Subwoofer design questions

[Theli]

apologies in advance if anything sounds vague....

I`m wanting to build a smallish sub to complement my micro system for listening to music. But I`m having trouble trying to decide what to build that won`t be overkill. I don`t consider myself an audiophile but I like a nice clean sound.

1. What kind of curve should the sub have? flat , peak at some frerq., or other? I've looked at various designs but they won`t really tell me anything about the final sound and how loud/effective it will be.

being a poor student , I can't really experiment too much so I`m trying to determine what would suit my needs best in advance.

Also, I don`t need a lot volume, my living area is fairly small at the moment. The micro system fills it nicely without cranking it up ( except for bass of course.

Thanks for looking and hopefully making a suggestion or two.

Subs I have to play with are:

eclipse 8122.4 12" sub
fs: 23hz
qts: 0.355
Vas: 8 cubic ft.
Z:4 ohm
DCR: 3.6
xmax(one way) : 0.177in
pe: 150W
sd (approx): 550 sq.cm.
91db sens.
or:

max pentivent 1030
fs: 19hz
qts: 0.35
qes: .37
qms 3.6
Vas: 4.6cubic ft.
Z:4 ohm
DCR: 2.9
xmax(one way) : +/- 4mm
pe: 125W
sd (approx): 360 sq.cm.
85db sens.

[kelticwizard]

I would take the Eclipse and put it into a 2 Ft³sealed box. It should work out fine.

With the small excursion of the Eclipse, I would hesitate to put it into a sealed enclosure. However, there does not seem to be a good way to port it without making a big box.

The Eclipse is 6 dB more sensitive than the Max Pentivent. That is very significant.

[Workhorse]

Have u decided about which amplifier to drive the subwoofer!

[sreten]

Just to put a different slant on KC's suggestion.

As its a micro system with limited SPL capability I'd suggest the
Pentivent is a better bet. At low frequencies power handling is
excursion limited and it has better excursion, i.e. it will produce
more low bass.

It will need only nearly half the box volume of the Pentivent,
mainly due to the diffrence in Sd causing the diffrence in Vas.

The 100W or so of a sub amplifier will be better utilised.

Converting your micro system speakers to sealed box may help.

A stuffed sealed box with Q around 0.6 will be fine.

For the two drivers ~ :

Eclipse : Volume = 3.5cuFt, Fb = 42Hz.
Pentivent : V = 2.2cuFt, Fb = 33Hz.

If a near 0.71 alignment is used ~ :
E : Vb=2.5cuFt, Fb=47Hz.
P : Vb=1.5cuFt, Fb= 38Hz.

The trade off is efficiency vs. box volume and extension, I suggest
with a 100w sub amplifier its power that you have going spare.

sreten.

[Theli]

Originally posted by kelticwizard
I would take the Eclipse and put it into a 2 Ft³sealed box. It should work out fine.

With the small excursion of the Eclipse, I would hesitate to put it into a sealed enclosure. However, there does not seem to be a good way to port it without making a big box.

The Eclipse is 6 dB more sensitive than the Max Pentivent. That is very significant.

Just for comparison, doing a 2 cu.ft. vented, tuned to 35hz, VS a 2cu.ft. sealed(yellow) would look like this. Would a curve like this sound bad?

I`ll be tracking down that speaker design book thats been mentioned here before. That should help, no??

[Theli]

Originally posted by amp_man_1
Have u decided about which amplifier to drive the subwoofer!

Not really, but it`ll probably be around 100-150 w sub plate amp, either from Apex Jr. or one from solen.ca

[Theli]

There seems to be some contradictions/confusion for me here...

Originally posted by sreten
Just to put a different slant on KC's suggestion.

As its a micro system with limited SPL capability I'd suggest the
Pentivent is a better bet. At low frequencies power handling is
excursion limited and it has better excursion, i.e. it will produce
more low bass.

It will need only nearly half the box volume of the Pentivent,
mainly due to the diffrence in Sd causing the diffrence in Vas.

Actually the eclipse has better excursion at 4.5mm vs 4mm one way. Or am I reading that wrong?

I`m assuming the pentivent only needs half the box vol. to what the eclipse needs.

The 100W or so of a sub amplifier will be better utilised.

Converting your micro system speakers to sealed box may help.

A stuffed sealed box with Q around 0.6 will be fine.

How do you determine Q?

For the two drivers ~ :

Eclipse : Volume = 3.5cuFt, Fb = 42Hz.
Pentivent : V = 2.2cuFt, Fb = 33Hz.

If a near 0.71 alignment is used ~ :
E : Vb=2.5cuFt, Fb=47Hz.
P : Vb=1.5cuFt, Fb= 38Hz.

The trade off is efficiency vs. box volume and extension, I suggest
with a 100w sub amplifier its power that you have going spare.

sreten.

This I understand, wellll except maybe how you decided on the
.71 alignment

[Theli]

Just to liven things up, I can get an ~2cu.ft. box from a friend for cheap ( meaning free ), that can be vented or sealed.

[Theli]

I managed to answer my own questions. thanks for the help.

[paulspencer]

Theli,

the curve of the vented box you showed doesn't look good - the tuning is too high and there is a bump in the response, so that its response it exaggerated at one point without really giving a significant gain over the sealed box - not a good design. Try tuning lower, closer to fs - more like 23 Hz as a starting point. Get the best looking response, and make a chart showing for your 2cu ft box both drivers vented and sealed. This would enable a better comparison, but it would seem to me a vented box would be the best way to go. All other things being equal, more efficient is better, but this doesn't always help for a subwoofer, as low end efficiency is determined by more than just the nominal efficiency.

regards,
Paul

PS - based on comments above, I don't think a satisfactory conclusion has been drawn as you need to compare on the basis of a simulation that shows the impact all the relevant factors - picking out numbers and comparing them won't really help you.