I was asked if all commercial ported subs have a hipass built in. I'm too lazy to search, so I thought I'd ask you guys. I know the DIY guys don't believe it is needed, I was just wondering what the industry does.

He was debating on building or ID purchasing. Thanx KG

whoa there cowboy.....who said "DIY guys dont believe it is needed"? :confused: I've been saying it all along that it certainly is not a bad thing, specially for those with very low tuned ported subs.

whoa there cowboy.....who said "DIY guys dont believe it is needed"? :confused: I've been saying it all along that it certainly is not a bad thing, specially for those with very low tuned ported subs.

Sherv, just curious why the hi-pass is needed more with very low tuning than with tuning that is not so low. I'd think it would be more important the other way around. The main purpose of the hi-pass filter is to protect the driver from content that occurs below the tuning. If you are tuned very low, let's say 13 or 14hz, there is very little content that you will find below that. On the other hand, if you are tuned at 20 or 22hz, it is not that uncommon to find high-powered content just below that in the high teens which can make a sub act crazy. Think "Pulse".

Sherv, just curious why the hi-pass is needed more with very low tuning than with tuning that is not so low. I'd think it would be more important the other way around. The main purpose of the hi-pass filter is to protect the driver from content that occurs below the tuning. If you are tuned very low, let's say 13 or 14hz, there is very little content that you will find below that. On the other hand, if you are tuned at 20 or 22hz, it is not that uncommon to find high-powered content just below that in the high teens which can make a sub act crazy. Think "Pulse".

not quite Mike.

There are a couple of issues with putting highpass filters high up the Frequency range (say closer to a 20hz tune for example). The 4th order rolloff will start to affect audible ranges and have a substantial impact at around tuning, and above. Additionally, the time required for a system to recover from the effect of the HP filter, at the lower frequency ranges of 10-13hz, will not have the degradation effect and the corruption on the signal as one with the HP filter operational at higher frequencies. "pulse" is irrelevant at this point. ;)

There is a difference between some of the "LLT" owners and some of us, in whether HP is needed at all. I'm under the camp that certainly if you have an EBS with a low tuning point, say 13hz, than an HP at 10hz is not gonna impact your system audibly, while giving you protection on frequency ranges below 10hz were your driver excursion limits are being tested. The coloration of the signal done by the HP filter that low, is not going to impact the visceral impact of the subwoofer at that range. The reverse is not true, however, if you are discussing the filter at a higher point (18hz, just as an example).

The audible effect of the filter is a whole 'nother issue altogether. For a higher tuned sub, the possible effect on the audio vs. the benefits of protection is a trade-off decision that any sub maker would need to make. I know that SVS, for example, does use filtering just below tuning and it doesn't seem to have any deleterious effects. For a low tuned sub, there doesn't seem to be much down side to filtering, but since there isn't much content down there anyway, the benfits are also few.

I've not looked to deeply. But I see that many commercial subs with measurements posted online have built in limiters which are also designed to limit low frequency over excursion. The way to tell from measurements would be to see whether they roll off at faster than 24dB/oct. It is sometimes easier to tell this if you have a program that can graph the target slope with the sub's Fc.

In the DIY world, most plate amps and amplifiers have some kind of DC filtering capacitors, and many manufacturers place the filter frequency to protect from subsonic content. I think that those that use no high pass make the assumption that electrical frequency response of their signal chain already includes a high pass (or perhaps measure it). Or they have no media with low frequencies, or they have infinite subwoofer displacement on tap.

The audible effect of the filter is a whole 'nother issue altogether. For a higher tuned sub, the possible effect on the audio vs. the benefits of protection is a trade-off decision that any sub maker would need to make. I know that SVS, for example, does use filtering just below tuning and it doesn't seem to have any deleterious effects. For a low tuned sub, there doesn't seem to be much down side to filtering, but since there isn't much content down there anyway, the benfits are also few.

what do you mean is a "whole nother issue".....that IS the issue. Certainly if there were no tradeoffs in audible effects vs. protection, then it would be a no brainer. THat's why KG asked, and I'm pretty sure that's why he said "DIY guys dont like to use it", when I think most DIY in fact would feel safer using one. Chuck spent many days developing the schematics for a simple one for that same exact reason. The benefits are not that "few" I'm afraid....there are substantial amount of information nowdays in the low teens and single digits, and at some of the levels these big ported subs are running, an HP filter can always help prevent damagin the driver for over excursion.

There are two issues to consider. One issue is the negative effect on the SQ that the filter may impart. The other issue is the positive protection the filter may add. As with almost everything else, tradeoffs are sometimes made. Perhaps decisions are made that a little bit of ringing is acceptable in exchandge for keeping the driver from overextension. Say you have your typical ported sub tuned at 20hz. Now you feed it a powerful soundtrack which includes material at, let's say, 18hz, would you rather have some filtering, preventing overextension and possible damage given that some ringing may be imparted, or would you rather run filter-free knowing that you might have to run for the volume control at any instant? It's a trade-off which many manufactures regularly make so that their subs will last.

Ok, educate me, and I'm being sincere here, not taking a shot. How does a HP filter induce ringing?

Thanks,

Tim

I not really sure how it happens, but I believe it to be a by-product of having a too-sharp roll-off slope.

So it's safe to say there is some sort of filter in most if not all commercial ported designs.

I'll let you boys continue and probably learn a bunch too. Thanx

KG

I not really sure how it happens, but I believe it to be a by-product of having a too-sharp roll-off slope.


IIRC Ed Mullen discribed at as a sharp knee at the tuning point. The lower the tune the less the effect is audible...not saying the ring isn't there, It's just less audible.

This is why PEQing mains is tricky and dangerous.You may fix one problem, but cause real audible distortion issues @ the same time (hence the sale of my three PEQ's).


KG

So it's safe to say there is some sort of filter in most if not all commercial ported designs.
I'd say it'd be rare to find one without. With most commercial products, the most important aspect of design is protecting a product from its owner. Even most sealed subs have them, the original AV123 little rosewood woofer had something like an 84dB/Oct rolloff. Of course, that it was so loved by many for "musicality" might perhaps speak to the audibility of such.

There are two issues to consider. One issue is the negative effect on the SQ that the filter may impart. The other issue is the positive protection the filter may add. As with almost everything else, tradeoffs are sometimes made. Perhaps decisions are made that a little bit of ringing is acceptable in exchandge for keeping the driver from overextension. Say you have your typical ported sub tuned at 20hz. Now you feed it a powerful soundtrack which includes material at, let's say, 18hz, would you rather have some filtering, preventing overextension and possible damage given that some ringing may be imparted, or would you rather run filter-free knowing that you might have to run for the volume control at any instant? It's a trade-off which many manufactures regularly make so that their subs will last.

it's not that simple. First, the protection the HP gives you to avoid damage is mostly due to the mechanical limitations of the driver you are using. So, although you could have a sub that is tuned to 20hz, it could have enough mechanical travel to perform down to the upper teens. Conversely, you could have another similar sub tuned to 18-16hz, but at its mechanical limits, it would be at overexcursion right below it's tuning point. Of course, all this depends on whether or not the power plant was maximized for its excursion capabilities.

second, the issue of coloration caused by a HP is very well documented, particularly as you go up the frequency range. In your example, at 18hz, the effects on the audible range caused by the HP will be very noticeable. At those particular wavelengths, the delta time required for the signal stimulus to come back to steady state is much farther than at the lower frequency, and furthermore, you are no corrupting frequencies of 20+ hertz, clearly in the audible range.

Here's a question: Which do you think would sound worse?

1. A woofer unprotected by a filter, driven into uncontrolled motion a few hz below it's tuning.

or

2. A woofer driven with the same signal hi-passed having very little uncontrolled motion, but now accompanied by some filter induced artifacts.

I'm thinking that #1 would not only sound worse but would be putting the woofer at risk. This is why in reality, compromises are made and frequently hi-pass filters are used in many commercial subs.

that's a bit of a generalization Mike...it's not that simple, I keep saying that.

1. in this scenario, how are you sure the woofer is "driven into uncontrolled motion" below it's tuning point? what if you are using a capable subwoofer such as an LMS5400, an Avalanche, an RL-P18, a Conquest driver, a TC2k, etc, and are giving it adequate power but less than its mechanical limits below tuning point?

take the avalanche driver just as an example (any driver at this point works). Here is the displacement driven with a 500W power plant in a large enclosure tuned to 13hz:
http://i44.photobucket.com/albums/f38/ssabripo/misc_stuff/zzz2.jpg
here is the displacement with 1000w in the same enclosure:
http://i44.photobucket.com/albums/f38/ssabripo/misc_stuff/zzz3.jpg

With 1000W, notice how not only are you pushing the limits of the driver at or close to tuning point, but you are hitting its Xmax a couple of hz below tuning. At the same time, with 1/2 the power (still very adequate), you are pushing that limit into single digits (a good 6-7hz below tuning) but are well within its limits without distortion at its tuning point.

2. The artifacts and coloration introduced at higher frequencies will have its effect long into the frequency range, than the same coloration stimulated at a lower treshold. As an example, here is Ilkka's measurement of a 20hz tuned ported sub and how long it took to reach full amplitude with a 20hz sine wave – first using an amp with a discrete high pass filter built in at 18hz:
http://personal.inet.fi/private/ilkka/misc/20hz_wave_sealed_vented_lp.png
and now with no filter:
http://personal.inet.fi/private/ilkka/misc/20hz_wave_vented_nad.png

With the filter engaged, it took nearly 200ms to reach stability, and thus, you can calculate how much coloration on the frequency range it would have impacted it. Without the filter engaged, it took less than 1/2 that.

So, to answer your question, it would all depend ;). If you give me a woofer with good mechanical limits, with more power headroom, and relatively efficient enclosure design, I'll take your number 1 option everytime! But, if you have a relatively basic woofer, with maximized power for a given enclosure and tuning point, then yes, option 2 is the most logical option.............my point is, it's not all black and white. :)

Whether filtering (whether it be HP, LP or BP) is audible has been debated and will be debated for long. Thus far I haven't seen any study or paper etc. that would clearly state that humans could hear slightly added low frequency group delay. Please point me wrong if there is such study.

It's basic signal theory that filtering rises the group delay around and below the filter, but is it audible? I mean there are subwofers and main speakers with steep filters even in ~40-50 Hz range, but they still sound very 'quick'. IMO it's not filtering that makes some subwoofers/systems sound 'slow'.

Another question is whether a HP below a tuning frequency is needed. We can of course discuss about listening levels and mechanical limits and such but there's no denying that when listening to regular program material, the lower the tuning frequency is, the less NEED for a HP filter there is. So when comparing a, say, 25 Hz tuned and 13 Hz tuned subwoofer, without doubt the 25 Hz one needs and also benefits from a HP filter more.

Whether filtering (whether it be HP or LP) is audible has been debated and will be debated for long. Thus far I haven't seen any study or paper etc. that would clearly state that humans could hear slightly added low frequency group delay. Please point me wrong if there is such study.

It's basic signal theory that filtering rises the group delay around and below the filter, but is it audible? I mean there are subwofers and main speakers with steep filters even in ~40-50 Hz range, but they still sound very 'quick'. IMO it's not filtering that makes some subwoofers/systems sound 'slow'.

Another question is whether a HP below a tuning frequency is needed. We can of course discuss about listening levels and mechanical limits and such but there's no denying that when listening to regular program material, the lower the tuning frequency is, the less NEED for a HP filter there is. So when comparing a, say, 25 Hz tuned and 13 Hz tuned subwoofer, without doubt the 25 Hz one needs and also benefits from a HP filter more.

Thank you Richard. You have restated my point precisely.

I agree with the generalization.

of course, 25hz and 13hz tuned subs are VERY different applications. I, for one, would NEVER get caught dead with a sub tuned to 20-25hz, HP filter or not. :p

I was asked if all commercial ported subs have a hipass built in. I'm too lazy to search, so I thought I'd ask you guys. I know the DIY guys don't believe it is needed, I was just wondering what the industry does.

He was debating on building or ID purchasing. Thanx KG
Yes, pretty much every commercial (whether it be B&M or ID) ported subwoofer has a high pass filter below its tuning frequency being built in.

Though IMO that is pretty much the least important thing you should worry about when shopping for a new subwoofer.

DIY or ID purchasing is a whole another matter.

I, for one, would NEVER get caught dead with a sub tuned to 20-25hz, HP filter or not. :p

Heavens, no!:p That's like a mid range!

Heavens, no!:p That's like a mid range!

:D

I think the title should say "infrasonic" filter, as high-pass filters usually meant for the satelite, or any speakres that has limited bass and high passed to the sub. In some cases it is built into the sub on it's speaker level outputs. Just a thought.

I think the title should say "infrasonic" filter, as high-pass filters usually meant for the satelite, or any speakres that has limited bass and high passed to the sub. In some cases it is built into the sub on it's speaker level outputs. Just a thought.
Yeah, that's what I thought he meant, too, until a read a few posts.

Yes, pretty much every commercial (whether it be B&M or ID) ported subwoofer has a high pass filter below its tuning frequency being built in.

Though IMO that is pretty much the least important thing you should worry about when shopping for a new subwoofer.

DIY or ID purchasing is a whole another matter.


The OP had no other question than the question asked. He never knew the side effects good or bad.

You guys are real eggheads, I love this place:D

kg