18" Subwoofer DIY Options & Theorem - AVS Forum
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post #1 of 68 Old 10-21-2012, 07:26 PM - Thread Starter
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I have a THT with an EP2500 powering it and I've recently been reading that the THT doesn't go as low as some other subs so I'm thinking of building a front radiating 18" Subwoofer however I have a few questions before I go on this endeavor. First off I've done graphs on my THT and I EQ with a behringer feedback destroyer and my graphs say that I'm flat to about 13-15 hz. Someone however told me that it's probably just distorted bass as the THT can't really go that low, not sure if this is true or not. I feel like my THT sounds amazing and goes super low, I do however feel like the midbass attack is slow and boomy, but I don't truly know how the THT compares because I've never heard an 18" or any super subs, so I'm not sure what the difference would sound or feel like. For my questions you can Assume I will use an 18" Driver in the $300 to $450 Range, powering it with the EP2500 and built in a ported box, unless you want to convince me sealed is better.

1. Will I be able to tell a difference between the sound of the THT and the 18"? Will the low bass be that noticeable? How about mid bass differences between the 2?

2. By using an 18" driver as opposed to a 15" driver are you losing anything? Will the 18" be more boomy or slower with less attack and accuracy?

3. How do the 18" do with music?

4. What manufacturers of 18" or 15" Drivers would you recommend? As many options you can think of in the $300 to $450 range as long as it can get me to super low frequencies. If a 15"

5. What specific 18" Build Thread would you recommend that takes minimal effort and great results.

Opinions Appreciated
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post #2 of 68 Old 10-22-2012, 04:20 PM - Thread Starter
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post #3 of 68 Old 10-22-2012, 10:04 PM
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hi,

the first step would be to get some measuring gear, so you can see what the response looks like in your room.

at a minimum an spl meter and some test tones, or a mic/soundcard/software setup for your computer.

subs and rooms form a system. if your upper bass from a tht is slow and boomy, you likely have a large room resonance.

room resonances don't decay very fast, so notes get blended together and can definitely sound slow and or muddy.

if it is there with your tht, it will be there with most anything else in the same location.

18" drivers can be just as good as 15" drivers. the better 18" drivers are better than lower quality 15" drivers for both music as well as home theater.

the mach5 audio uxl18 would be a good choice.

how large is your room?

Listen. It's All Good.
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post #4 of 68 Old 10-23-2012, 04:29 AM
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Some good subs in that price range are:

Mach5 IXL-18
Mach5 UXL-18
Fi Car Audio SSD-18
Dayton Reference 18

Just to name a few. I am in the same boat as you Evolvo, looking to build a really good 18" inch sub for my home theater, I am looking forward to seeing this build that you are going to do!
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post #5 of 68 Old 10-24-2012, 12:18 AM - Thread Starter
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Quote:
Originally Posted by LTD02 View Post

hi,
the first step would be to get some measuring gear, so you can see what the response looks like in your room.
at a minimum an spl meter and some test tones, or a mic/soundcard/software setup for your computer.
subs and rooms form a system. if your upper bass from a tht is slow and boomy, you likely have a large room resonance.
room resonances don't decay very fast, so notes get blended together and can definitely sound slow and or muddy.
if it is there with your tht, it will be there with most anything else in the same location.
18" drivers can be just as good as 15" drivers. the better 18" drivers are better than lower quality 15" drivers for both music as well as home theater.
the mach5 audio uxl18 would be a good choice.
how large is your room?



My room is 23x13x7.5. I've included graphs of my sub, but for some reason from 10hz down I have a huge spike. Looks like I have the deepest sub in the world. I know something is wrong, just not what. I used room eq wizard and calibrated the soundcard and am using the radioshack mic with calibration file so not sure where the hiccup is, or whether I can trust these results or not. I use a behringer feedback destroyer for eqing.

All things being equal would a 15" sub or 18" sound better, and would the diff just be spl levels.
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post #6 of 68 Old 10-24-2012, 12:39 AM - Thread Starter
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Quote:
Originally Posted by Martycool007 View Post

Some good subs in that price range are:
Mach5 IXL-18
Mach5 UXL-18
Fi Car Audio SSD-18
Dayton Reference 18
Just to name a few. I am in the same boat as you Evolvo, looking to build a really good 18" inch sub for my home theater, I am looking forward to seeing this build that you are going to do!

I think I"m a long way away because I have to still figure out whether to build a 15" or 18". I want to make sure that 18" subs sound good for music as well. I'm trying to get lots of information before I build. Cause I really think the THT sounds pretty good and I want to make sure I'm actually going to gain something such as deep cleaner bass. I have to admit though, the allure of an 18" sub sounds great. Seems like it would be a devastating force to reckon with.

I see the 18" drivers you've listed, do you know if all of these are capable of going lower than a THT, or how low you can get them to go. I want to make sure that if I do build an 18" sub it will definitely be better than the THT, so I want to make sure I'm using the best drivers and not cheap run of the mill that won't get me super low. I seen the mach 5 and that thing seems like a beast. I just don't know if I can spend 550 on a driver without my wife killing me. If I can get 400 for my THT maybe it's possible.
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post #7 of 68 Old 10-24-2012, 01:23 AM
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Quote:
Originally Posted by Evolvo View Post


My room is 23x13x7.5. I've included graphs of my sub, but for some reason from 10hz down I have a huge spike. Looks like I have the deepest sub in the world. I know something is wrong, just not what. I used room eq wizard and calibrated the soundcard and am using the radioshack mic with calibration file so not sure where the hiccup is, or whether I can trust these results or not. I use a behringer feedback destroyer for eqing.
All things being equal would a 15" sub or 18" sound better, and would the diff just be spl levels.


If you want the spike removed, try doing the measurements without the soundcard calibration.
Instead, use a loopback cable from one channel line out to one channel line in.
Be sure to apply those settings in REW.

This worked for me, and now I don't need to calibrate the soundcard because REW is doing the correction "on the fly"
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post #8 of 68 Old 10-24-2012, 05:38 AM
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If I were you, I would definitely go with an 18" driver, or possibly a pair of 15" drivers. A large, ported, 18" sub is most definitely going to go lower than your THT, but whether it will have the mid-bass output you desire, is mostly dependent on your room and listening taste. I find it strange that you say your THT goes really low but lacks mid-bass output as that is the exact opposit as what everyone else says about this horn loaded sub.
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post #9 of 68 Old 10-24-2012, 02:16 PM - Thread Starter
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Quote:
Originally Posted by Strike Ace View Post

If you want the spike removed, try doing the measurements without the soundcard calibration.
Instead, use a loopback cable from one channel line out to one channel line in.
Be sure to apply those settings in REW.
This worked for me, and now I don't need to calibrate the soundcard because REW is doing the correction "on the fly"

I use a behringer usb sound card thingy and it seems like the right audio input does not work, because whever I put the mic on that input the system doesn't respond. Could this be a settings problem? If my right channel input is messed up, I was wondering if I could use some kind of splitter for the loopback. Do you have to change any settings when doing the loopback?

Also how close do you think my graph actually is to what it shows considering I have the problem of the upward slope on my graph. Does that mean my readings are totally inaccurate or just off at 30hz and below.
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post #10 of 68 Old 10-24-2012, 02:19 PM - Thread Starter
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Quote:
Originally Posted by Martycool007 View Post

If I were you, I would definitely go with an 18" driver, or possibly a pair of 15" drivers. A large, ported, 18" sub is most definitely going to go lower than your THT, but whether it will have the mid-bass output you desire, is mostly dependent on your room and listening taste. I find it strange that you say your THT goes really low but lacks mid-bass output as that is the exact opposit as what everyone else says about this horn loaded sub.

Maybe I'm to midbass hungry. Do you think 2 15's would be better than 1 18" in my room. I like the the price of the Dayton 18". I've never heard about it till you mentioned it. How good is it and do lots of people use them? Does it even get close to the Mach 5?
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post #11 of 68 Old 10-24-2012, 03:46 PM
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If you are truly mid bass hungry and your room is not causing a suck-out from 80-160hz, then twin 15's will likely be better than a single 18 only because (all things being equal) you will have greater efficiency. However, a driver that handles output in the <30hz area should not also be tasked to handle the 80-160hz area.

YID DIY
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post #12 of 68 Old 10-24-2012, 04:21 PM - Thread Starter
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Quote:
Originally Posted by Looneybomber View Post

If you are truly mid bass hungry and your room is not causing a suck-out from 80-160hz, then twin 15's will likely be better than a single 18 only because (all things being equal) you will have greater efficiency. However, a driver that handles output in the <30hz area should not also be tasked to handle the 80-160hz area.

I'm sorry, I mispoke. My understanding of what midbass is is not accurate. I'm talking about from say 40-60, the type of bass that hits you in the chest. I think that is 40-60, maybe I'm confused. I thought 40-60 was midbass. The sub is great for movies and rumble but with music it doesn't quite give me that umph, it's kind of muddy.
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post #13 of 68 Old 10-25-2012, 03:14 AM
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I think chest pounding bass is from 60-95 which crosses in to what I cover as the midbass band. 60-40 is hit you in the gut bass but excess 55ish Hz has caused some systems I've worked on to be muddy. 40-20 I like to call Pants flapping bass. An interesting note: the lowest octave, when played loud, tends to make my head and face hot and kind of tingly. I think this effect is due to humans fight or flight response to ULF. Anyway sorry to jack the thread, I just love bass.

-Matt

-Matt Long
San Francisco, CA
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post #14 of 68 Old 10-26-2012, 08:54 AM
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I've posted this before but seems to fall on deaf ears, so I'll take this opportunity to repeat it here, FWIW:

An analog loopback measurement of a sound card has nothing whatever to do with a frequency response measurement. Since all analog devices have DC offset blocking capacitors whose values are completely arbitrary, and thus the huge variance in roll off from one card to another, an analog loopback will show this roll off. In almost every case (100% so in all of the cases I investigated), the blocking caps are in the analog output stage.

However, when you measure the FR of your room, the signal you feed through your SC into REW never sees the analog output stage of the sound card. It goes into the SCs A/D converter and stays in the digital realm from there to REW.

That means that if your particular SC has a roll off at or above 10 Hz (which many do, or worse) in its analog output stage and you run an analog loopback from which REW makes a correction file, in most cases that correction file ends up being a boost curve to the actual A=>D signal path.

Same goes for using a generic correction file for the RS meter, and I wouldn't pay much attention to any measurement result below 10 Hz using that method to measure.

Finally, there is the noise floor of the room/measurement system, which increases as frequency decreases. To safely clear that hurdle, you have to measure at 100dB minimum, well above the level your posted graph shows. This also would entail making sure REW is at least somewhat calibrated. Since I've never used the RS meter to make a measurement, I don't know if the SPL reads while the mic is fed to REW, but if it does, used a 1000 Hz tone (where the RS meter is probably the most accurate) and set the calibration before you measure. Then, bump the sweep level to 100 dB and lose the SC correction file.

Try that and repost, if you care to and get the time.
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post #15 of 68 Old 10-26-2012, 09:27 AM
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Dave,

The analog microphone input being used is not usually flat to 2Hz and neither is the analog sound card output, usually xlr, rca or trs, into the amplifier. These are prior to the signal being converted into 1's and 0's. What am I missing here?
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post #16 of 68 Old 10-26-2012, 09:31 AM
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Not to mention the output signal from REW comes from the analog output stage of the sound card and into the device / system under test in most setups I've seen.
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post #17 of 68 Old 10-26-2012, 11:52 AM
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Quote:
Originally Posted by Ricci View Post

Dave,
The analog microphone input being used is not usually flat to 2Hz and neither is the analog sound card output, usually xlr, rca or trs, into the amplifier. These are prior to the signal being converted into 1's and 0's. What am I missing here?

The sweep and sub system have nothing to do with the measurement hardware/software. You say that the SC input is not usually flat... do you have any examples? The answer is 'no' because no one knows how to measure what the A/D converter hands to REW much less actually measures it and posts that data.

Yes, there can be DC offset blocking caps in the analog input stage, but I haven't found that to be the case in my investigation of the subject in SCs, preamps, etc.

OTOH, I certainly have seen a wide variety in loopback measurements DC blocking caps values dictating the correction file curve.

varioussoundcardsloopbacks.jpg

The sweep generator signal and subwoofer signal chain are a different can of worms... first things first if you want an accurate measurement below 20 Hz.
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post #18 of 68 Old 10-26-2012, 12:34 PM
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If you connect the output of the sound card back to the input of the sound card and do a sweep you will measure the frequency response of the sound card. Yes, it combines the input and output stage into one measurement and you can't identify whether the input stage or output stage is responsible for the deviation from a flat response, but for the sake of measuring things with REW where you're using both the input and output stages in your measurement it's adequate to compensate for effect of the frequency response of the sound card on the final measurement.
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post #19 of 68 Old 10-26-2012, 12:49 PM
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I guess my point is that you are assuming that it is a straight A/D conversion into the speaker and back into REW. What about the analog microphone input and output stages of the soundcard? They are both being used in most cases. IOW going right through those DC blocking caps. The signal goes through the SC going both ways when doing an acoustic measurement. These input and output stages usually show some roll off which you show in your charts above. How are the measurements passing through them but not being affected by them is what I am not following. The signal is not digital the whole way.
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post #20 of 68 Old 10-26-2012, 12:59 PM
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Here are measurements of the sound card I use with REW. Left and Right channel respectively.

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post #21 of 68 Old 10-26-2012, 04:29 PM - Thread Starter
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Quote:
Originally Posted by Evolvo View Post

I use a behringer usb sound card thingy and it seems like the right audio input does not work, because whever I put the mic on that input the system doesn't respond. Could this be a settings problem? If my right channel input is messed up, I was wondering if I could use some kind of splitter for the loopback. Do you have to change any settings when doing the loopback?
Also how close do you think my graph actually is to what it shows considering I have the problem of the upward slope on my graph. Does that mean my readings are totally inaccurate or just off at 30hz and below.

Lol, so do you guys think my one of my input channels is broken or is there some setting that may only be making one side work
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post #22 of 68 Old 10-26-2012, 04:32 PM
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REW only monitors one of the channels on the input. When you switched to the right input did you also change the setting in REW?
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post #23 of 68 Old 10-26-2012, 06:07 PM
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Quote:
Originally Posted by Stereodude View Post

If you connect the output of the sound card back to the input of the sound card and do a sweep you will measure the frequency response of the sound card. but for the sake of measuring things with REW where you're using both the input and output stages in your measurement it's adequate to compensate for effect of the frequency response of the sound card on the final measurement.

Quote:
Originally Posted by Ricci View Post

I guess my point is that you are assuming that it is a straight A/D conversion into the speaker and back into REW. What about the analog microphone input and output stages of the soundcard? They are both being used in most cases. IOW going right through those DC blocking caps. The signal goes through the SC going both ways when doing an acoustic measurement. These input and output stages usually show some roll off which you show in your charts above. How are the measurements passing through them but not being affected by them is what I am not following. The signal is not digital the whole way.

Then explain the OP's posted response. Surely neither of you believes it is accurate? I'd be interested to know what you both believe is happening?

THTmeasurements.jpg

My sweep stays digital until the AVR converts is at the SW output. There are many ways to accomplish this. The OP said he used a Berry USB SC, which I'll bet has a digital output. If not, what is a SC with digital out, $20? How would anyone know that he didn't use the digital output of the Berry? I assumed he did.
Quote:
Yes, it combines the input and output stage into one measurement and you can't identify whether the input stage or output stage is responsible for the deviation from a flat response,

Make that YOU can't identify which stage has the blocking caps. Of course there's a simple way to determine which and digital out keeps the output stage in digits until your SW output, which, as I said, is another story unrelated to this one.
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post #24 of 68 Old 10-26-2012, 06:38 PM
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Quote:
Originally Posted by bossobass View Post

Then explain the OP's posted response. Surely neither of you believes it is accurate? I'd be interested to know what you both believe is happening?
Application of a correction table/file that doesn't apply to his exact measurement device. Outside noise during the sweep is another possibility.
Quote:
Make that YOU can't identify which stage has the blocking caps. Of course there's a simple way to determine which and digital out keeps the output stage in digits until your SW output, which, as I said, is another story unrelated to this one.
*sigh* I meant it's not possible to tell solely from the measurement. I didn't say that it wasn't possible to make the determination another way. Frankly, I would expect both the input and output to have filtering to block DC on a sound card.
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post #25 of 68 Old 10-27-2012, 12:40 PM - Thread Starter
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Ok, so my berry isn't broke then, it's just that REW only uses one input channel. So you guys are arguing, but I'm still wondering whats the best way to measure. Is it the loopback and are there any setting i need to check or uncheck to make this work? I want my measurements to be correct. When doing loopback is one of the input not supposee to be recieving a signal. Am I suppose to make REW read both inputs? Please let me know how to remove the up spike to get better measurements.

I feel like my threads getting highjacked and taking a turn for the worse, Lol.

Thanks.
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post #26 of 68 Old 10-27-2012, 12:55 PM - Thread Starter
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I do appreciate the extra info though even though I don't understand most of it, I'm sure some goodness will come out of the back and forth and result in me getting a real reading. Because if it turns out that my sub isn't going in the mid teen frequencies I will definitely build an 18.
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post #27 of 68 Old 10-27-2012, 12:58 PM - Thread Starter
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Just to clarify I used the analog outputs not the digital, it does have a digital optical out.
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post #28 of 68 Old 10-27-2012, 01:26 PM
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Here are a few suggestions:
1) Repeat the sweep with the subwoofer turned off and see what you measure at the very low end.

2) post the .cal file you're using for your meter.

3) post a graph without smoothing

4) sweep at a higher output level (higher than 70dB, like 95dB)
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post #29 of 68 Old 10-27-2012, 02:49 PM - Thread Starter
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Whenever I try to sweep high it says I cannot go higher than llike 93db. So even at sweep lvl of 75 it seems to get up to 93 and I get a message saying I'm close to my limit. I measured without sub and did get the upward spike at low frequency. I will post graphs later.

Thanks.
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post #30 of 68 Old 10-27-2012, 04:30 PM
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Quote:
Originally Posted by Evolvo View Post

Ok, so my berry isn't broke then, it's just that REW only uses one input channel. So you guys are arguing, but I'm still wondering whats the best way to measure. Is it the loopback and are there any setting i need to check or uncheck to make this work? I want my measurements to be correct. When doing loopback is one of the input not supposee to be recieving a signal. Am I suppose to make REW read both inputs? Please let me know how to remove the up spike to get better measurements.
I feel like my threads getting highjacked and taking a turn for the worse, Lol.
Thanks.

Your thread is not being jacked. All the info is there for you to get on track.

First, as I said, calibrate the level (see earlier post). If you don't, the dBSPL numbers on your graph are useless.

If you have a digital out option on your Berry, use it and lose the SC loopback cal file.

Not knowing what RS meter you're using and the procedure and settings is also a problem. I remember Ilkka and Ethan Winer posting this back when regarding the digital version:
Quote:
Digital:
Do not use any correction files
when measuring with TrueRTA or similar. The output of the RCA jack is unweighted when set to C-weighting.

More recently, notnyt said that when his digital meter was set to 'C' weight, the output jack WAS C weighted, so there is a HUGE difference in the 2 scenarios.

IOW, if your meter is NOT C weighted when set to C weight and using the output jack, using the correction file in REW would definitely give the huge boost we see down low.
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