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4 Pi Design Questions [message #61737] Sun, 17 January 2010 22:09 Go to next message
Nichol1997 is currently offline  Nichol1997
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Wayne,
I have been modeling the bass response of your 4 Pi design using the JBL 2226H drivers in WinISD. I have calculated the net volume of the enclosure to be approximately 2.74 cubic feet. Given your port dimensions and the net volume of the enclosure, the tuning frequency appears to be 27 Hertz.

I would like to alter the response curve by making a slightly larger enclosure (3.6 cu ft) and raising the tuning frequency to 40 Hertz. This can be achieved by increasing the height of the enclosure by 7 inches. I would like to keep the port on the front baffle but move it to the bottom of the enclosure. From your previous posts it seems that standing waves may become an issue, is this correct?

Do I also need to worry about midrange frequencies escaping from the port and canceling with the front-wave of the speaker?

Re: 4 Pi Design Questions [message #61738 is a reply to message #61737] Mon, 18 January 2010 06:36 Go to previous messageGo to next message
Nichol1997 is currently offline  Nichol1997
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Registered: December 2009
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I just realized that I made a mistake in the port dimensions. It appears that you have the original design tuned to 38 Hertz.

I would still like to make a larger enclosure since I like its response better.
Re: 4 Pi Design Questions [message #61739 is a reply to message #61738] Mon, 18 January 2010 08:46 Go to previous messageGo to next message
Wayne Parham is currently offline  Wayne Parham
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Registered: January 2001
Illuminati (33rd Degree)

Sure, you can make the cabinet larger, up to about 5.0ft3. In any loudspeakers with cabinets this large, you should always measure impedance and response to make sure you don't see any big blips from internal standing waves.

Re: 4 Pi Design Questions [message #61751 is a reply to message #61737] Wed, 20 January 2010 20:59 Go to previous messageGo to next message
Nichol1997 is currently offline  Nichol1997
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I have two different port designs (see attached). Is the slot port design better at attenuating midrange frequencies from the backwave of the bass driver?
Re: 4 Pi Design Questions [message #61752 is a reply to message #61751] Wed, 20 January 2010 21:09 Go to previous messageGo to next message
Wayne Parham is currently offline  Wayne Parham
Messages: 18670
Registered: January 2001
Illuminati (33rd Degree)

Generally, ducts that are long and thin tend to develop internal standing waves and those can be a problem. Then again, you can get around them with the right placement and just being long and thin isn't always a problem. In the end, you'll have to measure the cabinet to know for sure.

Re: 4 Pi Design Questions [message #62248 is a reply to message #61737] Thu, 01 April 2010 21:15 Go to previous messageGo to next message
Nichol1997 is currently offline  Nichol1997
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Just thought I would post a link to my build thread:
http://www.avsforum.com/avs-vb/showthread.php?t=1238362
Re: 4 Pi Design Questions [message #62249 is a reply to message #62248] Fri, 02 April 2010 09:25 Go to previous messageGo to next message
Wayne Parham is currently offline  Wayne Parham
Messages: 18670
Registered: January 2001
Illuminati (33rd Degree)

Good work so far! Thanks for the link, and please keep us posted with your progress.

Re: 4 Pi Design Questions [message #62252 is a reply to message #62249] Fri, 02 April 2010 20:58 Go to previous messageGo to next message
Nichol1997 is currently offline  Nichol1997
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Registered: December 2009
Location: Virginia
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Thanks for the compliment. The build is going pretty easy so far except for routing the recessed area for the horn driver. It was a little tricky but I think I am just rusty with my speaker building.

I noticed on your website that you can upgrade to the Jantzen Z-capacitors but you don't specify if they are the Standard, Superior, Silver, or Silver Gold type. Which ones do you provide?

Also, Jantzen doesn't appear to offer 20uF capacitors according to their cut sheet: http://www.jantzen-audio.com/download/Z-caps%20series%20list.pdf

Are you substituting a Dayton Audio capacitor for this one?
Re: 4 Pi Design Questions [message #62255 is a reply to message #62252] Sat, 03 April 2010 09:32 Go to previous messageGo to next message
Wayne Parham is currently offline  Wayne Parham
Messages: 18670
Registered: January 2001
Illuminati (33rd Degree)

I use Dayton capacitors sometimes, yes. If a person orders a standard crossover with no upgrade options, they will have Jantzen, Erse, Solen or Dayton polypropylene caps.

But as for the Jantzen 22uF capacitor, you can use it where the schematic calls for 20uF. If we get an order for Z-Caps, that's what we use. We use Z-Standard caps in all positions except for the 0.47uF part, which is a Z-Superior. Not because I think it needs this, but because the 0.47uF size isn't available in the standard line. If someone was interested, we would be happy to use Z-Superior parts in all positions for a little extra cost, but we don't stock them. Most people that want the high-end caps want Auricaps.

As a related aside, 16Ω resistors are substituted with 15Ω parts and 12.5Ω resistors are used in place of 12Ω when Mills resistors are chosen. We use Dayton non-inductive 10 watt resistors for the standard option, Mills 12 watters for upgrades. The Zobel resistor is a non-inductive 100 watt, 8Ω part with a built-in heatsinking case which doubles as a mounting bracket. The 15 guage coil used in the 0.5mH position is actually a Jantzen air-core 0.47mH part. No other substitutions are required for any values, in any options or lines. All coils are Jantzen air-cores, whether 18 guage (standard) or 15 guage (upgrade), but the large 5mH coil used on the cornerhorns is an Erse Super-Q. All capacitors are poly caps.

Re: 4 Pi Design Questions [message #62303 is a reply to message #61737] Wed, 07 April 2010 21:17 Go to previous messageGo to previous message
Nichol1997 is currently offline  Nichol1997
Messages: 21
Registered: December 2009
Location: Virginia
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Wayne,
Thanks for your help. That answered a lot of my questions in regards to crossover components. However, I am trying to find a source for the 8-Ohm, 100 Watt non-inductive resistor. I found one that Parts Express offers but I am not sure if it is what I need because they call it a "dummy load resistor". Here is the link:
http://www.parts-express.com/pe/showdetl.cfm?Partnumber=019-020

Is this the correct one to use?
Is there a better brand that I should be considering since I will be upgrading all the other crossover components?


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