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View Full Version : Need some help figuring this out...



brandon_s0854
02-20-2012, 12:37 PM
Yesterday I installed a new enclosure for my hdc3 10's. My old enclosure was built for my Grand Prix, which I no longer have. The box sounded great, but was extremely overbearing in the 35-45hz region; so much so that I had my subsonic filter on my 2200d turned way up just to even out the sound. Unfortunately, this also meant that anything below 35hz was pretty much non-existent. The biggest reason I rebuilt the box, though, was because it didn't fit in the back of my Edge very well. I figured I'd build a new box to gain more useable space in the Edge and try to alleviate some of the 35-45hz output, which in turn would allow me to turn down the subsonic and get that low bass back.

The old box was 3 cu. ft. @ 35hz with the subs and port facing the rear and the port on the right side of both subs. The new box is 2.6 cu. ft. @ approx. 38hz. Again, both subs facing the rear, but with the port in the middle. Port area per square foot is almost identical. I figured the slightly smaller, higher tuned box would help alleviate the earlier mentioned peak in response. The new box seems to be slightly louder in the 40-60hz range, but has much less output below 40hz; I'm talking at least 10dB, probably more. Also, there seems to be less output in the 60-80hz range as well. I figured there would be slightly less output below 40hz; that's what I was going for. I didn't think there would be a huge amount less. And what's going on with the midbass? The last thing I expected was less midbass! Bass above 80hz seems to be unaffected.

Any ideas what the problem is?! I need some suggestions.

duanebro
02-20-2012, 01:14 PM
ok, the port boosts then spl around where it is tuned to. You moved the peak up by tuning higher. The higher tuning will increase the spl you see at that frequency also. This also can be perceived as lowering the spl elsewhere, like the midbass. Below tuning the fr drops off.

I would recommend lowering the tuning on the new box... a lot! (try for 30 Hz.) This should give a response that rolls off through most of the subs range. Cabin gain will lift it back up.

brandon_s0854
02-20-2012, 02:06 PM
Thanks Duane. I thought about the fact that the midbass may seem quieter due to the fact that the lower range is louder, but I'm just amazed how much less below 40hz this box seems to be producing.

EDIT: Also, do you have any suggestions how to lower the tuning of a box that's already built? I can't think of a good way to do it. I can't easily extend the port, and the mouth of the port has a good-sized flare on it; so trying to reduce the size of the port would look pretty dumb.

ngsm13
02-20-2012, 02:17 PM
As stated, you basically did the opposite of your goals.

You'll want to keep tuning low, in the 28-32hz range if you like a flatter response and good low frequency response. In general, response will be within -3dB about half an octave below tuning. Also, peak will depend on the drivers, box size, and tuning.

I'd look at something like 2.5 cubes NET @30-32hz, play with your port area to get the enclosure within a reasonable overall size.

brandon_s0854
02-20-2012, 02:44 PM
Well, I wasn't going for a low end monster. I was thinking the slightly smaller, higher tuned box would give me roughly 6dB less below 40hz and then I could bring the subsonic filter back down to make up the difference. I was aware that the changes I made were going to reduce output below 40hz. It's just weird because the box is roughly 10% smaller and tuned roughly 10% higher. Despite the small changes, the sound is dramatically different.

brandon_s0854
02-20-2012, 02:47 PM
In general, response will be within -3dB about half an octave below tuning. Also, peak will depend on the drivers, box size, and tuning.

It's definitely more than 3dB down at 30hz; more like 10dB. So what you guys are telling me is that there's nothing wrong with the box or wiring, or anything. It's just the box behaving the way it should.

duanebro
02-20-2012, 03:33 PM
Thanks Duane. I thought about the fact that the midbass may seem quieter due to the fact that the lower range is louder, but I'm just amazed how much less below 40hz this box seems to be producing.

EDIT: Also, do you have any suggestions how to lower the tuning of a box that's already built? I can't think of a good way to do it. I can't easily extend the port, and the mouth of the port has a good-sized flare on it; so trying to reduce the size of the port would look pretty dumb.

This is a great example of why Winisd is a great tool. You should d/l it (look it up on facebook for the latest version.) You can load the original box and then a new box at the same time to see the differences are. If you already know what one of the boxes sounds like in your car you can get a very good idea if the new one will be better or worse.

As far as lowering the tuning of the box. If your using a slot port try adding a piece of wood in the middle of the port. It can end where the flare starts. Adding more pieces will lower tuning more. Do this temporarily to check the effect on the box. This is the same as making two ports. If it is easier set the piece in the bottom of the port and hold it in with some blue tac. Yes, this is just shrinking the port to lower tuning. I would do this so I wouldn't have to build several more boxes. A smaller port will work just fine at lower volumes. It is the air speed as you crank it up that causes problems with noise and port compression. Check what frequency you are at when you get to what you like. Now you might want to build another box. You can put things in the box to lower volume of the box to if you want to play with that. Bricks work well, just don't drive with them in!

brandon_s0854
02-20-2012, 03:47 PM
I've used WinISD for awhile now; learned not to rely on it. I've had mixed results with its accuracy. I've been building boxes for a long time, and this is the first one that didn't act like I expected. Live and learn I guess.

brandon_s0854
02-20-2012, 03:53 PM
As far as lowering the tuning of the box. If your using a slot port try adding a piece of wood in the middle of the port. It can end where the flare starts. Adding more pieces will lower tuning more. Do this temporarily to check the effect on the box.!

Thanks for the tips! I didn't think about modifying it that way. I might give it a try. Also, noticed you're from Grand Blanc; only an hour away from me. Good to see people from the area on here.

duanebro
02-20-2012, 03:58 PM
I've used WinISD for awhile now; learned not to rely on it. I've had mixed results with its accuracy. I've been building boxes for a long time, and this is the first one that didn't act like I expected. Live and learn I guess.

I've found it to be very accurate. BUT you must know its limitations. One of the biggest is that it can't model a car or room. Also the difference in distance from the user to the port and subs can cause phase issues that affect output. This is not modeled by winISD. I like to use it to see how much of a change I will see if I need to shrink a box to make it fit.

brandon_s0854
02-20-2012, 04:08 PM
I've found it to be very accurate. BUT you must know its limitations. One of the biggest is that it can't model a car or room. Also the difference in distance from the user to the port and subs can cause phase issues that affect output. This is not modeled by winISD. I like to use it to see how much of a change I will see if I need to shrink a box to make it fit.

I agree. There are too many variables in a listening evironment for any software to really be accurate. The only time I use it anymore is to get a general idea of how certain subs will respond to different enclosure volumes and tuning. I didn't use it in this case because I knew what it sounded like in a 3cf box @ 35hz, and made small changes to it to get what I was looking for. If I would've relied on WinISD for this, I probably would've tuned even higher. I'm actually interested to see what WinISD would predict in this exact scenario. I bet you it wouldn't be more than 10dB down @ 30hz!

ngsm13
02-20-2012, 04:33 PM
Well, I wasn't going for a low end monster. I was thinking the slightly smaller, higher tuned box would give me roughly 6dB less below 40hz and then I could bring the subsonic filter back down to make up the difference. I was aware that the changes I made were going to reduce output below 40hz. It's just weird because the box is roughly 10% smaller and tuned roughly 10% higher. Despite the small changes, the sound is dramatically different.
Indeed. Slightly smaller, and higher tuned actually makes for a "peak-ier" box.

It's definitely more than 3dB down at 30hz; more like 10dB. So what you guys are telling me is that there's nothing wrong with the box or wiring, or anything. It's just the box behaving the way it should.
Correct, they box is performing how it was designed.

I've used WinISD for awhile now; learned not to rely on it. I've had mixed results with its accuracy. I've been building boxes for a long time, and this is the first one that didn't act like I expected. Live and learn I guess.
WinISD is a great starting point. Obviously it can't account for cabin gain though, which may lend more pronounced peaks.

I've found it to be very accurate. BUT you must know its limitations. One of the biggest is that it can't model a car or room. Also the difference in distance from the user to the port and subs can cause phase issues that affect output. This is not modeled by winISD. I like to use it to see how much of a change I will see if I need to shrink a box to make it fit.Indeed.

brandon_s0854
02-20-2012, 04:48 PM
Indeed. Slightly smaller, and higher tuned actually makes for a "peak-ier" box.


According to WinISD, a smaller, higher-tuned box will increase output above tuning, increase the frequency of the enclosure's peak, and reduce output below tuning. All of the things that I was looking for. The box didn't seem to act that way in all aspects. It did increase the peak frequency, but didn't increase output above tuning from what I can tell. An SPL meter would be needed to verify. The box did lose output below tuning; just way more than expected.

Also, I've built smaller, higher tuned boxes that were less peaky than their larger, lower tuned counterparts for the same sub in the same vehicle; so that statement is obviously not correct.

ngsm13
02-20-2012, 05:00 PM
According to WinISD, a smaller, higher-tuned box will increase output above tuning, increase the frequency of the enclosure's peak, and reduce output below tuning. All of the things that I was looking for. The box didn't seem to act that way in all aspects. It did increase the peak frequency, but didn't increase output above tuning from what I can tell. An SPL meter would be needed to verify. The box did lose output below tuning; just way more than expected.

Also, I've built smaller, higher tuned boxes that were less peaky than their larger, lower tuned counterparts for the same sub in the same vehicle; so that statement is obviously not correct.
Correct. Which is EXACTLY what you described, and exactly the opposite of what your were looking for.

The new box seems to be slightly louder in the 40-60hz range, but has much less output below 40hz;
As for building small, high-tuned enclosures, application is the key. In my ten years of building and designing enclosures, a majority of the time I've experience what I described. :fyi:

Regardless, Duane's suggestion is on point, and a simple way to adjust incrementally. Adding a board internally to reduce port area is a good way to test for the response that YOU prefer the most. If you end up hacking up the box in the process of finding your sweet spot, at least you'll hopefully find it and then be able to create a box that is gives you the sound that your prefer. Good luck.

mlstrass
02-22-2012, 05:13 AM
x3 on reducing port area, but also do you have the ability to cut freqs around that area with an EQ?

Also you're in a diff vehicle, so response is different. Maybe your old box would have worked better in this vehicle...

brandon_s0854
02-22-2012, 08:52 AM
x3 on reducing port area, but also do you have the ability to cut freqs around that area with an EQ?

Also you're in a diff vehicle, so response is different. Maybe your old box would have worked better in this vehicle...

I was using the old box in the new vehicle. I was basing how the old box sounded in the new vehicle to make a new box. I just overshot the difference and was amazed how big of a difference the small changes made. After listening to it for a few days, I think the tuning needs to be dropped about 5hz. And unfortunately, I don't have an EQ of any kind.

duanebro
02-22-2012, 02:46 PM
I was using the old box in the new vehicle. I was basing how the old box sounded in the new vehicle to make a new box. I just overshot the difference and was amazed how big of a difference the small changes made. After listening to it for a few days, I think the tuning needs to be dropped about 5hz. And unfortunately, I don't have an EQ of any kind.

Sounds like you should be thinking about getting an eq. :)

duanebro
02-23-2012, 12:31 AM
I had some extra time tonight so I ran the numbers:
http://i1091.photobucket.com/albums/i386/duanebrow/Car%20Audio%20Designs/aqHDC310comparingboxes.jpg
The black line is the first box.
Red is the current box.
And green is my suggested design.
The specs used were provided by Audio Que. No break in and with alum. coils. In car response will be different from these of course, this is just to show the difference in the boxes. The subs do drop off very fast under tuning because they are a low Q design. So to get low these need to be tuned low. My suggested box is 2cf net tuned to 30hz. It will not be as loud, you are losing ~7db at 40hz. But the sound should be more even. Plus group delay and phase angle are affected by the lower tuning, this could make the system sound better. I say could because it might not have that much effect once installed.

I would try to use the current box as a test box to see what you like before building anything new.

FWIW using the peak as a reference, the current box is 12db down in the current box. :eek: