I just couldn't resist throwing my two cents into this one...
My issues are kind of backwards on this one. When I bought my car, it came with an aftermarket deck, and "oversized" door speakers (they stick out about 1/2 inch). My plan was to convert the deck back to factory, and use line output converters, to take take the signal from the deck (or bose amp), and send it to an aftermarket amp, with "proper sized" aftermarket door speakers.
I did this in my other car, and have incredible sound, with the classier and cleaner look of the factory deck. This also opens up the world of options for speakers.
I agree. But as I posted earlier in this thread, a 4-ohm speaker will work just fine.
No need to change the amp. If you cut power in half, most people can just barely detect that the sound is not as loud. But if having a new 4-ohm speaker play at the exact level that the original did is somehow important, then this could be compensated for by selecting a speaker that is more sensitive (3dB) than the original.
This is completely false. Have you got a technical explanation of why this would happen?
Quote:
Originally Posted by cthomson
I just couldn't resist throwing my two cents into this one...
My issues are kind of backwards on this one. When I bought my car, it came with an aftermarket deck, and "oversized" door speakers (they stick out about 1/2 inch). My plan was to convert the deck back to factory, and use line output converters, to take take the signal from the deck (or bose amp), and send it to an aftermarket amp, with "proper sized" aftermarket door speakers.
I did this in my other car, and have incredible sound, with the classier and cleaner look of the factory deck. This also opens up the world of options for speakers.
I recommend the LC-6 as the DSP you should use, if you want to leave the stock head and amp. It has an infinitely variable hot line in, so it won't damage your factory amp, and it really cleans up the signal quality. I used that product when I did the system in my BMW, and was very very pleased with it.
As to the general discussion, I agree that is the way to go if you want to keep the stock head and amp, but still change the speakers. Trying to power new 4ohm+ speakers with an original amp that was already only adequately powered when running 2ohm speakers just isn't going to work out very well for obvious reasons.
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Thanks for the advise Chris. I am a fan of audiocontrol too.
Of coarse...I still need to find the deck, and changer and original speaker mounts and grills.....but that is for a different forum......
Moderators: this thread is about audio, and audio is my particular area of expertise in electronics. I studied audio engineering under Professor Leach at Georgia Tech, a man who is renowned in the field: W. Marshall Leach, Jr.. For my senior project I designed, built, and tested a car stereo amplifier. Once I graduated from college my career path took a direction that had nothing to do with audio, but it has remained a hobby of mine and over the years I have designed and built numerous audio circuits for my own use. To the point: I'd like a little leeway here get a bit long-winded and maybe off-topic to discuss with Chris something I really enjoy.
Quote:
Originally Posted by chriswufgator
Cutting the amount of available power literally in half is guaranteed to yield a fairly commensurate reduction in volume...this is basic physics.
No, to cut loudness in half you have to reduce power by 90% -- not 50%. Reducing amplifier power by 50% results in only a slightly noticable decrease in loudness (3dB) -- a fact I believe is common knowledge among audiophiles and technical lay people. See this short article: http://rds.yahoo.com/_ylt=A0geu611Yf...ves/power.html.
Quote:
Originally Posted by chriswufgator
You can't compensate for a 50% drop in power just with sensitivity, especially in an automotive application.
Well of course you can. It's easy. The sensitivity difference is just 3dB -- a small variation that is not uncommon among different speaker models.
Quote:
Originally Posted by chriswufgator
First off, you won't be able to find speakers that are going to allow you to make up the entire difference with a higher sensitivity rating.
Done! This speaker has a sensitivity rating of 95 dB: Infinity - Car Audio, and this one from the same manufacturer has a sensitivity rating of 92 dB: Infinity - Car Audio.
Quote:
Originally Posted by chriswufgator
That's why car speakers have low sensitivity ratings in the first place.
Ironically, you have this backward. A typical car speaker is far more efficient than a typical home speaker. Just pick any manufacturer website, read the sensitivity specs and see for yourself.
Quote:
Originally Posted by chriswufgator
...But mismatching the speakers as you are describing by 2:1 is going to do 2 things. One, the speaker you replace will never sound right and the L/R balance in the cabin will be way off. Two, it will cause a hot-spot on the amp at the location where that channel is fed. It's the same thing as running a 2-channel stereo amp at full volume only on, say, the R channel. You cause heating problems.
If you have understood what I posted above about speaker sensitivity and read the article I cited, you should now be disabused of your notion that there will be sonic problems with substituting a 4-ohm speaker for a 2-ohm. Regarding the "hot spot", it simply does not exist and your example is wrong. Driving just one channel to full power instead of two causes no problems for a stereo amplifier.
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Moderators: this thread is about audio, and audio is my particular area of expertise in electronics. I studied audio engineering under Professor Leach at Georgia Tech, a man who is renowned in the field: W. Marshall Leach, Jr.. For my senior project I designed, built, and tested a car stereo amplifier. Once I graduated from college my career path took a direction that had nothing to do with audio, but it has remained a hobby of mine and over the years I have designed and built numerous audio circuits for my own use. To the point: I'd like a little leeway here get a bit long-winded and maybe off-topic to discuss with Chris something I really enjoy.
No, to cut loudness in half you have to reduce power by 90% -- not 50%. Reducing amplifier power by 50% results in only a slightly noticable decrease in loudness (3dB) -- a fact I believe is common knowledge among audiophiles and technical lay people. See this short article:
Well of course you can. It's easy. The sensitivity difference is just 3dB -- a small variation that is not uncommon among different speaker models.
Done! This speaker has a sensitivity rating of 95 dB:
Ironically, you have this backward. A typical car speaker is far more efficient than a typical home speaker. Just pick any manufacturer website, read the sensitivity specs and see for yourself.
If you have understood what I posted above about speaker sensitivity and read the article I cited, you should now be disabused of your notion that there will be sonic problems with substituting a 4-ohm speaker for a 2-ohm. Regarding the "hot spot", it simply does not exist and your example is wrong. Driving just one channel to full power instead of two causes no problems for a stereo amplifier.
Bob, I am afraid you're missing things. You are also trying to talk about theory in a vacuum, and this is a car...with all that entails. If someone actually does what you are suggesting, they REALLY aren't going to be happy with the results.
Rather than going back and forth, I will just quote your OWN article that YOU posted to address your viewpoint...I will even highlight the relevant portions...
START article:
"So far, so good. But what if it's party time, and you're listening to music "very loud," a level defined as about 90 dB Sound Pressure Level (SPL), and your speakers are gobbling up swings of 15 to 20 watts per channel on those musical peaks.
Drink in hand, you advance to the volume control on your receiver thinking, "I'll just crank this up to make the music twice as loud," and you turn up the volume control until there's a 10 dB increase in the sound level. Now your party-time goal of "twice as loud" will make huge electrical demands on your nice little multi-channel receiver or power amp. The receiver must deliver ten times as much power to double the subjective loudness. Between 6 dB and 10 dB is double the volume level, where 6 dB is four times the power and 10 dB is 10 times the power. In the aforementioned example, the amp must produce 150 to 200 watts per channel for those peaks in loudness. Therefore, every 10-dB increase in acoustic loudness--from 80 dB to 90 dB, or 90 dB to 100 dB--requires ten times as much electrical power in watts.
That's all very well if you have a monster amplifier or multi-channel A/V receiver with huge reserves of power output (most of us don't). If not, watch out. Your receiver or amp may "clip" or distort (or both), which will put a clamp on the output of the amp. When you push your amplifier into overload or "clipping," several things may happen. First, the top and bottom of the waveforms (representing the audio signals) are clipped off, generating distortion. Next, the amplifier's protection circuits are activated, removing those portions of the signal that are causing the overload, generating distortion. And finally, the amplifier's power supply may fluctuate according to the demands of the music signals.
Not everyone is affected by this scenario, of course. Some people (increasingly few, it seems) don't listen to loud music. They like background levels, and with average speakers, background levels demand 1 watt or less of amplifier power. Or they may have very efficient speakers (Klipsch, Cerwin-Vega, Tannoy, and the like) that will play extremely loud using modest amplifiers, the trade-off being a very large degradation in tonal accuracy, a definite harshness, and a complete loss of off-axis performance that accompanies horn-loaded designs. But in many situations, speakers will be damaged and distorted sound will offend many ears...
No discussion of decibels, acoustic loudness, and electrical watts is complete without an explanation of loudspeaker "sensitivity." (Another way to define a speaker's sensitivity is to look at how efficiently the speaker converts electrical power, in watts, to acoustic sound output in decibels.) Let it be said in a general way that speakers are not very efficient or sensitive devices. They need a lot of electrical power input to produce relatively little acoustic output. Nevertheless, speakers do vary quite a bit in sensitivity.
To determine a speaker's sensitivity, we feed the speaker with 1 watt of amplifier power, using a test signal of pink noise, and measure in decibels how loud the sound is at a distance of 1 meter (about 3 feet). A lot of domestic hi-fi speakers measure in at about 89 or 90 dB SPL at 1 meter. Larger speakers, with bigger woofers and more drivers, typically produce greater acoustic output; smaller bookshelf models have to work harder, and their output is typically less, often between 86 and 88 dB SPL at 1 meter.
*Have you seen the size of car speakers, Bob? Get where I'm going with this???*
Placing the speaker in a room helps (the walls, ceiling, and floor reflect and reinforce the speaker's sound), adding about 4 dB to its output. For example, a speaker like Axiom's M80ti has a measured sensitivity in an anechoic chamber of 91 dB SPL at 1 watt at 1 meter. But putting the M80ti in a room raises its sensitivity rating to 95 dB SPL at 1 watt, 1 meter. A 95-dB sound level happens to be "very loud," as most of us would subjectively describe it. And it is--from 3 feet (1 meter) in front of the speaker. But let's move our listening seat back twice as far, to 6 feet. Guess what happens? We instinctively know that sound gets weaker as the distance from the source is increased, but by how much? A formula called the "inverse square law" tells us that when the distance from the source is doubled, the sound pressure weakens by 6 dB. Among sound engineers, there's a common saying: "6 dB per distance double." So at a 6-ft. distance, the M80ti is now producing 89 dB. Now let's double that distance again to 12 feet, a fairly common listening distance. The speaker now produces 83 dB, which isn't all that loud at all. And if you sat 24 feet away, a not uncommon distance in big rooms, the speaker would produce 77 dB SPL.
But what about stereo, I hear you shout. Here's another oddity of loudness and the decibel. When one speaker is producing a level of 90 dB, adding a second speaker playing at the same level only increases the overall loudness by 3 dB! (The loudness does not double!). So the two speakers in stereo produce a loudness level of 93 dB.
So adding a second M80ti will raise the loudness at 12 feet from 83 dB to 86 dB. And don't forget we're still using 1 watt of amplifier power output into Axiom's most sensitive speaker. But how loud are real-life instruments, orchestras and rock bands? Now, while 86 dB SPL is "fairly loud," it's not nearly as loud as what you might hear from a good seat at an actual rock concert or from an orchestra or pianist in a concert hall. A solo grand piano can reach peak levels of 109 dB SPL, a full orchestra and chorus in a concert hall will measure 106 dB, and a rock group, 120 dB SPL. [b]Now let's try and get our peak speaker sound levels to 96 dB, "twice as loud" as our 86-dB listening level. That isn't that difficult because right now we're only using 1 watt per channel to drive the M80ti's to 86 dB. So we'll need ten times as much power, or 10 watts, to reach 96 dB. Big deal. We've got lots more.
[b]But things begin to change, and rather dramatically. Let's push the M80ti's to what we might experience from a solo grand piano, 109 dB. We're at 96 dB with 10 watts per channel. Let's go to 106 dB. So that requires 10 x 10, or 100 watts. Close, but not quite there yet. Just 3 dB more. Remember, we have to double the power for a 3-dB increase in sound level. So 100 watts becomes 200 watts. Yikes! Our receiver has only 110 watts maximum output! We've run out of amplifier power! And what about the rock concert? Let's lower our expectations and aim for 119 dB. Going from 109 dB SPL, which needs 200 watts per channel, to 119 dB SPL (get out your ear plugs) is another 10-dB jump and--you do the math--that requires 10 x 200, or 2,000 watts per channel! From all this you can see the huge power requirements inherent in reproducing real-life acoustic sound levels in average or big rooms.
*Common sense that a convertible car has MUCH worse acoustic properties than a big room, since there are no reflective surfaces, right Bob?*
The M80ti's are tested to levels of 1,200 watts of input power so they come very close. But the truth is that if we are seeking real-life acoustic sound levels in our listening rooms, there's a very persuasive argument for very large, powerful amplifiers. And if your speakers are less sensitive (and many are), then the power demands rise even more dramatically. Sizeable rooms and greater listening distances will also increase power demands tremendously.
And what many of us don't realize until we hear it, is that clean undistorted loud sound often does not sound that "loud." The key here is that in most or our home listening, there are small amounts of distortion caused by a lack of dynamic headroom (but more on that next month). It's the distortion that makes it sound "loud" in a domestic setting. To remove those distortions and increase dynamic headroom relates to even more power. We've become accustomed to accepting some distortion with our reproduced music, because all amplifier's distortion ratings gradually increase as they approach their output limits or slightly clip the audio signals. When that happens, we turn down the volume, because distortion starts to intrude on our listening pleasure, and it sounds "too loud."
*And I think this pretty much says it all...*
The lesson in all this is that you can never have too much power, and that big amplifiers rarely damage speakers. Little amplifiers driven into clipping burn out speakers. In the scheme of high fidelity, that last barrier to realism is having enough power and being able to approximate real-life loudness levels.
END
Bob, even you have to admit this is classic...cause' if you read through that article, you quickly find that the authors are 100% saying the SAME EXACT THING as I have been all along...which is that you can't compensate for a lack of power solely with a higher sensitivity rating without having it sound like total crap!
And I would point out that, for this example, the authors were using the highest sensitivity speakers I've ever even heard of...and your idea, of course, STILL didn't work. And that was just trying to approximate real life loudness levels... Common sense dictates that, when you're tooling down I-95 at 70 (ok, maybe more like 90 in my case), you will need something a LOT louder...
As I have said all along, you also need POWER. Which you won't have if you swap out 2ohm speakers with 4ohm speakers while leaving the original amp, since you're DOUBLING resistance without increasing POWER. The amp is going to wind up operating at a higher percentage of its capacity all the time, which will yield a very noticeable increase in distortion and a huge reduction in overall sound quality. It will sound like complete and total crap! This is a convertible CAR, with background NOISE. Nobody is going to be listening at levels that draw 2 watts!
And I don't have anything backwards...kind of the reverse. As the article you were kind enough to save me the time to locate clearly indicates, as volume levels increase it takes exponentially MORE amplifier power to produce every relatively SMALL increase in loudness, regardless of sensitivity. Sensitivity helps a bit, but not a whole lot because (and here's the thing you are missing) sensitivity is NOT variable according to desired volume, while amplifier power requirements ARE, so sensitivity only goes so far.
Trying to power the same number and size of speakers while cutting the available power in HALF, and still expecting only a small decrease in volume in an automotive listening environment where the listening range is already limited to higher volumes, is NEVER going to work out for you, regardless of sensitivity, unless the amp was GROSSLY overpowered in the first place...which this one is not. A 50% reduction in power will yield a huge reduction in the music you are able to hear in the vehicle. And notice that I am not talking about a sound-shielded room with a meter, I am talking in the real world with a convertible car and lots of background noise. 90db is probably a minimum listening level in a poorly insulated vehicle in traffic (and forget about with the top down), and then depending on your speed and the ambient noise around you it just goes up from there...
An orchestra is 98db, so you can extrapolate from there that listening to music in a car (with far more ambient noise than a concert hall) would need to be around that, if not more, in order for you to hear the music. Reducing available amp power by 50% will actually (in my opinion) yield MORE than a 50% reduction in what you can hear, since the entire audible range for this vehicle in normal conditions is already narrowed down to probably 75db-80db and up. The factory amp in this car is already operating at a high percentage of its capacity at 2ohms, so reducing its output by 50% is going to have a LARGE negative effect, while increasing sensitivity is going to kill sound quality by allowing in all sorts of line noise that would normally be filtered out, and also because sound quality tends to degrade as the percentage of amp capacity used increases, regardless of the sensitivity rating of the speakers, as your own article clearly pointed out...
It's exactly what I said from the beginning...
Last edited by chriswufgator : 04-02-2008 at 11:01 AM.
I started running out of space in the above post, due to the board's character limit per post, but to put it in a nutshell Bob wants to dismiss a 3db or 5db difference as "minor", but in an automotive application (and especially one like this...a convertible) that is NOT a minor difference at all. That could very well be the difference between hearing the words in the music at 80mph and hearing garbled garbage.
Because of the exponential increase in required amp power needed to achieve a linear increase in sound quantity, you CANNOT compensate for underpowering a speaker installation by 50% just by switching to speakers with higher sensitivity, and still maintain decent sound quality. You will achieve a reduction in the amount of power required at lower listening levels by doing that, sure, but it doesn't help once you start getting into the higher volumes needed in a car, because you will still run out of power if you have doubled the resistance of the speakers at the same time you increased the sensitivity.
Amp power requirements increase exponentially with the desired volume level, while sensitivity is a set figure that does NOT actually effect power delivery from amp to speaker (like resistance does). Therefore, the latter cannot completely outweigh the former as the power draw on the amp increases, as a function of basic mathematics. This fact will become quickly and excessively apparent in a car audio installation, given the high power requirements placed on the system in the first place, compared to the capacity of the factory amp.
Sensitivity is just a measure of how much sound output a specific voltage will yield using a specific speaker. It is an AURAL measurement not an ELECTRICAL measurement, and in NO WAY affects power delivery or power requirements. Nor does it stay the same when you start to change the power input or volume output of the speaker. And you can have the most sensitive speaker in the world, and it's still going to sound like complete crap if you underpower it by trying to use an amp that was already maxed out on 2ohms to power 4ohm speakers! Lol. At anything but the lowest listening levels, one really has very little to do with the other...
And I have more news for you: The factory-tested sensitivity rating is a virtually WORTHLESS measurement when you get into car audio, because the actual sensitivity of the INSTALLED speaker will be grossly disparate with the figure produced in a lab test. Enclosures, door panels, speaker grilles, backing material, etc. etc. etc. etc. ad naseum will alter the sensitivity of each component when installed in the vehicle, to the point that to get a REAL idea of sensitivity you would need to measure it once it was ALREADY INSTALLED in the car. Otherwise, you may as well quote the price of tea in china as a sensitivity figure, it will probably be about as accurate as the lab-tested one for a car speaker once you install it...
Here is one of MANY threads and articles dealing with this:
And that STILL doesn't change the fact that sensitivity really has NOTHING AT ALL to do with POWER DELIVERY, which will be the problem here....well, actually, to be accurate LACK of power will be the problem here...
As if not being able to hear your music wouldn't already be bad enough, you will still run into yet another problem with distortion. By doubling resistance without increasing the power like Bob suggests, you will have the amp running at a higher percentage of its capacity to achieve the desired volume level for the environment. This will result in increased distortion and crappy sound quality.
I'm telling you, if you change the speakers to 4ohms, you have got to change the amp or you will be very displeased with the results. Then, like I said before, get ready to change the CD player and the head unit as well since they won't be compatible any longer.
The one work-around is what cthompson and I were discussing, where you use a DSP with an infinitely variable hot input to keep your stock head and amp and then use another aftermarket amp and aftermarket speakers. Keeping the stock amp and going to aftermarket speakers is a no-go in this case.
Last edited by chriswufgator : 04-02-2008 at 12:17 PM.
Vehicle: 1997 SL600 Silver with grey/dark metal interior, 140K miles
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Good Lord!
When I bought my SL600, the passenger side 6 inch speaker had a bad coil so it worked part time (maddening). I too was shocked at the high price for the cheaply produced 2 ohm paper factory speakers. Why not replace cheap with cheap.
I went to my local Autozone store and Jensen (very cheap) makes a 6 inch co-axial 2 ohm speaker. It uses a blue plastic woofer cone (no more water damage) with a foam surround (like the Bose). I tried the speaker with the co-ax powered, but it changed the sound dynamics too much so I clipped (cut) the co-ax tweeter feeds and now it sounds the same as the Bose system before (well, minus the bad coil).
This was 3 years ago and I think the Jensens cost maybe $30. Of course you can't see anything behind the fabric speaker covers, so no one can tell the difference.
When I bought my SL600, the passenger side 6 inch speaker had a bad coil so it worked part time (maddening). I too was shocked at the high price for the cheaply produced 2 ohm paper factory speakers. Why not replace cheap with cheap.
I went to my local Autozone store and Jensen (very cheap) makes a 6 inch co-axial 2 ohm speaker. It uses a blue plastic woofer cone (no more water damage) with a foam surround (like the Bose). I tried the speaker with the co-ax powered, but it changed the sound dynamics too much so I clipped (cut) the co-ax tweeter feeds and now it sounds the same as the Bose system before (well, minus the bad coil).
This was 3 years ago and I think the Jensens cost maybe $30. Of course you can't see anything behind the fabric speaker covers, so no one can tell the difference.
So you just went and bought whatever speaker had a 2ohm rating, and then fit it inside the bose assembly? Hmmm...that's a pretty good idea.
I never thought about buying a 2ohm from another auto installation. I was getting hung up on the fact that 2ohm speakers are usually only OEM parts...nobody does them on the aftermarket. But if another car company uses one in the same size, then yeah...swapping that out for the Bose one is not such a bad idea at all...
Well Chris, you've written quite a bit in your new posts, and I continue to disagree with nearly everything you write both from a technical perspective and from my own extensive, practical, hands-on experience. But I'll respond by simply stating that I stand by all that I have written on this thread; and I have no doubt that if an engineer worth his salt were to scrutinize all that I have posted, then that individual would have no disagreements with me.
Well Chris, you've written quite a bit in your new posts, and I continue to disagree with nearly everything you write both from a technical perspective and from my own extensive, practical, hands-on experience. But I'll respond by simply stating that I stand by all that I have written on this thread; and I have no doubt that if an engineer worth his salt were to scrutinize all that I have posted, then that individual would have no disagreements with me.
Ok...well...just because you disagree doesn't make you right. And I would absolutely welcome your asking an audio engineer to explain this to you. But in the meantime, I think we can figure out who's right just by looking at reality...
Bob, if your understanding of the relationship between sensitivity and resistance was even remotely correct, then why does anyone in car audio have to drop big $$$ on high-power amps in order to achieve decent sound quantity and quality?
Because according to your understanding of resistance and sensitivity, everyone would just buy highly sensitive speakers and have no trouble whatsoever using a cheap 25 watt amp, right? Following your logic, that would work out fine...
So according to you, people must be paying $1k+ (or a lot more...I once dropped $3k just for one Rockford T150004) for amp sets just because it makes them feel good? Maybe it's like electronic prozac? Or maybe they just look so pretty in the trunk? Maybe they figure a lighter wallet will help a bad back? Lol...
If you were at all correct, Rockford and Alpine would have gone bankrupt years ago, and nobody would ever produce an amp rated at more than about 10 watts...
Come on Bob, gimme a break...clearly that isn't the way things work, and common-sense alone tells you that. I've read your other posts, and you're way above the intelligence curve. On many (probably most) things, you obviously know a lot more than me...A/C being a recent example. But by this stage in this particular discussion, you have got to realize that something just isn't adding up with the point you've been making...
And you keep trying to say that speaker sensitivity is an electrical function. It's NOT, it's an aural measurement. Any sound engineer will tell you that! Heck, any first year electrcial engineering major will tell you that.
Think of it this way...when it comes to analyzing speaker performance, you have a "front office" and a "back office". The "front office" is the speaker's aural performance, and the "back office" is the speaker's power handling characteristics. Sensitivity is a "front office" function, and resistance is a "back office" function. Does one sort of depend on the other? To some sort of degree, sure. But are the two the same thing? No way.
You can compensate somewhat for one with the other, but only to a point, and there are a lot of tradeoffs.
And I still find it entertaining that the very article you told me to read in your earlier post confirms everything I am saying here, but I guess you aren't going to address that either, other than saying "I continue to disagree". So I guess you're disagreeing with your own article that you posted?
As for "extensive practical and hands-on experience", Captain Smith had more of that than you do and yet the Titanic still sits on the bottom of the atlantic. Everybody is wrong at some point. Happens to me daily. But that kind of statement is a cop-out...I brought up in detail the problems you will encounter when trying to use your logic to modify an audio system, so why not just address my (valid) concerns? Maybe I'll learn something new...
Last edited by chriswufgator : 04-03-2008 at 06:37 AM.
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