quest for sub equalization...

OK....so this evening I got TrueRTA working...purchased the level 4 version to take measurements at 1/24th octave slices. After watching a movie, I decide to to set it up and take a measurement.....so here is the graph.
http://www.thechangs.us/first.JPG

If you can't read it, it starts at 60dB and 10Hz. It has been a very windy night, so I am not sure how that effected the measurement.

As you can see, it looks like I have a nasty dip at about 38Hz, and another at just about double that frequency.....how am I going to deal with those?? :confused:

I will mess around with it some more tomorrow afternoon.

".how am I going to deal with those?? :confused: "


Call Dr. Hsu. He'll have the correct answer as I'll have just AN answer.

David

Curtis,

I'm guessing those are room modes. Have you put your room dimensions into a mode calculator to see if it comes up with those frequencies?

Do you have a graph that shows the response higher up (maybe to 160Hz)?

Have you done the sweep with the phase reversed?

Talking to Dr. Hsu is a good idea. With room modes, your options are generally changing seating position (often not an option), room treatments or EQ. Since this is a severe dip, EQ might not be a good idea.

Yeah, it looks like you're about 15dB down at 38Hz. If you have a proper WAF battleplan, I would try 2 or 3 different room positions with measurements after each. You're battling the room's black hole it appears.

You might want to try messing with phase to see if you can better integrate the sub with your mains seeing that 75Hz kerplunker. It looks like you have another one at 90Hz too (which I have too). Does the VTF3 have a 0/180 toggle or infinitely variable dial?

Show us a graph out to 120Hz if you can. That will show how smooth the sub blends with your mains, very important for smooth transitions.

Working around that 15dB canyon at 38Hz is gonna be tough though.

Thanks guys!

I have no WAF issues, but unfortunately, I only have two places where I can put the sub.

The sub only has a phase switch.

I will do more graphs and try the other sub position when I have more time this weekend.

edit: I just looked around the room. With some small changes, I can possibly come up with two more locations.

OK.....did some more graphs:
http://www.thechangs.us/location1.JPG
These were done with the test CD that came with my VTF-3, a 200Hz to 10Hz sweep. Sub in 0 degree phase is in green, 180 degree in yellow. This is in the front left corner of my room. The sub is in maximum extension tune.

I still have that canyon at about 38hz....pretty happy with the response below 20hz, but I would trade that to get rid of the canyon.

The next graphs will be in a different location.

Second location:
http://www.thechangs.us/location2.JPG
orange - 0 degree phase
turquoise - 180 degree phase

Third location:
http://www.thechangs.us/location3.JPG
green - 0 degree phase
purple - 180 degree phase

Locations 2 and 3 are just about 7" apart....one being closer to the wall than the other.

Curtis,
Are these reading all near a corner? I had to move mine away from the corner to get a linear reading.

David

Well, at least you know which phase is best for integrating with your mains at the first position (0).

David, getting out of a corner does not mean you will get flatter response. Moving my sub one or two feet into the room along the wall got me a worse response curve. I could try a completely different position in the room, but I haven't taken the time yet.

David,

Yes, all of these measurements are near a corner.....in fact, they are all withing three feet of each other. I have two more locations to try, but it requires rearranging some furniture. For reference, my room is 14x18, with a sloping ceiling that goes from 8' to 9'.

Interesting, I was messing around with the BFD lastnight to learn about it, and came up with this:
http://www.thechangs.us/interesting.JPG
I also learned that taking measurements at different listening levels has a somewhat dramatic effect on FR.

Probably won't have much time to do much measuring today.

That looks like a great response there. I would be a bit worried about pushing the amp to hard if you added a 15db boost to defeat that dip.

Yeah....I know boost is usually a no no. I am going to send an email to Hsu about it. I was thinking that since I have a lot of headroom with the sub and my room, that it might be OK.

It sounds great at the listenning position...but really hot here at my computer in the next room through a doorway. I hear no distorting even at the highest of my listening levels.

I need to get myself an EQ to play with. :)

I'd be real careful about boosting that much, especially at relatively low frequencies. +15dB is a huge bump.

Quote:

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Originally Posted by Nicholas Mosher

I'd be real careful about boosting that much, especially at relatively low frequencies. +15dB is a huge bump.

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Totally understood....but had the sub volume extremely low, so I am thinking I have/had plenty of headroom. I'm not expecting this to be permanent....I still have other things to try. It was more of a BFD excersize.

Got to say, I am pretty pleased with the sound and extension, and still have that Hsu tonality. All the bass is there....but out of the way. Never realized I was getting useable extension below 15hz.

"David, getting out of a corner does not mean you will get flatter response. Moving my sub one or two feet into the room along the wall got me a worse response curve."

Didn't mean to imply that it would always work that way. Just relating my experience.

David

My second position is about 3' from the corner, and 2' from the side wall.

Those HK whitepapers that describe ideal subwoofer placements are very impractical because they assume perfect conditions in a sealed perfectly square room. I definetly noticed less boom moving my sub from corners to "non-corner" positions though.

I can't believe your low-frequency extension is down only 5dB under-average at 10Hz though! Thats incredible with a 20Hz tune. With a 16Hz tune my SVS is down almost 15dB under-average at 10dB, and thats with 3 open ports. I'm curious as to what other VTF3 owners have seen for in-room response in the 10-20Hz range. What kind of peak SPLs are you getting in that max-extension mode Curtis?

I have never check for peaks. Give me a choice of material to test with and I will do some more measuring. I will also do some manual frequency measurements with my SPL meter. But below 20hz, it is pretty much all room gain. You can see by placing my sub in the second location, I lose everything below 50hz.

I can say, that as loud that I have played some movies, I have never bottomed the sub. This sub has more than I will ever need, in this room. Hsu has always stressed accuracy and sound quality, only the last couple of years has output become more popular because it is a spec you can see and most people relate to it easier. IMO, nobody in their right mind will be playing reference levels at home. For me, I would rather have a car that handles well than go fast if given the choice.

The VTF-3 has been measured flat to 18hz, and Hsu conservative specs 20hz +- 1dB....and 18hz +-2dB in max extension mode....max output gives you about 2dB in the upper bass area, while losing out below 22hz. I would give up anything under that to get rid of that canyon I have at about 38hz. Stuff below 16hz-18hz is just gravy to me.

I think I got that extra output down low by moving the sub just a couple of inches.

In the next couple of days I will try other locations and measurement...tonight I am going to just enjoy.

Ok, indulge me with these experiments please Curtis... :D
(when you get time of course).

Max Extension Mode.
Turn your sub's volume up to 70dB using your pre/pro and an SPL meter.

What SPL's do you get for...
10, 15, and 20Hz?

If you have "The Incredibles", test this please.
(max extension, sub matched with mains)
Time 0:37:45 to 0:38:30
With an average SPL of 75-80dB and peaks in the 100-105dB range (using the RS meter in "fast" mode) what type of output do you get? Is the bass distorted, or does the sub bottom out at all? This is my weekend volume level which is about as loud as my favorite theater. The SVS bottomed in 12Hz mode at these SPLs.

SPL level is definetly an important number, just as frequency range, and a flat response are. If you can't go over 90dB without compression or the sub starts to distort at 25Hz, the accuracy of the sub is going to be poop unless you listen at 60dB and don't care about extension.. Now that I've experienced the difference a BFD can make, I think the biggest problem with speakers/subs not being "accurate" are huge swings in the FR. I'm not looking for 115-120dB reference peaks, just 100-105dB hits.

I'm definetly curious about what results you get! :confused: :) :confused:

Quote:

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Originally Posted by Nicholas Mosher

Turn your sub's volume up to 70dB using your pre/pro and an SPL meter.


SPL level is definetly an important number, just as frequency range, and a flat response are.

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What frequency at 70dB?

That is fair, but I disagree a bit...do you care how loud your speakers can play? Is it as important as FR and a flat curve? Those three numbers do not tell you how the sub will sound. Just like I can give you two speakers with the same specs and FR measurements, they will sound different.

For music, I don't think SPL is as important, for HT, it depends on your individual listening levels. Those 106dB peaks I just experience, I can't imagine someone listening to that movie louder than that and thinking it was safe.

OK...I just watched that time sequence on the Incredibles. First, that is around 10dBs louder than I would play it......wow, what an experience!

Anyways, during that sequence, with the meter set to fast and the 100dB scale, it pegged 106 two or three times. No adverse affects and no bottoming at all.

I will try the indvidual frequencies tomorrow.

That canyon I had at about 40hz....one of the Hsu guys told me that the best way to get rid of it is with a second sub and or room treatments. :) Other than that, he says the in-room response is not bad and that I might not benefit from a BFD much. And that dip around 95hz is a Radio Shack SPL meter issue....so how did I get rid of it I wonder?

More measuring this week to make sure I am doing it right. It has become more important to me now to make sure the measurements truly explain my room. It is a great learning experience in process.

I disagree that the 95Hz dip is a problem with your meter. It doesn't show on your third location sweep, and it isn't a general problem with the meters since mine didn't demonstrate that even when compared to my other measurement setup.

Yeah, 105dB peaks are my upper-limit. I usually peak between 100dB and 105dB on weekends.

Glad to hear you didn't bottom out or get any port chuffing in "Max Extension" with only one port free. I'm curious now what you get for SPLs with the Infrasonics. Just calibrate to 70dB with pink noise, then run some infrasonic tones from 10Hz to 20Hz.

What I meant by SPL importance is that if the sub can't fill-out your room with clean bass at SPLs you want, then no matter how accurate it is it will always be lacking. There is an interesting thread at AVS regarding transient response/accuracy in the sub section. Hopefully it flourishes into good reading, as I'm interested in learning more about this topic (TR).

With the test tones I have, they do have a pink noise level setting track.

70db is what they recommend. All freq's are referenced from that setting.

Gotta find enough free time, when wife and kids are not home, to take readings using this new disc. Still have to insert the BFD into the chain so the wife does not notice it :D (Hmmm....maybe Curtis is on to something being wifeless!!)

I gotta say, though, even un-EQ'd, "I, Robot" sounds pretty darn good!

Nicholas,
Did you hear chuffing with the PB10 with stuff below 25hz? I agree with your re-wording of SPL importance.

Thanks for the heads-up on the transient response thread....that will be interesting. I do know that there is a measurement/test for drivers that tests impulse response...testing how quickly a driver responds to a signal.

This transient response I think is directly related to how articulate a sub is, which is one of the big differences I have heard when comparing subs.

For the FWIW file - the gain on the VTF-3 is at about 25%, a quarter turn, and the sub level on my pre-pro is at -1.

I would love to see cumulative spectral decay for the various popular subs as Dave F. lists for his speakers.

In fact, I'd love to hear Dave F. give his opinion on spectral decay/transient response and speaker accuracy when it comes to subwoofers. In fact, in fact (double), I'd like to see AA release it's own subwoofer. :D

[/QUOTE[ In fact, in fact (double), I'd like to see AA release it's own subwoofer. :D[/QUOTE]

How about a matching powered sub/pedastal stand for the 170's?!! ;)

Quote:

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Originally Posted by Nicholas Mosher

I would love to see cumulative spectral decay for the various popular subs as Dave F. lists for his speakers.

In fact, I'd love to hear Dave F. give his opinion on spectral decay/transient response and speaker accuracy when it comes to subwoofers. In fact, in fact (double), I'd like to see AA release it's own subwoofer. :D

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I would too!

When I first got my Ascends, I asked about Ascend making their own subwoofer. The answer was something like "With as good as the Hsus are, and since we are able to sell them, there is no need to."

Quote:

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Originally Posted by Mag_Neato

How about a matching powered sub/pedastal stand for the 170's?!! ;)

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I'm not sure I would. Usually, the best place for a sub is not where the speakers are located. If I wanted a floorstander...then I would get a real floorstander.

That said, a floorstander from Ascend would be interesting.

Quote:

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Originally Posted by curtis

I'm not sure I would. Usually, the best place for a sub is not where the speakers are located. If I wanted a floorstander...then I would get a real floorstander.

That said, a floorstander from Ascend would be interesting.

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Hmmmm.......ya don't suppose.............!! :eek:

I got about the same answer from Dave regarding an Ascend sub. Something along the lines of while he's designed subs in the past with the SQ for the dollar of Hsu there isn't any real reason for him to do a sub.

Quote:

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Originally Posted by Nicholas Mosher

I would love to see cumulative spectral decay for the various popular subs as Dave F. lists for his speakers.

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I own the HW and SW to do this, but I know nothing about how to properly make this measurement. Maybe once I learn more about measurement, I can check out the decay and other aspects of subwoofer response.

OK Brad....we should put a deadline on your learning. :)

No measurements from me tonight...I played tennis for a couple of hours and I'm pooped.

So Curtis.....

Why'd Hsu say that the BFD may not help you? It should, at the very least, help flatten out any peaks. Nulls are a different story, but you may not even notice the one you have.

I'll have a little time tomorrow to take some quick sound levels with the latest test disc(1Hz increments) and get better resolution.

Because I really do not have any nasty peaks.

Yeah, with the exception of that canyon, your response is pretty decent.

Did you use a mode calculator to see if that frequency matches a room mode and which one it matches? That might be helpful in investigating room treatment options.

Quote:

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Originally Posted by Curtis

a floorstander from Ascend would be interesting

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That's an understatement! If Ascend came out with a speaker whose frequency response extended down to 35Hz or so, I think I'd take a pair without waiting for reviews and without asking about the price. Hope you're reading this, dave f.

Dave

Quote:

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Originally Posted by BradJudy

Yeah, with the exception of that canyon, your response is pretty decent.

Did you use a mode calculator to see if that frequency matches a room mode and which one it matches? That might be helpful in investigating room treatment options.

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Nope...have not done the mode calulator yet...I will. I have to finish my taxes!