Suggestions about woofer EQ - Home Theater Forum and Systems -

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post #1 of 7 Old 09-12-09, 01:58 AM Thread Starter
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Suggestions about woofer EQ

Hey you woofer freaks, I have a question for you:

When Eq'ing your subs, how do you do it? Do you go ahead and Eq way past their abilities, or do you stop at their F3 point (which is often disappointing)? If EQ'ing past their abilities, how so? Do you just nudge them, or push them hard? And what kind of woofers do you have (Sealed, ported, infinite etc (important))?

We're trying to set our standards, and I believe input from the experts (you) is what I'd really like. Thanks for your suggestions! (not too humble to ask)

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post #2 of 7 Old 09-13-09, 12:42 AM
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Re: Suggestions about woofer EQ

I can tell you that I have never looked at an F3 point on a sub I have owned or built. I generally consider the capabilities of the driver in DIY builds by modeling it on WinISD. My designs have always been based on the LLT platform, tuning to various frequencies, but most always between 12-18Hz. I missed a bit on one build at probably about an 8Hz tune, but the drivers easily handle it.

It seems that most people building subs will obtain drivers capable of extending below 20Hz... most seem to be able to extend to 15Hz. Most of your built-in equalizers are now equalizing to 10Hz or to what it measures the driver to be able to handle.

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post #3 of 7 Old 09-13-09, 06:09 AM
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Re: Suggestions about woofer EQ

I can tell you that I have never looked at an F3 point on a sub I have owned or built.
Same for me. Whatever box size and tuning frequency I use, it's all about using the proper Hi-Pass filter to get the most cone excursion and low frequency extension from the sub, within its rated Xmax.
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post #4 of 7 Old 09-22-09, 11:27 AM
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Re: Suggestions about woofer EQ

I'm late to the party but +2. I don't care about the F3 at all really. The room that the subwoofer will be used in dominates the FR and useful extension so completely that F3 just doesn't matter for me. When designing I'll look more at the -6 and -10db point in the base FR along with the power response and everything else. I have ported and sealed subs and will probably add tapped horn to that soon. I try to avoid EQ as much as possible.

IMHO it would be useful to have different options for vented/horn/ BP6 subs which should never be boosted below the tuning and sealed/IB/BP4 subs which are more tolerant of EQing the low end up.

I don't know if it's a good idea to generically boost below the knee for any subwoofer really. You should already be getting some gain from the room to your subwoofers low end anyway, which will be extending it's response a little lower. Wherever the sub is rolling off in room is the extent of the subs extension and clean output capabilities most likely. If it's a commercial sub design (SVS,JL,Rythmik, Velodyne, etc) then the extension of the sub is likely eq'd as deep as feasible by the Mfg already. DIY subs will either be really extended through porting already or will be LT'd or EQ'd by the DIYer as part of the design if they are sealed or IB.
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post #5 of 7 Old 09-22-09, 04:26 PM Thread Starter
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Re: Suggestions about woofer EQ

Hmm, interesting responses. Thanks to all of you.

Ricci, I have thought about having the user input the type of sub before. My logic was much along the same lines you said, that a vented sub should never be boosted below the tuning frequency. We have even tossed out the idea of near-fielding the sub to determine that frequency, and the type of enclosure. The problem is it would be too complicated to too many users. We strive to make our system nearly foolproof, but of course there is no such thing. The best we can hope for is fool-resistant.

What's interesting mostly is the lack of concern of F3 points. I'm guessing that is due to the types of subs people in this forum tend to favor. Granted, an F3 point is, in itself, of little value, unless it is caused by something like port tuning. It is usually the point where compensating below it starts to give diminishing results, but also the most improvement if you can obtain it.

Regarding manufacturers already getting as much extension as possible from a design, while that's what I would think too, it hasn't been my observation. I find that many go for SPL (which usually means higher (or boomy) bass) over extension.

Thanks for revisiting the vented vs sealed setup idea, I will re-think that one.

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post #6 of 7 Old 09-25-09, 01:50 PM
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Re: Suggestions about woofer EQ

We're trying to set our standards, and I believe input from the experts (you) is what I'd really like. Thanks for your suggestions!
I assume you’re dealing with your customers asking WRT your equalizer? It is a bit of a challenge, I’m sure, since you’re dealing with people with both manufactured subs and prodigious DIY fare.

There are some “accepted” rules of thumb, like you should only use cutting filters and minimize boosted filters, if they are used at all. This “rule” is based on the faulty premise that boosted filters places increased demands on the sub, while subtracting filters do not. But if you are equalizing to eliminate say, an 8 dB resonant peak at 40 Hz, you’ll find that afterwards your sub is not loud enough. What will you do? Adjust the sub level higher, of course, to compensate. Well, say goodbye to the “free” headroom you supposedly got by cutting the peak.

Another “rule of thumb” is that you shouldn’t boost a ported sub below the tuning frequency of the port. But the truth is, the program material in a movie can do the same thing despite equalizing “by the rules.” For instance, early in the latest Batman movie Dark Knight there is an extreme level of bass generated in the 25 Hz range and lower. Well, I’ll bet anyone with a ported sub tuned at 30 Hz or higher experienced some nasty noise there. It doesn’t matter if the low frequency boost comes from an equalizer or the program – it’s all the same to the sub.

As you can see, at the end of the day the “accepted rules” don’t matter much. When it gets right down to it, only rule that matters is “headroom,” because any equalization places additional demands on both the amplifier and the driver. You have to have headroom to spare – both before and after equalization, but especially afterwards. If not, there will be rude noises from the sub during demanding passages.

When advising customers on equalizing, I’d consider the sub they’re using. With few exceptions, most subs with small 8" or 10” drivers should keep equalizing to a minimum. The same holds for subs with larger drivers, but low-powered amplifiers.

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post #7 of 7 Old 09-30-09, 02:21 PM Thread Starter
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Re: Suggestions about woofer EQ

Hi Wayne, thanks for your reply! I have to say that I couldn't agree with your analysis more. Just using cut filters to equalize doesn't do anything but reduce the overall level compared with cut / boost, especially since the frequencies one is cutting are the loudest. After the EQ, ultimately the response is the same (or close) whether only cutting, or cutting / boosting. Once the level is set, the output will be the same. We do like to limit the boost just so if there is a deep null (if someone doesn't move the mic, or because it exists at all measuring locations) we don't drive the system into saturation due to compensation. Our goal is to equalize while maintaining the original levels (before we compensate for those as well, that is)

Having designed my share of subwoofer amplifiers for various manufacturers, I know that they usually specify steep filters below the Helmholtz frequency, so boosting a little down there isn't too detrimental; but it doesn't help either. Most of our customers have mass produced subs, so they do need to be designed to live with a vast array of situations. Then again, so does our product.

I appreciate your input and your knowledge. It lends confidence that we're doing the right things. That's never bad.

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