I've been scratching my head lately about a whole room suck out I have at 85 Hz with my horn woofer stacks. It's a little louder here and there but overall 85 hz is way down everywhere. 75hz too. So I got to wondering how that can be. How can the woofer be moving without making sound? Could the speaker cone be breaking up? Is the cone not moving for some reason? Is it a cancelation in the horn from the mouth feeding back to the driver? If it were, wouldn't the sound still be somewhere? Where there's a null there has to be a peak somewhere else, right? Not right?
The horns are 6 feet long, bifurcated and folded a few times before joining in a common exit. They've got an 18" Dayton woofer. The throat is 5" x 15" and the mouth is 18" by 20". There are four of them stacked in the corner with their mouths connected vertically.
I had some fun and did some experimenting this afternoon. I took the woofer out of one of the bass horn cabinets and put it in the prototype cabinet, which I happened to still have because I've been too lazy to dispose of it. Before installing the woofer I drilled a hole just big enough to let me drop the measuring microphone right into the throat area. I measured the sound pressure at the throat and also in the back chamber. The results can be seen in the attached graph.
The orange line is the throat, blue line is back chamber. What it shows is that while there is a deep notch in the throat, there's still a lot of sound pressure in the back chamber, which proves the driver is moving just fine and the cone is not breaking up or anything like that.
The next graph shows an average of the room response taken at several locations vs the measurement with the microphone a few feet into the horn, which is about 6 feet long. Notice the huge peak occurring inside the horn at about 79 Hz, right between the 85Hz and 75Hz nulls in the room measurements. There's the dip at 90Hz which corresponds to the dip measured at the throat but strangely that frequency plays in the room.
I've also included spectrograms for the measurement 3 feet inside the horn and another one 3 feet away from horn in room.
Also the REW file is attached if anyone is interested.
I'm trying to figure out if there is something tricky I could do to smooth things out. Could an FIR filter maybe do something better with this than my current IIR filters can?
You can see in my pictures that I tried putting some poly fill in the back chamber and in the throat, and stuffing a cushion into the mouth to see what would happen. The poly fill did practically nothing. The cushion caused the deep notch to become wider and not quite as deep.
The horns are 6 feet long, bifurcated and folded a few times before joining in a common exit. They've got an 18" Dayton woofer. The throat is 5" x 15" and the mouth is 18" by 20". There are four of them stacked in the corner with their mouths connected vertically.
I had some fun and did some experimenting this afternoon. I took the woofer out of one of the bass horn cabinets and put it in the prototype cabinet, which I happened to still have because I've been too lazy to dispose of it. Before installing the woofer I drilled a hole just big enough to let me drop the measuring microphone right into the throat area. I measured the sound pressure at the throat and also in the back chamber. The results can be seen in the attached graph.
The orange line is the throat, blue line is back chamber. What it shows is that while there is a deep notch in the throat, there's still a lot of sound pressure in the back chamber, which proves the driver is moving just fine and the cone is not breaking up or anything like that.
The next graph shows an average of the room response taken at several locations vs the measurement with the microphone a few feet into the horn, which is about 6 feet long. Notice the huge peak occurring inside the horn at about 79 Hz, right between the 85Hz and 75Hz nulls in the room measurements. There's the dip at 90Hz which corresponds to the dip measured at the throat but strangely that frequency plays in the room.
I've also included spectrograms for the measurement 3 feet inside the horn and another one 3 feet away from horn in room.
Also the REW file is attached if anyone is interested.
I'm trying to figure out if there is something tricky I could do to smooth things out. Could an FIR filter maybe do something better with this than my current IIR filters can?
You can see in my pictures that I tried putting some poly fill in the back chamber and in the throat, and stuffing a cushion into the mouth to see what would happen. The poly fill did practically nothing. The cushion caused the deep notch to become wider and not quite as deep.
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BassHornInisdeAndOut.mdat.zip773.2 KB · Views: 120
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