Greenie512

Subwoofer No 2 [Project No 3]

I promised with my original Formatube sub [Project No 1] to eventually try the speaker and amp in a traditional ported MDF cabinet for comparison purposes. I was really happy with this sub and my Mission 753's which I always thought needed extra bass support. Follow link on left for new cabinet details.

However I recently build a pair of Seas Thor TL's [Project No 2] which I think are absolutely "stunnin". With these speakers the sub doesn't fit in quite as well and "draws" attention to itself (see reason below). Also I want a nice beech veneered box to match my new Thor's.

I have been using WinISD software http://www.linearteam.dk/ to help with port design etc but my knowledge of the meaning of most of this software is ZERO.

I posted a question on the DIYAdio forum for some advice and got the following: -

Plot of original Formatube (green) and new cabinet solution (blue): -

BassAwdyO - [Forum - http://www.diyaudio.com]

Basically, if you keep the same enclosure volume and tuning the sub should sound the same in either enclosure. That is assuming that both enclosures are built with the same quality of construction. Looking at the plots, the higher they go on the y axis, the higher the SPL. The farther left they go on the X axis, the lower in frequency, the farther right, the higher the frequency. WinISD gives anechoic FR response. This means that it is a predicted response of the speaker in a completely non reflective sound environment. An example of this would be, if outer space were air, then the sub would be positioned in the middle of nowhere in outer space such that the sound would only travel away from the speaker and never back to it from reflection. In room response gives a boost of low frequencys due to there being reflections. Car cabin gain is an even higher boost. I'm assuming your using the sub for home audio correct? Looking at the response curves on WinISD I'd say your box is too big for the sub. I'm using the pre-entered WinISD specs for the sub, but an EBS alignment uses 23.9L@ 31.7hz for -3db shelf and 35.24L@ 22.3hz for the -6db shelf. I'd go with one of those two alignments. The 59L @ 28hz will give you a rather large dip at 45hz and a peak at 28hz. That might be rather boomyYes, the EBS (extended bass shelf) alignment is defined by the leveling of the curve before the rolloff below enclosure tuning. The older versions of WinISD didnt come with standard preset alignments, but the newer versions will automatically calculate 5 popular alignments. Two of these are EBS alignments, one being a -3db shelf and the other a -6db shelf. You can achieve a shelf at any level if you change the box volume and tuning frequency to the right values. How do you wish to augment the Thor?

Problem - so my Thor's were revealing the peak on the -3 db shelf which gave a lumpy/boomy lower response, which is very obvious when played with the deadly accurate Thor's.

In my ignorance I always thought big (volume) was best but wondered why I was seeing so many designs using the Peerless XLS driver in very small boxes. Now I know why, this speaker is designed for that very purpose. So now my new cabinet is a third of the volume of the original.

If I'd have taken more notice of the Peerless white paper application notes, I might have got the "hint".

http://www.d-s-t.com/main/tech/appxls2.htm

Multiple ports were also confusing me a bit and I found this in response to a similar question:

Ron E [Forum - http://www.madisound.com/cgi-bin/discuss.cgi]

Double area means double length for both.

The reason for this is that doubling the area doubles how springy the box appears to the port (which acts like a rigid piston at low frequencies), so you need more mass, longer ports, to get the same tuning frequency.