I think a better understanding of electricity will help me out as I try to learn more about installs..If anywone would care to elaborate on Ohm's law - or anthing else that would apply such as the unit of measure of everything and definitions I think it will be a big help...
Replies (8)
big_bass_chase on 06/28/2007 18:49:36
Well I guess I should've used the clubknowledge search engine before posting the new topic, as I see its already been covered to some degree...Feel free to still post reply's, cant hurt huh?
swez on 06/28/2007 20:51:02
One very helpful chart I use as a quick lookup and conversion chart for Ohm's law:
http://www.installer.com/tech/ohmslaw.html
If we know 2 parameters of a given circuit, one can calculate them all
Power (Watts)
Voltage (E)
Current (I)
Ohms (R)
Swez
MrBrownstone on 06/29/2007 15:53:21
another great comparison is that electricity is a lot like water.
There is a supply (alternator)
There is storage (battery & caps)
There is a hose (wiring)
There is demand (volume)
From a technical standpoint, electricity is a lot more complicated. Fun as it may seem, the only part of your car that is DC current is the power supply. Once the electronics take over, everything is in DC.
I'll look for a better reference later today. What specifically do you need to know about?
big_bass_chase on 06/29/2007 20:43:08
There's nothing in particular, I'm just trying to re-cap on some of the generalized topics..It helps to have a better understanding of what I'd be dealing with on a day to day basis.
swez on 06/29/2007 22:20:57
This is a hard thing to do on this forum. Most of us are problem solvers and need some direction in order to home in on a specific topic.
Some of us are techs, installers or serious hobbiest. Teaching in free style is pretty hard without some specific direction. It seems we do best with directed topics on a specific topic, need or problem to resolve.
When I first came to this forum, I had to break out my old electronics text books and get back in the groove with basic electronics and then advanced ones later. It had been 20 years since I really had a need for that type of info, so it was a crash course that came back in short order. But it was a directed/focused effort as well.
If I needed ohmic load calculations, went there. If it was about power and efficiencies, I'd go there. If it was about active and passive filter... I did not study the whole book from cover to cover like in a class room. I only grabbed what was needed and expanded as needed. That helped a lot and this may help you too. (It depends on what you want to learn and need to know)
In a nutshell, ask specific questions when possible and we'll try to help out.
Swez
big_bass_chase on 06/30/2007 23:17:31
Ok, Take this paragraph for instance...I've looked this over a few times and I cant really understand most of it...What exaclty is 90db SPL, 1w1m??
What is logrithmic, linear??
If we look at wattage to a given sub, (90dB SPL, 1w/1m) and feed it 500 watts, we get X SPL. Under the same conditions, we now feed the sub 1000 watts and see an SPL # of X + 3dB. SPL and wattage are logrithmic, not linear.
swez on 07/1/2007 12:04:02
Quote: "What exaclty is 90db SPL, 1w1m??"
This tells us a speaker's efficiency rating. This is often measured in a special soud proof chamber and the SPL is measured by a calibrated microphone and the speaker is not in any form of enclosure. (It is often suspended in free air... no box) The power applied to the speaker is often referenced at 2.83 volts input power and often at a specific frequency too. (Frequency used is dependent on the speaker function. (Sub, woofer, full range or tweeter)
Logrithmic and linearity: Speaker SPL is measured on a log graph and they take SPL plots at a wide range of frequencies and plot SPL as noted above. Here's a good example of a given speaker measured on a logrithmic graph:
http://www.partsexpress.com/pdf/295-120.pdf
This is a log graph plot of a the Dayton ST305-8 12" Series II Woofer. The left vertical side of this graph showes SPL. The lower part of this chart, (Horizontal part) of the graph shows the frequency steps in log style format.
Note the "linear ramp" of SPL as frequency rises from 20 - 100 Hz. The peak output of this speaker is between 100 - 200 Hz and is reasonably "flat" from 70 - 900 Hz. ("Flat" means same SPL #'s, +/- 2dB)
This plot shows the speaker in not "linear or flat" above 900 Hz. (See how the plot spikes up or down in irregular patterns above 900 Hz.?)
Looking at this plot, if we installed it in a given enclosure, (1.0 ft^3 sealed) it would be usable as a sub woofer between 35 - 120 Hz. In a ported box we'd see nice bass performance when tuned to about 40 Hz.
This speaker would be a decent subwoofer for car audio apps. (Sealed or Ported)
It is also a very good extended range MB/MR driver too. The highest output, (Efficiency) is nice and relatively flat between 70 - 900 Hz. That says a very good MB driver with good extended Midrange properties. This speaker would not be much good above 1000 Hz. It would make for a nice woofer in a solid 2-way or 3-way HT system, depending on the MR/TW components used. (Just a fair subwoofer though)
Does that give you an idea how to interpret log plots now?
Quote: "If we look at wattage to a given sub, (90dB SPL, 1w/1m) and feed it 500 watts, we get X SPL. Under the same conditions, we now feed the sub 1000 watts and see an SPL # of X + 3dB. SPL and wattage are logrithmic, not linear."
Here, there are many factors to consider If we double the input power, we get a +3 dB increase in SPL of a given speaker/sub.
In the woofer listed above, note the SPL # on the plot at say 40 Hz. It is about 85dB at 2.83 volts. (equal to an 8 ohm sub getting 1 watt of power at 40 Hz, mike at 1 meter away and no enclosure) Since the voice coil is actually 4 ohms, if we feed it 2.83 volts, that is actually 2 watts of power at 40 Hz, = +3bB already. Here's how power and dB work. Let's use the woofer and plot SPL at 40 Hz.
1 watt = +82 dB SPL @ 40 Hz, (No enclosure used)
2 watts = +85 dB....
4 watts = +88 dB...
8 watts = +91 dB...
16 watts= +94 dB...
32 watts= +97 db...
64 watts= +100 db...
132 watts = 103 dB...
264 watts = 106 dB...
528 watts = 109 db...
1056 watts = 112 dB
Now, if we made an enclosure for the woofer and installed it into a car, we have some added free SPL available from the enclosure and a big boost from "cabin gain" affects.
The box will give us +3 to +6 dB more bass, depending on the size of the box and whether it's sealed or ported. (Not a bad thing huh?) However, depending on the vehicle we have to work with, we can pick up an additional 10-15 more dB of free SPL as well. (Small cars are on the low side while large SUV's can deliver +15dB of "cabin gain" affect if not more.
This is not an exhaustive explanation by any means. There are other tricks some SPL Comp guys use to really kick up the SPL in their rides. Vented enclosures, BandPass and variations of the two can produce dramatic results in SPL when computer aided designs and advanced tuning techniques are employed.
The other trick is to eliminate air leaks, reduce panel flexing and make the vehicle as rattle free as possible. Many use "One Note Wonder" enclosure designs that determine the resonant frequency of the vehicle and tune their enclosures and test signals to the vehicle's resonance. This process takes years of experience, trial and error and loads of patience and $$$ to get there. These guys use huge amps, extra ALTs/BATs and enclosure designs that can produce over 175 dB of bass SPL in a finely tuned SPL rig.
I don't have much interest in huge SPL Comps details. For those who do, let them eat cake and enjoy the whole thing. It takes years to master all the minute details for World Class SPL rigs. (Not my cup of tea is all)
Hope that helps,
Swez
jamesp on 07/2/2007 09:03:04
Almost everything you need to know is explained well fron the link below. Look on the right side and click on pages of interest or start from the beginning and work your way thru....
http://www.clubknowledge.com/cgi-bin/car_audio_faq/faq.cgi?ourl=7
Replies (8)
big_bass_chase on 06/28/2007 18:49:36
Well I guess I should've used the clubknowledge search engine before posting the new topic, as I see its already been covered to some degree...Feel free to still post reply's, cant hurt huh?
swez on 06/28/2007 20:51:02
One very helpful chart I use as a quick lookup and conversion chart for Ohm's law:
http://www.installer.com/tech/ohmslaw.html
If we know 2 parameters of a given circuit, one can calculate them all
Power (Watts)
Voltage (E)
Current (I)
Ohms (R)
Swez
MrBrownstone on 06/29/2007 15:53:21
another great comparison is that electricity is a lot like water.
There is a supply (alternator)
There is storage (battery & caps)
There is a hose (wiring)
There is demand (volume)
From a technical standpoint, electricity is a lot more complicated. Fun as it may seem, the only part of your car that is DC current is the power supply. Once the electronics take over, everything is in DC.
I'll look for a better reference later today. What specifically do you need to know about?
big_bass_chase on 06/29/2007 20:43:08
There's nothing in particular, I'm just trying to re-cap on some of the generalized topics..It helps to have a better understanding of what I'd be dealing with on a day to day basis.
swez on 06/29/2007 22:20:57
This is a hard thing to do on this forum. Most of us are problem solvers and need some direction in order to home in on a specific topic.
Some of us are techs, installers or serious hobbiest. Teaching in free style is pretty hard without some specific direction. It seems we do best with directed topics on a specific topic, need or problem to resolve.
When I first came to this forum, I had to break out my old electronics text books and get back in the groove with basic electronics and then advanced ones later. It had been 20 years since I really had a need for that type of info, so it was a crash course that came back in short order. But it was a directed/focused effort as well.
If I needed ohmic load calculations, went there. If it was about power and efficiencies, I'd go there. If it was about active and passive filter... I did not study the whole book from cover to cover like in a class room. I only grabbed what was needed and expanded as needed. That helped a lot and this may help you too. (It depends on what you want to learn and need to know)
In a nutshell, ask specific questions when possible and we'll try to help out.
Swez
big_bass_chase on 06/30/2007 23:17:31
Ok, Take this paragraph for instance...I've looked this over a few times and I cant really understand most of it...What exaclty is 90db SPL, 1w1m??
What is logrithmic, linear??
If we look at wattage to a given sub, (90dB SPL, 1w/1m) and feed it 500 watts, we get X SPL. Under the same conditions, we now feed the sub 1000 watts and see an SPL # of X + 3dB. SPL and wattage are logrithmic, not linear.
swez on 07/1/2007 12:04:02
Quote: "What exaclty is 90db SPL, 1w1m??"
This tells us a speaker's efficiency rating. This is often measured in a special soud proof chamber and the SPL is measured by a calibrated microphone and the speaker is not in any form of enclosure. (It is often suspended in free air... no box) The power applied to the speaker is often referenced at 2.83 volts input power and often at a specific frequency too. (Frequency used is dependent on the speaker function. (Sub, woofer, full range or tweeter)
Logrithmic and linearity: Speaker SPL is measured on a log graph and they take SPL plots at a wide range of frequencies and plot SPL as noted above. Here's a good example of a given speaker measured on a logrithmic graph:
http://www.partsexpress.com/pdf/295-120.pdf
This is a log graph plot of a the Dayton ST305-8 12" Series II Woofer. The left vertical side of this graph showes SPL. The lower part of this chart, (Horizontal part) of the graph shows the frequency steps in log style format.
Note the "linear ramp" of SPL as frequency rises from 20 - 100 Hz. The peak output of this speaker is between 100 - 200 Hz and is reasonably "flat" from 70 - 900 Hz. ("Flat" means same SPL #'s, +/- 2dB)
This plot shows the speaker in not "linear or flat" above 900 Hz. (See how the plot spikes up or down in irregular patterns above 900 Hz.?)
Looking at this plot, if we installed it in a given enclosure, (1.0 ft^3 sealed) it would be usable as a sub woofer between 35 - 120 Hz. In a ported box we'd see nice bass performance when tuned to about 40 Hz.
This speaker would be a decent subwoofer for car audio apps. (Sealed or Ported)
It is also a very good extended range MB/MR driver too. The highest output, (Efficiency) is nice and relatively flat between 70 - 900 Hz. That says a very good MB driver with good extended Midrange properties. This speaker would not be much good above 1000 Hz. It would make for a nice woofer in a solid 2-way or 3-way HT system, depending on the MR/TW components used. (Just a fair subwoofer though)
Does that give you an idea how to interpret log plots now?
Quote: "If we look at wattage to a given sub, (90dB SPL, 1w/1m) and feed it 500 watts, we get X SPL. Under the same conditions, we now feed the sub 1000 watts and see an SPL # of X + 3dB. SPL and wattage are logrithmic, not linear."
Here, there are many factors to consider If we double the input power, we get a +3 dB increase in SPL of a given speaker/sub.
In the woofer listed above, note the SPL # on the plot at say 40 Hz. It is about 85dB at 2.83 volts. (equal to an 8 ohm sub getting 1 watt of power at 40 Hz, mike at 1 meter away and no enclosure) Since the voice coil is actually 4 ohms, if we feed it 2.83 volts, that is actually 2 watts of power at 40 Hz, = +3bB already. Here's how power and dB work. Let's use the woofer and plot SPL at 40 Hz.
1 watt = +82 dB SPL @ 40 Hz, (No enclosure used)
2 watts = +85 dB....
4 watts = +88 dB...
8 watts = +91 dB...
16 watts= +94 dB...
32 watts= +97 db...
64 watts= +100 db...
132 watts = 103 dB...
264 watts = 106 dB...
528 watts = 109 db...
1056 watts = 112 dB
Now, if we made an enclosure for the woofer and installed it into a car, we have some added free SPL available from the enclosure and a big boost from "cabin gain" affects.
The box will give us +3 to +6 dB more bass, depending on the size of the box and whether it's sealed or ported. (Not a bad thing huh?) However, depending on the vehicle we have to work with, we can pick up an additional 10-15 more dB of free SPL as well. (Small cars are on the low side while large SUV's can deliver +15dB of "cabin gain" affect if not more.
This is not an exhaustive explanation by any means. There are other tricks some SPL Comp guys use to really kick up the SPL in their rides. Vented enclosures, BandPass and variations of the two can produce dramatic results in SPL when computer aided designs and advanced tuning techniques are employed.
The other trick is to eliminate air leaks, reduce panel flexing and make the vehicle as rattle free as possible. Many use "One Note Wonder" enclosure designs that determine the resonant frequency of the vehicle and tune their enclosures and test signals to the vehicle's resonance. This process takes years of experience, trial and error and loads of patience and $$$ to get there. These guys use huge amps, extra ALTs/BATs and enclosure designs that can produce over 175 dB of bass SPL in a finely tuned SPL rig.
I don't have much interest in huge SPL Comps details. For those who do, let them eat cake and enjoy the whole thing. It takes years to master all the minute details for World Class SPL rigs. (Not my cup of tea is all)
Hope that helps,
Swez
jamesp on 07/2/2007 09:03:04
Almost everything you need to know is explained well fron the link below. Look on the right side and click on pages of interest or start from the beginning and work your way thru....
http://www.clubknowledge.com/cgi-bin/car_audio_faq/faq.cgi?ourl=7
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