Hi, I have been trying to learn a little about car audio lately and I am as usual, confused about the function of crossovers. My component speakers have 12dB/ octave passive crossovers and my 4 channel amp has a selectable switch for high pass, all pass or low pass. I assumed that if i chose, say, high pass and dialed the control to 300 Hz, that nothing under 300Hz would pass to the speaker. Now I find that the more dB's per octave the crossover has, the steeper the slope of the graph and the more confused I get.
Could someone explain or recommend a source for me to learn more about exactly what they do.Is the attenuation of a certain crossover signal point a linear function or does it block the signal at the selected crossover point completly? Thanks for the help...JamesP
Replies (15)
jamesp on 02/3/2007 14:56:44
I forgot to mention that I was trying to play with WinISD a bit and my sub was not in the data base. It is an Alpine SWR 1242D. Does anyone have the specs entered that could shoot me the file. again, thanks.
swez on 02/3/2007 20:58:12
You have the right idea. Crossovers are a very important part of any complex audio system. They are used to pass/block various frequencies to specific speaker elements in a given system.
As mentioned, most full range (Class A/B & T) amplifiers all have HP, LP and some have a full range option too. Class D amps are primarily use for subs/bass and only have a LP filter. (60 ~ 200 Hz., typ.)
Yes, the higher the dB/octave number given in a spec, the greater the slope the filter will offer. It always refers to attenuation. Most good car audio will offer a -12dB/octave slope.
What is Slope? This term refers to how rapidly the attenuation function of a given crossover can deliver.
Basically, let's say we have an amp with a -12dB/oct., slope. We set the HP filter at 100 Hz., and 100 watts power, The slope is a linear plot of attenuation, based on frequency, speaker impedance, Coil and Cap values. This is how much attenuation we can expect from such a crossover: 100 watts of power, 100dB SPL
100 Hz. = No attenuation, (100 dB)
87.5 Hz.= -3dB attenuation, (97 dB)
75 Hz. = -6dB attenuation, (94 dB) 1st order filter
50 Hz. = -12dB attenuation, (88dB) 2nd order filter
37.5 Hz, = -18dB attenuation, (82 dB) 3rd order filter
25 Hz. = -24dB attenuation, (76 dB) 4th order filter
A side note here... filters come in several slopes. It depends on the nature of the speakers used and how much protection they need against frequencies they cannot handle. It breaks down like this:
1st order filter: -6dB slope (A simple Cap or Coil)
2nd order filter: -12dB slope (a combination of Cap & Coil)
3rd order filter: -18dB slope (A combination of several Caps & Coils)
4th order filter: -24dB slope (A very complex grouping of Caps, Coils and often resistors as well)
If you wish to read more, you can look at the links below. This gets very complex and perhaps more confusing than what you understand now. Passive and Active filters can be very difficult to understand. It takes about 18 months of ET level classes to really get a feel for the theory and math behind such devices.
http://www.bcae1.com/xovrslop.htm
http://www.bcae1.com/elecxovr.htm
http://www.bcae1.com/passxovr.htm
http://www.bcae1.com/elxovsp2.htm
This should keep you busy for a time... enjoy the reading.
Swez
PS Some of these links are NOT for the average Novice. You are pretty sharp Jim, so don't feel like a dummy if some of these links are well over your head. This is one topic BSEE's and MSEE's need to study for some time to master all the details. That's why they make the big money too.
swez on 02/3/2007 21:01:54
Jim,
Here are the T/S specs for Alpine SWR series subs. They are noted on page 2 of the PDF file linked below:
http://akamaipix.crutchfield.com/Manuals/500/500SWR1242.PDF
Swez
cplkittle on 02/4/2007 00:32:32
a less technical explination:
The crossover frequency or crossover point is where the slope starts, and the dB/Oct is the steepness of the slope.
An octave up is double the frequency, an octave down is half the frequency. A tuning fork resonates at 440 Hz (that's an A on the piano). An octave up would be 880, and an octave down would be 220, one more down 110, then 55, 27.5 and so on.
Now, +3dB is twice the volume, therefore -3dB is half the volume.
Let's put dB and octaves together.
Say we set our crossover at 300Hz with a -12dB/oct slope.
Now let's assume we are listening to a test tone sweep that plays 300Hz down to 75Hz, and our listening volume is around 100dB.
at 300Hz, the volume is 100dB
at 150Hz (one octave down) the volume is 88dB (100 minus 12)
at 75Hz (one more octave down) the volume is 76 dB (88 minus 12)
I'm not trying to talk down to anyone, this is the way it was explained to me when it stuck in my brain.
cplkittle on 02/4/2007 00:39:19
reguarding the title of this post.. I would suggest that you write the tutorial, James. That is how I learned. I spent about a week reading and studying each type of enclosure, then wrote a DIY article on them. That is, if you have time.
swez on 02/4/2007 09:06:17
Ditto... the best way to learn new things, is to research the topic until one grasps enough of it to spell things out in terms they can explain. Then, share it with others.
The hardest part about teaching complex things, is bringing the key points down to the lower shelves for others to see and use, at the level they can understand. (Sort of like being a parent at 45 years old and teaching teens about getting ready for adult life.... very hard at times huh?)
Swez
jamesp on 02/4/2007 17:42:14
Thanks guys, I have a clear picture in my foggy mind now. Both of you are good at explaining concepts in writing in understandable and concise ways. It is not always easy to do that. Sometimes I dont get my point across in writing when I am usually able to talk someone through the process. One of my physics professors used to fill the board up with a lot of detailed, complex information and then comment,"of course this is all intuitive". I remenber sometimes thinking, yea, it might be intuitive after teaching it for 20 years.
I havent had a chance to dig into any of the links posted but will soon.
swez on 02/5/2007 08:07:52
Had the same experience with the Prof, (Also the Dean of EE) that taught EE 101, pre-Calc and Chemistry 101 classes. He skimmed through the details as if the class had already been through such things in HS. (More like a review pace)
Since I did not have much advanced math in HS, I was lost and failed miserably in all tech/math classes, but did well in English Comp. I washed out in the 1st semester, gave up my scholorship in Swimming and just said "screw this" and went into the work force.
After a few years of back-breaking grunt work as a skilled trades Tech, went back to college at a more relaxed pace and practically aced every class. (2 year ET program) Dang... working 72 hours a week, classes 3x/wk and studied my butt off whenever I could, was a test of endurance and motivation. Did that for over 3 years too. Looking back, it was the best option available.
But ya know what, all that education did not prepare me one wit for life in the "white collar" world. Yes, the technical skills were of some help then and now. But as I look back over the years, there is no substitute for hands on experience and working with other people. (Especially the jerks)
IMHO, it's a good idea to have a college education if one can get that. But in many cases, "Common Sense" is even more important. They don't teach that in any University I know about. There's only one way to get that one straight... get out and work with others and learn as we earn.
End Rant!
Swez
jamesp on 02/5/2007 12:48:01
Swez, my story is very similar. I went off to school right out of high school and after 4 quarters of trying to get by without attending class very often, I flunked out and was asked not to return.
I went out on the road and built cooling towers all over the country. I worked in 32 states in 4 years. Hot, cold, wet,hard work. Left a job in S. Ga. in August and supposed to be in Pheonix on Monday and saw it was like 110 degrees there.
Enrolled back in school here and as I blew my free ride eariler, had to pay my own way this time. I tried studying a bit this go round and got my BS in Geology.
Went to work for big oil and racked up untill they shut down oil exploration , came back home and bought the family business and an old fashioned wood floored hardware store. It was all good till Home Depot came to town...Anyway, I think a lot of guys our age didnt do too well the first go round at "higher education". A BS degree is good for 1 thing anyway, it shows a potential employer that one has the ability to see a project through to completion. As long as they dont pay attention to the "false starts". Have a good day. JamesP.
swez on 02/5/2007 14:40:35
Yes, "potential" is one thing... experience and due diligence are not part of the "Sheep Skin" package for many grads. It's good to have one, but not a guarantee you'll get a a well rounded employee though. Give me a "Common Sense" team player anyday!
Speaking of "Big Box" super stores VS "Mom & Pop" hardware stores, I prefer the local M/P stores in many situations. They are local, know the area needs and have most things on hand as needed. If the price is only a few buck more, will use the local stores anytime.
Case in point... the water heater finally pooped out after 11 years of service. I called HD and the local hardware store for stock and prices. The difference was only $1.00, so I went local. Was in and out with the tank in under 15 minutes. (1 mile away too)
After removing the old tank and installing the new one, saw I needed a close nipple for the gas line. It was 9:15 PM and I scampered up to HD for a 50 cent nipple, before they closed at 10:00 PM. Think I could find one easily at "Ain't Gots"? Not a chance. They had 1 black close nipple left and it was in a box, mixed with galvanized nipples.
Frankly, it took longer to go fetch this item, then to install it. At 11:00 PM, we had hot water again. Yippie!!!
In short, would rather do business with the M/P stores when it makes sense. I'll gladly pay a small premium for the extra service and knowledgeable help in these stores. The Big Box stores are fine for building materials and a larger selection of tools, but as for customer service... it just ain't there. (Too much turnover?)
God Bless the local hardware folks,
Swez
cplkittle on 02/5/2007 17:21:44
I agree with the mom and pop shops. They generally know more than the 17 year old hungover stoner kid at walmart drawing his name in the dust on the floor. Plus you don't have to push a button to page them that you need assistance. I like to walk through Kmart and just push those buttons as I pass listening to the recorded voice "customer needs assistance in women's plus size lingerie."
swez on 02/6/2007 14:32:24
That's funny. Our local K-Mart was the very first one they opened. For years, it was the place to go for all kinds of stuff. Today, it's so dead in there, I could probably roll a bowling ball down each isle and not hit a single person. (Staff of customers)
The staff shuffles around like they dead lice falling off a dog's back. No direction, no motivation and they cluster in small groups to complain about this or that... very sad... sad indeed.
Thanks to Wal-Mart, most local K-Mart stores have long since closed in this area too. Not that I have anything against Wal-Mart, but they do have a well trained staff and you can get almost anything in one trip at very fair prices too. (Especially the Super Wal-Mart stores)
Swez
cplkittle on 02/6/2007 19:15:41
The most unbelieveable story came out of that scenario. I heard for years Kmart was going out of business, then a friend told me that Kmart bought Sears. I argued with him telling him he must have heard it wrong. Sears must have bought Kmart..
I was wrong, that move was brilliant. Or so I thought. I have seen Kmart continue to go downhill even after the buyout. Actually, come to think of it, I have seen a few Sears stores go down as well.
swez on 02/6/2007 20:31:24
Yep, all the old school depertment stores are struggling to maintain their footing since Wal-Mart came into being. Sam Walton was the genius behind Wal-Mart and Sam's Club.
He knew if he could buy in huge lots and sell at very low daily prices, people would flock to his stores. He was right! Unfortunately, Sam believed in treating his associates well and fairly. If he were alive today and saw how Wal-Mart Corporation treats their employees now, he'd come out of his grave and raise the roof.
Swez
cplkittle on 02/6/2007 21:01:19
Back to the topic.
I wonder if there could be an equation for setting x-over points and slopes based on speaker size, wattage, sensitivity, and a loose variable to accommodate for location and obstructions.
I'll work on that next time I'm bored.
Could someone explain or recommend a source for me to learn more about exactly what they do.Is the attenuation of a certain crossover signal point a linear function or does it block the signal at the selected crossover point completly? Thanks for the help...JamesP
Replies (15)
jamesp on 02/3/2007 14:56:44
I forgot to mention that I was trying to play with WinISD a bit and my sub was not in the data base. It is an Alpine SWR 1242D. Does anyone have the specs entered that could shoot me the file. again, thanks.
swez on 02/3/2007 20:58:12
You have the right idea. Crossovers are a very important part of any complex audio system. They are used to pass/block various frequencies to specific speaker elements in a given system.
As mentioned, most full range (Class A/B & T) amplifiers all have HP, LP and some have a full range option too. Class D amps are primarily use for subs/bass and only have a LP filter. (60 ~ 200 Hz., typ.)
Yes, the higher the dB/octave number given in a spec, the greater the slope the filter will offer. It always refers to attenuation. Most good car audio will offer a -12dB/octave slope.
What is Slope? This term refers to how rapidly the attenuation function of a given crossover can deliver.
Basically, let's say we have an amp with a -12dB/oct., slope. We set the HP filter at 100 Hz., and 100 watts power, The slope is a linear plot of attenuation, based on frequency, speaker impedance, Coil and Cap values. This is how much attenuation we can expect from such a crossover: 100 watts of power, 100dB SPL
100 Hz. = No attenuation, (100 dB)
87.5 Hz.= -3dB attenuation, (97 dB)
75 Hz. = -6dB attenuation, (94 dB) 1st order filter
50 Hz. = -12dB attenuation, (88dB) 2nd order filter
37.5 Hz, = -18dB attenuation, (82 dB) 3rd order filter
25 Hz. = -24dB attenuation, (76 dB) 4th order filter
A side note here... filters come in several slopes. It depends on the nature of the speakers used and how much protection they need against frequencies they cannot handle. It breaks down like this:
1st order filter: -6dB slope (A simple Cap or Coil)
2nd order filter: -12dB slope (a combination of Cap & Coil)
3rd order filter: -18dB slope (A combination of several Caps & Coils)
4th order filter: -24dB slope (A very complex grouping of Caps, Coils and often resistors as well)
If you wish to read more, you can look at the links below. This gets very complex and perhaps more confusing than what you understand now. Passive and Active filters can be very difficult to understand. It takes about 18 months of ET level classes to really get a feel for the theory and math behind such devices.
http://www.bcae1.com/xovrslop.htm
http://www.bcae1.com/elecxovr.htm
http://www.bcae1.com/passxovr.htm
http://www.bcae1.com/elxovsp2.htm
This should keep you busy for a time... enjoy the reading.
Swez
PS Some of these links are NOT for the average Novice. You are pretty sharp Jim, so don't feel like a dummy if some of these links are well over your head. This is one topic BSEE's and MSEE's need to study for some time to master all the details. That's why they make the big money too.
swez on 02/3/2007 21:01:54
Jim,
Here are the T/S specs for Alpine SWR series subs. They are noted on page 2 of the PDF file linked below:
http://akamaipix.crutchfield.com/Manuals/500/500SWR1242.PDF
Swez
cplkittle on 02/4/2007 00:32:32
a less technical explination:
The crossover frequency or crossover point is where the slope starts, and the dB/Oct is the steepness of the slope.
An octave up is double the frequency, an octave down is half the frequency. A tuning fork resonates at 440 Hz (that's an A on the piano). An octave up would be 880, and an octave down would be 220, one more down 110, then 55, 27.5 and so on.
Now, +3dB is twice the volume, therefore -3dB is half the volume.
Let's put dB and octaves together.
Say we set our crossover at 300Hz with a -12dB/oct slope.
Now let's assume we are listening to a test tone sweep that plays 300Hz down to 75Hz, and our listening volume is around 100dB.
at 300Hz, the volume is 100dB
at 150Hz (one octave down) the volume is 88dB (100 minus 12)
at 75Hz (one more octave down) the volume is 76 dB (88 minus 12)
I'm not trying to talk down to anyone, this is the way it was explained to me when it stuck in my brain.
cplkittle on 02/4/2007 00:39:19
reguarding the title of this post.. I would suggest that you write the tutorial, James. That is how I learned. I spent about a week reading and studying each type of enclosure, then wrote a DIY article on them. That is, if you have time.
swez on 02/4/2007 09:06:17
Ditto... the best way to learn new things, is to research the topic until one grasps enough of it to spell things out in terms they can explain. Then, share it with others.
The hardest part about teaching complex things, is bringing the key points down to the lower shelves for others to see and use, at the level they can understand. (Sort of like being a parent at 45 years old and teaching teens about getting ready for adult life.... very hard at times huh?)
Swez
jamesp on 02/4/2007 17:42:14
Thanks guys, I have a clear picture in my foggy mind now. Both of you are good at explaining concepts in writing in understandable and concise ways. It is not always easy to do that. Sometimes I dont get my point across in writing when I am usually able to talk someone through the process. One of my physics professors used to fill the board up with a lot of detailed, complex information and then comment,"of course this is all intuitive". I remenber sometimes thinking, yea, it might be intuitive after teaching it for 20 years.
I havent had a chance to dig into any of the links posted but will soon.
swez on 02/5/2007 08:07:52
Had the same experience with the Prof, (Also the Dean of EE) that taught EE 101, pre-Calc and Chemistry 101 classes. He skimmed through the details as if the class had already been through such things in HS. (More like a review pace)
Since I did not have much advanced math in HS, I was lost and failed miserably in all tech/math classes, but did well in English Comp. I washed out in the 1st semester, gave up my scholorship in Swimming and just said "screw this" and went into the work force.
After a few years of back-breaking grunt work as a skilled trades Tech, went back to college at a more relaxed pace and practically aced every class. (2 year ET program) Dang... working 72 hours a week, classes 3x/wk and studied my butt off whenever I could, was a test of endurance and motivation. Did that for over 3 years too. Looking back, it was the best option available.
But ya know what, all that education did not prepare me one wit for life in the "white collar" world. Yes, the technical skills were of some help then and now. But as I look back over the years, there is no substitute for hands on experience and working with other people. (Especially the jerks)
IMHO, it's a good idea to have a college education if one can get that. But in many cases, "Common Sense" is even more important. They don't teach that in any University I know about. There's only one way to get that one straight... get out and work with others and learn as we earn.
End Rant!
Swez
jamesp on 02/5/2007 12:48:01
Swez, my story is very similar. I went off to school right out of high school and after 4 quarters of trying to get by without attending class very often, I flunked out and was asked not to return.
I went out on the road and built cooling towers all over the country. I worked in 32 states in 4 years. Hot, cold, wet,hard work. Left a job in S. Ga. in August and supposed to be in Pheonix on Monday and saw it was like 110 degrees there.
Enrolled back in school here and as I blew my free ride eariler, had to pay my own way this time. I tried studying a bit this go round and got my BS in Geology.
Went to work for big oil and racked up untill they shut down oil exploration , came back home and bought the family business and an old fashioned wood floored hardware store. It was all good till Home Depot came to town...Anyway, I think a lot of guys our age didnt do too well the first go round at "higher education". A BS degree is good for 1 thing anyway, it shows a potential employer that one has the ability to see a project through to completion. As long as they dont pay attention to the "false starts". Have a good day. JamesP.
swez on 02/5/2007 14:40:35
Yes, "potential" is one thing... experience and due diligence are not part of the "Sheep Skin" package for many grads. It's good to have one, but not a guarantee you'll get a a well rounded employee though. Give me a "Common Sense" team player anyday!
Speaking of "Big Box" super stores VS "Mom & Pop" hardware stores, I prefer the local M/P stores in many situations. They are local, know the area needs and have most things on hand as needed. If the price is only a few buck more, will use the local stores anytime.
Case in point... the water heater finally pooped out after 11 years of service. I called HD and the local hardware store for stock and prices. The difference was only $1.00, so I went local. Was in and out with the tank in under 15 minutes. (1 mile away too)
After removing the old tank and installing the new one, saw I needed a close nipple for the gas line. It was 9:15 PM and I scampered up to HD for a 50 cent nipple, before they closed at 10:00 PM. Think I could find one easily at "Ain't Gots"? Not a chance. They had 1 black close nipple left and it was in a box, mixed with galvanized nipples.
Frankly, it took longer to go fetch this item, then to install it. At 11:00 PM, we had hot water again. Yippie!!!
In short, would rather do business with the M/P stores when it makes sense. I'll gladly pay a small premium for the extra service and knowledgeable help in these stores. The Big Box stores are fine for building materials and a larger selection of tools, but as for customer service... it just ain't there. (Too much turnover?)
God Bless the local hardware folks,
Swez
cplkittle on 02/5/2007 17:21:44
I agree with the mom and pop shops. They generally know more than the 17 year old hungover stoner kid at walmart drawing his name in the dust on the floor. Plus you don't have to push a button to page them that you need assistance. I like to walk through Kmart and just push those buttons as I pass listening to the recorded voice "customer needs assistance in women's plus size lingerie."
swez on 02/6/2007 14:32:24
That's funny. Our local K-Mart was the very first one they opened. For years, it was the place to go for all kinds of stuff. Today, it's so dead in there, I could probably roll a bowling ball down each isle and not hit a single person. (Staff of customers)
The staff shuffles around like they dead lice falling off a dog's back. No direction, no motivation and they cluster in small groups to complain about this or that... very sad... sad indeed.
Thanks to Wal-Mart, most local K-Mart stores have long since closed in this area too. Not that I have anything against Wal-Mart, but they do have a well trained staff and you can get almost anything in one trip at very fair prices too. (Especially the Super Wal-Mart stores)
Swez
cplkittle on 02/6/2007 19:15:41
The most unbelieveable story came out of that scenario. I heard for years Kmart was going out of business, then a friend told me that Kmart bought Sears. I argued with him telling him he must have heard it wrong. Sears must have bought Kmart..
I was wrong, that move was brilliant. Or so I thought. I have seen Kmart continue to go downhill even after the buyout. Actually, come to think of it, I have seen a few Sears stores go down as well.
swez on 02/6/2007 20:31:24
Yep, all the old school depertment stores are struggling to maintain their footing since Wal-Mart came into being. Sam Walton was the genius behind Wal-Mart and Sam's Club.
He knew if he could buy in huge lots and sell at very low daily prices, people would flock to his stores. He was right! Unfortunately, Sam believed in treating his associates well and fairly. If he were alive today and saw how Wal-Mart Corporation treats their employees now, he'd come out of his grave and raise the roof.
Swez
cplkittle on 02/6/2007 21:01:19
Back to the topic.
I wonder if there could be an equation for setting x-over points and slopes based on speaker size, wattage, sensitivity, and a loose variable to accommodate for location and obstructions.
I'll work on that next time I'm bored.
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