Unibox Questions

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Okay, I've started thinking about re-designing my current passive subwoofers. (I'm tired of their current look and have some approval from the spouse to do this) So I started playing with Unibox to see what I can do to make them better. (I didn't pay close attention so some details when they were originally made about 6 years ago) They're a peerless 10" driver. (I believe they're the SWR 260 model, at least that's close enough to get ideas) My question is this, as I was working on modeling the different boxes, I've discovered some interesting things that confuse me. First, has to do with the cone excursion plot, everything I enter for either the sealed or vented shows the cone excursion being greater then the 8mm Xmax at about 50Hz. Is this really a bad thing and is this modeling correctly? (I don't think I'm hearing distortion in them currently, and I know they go deep now) Secondly, the port lengths for the ported box, when it gives a port length and I specify two ports, is the port length given for each port, or the combined length?

Finally, how much do I balance size versus how deep the woofer will go? (I can build the box bigger and go deeper, but is there a point of diminishing returns?) Thanks for the help/suggestions!
diyAudio Moderator Emeritus
Joined 2001

I have not yet downloaded Unibox. However, I have built speakers with the Peerless 260 subwoofer.

The Peerless 260 subwoofer worked very well in a 2 cubic foot enclosure tuned to 30 Hz. It will be about minus 3 dB at 30 Hz or so. It worked for me, and I tested it.

Why do you get 8 mm Xmax in both a sealed and ported enclosure at 50 Hz? Two possible reasons. Either:
a) The sound output of the ported box is higher than that of the closed box at 50 Hz for the same 8 mm excursion;
b) The box is tuned to 25 Hz or below. The benefit of the port is that the speaker's cone moves less, but produces equal or greater volume of bass than a closed box speaker at the same frequency. This effect usually lasts only for an octave above the box tuning frequency, (Fb). Above that, the closed box and the ported box are on an equal footing.

At Fb, the cone of a speaker in a ported box will typically move only one fourth the distance that the same speaker in a closed box will have to move to produce the same volume. At half an octave above Fb, the ported box speaker will have to move half the distance as the closed box speaker.
An octave above Fb, the two boxes will act alike.

[Edited by kelticwizard on 11-09-2001 at 05:54 PM]
diyAudio Moderator Emeritus
Joined 2001

I just ran Boxplot on it and found that it actually tunes out well in a 6 cubic foot box tuned to 22 Hz. Boxplot shows it being 3 dB down at 21 Hz or so.

I would point out that Peerless doesn't give such a large box as a recommendation. The Peerless 260 is an oldie but goodie, still a great buy for the money, but it has been supplanted by 10 inchers with superior excursion and power handling. Also, it has a polypropylene cone, which was all the rage 10 years ago, but has been supplanted by better cone material. If you are going to make a commitment to such a large box-6 cubic feet-you might wish to consider an upgrade.

What is the box you now have it in? If you don't know the internal volume, just give me the external dimensions and let me know how thick the building material is, (or we can just assume three quarter inch or 1 inch). Let me know the diameter and length of the port also. I am interested in what you have it in now.

Also, how big a box are you planning to build?

[Edited by kelticwizard on 11-09-2001 at 06:06 PM]
Off hand, I'm not sure of the dimensions, they're about end-table sized. (At least that's what they're doing double-duty as) I think the 6ft^3 box would fail the SAF test. (Not to mention my own, as I do want them to blend into an already small room) The idea (I wouldn't really call it a design, I didn't know much of what I was doing) was a following of the sonotube design, namely they're in a pair of tubes with particle board on the top and bottom with some insulation on the inside. (Don't cringe too much, they work for what they were intended with the tools I had available and the funds I had available) Now I want to do it a little better.

Size-wise, I would like to keep them about end-table sized, not much larger. Also keep in mind buying new drivers is not an option, the only reason I get to re-do the boxes is because the better-half would like a change as well, and knows I can do new boxes for less than $100.

I ran your suggestion through unibox and it still showed that the max excursion of 8mm was around the 50Hz area. I'm wondering if this is something I should really be concerned about. They're most likely going to be running passive for a while yet (at the very least until I go digital on the home receiver) and my current receiver only puts out about 70watts (Denon AVR1000).

Thanks for the suggestions and help kelticwizard!

P.S. - is boxplot free or have a free demo? Where can I see more about it?
diyAudio Moderator Emeritus
Joined 2001

Boxplot is free to download, but apparently will have additional features if you register for $25. I use the free version. It can be downloaded at Steve Ekblad's excellent site, http://www.wssh.net/~wattsup/audio/.

As for excursion, try running through Unibox the following:

Box size = 1.2 cu. ft. (34 liters)
Tuning = 31 Hz

See if X max is still at 50 Hz.

The Peerless is a fine speaker. You don't have to upgrade-that was just a suggestion if you wanted to commit to a really big expensive project, which this does not have to be.

This was just a quick message. More posts to come.
I just tried the values and sure enough Xmax moved down to about 24~25Hz! I also played with it some more this morning and was able to create a 3cu.ft. box with a tuning of 32Hz that ended up with an F3 of 30Hz. So, it looks like I'm starting to grasp what's going on here. BTW, I was also experimenting with a sealed enclosure, but the best I can get is an F3 of around 50Hz! Is a 20Hz difference between sealed and ported normal? I knew they would be different, but that's a pretty big difference! (At least I think it is...)

Thanks for the link, I'll download it and compare it with unibox and I just saw a link for winISD as well, so I'll be playing for a while!
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