively at any given frequency depending on the path length differences, and hence phase, at the listening position.
In the olde days subwoofers were measured into half-space by digging them into the ground until the baffle was flush outside in a large open space. Atmospheric conditions frequently played havoc with that approach. In the 1980s I was able to make subwoofer measurements on a large performance stage with a fly tower above. By putting the subwoofer on a small footprint hydraulic lift (normally used for setting lights) I could position the loudspeaker so the closest reflection paths were more than 12 metres long, (i.e. reflecting surfaces >6m away) allowing valid gated measurements down to 30Hz or so.
I am somewhat dubious about the modern measurement method of stitching near-field cone and port aperture measurements together, because neither measures total radiated sound power particularly accurately, so the result is a bit of a kludge. A good sub should never reveal itself as the source of sound when properly integrated into a system. Most commercial HT/HiFi subs fail as far as I am concerned.
In the olde days subwoofers were measured into half-space by digging them into the ground until the baffle was flush outside in a large open space. Atmospheric conditions frequently played havoc with that approach. In the 1980s I was able to make subwoofer measurements on a large performance stage with a fly tower above. By putting the subwoofer on a small footprint hydraulic lift (normally used for setting lights) I could position the loudspeaker so the closest reflection paths were more than 12 metres long, (i.e. reflecting surfaces >6m away) allowing valid gated measurements down to 30Hz or so.
I am somewhat dubious about the modern measurement method of stitching near-field cone and port aperture measurements together, because neither measures total radiated sound power particularly accurately, so the result is a bit of a kludge. A good sub should never reveal itself as the source of sound when properly integrated into a system. Most commercial HT/HiFi subs fail as far as I am concerned.
DC, can't see the images in the OP.
Modern way to measure the bass is outdoor, groundplane. See here;
Data-Bass: Subwoofer Measurements
Modern way to measure the bass is outdoor, groundplane. See here;
Data-Bass: Subwoofer Measurements
Parenthetically, I'm very impressed with the Heil ESS AMT tweeter.
Original Great ESS Heil Air Motion Transformer™ I - LARGE (LIMITED EDI – ESS Speakers USA
There is something going on with ESS management and the products are all sold out... but there is something in the Original Great" moniker they use for the original ESS Heil Air Motion Transformer. It does an amazing job above 1khz. Incredibly transparent, no boxes to build, substantial output. Really extraordinary.
Original Great ESS Heil Air Motion Transformer™ I - LARGE (LIMITED EDI – ESS Speakers USA
There is something going on with ESS management and the products are all sold out... but there is something in the Original Great" moniker they use for the original ESS Heil Air Motion Transformer. It does an amazing job above 1khz. Incredibly transparent, no boxes to build, substantial output. Really extraordinary.
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