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Round Sub Enclosure

 

jogn cocksure
New member
Username: 0123456789

Post Number: 1
Registered: Apr-07
Posted on   
looking for some help and thought this might be the placei found this really cool 70's round speaker enclosure in the garbage the other day and i would like to turn it into a sub, it it really solidly built out of 3/8" hard wood ply and already has a 7.25" hole cut so i though i could build a 8" sub woofer. i have attached some dimensions drawings to give you a good idea of what i am working with, so...

is there any special considerations that might occur with a round enclosure?

if i am looking to build a sub that accurately reflects the music it is playing rather than than just playing stuff loud is there any combination of speaker/crossover you might suggest?

there was also what i think is a cross over already in the box when i found it, i don't know if it works but i have included a rough drawing of how i think it is put together with the components labeled as per what is written on them (as well as i can read them anyway), any idea what this might be?

there is a 1.5" port at the back (base) of the box, the tub extends about 2" into the box with the inside end cut a a 45 deg angle, i was planning on just sealing this up, what do you think?

any way, i would really appreciate any help you might be able to offer, even just pointing me in the correct direction to answer these questions on my own would be great. thanks in advance for you time.
application/pdfUpload
SPEAKERBOXSPECS.pdf (17.1 k)
 

leo stierer
Bronze Member
Username: Leonski

Post Number: 65
Registered: Jan-07
Posted on   
Round enclosures have a few....mostly theoretical advantages. One that seems to hold water is that there are no weak points and stress is evenly distributed. The original HSU Research Subs were this configuration, but were later dropped in favor of more conventional boxes. These days, most round subs are made from SonoTube, a very inert, compressed material used as a form for poured concrete pillars! This stuff is tough.
The DIY gang Loves SonoTube!

To answer your question, though, you will need a selection of drivers and there respective T/S parameters. You will need to either 'reverse engineer' going backwards from the box size OR starting with a driver, compute enclosure volume and find one that closely matchs your new enclosure. Some drivers are better suited to Sealed and others to Vented enclosures.
If you go the Sealed route, don't forget to choose the Qtc you prefer. This is a dimensionless number which refers to the Q of the entire system, and all mechanical / electrical losses. This is a fairly important number, since for sealed enclosures it effects bass quality. A high number will give flabby / boomy bass while a low number will be excessively tight. Low=<.6>.9 or so. The 'theoretical' perfect number is .707, which gives the flattest response.
The GOOD NEWS is that there are a number of freeware programs available as well as books and 'expensive'-ware. Try the free stuff 1st, to get an idea of how the numbers relate. It is fairly easily done and once you get the hang of it, you will see what your limits are with this enclosure.

I haven't ponied up for the 'expensive' software yet, but there claims (easily verified) are for multiple solutions to a set of T/S parameters.

I'd start reading.....you can 'google' any number of DIY sites and check out Madisound and Parts Express for the goods.

Don't forget, if you don't already have an amp and x-over, you'll need one....the most common style is the 'plate' amp. These have (typically)all the stuff needed for hi-level or line level connections, variable x-over, and phase control (important!)

This is a pretty ambitious project.
Welcome to the DIY zone.
 

jogn cocksure
New member
Username: 0123456789

Post Number: 2
Registered: Apr-07
Posted on   
Thanks for your help, did not quite realize how much thought and number crunching would be involved in this project. definitely makes it more fun. I plan to reverse engineer from the enclosure as I want to maintain the uniqueness of the box. any way, as usual more knowledge leads to more questions, so...

Any thoughts as to how much I could get away with fudging the calculated ideal volume of the enclosure? for example, if my volume is .81 cuft what would be the highest and lowest ideal volume speaker I could reasonable use, or should I just stick to getting as close to .81 as possible?

Is there anyway to calculate the higher volume that the speaker "sees" with the addition of damping material?

If a speaker's ideal enclosure volume is exactly the same or slightly higher than that of my enclosure is there any need for damping?

I currently use a NAD C272 power amplifier rated at 150 watts per channel to power my stereo speakers, any thoughts on whether it would be better, in terms of sound quality, to buy another (smaller) amp and bridge it or install a car amp in the box itself and make it a powered sub?

Any way, thanks so much for any help you all could offer me.
 

Nuck
Gold Member
Username: Nuck

Post Number: 6752
Registered: Dec-04
Posted on   
Fudging an input figure usually gives you an amplified fudged answer.
 

leo stierer
Bronze Member
Username: Leonski

Post Number: 77
Registered: Jan-07
Posted on   
Nuck, I don't understand? Fudging?
It seems all JC has to do is run some numbers to find a driver compatible with his 'found' enclosure size. Vented is more complicated, but sealed seems to be pretty a pretty straightforward calculation.
What worries me is that he is even thinking of a Car Amp. A decent Plate amp would even cost less than a Car Amp, even if he stole a neighbors battery to run it!
He's even starting to ask a few better questions, which are past what I know, so I'll recommend a good DIY site with expertise in this line of questions.
He might even make a decent, small sub out of it!
than be back to tell everyone about it.
 

jogn cocksure
New member
Username: 0123456789

Post Number: 3
Registered: Apr-07
Posted on   
thanks for all the input, I'm trying to get a handle on all this audio stuff and you have all been a great help.
so, as no good deed goes unpunished, I am back for more free advice.
just trying to narrow down my choices and was wondering if any one had some advice on which combination of speaker and amp might work best.
as the enclosure is a cylinder I don't have much room to mount the plate amp, the largest rectangle I can fit on the bottom of the box is about 8.5" x 10.5" (depending on the LxW ratio).
have been looking for suppliers and so far I have found madisound, parts express and apex jr, any of these I should steer clear of or others I am missing?
also, how worried should I be about low efficiency?
Are there any specific values that one should try to obtain for the F3 and/or Fb?
I have been doing some looking at the above suppliers web sites and my choices have come down to these:

speakers:

1. Apex Jr Super 8 Subwoofer ($39.95)
fs = 47.75 Hz
Qes = .552
Qts = .5140
Qtc = .707

F3 = 33.5894 Hz
Fb = 37.2682 Hz?
Vb = .8364 cuft
1.5" dia port L = 2.8771"

Ref eff. = 85.0153 db/w
EBP = 86.5

2. Peerless 8" CSC-X Woofer ($50.05)
fs = 28.2
Qes = .29
Qts = .27
Qtc = .707

F3 = 50.5191 Hz
Fb = 42.5250 Hz?
Vb = .7442 cuft
1.5" dia port L = 2.3192"

Ref eff. = 89.6687 db/w
EBP = 97.2414

1. Dayton QT210-4 8" Quatro series subwoofer ($49.75)
fs = 36 Hz
Qes = .42
Qts = .4
Qtc = .707

F3 = 36.4467 Hz
Fb = 36.3141 Hz?
Vb = .7973 cuft
1.5" dia port L = 3.3043"

Ref eff. = 85.9084 db/w
EBP = 85.71


Amplifiers:


Dayton SA100 plate amplifier ($94.34)

W @ 4 ohm = 100
W @ 8 ohm = 75


Dayton SA70 plate amplifier ($52.59)

W @ 4 ohm = 70
W @ 8 ohm = 45

I would appreciate any advice you could give me. thanks for your time.
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