If my enclosure is tuned at 20hz does it work as a subsonic filter?

[cameron paterson]

I never run my sub very hard with movies otherwise the bass overpowers everything! I have a TC Sounds LMS- Ultra 5400 18" subwoofer in a 7.3ft 3 ported enclosure after all displacements. Its tuned at 20hz. Since its tuned at 20hz will that act as a subsonic filter for 10 to 15hz or not at all? I don't have it turned up loud enough to ruin my sub even at 10hz so I am not worried about that just wondering what the lower bass notes will be like tuned at 20hz.

 

[lovinthehd]

Looking at your other thread @Winkleswizard did some calculating for you and arrived at the conclusion your box was tuned to 13hz for your driver:

"Right now, your box is tuned to about 13 Hz. In this case, your f3 is around 43 Hz. These results are BassBox Pro simulation.

BassBox Pro set for extended bass requires a 7.4 cu ft box tuned to 20 Hz. This would yield a f3 of 37 Hz. This would be a difficult box to do well as it needs really thick walls and significant bracing.

As stated earlier, a more optimal box for this subwoofer is a 2.5 sealed one. While needing eq to get to subwoofer territory, the box would be much easier to get right..."

Or did you modify the box?

Some box/driver combos do use protective high pass filters below tuning...some don't need it....and you may not have content that low to worry about it....yet?

ps Missed this further on in your thread:
If am correctly understanding your stated box size, that vent is tuned to 20 Hz. My earlier calculations were for a cylindrical vent. However, despite the cabinet size, you are not getting the best performance from that woofer. The design has an ugly group delay and other issues.

Without knowing how your subwoofer crossover is designed, can only speculate on what other issues you might hear. In any case, you would be better served with a smaller box. A much better vented box would be about 4 cubic ft.

 

[lovinthehd]

If the sub is drowning out your speakers, then sounds like you haven't matched the levels well....

 

[annunaki]

The short answer to your question is no. Below tuning the enclosure "unloads" the pressure in the enclosure and it no longer acts as a spring. As a result power handling decreases dramatically and excursion is uncontrolled which could result in damage to the driver, specifically physical damage as a result of over excursion at even modest power levels.

Anytime a vented application is in play a high pass infrasonic filter should be utilized, typically with a 4th order (48db/octave slope).

 

[highfigh]

I never run my sub very hard with movies otherwise the bass overpowers everything! I have a TC Sounds LMS- Ultra 5400 18" subwoofer in a 7.3ft 3 ported enclosure after all displacements. Its tuned at 20hz. Since its tuned at 20hz will that act as a subsonic filter for 10 to 15hz or not at all? I don't have it turned up loud enough to ruin my sub even at 10hz so I am not worried about that just wondering what the lower bass notes will be like tuned at 20hz.

They're right- the answer is No.

Looking at the parameters in the other thread, the Vas alone tells me this woofer needs to be in a sealed enclosure. Add the high compliance and Xmax and it definitely shows a need to be in a sealed enclosure.

To give you an idea of what that spec means, it's called 'equivalent volume' and it relates to the 'springiness' of the suspension. Put a woofer in a small, sealed box and thump the cone- the air inside will vibrate at a certain frequency. Put it in a larger sealed box and thump the cone- you'll find that it vibrates at a different frequency. This is because air can be compressed, but only to a specific extent. Less air that's compressed by some percentage (without squeezing it into a storage tank of some kind) will be considered 'stiffer' and a larger volume of air will be softer if it's compressed by the same percentage. The TC woofer shows the Vas as 8.5 ft³- that's very large and if it's driven hard in a vented box, it won't handle much power at low frequencies because it will vibrate too wildly.

 

[cameron paterson]

when I run a movie I have to find the right setting because every movie sounds different. so if the bass is up too high it drowns out everything else. so I find where it sounds perfect and leave it there. I actually go into the movie if its an action movie and set the bass to match some explosions and then watch the movie so I don't have to change it during the movie. and I guess I don't run my sub hard enough because on "bass I love you" which goes down to 10hz I believe it doesn't move that much more than at 20hz. and the way I have seen people blast their subs in their cars with huge amounts of cone movement... I never do anything close to that with my sub because I don't want to blow it. and I have a light on my amp that turns red when clipping and if that happens I turn the gain down.

 

[j_garcia]

Well, with the box being not quite the right size for the driver, that's most likely why it never sounds quite right. Are you using any kind of EQ on it or have you at least taken any sweeps of it in your room? Doesn't sound like it if you are constantly adjusting.

 

[cameron paterson]

I adjust it because each movie has a different amount of bass so you have to set it up just right. I have a sine sweep but have nothing to record the frequencty response and no eq either. other than a high pass filter set to 80hz. and a low pass for the other 7 speakers at 80hz. I'm actually very happy with it!

 

[j_garcia]

I setup my sub one time and have not touched it once since then (EQ'ed though). Yes, every single recording is different, but adjusting to each film should still not be necessary (I agree that it isn't perfect all the time). I tend to spend more time up front getting it where I think it is good, by testing like you do, with a variety of music and movies and adjust for probably a few weeks until I get something that suits my needs. Of course, can always adjust for an anomaly track.

 

[lovinthehd]

I rarely touch sub levels. Do it in the avr when I do, but it's rare I need more (or less). You're setting levels entirely by ear ? You using an avr?

 

[cameron paterson]

yes an avr and a Dayton plate amp

 

[highfigh]

when I run a movie I have to find the right setting because every movie sounds different. so if the bass is up too high it drowns out everything else. so I find where it sounds perfect and leave it there. I actually go into the movie if its an action movie and set the bass to match some explosions and then watch the movie so I don't have to change it during the movie. and I guess I don't run my sub hard enough because on "bass I love you" which goes down to 10hz I believe it doesn't move that much more than at 20hz. and the way I have seen people blast their subs in their cars with huge amounts of cone movement... I never do anything close to that with my sub because I don't want to blow it. and I have a light on my amp that turns red when clipping and if that happens I turn the gain down.

Regardless of cone movement, a car is a very different environment from a room- in principal, it's similar (a speaker box firing into another space) but the dimensions and scale are far from the same. Sitting in a car, your position is similar to being in the chamber of a bandpass box between the woofer and port to the outside world and by adjusting the windows, it's tunable. Close the windows and the sound will change drastically. Opening doors and windows in a house makes similar changes happen, to a different degree.

IMO, the need to change the sound for every movie means that you need to find the best location for your speakers. Small changes often make a big difference and once you find their 'happy place', you'll be able to stop messing with the controls. For music, you'll hear large differences in sound quality, even if the speakers are in the best location because they weren't all mixed to a particular standard, like THX, Dolby surround, etc.

However, the best thing about finding the best place for your speakers- you'll find yourself just listening or watching, not thinking about it.

 

[lovinthehd]

yes an avr and a Dayton plate amp

Which avr? Does it have a room eq/setup feature with a mic? Dayton plate amp may have a built in protective high pass filter depending on model.

 

[cameron paterson]

its an older pioneer AVR and yes it has a room eq setup feature with a mic.

 

[lovinthehd]

its an older pioneer AVR and yes it has a room eq setup feature with a mic.

So you used MCACC to set speaker/sub levels?

 

[cameron paterson]

yes MCACC was used.

 

[cameron paterson]

Tis sub has a 7.3ft3 box made of 1" MDF tuned @ 20Hz with a slot port that is 16" wide 3" tall x 39". Not a 3" round port.

I used MCACC and the crossover point is 80Hz.

 

[highfigh]

Tis sub has a 7.3ft3 box made of 1" MDF tuned @ 20Hz with a slot port that is 16" wide 3" tall x 39". Not a 3" round port.

I used MCACC and the crossover point is 80Hz.

Is the volume of the slot port the same as what it showed for a 3" round port?

 

[cameron paterson]

Not even close! A round port is 3" x 3". My port is 16" wide x 3" high and 39" long. And tuned @ 20Hz.

 

[cameron paterson]

My sub with my port had 111db at 15Hz and 116 at 20Hz.