Subwoofer questions

[ledi51]

I have two questions about car subwoofers. I realize that this site is focused on home audio but maybe you guys can help.

1. I bought a kicker 10" 150 W rms speaker and mounted it in a 0.6 ft^3 sealed enclosure (couldn't find one that was 1+ ft^3 and would fit in my truck). When I listen to it at normal volumes, it makes an annoying sound and I can't figure out what the source may be. The best way to describe it is, instead of the subwoofer making the mmmmmm sound it should make on an extended note, it's more of a vvvvvvv sound. It has this weird ffffff sound along with it. It doesn't do it for every note and it's not loud enough to be heard over the music when it's loud, but during quiet parts it is clearly audible. I set it up with a DMM so I know I'm not overworking it, and I just set it up yesterday and it had this sound from the beginning.

I'm kind of hoping it's because the sub is new and stiff and maybe it'll work itself out over time? Does anybody here have any experience with a similar problem?

2. Right now I just have the one sub set up, but I bought a second one with the intention of having both in my truck (the amp can handle > 600 W rms at 2 ohms). I was playing around with the placement of the first one and discovered that when it's directly behind the driver's seat, I'm missing out on a lot of the low-frequency sound and it overall just sounds quieter. Right now I have it in the corner behind the passenger's seat, because that seems to maximize the bass. But if I put in the second one, it will be behind the driver's seat. Would that even be worth it? In other words, will I get the same non-bassy results from the second one as I did with the first one when I put it behind the driver's seat? I guess I'm hoping that since there are two it will be different somehow

Thanks!

 

[TLS Guy]

I have two questions about car subwoofers. I realize that this site is focused on home audio but maybe you guys can help.

1. I bought a kicker 10" 150 W rms speaker and mounted it in a 0.6 ft^3 sealed enclosure (couldn't find one that was 1+ ft^3 and would fit in my truck). When I listen to it at normal volumes, it makes an annoying sound and I can't figure out what the source may be. The best way to describe it is, instead of the subwoofer making the mmmmmm sound it should make on an extended note, it's more of a vvvvvvv sound. It has this weird ffffff sound along with it. It doesn't do it for every note and it's not loud enough to be heard over the music when it's loud, but during quiet parts it is clearly audible. I set it up with a DMM so I know I'm not overworking it, and I just set it up yesterday and it had this sound from the beginning.

I'm kind of hoping it's because the sub is new and stiff and maybe it'll work itself out over time? Does anybody here have any experience with a similar problem?



2. Right now I just have the one sub set up, but I bought a second one with the intention of having both in my truck (the amp can handle > 600 W rms at 2 ohms). I was playing around with the placement of the first one and discovered that when it's directly behind the driver's seat, I'm missing out on a lot of the low-frequency sound and it overall just sounds quieter. Right now I have it in the corner behind the passenger's seat, because that seems to maximize the bass. But if I put in the second one, it will be behind the driver's seat. Would that even be worth it? In other words, will I get the same non-bassy results from the second one as I did with the first one when I put it behind the driver's seat? I guess I'm hoping that since there are two it will be different somehow

Thanks!

I think you have the wrong driver for that size box. It is too small by a factor of 100%. You can't use any size box. You have to model a driver using the Thiele/Small Parameters to find one that will work well in a box you can fit in your vehicle. If the box volume is not in the ball park, the sub will not work.

 

[ledi51]

Thanks for your response, TLS Guy. I guess I made the mistake of underestimating the importance of the box size. I relied on the amazon reviews for the box, few of which had complaints about it being a problem. I guess most people probably don't know what they're talking about when it comes to audio!

If I were to custom-build a box with a volume of 1-1.5 ft^3, assuming I do it correctly, would the sub noise go away? And would the sound be more evenly distributed around the cab so that even if the box is right behind me I can hear it clearly?

 

[TLS Guy]

Thanks for your response, TLS Guy. I guess I made the mistake of underestimating the importance of the box size. I relied on the amazon reviews for the box, few of which had complaints about it being a problem. I guess most people probably don't know what they're talking about when it comes to audio!

If I were to custom-build a box with a volume of 1-1.5 ft^3, assuming I do it correctly, would the sub noise go away? And would the sound be more evenly distributed around the cab so that even if the box is right behind me I can hear it clearly?

I have the T/S parameters. I will do some modelling and get back to you.

 

[ledi51]

I appreciate it!

 

[TLS Guy]

I appreciate it!

Yes, your small box gives a total Q around 9 which is much too high and why you don't like it.

The optimal air volume in the sealed box for that driver, is 1.22 cu.ft, which gives you a warm but acceptable Q of 0.707. The Fs is 48 Hz.

Now you need to fill the box with acoustic stuffing. The cabinet needs to be well braced, as the pressure in the box is high. The driver displaces 0.125 cu.ft and that has to be added to the box volume. That gets you to 1.345 cu.ft. You will have to add the volume of your bracing to that volume.

Now sealed enclosures do not produce enough deep bass without equalization. You need to add a boost of 12 db per octave stating at 50 Hz and then cutting off at 25 Hz with a high pass 12 db per octave filter to limit cone excursion and prevent damage. The driver has enough xmax (linear cone excursion) to allow it.

I think if you use this driver correctly one sub will be plenty.

 

[ledi51]

http://s27.postimg.org/b3zssyjur/box.png

Thanks for the help! So would this sort of design be feasible? I can't expand the depth of the box past 12-13 inches so I would have to make it tall and wide, it would have to be slightly bigger than this though but as a concept.

I put the url in the title

 

[Bass_Junkie]

If you don't have enough room for correct cu.ft. sealed box or don't have the budget/ability to buy/build a custom box, You could always try porting the one you have, it shouldn't cost more than $20 or so for a cheap hole saw (don't need a pro grade for 2 holes in MDF).
Just a thought/opinion. I couldn't fit a sealed box in my truck, got great results from ported box.

 

[crossedover]

If you don't have enough room for correct cu.ft. sealed box or don't have the budget/ability to buy/build a custom box, You could always try porting the one you have, it shouldn't cost more than $20 or so for a cheap hole saw (don't need a pro grade for 2 holes in MDF).
Just a thought/opinion. I couldn't fit a sealed box in my truck, got great results ported box.

Wrong on so many levels.....

 

[TLS Guy]

If you don't have enough room for correct cu.ft. sealed box or don't have the budget/ability to buy/build a custom box, You could always try porting the one you have, it shouldn't cost more than $20 or so for a cheap hole saw (don't need a pro grade for 2 holes in MDF).
Just a thought/opinion. I couldn't fit a sealed box in my truck, got great results ported box.

You can't load that diver in a ported box. It is a high Qts driver with a lax suspension. In addition a ported box will always be much bigger than a sealed box for a given driver.

A word of advice: - if you are totally clueless, please don't offer advice.

 

[ledi51]

TLS guy, any thoughts on my design as above? In case you didn't see it, it's 14 in x 14 in on the front and depth of 12 on the bottom and 9 on top, I had a concept picture above. (After doing some calculations I found that to get 1.36 cu ft I would need 15x15 on the front though.)

I guess the real question is, how important is the actual box shape? The Kicker manual suggests a shape with more depth than height, but that isn't really an option for me; The only way I can expand is width and height. How much does it matter?

 

[TLS Guy]

TLS guy, any thoughts on my design as above? In case you didn't see it, it's 14 in x 14 in on the front and depth of 12 on the bottom and 9 on top, I had a concept picture above. (After doing some calculations I found that to get 1.36 cu ft I would need 15x15 on the front though.)

I guess the real question is, how important is the actual box shape? The Kicker manual suggests a shape with more depth than height, but that isn't really an option for me; The only way I can expand is width and height. How much does it matter?

I think that will actually work pretty well. The downside of the small box is reflection behind the driver. I would handle this problem by placing Rockwool on the back face behind the driver.

This is obviously the box you have to build if you want to use that driver.

 

[lsiberian]

Yes, your small box gives a total Q around 9 which is much too high and why you don't like it.

The optimal air volume in the sealed box for that driver, is 1.22 cu.ft, which gives you a warm but acceptable Q of 0.707. The Fs is 48 Hz.

Now you need to fill the box with acoustic stuffing. The cabinet needs to be well braced, as the pressure in the box is high. The driver displaces 0.125 cu.ft and that has to be added to the box volume. That gets you to 1.345 cu.ft. You will have to add the volume of your bracing to that volume.

Now sealed enclosures do not produce enough deep bass without equalization. You need to add a boost of 12 db per octave stating at 50 Hz and then cutting off at 25 Hz with a high pass 12 db per octave filter to limit cone excursion and prevent damage. The driver has enough xmax (linear cone excursion) to allow it.

I think if you use this driver correctly one sub will be plenty.

Adding to the above.

This is a truck so you would get a significant amount of cabin gain and lots of nasty vibration with a properly designed sub. I suggest you use rhino lining or peel and seal to reduce that. YOu might also check out 12volt which is a site more focused on car audio.

 

[ledi51]

I finished the enclosure per our discussion and installed it in my truck! Instead of the design I drew up earlier, I made a box design and put it all the way against the wall, but since there was a bump along the wall I built a stand to support the front. The interior has poly-fil stuffing all around. See the picture below.

http://s10.postimg.org/wbkmoquvt/20140714_011130090_i_OS.jpg

It sounds INCREDIBLE. I did notice slight drops in volume at very low frequencies like you said, TLS guy, but they are barely noticeable when I listen to music. My Rockford Fosgate amplifier has a 40 Hz boost that I turned up slightly to combat it a little, so the drop doesn't actually happen until about 30Hz. I can deal with that, anything lower would just be drowned out by my truck anyway.

Thank you to all who helped, especially TLS guy! This thing sounds great! Some songs make me feel like I got punched in the chest. Installing the second one would be overkill... so I'll probably do it next summer . It would be a shame to only have one 150W sub when the amp can handle 600W at 2 ohms, right .

Thanks again!

 

[TLS Guy]

I finished the enclosure per our discussion and installed it in my truck! Instead of the design I drew up earlier, I made a box design and put it all the way against the wall, but since there was a bump along the wall I built a stand to support the front. The interior has poly-fil stuffing all around. See the picture below.

http://s10.postimg.org/wbkmoquvt/20140714_011130090_i_OS.jpg

It sounds INCREDIBLE. I did notice slight drops in volume at very low frequencies like you said, TLS guy, but they are barely noticeable when I listen to music. My Rockford Fosgate amplifier has a 40 Hz boost that I turned up slightly to combat it a little, so the drop doesn't actually happen until about 30Hz. I can deal with that, anything lower would just be drowned out by my truck anyway.

Thank you to all who helped, especially TLS guy! This thing sounds great! Some songs make me feel like I got punched in the chest. Installing the second one would be overkill... so I'll probably do it next summer . It would be a shame to only have one 150W sub when the amp can handle 600W at 2 ohms, right .

Thanks again!

Glad to be of help. I doubt adding another sub will make much difference. It won't go lower just louder. Since the subs will be virtually side by side, you will get 6 db gain.

If it plays loud enough you will gain nothing by adding another sub.