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post #1 of 12 Old 02-06-2016, 04:11 PM - Thread Starter
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Value of subwoofer crawl

I'm preparing to add a home theater system in my basement, and have been reading MANY threads here and learning a ton!
I received a free HTiB from a friend, so I hooked it up and can now play around before I install my real system.

I'm a noobie, so I'm still trying to grasp some of the impacts my specific room will have on the output of my subwoofer. One of the things I've read many places is the value of the subwoofer crawl, as it will point to where a sub should (and shouldn't) be placed.

I've also read many subwoofer threads where a poster will state "I just upgraded my sub and I'm disappointed it doesn't sound any different. I put it in the same spot as my previous/inferior sub... Then I moved it's location....wow, what a difference!".

In my basement I have 2-3 spots where a large 15" (HSU, Rythmik, etc.) sub can go. If those locations are a null, then I would need to go to a small form factor (ie - Sunfire, Supercube, etc.) due to WAF.

Question: Does a subwoofer crawl tell you where that specific sub works best/worst, or does it tell you where your room has the best/worst sub location?

I would like to use my HTiB sub to determine my location(s) so I can purchase the right size sub for my HT (really hoping the 15" will work! ). Will a subwoofer crawl help me determine which locations will work for any sub?

Thanks for the input!
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post #2 of 12 Old 02-06-2016, 04:44 PM
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Based on your title, the Subwoofer Crawl has great value if used correctly.

Having a free cheap sub to play around with and learn from is a fantastic thing. You can experiment with output, distortion, SQ, and lots more. They aren't typically heavy, so moving them around is fairly simple. It's also good to know that if anything "accidentally" happens, you're not out any money. I've ripped apart a few old drivers out of very old speakers just for some fun

Your question: Subwoofers will act differently in every room, even if the subwoofer is the same. The subwoofer isn't the one acting though. It's the room and something called room "modes". These are peaks and nulls based on waves that your subwoofer is reproducing either bouncing off walls to create peaks, or canceling each other out called nulls. The "wub" is the subwoofer producing a wave based on the frequency it was sent. Each frequency has a wave length. The lower the frequency, the larger the wave length. This is all said in a huge nutshell, but hopefully you are starting to get the concept.

The idea behind the Subwoofer Crawl is to find a good balance of peaks and nulls. With a single subwoofer, nulls are inevitable due to wave theory, physics, and simply - room modes. That is mostly why people serious enough about their bass end up getting a 2nd matching sub, and some people keep on adding more and more . The reason behind getting a 2nd subwoofer (or more) isn't always to "have more bass", but to rather help eliminate nulls which is why you might hear people talk about a smooth (or flat) frequency response. Yes, adding another subwoofer to the mix adds some output.

So to some extent, yes the room really tells you where it wants the subwoofer to be placed. Experimenting with the HTiB sub, and your room is a good thing. But re-doing the Subwoofer Crawl when you finally step into the category of these bigger subwoofers is something that should be done just to double check everything. Its kind of like re-watching a movie you have already seen before and finding new things you missed the first run around.
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post #3 of 12 Old 02-06-2016, 06:40 PM - Thread Starter
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Thanks for the quick reply, and the explanation.

It makes sense that bass wave lengths would act the same (regardless of which sub produces the sound). It must be that the other posts had other "noise" (ie - sub setup, AVR setup, RC, etc.) that caused them to think the better sub was producing a worse experience.

Thanks again!
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post #4 of 12 Old 02-08-2016, 04:59 AM
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Wear knee pads if you have a big room, lol.
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post #5 of 12 Old 02-08-2016, 11:27 AM - Thread Starter
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I plan to throw my sub on my couch; then find a looping low hertz music file, and then run crawl around the perimeter of my room with my iPhone app and measure dB's.

Is there anything wrong this approach?

Are there any suggestions (does it matter) what I play?

Is there a minimum dB "delta" needed to differentiate a "null" from a "peak"?
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post #6 of 12 Old 02-08-2016, 11:46 AM
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Quote:
Originally Posted by Kamper View Post
I plan to throw my sub on my couch; then find a looping low hertz music file, and then run crawl around the perimeter of my room with my iPhone app and measure dB's.

Is there anything wrong this approach?

Are there any suggestions (does it matter) what I play?

Is there a minimum dB "delta" needed to differentiate a "null" from a "peak"?
You're not looking for the "loudest" spot. You're looking for the spot that has the smoothest response. All notes should sound correct in volume and there should be no notes that are over-accentuated and no notes missing. If you find a spot that sounds like that, put your sub there.

Better yet, download REW:
http://www.roomeqwizard.com/
Then get yourself a relatively inexpensive mic:
http://www.amazon.com/s/?ie=UTF8&key...l_603hmj1nh8_b

Then you'll be able to "see" when you've found the best spot.

Craig
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post #7 of 12 Old 02-08-2016, 04:58 PM
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The HTiB sub is probably not the best thing to use for selecting an eventual position for the new sub. First, it is probably very limited in it's bass extension, more than likely running out of steam at about 50-60 Hz. This will tell you next to nothing about a sub that has good output to 20, or even 16 Hz. Second, it may not be the most accurate at reproducing a flat frequency response in the "bass" frequencies it does reproduce. You could easily "tune" using a very uneven response (makers of cheap subs like to build in a bump in the output to simulate real bass).

So, if you want to experiment with it, go ahead, it's good practice for the real thing. But, don't draw any permanent conclusions.

Last edited by RayGuy; 02-08-2016 at 05:02 PM.
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post #8 of 12 Old 02-08-2016, 08:53 PM
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I've never understood the logic of a sub crawl. You crawl around and find the corner by the TV the best position because you put the SW at your normal listening position in the middle of the room. Once you move that SW over to the corner the dynamics of the SW's position has now changed again because the SW is no longer sitting by your listening position. It's now in the corner which means the waves won't react the same as it did initially by your listening position. Logically the best position will have moved elsewhere and chances are it won't be your listening position.
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post #9 of 12 Old Yesterday, 09:17 AM - Thread Starter
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Thanks for the input... so let me summarize what I've read/learned.

- A subwoofer crawl is useful (when executed the right way) to help you hear the best and worst location(s) to put your sub
- You shouldn't listen for the loudest location, but the location with the smoothest response (REW can be a big help)
- An inferior sub can be used to learn the method, but shouldn't be used for locating a future sub. You need to use your intended sub for the subwoofer crawl

Based on the above, I'm going to purchase a large sub and 'hope' that it will work well in one of my two locations.

Question: Is there a recommended track that I should play during the crawl? (ie - same repetitive tone/freq vs a range of freq. vs music)

Thanks,
Kamp
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post #10 of 12 Old Yesterday, 09:58 AM
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Pink noise is usually recommended. You might also consider investing in a measurement mic and using software like REW.
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post #11 of 12 Old Yesterday, 03:04 PM
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Quote:
Originally Posted by Kamper View Post
Thanks for the input... so let me summarize what I've read/learned.

- A subwoofer crawl is useful (when executed the right way) to help you hear the best and worst location(s) to put your sub
- You shouldn't listen for the loudest location, but the location with the smoothest response (REW can be a big help)
- An inferior sub can be used to learn the method, but shouldn't be used for locating a future sub. You need to use your intended sub for the subwoofer crawl

Based on the above, I'm going to purchase a large sub and 'hope' that it will work well in one of my two locations.

Question: Is there a recommended track that I should play during the crawl? (ie - same repetitive tone/freq vs a range of freq. vs music)

Thanks,
Kamp
Test using static tones or tone sweeps as the source (these can be downloaded off the web - google), but, listening is the ultimate arbiter. If your testing and measurements tell you one thing and your ears tell you another, ears win every time.

I would add one additional item to your list ... listening position is just as important as speaker or sub position. They interact. Try to place your seating (ears) at 3rds, 5ths, 7ths, of the overall length of the room. This will assist in limiting the room modes you encounter. The exact center of a room is to be avoided at all costs!

Have you already chosen the sub? If not, what's your budget and what are your expectations?

Last edited by RayGuy; Yesterday at 03:15 PM.
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post #12 of 12 Old Today, 07:47 AM - Thread Starter
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Quote:
Originally Posted by RayGuy View Post
Have you already chosen the sub? If not, what's your budget and what are your expectations?
Hi Ray,
At work we call it scope creep, on the forums I thinks it's called upgradeitous!

(In my mind) I started with a $500 PB1000... then increased my budget to a PB2000, and am now thinking my best option is to start with a $1000 VTF-15H MK2. (I have a LARGE area, as my primary listening is 4800 cf, but am opened up to another adjoining 3300 cf kitchen/rec area).

I plan to start with one sub, but suspect I'll add another! . (remember my baseline is HTiB, so I'm expecting to be very happy with any upgrade).

A friend of mine from work has A LOT more experience in HT than I do (he's built his own refrigerator sized sub, capable down to 10Hz w/ significant SPL!) suggested I go to servo driven sub because it will perform better. The Rythmik (FV15HP) is an extra $200.

Question: Is it worth the extra $200 for servo driven, or should I save the money for the next sub that will be needed to fill my space?

My goal is to spend $1k now (+/- ~$200), and set myself up for an 'adder' if needed.
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