Can signal shaping affect the sweet spot? - AVS Forum
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post #1 of 16 Old 05-08-2012, 04:38 PM - Thread Starter
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I just completed a sealed AV15 build and was disappointed to say the least in the performance I was getting. It fell off the cliff under 30 Hz. Enter the minidsp and things are much, much better after applying the LT. I let Audyssey XT do its thing and according to the measurements, it's much flatter. However, it seems like I'm missing some output down low. I can see the woofer moving a lot, but sometimes I'm not getting the expected feel. This is my first sealed HT sub and I don't know if it's a function of me having to get used to the sound, or can the rooms sweet spot change once you change the subs fr?
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post #2 of 16 Old 05-08-2012, 04:58 PM
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If you placed the mic in the "sweet spot" (listening position), then it should have optimized for that location. You may find that you prefer to run the sub a few dB hot from where Audyssey sets it though, I bump mine about 3-4 dB.
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post #3 of 16 Old 05-09-2012, 11:16 AM
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Quote:
Originally Posted by wth718 View Post

I just completed a sealed AV15 build and was disappointed to say the least in the performance I was getting. It fell off the cliff under 30 Hz. Enter the minidsp and things are much, much better after applying the LT. I let Audyssey XT do its thing and according to the measurements, it's much flatter. However, it seems like I'm missing some output down low. I can see the woofer moving a lot, but sometimes I'm not getting the expected feel. This is my first sealed HT sub and I don't know if it's a function of me having to get used to the sound, or can the rooms sweet spot change once you change the subs fr?

It's a single 15" driver with about 2litres of Vd, not a great deal of output. LT also applies a shelving filter than unless you specifically roll it off to limit excursion at subsonic, it will eat up Xmax. Single sub, depending upon where it's placed may have issues with nulls. You'd need to provide measurements so others can comment more.
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post #4 of 16 Old 05-09-2012, 04:17 PM - Thread Starter
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Yeah, that be the issue. With the last minidsp settings I applied, Audyssey had it flat to 10 Hz and even though the bass was lacking that sucka was moving! But when I turned Audyssey off, it didn't measure as well, but the bass was much, much better. I think I'll a final fc of 20hz and then apply a high pass at 15-17 and see what that does. Will post measurements later....
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post #5 of 16 Old 05-09-2012, 06:04 PM
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"when I turned Audyssey off, it didn't measure as well, but the bass was much, much better."

you mean that it didn't measure as well according to audyssey. whatever correlates best with your ears is what "measures best".

Listen. It's All Good.
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post #6 of 16 Old 05-09-2012, 06:14 PM - Thread Starter
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No, I mean with rew. It showed flat to 10, albeit at only 75 db. Just didn't sound right with actual content. Quick question: when using the coefficient spreadsheet, what am I supposed to be entering for the corner frequency? Where it starts to drop off, or where I want it to start dropping off? Or am I completely out in left field?
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post #7 of 16 Old 05-09-2012, 06:29 PM
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"when using the coefficient spreadsheet, what am I supposed to be entering for the corner frequency?"

not sure what spreadsheet that you are referencing.

Listen. It's All Good.
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post #8 of 16 Old 05-09-2012, 07:03 PM - Thread Starter
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I'm sorry, the one to calculate biquads. Available from minidsp's website and other places as well, I'm sure.
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post #9 of 16 Old 05-10-2012, 04:56 AM
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We can start with a close mic sweep of your sub, just to see where you are starting. no EQ no Audyssey, just a straight sweep. Here's a close mic of one 15 in my quad array... Talk about a sealed rolloff... Almost a perfect 12db/oct rolloff. From the peak at or around 35hz down to 17hz...



Post some graphs and we'll see whats up with your sub...Be careful with the LT type filters, you will be eatting up stroke and power as mentioned. I'm curious what cabin gain you will get from different locations. Dont give up though, its a journey :0)
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post #10 of 16 Old 05-10-2012, 06:27 AM - Thread Starter
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I think I may have dialed it in using a 48db high pass and by adjusting the lt. I've gotten it to a point where it actually measures better with aud off than with it on.

One issue I came across is that of the only 2 places in the room available to place the sub, one had a huge null at 40, and the other has much smaller nulls at 28 and 25. Another wrinkle is that the av was reconed by AE prior to me acquiring it, and they used a different cone. It probably affected the t/s parameters because the rolloff started a lot higher that it showed in winisd.

I still have to test it for any distress at listening volumes because I finished real late last night. Will post both close mic and eq'd responses when I get home.
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post #11 of 16 Old 05-10-2012, 08:33 AM
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Quote:
Originally Posted by wth718 View Post

I think I may have dialed it in using a 48db high pass and by adjusting the lt. I've gotten it to a point where it actually measures better with aud off than with it on.

One issue I came across is that of the only 2 places in the room available to place the sub, one had a huge null at 40, and the other has much smaller nulls at 28 and 25. Another wrinkle is that the av was reconed by AE prior to me acquiring it, and they used a different cone. It probably affected the t/s parameters because the rolloff started a lot higher that it showed in winisd.

I still have to test it for any distress at listening volumes because I finished real late last night. Will post both close mic and eq'd responses when I get home.

Subscribed if i didnt already.......
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post #12 of 16 Old 05-10-2012, 07:57 PM - Thread Starter
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I think I've pushed the envelope as much as I can. I played the heavy hitters at volumes I normally don't and there was little audible distortion.

My other subs are a SVS PB-10 that I got off CL for $100 and a Velodyne DPS-12. The SVS gave me pretty flat response down to ~17Hz, but couldn't touch the output of this project, even when paired with the Velo.

I'm still confounded by weird in-room response with the nulls at 25 and 19 Hz (I misremembered in my previous post), but it's the lesser of 2 evils. I don't know if it's the nulls that contribute to the shelf at 30 Hz, but even though it's lower there, I have good output down to about 15. I figure I need a second sub to iron out the null, but I've let my brother use the SVS and I can't get the Velo to play nice.

Anyway, here are some graphs. Close mic, EQ'd FR with and without Audyssey, an overlay of all 3, and another overlay with 1/6 smoothing, and the spectrogram for good measure.
LL
LL
LL
LL
LL
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post #13 of 16 Old 05-11-2012, 07:07 AM
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The no Audyssey pink line is nice. I would like to see your response get at least to 20hz..... Have you toyed with a plain shelf filter and a Hipass to get you to 20hz, but not below......

I do understand doing so would eat up stroke and amp... Damn compromise.....
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post #14 of 16 Old 05-11-2012, 07:21 AM - Thread Starter
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Quote:
Originally Posted by kgveteran View Post

The no Audyssey pink line is nice. I would like to see your response get at least to 20hz..... Have you toyed with a plain shelf filter and a Hipass to get you to 20hz, but not below......

I do understand doing so would eat up stroke and amp... Damn compromise.....

Frankly, I'm not sure how. No matter what I try it doesn't seem to change the basic shape of the signal below 30. I can get lower or higher output, but that drop at 30 always remains. Would a shelf help with that? Even if those nulls remain, could it get the portion between the 25 and 19 to increase? Guess trial and error might be the best option.

If all else fails I can leave it as is. Even though it's not flat, I certainly do hear the sub 20 content much stronger than I did with my old setup.
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post #15 of 16 Old 05-11-2012, 09:04 AM
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I'm thinking placement will dictate low frequency response, are you limited in placement ?

If so, leave it and enjoy :0)
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post #16 of 16 Old 05-11-2012, 07:48 PM - Thread Starter
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Yeah, it's definitely the room. When I moved the mic out into space, far away from where the LP could be, it was strong and flat down to 15 or so in my room before rolling off.
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