STF-2 Port Chuffing

[danmagicman7]

Hello,

I received my STF-2 just over a month ago and have been mostly impressed.

I have a full Axiom system coupling the sub.

Anyways, for music it does supurb. I can play very loud with no problems whatsoever. Keep in mind, I am in a dorm room that is 8x20, but the listening area is more like 8x15.

For movies, I am getting frustrated with the sub. It gets lots of port chuffing whenever there are scenes with deep (I'm guessing <25 Hz) scenes. Even if I turn the volume of the sub down significantly on my receiever (I have calebrated the sub via an AVIA test CD and SPL meter) it will still give me port chuffing. It's interesting when sometimes a large thump in a movie is just as loud, but doesn't have the extension, the STF-2 does just great, vibrates everything in the room.

But every time something low comes along, I hear the "Plu-chug chug chug" of port chuffing. Sound's like you are blowing into your hand with wet lips and really ruins the effect of the scene. The base is limited to a mere rumble and not really what the movie sounds like. I had a cheap Klipsch Promedia 5.1 sub and it never did that, you could just tell it was getting distorted at those levels.

I already emailed HSU Tech Support once and we exchanged e-mails checking everything, but they didn't reply to my last email which was about a week ago. I just e-mailed Sales to see what can be done.

Think it's a problem with the sub? This makes me want to trade it in and get a VTF-2 for only $100 more.

I know people are going to ask, so here is how the sub is set up:

- Calibrated via SPL meter to match mains
- I have a small, thin peice of 1/4 thick carpet cut to the size of the sub that it is sitting on.
- Sub is under a desk but has at least 6-8 inches of space around it
- Chuffing occurs even if I have the sub at -7 db and the main receiver volume around -20db to -5 db.
- Crossover is at 80 Hz
- Room size is 8x20x8

Thanks guys!

[tdekany]

what is the volume level on the sub?

[danmagicman7]

It is around the 9:30-10:00 position. Barely past the 2nd hash mark.

[Michael Bain]

There could be something wrong with your unit. Why don't you send it back and have them check it out?

[danmagicman7]

There could be something wrong with your unit. Why don't you send it back and have them check it out?

$100 shipping there and back :-/

I'd rather just upgrade if I'm paying for shipping.

Is there a difference between the VTF-2 and STF-2 if the VTF-2 is tuned to deeper extension?

Any other advice for me?

[Dudley]

Have you checked to see if something in the room is vibrating at the lower frequencies? If you can play a test tone for an extended period of time and walk around the room maybe you can find the culprit.

It is not normal for an STF-2 that is properly calibrated to make those noises - mine certainly does not.

[danmagicman7]

Have you checked to see if something in the room is vibrating at the lower frequencies? If you can play a test tone for an extended period of time and walk around the room maybe you can find the culprit.

It is not normal for an STF-2 that is properly calibrated to make those noises - mine certainly does not.

I did a test tone sweep at -10 on my receiver with earplugs in. No vibrations in the room or port chuffing. I did get a high pitched buzz at one frequency, but that was 100 db and was a little clock on my desk vibrating a tiny bit. Nothing to cause the sounds I am hearing.

Output was from 90-100 db.

All of the settings are exactly the same in how I listen to movies, except I have to turn the sub down on the receiver to -5 or -7 db to prevent this chuffing from occuring.

Dudly since you have an STF-2 what do you get when playing movies such as these, and you can tell your STF-2 is being overloaded?

For instance, if I play the podrace scene in Episode 1 and am listening at -15 or -10, I will get port chuffing.

Or, there are times in the village I get that.

In Saving Private Ryan, the tanks coming cause no port chuffing, but any things such as the buliding falling down in that last scene, port chuffs galore, the explosions usually are fine, but the huge explosions cause port chuffing.

In Finding Nemo, many scenes do it, the darla tap scene, the scene inside the whale, and some other times like Mr. Johaneson (the stingray) swooping down onto the sand made that noise. Things that are high impact but have a variable low rumble do it.

What should I do? I really hope HSU comes through for me here.

[wid]

When doing your test tone sweeps have you taken into account the compensation chart to adjust for the readings of your SPL meter? If not you will be running your sub way to hot.

12Hz add 16.5dB
16Hz add 11.5dB
20Hz add 7.5dB
25Hz add 5dB
31.5Hz add 3dB
40Hz add 2.5dB
50Hz add 1.5dB
63Hz add 1.5dB
80Hz add 1.5dB
100Hz add 2dB
125Hz add .5dB

[danmagicman7]

When doing your test tone sweeps have you taken into account the compensation chart to adjust for the readings of your SPL meter? If not you will be running your sub way to hot.

12Hz add 16.5dB
16Hz add 11.5dB
20Hz add 7.5dB
25Hz add 5dB
31.5Hz add 3dB
40Hz add 2.5dB
50Hz add 1.5dB
63Hz add 1.5dB
80Hz add 1.5dB
100Hz add 2dB
125Hz add .5dB

Yea, the sub was following that curve. No distortion when everything was at 90 db.

The volume knob is only on the 2nd tick mark, at around 9:30 o'clock. Don't most people have their volume at around 10-11 o'clock.

[wid]

So are you saying you added the required dbs to your readings? If you calibrated your system at 85 db when playing a 25 hz test tone you added the the 5 db to it? Your rat shack meter should be reading 80db when playing a 25hz test tone.

[Dudley]

I can't help but think it is running hot as well. I get absolutely no chuffing during Nemo. It just feels like the house is going to fall down. I have even used the sub in a huge room (35 x 55) for a movie night, and it is still very impressive.

[danmagicman7]

Sorry for being vague.

I meant that the sub was producing 90 db the entire time.

The rat shack meter said 90 around 80, then dipped to 80~85 around 25.

When I get back to my dorm I'll try to test it out again. One of my roomates is a bear to work with (sometimes I want to strangle him) but I'll measure it again. If he doesn't leave he can go deaf sitting next to it.

Anyways, if I have time, I'll pull the sub out into a more open space and watch a movie.


Also, Dudly, what do you have your receiver set at when watching Nemo?

-10 db?

If so, how much do you have the volume knob on your STF-2 turned up?

Thanks guys for your help!

[Dudley]

My reciever is +7 and my sub is at about 11:00. I have an early STF-2 though, and they made the volume knob much more sensitive, so it is hard to compare. I run the sub flat as set up with the reciever test tones and measured by the Rat shack meter and adjusted for accuracy. My reciever (onkyo 600) does not display volume in -db to reference, but I have tried it turned up as loud as I felt comfortable and no chuffing.

Try using the reciever test tones and see if that makes a diff. I know one of the test DVD's had an error in the level.

Do you have enough clearance around the port?

[danmagicman7]

Somehow I think I kept on bumping the level up during music. I like lots of bass in music. Anyways, the sub was running about 10 db too hot. I moved it into a more open area, gave it more breathing room.

A movie might do the test for tonight :D.

[finchna]

Is the chart valid for both the analog and digital RS meters? Thx.

When doing your test tone sweeps have you taken into account the compensation chart to adjust for the readings of your SPL meter? If not you will be running your sub way to hot.

12Hz add 16.5dB
16Hz add 11.5dB
20Hz add 7.5dB
25Hz add 5dB
31.5Hz add 3dB
40Hz add 2.5dB
50Hz add 1.5dB
63Hz add 1.5dB
80Hz add 1.5dB
100Hz add 2dB
125Hz add .5dB

[wid]

Yes it is.

[Kelly]

I had a sub make the sound you describe, but the problem was a tear in the speaker surround. Have you inspected the speaker?

[danmagicman7]

Alright, I moved the sub into a more open area, cleared up a few things, recalibrated it, then watched The Day After Tomorrow in DTS.

It only chuffed once. Sounds good to me!

Funny thing is I don't really notice the bass being quieter. The gain control on the STF-2 is really sensitive. I have to set it half way between the 1st hash mark and all the way down! Since about 6:30 is off, the knob is sitting at about 7:30 or 8 o'clock position.

Oh well, problem solved.

Thanks guys for your help!