Tube to cabinet move

[greenie512]

I'm thinking of migrating my Peerless 10" XLS woofer and plate amp currently in a Formatube (sonatube) ported "box" into a nicely veneered standard MDF cabinet. Volume about 59 litres with single port tuned to 28 Hz

Heres the plots from WinISD, obviously the 28 Hx is offset because it's a higher feq than current. Can anyone cast futher wisdom/meaning on these plots as I'm afraid my knowledge in reading them is Zero.

Thanks for any help.

 

[BassAwdyO]

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 boomy

 

[greenie512]

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,....................or 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 boomy

Thanks for the detailed response, it is very helpful. I was thinking that my Formatube sub "may" be slightly boomy, so I will digest your advise and adjust accordingly.

 

[greenie512]

BassAwdyO, just plugged your figures into WinISD and see what you mean.

When you talk about a "shelf" I'm assuming thats the leveling out of the curve after the main incline?

I think I'll go for the 35.24L @ 22.3Hz as this new set up is to augment my new Thor TL and so do not need vast SPL's.

 

[BassAwdyO]

Yes, 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?

 

[greenie512]

BassAwdyO - have just downloaded the latest version of WinISD Pro and charts are much clearer.

Well, the Thor transmission line produces 4 dB of bass lift from 20Hz to 110HZ, with less than 1 dB of ripple. The -3dB point is 45Hz, with roll off of 12dB per octave below 45Hz. Usable in-room bass response extends well into the low 30Hz range (Madisounds spec).

And to be honest I could live without a sub as I’m really quite happy with low end of the TL’s But I have the Peerless XLS and plate amp so want a “discreet” sub to pick up the lower range. Which is why I thought your 35.24L @ 22.3 Hz suggestion might be best.

 

[BassAwdyO]

I see, It seems like that alignment would give you a bit more extension down to at least 25hz. How large is the TL?

 

[greenie512]

I see, It seems like that alignment would give you a bit more extension down to at least 25hz. How large is the TL?

Here's the construction pics of the Seas Thor TL's

http://www.users.on.net/~byindex/ThorProject/index.htm

Original Spec etc - http://www.seas.no/thor.htm

 

[BassAwdyO]

Very nice... I'll say the XLS should give you a bit more thunder in the low end. Keep me posted on how the sub turns out😉

 

[greenie512]

Very nice... I'll say the XLS should give you a bit more thunder in the low end. Keep me posted on how the sub turns out😉

I've been busy this weekend and built version No2 of my subwoofer, similar to our discussions, see pics etc at -

http://www.users.on.net/~byindex/subwoofer_no_2.htm

Thanks for the help and have quoted you with credits on the above page.

 

[BassAwdyO]

No problem, the sub looks good. I took a look at the pictures of it and the formatube sub and I was wondering where the port exits were on the formatube sub? The port you used on the MDF sub seems to be pretty small in diameter. Port chuffing near resonance might occur if the ends arent rounded and flanged. Because port length gets so long for small boxes when an appropriate cross section is used typically slotted type ports are used and the port wraps around the box.

 

[greenie512]

Yes, see what you mean .. the fabric cover hides 2 port outlets on bottem to one edge of the woofer on the Formatube version.

Yes I was a bit worried re port diameter of 50mm and possible air velocity noise - but haven't noticed anything on current brief listening. That was a consequence of me keeping the footprint probably too small.

Could you give me an example of "slotted type" ports??

 

[BassAwdyO]

I've attached a picture showing the difference. Basically the tuning of the box is dependant on 3 measures.
1. Box volume - AIR volume in the box (doen't include port volume)
2. Port cross section - Area of cross section
3. Port length - Length of port (including end correction)

When I started in DIY audio I though tuning had something to do with the driver, but this is wrong. The box is tuned to a specific frequency regardless of what driver is used. The curves you see on WinISD represent how the driver does in a specific box size and tuning frequency. With different box sizes and tuning frequencys the driver is damped more/less to achieve a specific response curve. The relationship of the 3 factors are as follows.

If box volume and tuning frequency are constant then:
If cross section increses, port length increases
If cross section decreses, port length decreses

If port cross section and length are constant then:
If box volume increses, tuning frequeny decreses
If box volume decreases, tuning frequency increases

Other relationships can be made, but those should give you the basic idea how the enclosure works. The difference between slot ports and round ports are only shape. They both have a specific cross section and length which along with enclosure volume determine tuning frequency. The advantage to slot ports is simply the ability to build a long slot port that bends to fit inside the box. This allows a smaller enclosure to have a low tuning frequency without comprimising the cross section of the port. The only other alternative, Passive radiators...

 

[greenie512]

G'day - BassAwdy0

Now I get the slotted port, I've seen them in various designs.

Thanks for all this info, hope I'm not bugging you.

One final request!!! - have you any recommended books/reading thats easy for a beginner like me to digest on speaker design in general (keep hearing about the Loadspeaker Cookbook).

 

[BassAwdyO]

Yes there is Vance Dickason's The loudspeaker cookbook. I've read it myself, but found it to be entirely boring in many parts. It is a good book if you really want to learn about enclosure design, but it goes into great detail and gets fairly technical. I would consider it slightly beyond beginnier reading however. http://www.diysubwoofers.org has a fairly good amount of information and would probably be a good starting point. I'd say if you read about the enclosure types and their design concepts at diysubwoofer.org and still want more, Vance Dickason's book would be a good place to head.

BTW, its no problem. I'm glad to help out