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Discussion Starter · #1 ·


Leaving the real life trade offs aside, just judging by the FR alone, how much difference would the slightly better LF extension in the lower tune version make in practical terms? Is this something readily audible?

thank you
 

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I myself would go with the 15hz tune. You will gain a few more db's of SPL from 15hz to roughly 30hz. And from there you are 1.5db hotter than the 12hz tune.

Down low the 12tune wins by a huge margin. At 10hz you have a 5db gain but at 13hz they are the same. You will have lots of room gain also to aid both.

16cuft 15hz tune Hpass at 14hz 2nd order 550watts to hit Xmax and hits 113db at 20hz.
16cuft 12hz tune Hpass at 12hz 2nd order 450watts to hit Xmax and hits 111db at 20hz.

You will enjoy most of your movies bass from 20hz and up. But maybe you want this extension verse the 20hz db.
 

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Discussion Starter · #3 ·
I myself would go with the 15hz tune. You will gain a few more db's of SPL from 15hz to roughly 30hz. And from there you are 1.5db hotter than the 12hz tune.

Down low the 12tune wins by a huge margin. At 10hz you have a 5db gain but at 13hz they are the same. You will have lots of room gain also to aid both.

16cuft 15hz tune Hpass at 14hz 2nd order 550watts to hit Xmax and hits 113db at 20hz.
16cuft 12hz tune Hpass at 12hz 2nd order 450watts to hit Xmax and hits 111db at 20hz.

You will enjoy most of your movies bass from 20hz and up. But maybe you want this extension verse the 20hz db.

thank you. I suspect you are talking about different models/drivers though. As you can see, in my models, output above 17Hz is identical for both versions.
What I am trying to figure out is how much difference the LF advantage of the 12 tune really makes. yes, it has 6 dB advantage at 10 Hz but it is already -14dB at that point anyway. so does it really matter?

what do you think?
 

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I am looking at spl, excursion and applying wattage.


SO I am sure we are on the same page but you are only looking at the Transfer Function Magnitude screen.
 

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Discussion Starter · #5 ·
and while I have your ear, chrapladm.
what options are there for precise HPF below 20Hz other than MiniDSP?
well, I know how to mimic 15 Hz 2nd order with inuke DSP but nothing lower than that. There is berry FBQ3102 that has variable 3rd order HPF from 10 to 400 Hz but it's controlled by a knob, I am not sure it can be trusted for this job. do you have any experience with it?
 

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Discussion Starter · #6 ·


this is with 1000W input power. excursion is a little over Xmax at this power but definitely within Xlim.

yours is probably D2 version. Mine is "unofficial" D4. the driver is attached.

I am looking at spl, excursion and applying wattage.


SO I am sure we are on the same page but you are only looking at the Transfer Function Magnitude screen.
 

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You simulation still is different than mine. Why do you have a Hpass of 20hz on the 15hz tune?

Here is my simulation with your driver file and EQ. The Xmax is 22.5mm on the SI website not 23.5mm. I also only took the drivers to Xmax in the simulation. 715watts for the 15hz tune and 550 watts for the 12hz tune.

I believe the Behringer DCX2496, Mic2200 and a few others out there work down to 10hz just fine for Hpass.
 

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Discussion Starter · #8 ·
I understand what you are doing now. Looking at what can be squeezed from each alignment without exceeding Xmax is a great way to compare, one I have not thought of before. Thank you.

I was approaching this from a slightly different perspective. I have Inuke NU3000DSP which allows me to power a pair of these for a total of 4 Ohm load, giving approximately 900W RMS per driver. So I was looking at what each alignment can offer at that power while keeping the driver safe though not necessarily linear. Based on my listening habits I will almost never be at max power any way.

the 20Hz 1st order HPF combined with 2dB boost @20Hz with Q=1 models very close to 15Hz 2nd order HPF. I am doing this because it is not possible to set any filters below 20Hz in Inuke DSP (the same is true for DCX2496 AFAIK).

I think I am going to follow your advise and settle on 15Hz tune.

You simulation still is different than mine. Why do you have a Hpass of 20hz on the 15hz tune?

Here is my simulation with your driver file and EQ. The Xmax is 22.5mm on the SI website not 23.5mm. I also only took the drivers to Xmax in the simulation. 715watts for the 15hz tune and 550 watts for the 12hz tune.

I believe the Behringer DCX2496, Mic2200 and a few others out there work down to 10hz just fine for Hpass.
 

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I want to ask the exact same question. So I hope everybody doesn't mind if I ask it in this thread rather than start a virtually identical thread.

I have a couple SI HT18D4s coming. Originally, I was planning a 12Hz tune, but given the size of the tubes I'm ordering (750mm), and the height of my ceiling, I can do 700L, and have enough room to make a port long enough to reach down to 10Hz.



In my simulation, I put a 1st order HP filter at 8Hz to simulate signal chain rolloff. I'm planning on actually measuring my signal chain to see where I truly stand, but at this point, I'm planning on running no HPF. At 50Hz, I aligned all three curves at 112db because I am building two of these, and as such I should gain a 3db advantage which will get me to 115db. Also, my room gain should start at 30Hz, so by the time I get to 20Hz, I should have at least a few db of room gain to boost 20Hz pretty close to 115db.

For power I'm planning an iNuke3000DSP. I like that it has a programmable peak limiter so that I can throw in some protection against >0dbFS peaks which are theoretically possible, from what I've read.

Is there something I'm not thinking about which might make me want to dial back to a 11 or 12Hz tune?
 

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Discussion Starter · #10 · (Edited)
I want to ask the exact same question. So I hope everybody doesn't mind if I ask it in this thread rather than start a virtually identical thread.

I have a couple SI HT18D4s coming. Originally, I was planning a 12Hz tune, but given the size of the tubes I'm ordering (750mm), and the height of my ceiling, I can do 700L, and have enough room to make a port long enough to reach down to 10Hz.



In my simulation, I put a 1st order HP filter at 8Hz to simulate signal chain rolloff. I'm planning on actually measuring my signal chain to see where I truly stand, but at this point, I'm planning on running no HPF. At 50Hz, I aligned all three curves at 112db because I am building two of these, and as such I should gain a 3db advantage which will get me to 115db. Also, my room gain should start at 30Hz, so by the time I get to 20Hz, I should have at least a few db of room gain to boost 20Hz pretty close to 115db.

For power I'm planning an iNuke3000DSP. I like that it has a programmable peak limiter so that I can throw in some protection against >0dbFS peaks which are theoretically possible, from what I've read.

Is there something I'm not thinking about which might make me want to dial back to a 11 or 12Hz tune?
AFAIK peak limiter is not a good way to protect drivers in vented boxes because they may unload with power well short of the limit. Both 15 and 12 Hz models I tried needed HPF.

Another important consideration is port velocity vs. port first resonance frequency. They say that for LLT with LPF no higher than 80Hz one should aim for at least 190Hz first res. freq. I personally opted for much higher number because my surrounds are crossed over higher and LFE channel can have content upto 120Hz. What numbers are you getting with your models?
 

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AFAIK peak limiter is not a good way to protect drivers in vented boxes because they may unload with power well short of the limit. Both 15 and 12 Hz models I tried needed HPF.

Another important consideration is port velocity vs. port first resonance frequency. They say that for LLT with LPF no higher than 80Hz one should aim for at least 190Hz first res. freq. I personally opted for much higher number because my surrounds are crossed over higher and LFE channel can have content upto 120Hz. What numbers are you getting with your models?
How about their DEQ as an alternative? From what I understand, I can set it up so that once power gets to a certain point (which in my case would be above reference), it will start filtering. Does your iNuke work this way, or is their DEQ limited to higher frequencies?

For my resonances, for 10, 11, and 12Hz it's giving me 146, 182, and 223Hz respectively. And my port velocities even without the low frequency rolloff is about 20m/s, which is below the chuffing limit according to "Flare-It" So it looks like 146 is perhaps a bit low for a first port resonance, and I should opt for an 11Hz tune.
 

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Discussion Starter · #12 ·
How about their DEQ as an alternative? From what I understand, I can set it up so that once power gets to a certain point (which in my case would be above reference), it will start filtering. Does your iNuke work this way, or is their DEQ limited to higher frequencies?

For my resonances, for 10, 11, and 12Hz it's giving me 146, 182, and 223Hz respectively. And my port velocities even without the low frequency rolloff is about 20m/s, which is below the chuffing limit according to "Flare-It" So it looks like 146 is perhaps a bit low for a first port resonance, and I should opt for an 11Hz tune.
DEQ would work if you could use it below 20Hz which is not an option.

20m/s port velocity maybe too conservative. In your case it will only be reached at max output and at very low frequencies. The port shuffling, if any, would likely be masked by the legit output. You may consider using smaller port in favor of higher port res. frequency. That's the advise I was given anyway. The logic is that if port res. is a problem then it is a problem at any volume level, where as port velocity, within reason, maybe a problem only at extreme SPL when it almost does not matter.
 

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Discussion Starter · #14 ·
To the OP, that FR tells me you need a larger enclosure.
I agree. But two 16 cu.ft boxes is the max I could fit behind my screen. Well I could have done 18 cu.ft. but the difference is insignificant. If I could do 26 cu.ft per driver - now that would be closer to optimum.
 

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I wouldnt worry too much. My old Q18's needed 28 cu ft boxes each for 16hz tune opt size but I put mine in 15 cu ft each and for a 17hz tune I was flat to 15hz.
 

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Great progress so far. :T
 

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Very well thought of sub. :T

In the movie I see the surround deforming. Are you driving the woofer over xmax?
Didn't the coil heat up too much? Looks like a long punishment for the coil.:gulp:
 

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It may be over xmax, I don't know exactly how far the cone was moving but it was not making any bad noises so I think it was still within safe excursion limits.

As for the coil heating it was 400w at most for about 30 seconds I doubt the VC even heated up all that much.
 

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Discussion Starter · #20 ·
Very well thought of sub. :T

In the movie I see the surround deforming. Are you driving the woofer over xmax?
Didn't the coil heat up too much? Looks like a long punishment for the coil.:gulp:

I was told that "All tall style surrounds crease like that. Even the LMS-Ultra does at the extremes of excursion."
fwiw
 
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