Comment on my DIY Sub Design

[htgeek]

Please feel free to comment on my design.
It is my first DIY home theater sub, although I have built several for car audio.
Its based on a Lambda Acoustics PB-15.
The power will come from a Rythmik Audio 350w plate amp.

http://img.photobucket.com/albums/v160/lobo2401/Subwooferrev2Model1.jpg

Ben

 

[simon5]

It's nice but it seems to be tuned flat anechoic, remember that room gain will lift the lowest frequencies so you could tune your subwoofer even lower and stay flat in room.

 

[mike.e]

Also most modeling programs are 2pi

 

[htgeek]

mike.e

What do mean by "Also most modeling programs are 2pi"?

 

[Rademakers]

It means that almost all simulators, simulated as if the enclosure is placed in half space.

Half space would be the enclosure placed on the floor, full space way up in the air, quarterspace against a wall and on the floor (or two walls, etc.), eight space on the floor in the corner of your room.

Mvg Johan

 

[htgeek]

So according to WinIsd the easiest to lower the tuning frequency is to lengthen the ports. Keeping the same heigth I could make the ports 33" long and tune to about 14.75 hz. Of course I would need to take into account the added volume of the new port lenght and adjust my total enclosure volume. Does that sound right?

 

[kingdaddy]

So according to WinIsd the easiest to lower the tuning frequency is to lengthen the ports. Keeping the same height I could make the ports 33" long and tune to about 14.75 hz. Of course I would need to take into account the added volume of the new port lenght and adjust my total enclosure volume. Does that sound right?

Unfortunately in all modeling programs this is a catch 22, every time you adjust the net volume to account for the port volume it will tell you to use a longer port, so when you lengthen the port you must recalculate the new net volume and again it will tell you to lengthen the port, it never ends. The only way I've found to accurately tune the port is to cut it long and play test tones while feeling the cone movement, when you hit the Fb the cone will barley move compared to just 1Hz above or below. In addition, I agree with others, tune a little lower, say 17-18Hz

 

[DcibeL]

The added volume from the port will make such a little difference I'm sure you'd never be able to tell the difference if you did change the box volume accordingly anyways.

Nevertheless, that's a mighty fine sub you have there. I am also working on my first home sub after making several for the car audio. I have to wait for the driver I want to use to come available though (Peerless XXLS), so it will be a summer project.

 

[spots25]

well, if you made the box bigger to compensate for the volume of the port, wouldn't the box still be the same size internally?

 

[simon5]

If I look at your drawing, you need to stay under 32 inches to have one port diameter distance for breathing.

I would make them 32 inches long if you can. Could you post a graph with 32 inches long pipes? If you get a shallow rolloff, ruler flat, with around -5 dB at 20 Hz compared to 0 dB at 100 Hz, that's about perfect, IMHO.

 

[kingdaddy]

well, if you made the box bigger to compensate for the volume of the port, wouldn't the box still be the same size internally?

No, making the box bigger changes the tuning of the port (not by much though) so this changes the length of the port, which again changes the net volume of the box. Not a big deal really, but for those who want to hit a target Fb as close as they can just use the WinISD port length and cut it a few inches longer then use test tones and trim 1" per Hz until you hit your target. I reverse engineered my last sub after modeling and my port came out about 2" longer then WinISD calculated for that given tuning.

 

[htgeek]

Here is a pic of the new graph with 32" ports. It's tuned to 15.175 Hz. The magenta curve is the new one and the green is the old 16.81" ports. Please keep those comments coming.

 

[htgeek]

I suppose a link would have been nice.

http://img.photobucket.com/albums/v160/lobo2401/32inGraph.jpg

Sorry about the double posting.

 

[htgeek]

By the way kingdaddy, you have got some fantastic unique looking speaker designs. I dig the hell outta adjustable ported subwoofer idea. Some very cool stuff.

 

[kingdaddy]

By the way kingdaddy, you have got some fantastic unique looking speaker designs. I dig the hell outta adjustable ported subwoofer idea. Some very cool stuff.

Thanks for the compliment. BTW don’t forget to check your port velocity; it's been my experience that you need to be under 20M/s to avoid cuffing.

I posted some pics of an equally strange new center channel prototype a few weeks ago as well.

 

[htgeek]

Yeah port velocity is OK. Its at .07. WinISD does not tell me what units they are though. Just in the help file they day to keep it below .16.

 

[kingdaddy]

Yeah port velocity is OK. Its at .07. WinISD does not tell me what units they are though. Just in the help file they day to keep it below .16.

Just click the mouse on the upper most portion of the graph curve to put the crosshair there the units will show up in a small black box at the top right corner of the graph window, .07 doesn't sound right

 

[htgeek]

Ahh I was wondering where that information was in WinISD Pro. I've been using the non Pro version because I thought the Pro didn't have port speed. According to the Pro version my port speed is 1.22 meters/second. In the non-Pro version the port speed is in "The Mach" rating. That makes more sense. Thanks!

 

[kingdaddy]

Cool your good to go, probably could go with a smaller diameter port if you wanted.

 

[simon5]

1.22 meter per second with 300W imput??? Are you sure?

This new curve looks nice, it's up to you to choose what you want, I think this new curve will be flatter in your room, the old one will have a small peak centered around 30 Hz. If your a movie lover, it will be ok, but the new curve will be better for music. Well, always depend on what kind of music you listen to!