port noise

[davepellegrene]

I am having issues with port noise. Not sure what is causing it. I am using the RS100-4 in a 3.5L box. The port it 1.25 x 4.25 in length, with the ends flaired. This tunes the system to 72hZ. WinISD shows the air velocity peaking at 65hZ at 25m/s. When I play a test tone at 80dBs I start to get port noise at around 100 hZ. As I go down it gets louder. If I put my finger over the port the noise stops. I am not sure what chuffing sound like. The sound I am hearing is more like a vibration coming from the port. At first I thought is was something on the table. If I reach into the port with a screw driver and hold it to the side of the port I don't hear any change in noise, so I don't think it is the port vibrating.
I tried putting an elbow on the port and added another piece so the total length was 8". This should have lowered the peak to 45hZ, tuning at 54 with a 23m/l. That only made it worse. I took the port completely out with just the hole through the baffle. that should have moved the peak to over 110 hZ with tuning at 117hZ and speed at 32m/l, There was less noise, but it still made noise.
Does this sound like my only choice is to make the port larger? I thought if the air velocity was under 25m/l I shouldn't have any problems.
Dave

[mzisserson]

I am having issues with port noise. Not sure what is causing it. I am using the RS100-4 in a 3.5L box. The port it 1.25 x 4.25 in length, with the ends flaired. This tunes the system to 72hZ. WinISD shows the air velocity peaking at 65hZ at 25m/s. When I play a test tone at 80dBs I start to get port noise at around 100 hZ. As I go down it gets louder. If I put my finger over the port the noise stops. I am not sure what chuffing sound like. The sound I am hearing is more like a vibration coming from the port. At first I thought is was something on the table. If I reach into the port with a screw driver and hold it to the side of the port I don't hear any change in noise, so I don't think it is the port vibrating.
I tried putting an elbow on the port and added another piece so the total length was 8". This should have lowered the peak to 45hZ, tuning at 54 with a 23m/l. That only made it worse. I took the port completely out with just the hole through the baffle. that should have moved the peak to over 110 hZ with tuning at 117hZ and speed at 32m/l, There was less noise, but it still made noise.
Does this sound like my only choice is to make the port larger? I thought if the air velocity was under 25m/l I shouldn't have any problems.
Dave

With the ends flared... Both in the cab, and at the mouth? I have had issues with only one end flared before.

Sounds like the driver(s) may be noisy. Bad Batch? Take them out free air and run a tone through them, put your ear to the back and see ofyou can hear any lead-slapping, rubbing, or any other mechanical noise.

[davepellegrene]

With the ends flared... Both in the cab, and at the mouth? I have had issues with only one end flared before.

Sounds like the driver(s) may be noisy. Bad Batch? Take them out free air and run a tone through them, put your ear to the back and see ofyou can hear any lead-slapping, rubbing, or any other mechanical noise.

Yes both ends are flared. Never thought about it being the driver. I will try that.
Thanks Dave

[davepellegrene]

Took the driver out and ran some tones. No noise at all. I took the port out of one of the speakers and sealed it up. With the test tone going as I put the driver back in the hole and I start to feel the air off the cone the noise starts even with the driver in the sealed cabinet. The only difference is the noise comes from the cone instead of the port. The sealed speaker doesn't have as much base in the lower tones and the noise seems a little worse.
Dave

[Wolf]

It sounds like pole-piece/phase-plug chuffing, or over-throw intermodulation distortion. What kind of drive-level are you using? Seems like you could just be overdriving the driver, and getting the backlash.

Later,
Wolf

[davepellegrene]

It sounds like pole-piece/phase-plug chuffing, or over-throw intermodulation distortion. What kind of drive-level are you using? Seems like you could just be overdriving the driver, and getting the backlash.

Later,
Wolf

I had my decibel meter set up a meter in front of the speaker. It was reading around 80 dBs at 80 hz. On average playing music I get around 82dBs before I hear the woofer start to distort. I am set up in a 16 x 25 well damped room and measuring at listening position, about 9' back. Maybe I am expecting to much out them. Never had a small set of speakers before. At 75 dBs they sound great. They are the best imaging speakers I have built so far.
Dave

[Brian Steele]

Took the driver out and ran some tones. No noise at all. I took the port out of one of the speakers and sealed it up. With the test tone going as I put the driver back in the hole and I start to feel the air off the cone the noise starts even with the driver in the sealed cabinet. The only difference is the noise comes from the cone instead of the port. The sealed speaker doesn't have as much base in the lower tones and the noise seems a little worse.
Dave

Tinsel-lead slap?

[davepellegrene]

Tinsel-lead slap?

Is there a way to tell this? Or is it something you know by the sound?

[Paul K.]

The general rule of thumb is that the port air velocity should not exceed 10 m/s, which is 3% of the speed of sound. Your WinISD indicates your port's air velocity is peaking at 25 m/s, 2.5 times the recommended maximum. You should expect, then, to hear the port making noise and that noise will start becoming audible at frequencies above the peak at 65 Hz. There's another rule of thumb that says the port air velocity shouldn't exceed 5% of the speed of sound, which would be ~17 m/s, also below your predicted velocity of 25 m/s.
Paul

I am having issues with port noise. Not sure what is causing it. I am using the RS100-4 in a 3.5L box. The port it 1.25 x 4.25 in length, with the ends flaired. This tunes the system to 72hZ. WinISD shows the air velocity peaking at 65hZ at 25m/s. When I play a test tone at 80dBs I start to get port noise at around 100 hZ. As I go down it gets louder. If I put my finger over the port the noise stops. I am not sure what chuffing sound like. The sound I am hearing is more like a vibration coming from the port. At first I thought is was something on the table. If I reach into the port with a screw driver and hold it to the side of the port I don't hear any change in noise, so I don't think it is the port vibrating.
I tried putting an elbow on the port and added another piece so the total length was 8". This should have lowered the peak to 45hZ, tuning at 54 with a 23m/l. That only made it worse. I took the port completely out with just the hole through the baffle. that should have moved the peak to over 110 hZ with tuning at 117hZ and speed at 32m/l, There was less noise, but it still made noise.
Does this sound like my only choice is to make the port larger? I thought if the air velocity was under 25m/l I shouldn't have any problems.
Dave

[davepellegrene]

The general rule of thumb is that the port air velocity should not exceed 10 m/s, which is 3% of the speed of sound. Your WinISD indicates your port's air velocity is peaking at 25 m/s, 2.5 times the recommended maximum. You should expect, then, to hear the port making noise and that noise will start becoming audible at frequencies above the peak at 65 Hz. There's another rule of thumb that says the port air velocity shouldn't exceed 5% of the speed of sound, which would be ~17 m/s, also below your predicted velocity of 25 m/s.
Paul

So what you are saying I need a larger port. I do have a 2" hole cut in the back panel for the terminal cup. I could plug the front port and try a rear port of a larger size. 2" port needs to be around 11". I will try it just as an experiment. Thanks Dave

[Phil_RC_1]

I am having issues with port noise. Not sure what is causing it. I am using the RS100-4 in a 3.5L box. The port it 1.25 x 4.25 in length, with the ends flaired. This tunes the system to 72hZ.

I checked this out in UniBox. With that port dia you're going to have port noise at those freq's with any wattage over 3 or 4 watts.

Unibox shows two 1.5" x 9.125" should tune you the same (72hz) but gets your port airspeed under control. Using one 2" x 11.5" port models even better but I'm sure you don't have room for a 11.5" port.

[davepellegrene]

I checked this out in UniBox. With that port dia you're going to have port noise at those freq's with any wattage over 3 or 4 watts.

Unibox shows two 1.5" x 9.125" should tune you the same (72hz) but gets your port airspeed under control. Using one 2" x 11.5" port models even better but I'm sure you don't have room for a 11.5" port.

I could probably get a 2" port in with a 90 degree bend. But that is going to eat up some volume. I am going to have to figure that out.
I was reading an article this weekend that stated that a vent in a small box is not really going to be of any benefit.
Wonder if I should consider sealed?
Thanks Dave

[Phil_RC_1]

I could probably get a 2" port in with a 90 degree bend. But that is going to eat up some volume. I am going to have to figure that out.
I was reading an article this weekend that stated that a vent in a small box is not really going to be of any benefit.
Wonder if I should consider sealed?
Thanks Dave

No rule says the port has to be inside the box, Since your 2" hole is in the rear, using a 2" 90* could you possibly run the port on the outside, up the back of the box? It might not be pretty but it would be in the rear where it wouldn't be typically seen.

If sealed suits you, it might be worth it to try.

Phil

[davepellegrene]

No rule says the port has to be inside the box, Since your 2" hole is in the rear, using a 2" 90* could you possibly run the port on the outside, up the back of the box? It might not be pretty but it would be in the rear where it wouldn't be typically seen.

If sealed suits you, it might be worth it to try.

Phil

I was going to test it on the outside just to see how it did. I did oversize the cabinet a little bit so I had some volume to work with if needed. Figured it would be easier to add mass to lower the volume if needed.
I will probably pursue a sealed version just to see how it sounds.
dave

[davepellegrene]

Found a piece of vacuflow tubing measures 2" on the outside. Cut it 11.5" stuck it out the rear hole. It worked. I had to cut the volume down considerably to get it back down to 80 dBs on my meter. Even at 95 Dbs, were the volume was originally, I didn't have any noise.Not sure why I got so much more volume unless the smaller tube could have been chocking the driver? Guess that makes sence. Looks like with the tube, crossover and braces I still have 3L. So looks like I can tune it to 78hZ with a 1.87 x 10" tube. That gives me 70hZ peak at just over 10m/s.
Thanks for the help.
dave