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Discussion Starter #1
Kevin,
I'm curious as to a comnent that you made about needing a subsonic filter for a Maelstrom-X subwoofer. If the excursion is <40mm through about 6Hz, do you still need something? I was looking at an 800L enclosure ported to 10Hz. At 1500W, the cone displacement doesn't hit 40mm until about 9Hz (which you really don't get much of in HT software anyway). Can you tell me if you'd still recommend a subsonic filter and why?

Thanks!
m.
 

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Technically yes you will still need one. I'd recommend a Rane PE-17 EQ. Don't think for a second that there isn't much <10hz content in movies. It's there trust me. It's not in every other movie, but more and more are using crazy low bass and I can think of at-least 20 off hand.

If you do want to go with an alignment like this just be aware that you will also be asking for a massive amount of displacement from the Mal X between 15-20hz and will have higher distortion levels there. (probably not something to really worry about at that low of freq's but it's there). 15-20hz is material that is in a lot of movies at high levels and you may run into over excursion there depending on how hard you push things.

What amp are you considering?
 

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I recommend a subsonic filter on all resonant system builds. Why? Because I have to. If I tell people they don't need them in situation 'XYZ' then the customer does 'ABC' and blows the driver, who do you think they are going to blame?

From good design perspective, every ported system should include a subsonic filter. I wouldn't design a commercial system without one and I won't recommend DIY solutions without one either.

Kevin Haskins
Exodus Audio
www.diycable.com
 

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Discussion Starter #5
Kevin,
I've got a Buttkicker BKA1000-4A amp that I may not end up using anymore for my buttkicker system (provided my planned subwoofer can do an adequate job filling in). Also, I've got an old AVAhifi amp that is rated down to 1 Ohm that I've got running my current dual Tempest 350L Sealed Sonotube (AdireAudio drivers) . I probably won't need the whole 1500W capability of the Maelstrom-X - I typically don't get my home theater much above 95dB, I'm just looking for better lower end.
The SMS-1 I've got in the system to EQ out the sealed sub, helps, but I'm looking for more. The buttkickers that I'm using don't sync well with the bass from the subwoofer (delayed compared to the sound even though I'm only running them on freqs <35Hz), so I was hoping to fill in the other freqs with a better subwoofer and sell off the buttkickers to pay for it.

Some More Questions:
1) Can you explain a little more about the subsonic filter - Straight Cut, or 12dB / Octave?
2) Is the necessity for it driven by the maximum excursion (Xlim) of the driver?
3) I thought that most electronic equipment is only rated for 20-20kHz, and that below 10 Hz, the output drops off considerably. If that's the case, when would I ever see stuff below 10Hz?
4) How do you find out whether or not your hardware can go in the sub-10Hz domain? I've got a DVD that I found online that someone made with Sine waves starting at 4Hz, but when I try to play it, I get a small amount of movement from my speakers, and no air movement at all....

Thanks for the feedback!
Mike
 

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Mike,

1). Most of the opamp based ones are 12dB-18dB/oct. That is sufficient. The SMS-1 has one that is steeper because the DSP is more flexible than an opamp based circuit.

2). You have transients. Most models are just a simplified static picture of the system. In real world use you get peaks that are often considerably higher than your average SPL level. Also amps typically can deliver transient peaks of power that are greater than you might think. That translates into the ability to damage the system if you don't plan carefully.

3). I depends on the equipment obviously. It doesn't drop like a rock though. The LF corner is typically around 8-9Hz but often it is only set by a DC blocking cap on the input of the equipment (6dB/oct). If the recorded material has content at high levels, being 3-5dB isn't enough to protect the system.

4). You would need to measure it. You need a measurement system like Praxis that can measure the FR of equipment. Either that or trust the manufactures specs.

My take on the entire 10Hz thing is that it requires a substantial investment in drivers to be able to produce anything down there. A single subwoofer isn't enough, Maelstrom or otherwise. If you want to plan a system around reproducing 10Hz at high levels, you need to be looking a Thigpin rotary subwoofer. Traditional drivers just are not efficient at those frequencies.

Of course... I don't see the point in doing 10Hz content to begin with. It is in only a very small percentage of source material. When it is, you cannot tell 8-10Hz from 15Hz. All it would do is create additional distortion by rattling things in the room. Most of the action in movies is in the 25-60Hz range. If you plan a system that reaches to 18Hz or so you cover 99% of the source material and the other 1% is not all that critical to enjoying the experience so why spend many thousands of dollars chasing it?

Kevin Haskins
Exodus Audio
www.diycable.com
 

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$400 for a Rane PE-17 EQ is a bit steep for anyone who just needs a subsonic filter. There are cheaper alternatives.
More like $130 on Ebay. I got mine for less than that and it does do many other things besides SSF.

Kevin,
I agree with everything except parts of #4. 10hz can be done and is worth doing AFTER the normal 20hz and up range is good enough for YOU. It does take a massive amount of cabinet, diplacement and power with extra care and attention to system limits as well. There is a very large difference between the way 15hz and 10hz is percieved at loud levels. It's nearly an octave difference. It's probably asking too much from one MAL X, but 2 in the right set-up could provide room dominating output from 10hz up. Like I said before you are trading off some headroom in the 15-22hz range though. It is a trade off like anything else.

I'm not trying to steer the OP there to try it. I'm just trying to give an informed opinion on the things to look out for and what sacrifices are involved with trying to go that deep.
 

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...
Of course... I don't see the point in doing 10Hz content to begin with. It is in only a very small percentage of source material. When it is, you cannot tell 8-10Hz from 15Hz. All it would do is create additional distortion by rattling things in the room. Most of the action in movies is in the 25-60Hz range. If you plan a system that reaches to 18Hz or so you cover 99% of the source material and the other 1% is not all that critical to enjoying the experience so why spend many thousands of dollars chasing it?
Kevin,

I can see a few advantages to chasing 10Hz. Of course, the totally non-scientific, but still completely valid answer as to why would be 'Because I can'. :jiggy: I don't agree that it takes thousands of dollars, though. I started with a $200 Kenwood amplifier and $89 Dayton Quatro. Fed 10 Hz, the whole corner of the room shook and the vents sound like a steam train, which I happened to think was pretty cool. :bigsmile:

As for a few more practical reasons, I can think of these:

1. Tuning low in the 10 Hz range extends your power handling in the 10-20Hz octave. Tuned to a more typical Fs of the driver, say 18-20 Hz, your power handling drops like a rock a couple Hz below Fb. Just as an example, a Tempest X in my 315l enclosure will handle only 80w at 10Hz when tuned to 18.5Hz. If tuned to 10Hz, it will handle 600w at 10Hz. If it can be said that sub 20Hz information is a very small percentage of actual source material, then I believe it could be argued that sub 10Hz information is a significantly smaller percentage. Tuning to 10Hz, for people not using insane amounts of power (to me that's over 500 watts), I believe allows safe use without a subsonic filter for the overwhelming majority of program material. For those of us using external amplifiers, this can noticeably reduce total cost (cheapest filter I have found is $100) and clutter. I fully understand why you can't and don't ever advise use of a resonant system without such a filter, however. :yes:

2. Tuning lower will reduce group delay at higher frequencies, where it is likely to be more audible. To me, this is the best of both worlds, you get augmentation of the extreme low end, and resultant better power handling above Fb, but the box behaves and sounds like a sealed box at higher frequencies. True, you could add another driver to your sealed system and add some EQ, but that's $$$$ and complexity.

3. Tuning lower will allow you to get away with using vents which otherwise would be significantly undersized for your driver and input power, because the air speed at frequencies you can actually hear (ie 16-20Hz and above) is considerably lower. This also speaks to expense, as 6"-8" ports can be pricey. For example, same box I mentioned in #1: Two 3" vents tuned to 18.5Hz with 400w input gives you an insane 45 m/s air speed at 20Hz. Tuned to 10Hz, air speed at 20Hz is only 9 m/s.


So basically it comes down to frugality, and bang for the buck. Sealed doesn't provide quite the extension I want, yet I'm too cheap to buy all the add-on devices for that <1% of the time that I might need protection below 10Hz. :bigsmile: And hey, if there is any information from 10-20Hz, why not give the system a chance to make you feel it, when all it costs is a larger cabinet? What's the threshhold of feeling at 10Hz? I'm pretty sure you won't feel 87dB, but 103dB (not including room gain)?
 

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"Tuning lower will allow you to get away with using vents which otherwise would be significantly undersized for your driver and input power, because the air speed at frequencies you can actually hear (ie 16-20Hz and above) is considerably lower."

I don't think Fb is relevant to audibility of port noise; the turtbulence sounds are a function of the air speed itself.

Besides the noise, you'll have output compression.

But just get some sonotube for relatively cheap big ports.
 

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"Tuning lower will allow you to get away with using vents which otherwise would be significantly undersized for your driver and input power, because the air speed at frequencies you can actually hear (ie 16-20Hz and above) is considerably lower."

I don't think Fb is relevant to audibility of port noise; the turtbulence sounds are a function of the air speed itself.

Besides the noise, you'll have output compression.

But just get some sonotube for relatively cheap big ports.
I think this is right. Let me make myself more clear. I didn't mean to say that it's the frequency of the tuning itself which makes the turbulence more audible. It's the fact that there is typically much less signal input at 10Hz, vs 20Hz, which means less chances to drive the air speed up.

Sonotube for large ports is a good suggestion, but tuning to 12Hz with a 6" port results in a port that's way too large for my enclosure, even with a bend, not to mention it has a resonance in the passband. Using smaller ports keeps the air speed at Fs and above at reasonable levels if you tune low, and still allows the vents to physically fit inside the cabinet. :)

As for the output compression, will it compress to a level lower than output would be in a sealed enclosure? If not, I don't see the problem.
 

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Discussion Starter #12
Mike,

1). Most of the opamp based ones are 12dB-18dB/oct. That is sufficient. The SMS-1 has one that is steeper because the DSP is more flexible than an opamp based circuit.
Kevin, I wonder if it is my SMS-1 that is limiting my current system. What freq does it cut off at on the low end, and is it adjustable? I just used the auto setup and didn't really play with the low end.

Thanks, Mike
 

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It is adjustable via software. This is what their spec's claim. I don't have one set-up right now to look through the menu but it should be in your documentation.

Subsonic Filter: 15 Hz - 35 Hz (adjustable)12 dB/octave, initial to 48 dB/octave, ultimate

Kevin Haskins
Exodus Audio
 
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According to the info I read on the web, Velodyne's lastest version of firmware for the SMS-1 is Release 2.1.3. This takes out the 15 Hz subsonic filter and allows you to set it all the way down to 1 Hz. But the hardware is actually limited to 5 Hz.......
 

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That is plenty.... you don't want a subsonic filter working that low anyway. They are for protecting the driver and once you are down to 10hz, it is a moot point anyway.

Kevin Haskins
Exodus Audio
 

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My take on the entire 10Hz thing is that it requires a substantial investment in drivers to be able to produce anything down there. A single subwoofer isn't enough, Maelstrom or otherwise. If you want to plan a system around reproducing 10Hz at high levels, you need to be looking a Thigpin rotary subwoofer. Traditional drivers just are not efficient at those frequencies.

Of course... I don't see the point in doing 10Hz content to begin with. It is in only a very small percentage of source material. When it is, you cannot tell 8-10Hz from 15Hz. All it would do is create additional distortion by rattling things in the room. Most of the action in movies is in the 25-60Hz range. If you plan a system that reaches to 18Hz or so you cover 99% of the source material and the other 1% is not all that critical to enjoying the experience so why spend many thousands of dollars chasing it?

Kevin Haskins
Exodus Audio
www.diycable.com
This is one of the most realistic posts I've read for a long time!

I wish more forum regulars understood and preached this common sense approach to designing an enjoyable sound system. Instead we see the fad of some braggarts chasing single digit FR sweep graphs at the expense of usable headroom in the most commonly used frequencies a subwoofer is asked to handle. To each his own, but its good to see not everyone has lost sight of reality!

Dr V
 

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Hey to each there own. Believe me that when you do have enough output at 10hz it sounds WAY different from 16hz.

I look at it like this. Once you have more than enough headroom for your needs at 20hz and above, what do you do next?

Should people with one 15 or 18 be trying to chase 10hz? No. If you had 4 sealed Mal X's with thousands of watts available or a big IB system it suddenly doesn't seem so crazy.
 

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Hey to each there own. Believe me that when you do have enough output at 10hz it sounds WAY different from 16hz.

I look at it like this. Once you have more than enough headroom for your needs at 20hz and above, what do you do next?

Should people with one 15 or 18 be trying to chase 10hz? No. If you had 4 sealed Mal X's with thousands of watts available or a big IB system it suddenly doesn't seem so crazy.
How do you know you really have more than enough headroom at 20Hz when the port is tuned an octave below?

Now what if you had your port tuned to 18-20Hz. You'd have a ton more headroom and much lower distortion in frequencies used more often than not in movies. With "knock your socks off" performance in most real life material you'd still have plenty of in room SPL down to 14-16Hz.

I think this sounds like your next subjective experiment! :yes: :yes: :yes: 10" sonotube is cheap! :yes:

Dr V
 
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