Anyway to reduce port noise from Velodyne CHT-12

BjornB17

I have a Velodyne CHT-12, which I really enjoy in my smallish 11'x14' listening room. The problem is that somtimes the port noise can be audible in scenes which have very deep bass. Running test tones, i don't hear port noise until i get to about 23 Hz or so (which makes sense, since that is below the tuning frequency). The sub will play below 25Hz but with the thud of air coming out of the port.

Is it possible to supress this at all with some sort of damping material? If so, how would this affect the overall sound or response? Thanks!

Dobermann

I haven't tried this myself, but I've heard a lot of people that roll up a sock (or a couple socks) and jam them in the port.

Joey_V

You roll a sock and shove it into the port and you might bust your woofer. You are messing with the tuning and you will inevitably turn a ported sub into what it's not.. a sealed sub. Basically, if you're experiencing port turbulence, you're running the sub too hot. If you want to get rid of the port turbulence, you can 1 of 2 things:

1. Turn down the sub.
2. Get a more powerful sub.

BjornB17

Joey_V wrote:

You roll a sock and shove it into the port and you might bust your woofer. You are messing with the tuning and you will inevitably turn a ported sub into what it's not.. a sealed sub. Basically, if you're experiencing port turbulence, you're running the sub too hot. If you want to get rid of the port turbulence, you can 1 of 2 things:

1. Turn down the sub.
2. Get a more powerful sub.

I was afraid of getting this response, even though it is possibly true. The funny thing is that it even happens when the volume is reasonably low (right now its 50% on the back of the subwoofer, -10 db on the receiver while the master sound volume is at -35 db or so), so that definately is not very loud at all. I guess the CHT-12 can get man-handled by frequencies below 25 Hz, even though it sounds fantastic through the rest of the range.

aaharvel

Could be your method of hookup. Are you using a Y-splitter (running the sub too hot) and or bypassing your subs internal crossover?

When you bypass the low-pass filter on your sub, it's high-pass filter kicks in and operates only on a 6db. slope, which means that the sub will still end up playing frequencies up to around 150 hz even if its high pass filter is set to "80hz". IMO this is a major no-no when it comes to subwoofer hookup that most people do not realize. This is the fault of all the magazines who assume that all subs' high pass filters are relatively steep & operate on a 24db. per octave slope and this simply not so. Even your manual suggests to use/stagger both crossovers (the one in your receiver and the low-pass on your sub) to avoid port noise and higher frequencies that have no business being there- unless you're into using cute little Bose cubes.

With all due respect to those who say to ALWAYS bypass their subs low pass filter when setting speakers to "SMALL" on their receiver, they don't know what they're talking about b/c not every sub's high-pass is equipped with the aforementioned steep 24db/octave slope on their subs high pass filter. Many if not most subs use a mild, 12db or worse yet 6db. per octave slope on the high pass, such as our Velodynes (6db).

I suggest enabling your subwoofers crossover to work in tandem with your receivers crossover. This bypasses the 6db. high-pass filter in your sub for a more suitable 12db. low-pass filter. The sub's lowpass filter has a more respectable 12db. per octave, resulting in a steeper rolloff with more clean output from your sub. The only concern with using both the receiver and subs crossovers is that you might be susceptible to bass traps and uneven responses. If you use an SPL meter and fiddle with room placement then using 2crossovers should not be an issue- and at the same time you don't have to worry about your sub reproducing frequencies that it has no business in reproducing.

Good luck.

BjornB17

aaharvel wrote:

Could be your method of hookup. Are you using a Y-splitter (running the sub too hot) and or bypassing your subs internal crossover?

When you bypass the low-pass filter on your sub, it's high-pass filter kicks in and operates only on a 6db. slope, which means that the sub will still end up playing frequencies up to around 150 hz even if its high pass filter is set to "80hz". IMO this is a major no-no when it comes to subwoofer hookup that most people do not realize. This is the fault of all the magazines who assume that all subs' high pass filters are relatively steep & operate on a 24db. per octave slope and this simply not so. Even your manual suggests to use/stagger both crossovers (the one in your receiver and the low-pass on your sub) to avoid port noise and higher frequencies that have no business being there- unless you're into using cute little Bose cubes.

With all due respect to those who say to ALWAYS bypass their subs low pass filter when setting speakers to "SMALL" on their receiver, they don't know what they're talking about b/c not every sub's high-pass is equipped with the aforementioned steep 24db/octave slope on their subs high pass filter. Many if not most subs use a mild, 12db or worse yet 6db. per octave slope on the high pass, such as our Velodynes (6db).

I suggest enabling your subwoofers crossover to work in tandem with your receivers crossover. This bypasses the 6db. high-pass filter in your sub for a more suitable 12db. low-pass filter. The sub's lowpass filter has a more respectable 12db. per octave, resulting in a steeper rolloff with more clean output from your sub. The only concern with using both the receiver and subs crossovers is that you might be susceptible to bass traps and uneven responses. If you use an SPL meter and fiddle with room placement then using 2crossovers should not be an issue- and at the same time you don't have to worry about your sub reproducing frequencies that it has no business in reproducing.

Good luck.

Thanks for the great advice! I see that you have a Velodyne CHT as well I have the CHT-12, and both of my brothers each have a CHT-10 which are also very nice. I have my crossover setting set to "internal" instead of "direct." When using the "direct" setting, I notice lots of sloppy bass well above the crossover setting of 60 Hz that I have it set to.

It seems that my problem is arising from a small collection of DVDs which have exaggerated bass. one example is the U2 Vertigo live in Chicago, which seems to have its bass track recorded at a really high volume. I'm starting to think that I have put too much thought into this scenario