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Old 1st March 2013, 07:51 PM   #11
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Hey guys,

Thanks for all of the helpful replies. I took some time today to run some more tests.

First, I tested to see what the response was like without a box. I just removed the back of the box. Unfortunately, any semblance of bass was lost here. I've posted a spl chart. The dark green line is a test without the box while the light green line is a test with the properly vented box (acousta-stuff taped to the sides).

Then, I volume tested the box to the best of my abilities. 2 liters of water filled the back half of the box to the brim and .5 liters filled the small piece that is jutting out to the right of the speaker on the top half. There is additional space in the top half but this is difficult to measure. I'm guessing that it is approximately .5 liters, judging by the volume of the other parts. Thus, I can fairly safely assume that the box is 3 liters in volume.

Blocking the port doesn't seem to have much of an effect, but I know that the port is the wrong length. Although there is a bend in it, I've determined that the port is about 14 cm long! According to WinISD a vent of about 2.7cm in width should be 10.5 cm in a box approximately 3 liters in size. Should I cut the port back until it is 10.5 cm in length?

tuxedo, I know that this test environment isn't ideal. Neither is a car environment though so I would like to get the speaker performing the best it can before dropping it into my Z. I also can't feasibly take all of my test equipment to my car right now.

Click the image to open in full size.
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File Type: jpg vented box vs baffleresize.jpg (132.0 KB, 222 views)
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Last edited by techbiker; 1st March 2013 at 08:00 PM.
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Old 1st March 2013, 10:51 PM   #12
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Originally Posted by techbiker View Post

tuxedo, I know that this test environment isn't ideal. Neither is a car environment though so I would like to get the speaker performing the best it can before dropping it into my Z. I also can't feasibly take all of my test equipment to my car right now.
True a car isn't a great acoustic environment. Neither are many living rooms. But if you want to "get the speaker performing the best it can" before working with it, and you plan to use measurements to do that, then you need to understand what the measurements mean.

You need reflection free measurements in order to be able to understand any shortcomings the driver has.

First, move the mic and speaker out in the the room away from walls and furniture. Prop the speaker up on a stand, about 4 feet off the ground.

Second, place the tip of the microphone about 2 inches away from the center of the cone.

Third, Take a sweep.

Fourth, Apply 24db/oct smoother.

Don't look at any of the response above 500hz, it's not very useful with this type of measurement.

Fifth, back the mic up about 2 feet from the driver.

Take a sweep.

Raise the right window time to 4ms. In REW, there is a button above the graph called window. Click on it. Change the right window to 4ms. Keep the smoothing at 24db or no smoothing.

Don't look at any of the response below about 500hz, it's not very useful with this type of measurement.

Now you have a complete on axis measurement which can tell you a tiny bit about how this speaker will perform. If you'd like to know more about how it'll perform, you'll need to:

1. Take an impedance sweep;
2. Take a series of off axis measurements;
3. Measure the sensitivity;
4. T/S parameters;
5. Harmonic distortion;
6. CSD;
7. And a few other things can help to.
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Old 2nd March 2013, 12:39 AM   #13
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i think the problem is two fold. I reckon the plastic is resonating, the port is too long versus its surface area also, and that you are suffering both. Not to mention that cabin gain and the intended location arent included in the measures. Id think that the remainder of the door structure may contribute to the enclosure rigidity.
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Old 3rd March 2013, 03:19 AM   #14
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Tuxedo,

Thanks a bunch for the recommendations! I followed them and measured my speaker from 2" and from 2 feet, then encorporated the time delay in the 2 foot measurement. I might not have done it correctly because I am using the new beta version of REW, but these results look much more consistent. Unfortunately, I didn't get them lined up but yellow is the <500hz measurement and purple is the >500hz measurement.

Clearly, there is a roll-off at around 13khz and gently sloping bass up until around 130hz with a bit of a boost at 65hz (which could be the work of the vent).

Do you think I could cut another .5-1cm off the length of this vent to move the bass boost up a bit more? It still isn't too boomy (except at the peak of 150hz).

What is your verdict on this speaker and do you think I could do anything else to improve it? I'm thinking about adding some EQ at around 16khz until I can install a couple of tweeters.

Thanks!
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Old 4th March 2013, 03:32 PM   #15
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Much better, although the scales are really hard to read on the graph.

Things from 500hz and up look pretty decent imo, and I don't really see any problems. Sure, a little bit of roll off in the top octave. In a car way off axis this would likely be a large roll off. So eq will only help so much. But worth a shot.

I think the most telling thing is your nearfield, yellow line. Looks like a classic case of having an undersized vented enclosure. You could try moving up the tuning, but not sure how much that'll help. Any chance you could just run it sealed and cross your subs in a little high, like 120hz?
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Old 4th March 2013, 05:56 PM   #16
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Originally Posted by tuxedocivic View Post
Much better, although the scales are really hard to read on the graph.

Things from 500hz and up look pretty decent imo, and I don't really see any problems. Sure, a little bit of roll off in the top octave. In a car way off axis this would likely be a large roll off. So eq will only help so much. But worth a shot.

I think the most telling thing is your nearfield, yellow line. Looks like a classic case of having an undersized vented enclosure. You could try moving up the tuning, but not sure how much that'll help. Any chance you could just run it sealed and cross your subs in a little high, like 120hz?
Tuxedo,

I was initially frustrated after reading your reply. Then, I realized that sealed enclosures might have been the best way to go all along. Correct me if I am wrong, but these Tang-Bands are apparently quite flat from ~200hz-13,000. I realized that this is a prime opportunity to drill out the ports and replace them with tweeters.

Do you think the following will work well?

Vifa OX20SC00-04 3/4" Fabric Dome Tweeter 264-1002

I could experiment with a crossover at anywhere from 10khz to 13khz to the tweeters and they should be fairly well phase aligned already due to placement.

If I can get everything in the high-end taken care of, I can cross over to a sub in my trunk at around 120hz like you recommend, then phase delay it properly with a 2x8 minidsp. Each driver would be driven independently by a 50 watt chipamp channel (except for the subwoofer).

Do you think that this is a "sound" plan?

Thanks again for your help!

P.S. My apologies for the wonky scale.
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Last edited by techbiker; 4th March 2013 at 06:19 PM.
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