High pass filter for ported sub, is it necessary? - AVS Forum
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post #1 of 14 Old 12-05-2013, 07:17 PM - Thread Starter
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I've been working hard on my first subwoofer modeling project. My first build was a sealed enclosure and i did a lot based on gut feel eek.gif

Anyway, here's my current cone excursion graph in winisd pro (yellow line):



Build specs:
Dayton Ultimax 15''
525W input power (probably powered by Crown XLS 1000)
11.1 ft^3 box
17Hz tune
4'' Flared ports (18'' long) (2 of them)

As can be seen from the excursion graph, at about 15hz the cone excursion rockets off. Having never built a ported enclosure i'm a little concerned. Is my driver in danger of damage? Do I need to design a high pass filter for the system? I know the Crown XLS has either a high or low pass filter (cannot use both at the same time). I was planning on using it's low pass filter to avoid higher frequencies, but maybe i need to use the high pass filter?


Any help appreciated! I'm new at this still...
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post #2 of 14 Old 12-05-2013, 07:28 PM
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Definitely should have a hpf. Just takes one killer track to fry your sub. Don't have a crown but someone will chime in with how to.
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post #3 of 14 Old 12-05-2013, 07:30 PM
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Your preamps or receiver should do the lpf and the crown the hpf.
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post #4 of 14 Old 12-05-2013, 07:42 PM - Thread Starter
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I have a Pioneer SC-65 AV receiver running the system, but no other pre-amps. I looked around but couldn't find anyway to set a filter in the pioneer. Is there any standalone DSP high pass filters I could purchase? All of the stuff I have seen is manually wiring cards to accomplish it, that seems way out of my league
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post #5 of 14 Old 12-05-2013, 07:56 PM
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Quote:
Originally Posted by jeremymef View Post

I have a Pioneer SC-65 AV receiver running the system, but no other pre-amps. I looked around but couldn't find anyway to set a filter in the pioneer. Is there any standalone DSP high pass filters I could purchase? All of the stuff I have seen is manually wiring cards to accomplish it, that seems way out of my league

The pioneer must have a lfe setting . Set that to 120hz. Set your main speakers to. 80 hz.
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post #6 of 14 Old 12-05-2013, 11:03 PM - Thread Starter
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Originally Posted by chalugadp View Post

The pioneer must have a lfe setting . Set that to 120hz. Set your main speakers to. 80 hz.

After going through every menu item possible on my AVR i found that the xover for my system is at 80Hz. I guess this can mean a great deal of things based on how I have it set up, but if I got with an LFE line out to the Crown, i'm fairly positive that my AVR will act as the LPF for the system. According to some other reading i've done the crown supports a HPF which I can use to keep excursion down and save my driver.

Has anyone used the Crown XLS HPF? I'm going to be looking into the crown manual more tomorrow to make sure that it supports what i've read....
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post #7 of 14 Old 12-06-2013, 04:48 AM
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Consider hooking up a tone generator to the AVR and see if it and the amp (assuming you have it) will even pass signals below 20 Hz. Perhaps one of the engineers didn't see a reason to pass a signal below 20 Hz since it is hard to hear and often destroys gear.
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post #8 of 14 Old 12-06-2013, 05:17 AM
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The Pioneer receivers have a single, universal crossover for all of the channels, (I think), so if your crossover in the receiver is set to 80hz, that is your low pass filter. IIRC the Crown XLS series of amps rolls off or has a built in hpf at 20hz. So you should be good!
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post #9 of 14 Old 12-06-2013, 03:44 PM
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Quote:
Originally Posted by jeremymef View Post

Has anyone used the Crown XLS HPF? I'm going to be looking into the crown manual more tomorrow to make sure that it supports what i've read....

Usually there's a too-high selectable HPF at 30 Hz and a nondefeatable one at a too-low freq, unless you tune to 10 Hz

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post #10 of 14 Old 12-07-2013, 08:09 AM
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I'm in the minority, but needing a HPF to protect a ported alignment Is not *absolutely* necessary. It depends on your SPL preference, the frequency content of the source material, the driver's impedance curve below tuning, and any natural frequency rolloff in your equipment. I've been running a pair of Dayton RSS315HF-4 in ported cabinets without a HPF for years without issue. I do have the available power and frequency response to overdrive them according to the models, but it hasn't been an issue in the real world. Typical playback level is -10dB below Reference. YMMV. .

That said, 11 ft^3 seems like an extremely large cabinet, which probably contributes significantly to the excursion below tuning due to the lack of air spring. If you're prone to turning it up to "11", then some sort of electronic nanny is probably a good thing. I don't have modelling software on this computer to see what your impedance profile looks like to see what kind of mitigation that might offer.

-Brent
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post #11 of 14 Old 12-07-2013, 11:27 AM
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Originally Posted by riverwolf View Post

I'm in the minority, but needing a HPF to protect a ported alignment Is not *absolutely* necessary.
+1. If you want to play at the maximum average SPL possible then you need a HP filter, and you have to accept the lessened pass band, whether ported, sealed, IB, OB or horn. If you want maximum bandwidth you don't need to HP, so long as you know how much voltage you can apply to the driver without exceeding xmax, and you have a limiter to insure that it doesn't.
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That said, 11 ft^3 seems like an extremely large cabinet,
That's what happens if you use a low EBP driver intended for a sealed cab in a ported cab. Actually the UMax 15 models best in 16 cu ft.

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post #12 of 14 Old 12-07-2013, 02:45 PM - Thread Starter
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Quote:
Originally Posted by Bill Fitzmaurice View Post

That's what happens if you use a low EBP driver intended for a sealed cab in a ported cab. Actually the UMax 15 models best in 16 cu ft.

So i've heard that before and I can't really find any higher ebp drivers for the same price point. Do you have any suggestions?
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post #13 of 14 Old 12-07-2013, 03:13 PM
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Quote:
Originally Posted by riverwolf View Post

That said, 11 ft^3 seems like an extremely large cabinet, which probably contributes significantly to the excursion below tuning due to the lack of air spring.

Any size box has essentially no air spring below Fb.

Noah
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post #14 of 14 Old 12-07-2013, 04:44 PM
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Quote:
Originally Posted by jeremymef View Post

So i've heard that before and I can't really find any higher ebp drivers for the same price point. Do you have any suggestions?
RSS 390HO.

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