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Plugging Ported Speakers
Old 19th February 2012
  #1
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Plugging Ported Speakers

Alright, so the question just came up - Is it more of a benefit or danger plugging the port on your speakers?

I did a little bit of searching, found nothing of real use, so here I am, looking for some opinions.

I personally own the HS80's and from what I hear, being ported makes them a bit inaccurate in the low end. I just read a thread where someone said they plugged their port, and it made a good amount of difference, so I want to know if that difference is for the better or the worse.

I assume that because they are ported, there is a reason, possibly to let the speakers breath? So what are the benefits of being ported, and what are the benefits/damages to plugging it off?
Old 19th February 2012
  #2
I wouldn't block the port. It will create air pressure in the cabinet that can effect the response and excursion of your woofer. If the speaker has a port it was designed to utilize it in one way or another. Would you plug your cars exhaust pipe or your chimney with a fire going.

Try some bass traps behind the speakers, or moving them off the wall a bit so the port air isn't hitting the walls if it is.

Have you used other speakers in that room, have you analysed the room, is this a symptom of a bass build up in the room or these particular monitors.
Old 19th February 2012
  #3
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Quote:
Originally Posted by daez View Post
I wouldn't block the port. It will create air pressure in the cabinet that can effect the response and excursion of your woofer. If the speaker has a port it was designed to utilize it in one way or another. Would you plug your cars exhaust pipe or your chimney with a fire going.
Thats kinda how I am looking at it.

Quote:
Try some bass traps behind the speakers, or moving them off the wall a bit so the port air isn't hitting the walls if it is.

Have you used other speakers in that room, have you analysed the room, is this a symptom of a bass build up in the room or these particular monitors.
I'm not complaining about my speakers. I love them actually. I am just trying to get my facts straight. My question doesn't relate to my experiences with using the monitors, or the room that they were placed in, but rather what the speakers are doing regardless of environment.

Thank you for the response!
Old 19th February 2012
  #4
Anytime a friend of myne has the 50's and there pretty nice so I would imagine the 80's to be pretty [email protected]$$...
Old 19th February 2012
  #5
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If you know the Thiele-Small parameters and the internal box volume, you can predict the closed box response. There are several online calculators for that. The parameters are free air resonance (Fs), equivalent compliance volume (Vas) and total resonant magnification (Qts).

Typically, drivers are designed to work best for either one style of cabinet or the other. Even if a driver works well in both types of system, the optimal box size is usually different for the two applications.

Of course you may be lucky and find that it gives a good response as a closed speaker. Probably will not damage the speaker to try it. The more likely thing is that the box is smaller than optimal for a closed system, which will give an overly peaked response.

IMO, the better course is to get (or make) a good set of optimally-designed sealed speakers, but then that's because I prefer them.

Cheers,

Otto
Old 19th February 2012
  #6
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I'd try it. There's no danger and sometimes it works
Old 19th February 2012
  #7
Quote:
Originally Posted by JoRillo View Post
Thats kinda how I am looking at it.



I'm not complaining about my speakers. I love them actually. I am just trying to get my facts straight. My question doesn't relate to my experiences with using the monitors, or the room that they were placed in, but rather what the speakers are doing regardless of environment.

Thank you for the response!
There are two primary types of speaker enclosures: ported enclosures and 'infinite.'

Ported speaker enclosures are generally designed to use the enclosure's resonant properties in order to 'reinforce' the lowest bass ranges the speaker is capable of.

Infinite baffles come in two types: those which use a driver of 'normal' resonance properties and have two 'infinite' spaces on either side of the baffle (as with drivers mounted directly in walls or ceilings) and so-called acoustic suspension speaker systems which pair an extremely low resonance driver [so low that it would sound woofy and distorted in free air] with a small-ish sealed enclosure.

Because the finite amount of air behind the speaker effectively raises its resonance, the "woofiness" should be eliminated -- but with optimal design, that resonance can still be quite low, allowing a relatively small enclosure to produce a fair amount of bass. The tradeoff in such systems is efficiency. Acoustic suspension speakers can require considerably more power for a given SPL.
Old 19th February 2012
  #8
Registered User
Try plugging with a piece of foam. It won't allow excessive pressure to build up, but it still does something. My Dynaudio BM15s came with foam plugs for exactly this purpose. It's worth trying - I didn't leave them in, but see what it does.
Old 20th February 2012
  #9
Quote:
Originally Posted by daez View Post
I wouldn't block the port. It will create air pressure in the cabinet that can effect the response and excursion of your woofer. If the speaker has a port it was designed to utilize it in one way or another. Would you plug your cars exhaust pipe or your chimney with a fire going.
Such a false analogy. So not the same thing at all. Blocking the port will not cause any harm.

The speaker itself has a fundamental frequency that is as low as it can output before it's response dramatically drops off. The smaller the speaker the higher this frequency. A reflex port is an attempt to get more bass from a given enclosure and speaker size. It works by having the port designed so that the frequency the air in the port resonates at is just below the resonance of the driver itself. This helps increase bass response. But at a cost of time smearing. Because the sound that exits the port is always late compared to the sound that leaves the front of the driver.

This time smearing is made worse by driver protection circuitry used to keep the driver from being damaged due to having such freedom of movement as an opening in the cabinet allows. That circuitry causes further time delay.

That combined with the time delay in a typical port design makes for a bass response that while deeper than a comparably sized sealed speaker, and while more efficient in that it doesn't require as much power to output the same SPL as a similarly sized sealed design, is subtly less defined. The bass notes never stop and start completely in time as they should which makes it subtly more difficult to balance overlapping timing information in that area (like kick drums and bass guitars). It also makes transient detail less prominent in the bass frequencies. That is what people tend to notice when they say the bass in certain speakers isn't "tight". That "tightness" is due to good transient and time domain response. Conventional ported designs sacrifice that in order to have deeper audible bass for less amplifier power output and a smaller cabinet.

With a sealed box speaker the frequencies below resonance are barely, if at all heard, so there isn't a problem of low frequency time smearing. This greater time domain accuracy is what makes it significantly easier for a mix engineer to mix the bass frequencies, one of the reasons the NS10 have been popular. It's easy to get things to sit right when you can hear the transient details clearly, frequency domain information aside.

Plugging the ports of a conventional ported design will help to eliminate the frequency lag from the port. But it will do nothing to help the electronics of the speaker be more time coherent. When you plug the port you will notice a loss of bass extension. That's not harmful. It's just less bass. But the bass will be subtly "tighter", though not as "tight" as it would be had the entire speaker been designed as a sealed cabinet in the first place. It most certainly isn't like an automobile tailpipe.
Old 20th February 2012
  #11
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Quote:
Originally Posted by Enlightened Hand View Post
Such a false analogy. So not the same thing at all. Blocking the port will not cause any harm.
Yes, it is unlikely to cause harm. The only thing to watch for would be the (probably less likely) case where it happened that the resulting, closed box was somehow larger than optimal as a closed system. In that case, it would be underdamped, which reduces power handling and one should be careful powering at rated volume for the stock speaker.

Cheers,

Otto
Old 20th February 2012
  #12
DAH
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[QUOTE=flatfinger;7583755]Q. What's the difference between ported and un-ported monitors?


6 db\octave and 12db\octave are wrong, 12 and 24 are correct, respectively.
http://www.barefootsound.com/homerec...-vs-ported.jpg
Old 20th February 2012
  #13
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[QUOTE=DAH;7585093]
Quote:
Originally Posted by flatfinger View Post
Indeed. That jumped out at me, too.

Cheers,

Otto
Old 20th February 2012
  #14
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Quote:
Originally Posted by Enlightened Hand View Post
That combined with the time delay in a typical port design makes for a bass response that while deeper than a comparably sized sealed speaker, and while more efficient in that it doesn't require as much power to output the same SPL as a similarly sized sealed design, is subtly less defined.

...

With a sealed box speaker the frequencies below resonance are barely, if at all heard, so there isn't a problem of low frequency time smearing.
Much of what you said is dead on but these are not.

reflex does NOT go deeper than sealed. reflex is merely flat a bit longer before the low end response falls off a cliff (sometimes after a prebump, depending on tuning - see above re rolloff slopes). This gives a psychoacoustic illusion of more/deeper bass without actually having more or deeper bass. The smearing thing is correct and a product of the port (basically a helmholtz resonator).

Freqs below resonace in a sealed enclosure can be audible and useful (and merely being below resonance is not what causes low end smear; as stated the resonance of the speaker can be changed by varying box volume; possibly what you meant is the resonant freq spec of the drive unit - i.e. resonance in 'free air', below which there tends to be little to no output as that's the impedence peak of the speaker, the point at which it provides the most resistance to electrical signal and is therefore least efficient, though still producing output that can be harnessed, i.e. with w Transmission line or TQWT cabinet) - a speaker's (a speaker being a driver and cabinet combo) F10 point (the point whetre the speaker's response is -10db from flat or the nominal efficiency rating; i.e. the generally accepted point where response starts to be useless) can be up to an octave below resonance depending on the driver and cabinet match and design. The low end tends to sound more accurate and natural because of the gradual rolloff; just like every sound source in nature, as well as your ears vs the fall off a cliff low end response of a ported cabinet.
Old 20th February 2012
  #15
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Quote:
Originally Posted by Kiwi View Post
Try plugging with a piece of foam. It won't allow excessive pressure to build up, but it still does something. My Dynaudio BM15s came with foam plugs for exactly this purpose. It's worth trying - I didn't leave them in, but see what it does.
This will make an (unoptimised) aperiodic type enclosure (like the original Dynaudio A series back in the 70s). Google that for more info. Basically sounds like a sealed but with smaller box size ... which brings me to:

Quote:
Originally Posted by ofajen View Post
Yes, it is unlikely to cause harm. The only thing to watch for would be the (probably less likely) case where it happened that the resulting, closed box was somehow larger than optimal as a closed system. In that case, it would be underdamped, which reduces power handling and one should be careful powering at rated volume for the stock speaker.
This would never happen; a (properly designed ) ported cab will always be smaller (significantly; that is their appeal and one of the main reasons most speakers are ported today) than a sealed design for the same drive unit.

But if it did, the driver would behave more like it was in 'free air' (i.e. as per the driver's spec sheet - power handling will never go below that, putting it in a sealed cab increases power handling over the 'free air' spec due to the acoustic suspension effect as already described).
Old 20th February 2012
  #16
Quote:
Originally Posted by Granny Gremlin View Post
Much of what you said is dead on but these are not.

reflex does NOT go deeper than sealed. reflex is merely flat a bit longer before the low end response falls off a cliff (sometimes after a prebump, depending on tuning - see above re rolloff slopes).
That is one way to say it. And essentially what I meant. For all intents and purposes to the listener it sounds like "more" bass. It's actually more audible bass extension because the bass doesn't roll off as soon.
Quote:
...This gives a psychoacoustic illusion of more/deeper bass without actually having more or deeper bass.
Well it's not an illusion. You're actually hearing bass that you didn't hear before. It was there before, you just couldn't hear it. Sure no additional bass has been added. But what was once less audible is now audible due to the augmentation from the port. That's a real thing, not an illusion. It's not psychoacoustic in that your brain is not making up the difference. The actual output can be measured. Psychoacoustic phenomena come not from the physical process of sound but from your brain perceiving things that are not really there. The increased audible bass extension from a port is actually, physically there.

Quote:
...Freqs below resonace in a sealed enclosure can be audible and useful (and merely being below resonance is not what causes low end smear;
No what causes the smear is the fact that the frequency response below resonance is out of phase with the frequency response above resonance. But since it's so low in output SPL it's not problematic in a sealed enclosure.
Old 20th February 2012
  #17
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Quote:
Originally Posted by Enlightened Hand View Post
That is one way to say it. And essentially what I meant. For all intents and purposes to the listener it sounds like "more" bass. It's actually more audible bass extension because the bass doesn't roll off as soon. Well it's not an illusion. You're actually hearing bass that you didn't hear before. It was there before, you just couldn't hear it. Sure no additional bass has been added. But what was once less audible is now audible due to the augmentation from the port. That's a real thing, not an illusion. It's not psychoacoustic in that your brain is not making up the difference. The actual output can be measured. Psychoacoustic phenomena come not from the physical process of sound but from your brain perceiving things that are not really there. The increased audible bass extension from a port is actually, physically there.

No what causes the smear is the fact that the frequency response below resonance is out of phase with the frequency response above resonance. But since it's so low in output SPL it's not problematic in a sealed enclosure.
No.It's more upper bass exaggeration in a reflex design vs actual lower bass in a sealed:



Red being ported (not to scale; quick mock up.... very bad actually, but illustrates the point). It is a well documented psychoacoustic illusion (not lower bass, just more upper bass creating a boomier in your face sound vs the more natural sealed cabinet sound).
Old 20th February 2012
  #18
The sealed cabinet rolls off earlier, but more gradually. But the frequencies below resonance get less audible sooner. With a port you hear the frequencies just below resonance because they aren't rolling off as soon. They are being augmented by the port, physically augmented as in actual air is moving in the port and you're actually hearing that at those actual frequencies. That's measurable, not psychoacoustic. You HEAR more bass. It is true that at a certain point the bass response drops off dramatically with a port, but that's not the point here. The point is that you as a listener will hear bass just below resonance more than you would with a sealed cabinet and then, as the response drops low enough it will suddenly drop off, using a port. In any case it's a physical phenomenon, not mental.

Your brain isn't tricking you into thinking more bass is there. You're actually hearing bass that you previously couldn't hear because it's not rolling off as high up the frequency scale as it was. That's not a psychoacoustic phenomenon.
Old 20th February 2012
  #19
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Quote:
Originally Posted by Kiwi View Post
Try plugging with a piece of foam. It won't allow excessive pressure to build up, but it still does something. My Dynaudio BM15s came with foam plugs for exactly this purpose. It's worth trying - I didn't leave them in, but see what it does.
+1

I've never read anything about plugging the ports completely.
Mike Senior has written about ported monitor behavior, maybe in SoS but definitely in his Mixing Secrets book. I think socks may have beeen his suggestion.
Old 20th February 2012
  #20
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Quote:
Originally Posted by Granny Gremlin View Post
This would never happen; a (properly designed ) ported cab will always be smaller (significantly; that is their appeal and one of the main reasons most speakers are ported today) than a sealed design for the same drive unit.

But if it did, the driver would behave more like it was in 'free air' (i.e. as per the driver's spec sheet - power handling will never go below that, putting it in a sealed cab increases power handling over the 'free air' spec due to the acoustic suspension effect as already described).
On further reflection, I'm pretty sure you are right that power handling won't be harmed.

Cheers,

Otto
Old 21st February 2012
  #21
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Quote:
Originally Posted by Enlightened Hand View Post
Your brain isn't tricking you into thinking more bass is there. You're actually hearing bass that you previously couldn't hear because it's not rolling off as high up the frequency scale as it was. That's not a psychoacoustic phenomenon.
This is where we disagree; just because the rolloff in a sealed cab starts earlier doesn't mean you can't hear those same freqs. It's usually about 1 octave - 6 to 12 db difference so given an average-ish 90 db/watt efficiency, that's still above 75 db and therefore audible. You can totally still hear all those frequencies in a sealed cab, just a bit quieter but they continue to be audible longer/lower. What they aren't is bold and in your face, but they're there and you do hear them. On the other hand, they are exaggerated (compared to what the driver can do on it's own) in a ported design, but can only do so to a max of about the resonant freq of the drive unit (or slightly more if you don't mind a bit of a prerolloff dip and then a back-up-to-fall-off-a-cliff-ish thing). The psychoacoustic effect is how your brain fills in the (for lack of a better example) fundamental that isn't there in a ported cab based on hearing the (again, e.g.) 2nd harmonic and being wired to expect gradual rolloff (like all sounds in nature), unlike the reality of a ported design which just stops (almost; 24 db/octave is pretty bloody steep though, and audio is log and we're at the bottom end of it right now).

A sealed cab has USABLE response that extends LOWER than the same driver in a ported cab; it's just not flat on a response graph for quite as much of the spectrum as the ported cab would be (insanely flat and extended response graphs are really over-rated and don't tell the whole story anyways, but that is it's own separate argument).

This is why audiophiles who like pipe organ music tend to not use ported cabs, not even with 15" woofers (when is actually when bass reflex cabs make the most sense; drivers with low Fs spec).
Old 21st February 2012
  #22
Gear Maniac
Quote:
Originally Posted by Kiwi View Post
Try plugging with a piece of foam. It won't allow excessive pressure to build up, but it still does something. My Dynaudio BM15s came with foam plugs for exactly this purpose. It's worth trying - I didn't leave them in, but see what it does.
Same speakers here and I also decided not to plug them.
Old 21st February 2012
  #23
Quote:
Originally Posted by Granny Gremlin View Post
...
I don't think we disagree. I think we're talking about different things.

What I'm saying is that in practical use the response of a driver in a sealed enclosure below resonance is out of phase with the response above resonance. But since the response below resonance is so low in output it's not an audible problem in the time domain, which is why sealed cabinets work in the time domain. I'm NOT saying you can't hear anything at all below resonance. I'm saying that it's inconsequential because it's so low in output.

A ported speaker physically augments the response just below resonance of the driver. That is NOT psychoacoustic. That just below resonance response is now very audible (we actually hear more low frequency content because we're hearing much more of the response below driver resonance due to the port). Unfortunately that response is out of phase, so it causes time domain issues.

Yes it's true that ultimately the response of the ported enclosure drops off much quicker than it would in a sealed enclosure. But not before we are able to more easily hear the response just below driver resonance in a ported enclosure much more audibly than we would in a sealed enclosure. Which means that for the listener there is "more" bass coming from a ported speaker as judged against a comparably sized and powered sealed speaker. And this is not psychoacoustic bass.

The example you gave of people listening to organ music preferring sealed cabinets due to the slower low frequency roll off can make sense. But it's not an absolute. The question with a ported design isn't a trade off of not having infrasonic bass and having a port or having infrasonic bass due to using a sealed cabinet. It's a question of how deep the entire speaker design will reach. There will come a point with either design, sealed or ported, where the designer must decide how deep the speaker will reach and either design can be made to extend as deep as can be perceived. They won't necessarily be of the same size and power however.

Your other assertion that the below resonance response that has been augmented by the port is "exaggerated" is true depending on what we're considering authentic "response".

If we are to call the action of the port "exaggerating" the response of the driver then I can agree. If however, we are looking at the speaker system's frequency response as a whole then nothing is exaggerated. It is what it measures to be. How is comes to be that way is a matter of design. Some people like to say ports add "fake" bass (and on a certain level I would agree). But to the ear, speaking in terms of frequency domain only, the frequencies you physically hear are what you physically hear and they are no more "fake" than anything else.

It's when you add the time domain that the issue of "real" versus "fake" makes a difference. Because the lessened transient detail from a conventional ported design leaves the listener with less of a sense of dimension, definition and impact from the sound and that's a big deal. In that case I would say yes, the bass from a ported design comes across as less real. That combined with the fact that it ultimately rolls off quicker (even though it initially takes longer to roll off), and that in a typical design it would not extend deep enough to mask that roll off does leave the listener with a lessened sense of realism from their listening experience and would tie in directly with what you say about listeners and the organ regarding sealed cabinet speakers.
Old 23rd February 2012
  #24
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Alright then.

I look forward to your thoughts when I post about the monitors I designed and am building with a carpenter bud to sell locally.
Old 23rd February 2012
  #25
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There seems to be a debate amongst the audioPILE crowd about whether FAST and SLOW bass really exist . If a kick drum has it's fundamental at say 40hz , plus it has a pretty prominent beater click up in the mid-range somewhere , is the brain using the beater click to judge the envelope of the drum ??

I've have had fun chasing my tail on some ported monitors where I eq'd a bass note that was resonating and causing the cabinet to buzz ever so slightly and thus elongating that note in particular ( Only Alesis monitor ones .. not high $$ units I know) With the flechture -munson curves being what they are , IS a 40hz notes release curve going to be heard that well.
Old 23rd February 2012
  #26
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Quote:
Originally Posted by Enlightened Hand View Post
What I'm saying is that in practical use the response of a driver in a sealed enclosure below resonance is out of phase with the response above resonance. But since the response below resonance is so low in output it's not an audible problem in the time domain, which is why sealed cabinets work in the time domain. I'm NOT saying you can't hear anything at all below resonance. I'm saying that it's inconsequential because it's so low in output.
No, this paragraph is essentially entirely incorrect.

The 3 dB cutoff point for a sealed box is a function of system resonance frequency and system Q. For a critically damped system with a Q of .707, the 3 dB cutoff is equal to the system resonance. Below that point, the response rapidly lines up with a 12 dB/octave drop off, giving usable response below system resonance. After all, it's only 3 dB down at resonance and will be slightly less than 15 dB down an octave lower. Other things being equal, the ported system would be far lower (about 12 dB) in output an octave below the cutoff.

Also, the sealed box response is actually much more coherent in terms of phase than the ported speaker because it is a single point source relative to the wavelengths in question. Ported speakers on the other hand, have radiation from both the cone and port and the phase difference between the two below resonance affects the response in both frequency and time domain.

However, I agree with your point that ported systems can be designed to have extended low end response. Back when I was in college, I designed and built a huge three way system using Peerless components, including a 12" woofer in a ported 8.3 cu. ft. box tuned to 20 Hz. The low end on those speakers was unlike anything I've heard elsewhere. Took my breath away playing classic synth stuff of the day like Synergy. One of the mistakes of my youth was to repackage the drivers in smaller, prettier enclosures and sell them to a friend.

Cheers,

Otto
Old 23rd February 2012
  #27
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Bigger IS better !!!!
Old 24th February 2012
  #28
DAH
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I take better time domain behaviour and smooth roll-off any day over lower -3 db point.
Old 24th February 2012
  #29
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Quote:
Originally Posted by DAH View Post
I take better time domain behaviour and smooth roll-off any day over lower -3 db point.
Words to live (mix) by for sure.
Old 24th February 2012
  #30
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Quote:
Originally Posted by PhilDW View Post
+1

I've never read anything about plugging the ports completely.
Mike Senior has written about ported monitor behavior, maybe in SoS but definitely in his Mixing Secrets book. I think socks may have beeen his suggestion.
I plugged my Tannoy Reveals with socks when I got a subwoofer. I ran some sine wave sweep tests and with the ports open (no sub) the volume would swell and diminish all over the lower frequencies. Then I plugged the ports, ran the same sweep and it smoothed it out a bit, but lost some bass. Added a subwoofer and ran the test again, and got all the bass back (and then some) and after setting the crossover point correctly, it seems to have smoothed out the frequency response on the system a bit further. They never were great monitors for monitoring bass, and while all this helped, it didn't turn a crap system into a pro studio setup.

I would give it a try and see. You may like it better, then again, you may not. But you'll need to try it to find out. All in all, my next set of monitors will not be ported. But I've learned these pretty good, and I won't be replacing them anytime soon, so my current setup works for me for the time being.
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