# Looking for advice on room



## amt (Jan 31, 2010)

I think I have REW running running well now, and I wanted to get some feedback on what I should be considering for room treatment. Here are the details:

The room itself:
~14' x 17' x 8', wall-to-wall carpet, sheet-rock walls, lightweight double doors along one of the 17' walls (centered). Front speakers and 120" diagonal vinyl projection screen are along one of the 14' walls. There are velvet curtains on all walls, but not where screen is, to absorb light to enhance projector performance for good ANSI contrast, which may have some (minimal?) effect on acoustics. There is also a couch and daybed in the room.

The equipment:
- No subwoofer at this time
- L & R speakers are Def Tech BP 30, center is Def Tech CLR-2000. The L & R speakers are bipolar
- Surrounds are very old Paradigms
- Processor is Emotiva UMC-1, with no EQ applied for the REW measurements
- Amplifier is Sunfire Cinema Grand

Here is a 1/6th octave frequency response:http://www.hometheatershack.com/for...st-time-rew-how-does-look-fr-1-6th-octave.jpg

And here is the waterfall:http://www.hometheatershack.com/for...00-first-time-rew-how-does-look-waterfall.jpg

some questions:

1) I would like to get a sub back in the room. Would I be better off doing something like 4 small subwoofers instead of 2 or 1?

2) Should I be doing something like floor to ceiling bass traps in all 4 corners? Is there a concern about too much dampening, and if so, should I face the bass traps with something?

3) I take it doing something with the first reflection points is generally a good idea?

4) Is there anything in the graphs that screams, "fix this!"?

Thanks!


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## bpape (Sep 14, 2006)

Having velvet curtains on all the walls is introducing WAY too much high frequency only absorption.

Can you post an unsmoothed frequency plot from 20-500Hz only and also the waterfall in the same range? Really hard to see much of what's going on with a full range plot.

Multiple subs can be a big benefit IF (big if) you can and are willing to put them where they want and need to be

Addressing reflections on the side walls with as thick as you can tolerate is a good idea.

Broadband bass control in the front corners and middle of the rear wall will help a lot. You have some pretty big swings, even with the very heavy smoothing you did. Definitely need to address some things.

Bryan


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## ricardo_lee (May 30, 2012)

http://www.hometheatershack.com/for...st-time-rew-how-does-look-fr-1-6th-octave.jpg
Is this the response of both your speakers in mono to your listening position? Is the 'flatter' curve the EQ'd response using REW? If so,


it will sound too bright. Have a look at some 'House Curves'
Bringing your huge peaks down to the level of the dips is the same as EQing the dips. Have you read 'The Limits of EQ' in the Help?

http://www.hometheatershack.com/for...00-first-time-rew-how-does-look-waterfall.jpg
The row of spikes on the ridges above 1kHz are a series of very close early reflections. 1ms is about 1 foot so look for stuff near the spacing of the spikes.

I'm new to REW so won't attempt to answer your questions but I've been doing 'waterfalls' and measuring speakers in room since the late 70s.


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## amt (Jan 31, 2010)

Attached are the plots for 20-500 with no smoothing.

I am hoping I can keep the curtains, but everything is on the table I suppose. I think I'll try to take care of the first reflections first. I'll see if I can use 4" think 703 or Rockwool and measure again.

The response is from both L & R speakers doing the sweep at the same time.

The flatter curve is the microphone calibration. I have not attempted any EQ-like correction, and I'd like to do all other things (namely treatments) before I get in to EQ). Thanks for the help!


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## bpape (Sep 14, 2006)

The wider nulls at about 45 and 120Hz are caused by several different things. Each time you see a "squiggle" (technical term....) in the curve down or up, it's one interaction. When you see a narrow one like around 280Hz, that's likely just one thing. 

If you're set on keeping the curtains, you may just need to move them out away from the wall to be able to do the thicker treatments behind them. 

At 14x17x8, the peak in the mid 30's looks like your length mode. The big dip in the 40's is partially your width mode (40hz - see the small hump on the way down in that null where it crosses 40).

Above 111Hz in your case, things are less likely to be purely modal in nature but more likely to be phase interactions from reflections, SBIR, etc.

Bryan


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## amt (Jan 31, 2010)

OK, I picked up 12 x OC 703 2 inch thick panels. I have not done anything with them other then sticking a pair together to form 4 inch think panels. I have positioned them in the room in various places, like:

MSW = the middle of the side walls
MFSW = the middle-front of the side walls
FC = 45 degree span across a from and side wall, resting on the floor (top of panel is 1/2 way up the wall)
RC = same as above, but the side and rear wall, and on a stand (about 2 feet off the ground)
FB = placed horizontally along the front wall, one left of the center channel and one right of the center channel

Eventually these panels would be covered in fabric and possibly have a sturdy frame. Panels would most likely go behind the curtains once their optimal position has been found.

Here's the measurements I took:

Baseline: a new baseline with no panels
MFSW: just 2 panels on each side wall, in the "middle-front" position
MSW plus MFSW: added 2 more panels on the middle of the side walls
MSW plus MFSW plus FC: added 2 more panels in the front corners
MSW plus FC plus RC: MFSW panels removed and moved to rear corners
MFSW plus FC plus FB: MSW panels moved to MFSW, rear corner panels moved to bottom of the front wall.

I will attach graphs in next few posts


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## amt (Jan 31, 2010)

Here's the baseline 20-500


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## amt (Jan 31, 2010)

And now 1 panel on each side wall, middle-front position (MFSW)


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## amt (Jan 31, 2010)

Now adding a panel to the middle of each side wall


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## amt (Jan 31, 2010)

and now adding a panel in each of the front corners


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## amt (Jan 31, 2010)

and now taking the middle-front sidewall panels and moving them to the rear corners


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## amt (Jan 31, 2010)

and now moving those rear corners panels to the bottom of the from wall (horizontally) and moving the middle-sidewall panels to middle-front


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## amt (Jan 31, 2010)

I am not sure what to make of all this, other than I have this feeling I need a lot more 703 to make a difference. The last graph IMO seems like the most effective layout so far, but that's going on no experience from me. Am I approaching this the wrong way?


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## ricardo_lee (May 30, 2012)

You may want to try moving the speakers before applying damping. There's a couple of Room Simulation programmes in another recent thread. Don't take them as Gospel but they'll give you an idea of what to try. Also do responses of each speaker individually too. You need an overview of _everything_ that is happening.
http://www.pvconsultants.com/audio/reflection/rrc.htm
Try simulating and measuring at positions away from your normal seat too.


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## bpape (Sep 14, 2006)

4" isn't going to impact the 45Hz dip. When doing this you also need to look at the waterfalls where you'll see a difference certainly. 

You should also look at things a bit more technically and figure out where the problems you're trying to address are coming from and then treat those points rather than just guessing middle of a wall here or there. If you move the mic front to back or side to side - what changes? What are the modes of your room dimensions so you know where some things could be.

On the brighter side, some of your nulls look pretty narrow so they're likely just one thing as opposed to a combination of things.

Bryan


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## amt (Jan 31, 2010)

I used a mode calculator at http://www.bobgolds.com/Mode/RoomModes.htm (17 x 13-10 x 8)
To be honest I am not sure what I am looking for, but I am trying to correlate some of these frequencies with either the peaks or nulls in the frequency response graphs. Am I correct in that each of these frequencies could create a peak -or- a null?

Freq	%	Wavelength, 1/2, 1/4	p,q,r Mode Group Weighting
33.2 hz 34'0", 17'0", 8'6"	(1,0,0 Axial) Start iso, End iso
40.9 hz 18.8% 27'8", 13'10", 6'11"	(0,1,0 Axial) Start iso, End iso
52.7 hz 22.3% 21'5", 10'9", 5'4"	(1,1,0 Tangential) Start iso, End iso
66.5 hz 20.7% 16'12", 8'6", 4'3"	(2,0,0 Axial) Start iso
70.6 hz 5.8% 16'0", 8'0", 4'0"	(0,0,1 Axial) 
78.0 hz 9.4% 14'6", 7'3", 3'7"	(2,1,0 Tangential) 
78.1 hz 0.1% 14'6", 7'3", 3'7"	(1,0,1 Tangential) 
81.6 hz 4.2% 13'10", 6'11", 3'6"	(0,1,1 Tangential) 
81.7 hz 0.1% 13'10", 6'11", 3'5"	(0,2,0 Axial) Near
88.1 hz 7.2% 12'10", 6'5", 3'2"	(1,1,1 Oblique) 
88.2 hz 0.1% 12'10", 6'5", 3'2"	(1,2,0 Tangential) Near
97.0 hz 9% 11'8", 5'10", 2'11"	(2,0,1 Tangential) 
99.7 hz 2.7% 11'4", 5'8", 2'10"	(3,0,0 Axial) 
105.2 hz 5.2% 10'9", 5'4", 2'8"	(2,1,1 Oblique) 
105.3 hz 0% 10'9", 5'4", 2'8"	(2,2,0 Tangential) 
107.8 hz 2.3% 10'6", 5'3", 2'7"	(3,1,0 Tangential) 
108.0 hz 0.1% 10'6", 5'3", 2'7"	(0,2,1 Tangential) 
113.0 hz 4.4% 10'0", 5'0", 2'6"	(1,2,1 Oblique) Near
122.2 hz 7.5% 9'3", 4'7", 2'4"	(3,0,1 Tangential) 
122.6 hz 0.3% 9'3", 4'7", 2'4"	(0,3,0 Axial) 
126.8 hz 3.3% 8'11", 4'5", 2'3"	(2,2,1 Oblique) 
127.0 hz 0.1% 8'11", 4'5", 2'3"	(1,3,0 Tangential) 
128.8 hz 1.3% 8'9", 4'5", 2'2"	(3,1,1 Oblique) 
128.9 hz 0% 8'9", 4'5", 2'2"	(3,2,0 Tangential) 
132.9 hz 3% 8'6", 4'3", 2'2"	(4,0,0 Axial) 
139.1 hz 4.4% 8'1", 4'1", 2'0"	(4,1,0 Tangential) 
139.4 hz 0.2% 8'1", 4'1", 2'0"	(2,3,0 Tangential) 
141.3 hz 1.3% 7'12", 3'12", 1'12"	(0,0,2 Axial) 
141.5 hz 0.1% 7'12", 3'12", 1'12"	(0,3,1 Tangential) 
145.1 hz 2.4% 7'9", 3'11", 1'11"	(1,0,2 Tangential) 
145.3 hz 0.1% 7'9", 3'11", 1'11"	(1,3,1 Oblique) 
147.0 hz 1.1% 7'8", 3'10", 1'11"	(0,1,2 Tangential) 
147.0 hz 0% 7'8", 3'10", 1'11"	(3,2,1 Oblique) 
150.5 hz 2.3% 7'6", 3'9", 1'11"	(4,0,1 Tangential) 
150.7 hz 0.1% 7'6", 3'9", 1'10"	(1,1,2 Oblique) 
156.0 hz 3.3% 7'3", 3'7", 1'10"	(4,1,1 Oblique) 
156.0 hz 0% 7'3", 3'7", 1'10"	(4,2,0 Tangential) 
156.1 hz 0% 7'3", 3'7", 1'10"	(2,0,2 Tangential) 
156.3 hz 0.1% 7'3", 3'7", 1'10"	(2,3,1 Oblique) 
158.0 hz 1% 7'2", 3'7", 1'9"	(3,3,0 Tangential) 
161.4 hz 2.1% 7'0", 3'6", 1'9"	(2,1,2 Oblique) 
163.2 hz 1.1% 6'11", 3'6", 1'9"	(0,2,2 Tangential) 
163.4 hz 0.1% 6'11", 3'5", 1'9"	(0,4,0 Axial) 
166.2 hz 1.6% 6'10", 3'5", 1'8"	(5,0,0 Axial) 
166.5 hz 0.1% 6'9", 3'5", 1'8"	(1,2,2 Oblique) 
166.8 hz 0.1% 6'9", 3'5", 1'8"	(1,4,0 Tangential) 
171.1 hz 2.5% 6'7", 3'4", 1'8"	(5,1,0 Tangential) 
171.3 hz 0.1% 6'7", 3'4", 1'8"	(4,2,1 Oblique) 
172.9 hz 0.9% 6'6", 3'3", 1'8"	(3,0,2 Tangential) 
173.1 hz 0.1% 6'6", 3'3", 1'8"	(3,3,1 Oblique) 
176.2 hz 1.7% 6'5", 3'2", 1'7"	(2,2,2 Oblique) 
176.4 hz 0.1% 6'5", 3'2", 1'7"	(2,4,0 Tangential) 
177.7 hz 0.7% 6'4", 3'2", 1'7"	(3,1,2 Oblique) 
178.0 hz 0.1% 6'4", 3'2", 1'7"	(0,4,1 Tangential) 
180.6 hz 1.4% 6'3", 3'2", 1'7"	(5,0,1 Tangential) 
180.8 hz 0.1% 6'3", 3'2", 1'7"	(4,3,0 Tangential) 
181.1 hz 0.1% 6'3", 3'1", 1'7"	(1,4,1 Oblique) 
185.1 hz 2.1% 6'1", 3'1", 1'6"	(5,1,1 Oblique) 
185.2 hz 0% 6'1", 3'1", 1'6"	(5,2,0 Tangential) 
187.0 hz 0.9% 6'1", 3'0", 1'6"	(0,3,2 Tangential) 
189.9 hz 1.5% 5'11", 2'12", 1'6"	(1,3,2 Oblique) 
190.0 hz 0% 5'11", 2'12", 1'6"	(2,4,1 Oblique) 
191.2 hz 0.6% 5'11", 2'11", 1'6"	(3,2,2 Oblique) 
191.4 hz 0.1% 5'11", 2'11", 1'6"	(3,4,0 Tangential) 
194.0 hz 1.3% 5'10", 2'11", 1'5"	(4,0,2 Tangential) 
194.1 hz 0% 5'10", 2'11", 1'5"	(4,3,1 Oblique) 
198.2 hz 2% 5'8", 2'10", 1'5"	(4,1,2 Oblique) 
198.2 hz 0% 5'8", 2'10", 1'5"	(5,2,1 Oblique) 
198.5 hz 0.1% 5'8", 2'10", 1'5"	(2,3,2 Oblique) 
199.4 hz 0.4% 5'8", 2'10", 1'5"	(6,0,0 Axial) 
203.6 hz 2% 5'7", 2'9", 1'5"	(6,1,0 Tangential) 
204.0 hz 0.1% 5'6", 2'9", 1'5"	(3,4,1 Oblique) 
204.3 hz 0.1% 5'6", 2'9", 1'5"	(0,5,0 Axial) 
206.5 hz 1% 5'6", 2'9", 1'4"	(5,3,0 Tangential)


Also, attached is the waterfall from the latest measurement


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## bpape (Sep 14, 2006)

The length mode appears to be the hump in the mid 30's. Best to try to simply move out of it as that's pretty low to try to treat.

The width mode looks to maybe be a piece of the larger dip but not all of it certainly. 

The question was largely rhetorical. I was saying you need to measure in more than one place to see what changed from to back side to side, up and down so you know what is causing what and what you can and can't do to help it.

Bryan


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## amt (Jan 31, 2010)

When moving the microphone, how much should I move each time? Are we talking inches or feet?

FWIW, I have no problem treating with as much as 1 foot thickness (possibly more) in the back of the room if that can help mitigate the lower frequency room modes.


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## bpape (Sep 14, 2006)

At this point, we're just looking for generalities. Move say 1'. Just make sure you only move 1 thing at a time - so no moving back and sideways at the same time.

Bryan


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## amt (Jan 31, 2010)

I took some measurements of just the front left speaker, this time with moving the mic 1 foot forward each time. This certainly changed things. The problem, IMO, is I can't really move my seating forward for viewing angle/width reasons.


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## ricardo_lee (May 30, 2012)

amt said:


> The problem, IMO, is I can't really move my seating forward for viewing angle/width reasons.


 Like in real estate, its position, position & position. If I want to know how serious someone is about sound, I don't look at the price tag on his gear. I look at where he puts his speakers.

The rules have changed with 21st century digits like REW and the gear it programmes. Don't worry about big wide bumps. Digital EQ handles these easy. It's the big dips like your 45Hz which are a problem.

If you won't move yourself, move the speakers. Having several subs gives you more flexibility.

Get it as good as you can without room treatment first by positioning speakers & listener. Then treat. Then lastly, EQ. That's the way to the best results.

Play around with http://www.pvconsultants.com/audio/reflection/rrc.htm to see what options you have.


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## amt (Jan 31, 2010)

So I have been thinking about this problem (can't seem to think about any other single thing since I've started measurements) and what can be done about it. I am in total agreement on the effectiveness of moving the listening position and the speakers. I, however, do not have a lot of options on what to do there so far. Eventually I'd like to get possibly 4 subwoofers (more on that later), but for now, I'd like to still concentrate on room acoustics. That got me thinking, why should I just accept the room modes? Yes, of course those modes are backed by things like physics , but why not change the room itself? I am talking about the shape. Can I start with altering one of the walls to change how sounds is reflected back and forth? Lets take the rear wall. Could I change the shape dramatically, where the surface is not even parallel to the front wall anymore? What if I divided up the wall in 2 foot by 2 foot sections, and each section could have a different shape a protrusion? I could literally bolt "extensions" to the wall, which are perhaps make of plywood and filled with insulation, and possibly covered with different materials. Could something like that reduce the resonating frequencies?

As for subs, since I am considering 4, does anyone have any recommendations? I am open to DIY, but would like to keep it under $1000 if possible. I do not care how they look. I would just like them to perform acceptably. Thanks!


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## amt (Jan 31, 2010)

OK, although I do not have subs right now, that did not stop me from testing dual "subs"! I just decided to use my two mains (DefTech BP30's) for sub testing. I wanted to see how I could change the frequency response by moving them around, in order to understand the potential benefits of having more than one sub (which were not as restricted on placement as say a L & R front speaker). Since the drivers are on the top half of the BP30's, I just flipped the speakers upside-down, so the drivers would be closer to the ground, like real subs would be. I also only tested only 20-500Hz. I arranged the speakers to have one right behind the couch (the rear sub) and one somewhere in front of the couch (I don't care where it ends up as long as it works well). Both are centered left-to-right in the room and drivers face left and right walls (these are bipolar). I did come up with an interesting measurement, where the each of these subs happen to be about 2 feet from the front and rear walls. Notice that the peak at ~35 and null at ~45 are nearly gone! There is no sub crossover, so I obviously do not drop off. In fact, I seem to start picking up SPL after 50Hz. Would that be taken care of with either a sub crossover or a PEQ?

Also, it did not occur to be, but I could have been driving these through the sub-preout on my processor, which can employ a crossover. So I guess I could test again with a crossover and a EQ.

In summary, this tells me 2 subs with the right placement could make a huge difference in my room. Is this not the right conclusion? Thanks.


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## ricardo_lee (May 30, 2012)

amt, You are definitely on the right track.

The issue of multiple subs is complex and you have to factor in the crossovers too. Definitely not easy. Personally, I would have the mains (& rears) running down and ju..uuust attenuated so they overload at about the same time as the subs but that's a very complex system to design.

Theoretically, if you can distribute bass sources evenly around the room (ie both subs & mains), you are always close to a speaker and so less beholden to the room. But there's a lot of salt you need to digest this. Try and think of the images of the speakers in the walls, floor & ceiling too. You want to distribute them evenly.

But it's what you measure & hear in your listening position(s) which is important.

And don't pooh pooh corner placement for subs either. There will be a big boost but this isn't a problem with digital EQ. What you want is as few & as shallow big dips as possible and sometimes, corner placement will do this for you. Roy Allison (ex AR) designed many speakers for wall & corner mounting.


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## tubamark (Jun 25, 2009)

amt said:


> . . .but why not change the room itself? I am talking about the shape. Can I start with altering one of the walls to change how sounds is reflected back and forth? Lets take the rear wall. Could I change the shape dramatically, where the surface is not even parallel to the front wall anymore?


Assuming that the only real problems are in the bass (which generally is the case), the changes you are describing are far more expensive, and usually less effective than _proper_ implemintation of multi-subs. If you haven't looked into it, the Multisub approach used by Dr. Earl Geddes is extremely effective if followed with care; it requires patience and measurement - which you have a handle on. It really accounts for all variables and tradeoffs, yet allows flexibility in sub placement. It involves adjusting phase and volume of each sub in sequence. EQ'ing is the very _last_ step, and is usually subtle and optional.

Another method that can work is a Double Bass Array, which effectively prevents the buildup of modal resonances by extreme directivity in two dimensions, and wave cancellation in the third dimension. Unfortunately, this requires a delay unit for the second array. Not a big deal, but something most audiophiles don't want to deal with. Also requires very specific placement of drivers.

The mathematical (ie modal analysis) or geometric placement methods for multisub are innacurate - they simply cannot account for real world variables. Resonances exist in _every_ room that are not predicted by modal analysis. Likewise, the basic resonances that "should" exist by predictive formulas rarely exist like predicted.

-- Mark


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## amt (Jan 31, 2010)

I am definitely going to go with multi-sub. I, however, am not sure when exactly I'll be able to do so due to cost. I am leaning towards building a couple servo subs with parts from Rythmik & GR research. In the mean time, I am addressing a couple issues like reducing the velvet drapes from all walls to just the screen wall, and adding absorption panels at first reflection points.


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## ricardo_lee (May 30, 2012)

tubamark said:


> If you haven't looked into it, the Multisub approach used by Dr. Earl Geddes is extremely effective


Have you got an electronic copy of this?

What experience have you with this method?


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## tubamark (Jun 25, 2009)

ricardo_lee said:


> Have you got an electronic copy of this?
> 
> What experience have you with this method?


http://mehlau.net/audio/multisub_geddes/

http://www.geddes-audio.com/forum/showthread.php?44-Setting-up-Multiple-Subs

http://www.geddes-audio.com/forum/showthread.php?21-Why-do-we-use-multiple-subs

Every room is different, but it works. If one can't get good results using this method, than something is wrong.
The only thing I would add is that if room arrangement permits, it's okay to experiment with sub placement (using measurement as he prescribes, not ear) as one of the first steps in optimization. 

The important things are spatial averaging, and optimizing each sub in context -it's pointless to adjust any individual sub outside of the context of the mains playing, etc.

-- Mark


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