subwoofer design problem

[pkgum]

BP1503 t/S parameters

fs ...25.52Hz
Re ...3.9ohm
Qms ...4.46
Qes ...0.41
Sd ...737cm2
Vas ...92L
Xmax peak ...25.86mm
Le ...4.28mH
Nomimal power ...1000W
series resistance ... 0.2ohm

basic 18.56Hz tuned subwoofer

port inside diam. ...5.75inches
port area ...167.64cm2
port end correction ... 0.519
desired Physical Vb ...200L
Absorption, Qa ...20
Leakage, Ql ...15
Port, Qp ...140
Alpha, a ... 0.434
Vb ...212L
Fb ...18.56Hz
h ... 0.727
F3 ...17.37Hz
Response peak ...0
Peak at ...none
Port min diameter ...20.14cm
Port length ...61.58
Port 1. resonance ...249Hz
Vb + driver displacement + two large internal braces = 234L
INTERNAL dimensions are 38cm*77cm*80cm (W*D*H)
Flared ports
Parametric EQ

Unibox states that minimum port diameter is 20.14cm while my one was 5.75inch (14.6cm)
Anything seriously wrong or can you just ignore it?

thomas

How is this different to your as-15 subwoofer?

[ThomasW]

The design looks ok. I imagine Unibox's bigger port suggestion is to decrease the potential for port compression. Using a port with flares allows a smaller port to flow as much air as a larger one without compression. Using a smaller port means the box itself can be slightly smaller since the port takes up less space.

Ported designs somewhat forgiving, and can tolerate about a 10% 'fudge factor' before there's a major change in performance. I recommend building a prototype; so as to test the real world performance of the design before making serious investemt in finish grade materials. This though time and labor intensive, can save $$$ in the long run, particularly for the novice.

[pkgum]

everyone,

How can this design be improved in your opinion?

[Edited by pkgum on 11-02-2001 at 03:44 PM]

[ThomasW]

How can this design be improved in your opinion?

Well IMHO it can't

[pkgum]

Do you recommend me start ordering MDF,drivers, etc and start building the subwoofer using this basic design done by Unibox?

[ThomasW]

Yes certainly order the driver. Get the Lightning Audio flares, only if you can find PVC that has a 6.25" OD. Now the ID may vary depending on what you have available. So the final port length may need to be altered depending on what size pipe you're able to find. If you can't find PVC with a 6.25" OD, then don't order the Lightning Flares

Don't build the box in advance of having the driver; and until you know you can duplicate the port with flares, or know what size straight port you will be substituting if getting the flares isn't practical.

When deciding on the dimensions of your box, it's important to have the inside opening of the port approx 6" away from the back wall of the cabinet. Height, width, aren't critical, so they can be what you like, as long as the net interior volume is within the needed parameters, and the cabinet depth is be sufficient for 6" of clearance behind the port.

Once you have everything in hand, driver, port, etc, then I'll run LspCAD calculations from the final net internal volume you get. You can compare them to what you get with UniBox. They should be very close.

[Edited by ThomasW on 11-02-2001 at 10:41 PM]

[pkgum]

Here is a quote from a previous post:

"Making any changes in the design will result in a sub that doesn't perform up to the full potential of the HE15/BP1503"

I have a very different design. Is the as-15 is the only way to go to get the ultimate performance out of the driver? If so, then give me its physical Vb excluding driver displacement,bracing,damping,losses, etc. From this Vb I'll make a similar as-15 design-- the only difference is that it is simpler in the woodwork.
Or is the design I created with unibox is enough to get the ultimate performance out of the driver?


Say that unibox calculated your port length is 11". The front baffle of your designed subwoofer is 1.5 inches thick. The port is mounted through the hole you cut in the front baffle.
Should the port be cut and mounted in the subwoofer with a finalised length of 12.5"(plus the thickness of the front baffle) OR to a finalised length of 11"(ignoring the thickness of the front baffle)?

[ThomasW]

Ok first let's not get too literal....

And second why has this conversation starting over again? You have a design and it's very similar to the AS-15.

The AS-15 was designed to obtain max performance from the smallest reasonable sized box, with no compromises. This goal was achieved.

I already answered the port behind the baffle question. Of course IF the ported is butted to the baffle, the hole in the baffle adds to the length of the port. This is common sense. However it's a better idea to have the port pass through the baffle. This way the baffle gives added support to the port.

The cabinet work for the AS-15 is part of the design to get the best performance. It's not that difficult. The cabinet MUST be sufficiently braced. If not, the driver is so powerful that serious wall flexing will result, and the performance will suffer.

Why? Well if the walls of the box are vibrating, then they are acting like the cone of a speaker, and the sound waves they generate will cancel those made by the woofer.

Also you need to understand I don't have hours and hours of time to walk you through every question you can think up regarding loudspeaker design. That's what books are for. If you want to build a close copy of the AS-15, I'll give you assistance.

[pkgum]

I'll try borrow the book 'The loudspeaker Cookbook'

then I start ordering everything and begin the practical work

[pkgum]

Can you buy high power car audio amps to power the subwoofer? Car audio amps are much much cheaper than the samson,qsc,etc amps.