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Old 17th September 2003, 07:50 PM   #1
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Default My 15" Sub - Project in progress

I am using 2 Eminence Beta 15s. They will be in ~60L boxes, which are going to be a 40cm square cube. I am going to use the linkwitz transform circuit to change the Fs and Qts of the drivers.

If I am not happy with the subs, I am going to build a ~400L box, another cube, but 75cm squared this time. It will be ported, and will be tuned to 25Hz with one port, 5cm by 20cm, using the thickness of the box (25mm) (1"). It will use both drivers, in isobarik configuration.

I have attached a basic design, which I will use for all the boxes, just changing the dimensions. I may change the braces, having many small holes, instead of one large one. Also, where will be a third plane to the bracing, but I did not include it in the diagram, as it overcomplicates it.
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File Type: jpg box.jpg (19.7 KB, 1682 views)
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Old 17th September 2003, 09:02 PM   #2
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Bear in mind that the Beta 15s only have 4mm Xmax so be VERY careful how much boost you apply with the Linkwitz transform.

I imagine that the kind of surface area offered by 2 x 15" drivers means that you wouldn't have to set the boost too high to get respectable bass, so you should be okay. Despite this, I would suggest a high pass filter at 20Hz to reduce the highest excusion from damaging your drivers.

I would also suggest that you place the braces non-uniform so as to maximise the break-up of resonances.

Nice one,
David.
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Old 17th September 2003, 09:21 PM   #3
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Quote:
Originally posted by daatkins
Bear in mind that the Beta 15s only have 4mm Xmax so be VERY careful how much boost you apply with the Linkwitz transform.

I imagine that the kind of surface area offered by 2 x 15" drivers means that you wouldn't have to set the boost too high to get respectable bass, so you should be okay. Despite this, I would suggest a high pass filter at 20Hz to reduce the highest excusion from damaging your drivers.

I would also suggest that you place the braces non-uniform so as to maximise the break-up of resonances.

Nice one,
David.
thanks for the advice.
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Old 17th September 2003, 09:24 PM   #4
Bull is offline Bull  United Kingdom
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The Eminence Beta 15 is a bass driver not a sub bass driver.
The new version is rated 350w rms and old version 150w rms,with a 2 inch voice coil and pretty small 34 oz magnet for a 15 inch.
The wattage won't matter for hifi use,but the lousy 34oz magnet your get some boomy unnatural sounding bass instead of tight,punchy and clean sounding bass[with a bigger stronger magnet,higher BL product]. where you clearly can hear the difference between different bass notes,instead just a one note boom.
The Eminence Beta 15 will need a big box to get good results.
But tuning them at 25hz will damage the driver overtime because the range it handles is 35hz-4khz.
Last but not least,not to be rude a square box with parellel sides is a bad idea because resonances resulting from standing waves inside the cabinet reinforce and cancell out each other resulting in distortion.So if you have to use a square box with parellel sides,then apply some acoustic wadding to the sides to help get rid of the standing waves inside the box.
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Old 17th September 2003, 10:10 PM   #5
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Quote:
Originally posted by Bull
The Eminence Beta 15 is a bass driver not a sub bass driver.
The new version is rated 350w rms and old version 150w rms,with a 2 inch voice coil and pretty small 34 oz magnet for a 15 inch.
The wattage won't matter for hifi use,but the lousy 34oz magnet your get some boomy unnatural sounding bass instead of tight,punchy and clean sounding bass[with a bigger stronger magnet,higher BL product]. where you clearly can hear the difference between different bass notes,instead just a one note boom.
The Eminence Beta 15 will need a big box to get good results.
But tuning them at 25hz will damage the driver overtime because the range it handles is 35hz-4khz.
Last but not least,not to be rude a square box with parellel sides is a bad idea because resonances resulting from standing waves inside the cabinet reinforce and cancell out each other resulting in distortion.So if you have to use a square box with parellel sides,then apply some acoustic wadding to the sides to help get rid of the standing waves inside the box.
im not bothered by boomy bass. i might try tuning to 30 or 35Hz then. i am going to stuff the sub, or at least line the edges with wadding, i forgot to add this to the thread starting post.
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Old 17th September 2003, 10:25 PM   #6
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Hi there,

Don't worry too much about the details. Once you've started building and messing around with it, you can think about why it sounds the way it does and how it could be better etc. I think the most important thing is integration with the main speakers so think carefully about that x-over/filter.

Didn't realise you were going to use two drivers Good idea.

Btw FAO other ppl, one of these drivers is costing nothing, making this a high-value project, not the be all and end all...

Have fun!


-Simon
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Old 18th September 2003, 06:27 AM   #7
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Quote:
Originally posted by SimontY
Hi there,

Don't worry too much about the details. Once you've started building and messing around with it, you can think about why it sounds the way it does and how it could be better etc. I think the most important thing is integration with the main speakers so think carefully about that x-over/filter.

Didn't realise you were going to use two drivers Good idea.

Btw FAO other ppl, one of these drivers is costing nothing, making this a high-value project, not the be all and end all...

Have fun!


-Simon
well, i could only afford one driver+ materials, so when you offered me your for free, i thought i would buy one anyway, and use two.
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Old 18th September 2003, 06:32 AM   #8
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here is an updated diagram. i didnt move the braces, as it would have been very difficult, but i know where i am going to put them.
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File Type: jpg sub.jpg (26.1 KB, 1542 views)
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Old 18th September 2003, 07:03 AM   #9
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Default Re: reply to MatttCattt

Quote:
Originally posted by Bull
Last but not least,not to be rude a square box with parellel sides is a bad idea because resonances resulting from standing waves inside the cabinet reinforce and cancell out each other resulting in distortion.So if you have to use a square box with parellel sides,then apply some acoustic wadding to the sides to help get rid of the standing waves inside the box.
This box is too small to produce standing waves at the frequencies it is going to be used at so it's cube shape is not a detriment.

The braces thou shuld not divide the panels exactly in 2 -- they should divide each panel into different size rectangles. Even better is if they are run at somewhat of an angle so that the panels are divided into non-retangular sub-panels.

Woofers should also be mounted opposite each other (push-push) and rigidly coupled together.

dave
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Old 18th September 2003, 01:11 PM   #10
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Quote:
Originally posted by planet10
The braces thou shuld not divide the panels exactly in 2 -- they should divide each panel into different size rectangles. Even better is if they are run at somewhat of an angle so that the panels are divided into non-retangular sub-panels.
Ok

Quote:

Woofers should also be mounted opposite each other (push-push) and rigidly coupled together.
dave
I might try this, but the reson for isobarik configuration is size. (500l instead of 2000l )
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