Speaker dust issues
08-07-2007, 03:45 PM
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Speaker dust issues
This impetus of this post came from a recommendation from RallyJon to frequently “Turn your radio volume up to maximum to purge any electrons that may have accumulated.” I agree wholeheartedly with this recommendation, but I feel that there is another factor that many drivers overlook.
I have noticed that there is a dust related problem in 993s (this may affect other cars as well) with rear speaker high frequency response. Dust settles on the surface of the cone increasing its mass. More mass reduces transient and high frequency response as the cone has to overcome the inertia created by the extra layer of dust.
I would suggest that when you are turning up the radio to purge the electrons as RallyJon suggested in his post here: https://rennlist.com/forums/showthre...=1#post4437623
that you perform this procedure at a speed of at least 45MPH or higher with the windows and sunroof open. This way as the cone tosses the dust particles up they get blown away rather than falling back down on the cone again.
A couple other problems occur here however. First the speaker grill is restrictive, so when high frequencies and transients are reproduced, as the cone is moving forward (or up in the case of the rear deck speakers) there will be an instantaneous damping affect because the factory grills have such small holes the pressure cant escape fast enough and a high pressure zone is created between the cone and the grill. Obvious to all is that the reverse happens on negative excursion of the cone - a mild vacuum is created.
Fabspeed I hear may be making carbon fiber speaker grills that leave the entire area over the cone open to prevent this pressure build up. The projected price I think $432 US a pair. I’m sure that there are some Rennlisters that have drilled out their own speaker grills for a similar and less expensive effect.
Having a drilled. or “open” speaker grill may also help with removal of the aforementioned dust particles.
One problem with the earlier solution of rolling down the windows and opening the sunroof and driving at least 45mph with the windows down to clean out the accumulated dust mass is:
With the speaker grills on, some of the larger and fuzzier of the dust particles may not make it through the stock grill and will remain, only to fall back on the cone. This effect is negated with the drilled or cut speaker grill.
Now I am sure there are a lot of Rennlisters who will argue, Porsche designed it that way so that must be the proper grill venting.
I understand this argument, especially with regards to heat. In a rear window the sunlight hits the speakers during the day and heats them up, by providing smaller holes, less sunlight penetrates and the cone doesn’t get as hot in this shade. Therefore the air mass inside stays cooler. With a cooler and denser air mass sound will propagate faster. So the cut or drilled speaker grills may not actually increase sound output as much as is claimed, especially on sunny days. Notice I said sunny, not hot, because the inside temperature of the speaker /grill assembly can get much hotter that the ambient outside air temperature when it is sunny. (Also remember that leaving the engine tray on can increase the temperature at the speaker at least .2 degrees F which can decrease speaker performance further (the speakers sit in holes in the insulation, so there is no heat dampening aside from the sound pad in the engine compartment)
While this may sound like a valid argument for keeping the stock speaker grills-(after all who is to argue with Porsche’s engineers,) remember, Porsche sells cars all over the world, so the same speaker grill has to be used in Seattle with more overcast days per year than in Phoenix. Also there is a rumor that Porsche used the smaller holes in order to get the stereo volume to comply with Swiss stereo rear speaker noise laws, (see section c of the infamous Automobillautsprechergeräuschgesetz.) Obviously, having region specific speaker grills would have raised the overall cost of the car.
I have put temperature sensors under the speaker grills and can attest to a .32 degree F drop in air temperature with the grills on vs. off, but the over all sound output seems to be the same due to the restrictive factory holes.
The dust factor however, contributes much more. There is easily a .001 micro Pascal pressure drop above 15kHZ, I haven’t done the math, but roughly that would equate to a .0001dB drop.
This is more important when tracking the car, as a driver needs the extra high frequency response due to the high frequency dampening created at the drivers’ ears by the helmet. It may not be all that important for those who don’t track their cars.
Some have recommended blowing the speaker cones off with compressed air, I would advise against that, because if the pressure is too high or to near the cone, the cone could be forced down and bottom out the voice coil and distort it causing it to no longer move freely in the magnet groove.
My recommendation for street driving is: Every 3000miles, (more frequently in dusty climates or if the car is used a lot with the windows down,) remove the speaker grills, roll down the windows and open the sunroof. Turn the radio up to maximum volume before distortion (This will vary depending on amplifier, head unit etc.) then gradually increase speed to at least 45MPH for at least five minutes or longer depending on the type of music used (see below). For people who track their cars, there is a high percentage of oil and rubber particles in the dust, these are much heavier than particles in standard street dust. These can increase the mass even further. For these drivers the car should be taken up to at least 75 MPH to knock loose the heavier particles.
I am sure there have been many articles, and posts written on this subject, but admittedly I have not done a search, Ill just put out my recommendations on program material to be played while cleaning the dust out of the rear speakers:
Some are vehemently against classical, due to its lack of transients. Others claim “what can be more transient than a full orchestra hit?” After all classical music is some of the most dynamic music ever recorded. While this is true, it’s not just the dynamics that are of concern, it is the repetition of the dynamics that is needed to break loose stubborn dust particles. Unfortunately for a lot of Rennlisters, the best music for this procedure seems to be Hip-hop or rap. With very punchy lows and compressed snappy snare drums nothing works better to work the dust particles free. I would recommend using at least three different songs, at three different tempos, to overcome “dust particle bounce resonance” Although finding three different Hip-hop songs at different tempos may be difficult.
This post is so long I wont get into the effect on bass response in the rear deck speakers when decklid shocks are worn
I would be very interested on what Steve Weiner and Rod Birch have to say on this subject
I have noticed that there is a dust related problem in 993s (this may affect other cars as well) with rear speaker high frequency response. Dust settles on the surface of the cone increasing its mass. More mass reduces transient and high frequency response as the cone has to overcome the inertia created by the extra layer of dust.
I would suggest that when you are turning up the radio to purge the electrons as RallyJon suggested in his post here: https://rennlist.com/forums/showthre...=1#post4437623
that you perform this procedure at a speed of at least 45MPH or higher with the windows and sunroof open. This way as the cone tosses the dust particles up they get blown away rather than falling back down on the cone again.
A couple other problems occur here however. First the speaker grill is restrictive, so when high frequencies and transients are reproduced, as the cone is moving forward (or up in the case of the rear deck speakers) there will be an instantaneous damping affect because the factory grills have such small holes the pressure cant escape fast enough and a high pressure zone is created between the cone and the grill. Obvious to all is that the reverse happens on negative excursion of the cone - a mild vacuum is created.
Fabspeed I hear may be making carbon fiber speaker grills that leave the entire area over the cone open to prevent this pressure build up. The projected price I think $432 US a pair. I’m sure that there are some Rennlisters that have drilled out their own speaker grills for a similar and less expensive effect.
Having a drilled. or “open” speaker grill may also help with removal of the aforementioned dust particles.
One problem with the earlier solution of rolling down the windows and opening the sunroof and driving at least 45mph with the windows down to clean out the accumulated dust mass is:
With the speaker grills on, some of the larger and fuzzier of the dust particles may not make it through the stock grill and will remain, only to fall back on the cone. This effect is negated with the drilled or cut speaker grill.
Now I am sure there are a lot of Rennlisters who will argue, Porsche designed it that way so that must be the proper grill venting.
I understand this argument, especially with regards to heat. In a rear window the sunlight hits the speakers during the day and heats them up, by providing smaller holes, less sunlight penetrates and the cone doesn’t get as hot in this shade. Therefore the air mass inside stays cooler. With a cooler and denser air mass sound will propagate faster. So the cut or drilled speaker grills may not actually increase sound output as much as is claimed, especially on sunny days. Notice I said sunny, not hot, because the inside temperature of the speaker /grill assembly can get much hotter that the ambient outside air temperature when it is sunny. (Also remember that leaving the engine tray on can increase the temperature at the speaker at least .2 degrees F which can decrease speaker performance further (the speakers sit in holes in the insulation, so there is no heat dampening aside from the sound pad in the engine compartment)
While this may sound like a valid argument for keeping the stock speaker grills-(after all who is to argue with Porsche’s engineers,) remember, Porsche sells cars all over the world, so the same speaker grill has to be used in Seattle with more overcast days per year than in Phoenix. Also there is a rumor that Porsche used the smaller holes in order to get the stereo volume to comply with Swiss stereo rear speaker noise laws, (see section c of the infamous Automobillautsprechergeräuschgesetz.) Obviously, having region specific speaker grills would have raised the overall cost of the car.
I have put temperature sensors under the speaker grills and can attest to a .32 degree F drop in air temperature with the grills on vs. off, but the over all sound output seems to be the same due to the restrictive factory holes.
The dust factor however, contributes much more. There is easily a .001 micro Pascal pressure drop above 15kHZ, I haven’t done the math, but roughly that would equate to a .0001dB drop.
This is more important when tracking the car, as a driver needs the extra high frequency response due to the high frequency dampening created at the drivers’ ears by the helmet. It may not be all that important for those who don’t track their cars.
Some have recommended blowing the speaker cones off with compressed air, I would advise against that, because if the pressure is too high or to near the cone, the cone could be forced down and bottom out the voice coil and distort it causing it to no longer move freely in the magnet groove.
My recommendation for street driving is: Every 3000miles, (more frequently in dusty climates or if the car is used a lot with the windows down,) remove the speaker grills, roll down the windows and open the sunroof. Turn the radio up to maximum volume before distortion (This will vary depending on amplifier, head unit etc.) then gradually increase speed to at least 45MPH for at least five minutes or longer depending on the type of music used (see below). For people who track their cars, there is a high percentage of oil and rubber particles in the dust, these are much heavier than particles in standard street dust. These can increase the mass even further. For these drivers the car should be taken up to at least 75 MPH to knock loose the heavier particles.
I am sure there have been many articles, and posts written on this subject, but admittedly I have not done a search, Ill just put out my recommendations on program material to be played while cleaning the dust out of the rear speakers:
Some are vehemently against classical, due to its lack of transients. Others claim “what can be more transient than a full orchestra hit?” After all classical music is some of the most dynamic music ever recorded. While this is true, it’s not just the dynamics that are of concern, it is the repetition of the dynamics that is needed to break loose stubborn dust particles. Unfortunately for a lot of Rennlisters, the best music for this procedure seems to be Hip-hop or rap. With very punchy lows and compressed snappy snare drums nothing works better to work the dust particles free. I would recommend using at least three different songs, at three different tempos, to overcome “dust particle bounce resonance” Although finding three different Hip-hop songs at different tempos may be difficult.
This post is so long I wont get into the effect on bass response in the rear deck speakers when decklid shocks are worn
I would be very interested on what Steve Weiner and Rod Birch have to say on this subject
08-07-2007, 04:23 PM
#2
Seared
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Andrew,
That made my afternoon!
I've found that removing the speaker undertrays will significantly aid in the reproduction of mid-range tones.
Andreas
That made my afternoon!
I've found that removing the speaker undertrays will significantly aid in the reproduction of mid-range tones.
Andreas
08-07-2007, 04:38 PM
#4
Race Car
Originally Posted by Amfab
I have put temperature sensors under the speaker grills and can attest to a .32 degree F drop in air temperature with the grills on vs. off, but the over all sound output seems to be the same due to the restrictive factory holes.
The dust factor however, contributes much more. There is easily a .001 micro Pascal pressure drop above 15kHZ, I haven’t done the math, but roughly that would equate to a .0001dB drop.
This post is so long I wont get into the effect on bass response in the rear deck speakers when decklid shocks are worn
The dust factor however, contributes much more. There is easily a .001 micro Pascal pressure drop above 15kHZ, I haven’t done the math, but roughly that would equate to a .0001dB drop.
This post is so long I wont get into the effect on bass response in the rear deck speakers when decklid shocks are worn
One-ten-thousandth of a decibel, .32 of a degree? What?
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08-07-2007, 05:40 PM
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Rich, at the risk of being called an armchair 'expert', handling dynamicist & Porsche reverse engineer, or a kettle black caller, I would consider this to be an issue with Cabs also, especially with one driven as much in all conditions as yours- although the dynamics work a little differently.
In case you are wondering where my expertise on this subject comes from, I was an acoustic engineer involved in designing sound systems for late model Zeppelins in a former life. From that experience, recalled during past regression therapy sessions I can say that this has been an issue plaguing German speaker placement in motorized transport since the late 1920s.
Anyway, enough of my credentials, back to the topic.
The dust layer would tend to accumulate on the bottom half of the cone, because it is not quite vertical, or past vertical like the top half of the cone. The added dust mass at the bottom would cause the top half of the cone to out-accelerate the bottom half, so the resultant excursion angle would tend to focus the sound in a more downward direction, which may have been how Porsche originally intended it as the rear seats can really only accommodate small children, who would obviously be shorter.
So the rear speakers over time may actually increase in listenability for children or smaller friends. However for the front passenger or driver the sound would be directed away (downward) and therefore some high frequency or transient response would be diminished for the people in the front.
Another thing to consider not just for cabs, but for coupes and targas and merlots as well is the absorption coefficient of small children. A friend of mine who does a lot of AutoX and other racing absolutely refuses to take his children when he is racing because the high frequency loss due to their presence in the rear. Now you may think this extreme, but consider the childrens' absorption combined with the above mentioned drivers' helmet loss, and the fact that he is 56 years old so his ears have some high frequency loss anyway, he could possibly completely miss a high note off of a Miles Davis CD in the middle of a chicane, which could be distracting enough to be dangerous. So even though his wife tries to dress them in as light and sonically reflective outfits as possible, and wont let them have any soda or juice box drinks before an event, (the extra fluid acts as a sonic dampener, plus he has to pull over to let them pee, which has been shown to reduce lap times) he still refuses to take the children in the back seat during the race.
I hope this helps
In case you are wondering where my expertise on this subject comes from, I was an acoustic engineer involved in designing sound systems for late model Zeppelins in a former life. From that experience, recalled during past regression therapy sessions I can say that this has been an issue plaguing German speaker placement in motorized transport since the late 1920s.
Anyway, enough of my credentials, back to the topic.
The dust layer would tend to accumulate on the bottom half of the cone, because it is not quite vertical, or past vertical like the top half of the cone. The added dust mass at the bottom would cause the top half of the cone to out-accelerate the bottom half, so the resultant excursion angle would tend to focus the sound in a more downward direction, which may have been how Porsche originally intended it as the rear seats can really only accommodate small children, who would obviously be shorter.
So the rear speakers over time may actually increase in listenability for children or smaller friends. However for the front passenger or driver the sound would be directed away (downward) and therefore some high frequency or transient response would be diminished for the people in the front.
Another thing to consider not just for cabs, but for coupes and targas and merlots as well is the absorption coefficient of small children. A friend of mine who does a lot of AutoX and other racing absolutely refuses to take his children when he is racing because the high frequency loss due to their presence in the rear. Now you may think this extreme, but consider the childrens' absorption combined with the above mentioned drivers' helmet loss, and the fact that he is 56 years old so his ears have some high frequency loss anyway, he could possibly completely miss a high note off of a Miles Davis CD in the middle of a chicane, which could be distracting enough to be dangerous. So even though his wife tries to dress them in as light and sonically reflective outfits as possible, and wont let them have any soda or juice box drinks before an event, (the extra fluid acts as a sonic dampener, plus he has to pull over to let them pee, which has been shown to reduce lap times) he still refuses to take the children in the back seat during the race.
I hope this helps
08-08-2007, 08:49 PM
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Rich, you are absolutely right, I shouldn't mix up my units. Thats what comes from being American and having a past life as a European I suppose.
Even though Im not sure it is the best way to go I am posting a picture of the open style carbon fiber grills I referred to earlier. The company is mFabspeed I believe.
Even though Im not sure it is the best way to go I am posting a picture of the open style carbon fiber grills I referred to earlier. The company is mFabspeed I believe.
08-12-2007, 02:28 PM
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Due to the recent threads on removing the belts for more performance, I wanted to update this thread because of an issue not previously mentioned: The increased power draw of the speaker due to the dust layer. Previous posts only referred to the diminished sound quality, but it is important to remember, if you have to move more mass (cone and dust, rather than just simply cone), you need more energy to move it - even if the transients aren't being reproduced it is only because of the extra mass, the amplifier is still trying to move the mass back and forth, therefore more electricity is being drawn from the system, putting a bigger strain on the alternator, and therefore the motor.
Of course by removing the alternator belt, as Andreas so brilliantly did, you eliminate this power drain. However, when listening to the stereo system, the extra mass will then dissipate battery power faster. So for those removing their belts, be sure to clean off the speaker dust as described above for more battery life. For those who don't it will still make a performance difference, because of reduced load on the alternator.
Another suggestion would be to disable the belt sensor, the dash warning light will also cause battery drain faster.
Another benefit of removing the fan belt is that the fan stops turning. This means air is not being forced through the motor to the ground below. This air can kick up small dust particles, even on what appears to be rather clean asphalt. This dust, especially if the car is standing still when stopped at a stop light, or sitting in a driveway, can rise into the air and land, you guessed it, on the speaker cones. This problem is more apparent on Cabs and Targas with the roofs open, but it can affect coupes as well. This is why at stoplights or in the driveway, if you still insist on running your car with a fan belt, be sure the top is up, sunroof is closed and windows are closed.
Pollen filters should also be properly installed. Pollen, due to its nature, tends to contain more moisture than regular dust, and therefore accumulation of pollen on the speakers can actually cause more of a problem than regular dust. This is why Porsche installed them in the first place, to prevent "pollen cone loss" (Blütenstaubausgleichstromverlust). You can disassemble the blower housing to check to see that the pollen filters are properly installed, but an easier way is to simply roll up the windows, close the roof and play Hip Hop music at maximum volume for five minutes, then check for sneezing or watery eyes. If you or anyone in the car exhibits these symptoms, you have a cone-pollen issue. In case you are wondering why Porsche did not install dust filters and instead went for the more porous pollen filters, it is because back in the 90's dust cone loss was not percieved to be as serious a problem, perhaps advancement in digital audio measuring and test equipment is what brought this serious issue to light.
It is my understanding the the 996, 997 and Boxters all have dust filters rather than simple pollen filters. (but don't tell them about this, I dont want a bunch of water cooled guys coming over to this forum trashing 993s for bad transient response due to our "archaic" filters. On the other hand it is also my understanding that the watercooled cars have a Check Speakers Light that comes on every time the amplifier notices an impedance increase, which will happen as mass increases on the cones, because both the inductive and capacitive reactance will increase as cone mass increases. It was designed as a warning for extra mass due to dust and or pollen, but from what I've read on the 996 forums, while it does let you know when it is time to clean the cones, it is a big problem in humid climates. Porsche supplied paper speaker cones on all its cars so in humid climates these cones can absorb enough moiture to increase mass enough to trigger the CSL. Some think that this was done on purpose to get people to take their cars into the dealer for service.
Those of you with OBDII scanners will notice your device probably doesn't have a way of resetting the CSL. I haven't found one that does.
So if a 996 person starts bashing you for old style pollen filters, hit him back with, "Well, at least we don't have to deal with the CSL everytime we go to the beach!" (Due to customer complaints, 997 now have heated speaker baskets which fix this problem by evaporation)
Of course by removing the alternator belt, as Andreas so brilliantly did, you eliminate this power drain. However, when listening to the stereo system, the extra mass will then dissipate battery power faster. So for those removing their belts, be sure to clean off the speaker dust as described above for more battery life. For those who don't it will still make a performance difference, because of reduced load on the alternator.
Another suggestion would be to disable the belt sensor, the dash warning light will also cause battery drain faster.
Another benefit of removing the fan belt is that the fan stops turning. This means air is not being forced through the motor to the ground below. This air can kick up small dust particles, even on what appears to be rather clean asphalt. This dust, especially if the car is standing still when stopped at a stop light, or sitting in a driveway, can rise into the air and land, you guessed it, on the speaker cones. This problem is more apparent on Cabs and Targas with the roofs open, but it can affect coupes as well. This is why at stoplights or in the driveway, if you still insist on running your car with a fan belt, be sure the top is up, sunroof is closed and windows are closed.
Pollen filters should also be properly installed. Pollen, due to its nature, tends to contain more moisture than regular dust, and therefore accumulation of pollen on the speakers can actually cause more of a problem than regular dust. This is why Porsche installed them in the first place, to prevent "pollen cone loss" (Blütenstaubausgleichstromverlust). You can disassemble the blower housing to check to see that the pollen filters are properly installed, but an easier way is to simply roll up the windows, close the roof and play Hip Hop music at maximum volume for five minutes, then check for sneezing or watery eyes. If you or anyone in the car exhibits these symptoms, you have a cone-pollen issue. In case you are wondering why Porsche did not install dust filters and instead went for the more porous pollen filters, it is because back in the 90's dust cone loss was not percieved to be as serious a problem, perhaps advancement in digital audio measuring and test equipment is what brought this serious issue to light.
It is my understanding the the 996, 997 and Boxters all have dust filters rather than simple pollen filters. (but don't tell them about this, I dont want a bunch of water cooled guys coming over to this forum trashing 993s for bad transient response due to our "archaic" filters. On the other hand it is also my understanding that the watercooled cars have a Check Speakers Light that comes on every time the amplifier notices an impedance increase, which will happen as mass increases on the cones, because both the inductive and capacitive reactance will increase as cone mass increases. It was designed as a warning for extra mass due to dust and or pollen, but from what I've read on the 996 forums, while it does let you know when it is time to clean the cones, it is a big problem in humid climates. Porsche supplied paper speaker cones on all its cars so in humid climates these cones can absorb enough moiture to increase mass enough to trigger the CSL. Some think that this was done on purpose to get people to take their cars into the dealer for service.
Those of you with OBDII scanners will notice your device probably doesn't have a way of resetting the CSL. I haven't found one that does.
So if a 996 person starts bashing you for old style pollen filters, hit him back with, "Well, at least we don't have to deal with the CSL everytime we go to the beach!" (Due to customer complaints, 997 now have heated speaker baskets which fix this problem by evaporation)
08-12-2007, 05:38 PM
#15
Seared
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Originally Posted by Amfab
Due to the recent threads on removing the belts for more performance...
Andreas
