Official Rythmik Audio Subwoofer thread - Page 568 - AVS Forum
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post #17011 of 17016 Old Today, 09:01 AM
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Originally Posted by JT78681 View Post
Hard for me to grasp this when my room is not outdoors, so I'd expect some kind of gain even if minute. What do I know though. :blush:

All you need is REW and a mic, then you can run compression tests like Tuvong did and know exactly what you are getting.



btw don't not be afraid to run REW compression tests...I am only saying this because Dom might have put some fear in those that read his post. REW uses a short 5 sec tone burst sweep. It is not really any harder on equipment then using source material and nothing like playing with steady state tones for extended periods of time.
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post #17012 of 17016 Old Today, 09:49 AM
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+1.

For me personally, I haven't done them because it's more of I don't really need to know; I already have a good idea of my subs capability through other tests (vid of FR of Hulk and Abomination scene, 10hz FV challenge, etc.)...and that's good enough for me right now.

The act of performing the test is really an irrational fear of mine...1) I have OM and I don't know of a 5sec sweep, 2) I don't have the equipment or know how for REW, 3) it is damn loud 4) And I am boosting the low end

Having said that, I would encourage everyone if you really want to know to do these tests. JT, especially in your case where you want to understand what you're getting below tune. Like bass said, the 5 sec burst should be fine.

A few years back when I had a pair of eD A7S-450s (put me at a 3.5 star ULF score to 12.5hz; no 10hz ULF score), an avs member came over with his PC and mic and we did do some sweeps of them:



I decided to not go any further because...well I was chicken basically because I was boosting the heck out of my eD's back then (for reference, they had a built in 17hz HPF that I boosted through!); and I was pretty happy with the 111db @ 10hz too.

As you can see, I have some nice room gain in my small room.
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post #17013 of 17016 Old Today, 09:59 AM
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^^ I missed the 10hz fv challenge. Do you happen to have a link to that?
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post #17014 of 17016 Old Today, 10:58 AM
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post #17015 of 17016 Old Today, 11:19 AM
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OFF TOPIC:

For those interested, here is the vid of my FR during the Hulk vs Abomination fight scene. The extension is from my FTW21s, not the FV15HP.

Vertical axis: Very top line is 130db separated by 10db increments

Horizontal axis: 5hz to 200hz

Fast forward to 1:22 or so to see the 5hz ULF action.


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post #17016 of 17016 Old Today, 02:43 PM
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Quote:
Originally Posted by Rythmik View Post
Basshead, you didn't read the plots right. Let me explain and it is totally opposite of what you have previously thought. The following is where databass provides you with the "maximum output plot" for PB13. The plot is very simple, Josh just incrementally increased the input in 5db increment. If the output also increases accordingly, it means the subwoofer is still not hitting the limit. Note that this has to be read at individual frequency point. For instance, the light green (second topmost) is labelled as 110db. The orange is labelled as 115db. It is clear PB13U has already hit the limit below 35hz because the input asks for 5db increase, the output only gives us about 3db in return. Same thing is above 65hz. It clearly shows PB13U has already topped out.





The following is the plot for FV15HP. Notice the orange is 113db while the light green is 110. So the input only increases by 3db and coincidentally the output also increase exactly 3db for frequency above 30hz, meaning the sub is not hitting the limit yet above 30hz. So the question is why Josh only plotted up to the 113db curve , not 115db curve. As you may have known, testing is a quite a task. There can be a lot of tiny things being overlooked. But fortunately, Josh did test 115db for 2port mode as shown in the last plot. And you can see the output from 110db to 115 increases a solid 5db from 30hz above without any hint of topping out. So the actual ouptut above say 40hz can be even higher. My question is how much more credit are you willing to give to FV15HP. BTW, CEA-2010 burst tests shows just how much more FV15HP can output beyond this unplotted area. I hope this convinces you.


[EDIT] Since we are on the subject of FR, there is another difference among these plots. Frequency plots from non-servo subwoofers are highly dependent on the temperature of voice coil. Since Josh swept these plots incrementally from 90db to 115db or higher, one can imagine the the voice coil was cold when he did the very first 90db sweep. When it got to the highest 115db, the voice coil has already heated up. Normally Josh will stop at the highest SPL sweep and move on to the next test suite. I asked Josh to change the routine so that immediately after he was done with the highest sweep, run another 90db sweep again to see if the exact same 90db FR curve is repeatable. The new curve is labelled as "90db REPEAT". This is to test how "consistent/coherent" the subwoofer frequency response is under various operating conditions. As one can see in PB13U, there is a broad -1db difference at around 20hz and above 60hz. So what makes the voice coil heat up? It is the large bass signal which causes the voice coil to heat. But only it affects the FR of the large signal, it also affects the FR of the small signal even after the large bass signal is gone. This is worse than intermodulation distortion because intermodulation distortion will be gone as soon as the large bass signal is removed. But the thermal compression effect will linger longer even after the large bass signal is gone. This leads to fluctuation in FR. But in plots of our subs, they are almost identical except a couple of places with local ups and downs that were due to noise in measurements (Noise is different from compression because noise can be up and down and compression on the other hand is almost down). In fact, Josh commented that our compression perform so well compared to non-servo subwoofers. As long as our amplifier still have juice, there will be no compression due to voice coil tempeature. The observed compression on FV15HP at low frequency is due to port air compression. That type of compression will be absent in sealed subwoofers. Does this make sealed subwoofers better? It is one of the contributing factors.







Great explanation. Thanks Brian.
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Rythmik , Rythmik Audio , Rythmik Audio F12 Direct Servo Subwoofer , Rythmik Audio F15 Subwoofer

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