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View Full Version : loudest box with out sacrificing to much sq on 12 w7?



grimreaper253
04-17-2007, 01:35 AM
ive got two sheets of 3/4 mdf laying around and i want to build a different box. im currently running sealed to jls specs. i want to make it louder with out losing a bunch of sq. should i go with ported with jls specs or is there any other better designs out there? any info would be appriciated.

thanks,
nick

Trixter
04-17-2007, 12:58 PM
try it and see...what sound good to ma may not sound good to you. the mfg's specs would be a good place to start.

PV Audio
04-17-2007, 06:35 PM
2.25 cubes net tuned to 32hz will knock your block off w/ 12W7. Never had a dissatisfied customer.

grimreaper253
04-17-2007, 08:37 PM
what effect do diiferent port frequencies have? if i went to a larger box would that effect how the bass hits? im gonna build that 2.25 but ill still have some mdf left over so i would like to build another box.

thanks,
nick

PV Audio
04-17-2007, 11:52 PM
Your tuning frequency, Fb, controls the "point" of accentuation. The backwave travels through the port and emerges in phase with the sound of the front of the speaker, which boosts your output. Problem is, you can sacrifice the range of sound, although you typically don't notice it unless you have an extreme tuning. A larger box lowers your tuning frequency with all other factors constant (i.e. increasing the width of the box on one side so the port dimensions and length stay the same).

Immacomputer
04-18-2007, 12:17 AM
The backwave travels through the port and emerges in phase with the sound of the front of the speaker, which boosts your output.

Actually, that's not what is happening but you're right about everything else.

Ported enclosures boost the response of the sub centered around the tuning frequency. Below this frequency, the response begins to drop. It doesn't fall off right away, but your output begins to drop off.

Increasing the enclosure size will usually increase low end efficiency and can sometimes limit upper frequency extension. Also, increasing enclosure volume will increase group delay which is what often gives the "slow" bass sound and not as nice transient response. This is all sub dependent as well.

PV Audio
04-18-2007, 07:00 AM
Why, what is happening then? The output from the rear of the driver emerges from the port, and it has to be in phase otherwise you'll either get cancellation or delicious comb filtering :yumyum:

Trixter
04-18-2007, 01:36 PM
i would think the wave coming from the back and meeting the front would only be exactly in phase at one freq....since each freq. has a different wave length to it. if you compete and use the 1/4 wave theory, then you only play one freq. because the back of the box is measured exactly, for that freq., to make it in phase when it reaches a given point, usually mic placement, up front.

another way to think of it is air comes out as the sub goes in......

hoodkid
04-18-2007, 01:39 PM
3.25 @ 34 hz

PV Audio
04-18-2007, 04:28 PM
i would think the wave coming from the back and meeting the front would only be exactly in phase at one freq....since each freq. has a different wave length to it. if you compete and use the 1/4 wave theory, then you only play one freq. because the back of the box is measured exactly, for that freq., to make it in phase when it reaches a given point, usually mic placement, up front.

another way to think of it is air comes out as the sub goes in......Yes, but I fail to see how the backwave could be out of phase when it exits the port, because the purpose of IB is to isolate the rear wave from the front depending on the baffle dimensions. If what you're saying is true, would you not get loads of destructive interference? I mean, you cannot really be off axis with a subwoofer (yes you can, but the chances of noticing are low), but if you could, wouldn't it be startlingly apparent that something is wrong?

grimreaper253
04-18-2007, 07:26 PM
hey hoodkid would you by any chance have the plans for that box? thanks for all the input.

PV Audio
04-18-2007, 07:56 PM
That is too large anyway. I'm telling you, 2.25-2.5 cubes in the low 30s is the winner.

Immacomputer
04-18-2007, 08:01 PM
Yes, but I fail to see how the backwave could be out of phase when it exits the port, because the purpose of IB is to isolate the rear wave from the front depending on the baffle dimensions. If what you're saying is true, would you not get loads of destructive interference? I mean, you cannot really be off axis with a subwoofer (yes you can, but the chances of noticing are low), but if you could, wouldn't it be startlingly apparent that something is wrong?

In phase and out of phase are both terms that can mean a number of different things. You're thinking that the physics of a ported enclosure are similar to a transmission line when it really isn't. In order for the rear wave to be in phase with the front wave, it's going to need to travel quite a long distance, even at higher frequencies. That's what's happening in transmission line enclosures. The line length is set to either 1/4, 1/2, or 3/4 the wave length of the Fs of the driver you're using. Ported enclosures do not use 1/4 wave theory but rather, they're based on Helmholtz resonators. At tuning, the enclosure is set into resonance which drives the air in the port to move in and out. This mass of air stimulates the air outside of the enclosure and causes a change in pressure just like the cone of a sub does when it moves in and out.

This mass of air is what causes the majority of output at the tuning frequency. The sub also plays a role as the driving force and also adds to the output. These two moving objects are not going to be 100% in phase with each other. They will also not be 180* out of phase either. There will be a slight delay between the two but the delay will usually be in milliseconds and should be small enough to not cause any audible losses.

If you're still lost thinking that the slight difference in phase would cause all sorts of issues, think about it like placing two speakers directly in front of you but put one about a foot further away than the other. Then listen to music and see how it sounds. Then place the two side by side and play music. See if you could notice a difference. The two drivers would be slightly out of phase from each other by the time the sound reached your ears. It's the same idea here. Now if you placed the two speakers 1/2 of a wavelength and then played that frequency, you would hear a noticeable difference in the sound.

bikinpunk
04-18-2007, 08:04 PM
From the 6 boxes I've built, anything above 33hz sounds like garbage. IMO, the w7 shouldn't be made into an SPL sub.

I say around 3 cubes, tuned no higher than 32hz.

Right now I'm at 2.9 cubes @ 27hz and I love it. Though, I'm more into SQ.

PV Audio
04-18-2007, 08:55 PM
In phase and out of phase are both terms that can mean a number of different things. You're thinking that the physics of a ported enclosure are similar to a transmission line when it really isn't. In order for the rear wave to be in phase with the front wave, it's going to need to travel quite a long distance, even at higher frequencies. That's what's happening in transmission line enclosures. The line length is set to either 1/4, 1/2, or 3/4 the wave length of the Fs of the driver you're using. Ported enclosures do not use 1/4 wave theory but rather, they're based on Helmholtz resonators. At tuning, the enclosure is set into resonance which drives the air in the port to move in and out. This mass of air stimulates the air outside of the enclosure and causes a change in pressure just like the cone of a sub does when it moves in and out.

This mass of air is what causes the majority of output at the tuning frequency. The sub also plays a role as the driving force and also adds to the output. These two moving objects are not going to be 100% in phase with each other. They will also not be 180* out of phase either. There will be a slight delay between the two but the delay will usually be in milliseconds and should be small enough to not cause any audible losses.

If you're still lost thinking that the slight difference in phase would cause all sorts of issues, think about it like placing two speakers directly in front of you but put one about a foot further away than the other. Then listen to music and see how it sounds. Then place the two side by side and play music. See if you could notice a difference. The two drivers would be slightly out of phase from each other by the time the sound reached your ears. It's the same idea here. Now if you placed the two speakers 1/2 of a wavelength and then played that frequency, you would hear a noticeable difference in the sound.Mmm, got it now. I had always figured that the backwave was in phase, otherwise you would have nice DI effects, thus rendering the ported box useless. Ya learn something new every day. :)

grimreaper253
04-18-2007, 10:39 PM
im building the 2.5 at 32hz. so can you notice a noticible difference between say 28 and 34 hz? how do they sound different? i am trying to read and understand what you guys are saying but i dont realy understand. if some one could please put it in simpler words id be greatly appreiciative.

thanks ,
nick

Immacomputer
04-18-2007, 11:06 PM
An enclosure tuned to 28hz will be louder from about 20-28hz than an enclosure tuned to 34hz. The enclosure tuned to 34hz will be louder from about 30-40hz than the enclosure tuned to 28hz. The upper frequency extension will be about the same between the two. The enclosure tuned to 28hz will have a flatter sound in the response while the enclosure tuned to 34hz will have more of a peak around 34hz and slightly higher.

While there are a ton of other factors, that's a basic view of it. I went from an enclosure tuned to 28hz to 32hz and there was an audible difference between them.

bikinpunk
04-18-2007, 11:17 PM
An enclosure tuned to 28hz will be louder from about 20-28hz than an enclosure tuned to 34hz. The enclosure tuned to 34hz will be louder from about 30-40hz than the enclosure tuned to 28hz. The upper frequency extension will be about the same between the two. The enclosure tuned to 28hz will have a flatter sound in the response while the enclosure tuned to 34hz will have more of a peak around 34hz and slightly higher.

While there are a ton of other factors, that's a basic view of it. I went from an enclosure tuned to 28hz to 32hz and there was an audible difference between them.

Pretty much what I would've said.

To add:

The thing you have to realize with low tuned boxes is that you're ultimately bringing the output across all frequencies to a similar level (think of it as a line) which is known as a flat response. This is particularly nice for SQ setups where you don't want that pronounced response in a certain frequency range; rather you want all frequencies to have the same output (or SPL). Now, your sub plays a huge part of how flat the output will be, but the w7 is actually quite easy to get that flat response. This is good for a number of reasons, but the most important (from an SQ standpoint) is that you rid yourself of a tremendous peak in the mid 40hz range. When you tune high, you have that peak. The peak is what causes ME to dislike the response and I feel it makes the output muddy (not distorted, just too boomy).

Size of enclosure brings that peak either to the lower frequencies (large box) or to the higher frequencies (small box). Depending on your tastes you can either have a smaller box tuned high (heavy output @ 50hz range, but lacking in the 30hz range) or a larger box tuned low (flat response, but brings up the low 30hz range on par with the rest).