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Discussion Starter · #1 ·
My Setup:
2 SI HT18 D4 in heavily stuffed sealed boxes, each on inuke3kdsp channel @ 2ohms. ie. 1100w of power RMS to each sub. in the front corners of my space (1/8th space).

Measurements:
I measured three spots in the room, audyssey off, and averaged them. I then eq'ed the average at 1/12th smoothing. I try to avoid filters with a Q above 8 as the room will have infinitely more spots i haven't measured and I don't want to cut out/notch the bass too much. In the screenshot you see thanks to room gain, my si18's are down 3db at 16hz, not too shabby.

So i thought, let's go for more extension.. below that...

Proposed filters:
LS12 at 20hz +15db
PEQ at 20hz -15db Q=5

The rest are specific to my room.

Now onto my questions...

Am i going to blow these subs up doing this???

Should i set a limiter? at what? Hold setting? Release Setting? I do 50/50 music/movies.

I've seen @LTD02 talk about a HS12 with neg gain and then raise the overall gain on the inuke by the same amount. Am i doing the same thing with what i've proposed above? They look different as i play with the eq in REW, so i'm not sure.

Should i set delays that are different per sub? They are on the front wall about 7' apart and equidistant from all boundaries.

here is my REW file, should anyone want to check it out:
https://www.dropbox.com/s/md7ww1sdgchmjcg/3-6-2015.mdat?dl=0

thanks,

Pete
 

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the rolloff of the sub is about q=.7, so simply applying a 12db/oct shelf filter should for fine for bring up the low end.


each 3db added to the low end however takes 3db of headroom out of the rest of the bass.
i wouldn't add any more than about 6db, which is pretty close to where you are now, effectively, unless you are happy to turn the whole subwoofer channel down in volume.
if you are out of headroom as it is on the higher frequencies, then you need more subs.
if you have tons of extra headroom on the higher frequencies, then by all means boost the heck out of the low end.


also each 3db of boost requires twice the amp power and 40% more cone excursion. adds up fast.
 

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Discussion Starter · #3 ·
the rolloff of the sub is about q=.7, so simply applying a 12db/oct shelf filter should for fine for bring up the low end.


each 3db added to the low end however takes 3db of headroom out of the rest of the bass.
i wouldn't add any more than about 6db, which is pretty close to where you are now, effectively, unless you are happy to turn the whole subwoofer channel down in volume.
if you are out of headroom as it is on the higher frequencies, then you need more subs.
if you have tons of extra headroom on the higher frequencies, then by all means boost the heck out of the low end.


also each 3db of boost requires twice the amp power and 40% more cone excursion. adds up fast.
Thanks, I'm glad I'm on the right track. Do you think boosting like this has any effect on distortion? I think I'll set a 3db limit on the inuke to keep things safe. Good idea? Bad?
 

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The more you max out the output of the subs, ie keeping them thumping away at Xmax, the more distortion you'll have. The boost could make it easier to do that. But I wouldn't worry about it too much. On my subs, music* doesn't push them to their limits at all, not even close. Movie LFE does, but when things are exploding, I'm not sure I could tell the difference.

I wouldn't bother with a limiter. The driver can take every drop of power that amp has; it's not like the boost can make an NU30000 start pushing 5000W per channel.

* Normal music, not bass torture test type stuff
 

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Discussion Starter · #5 ·
The more you max out the output of the subs, ie keeping them thumping away at Xmax, the more distortion you'll have. The boost could make it easier to do that. But I wouldn't worry about it too much. On my subs, music* doesn't push them to their limits at all, not even close. Movie LFE does, but when things are exploding, I'm not sure I could tell the difference.

I wouldn't bother with a limiter. The driver can take every drop of power that amp has; it's not like the boost can make an NU30000 start pushing 5000W per channel.

* Normal music, not bass torture test type stuff
Thanks. What tends to scare me is when you model a driver like this in winisd in a sealed box and you apply filters to mimic the ls12 and peq combo I listed above, the excursion goes way up and you have to lower the watts in winisd drastically or it shows over excursion. That thinking (not sure if it's right or wrong) made me ask if I should put a limiter on there because all the extra signal down low would cause the sub's to over extend and destroy themselves. I wish I studied these things in college rather than the limits of alcohol consumption.
 

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Increasing the power is exactly what the boost does. +3dB boost literally doubles the power at the boosted frequency. Look at the apparent amplifier load graph. That will show you the power being drawn from the amp at each frequency.

Now, no matter how much boost you apply, you can't get more power than the amp can actually apply. So even you set WinISD for 1000W signal and +3dB boost, you can't get 2000W from one channel of that amp. Of course, if you apply the boost and all it does is make the amp clip (or trigger the limiter), there isn't much point to the boost.

So lowering the Signal in WinISD is exactly what you want to do. Think of Signal as the baseline power level, not a max or min. Actual power will be a function of impedance of the driver, box, and filters applied.

Another thing to consider is that you don't have to boost the bottom at all. You can cut the high end as well. The end result is exactly the same.
 

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Also, the question of "how much can I boost the low end" isn't one that WinISD can address. It depends on everything else. If you listen with AVR volume set to +5 with the upper bass 10 dB hot, you probably can't boost at all. If your AVR never goes above -20, maybe you can boost the bottom by 15 dB.
 

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the best way to see your power limit on excursion is to model your sub and turn all the eq/filters etc. OFF.
apply the max power that your amp can output and check excursion. if it is ok, then it doesn't really matter what eq you put on the sub, because the amp is just going to run out of power and clip or compress the signal before the driver overshoots anyways.
 

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Discussion Starter · #10 ·
Thanks guys, I'm going to spend some time studying my data more. I think I'm starting to understand this. Bottom line take away right now is the inuke 3kdsp cant take my si ht18 d4's to xmax in 4cuft with its 1100w RMS capability. That makes me feel better about playing around with these settings.

Once I update the inuke with these new filters, I'll dial it back in at 75db with zero gain on the avr to match the other channels on my avr (using rew and the umm6 as an spl meter) that are -1 or -2 at 75db on the avr. Then I'll see how much of the external dials "clicks" i have left on my inuke. That is my headroom, right?
 

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Thanks guys, I'm going to spend some time studying my data more. I think I'm starting to understand this. Bottom line take away right now is the inuke 3kdsp cant take my si ht18 d4's to xmax in 4cuft with its 1100w RMS capability. That makes me feel better about playing around with these settings.

Once I update the inuke with these new filters, I'll dial it back in at 75db with zero gain on the avr to match the other channels on my avr (using rew and the umm6 as an spl meter) that are -1 or -2 at 75db on the avr. Then I'll see how much of the external dials "clicks" i have left on my inuke. That is my headroom, right?
Several thoughts

1, if you EQ flat and then turn up the sub amp, your acoustic cross over will be raised, this may or may not be desirable

2, Staying within the xmax of a driver will protect form over excursion, but it doesn't mean your voice coil is safe from over heating. It is easily possible to destroy a driver without ever hitting xmax (this is a generality, I don't have enough experience with this specific driver, but unless SI has magic unobtanium, the physics are the same)

3, I am firmly in the camp of belief that one should never boost with an EQ. Make Cuts to compensate for room issues, but you can't boost your way around room issues, or the limits of a driver/enclosure. If the frequency response of the driver/enclosure combination doesn't provide the frequency response you want, change the driver/enclosure design/combination to something that does. Model, measure outside in half space to see if the design performs as the model indicates. Repeat until you get the result you want.

That said - good luck!
 

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Discussion Starter · #12 ·
Hoping to take some measurements today to dial in the new settings and I will also see if I have time to cut using the hs12 with neg boost at 20hz. I'm not sure what you mean my moving the acoustic crossover, does that mean like a linkwitz transform? Many boost their sealed sub's to go beyond what room gain provides naturally. I didn't think that was a bad thing.
 

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I just fired up the software for the first time; I've been using the front panel until now.
It erased all my settings, which, of course, I hadn't written down anywhere, so now I get to start all over.
I am NOT a happy camper at the moment.
:mad:
Thank you for letting me vent. And be forewarned.
Michael
 

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Oh no! Sorry man!!! I started out using the software so my settings were asked there.
How do you go about using a laptop to work with the dsp in the inukes? I can't find where to download anything on the Behringer website. And plugging the amp into my laptop with the supplied usb cable has not done anything. I ran a quick eq with REW and manually input the PEQ filters via the front panel.
 
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