Author Topic: Bass acoustic issues  (Read 14336 times)

Offline jimbones

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Re: Bass acoustic issues
« Reply #15 on: December 10, 2014, 06:15:07 PM »
OK so the ceiling is 7'2" to the bottom of the joists and 6'10" to the ceiling tile.

I never used Omnimic to do room response so I tried several different measurements. see attached we can discuss once we take a look.

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Offline richidoo

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Re: Bass acoustic issues
« Reply #16 on: December 10, 2014, 07:39:07 PM »
Disregard my last post, I deleted it.

I was reading the graphs you posted as FR graphs, but they are actually decay graphs. Can you post the frequency responses from those two sweeps near sub and listening chair?  Thanks

Offline richidoo

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Re: Bass acoustic issues
« Reply #17 on: December 10, 2014, 08:02:31 PM »
Looking at the 3rd plot you have there labeled Spectrum, that is kinda like RTA frequency response.

It shows a bump at 25Hz, which corresponds to the fundamental resonance of the room width 22feet, but that also contributes 2nd harmonic at 50Hz, which adds to the 53Hz 3rd harmonic of the long hallway. The big bump starts at 70 and stops at 140, those are the fundamental and 2nd harmonic of your 8 foot ceilings, but the long hallway also has harmonics with 70 and 140. Ceiling/floor have the largest area of parallel surfaces, so it is often a problem. That's what I think you are being annoyed by. The 25Hz bump is not as sensitive to our ears, and it's only +10. You can EQ that easily.  The ceiling bounce is the trouble, I think.

How thick insulation do you have in the drop ceiling? The whole thing drop ceiling is insulated or just above your seat?

The ceiling height is measured to the top of the joists where the upstairs floorboards reflect sound back down. So 8'-2" height, I'm assuming 12" joists right?

Forget the previous measurements. Can you post unsmoothed FR graphs of these three sweeps:
1. mic at listening spot, sweep as is for baseline.
2. Without moving the mic, sweep with sub turned off
3. Without moving mic, sub still off, stuff/seal the ports on your main speakers' woofers with small towels, etc.

Thanks
Rich

Offline jimbones

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Re: Bass acoustic issues
« Reply #18 on: December 11, 2014, 05:25:58 AM »
See response embedded Thanks professor!!  :thumb:

Looking at the 3rd plot you have there labeled Spectrum, that is kinda like RTA frequency response.<it is>

It shows a bump at 25Hz, which corresponds to the fundamental resonance of the room width 22feet, but that also contributes 2nd harmonic at 50Hz, which adds to the 53Hz 3rd harmonic of the long hallway. The big bump starts at 70 and stops at 140, those are the fundamental and 2nd harmonic of your 8 foot ceilings, but the long hallway also has harmonics with 70 and 140. Ceiling/floor have the largest area of parallel surfaces, so it is often a problem. That's what I think you are being annoyed by. < agreed>The 25Hz bump is not as sensitive to our ears, and it's only +10. You can EQ that easily.  The ceiling bounce is the trouble, I think.

How thick insulation do you have in the drop ceiling? <3 1/2 in Roxul> The whole thing drop ceiling is insulated or just above your seat? <90 % of the area has Roxul>

The ceiling height is measured to the top of the joists where the upstairs floorboards reflect sound back down. So 8'-2" height, I'm assuming 12" joists right? <I think 10in>

Forget the previous measurements. Can you post unsmoothed FR graphs of these three sweeps:
1. mic at listening spot, sweep as is for baseline.
2. Without moving the mic, sweep with sub turned off
3. Without moving mic, sub still off, stuff/seal the ports on your main speakers' woofers with small towels, etc.

<Yes except my floor standers are acoustic suspension bass>
Thanks
Rich
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Offline richidoo

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Re: Bass acoustic issues
« Reply #19 on: December 11, 2014, 06:20:42 AM »
<Yes except my floor standers are acoustic suspension bass>

Great! That's ideal for blending with a sub.

<3 1/2 in Roxul> 
<90 % of the area has Roxul>
<I think 10in>

OK, so ceiling height is exactly 8 feet, fundamental is 70Hz.  The floor is concrete, right? The wall at the end of the hallway is concrete too?

If the ceiling is the cause of the 70-140Hz bump, you may need to add thicker absorption in the ceiling.

But lets see the new scans without the sub.  Since your mains are sealed, they will not reach down low enough to ring the long hallway, but the ceiling ringing would remain. Their harmonics overlap, so it should be interesting.

Offline jimbones

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Re: Bass acoustic issues
« Reply #20 on: December 11, 2014, 04:23:52 PM »
measurements attached
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Offline richidoo

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Re: Bass acoustic issues
« Reply #21 on: December 11, 2014, 04:55:52 PM »
Nice!! That is a nice looking FR!

Looks like you're crossing the sub at 40Hz, 4th order. Your avg sensitivity (only on this chart) is 90-95ish. So you don't need a sub, although you might like more punch than flat allows. You must have large woofers on the mains? You named them Lambda so I guess packing something under the hood!

Two things worth looking into: The broad peak at 90Hz and the narrow dip at ~170Hz?  Could the narrow notch be driver cancellation? Are your driver polarities correct? 4th order crossover uses same polarity while 2nd order uses opposite polarity. Kinda low in freq for comb filtering, but the interval is right, dunno. Fortunately it is narrow so you probably won't notice it anyway.

The peak at 90 is probably what is bothering you. What might cause that? Hmmm..

edit: I don't see any standard room modes based on the room dimensions that could cause the peak at 90Hz. 90Hz is relatively clean frequency. It could be oblique modes bouncing around diagonally?

Next thing would be to take a couple more scans from different places around your listening room portion of the basement, to see what happens to the 90hz mode in different positions. Try one with mic moved 3 feet forward toward the speakers. Another one from dealers choice?
« Last Edit: December 11, 2014, 05:05:35 PM by richidoo »

Offline jimbones

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Re: Bass acoustic issues
« Reply #22 on: December 12, 2014, 05:02:30 AM »
Yea, I have 10 inch Daytons RS270's in the mains. Funny, the bass waas a bit cleaner and controller when I had my Aragon amp, but there is more basas with the Modwright. Also a spdif cable change added more low end so now there's actually too much of a good thing  :duh.

The mains (theoretically) roll off at around 48hz. They seem to go deeper. I am using dipoles above 275hz but that would not explain the cancellation would it?
in a 3 way system I think my XO are all 2nd orders, polarity is +, -, -. (I know the tweeter s/b + but it sounds better -)
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Offline richidoo

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Re: Bass acoustic issues
« Reply #23 on: December 12, 2014, 06:49:18 AM »
You got a good handle on it Jim. Different amps have different sound. This is why pro audio guys think we are crazy. But the output transistors all sound different, as do their circuits. Cables, well, you know the deal with that.

Rolling off at 48Hz means they are -3dB at that freq. Sealed means they roll off at 12dB per octave, so they are only -9 down at 24Hz. In addition, the room, especially a bass bowl like concrete basement reflects some (or a lot) of that bass back into the room and boosts the bass by 12dB/oct with dropping freq, matching the driver rolloff. You can get flat FR as low as you want if you choose the right diameter bass driver to match the size of your room. Seems like you got it about right with the 10s.

Definitely run a couple more sweeps of the room in different places. If you see that 90 Hz peak not going away or changing freq then you know it's coming from your system, not the room.  When you move the mic the room modes will rise and fall and different modes will make other freqs come up and down. When things stay the same despite moving the mic, then the EQ is being played into the room. If you find that it is a room mode or combination of them, the easiest thing to try since it is only 10dB bump is to move your speakers around. Measure once to establish baseline, then  move them 1 foot forward toward the listener and sweep again without moving the mic at all. If that changes the bump significantly then you can work on positioning the speakers. I recommend trying the Master Set procedure. It is described well on Audiocircle by Stephen Harr. It works pretty well to flatten the bass response.
http://www.audiocircle.com/index.php?topic=64320.0
http://www.audiocircle.com/index.php?topic=65908.0

If there's any chance you think the extra bass could be coming from the system, you should try applying EQ, as an experiment, to see if things get better. The easiest way I know to do that is to install trial JRiver, and play some tunes through their parametric EQ module. You should be able to measure the room on the same computer while playing tunes from JRiver, but you'll know by ear if it's working.

You can rip a couple tracks to the hard drive, play them through the headphone jack to your preamp. Hifi doesn't matter here, we're just thinking about the rough bass EQ which will be close enough through the PC. Any headphone jack will be well within 2dB correct FR.

You have mentioned aversion to applying EQ, but if the system is making the bump, then there is already EQ in the system and you are just correcting and removing what shouldn't be there. I agree that Behringer DEQ2496 shouldn't be in anyone's audiophile system, but there are many other ways to get the job done that don't hurt the SQ at all. Jriver and omnimic together will help you figure out what actually works, before you make a corrector.

What is the width of your woofer front baffle? Did you apply baffle step correction before your bass to mid crossover?

Offline tmazz

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Re: Bass acoustic issues
« Reply #24 on: December 12, 2014, 07:54:32 AM »
......This is why pro audio guys think we are crazy.

You mean we're not crazy????  #-o

I don't think you will ever get my wife to agree to that.  :rofl:
Remember, it's all about the music........

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Offline jimbones

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Re: Bass acoustic issues
« Reply #25 on: December 12, 2014, 07:59:53 AM »
See response embedded. Mucho Gracias

You got a good handle on it Jim. Different amps have different sound. This is why pro audio guys think we are crazy. But the output transistors all sound different, as do their circuits. Cables, well, you know the deal with that.

Rolling off at 48Hz means they are -3dB at that freq. Sealed means they roll off at 12dB per octave, so they are only -9 down at 24Hz. <wouldn't that be -15?>In addition, the room, especially a bass bowl like concrete basement reflects some (or a lot) of that bass back into the room and boosts the bass by 12dB/oct with dropping freq, matching the driver rolloff. You can get flat FR as low as you want if you choose the right diameter bass driver to match the size of your room. Seems like you got it about right with the 10s. <maybe 8's are more appropriate>

Definitely run a couple more sweeps of the room in different places. If you see that 90 Hz peak not going away or changing freq then you know it's coming from your system, not the room. <I do seem to remeber walking around the room with the mic and not seeing the Fr change all that much but I need to do it again> When you move the mic the room modes will rise and fall and different modes will make other freqs come up and down. When things stay the same despite moving the mic, then the EQ is being played into the room. If you find that it is a room mode or combination of them, the easiest thing to try since it is only 10dB bump is to move your speakers around. Measure once to establish baseline, then  move them 1 foot forward toward the listener and sweep again without moving the mic at all. If that changes the bump significantly then you can work on positioning the speakers. I recommend trying the Master Set procedure. It is described well on Audiocircle by Stephen Harr. It works pretty well to flatten the bass response.
http://www.audiocircle.com/index.php?topic=64320.0
http://www.audiocircle.com/index.php?topic=65908.0

If there's any chance you think the extra bass could be coming from the system, you should try applying EQ, as an experiment, to see if things get better. The easiest way I know to do that is to install trial JRiver, <I already used a paid version MC19 in my system. I didn't even use the equalizer although I aassume that is only when playing hires music files from my laptop> and play some tunes through their parametric EQ module. You should be able to measure the room on the same computer while playing tunes from JRiver, but you'll know by ear if it's working.

You can rip a couple tracks to the hard drive, play them through the headphone jack to your preamp. Hifi doesn't matter here, we're just thinking about the rough bass EQ which will be close enough through the PC. Any headphone jack will be well within 2dB correct FR.

You have mentioned aversion to applying EQ, but if the system is making the bump, then there is already EQ in the system and you are just correcting and removing what shouldn't be there. I agree that Behringer DEQ2496 shouldn't be in anyone's audiophile system, but there are many other ways to get the job done that don't hurt the SQ at all. Jriver and omnimic together will help you figure out what actually works, before you make a corrector.

What is the width of your woofer front baffle? Did you apply baffle step correction before your bass to mid crossover? <I think 11 + 3/4 side panels with 30 degree bevel so 12.5. I don't have baffle step correction because it occurs at or near the XO point>
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Offline jimbones

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Re: Bass acoustic issues
« Reply #26 on: December 12, 2014, 08:06:05 AM »
I know I'm not crazy because my therapist told me so!

 ](*,) ](*,)




......This is why pro audio guys think we are crazy.

You mean we're not crazy????  #-o

I don't think you will ever get my wife to agree to that.  :rofl:
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Offline richidoo

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Re: Bass acoustic issues
« Reply #27 on: December 12, 2014, 10:18:41 AM »
See response embedded. Mucho Gracias

<wouldn't that be -15?>  Yes. I need common-core refresher!  :duh

<maybe 8's are more appropriate>  Nah, you have a big room, and you're flat in bottom octave. The peak is not related to driver size. The reason woofers rolloff is because they are too small to play any lower. This is called acoustic impedance = the ability of the cone to grip the air. Air just spills out over the edge of small cones moving big excursion at a slow speed (LF.) At higher speed (HF) the air can't escape out of the cone quick enough, so it gets moved. 

<I do seem to remeber walking around the room with the mic and not seeing the Fr change all that much but I need to do it again> OK. That's really good, let's hope that pans out. The best thing would be for this problem to be in your system, cuz that's easy to fix.

<I already used a paid version MC19 in my system. I didn't even use the equalizer although I aassume that is only when playing hires music files from my laptop> It will EQ any file that you play, and the DSP is 64 bit.  :thumb:  Create a notch filter at 90db  -10dB amplitude and play with the Q of it to adjust the width. Higher Q makes a narrower notch. 

<I think 11 + 3/4 side panels with 30 degree bevel so 12.5. I don't have baffle step correction because it occurs at or near the XO point>

The BSC formula is F3 = 380 / baffle width (feet), so your filter should knee at 380, but it must be done by ear to suit the room, etc. A project for another day!  But now we know that incorrectly applied BSC is not the cause of the too loud bass.

Offline tmazz

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Re: Bass acoustic issues
« Reply #28 on: December 12, 2014, 12:13:43 PM »
I know I'm not crazy because my therapist told me so!

 ](*,) ](*,)




I don't need a therapist to tell me that. I keep hearing it from the voices in my head.  :shock:
Remember, it's all about the music........

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DigiBuss/TWL PC/MIT Cable

Offline jimbones

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Re: Bass acoustic issues
« Reply #29 on: December 12, 2014, 04:33:50 PM »
<<Two things worth looking into: The broad peak at 90Hz  and the narrow dip at ~170Hz? Could the narrow notch be driver cancellation? ((doubt it the XO is close to 300hz))Are your driver polarities correct? 4th order crossover uses same polarity while 2nd order uses opposite polarity>>

Looks like the 90 hz changed as I moved into the plane with the speakers. when I move to the wall the 170 moves to 220hz.
« Last Edit: December 12, 2014, 04:51:39 PM by jimbones »
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