Hi guys,
Re-arranged the bass reflex design from a 6" round port 11" deep to a 2 by 18" rectangle port 13" deep. A simple pink noise test with mic at the port shows a secondary peak at around 400hz, close to the 1/4 wavelength of the port. I never noticed that in the round port.
How does someone fix that?
Thanks,
SCott
Re-arranged the bass reflex design from a 6" round port 11" deep to a 2 by 18" rectangle port 13" deep. A simple pink noise test with mic at the port shows a secondary peak at around 400hz, close to the 1/4 wavelength of the port. I never noticed that in the round port.
How does someone fix that?
Thanks,
SCott
Yamaha has an expired patent on a small Helmholz resonator placed somewhere along the vent (opening connected to the vent) which is aiming to counteract vent resonance. Never tried it, so don't know if it works.
In general, I try to keep the cutoff frequency for the bass driver before the first pipe resonance. If this doesn't work, the only option is to decrease the diameter of the vent and shorten it. Or live with it.
In general, I try to keep the cutoff frequency for the bass driver before the first pipe resonance. If this doesn't work, the only option is to decrease the diameter of the vent and shorten it. Or live with it.
Yes, that works - can simulate in Akabak and works in practice. Just set the length of the stub ("T" to the vent near one end) to the 1/4-wave of the resonance you want to squash. Stuff the stub with fiberglass. Typically, the resonance will be at the half wave of the vent, so you will need double the length vent for the stub. Can all be done with PVC piping and T fittings and caps.
> How does someone fix that?
A perforated sheet + sheet of foam + backing board is widely used to absorb tonal noise. Here is an online calculator. The problem in this case is that it will pinch a significant amount of volume from the speaker but it is easy enough to experiment with and so perhaps a partial covering will work well enough.
A perforated sheet + sheet of foam + backing board is widely used to absorb tonal noise. Here is an online calculator. The problem in this case is that it will pinch a significant amount of volume from the speaker but it is easy enough to experiment with and so perhaps a partial covering will work well enough.
Hmm, with a 9:1 aspect ratio, this duct is somewhat acoustically resistive, especially at high power, so historically need some damping in the form of grill cloth or similar tightly stretched across it, which rolls off the bass a bit as the trade-off.
Haven't seen the Yamaha tweak, but 'sounds' like a band-stop filter [scroll down to 'C']: http://users.cms.caltech.edu/~ps/All.pdf
GM
Haven't seen the Yamaha tweak, but 'sounds' like a band-stop filter [scroll down to 'C']: http://users.cms.caltech.edu/~ps/All.pdf
GM
I started experimenting with stuffing to good affect. The AE TD15S I'm using works well in sealed boxes so the trade off of low bass for midrange clarity isn't so much. In fact I hardly notice it. I started with fiberglass and found a nice furnace air filter that looks lie it'll allow for varying the resistance nicely.
This poor box has had many, many configurations in it in the last 6-7 years.
Looks like I'm heading toward a giant Dynaco A25. Not such a bad thing.
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