Depth for a speaker enclosure

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Hello, I have some 8" x 12" mdf sheets and a pair of 6" woofers. I am planning to make a pair of woofer boxes with them, with dimensions of ~8" x 12" x 8" (w x l x d). There will also be a port (probably in the front) tuned @ 45-50Hz.

I wanted to make sure, if the above dimensions would be ok, or the depth of 7-8" is to much for the box and/or I will need better dimension values ?

I choose the above dimensions, because apparently they will require minimum cutting from these mdf sheets.



Thanks.
 
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PRR

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Joined 2003
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Sight un-seen, a "happy" Saled box tends to be about (D*1.1)^3, where D is the advertized diameter. (This actually goes back to most speakers' efficiency being near 1%.) Variations of 2:1 don't make a large difference. Vented box WILL need more space.

6" * 1.1 = 6.6"

6.6" ^3 = 287 cubic inches.

Your proposed box is like 7"x7"x11"= 540 cubic inches.

The box is 1.8X times the estimated "happy" size. This will work as a Sealed box and that is what I would do.

1.8X is a bit small for a Ported box. You need to consult the math (there are online calculators). You do NOT arbitrarily pick a box tune frequency-- the likely result is a fall-off below 150Hz then a big bump at 50Hz.
 
Sight un-seen, a "happy" Saled box tends to be about (D*1.1)^3, where D is the advertized diameter. (This actually goes back to most speakers' efficiency being near 1%.) Variations of 2:1 don't make a large difference. Vented box WILL need more space.

6" * 1.1 = 6.6"

6.6" ^3 = 287 cubic inches.

Your proposed box is like 7"x7"x11"= 540 cubic inches.

The box is 1.8X times the estimated "happy" size. This will work as a Sealed box and that is what I would do.

1.8X is a bit small for a Ported box. You need to consult the math (there are online calculators). You do NOT arbitrarily pick a box tune frequency-- the likely result is a fall-off below 150Hz then a big bump at 50Hz.


I am also thinking few other options.

1) I can increase the height to 24" by joining t sheets together. then the volume will be 7.5x7.5x25 cubic inches. Will it be ok for a ported box with 6" driver?

2) If i keep the original dimensions 7.5x7.5x11.5 cubic inches and make a 50Hz port with 0.5" pvc pice, will it sound awkward like that ?

3) I had a plan to make a sealed box with a 8" driver, but I am reading 8" large size driver are not good for 2 way systems, as they can not produce good high-mids, is this right ?

4) If I use 2x6" woofers for a sealed box, what will be the required dimension for the closed enclosure ? ((6+6) x 1.1)^3 = 2299 cubic inches ?
 
Do you have the Thiele-Small params? There are online calculators that will do the work for you from that info.


I have taken help of online calculator here :
Designing and Building a Speaker Box Example


And it has calculated huge box volume even for sealed box as well. If that is the calculation, then I should go for butterbox instead I guess. Confused.



Also, it seems the topic is kinda technical, not getting much response from members. :/


ZSse8oa.png
 
Last edited:

PRR

Member
Joined 2003
Paid Member
2 cubic feet is enough for a 12" woofer. If the math says 2cf for a Six, it is making-up for a small woofer with a huge box. This usually leads to a result that is flat for very low levels but slaps when you try to get real bass level.

Also note that your "Ported Box" solution calls for -negative- duct length, another sign that you are fighting the physics.

I would not ask for much under 100Hz from a Six. Yes, I know the woods are full of small woof-boxes with "satisfactory" bass, but I like some cone (air-paddle) to go with the empty box.
 
You would be well served sharing the make/model of the woofer you're wanting to use. If you don't know then perhaps posting some pictures will jog someone's memory.

Without the correct driver parameters you're not going to get very good results. No one can possibly give you the answer you seek with out the Theil-Small parameters for that exact driver, beyond what's already been given.

It's like asking what size tire does my vehicle need without knowing what the vehicle is, etc.. It's a matter of physics.


TJ
 
You would be well served sharing the make/model of the woofer you're wanting to use. If you don't know then perhaps posting some pictures will jog someone's memory.

Without the correct driver parameters you're not going to get very good results. No one can possibly give you the answer you seek with out the Theil-Small parameters for that exact driver, beyond what's already been given.

It's like asking what size tire does my vehicle need without knowing what the vehicle is, etc.. It's a matter of physics.


TJ
hi, it's exact same model i posted in here, in picture.
 
OK, I try: in ignorance, as I am, progress is rapid.

You can see the speaker as a resonant system, with a frequency at which it is capable of accumulating energy and returning it over time. The Quality factor is a measure of the ability to accumulate energy. If it is high, the accumulated energy will be greater, and the time to return it will be longer.

The driver you have chosen has a fairly high Qts.

A speaker in a box, couples a second resonant system: an air mass. That emits energy in the room (bass reflex) or dissipates it in the cavity (sealed).
Together they make it a third system.

The concern of those who answered you, refers the performance of this last whole system.

The experience of those who built a lot, and the simulation software
they recommend very large closed boxes, up to an infinite volume.
You can try other simulation programs, with more freedom, to understand why you got negative lengths.

Perhaps you can also explore an acoustic dipole or a transmission line.
 
OK, I try: in ignorance, as I am, progress is rapid.

You can see the speaker as a resonant system, with a frequency at which it is capable of accumulating energy and returning it over time. The Quality factor is a measure of the ability to accumulate energy. If it is high, the accumulated energy will be greater, and the time to return it will be longer.

The driver you have chosen has a fairly high Qts.

A speaker in a box, couples a second resonant system: an air mass. That emits energy in the room (bass reflex) or dissipates it in the cavity (sealed).
Together they make it a third system.

The concern of those who answered you, refers the performance of this last whole system.

The experience of those who built a lot, and the simulation software
they recommend very large closed boxes, up to an infinite volume.
You can try other simulation programs, with more freedom, to understand why you got negative lengths.

Perhaps you can also explore an acoustic dipole or a transmission line.


very large closed boxes ! :cannotbe:



but, thanks for the explanations. can you please suggest some online calculators that you like and trust ?
 
FWIW, when I use a typical 166 mm/6.5" woofer's 134.8 cm^2 effective cone area [Sd], published [BL], [Mmd] it becomes obvious that the specs are gibberish since both Fs, Qes average a ~65% drop, so short of measuring its specs can only recommend building the largest sealed cab you can tolerate since specs can be this far off in the other direction, i.e. published may be the mean of a wide production tolerance. :(

GM
 
Re programs calculating big boxes.......... driver effective motor strength dominates, so all else equal, the higher Qts is the disproportionately larger the box since it's raised to the 2.87-3.3 power depending on whose version of the formula is used, with Vas increasing it too, though until quite large isn't a major factor.

GM
 
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