Hello!
I am building a simple, cheap-o sub, something to cover the 35-100 Hz bandwidth. I am using the following speaker, Onkyo W20170A:
8 inch
Qms: 3
Qes: 0.372
Qts:0.331
Fs: 39 Hz
Vas: approx. 59 liters
Power rating: 30 W
I have placed it in a ~33 liter enclosure, with a 7.5 cm diameter vent, tuned to 35 Hz. Earlier it was tuned to 28 Hz, but there was a significant loss in power handling. Now I have tuned it to 35 Hz, there is an enormous hump (audibly) on about 33-34 Hz, and a huge loss on everything between 38-53 Hz.
Given the low Qts, should I tune it higher, like at Fs, or is there another issue? It seems what's happening is what you call "loss of headspace" for the bandwidth between the vent resonance and the -3 Db point at 55-60 Hz. Ideas?
Thank you in advance.
I am building a simple, cheap-o sub, something to cover the 35-100 Hz bandwidth. I am using the following speaker, Onkyo W20170A:
8 inch
Qms: 3
Qes: 0.372
Qts:0.331
Fs: 39 Hz
Vas: approx. 59 liters
Power rating: 30 W
I have placed it in a ~33 liter enclosure, with a 7.5 cm diameter vent, tuned to 35 Hz. Earlier it was tuned to 28 Hz, but there was a significant loss in power handling. Now I have tuned it to 35 Hz, there is an enormous hump (audibly) on about 33-34 Hz, and a huge loss on everything between 38-53 Hz.
Given the low Qts, should I tune it higher, like at Fs, or is there another issue? It seems what's happening is what you call "loss of headspace" for the bandwidth between the vent resonance and the -3 Db point at 55-60 Hz. Ideas?
Thank you in advance.
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Sounds like a room issue. Try putting your sub at your listening position, and crawling around on the floor (with music playing) to hear where it all comes together.
Once you've found the right spot, put the subwoofer there and return to your listening position to enjoy the music.
Chris
Once you've found the right spot, put the subwoofer there and return to your listening position to enjoy the music.
Chris
Just double checking your ports; were they approx 45cm (28hz tune) and 27cm (current 35hz)? A crude sim says you should have gained a decibel-plus between 31hz and 100+hz with your new tuning, not lost anything.
As presented it 'sounds' like the specs are bogus with a hump appearing around the higher tuning; if a room problem the dip would be in the 28 Hz tuning also.
GM
GM
Thanks for all the feedback.
I have tried repositioning the sub, and it helped a bit. Regarding the specs, I have measured them myself using the rig and instructions from this site:
Measuring Loudspeaker Driver Parameters
Regarding a hump in higher frequencies, yes, there is a huge one at about 64-65 Hz.I think the room positioning may have been the problem, the 28 Hz tuning check was in another room. Will try moving it there later to see if the issue disappears. I am sure the port tuning is as instructed, I tried some sims that gave me a vent size 25% longer than the needed one, I later checked it with a sine wave generator and the old poor man's method of laying the speaker on its back, putting some rice/sand in the cone and finding the point where the speaker movement is at a minumum, right now it's 34-36 Hz.
I have tried repositioning the sub, and it helped a bit. Regarding the specs, I have measured them myself using the rig and instructions from this site:
Measuring Loudspeaker Driver Parameters
Regarding a hump in higher frequencies, yes, there is a huge one at about 64-65 Hz.I think the room positioning may have been the problem, the 28 Hz tuning check was in another room. Will try moving it there later to see if the issue disappears. I am sure the port tuning is as instructed, I tried some sims that gave me a vent size 25% longer than the needed one, I later checked it with a sine wave generator and the old poor man's method of laying the speaker on its back, putting some rice/sand in the cone and finding the point where the speaker movement is at a minumum, right now it's 34-36 Hz.
OK, then my 28 Hz comment is moot for now and measurement done same as all the one's I've done, so fine by me 😉. At this point, the only thing comes to mine is there's a minor leak that didn't show up in finding Fb that causes a double tuning of sorts and what I started to 'knee jerk' post initially......and it can be truly tiny, to wit, I've had leaks around machine screws threaded into T-nuts!
GM
GM