help with enclosure for sub

[jp8869]

hello,
I have a jl audio 12w3 I would like to build a powered sub for ht with. I will be prchasing a dayton 240 watt plate amp to use with it. I have modled this sub in winisd (beta abd alpha pro) and am perplexed. everyone tells me I need 4 to 5 cubic feet to go ported (including winisd) but when I look at excursion numbers in winisd pro anything over about 3 cubic feet gives me excusion problems at over 25 hz. First off has anyone else used this sub in a ht setup before ? second how do you think it would do in a 2.5 to 3 ft>3 enclosure tuned to around 20-23 hz? any input or advice would be welcome.

 

[Dryseals]

hello,
I have a jl audio 12w3 I would like to build a powered sub for ht with. I will be prchasing a dayton 240 watt plate amp to use with it. I have modled this sub in winisd (beta abd alpha pro) and am perplexed. everyone tells me I need 4 to 5 cubic feet to go ported (including winisd) but when I look at excursion numbers in winisd pro anything over about 3 cubic feet gives me excusion problems at over 25 hz. First off has anyone else used this sub in a ht setup before ? second how do you think it would do in a 2.5 to 3 ft>3 enclosure tuned to around 20-23 hz? any input or advice would be welcome.

My take is that this is a woofer designed for use in a car where the small compartment of the car controls the response of the speaker. Without the extra dampning of the compartment, you'll have trouble.

 

[jp8869]

My take is that this is a woofer designed for use in a car where the small compartment of the car controls the response of the speaker. Without the extra dampning of the compartment, you'll have trouble.

Id say thats not an exact description the vas is high The manufacturer recomended enclosures are small. The recomended sealed enclosure is 1.25 cubes the recomended ported enclosure is 1.75 tuned to 30 hz. I guess they rely on cabin gain to reinforce the low end that and the fact that most music (generaly whats listened to in a car) doesn' have much if any content below 30 hz. I would realy like to hear from someone who has heard this sub in a home theater use. the 3 cube box seems like a decent tradoff on paper anyways

 

[Dryseals]

Makes you wonder why they suggest a box with a volume that is approx half the size of the Vas. The driver has an Fs of 24, yet the box Fc is 48 for the sealed enclosure. Knowing that the low frequency SPL gain in the compartment of a car can be outrageous, it would appear that they have designed this speaker to take advantage of the gain. The Qts puts this speaker in sealed or ported enclosures, From the Qms and without any other specs, I would suspect that the Cms would allow this speaker to go nuts in an enclosure close to its Fs. But thats just me.

 

[annunaki]

I plotted a 12" W3 in a 3.5 ft^3 ported enclosure tuned to 22hz, with a 4 inch port and it looked quite good (fairly linear). It had an Anechoic f3 of 24.63hz.

 

[jp8869]

Makes you wonder why they suggest a box with a volume that is approx half the size of the Vas. The driver has an Fs of 24, yet the box Fc is 48 for the sealed enclosure. Knowing that the low frequency SPL gain in the compartment of a car can be outrageous, it would appear that they have designed this speaker to take advantage of the gain. The Qts puts this speaker in sealed or ported enclosures, From the Qms and without any other specs, I would suspect that the Cms would allow this speaker to go nuts in an enclosure close to its Fs. But thats just me.

Huh............ could you put that in laymens terms.

 

[jp8869]

I plotted a 12" W3 in a 3.5 ft^3 ported enclosure tuned to 22hz, with a 4 inch port and it looked quite good (fairly linear). It had an Anechoic f3 of 24.63hz.

I plotted the box you mentioned and the box I mentioned together (I have no experience with ported enclosures much less for home theater) I see very little diference. At the risk of seeming like a real pita could you please explain the difference. I am trying to learn a little about why The choices are made. Also what would be the tradeoffs between these 2 different enclosures. Strenths and weaknesses of both. Thanks for letting me pick your brains

 

[Dryseals]

Huh............ could you put that in laymens terms.

Free air resonance is 24HZ, the manufacturer is shooting for an enclosure where the resonance is higher, almost double in a sealed enclosure (Fc). The Qts says that this speaker can be used for either sealed box or ported, not unusual, one size fits all manufacturing. Just looking at the published specs and what the manufacturer recommends for enclosures leads me to believe that they designed the speaker to work in a loaded enviroment, not Cheech and Chong but close.

Think of it this way, the strength of the coil/magnet system can out do the mechanical dampening of the speaker in an open air structure, this is your excursion. Now I'm sure there are tons of internet articles that will disprove what I'm saying, so be it. But I did this stuff 30+ years ago and just now have decided to get back into it and see the same things today that was present back then (I love the speaker wire stuff).

The fact is that a speaker is nothing more than a electro/mechanical device to move air, how it moves that air is strongly dependent its enviroment. Free air resonance (Fs) tells me where the mechanical properties of the speaker are at, but they give no indication of what the speaker is really doing there. For a manufacturer to suggest going up with box tuning, tells me that in order to get the Fs they publish, they have allowed the speaker to be very limber vs the weight and displacement of the cone and they are wanting you to keep the speaker in it's operating range to avoid damage.

Back in my time, trying to go to 24HZ was never heard of, what was the point, no music played there. Today, the trend is to be able to say "I'm tuned to 20HZ". The manufacturers know this and will play on it as far as they can, even to the point of decieving you into to hoping your 12" mega dollar speaker will be the king of all.

The key here will be to test your speaker at the ranges you want it to play. MDF is cheap, build a box and see how it does. Without a curve on the speaker, I would guess that the impedance rises very, very sharply at or near Fs, thus the ability to play down low in a car.

JMHO

 

[annunaki]

The 3.5 ft^3 enclosure tuned to 22 hz stays within the woofer's linear limits for excursion (within the response range of the enclosure) where as the larger enclosures exceed it. It (3.5 ft^3 enclosure) also offers the best comprimise of size vs. linearity and low frequency extension.

The smaller enclosures have poor low frequency extention and have a -3db point much above the tuning frequency. If you want to go smaller, you will have to raise the tuning frequency to get more linear response, though it causes a slight bump centered near 50hz.