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re: Mach 5 18", 180lt, 500watts tuned to 20hz

I'm in Australia and I imported an O-Audio 500 amp from the US about 7~8 months ago. I purchased directly from the O-Audio website. Works great and was approximately 33% cheaper to import than source locally. A major factor of this was the currency conversion was jumping wildly at the time. It has plenty of power for my needs, but you should be aware of the significant boost with the subsonic filters when planning your design. Either that or be prepared to get the soldering iron out.

I'm jealous of the choice and price of HT gear in the US! :crying:

Either way nothing in Australia can be found even close to AUD$300 delivered with similiar power and features. Just about all the other amps in a similar price range also had boost anyway.
 

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re: Mach 5 18", 180lt, 500watts tuned to 20hz

Mike, yes you're correct, this is possible to do when you are tuning around 20hz. My apologies for generalizing. It should be noted that it is not completely possible to cancel out the boost with the PEQ.

I have previously contacted OAudio in an effort to better model with the OAudio 500:
20hz Subsonic Filter: Filter Fc = 17.33Hz, Filter Q = 1.72
25hz Subsonic Filter: Filter Fc = 23.06Hz, Filter Q = 1.42
PEQ Q control varies Q from ~ 3 (LOW) to HI (20) with PEQ Level set at Maximum.
You can model these the subsonic filters with a HPF SOS Second Order Filter in WinISD.
Obviously there will be some variation from amp to amp but it should give you a good idea.

Below are models using a signal of 440w:


The graph above shows the amount of boost the OAudio amp will provide.




The amp would clip before the excursion is a problem here however. This also means that the real SPL that will be achieved will be a few dBs less than shown. Note that the 25hz subsonic filter with no PEQ on is in yellow. White is 20hz subsonic filter with some PEQ.

In my opinion the amp is ridiculously good value. However the issue is that the lowest the PEQ can be centred is 20hz and it is designed to combat room modes, not broad equalisation. Hence, it can be used somewhat to negate the subsonic boost but it is not ideal.

The graphs may not look pretty but realistically this is fine. Room interaction will make things look far worse.

I hope this enables informed decisions. For any other Aussies, the OAudio 500w amp is fantastic value for money. I'd buy it again in a flash. :bigsmile:

Cheers
 

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Discussion Starter · #47 ·
re: Mach 5 18", 180lt, 500watts tuned to 20hz

Thanks Mark for the great info on importing O-Audio amps.

Mike, Is the modelling right? Seems to have a big hump in the 20hz range? Can it be eliminated with the Amps eq?

I still haven't bought the amp so im up for any suggestions on how to proceed.


Thanks for the help.:T
 

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Discussion Starter · #48 ·
re: Mach 5 18", 180lt, 500watts tuned to 20hz

Just tracked the delivery of the Driver and it will be arriving tommorow. What are the best bolts for the driver as i've only ever used screws???

The entire front of the box is still removable and can make any adjustments to secure the sub into place or add more bracing. I have noticed in other builds threads that extra timber has been added were the screw from the driver enter the box, is this recomended?

With lining the internal of the box I have always used this...http://jaycar.com.au/productView.asp?ID=AX3694&keywords=dampening&form=KEYWORD
Is this the right material or should I look for the egg crate foam?
 

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re: Mach 5 18", 180lt, 500watts tuned to 20hz

The best way to mount it is using T-nuts and hex screws.
The T-nuts have spikes that bite into the timber and it is recommended to put a ring of ply on the back where they attach as mdf will sometimes strip and they will just spin and you cant tighten or loosen them. The ply is less prone to stripping.
The hex bolts have circular heads and are tightened using allen keys. Typically you would use M4 or M5 with appropriate washers.
 

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re: Mach 5 18", 180lt, 500watts tuned to 20hz

Thanks Mark for the great info on importing O-Audio amps.

Mike, Is the modelling right? Seems to have a big hump in the 20hz range? Can it be eliminated with the Amps eq?

I still haven't bought the amp so im up for any suggestions on how to proceed.


Thanks for the help.:T
The EQ will eliminate most of the boost at 20 hz.
 

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re: Mach 5 18", 180lt, 500watts tuned to 20hz

Mike is right, don't take the peaky response I modelled before as a serious problem.
As mentioned, room interactions (modes) will seriously swamp the "little" bump modelled.

Also, a model is just a model. Real world tests shown here which were done with the 12hz subsonic filter on show significantly less boost than what the specifications say. From this you could imply that there is less boost to negate in the first place.

For your particular build the OAudio 500w is great value. :sn:
 

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re: Mach 5 18", 180lt, 500watts tuned to 20hz

Real world tests shown here which were done with the 12hz subsonic filter on show significantly less boost than what the specifications say. From this you could imply that there is less boost to negate in the first place.

For your particular build the OAudio 500w is great value. :sn:
I believe your right about there being less boost then every one thinks there is with this amp. O Audio has told me that there is only 3db of boost with the 16hz setting and chucks test says there is 6db of boost at 10hz with the 12hz setting. So using this info and looking at the frequency graph on the O Audio site I would say the boost goes more like this....

6db with the 12hz setting
3db with the 16hz setting
2db with the 20hz setting
and 1db with the 25hz setting
 

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Discussion Starter · #53 ·
re: Mach 5 18", 180lt, 500watts tuned to 20hz

Thanks for all the replies.

The Driver has arrived and WOW its HUGE!!!!

As I said earlier, i've only ever used 12" subs and I thought they were great but this thing looks scary.

I will post some pics. I have made a start on the finish of the box. Am unsure of which way to go, Spoke with a painter and asked he's opinion on trying to blend it in to my lounge and he laughed and asked if i've taken any notice of the size of this enclosure. Just had to laugh. So I think it will be black.
 

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Discussion Starter · #54 ·
re: Mach 5 18", 180lt, 500watts tuned to 20hz

So the box arrived Today and the kids were so excited to be getting a new Sub :clap:!

resized17_640x480.jpg

Sorry for the misunderstanding, but they could not care much for the Sub, only for the box the driver came in. :rofl:

resized18_640x480.jpg

resized19_640x480.jpg

Anyway I was excited :T, Its hard to show the size of the driver, so i've placed it next to a large coffee mug for scale.

resized20_640x480.jpg

If this sounds as good as it looks I will be very happy.

Cheers for everybodies input and help and you guys should be proud of such a great forum for anything Home Theatre.

Well Done.
 

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Discussion Starter · #56 ·
re: Mach 5 18", 180lt, 500watts tuned to 20hz

I will be importing the O-Audio 500w Amp as it seems to be the best fit. I will be spending more time on finishing the box before I get it, as I think it will force me to fire the sub up with an unfinished box.

I will have a cabinet maker help with the front cover. I will be rebating it into the front panel. Should look great.

I was a bit scared as to the shear size of the enclosure, but after seeing the size of the driver it will put it into prospective.

Thanks.
 

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Discussion Starter · #58 ·
re: Mach 5 18", 180lt, 500watts tuned to 20hz

I believe your right about there being less boost then every one thinks there is with this amp. O Audio has told me that there is only 3db of boost with the 16hz setting and chucks test says there is 6db of boost at 10hz with the 12hz setting. So using this info and looking at the frequency graph on the O Audio site I would say the boost goes more like this....

6db with the 12hz setting
3db with the 16hz setting
2db with the 20hz setting
and 1db with the 25hz setting
If the info is correct, Could I lower the tune down to the 16hz high pass?

Here is what I modelled, Is it right?

resized21_640x480.jpg

resized22_640x480.jpg

resized23_640x480.jpg
 

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re: Mach 5 18", 180lt, 500watts tuned to 20hz

The boost on the O-Audio amp is more like 8, 6, and 4 db at 20 hz, there is not boost on the 25 hz setting. If there is 6 db of boost at 16 hz, the amps input power would be reduced to 125 watts in order to have enough power at handle the 6 db of boost at 16 hz.

Yellow is with a 20 hz HPF with the boost defeated by the EQ since the effective range of the EQ is 18 - 80 hz.
Pink is with a 16 hz HPF with 6 db of boost.

david ixl.JPG
 

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Discussion Starter · #60 ·
re: Mach 5 18", 180lt, 500watts tuned to 20hz

With lining the internal of the box I have always used this...http://jaycar.com.au/productView.asp...g&form=KEYWORD
Is this the right material or should I look for the egg crate foam?

The hole for the driver is cut and will be putting the ply behind for the T-nuts. I will be mounting the driver and attaching the first piece of the front panel of the box. (Pic's to follow)

I have decided on a semi gloss black enamel for the finish with a rebated front cover.
 
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