First diy didn't go so well - AVS Forum
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post #1 of 15 Old 06-01-2012, 09:03 AM - Thread Starter
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Looking for a little advice here, we got to were we are now with the help of this forum, thank ladies and gents.

We built a 2ft x 2ft x 2ft cube, with dual 4" diameter ports, 30" long. The ports have an elbow to make up the length. The internal volume is around 6.2 cubic ft after taking into account bracing, ports and subwoofer displacement.

Bash 300
dayton 15" HF

According to winisd, it should be tuned to around 20hz, and doesn't reach xmax until like 320 watts. We did a smaller box with long ports to avoid distortion, due to the smaller internal volume (even though this subwoofer would like a little more space). We weren't looking for high spl, just distortion free sound.

But distortion comes pretty easily. We watched a bluray at about -15 on the receiver, and whenever a bassy part happens, you can hear some distortion.

So I'm guessing we must have some leaks. The leaks can't be on the seams of the box, because we sealed the hell out of it. But could leaks on the ports cause this? Also, we used pvc pipe for the ports, and bent our own flares. One of the flares is a little uneven, and bowed in a little. I figured this may affect port noise and tuning, but not cause distortion? We can't even get it to play loud enough to cause any port noise.

Thanks for the help! If it is determined that its a leak, we will probably skip the hassle of a ported box and just go sealed.
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post #2 of 15 Old 06-01-2012, 10:05 AM - Thread Starter
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I just ran some test tones down to 16hz and didn't get distortion, and I could here a little port noise. Maybe the bass is spiking in the movie to levels that my "crooked" build can't handle?
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post #3 of 15 Old 06-01-2012, 10:22 AM
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Look at the level of the sub output and the gain (volume) setting of the amp. You may be overdriving (clipping) something.

Is the driver showing high excursion when you hear the distortion?

Also try another movie or music source.
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post #4 of 15 Old 06-01-2012, 11:03 AM
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Can you provide details about the movies/scenes that cause the distortion?

bg
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post #5 of 15 Old 06-01-2012, 11:14 AM - Thread Starter
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It was watchman, I can't remember which scenes, but it happened a few times so I rewind them and played them again to make sure I wasn't hearing things. There was high excursion, but not any higher than when I ran test tones through it (by eye). I have a watt thing, so when I'm done running around I'll see it its hitting 300watts and pushing the amp too far. I didn't hear any "clipping" though, just a little distortion.
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post #6 of 15 Old 06-01-2012, 11:24 AM - Thread Starter
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Ok I decided to stop in the living room to try another movie. I tried the scene in suckerpunch where she is fighting the big "rock monster" things. She cuts the ones throat and he falls over. I have a digital watt meter so I can't see the spike properly, but it only went up to about 140 watts at that point and I could hear what I think is some minor distortion. With this scene I can't tell if it's distortion or port noise though, I'll try another. Any one have any suggestions for movie scenes? I have quite a few blurays and dvds so chances are I may have it
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post #7 of 15 Old 06-01-2012, 11:48 AM
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It still seems possible that you're clipping the amp input. What is the subwoofer level in your AVR set at? As a test turn that down and the amp gain up (to compensate) and see if you still get the sound. Also (probably a dumb question but I'm not familiar with the amp) what kind of HPF does that amp have built in?
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post #8 of 15 Old 06-01-2012, 11:49 AM
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Not sure if you have heard clipping before, but in my experience it can sound like "distortion" so it seems like it could be a possibility.

Did you alter the high pass on the Bash at all? Are you using audyssey?
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post #9 of 15 Old 06-01-2012, 12:26 PM - Thread Starter
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Ok I tried messing with the settings on the receiver and the amp a little and played the same parts over and over. The highpass built into the bash is at 17hz or 17.7hz, I can't remember. Close enough though.

I have found so far that I get less distortion if I turn the amp down to halfway, and turn the subwoofer on the receiver a little more than half way. I always thought you were supposed to crank the amp up and use the remote to adjust the subwoofer. I'll keep messing with it.

I probably should have got the bash500, but the price was a little too steep.

After running an 18hz test tone at +10 on the receiver, the meter reads at 295 watts. If you go any higher, it stays at 295 and there isn't any distortion, so the amp is "throttling" the signal to avoid clipping it seems. Since the test tone is long and predictable, it has no problem with this. During a movie, it must be spiking above 295 watts and causing the distortion, you guys were right. I'm almost positive that's the problem now.

So I'm glad it wasn't my lack of wood working skills, it's the amp after all. Things wouldn't feel right if there wasn't always something to upgrade I guess...
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post #10 of 15 Old 06-01-2012, 02:36 PM
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The gain on the amp is not a volume control. Having it cranked was definitely your problem. It should set according to the output voltage of the receiver. I honestly never run mine more than 12 o'clock, usually around 9 or 10. If its not loud enough you'll need more power or more woofer.

Dan
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post #11 of 15 Old 06-01-2012, 09:14 PM - Thread Starter
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Quote:
Originally Posted by saabracer23 View Post

The gain on the amp is not a volume control. Having it cranked was definitely your problem. It should set according to the output voltage of the receiver. I honestly never run mine more than 12 o'clock, usually around 9 or 10. If its not loud enough you'll need more power or more woofer.

Dan

Completely agree. From messing around before I saw your comment, I discovered that 11 o'clock on the amp is the sweet spot. I know this driver can take more, but I wasn't looking for high spl, just good low clean bass for movies. With it set a 11 o'clock on the amp, and 3/4 on the receiver it sounds great. Part of the problem was placement. I ended up corner loading it, because we barely had any volume before clipping. It's a weird room, with the huge sliding doors and an open doorway, so I underestimated the power needed to fill the room.

So although it looks a little awkward where it is, it's no big deal. My new problem is keeping the windows from vibrating, because it's really annoying. We are getting strong 18hz bass without distortion, with port noise only audible if you stand next to the speaker.

So with it corner loaded, it ended up exceeding our expectations. A combination of placement, and the amp maxing out. With it corner loaded, we have it at half the volume, and more output, no more distortion like sounds thanks guys.
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post #12 of 15 Old 06-02-2012, 03:55 AM
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i'm not sure you actually have 6.2 cubic foot box...i just did a quick calculation in my head...figuring 22x22x22 as the internal....and did not subtract port, brace, or driver, you are at 6cuft.

My guess is you are not tuned correctly to the size of the box, and then your levels are off.

How did you set your levels?

Tim
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post #13 of 15 Old 06-02-2012, 07:48 AM - Thread Starter
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I used 3/4" mdf, so it would be 22.5 x 22.5 x 22.5 = 6.59, then I subtracted for ports, bracing, and driver displacement and came up with a little over 6 cubic feet. I can't find my plans so I can't recall the exact internal volume.

Also, I don't have any sound equipment to test it out, but I think it's tuned at about 18hz. 20 and 22hz give out a good amount of excursion, and at 18hz there is a lot of output, and little excursion. Then below 18hz, the excursion picks back up.
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post #14 of 15 Old 06-02-2012, 09:58 AM
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that's the arse thing about plate amps...no clip light!

glad you got it sorted out.

btw, winisd has you at ~18hz tuning, which is consistent with your driver excursion test.

Listen. It's All Good.
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post #15 of 15 Old 06-03-2012, 07:45 PM - Thread Starter
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I want to thank everyone again, like I said this project would have never existed without the help of this forum and winisd. We came from a polk psw10, so we have never really heard any actual output below like 40hz. What a difference! We're getting pretty strong output at 16hz, and enough at 10hz (without bottoming out) to make the doors, windows, and the floor shake. We're very impressed, this is an excellent driver for the $170 price tag. When we decide on a house were going to build maybe 4 dayton brand subs with an ep4000 for the basemet, can't wait to start building again

I'll have to post some pics when I get a chance.
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