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2 newbie questions about building a woofer box

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Tucker View Drop Down
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    Posted: 21 March 2020 at 7:53pm
I have Eminence Kappa Pro 18LF8's and I plan on building single 18 inch sub boxes based on these plans (the large SINGLE box starting on page 6):


My questions are:

1) Why do the large box plans say 500 watts in the title, 700 for the medium box, and 800 for small?
My guess is the smaller box requires more wattage to reach a certain dB due to less moveable air.

2) If I want to do 1 rectangular port instead of 4 round ports suggested, can I just take the combined surface area of the round ports and convert it to rectangular dimensions and use the same port depth?

Cheers, Tucker
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Post Options Post Options   Thanks (0) Thanks(0)   Quote smitske96 Quote  Post ReplyReply Direct Link To This Post Posted: 21 March 2020 at 8:13pm
The one which says '500 Watt' is tuned lower, which then needs more movement of the cone.
If you apply more Voltage (power) Xmax is exceeded (as you can see in the graph). 
Then again these are sims and real world practice gives you a better understanding.

Regarding the ports:
Round ports give best performance regarding velocity and turbulence, however, they can be harder to fit if square surface is high and port depth is long. You can combine the surface of the 4 round ports and use one rectangular port. But, simulation programs simulate the port without interference (or help) from the cabinet walls. If you go for a shelf port (so with one or more cabinet walls are part of the port) you have to keep in mind that these extend the port further. So again real world tests are needed to get the right tuning.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Tucker Quote  Post ReplyReply Direct Link To This Post Posted: 21 March 2020 at 8:27pm
Originally posted by smitske96 smitske96 wrote:

The one which says '500 Watt' is tuned lower, which then needs more movement of the cone.
If you apply more Voltage (power) Xmax is exceeded (as you can see in the graph). 
Then again these are sims and real world practice gives you a better understanding.

Regarding the ports:
Round ports give best performance regarding velocity and turbulence, however, they can be harder to fit if square surface is high and port depth is long. You can combine the surface of the 4 round ports and use one rectangular port. But, simulation programs simulate the port without interference (or help) from the cabinet walls. If you go for a shelf port (so with one or more cabinet walls are part of the port) you have to keep in mind that these extend the port further. So again real world tests are needed to get the right tuning.


So if I operate the speakers over 500 watts of power I run the risk of ruining the drivers because I exceeded xmax?

I guess I'll just do plot it out in winISD to figure out the port depth for a shelf style port. Unless there's an easier way to figure out the depth needed.
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Tucker View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Tucker Quote  Post ReplyReply Direct Link To This Post Posted: 21 March 2020 at 10:31pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote dlyxover Quote  Post ReplyReply Direct Link To This Post Posted: 21 March 2020 at 11:34pm
winISD or BassBox pro are your best bet for a staring point.

Bare in mind that the software will only estimate the port length, you will need to measure the tuning when the cab is constructed.

Until you have verified the tuning is correct don't glue the port in.  
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Post Options Post Options   Thanks (0) Thanks(0)   Quote DMorison Quote  Post ReplyReply Direct Link To This Post Posted: 22 March 2020 at 2:18pm
Originally posted by Tucker Tucker wrote:

So if I operate the speakers over 500 watts of power I run the risk of ruining the drivers because I exceeded xmax?

Not, immediately, though if you kept at it long enough you might.

The first 2 things that happen when you exceed XMax are that distortion will rise, and it will stop getting louder in proportion to your attempted increase in power - IOW if you try to give it 3dB more power than it took to reach XMax, you might only get 1 or 2 dB more out of it.
If you pay attention to these warning signs you'll have plenty chance to back it off before damage occurs.

Or, just stick to the power levels indicated on the models to start with ;-)

Quote I guess I'll just do plot it out in winISD to figure out the port depth for a shelf style port. Unless there's an easier way to figure out the depth needed.

As said by diyxover, WinISD etc don't account for the virtual lengthening of the vent when it's built in along the side of the cab.

Some people have tried to calculate corrections for this, I put the maths into a spreadsheet which can be found here: https://drive.google.com/open?id=1tl8A4Fbkk07TmR7h2vyxVBQcDaCFOwri ;
After you calculate the area and shape of the vent you want to use, put that and the box volume & tuning into the spreadsheet and it'll give you a revised length.

Bear in mind, this is still only an attempt to approximate real world effects, so it's best to build your 1st box with some way of getting at the interior to adjust the port lenght after it's built, eg by making one side removeable.

HTH,
David.
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Tucker View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Tucker Quote  Post ReplyReply Direct Link To This Post Posted: 22 March 2020 at 4:34pm
Originally posted by DMorison DMorison wrote:

Originally posted by Tucker Tucker wrote:

So if I operate the speakers over 500 watts of power I run the risk of ruining the drivers because I exceeded xmax?

Not, immediately, though if you kept at it long enough you might.

The first 2 things that happen when you exceed XMax are that distortion will rise, and it will stop getting louder in proportion to your attempted increase in power - IOW if you try to give it 3dB more power than it took to reach XMax, you might only get 1 or 2 dB more out of it.
If you pay attention to these warning signs you'll have plenty chance to back it off before damage occurs.

Or, just stick to the power levels indicated on the models to start with ;-)

Quote I guess I'll just do plot it out in winISD to figure out the port depth for a shelf style port. Unless there's an easier way to figure out the depth needed.

As said by diyxover, WinISD etc don't account for the virtual lengthening of the vent when it's built in along the side of the cab.

Some people have tried to calculate corrections for this, I put the maths into a spreadsheet which can be found here: https://drive.google.com/open?id=1tl8A4Fbkk07TmR7h2vyxVBQcDaCFOwri ;
After you calculate the area and shape of the vent you want to use, put that and the box volume & tuning into the spreadsheet and it'll give you a revised length.

Bear in mind, this is still only an attempt to approximate real world effects, so it's best to build your 1st box with some way of getting at the interior to adjust the port lenght after it's built, eg by making one side removeable.

HTH,
David.


Thanks a bunch for the reply David.

I think I will just go for one of the smaller box plans instead so I don't have to worry about the over excursion. I like my music loud and I think I'm willing to sacrifice some frequencies for a louder, more idiot-proof setup.

Also the link you posted does not work for me.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Tucker Quote  Post ReplyReply Direct Link To This Post Posted: 22 March 2020 at 4:51pm
Originally posted by DMorison DMorison wrote:

Originally posted by Tucker Tucker wrote:

So if I operate the speakers over 500 watts of power I run the risk of ruining the drivers because I exceeded xmax?

Not, immediately, though if you kept at it long enough you might.

The first 2 things that happen when you exceed XMax are that distortion will rise, and it will stop getting louder in proportion to your attempted increase in power - IOW if you try to give it 3dB more power than it took to reach XMax, you might only get 1 or 2 dB more out of it.
If you pay attention to these warning signs you'll have plenty chance to back it off before damage occurs.

Or, just stick to the power levels indicated on the models to start with ;-)

Quote I guess I'll just do plot it out in winISD to figure out the port depth for a shelf style port. Unless there's an easier way to figure out the depth needed.

As said by diyxover, WinISD etc don't account for the virtual lengthening of the vent when it's built in along the side of the cab.

Some people have tried to calculate corrections for this, I put the maths into a spreadsheet which can be found here: https://drive.google.com/open?id=1tl8A4Fbkk07TmR7h2vyxVBQcDaCFOwri ;
After you calculate the area and shape of the vent you want to use, put that and the box volume & tuning into the spreadsheet and it'll give you a revised length.

Bear in mind, this is still only an attempt to approximate real world effects, so it's best to build your 1st box with some way of getting at the interior to adjust the port lenght after it's built, eg by making one side removeable.

HTH,
David.


One more question, do you think it's even likely that I'll push the speakers over 500 watts if I'm playing to 50-60 people? I just don't really know what 500 watts in a speaker like that sounds like loudness-wise
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Post Options Post Options   Thanks (1) Thanks(1)   Quote Elliot Thompson Quote  Post ReplyReply Direct Link To This Post Posted: 22 March 2020 at 7:30pm
Originally posted by Tucker Tucker wrote:


One more question, do you think it's even likely that I'll push the speakers over 500 watts if I'm playing to 50-60 people? I just don't really know what 500 watts in a speaker like that sounds like loudness-wise


You can easily cover 50 - 60 people with 200 watts. However, you cannot congregate more than 10 persons in the United States at the moment. If you are looking at things further down the line when the ban is lifted, 500 watts is more than enough for 50 - 60 people.

Best Regards,


Elliot Thompson
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Tucker View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Tucker Quote  Post ReplyReply Direct Link To This Post Posted: 22 March 2020 at 7:52pm
Originally posted by Elliot Thompson Elliot Thompson wrote:

Originally posted by Tucker Tucker wrote:


One more question, do you think it's even likely that I'll push the speakers over 500 watts if I'm playing to 50-60 people? I just don't really know what 500 watts in a speaker like that sounds like loudness-wise


You can easily cover 50 - 60 people with 200 watts. However, you cannot congregate more than 10 persons in the United States at the moment. If you are looking at things further down the line when the ban is lifted, 500 watts is more than enough for 50 - 60 people.

Best Regards,




Sweet, thanks for that, looks like I'll be going back to the large box plans then.

I just want to start cutting wood!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote DMorison Quote  Post ReplyReply Direct Link To This Post Posted: 22 March 2020 at 9:43pm
Hmm, linking to that usually works.
I think the speakerplans forum software managed to add the space after then end of the address to the link, hopefully this version works better.
If you get a 404 error, just edit off any spurious characters in the address bar of your browser so that the last character left is the "i" as you can see here and it should work fine.
Cheers,
David.
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