My Bass Story - AVS Forum
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post #1 of 13 Old 07-13-2004, 10:22 AM - Thread Starter
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By reading this forum as well as http://www.hometheaterforum.com/htfo...?s=&forumid=46 and www.recording.org and other's, I have increased my knowledge and understanding of subwoofer and in-room bass response theory.

Here is my story:

My HT is in my basement. Carpeting ontop of a cement slab. Thin wood paneling on top of cement cinderblocks. Large 50 x 22 x 7.5 ft basement, with a portion of it finished off as the HT room. In short, this room sucks for bass. The cement/cinder block walls/floor create the ideal environment for resonance peaks, room modes, and other undesirable bass effects. The carpeting and sectional sleeper sofa absorbs a bit of the high freq's and leave the boomy bass behind.

My Odessey Begins:
Yamaha YST-SW200 Subwoofer http://www.yamaha.com/yec/customer/manuals/14YST-S3.PDF
Bookshelf speakers good down to 45 hz.
Panasonic SA-XR45 Digital Amplifier with cross over freq set to 100hz.

The Yamaha subwoofer is not very impressive with its stats: dual 7" woofer's, yamaha active servo design with 100 w amp. Specs say it goes down to 20 hz but at -10db down. If I had to guess, I would say that the -3db down point is at about 28hz.

I used etf software to measure my room. You will see several of these plots in this thread. You cannot directly compare them since ETF tends to normalize the highest measured peak to 100 db. So look at the trends not the absolute y axis measurements. I have a RadioShack analog SPL meter which has a mic output that works with ETF software. ETF software also has a calibration file for the RadioShack meter.

http://www.etfacoustic.com/

The ETF calibration file for the Radio Shack SPL meter does not have values for the lower freqs. You need to look at these postings to adapt the ETF cal file for low frequency measurements:

http://www.hometheaterforum.com/htfo...tf+radio+shack

Figure attached is my starting point. Note that the plot is truely awful. Signficant peaks and nulls measured at my primary listening position. Almost no low end response measured at all. This sounds as bad as it looks:
LL
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post #2 of 13 Old 07-13-2004, 10:23 AM - Thread Starter
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The room response and the way my yamaha sub sounded in my room was awful. Boomy, single noted, etc.

I begain reading heavily about room modes and the like. I decided that I need room treatments.

I constructed wood panel traps. (Sentence is easy to say, but the panels took 6 months to research and construct.)

http://www.ethanwiner.com/basstrap.html
http://www.ethanwiner.com/BTPlans.gif

The panel traps are broad bass absorbers that can be installed thruout the room starting in the corners. I built six of these beasts. It is an interesting fact that by adding bass ABSORBERS you actually get MORE bass and more even at that. The absorbers help to tame the room modes and cancellations that occur.

Figure attached shows significant improvement in my bass response. Besides the plot, it sounded better too! Note that as I learned more about the ETF software I did change the x axis in this plot (10-100hz). Also several months transpired between the plots. So the location of the recording mic was not identical (but similar) in location. So keep that in mind if you are comparing the previous plot. The trend in response is what is important. It is improving!
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post #3 of 13 Old 07-13-2004, 10:23 AM - Thread Starter
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But I was still not satisfied. Given that I believed that I was getting all I could out of my yamaha sub, it was time to consider a replacement.

Lots of choices, lots of folks have reviewed and compared the regular subwoofer equipment suspects (SVS, HSU, rocket, outlaw, etc). I chose a HSU TN 1220. I have several room location constraints. The preferred front corner location required a sub with a very small foot print. The TN1220 is a 12" round cylinder that is 51" tall but takes up very little floor space. I already had a spare Parasound 2 channel power amp. So the TN 1220 (which is passive) seemed perfect.

http://www.hsustore.com/tn1220ho-bo.html

As you can see by the plot. Much improved lower end extension. But still the room modes and peaks are a problem.
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post #4 of 13 Old 07-13-2004, 10:24 AM - Thread Starter
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But I was still not satisfied. I had tried to tame the room with accoustic treatments. Now it is time to consider a parametric equalizer. The EQ can be used to reduce (or increase) the gain of specific frequencies in the line level LFE signal that is feeding your subwoofer amp.

I read all about the wonder BFD (Behringer Feedback Destroyer) at the links below. I purchased the BFD for $120 at partsexpress.com, a bargain for a full dual 12 channel Parametric EQ. (There are some caveats about using the BFD in the EQ mode. Specifically you have to worry about driving the inputs high and watching for clipping. links below have the details.)

http://www.snapbug.ws/bfd
http://www.snapbug.ws/brucekreviewofbfd.htm

Common recommendations is to reduce the peaks and NOT boost the gain on the nulls. EQ boosts use up the headroom of your amp and can cause damage to your woofer driver if it gets over extended. My EQ setup includes 3 filters to reduce the peaks and a "house curve" filter.

What is a "house curve"? The human ear does not "hear" the bass below 0-30 hz with the same response as the mid-upper bass. So with the EQ you can reduce the bass 30-100hz and therefore in comparison relatively boost the 20-30hz region. Although the slope of the attached plot does not measure flat, it SOUNDS flat (or relatively flat).

I could probably go on with the EQ with additional settings and filters and try and make the response completely flat. However, I have found that there is a fair amount of uncertainty in measuring bass response with the equipment I have. Also the measurement is completely dependent on exactly where you place the microphone that records the test sounds. (Mic locations that differ in inches and angle of the mic make a difference.) The plot attached sounds much better than where I started and has given me the bass response I was looking for in my HT.
LL
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post #5 of 13 Old 07-13-2004, 11:30 AM
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dm, that was a lot of good information.

I'm getting ready to set up my home theatre in our new house next week. I've just downloaded ETF, but my laptop doesn't have line in, so I'll have to use my desktop.

I think I might set up my old speaker and new speakers and compare.

Craig

My Media Room Construction thread. Work began 2/15/05, finished 7.1 install 6/2005. Sold house 7/2007.
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post #6 of 13 Old 07-13-2004, 11:39 AM
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Outstanding! Feel free to try different cross over settings, and maybe even move the sub around and post some more graphs. I'm sure there are plenty of us living vicariously through your experience.

Well, it's life, Jim, but not as we know it, not as we know it, not as we know it
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post #7 of 13 Old 07-13-2004, 11:46 AM - Thread Starter
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The panasonic XR45 is a great sounding receiver using that latest PWM digital amp technology. However its one shortcoming (besides crappy spring clips for speaker wire connections) is that it has very limited bass cross over freq support. You can choose 100, 150 or 200hz. The 100 hz cross over is really the only reasonable choice for anyone with front speakers of any quality.

I have found other areas of the room that sub placement might give me better results. However, most subs, even the TN1220 with its small foot print, are beasts to look at. So the front corner is where it stays hidden behind my rack of audio/video equipment.
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post #8 of 13 Old 07-13-2004, 12:04 PM
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Nice job. Well worth reading.

What I can afford, when I can afford it...
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post #9 of 13 Old 07-13-2004, 12:12 PM - Thread Starter
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Quote:
Originally posted by Toeside
dm, that was a lot of good information.

I'm getting ready to set up my home theatre in our new house next week. I've just downloaded ETF, but my laptop doesn't have line in, so I'll have to use my desktop.

I think I might set up my old speaker and new speakers and compare.

Craig
I have not really tried to use ETF and my Radio Shack SPL meter for full frequency plots. To do a good job with the upper frequencies you really need a better calibrated mic. The Radio Shack is ok for the bass freqs, since the room modes are usally pretty obvious to spot and measure roughly.
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post #10 of 13 Old 07-13-2004, 12:14 PM - Thread Starter
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Quote:
Originally posted by Andrikos
dm,
since the cylinder sub is pretty skinny and long, can you lay it on its side?
Is that not recommended by Hsu?
It seems to me that it would make it much easier to disappear in your room.
I have young children in the home. The cylinder sub on the floor would make a nice climbing/balance beam toy for them. No go here.

But you are correct, Dr. Hsu does recommend the sub on its side on the floor behind the sofa as an ideal location.
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post #11 of 13 Old 07-17-2004, 12:13 PM - Thread Starter
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I just replaced the 15 year old original monster speaker zip cord (12 or 14 Ga) I was using with the HSU, with cobaltcable.com ultimate speaker cable. It is 10Ga with nice spade lugs (vs the pins I was using). Not dramatic, but another jump up in tightness and quality of bass I think.
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post #12 of 13 Old 08-16-2004, 10:08 AM
 
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Thanks for all your effort in sharing this knowledge. Outstanding thread - definitely one for the Meta-FAQ. Just curious- have you checked the response graphs from other seats (especially the least optimal seats) in your HT? I would think that the next step (if you're even going to go any further) would be to try to find settings that yield the best overall response averaged out over the entire seating area.
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post #13 of 13 Old 08-16-2004, 11:16 AM - Thread Starter
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My current seating setup is not the most optimal. I have a sectional couch in the shape of an "V". The vertex of the "V" is my primary sweet spot seating areas. the 3 seats in the "v" are really close together and while I did not graph the bass response for all of them, they are close enough that they respond similarly. The rest of the seats are off to the left and right from the main speakers and are not well position for imaging anyway.
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