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Discussion Starter · #1 ·
I am building my 1st DIY sub, so I am new to winisd and everything else. I was wondering how to model the Oaudio 500w plate amp with the different subsonic filter settings and the eq. any help on this matter would be appreciated.
 

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Tricky question. O-Audio will not say what amounts of boost come with the 4 subsonic filter settings but their published graph tell a story.

If I'm reading the graph correctly, +55 is the base line according to the 12 hz setting which appears to have about 8 db of boost.

The 16 hz setting shows about 5 db of boost.

The 20 hz setting is about 3 db of boost.

The 25 hz setting is about 2 db of boost.

oaudio.JPG




Regarding the amps EQ, its effective range is 20 - 80 hz. You can cut the 20hz and 25 hz HPF boost.

The boost in the 12 and 16 hz subsonic filters is out side the range of the amps EQ (20 -80hz) you can't defeat it. Those filters are for sealed subs where they can benefit from the boost.

All the above is my understanding of the amp. Many an email to O-Audio resulted in no information when they were questioned about specifics. All I got out of them was " the amp works well for ported and sealed subs."
 

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Discussion Starter · #3 ·
I asked this same question on another forum and there I was told to use the peaking 2nd order highpass. I was wondering if anyone else knew which way was the correct way to do this? I know there are alot of Oaudio amp users out there.
 

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Discussion Starter · #5 ·
Thaks Mike, this is alot of info to take in for a newbee so the help is greatly appreciated.
 

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Their graph just looks like a typical 2nd order Sallen-Key filter. In WinISD, you choose highpass/SOS, User specified Q & Fc and play with the Q & Fc (the order is fixed in the actual calculation, even though the WinISD dialog box lets you change it...SOS = Second Order Sallen I think). Choosing highpass/sos will take care of the boost and rolloff at the same time, no need to play with separate hp and PEQ filters although they should be able to accomplish the same results.

A quick first cut using these values produced my approximation of the OAudio filters. Probably can be used as a good starting point if you want to try to get closer to the OAudio graph.

25Hz = 20, 1.2 green
20Hz = 16, 1.4 yellow
16Hz = 14, 1.6 orange
12Hz = 8, 1.8 green (oops, forgot to pick a different color)

WinISD's filter only graphs shows this.

-Brent
 

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Discussion Starter · #7 ·
So, in your numbers above :
25Hz = 20, 1.2 green
20Hz = 16, 1.4 yellow
16Hz = 14, 1.6 orange
12Hz = 8, 1.8 green

for example are you saying for 16hz you enter 14 in hz and 1.6 in q ?
 

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Discussion Starter · #9 ·
So I guess the peaking 2nd order would be the most accurate (and easiest) one to use then?
 

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For the 20 hz filter, a Fc of 16 and Q of 1.4 is awfully close to a peaking 2nd order highpass with a 20 hz filter and 3 db of boost.

EDIT: Nope, although the SPL looks the same the cone excursion does not match.
Mike, you might want to double check your models all the way thorugh, it sounds like you've got some parameter different between the two. I just overlaid a HP/SOS=20/1.2 with a peaking HP=25Hz/2.4dB. The filter only transfer functions overlapped almost perfectly (less than .1dB delta) as did the cone excursion and SPL graphs.

FWIW, in the WinISD Pro.50a7 filter simulation example in the help files, they use the HP/SOS to build a plate amp model, which is why I typically recommend that path for modelling most plate amp filters (P-E's HPSA series uses a 3rd order S-K filter just to make life difficult). As described in the filter behaviour help section, HP/SOS and Peaking 2nd order HP really should accomplish the same thing mathematically; one just uses the f3 (f3=fc) point and Q to establish the peak height/width and the other reverse calculates the f3 and Q based on the center frequency and magnitude of the peak.

-Brent
 

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Discussion Starter · #12 ·
So Brent, are you saying that I should be using hp / sos instead of peaking 2nd order or that they both come to the same conclusion?
 

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I saw that. I'm not sure why he added 5 db when the graph shows it's clearly not that much. I asked Brent for some input on this, hopefully he'll drop in.
For reference, I used the peaking high-pass with 5 db gain, but one of my other filters was a PEQ to cut the gain from the 20Hz highpass boost to even out the response.
 

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Discussion Starter · #15 ·
When I am modelling a sealed SDX15 at 4cu.ft. using Brents #'s for 20hz, the amplifier apparent load is way above 500. Does this mean that the amp is going to be clipping at those frequencies?
 

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Thanks to Jasonpctech, his inquiries to O-Audio has resulted in obtaining O-Audio's spec sheet for changing the Hi-Pass filter frequency and the amount of boost. The following charts shows the resistor values needed for various Hi-Pass frequencies and boost. This opens up a lot of possibilities for the O-Audio Bash 500 amp.

Note: The charts below only apply to the O-Audio brand Bash 500 Watt amp and not any other Bash amp.

Link to document provided by O-Audio:

https://spreadsheets.google.com/spr...LLdE1hb1hSakF5Z3A3MmdCdHlzbkFnakE&output=html

Thank you Jason! :T

boost1.JPG
boost2.JPG
 

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That chart is great news, i just purchased the 500w oaudio amp and it is going into a 20hz ported box and would like to change the resistors to the 1db boost at 18.7hz. does anyone know where to find the 4.4k ohm resistors? i tried digikey and mouser but no luck.

thanks
James
 

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After investigating the owner's manual on my O-Audio 300W plate, the 25Hz extension setting on the 500W plate seems to closely match the "factory" setting of the 300W amp. For anyone's reference, for what it's worth for modelling purposes. They may not be exactly the same but they are close. Makes it easy to model by just toggling 300W/500W.
 
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