High pass filters for ported designs.

[Not2Evil]

I've read material about ported subs unloading and damaging drivers when presented with frequencies lower than the port tuning. The normal approach seems to be an 18Hz or so high pass ahead of the amp.

Actually, I shouldn't say normal approach. Most of the hackish car apps I've seen, look like they totally ignore the possibility of xmax being exceeded.

Open for discussion:

Why have I only found discussions concerning subs? Would not the same problem of exceeding XMAX occur with ported woofers in DIY speakers also?

If the consensous is that there are potential problems. How do we prevent it? Passives would be huge. Actives would be expensive. Or, maybe the answer is, ported designs are completely at the users risk.

[A9X]

Would not the same problem of exceeding XMAX occur with ported woofers in DIY speakers also?

Potentially an issue for any ported speaker, DIY or manufactured.

If the consensous is that there are potential problems. How do we prevent it? Passives would be huge. Actives would be expensive. Or, maybe the answer is, ported designs are completely at the users risk.

If your amp has pre outs and power amp in, then a passive line level filter could be implemented cheaply.
PLLXO

If you need to use active stages, even a 24dB LR is only a pair of opamps/ch so unless you get silly on the opamps chosen, still not too expensive to build, especially in a case re-used from another device, ie cheap amp gutted, which may also give you a PSU.

[JonMarsh]

Why have I only found discussions concerning subs? Would not the same problem of exceeding XMAX occur with ported woofers in DIY speakers also?

If the consensous is that there are potential problems. How do we prevent it? Passives would be huge. Actives would be expensive. Or, maybe the answer is, ported designs are completely at the users risk.

This is where a little common sense and judicious use of the volume control goes a long way...

Music speakers played with music tracks rarely see much material below 30 Hz, only occasionally. Not much risk at sensible volume levels. Still, one could make the argument to employ a high pass, but in many years of music listening, I've never bottomed a music speaker... maybe, in spite of being a former working rock musician, I just don't have enough of "turn it up to 11" in my blood.

Home Theater seems to bring out the crazies- everyone wants to hear Phantom Menace race or Blackhawk Down or Master and Commander at theater class or beyond SPLs in their home- 110 dB? 7 Hz? Why not?

Well, if you've got the equipment to go along with that inclination, like a manifold array IB with lots of drivers, sure thing. If you've got a ported box with one or two twelves, a little dose of reality may be in order. :W

[evilskillit]

Yeah, I agree with John. Just to see what would happen I turned my mains up waay louder than I would ever listen to them and then listened to various pieces of bassy electronic music that probably have notes below the tuning of the speakers. I never saw the woofers moving beyond what looked like 3-5mm peak to peak, which is well within the x-max, not to mention the x-mech. If you use a ported sub tuned to something like 25-30hz and watch movies at high volumes you can have some issues. The fix is either tune way low, like 15hz so that you'll never get a high amplitude signal far enough below your tuning frequency to actually overdrive the woofer... or use some sort of high pass filter. I think the BASH300 is great for this because it comes from the factory with a high-pass filter around 20hz and it is adjustable up or down if need be. But thats perfect for most low to mid budget diy home subs.

[ThomasW]

The fix is either tune way low, like 15hz so that you'll never get a high amplitude signal far enough below your tuning frequency to actually overdrive the woofer...

Wishful thinking.

There are numerous soundtracks containing single digit sonic effects. For example....

If someone with a 15Hz tuning does a 'let's see how loud it can play' with something like the 'f**king Irene scene' in "Blackhawk Down" (5Hz info) they'll unload the driver.

[evilskillit]

Wishful thinking.

There are numerous soundtracks containing single digit sonic effects. For example....

If someone with a 15Hz tuning does a 'let's see how loud it can play' with something like the 'f**king Irene scene' in "Blackhawk Down" (5Hz info) they'll unload the driver.

While that may be true, in practice I believe most electronics begin rolling off between 8 and 12hz at a rate that would usually keep a subwoofer with a tuning frequency in the mid to low teens from ever bottoming out. I'm sure with enough power and enough stupidity anything is possible but most people as far as I know several people with large ported subs tuned extremely low run them without any high pass filter and have not bottomed out their drivers.

[ThomasW]

in practice I believe most electronics begin rolling off between 8 and 12hz at a rate that would usually keep a subwoofer with a tuning frequency in the mid to low teens from ever bottoming out.

In practice 'some' electronics roll-off early, it is incorrect to say "most"

I know several people with large ported subs tuned extremely low run them without any high pass filter and have not bottomed out their drivers.

What has 'saved' people in this situation is they've been lucky enough to use specific drivers designed to be inherently bottomless, this helps protect from unloading. Avalanche and SoundSplinter are two such drivers. Claims that the so called LLT design inherently protects ALL drivers in ALL instances is preposterous.

[evilskillit]

True, I guess its better safe than sorry in any case. Tho I don't know off the top of my head, many pieces of equipment that will allow you to create a high pass filter in the low teens or high single digits, which is what would be most desirable for a ported sub that is tuned very low.

[ThomasW]

There are quite a few, some just off the top of my head are...

Rane PE17, Symetrix 551/552, Behringer MC2200, elemental Designs eQ.2, Reckhorn B-2, most of the Marchand active XO's

[evilskillit]

Ahh, cool. Good to know, thanks.

There are quite a few, some just off the top of my head are...

Rane PE17, Symetrix 551/552, Behringer MC2200, elemental Designs eQ.2, Reckhorn B-2, most of the Marchand active XO's

[A9X]

This is where a little common sense and judicious use of the volume control goes a long way...

Absolutely. However there are many small ported speakers in use out there, many with quite high tunings which can (I've witnessed it several times) overexcurse the LF driver with even deep music, let alone movie SFX. The OP didn't specify a design, so I was talking generalities.

[Not2Evil]

No, this is supposed to be a general theory discussion.

I was currious why some systems blow. It was sparked by a post from Jim Holtz a while back about blowing two RS315HFs at very modest levels. Which led to the thought of why don't more mains blow when unloaded.

The insight so far has been great! I hope more people chip in.

[augerpro]

I have friends that have blown woofers, some on speakers that served them well since the 1970's. But once they integrated them into a home theater they started ruining woofers. I know one guy telling me how everything was shaking in his room watching War of the Worlds and a couple days later says is woofer is makign scratching noises. On AMT 1Bs with no easy replacement.

[A9X]

No, this is supposed to be a general theory discussion.

I was currious why some systems blow. It was sparked by a post from Jim Holtz a while back about blowing two RS315HFs at very modest levels. Which led to the thought of why don't more mains blow when unloaded.

The insight so far has been great! I hope more people chip in.

Notwithstanding system damage, the small monitors started to sound noticeably worse at lower levels than I would expect. I've tested some by making them a 3 way with a dedicated midbass under each and found there is a very noticable improvement in clarity at similar levels by crossing even just above the monitor's tuning freq and better still an octave or more higher. I've never done measurements in detail on this, but I would presume IMD reduction to be the source of the improvement. It was some proof testing for myself only. I've never gone back to small speakers since and have no plans too.

My PA's all used to run an LR12 or 24 below tuning in the subs to avoid damage. They were used hard for many years, and I never blew a 2226 like many others I know who did.

Brandon's comments on old stereo systems being used for HT and then damaged has happened to a few people I know.

[evilskillit]

I know with no low pass filter my Dayton BR1-S that were out in the living room would shake the house a bit. They never died, tho if they did I wouldn't have cared.

Now I have Roman's Microbes out there. It would be a bit of a shame if the little 5" Dayton Reference woofers in those got toasted, but at least I know where to get a replacement, and they're not that expensive. Tho I do hope to get a receiver with a high pass filter for them eventually.

[Paul Spencer]

I prefer to use a high pass to keep the system more robust. It's a personal preference - I like to set things up to be as bullet proof as I can and then on top of that I use things sensibly. At those times when you turn things up, it spoils the fun if you leap off your seat in a panic thinking you're about to damage a woofer. There is always that one track that is the exception with high levels of very low frequencies. Why leave your system open to that?

I've found that 3rd order filters are a good compromise. Steeper slopes aren't needed and shallower don't quite do the job. Rule of thumb. Use a 3rd order HP on a 20 Hz tuned sub and the excursion below tuning will never be the bottleneck. Shallower slopes mean you will be limited by content below tuning and max safe SPL is thus limited.

Of course, if you have 10 x 18" ultra high excursion subs but slim floorstander mains, then you have so much headroom in the subs that you really don't need the rumble filters.