i’m confused about caps and coils
Printed From: the12volt.com
Forum Name: Car Audio
Forum Discription: Car Stereos, Amplifiers, Crossovers, Processors, Speakers, Subwoofers, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=113271
Printed Date: May 13, 2025 at 1:10 AM
Topic: i’m confused about caps and coils
Posted By: jetmech_jt8
Subject: i’m confused about caps and coils
Date Posted: April 19, 2009 at 1:03 PM
I read the diagrams on 2nd order caps and coils. I think thats what Im after. I'm trying to cut the low end and volume to my dash speakers, more so the volume. There 4 ohm 4x6 speakers. There running parallel with the kick panel components off the amp, which is set to 100 hz high pass. The amp is 2 ohm stable in stereo. To figure on the right cap I need to know the impedance. Is the impedance the speaker rating, 4 ohms? or the load rating, which I guess would be 2 ohms. I've got my head in a knot over this.
Replies:
Posted By: i am an idiot
Date Posted: April 19, 2009 at 2:03 PM
The impedance is going to be 4 ohms. You want the cap in series with the dash speaker only. Door speaker directly to amp. Cap or coil only in the path to dash speaker.
Posted By: jetmech_jt8
Date Posted: April 20, 2009 at 10:34 AM
Will a cap actually drop the volume level as well? Or am I misunderstanding the idea of 1st, 2nd and 3rd order?
thanks
Posted By: DYohn
Date Posted: April 20, 2009 at 10:42 AM
Posted By: haemphyst
Date Posted: April 20, 2009 at 10:45 AM
jetmech_jt8 wrote:
Will a cap actually drop the volume level as well? Or am I misunderstanding the idea of 1st, 2nd and 3rd order?
thanks
No. The caps and coils ONLY perform crossover functions, not broadband attenuation. For that, you need either a padding network or a simple attenuating resistor IN FRONT OF the crossover. The preferred method is the padding network, but there are additional calculations required for those. There are additional calculations required for the resistor, as well, but they are easier to implement, and require fewer components.
The order numbers you are asking about describe how fast the crossover slope affects the output of the frequencies below the crossover point.
First order = 6dB/octave rolloff
Second order = 12dB/octave rolloff
Third order = 18dB/octave rolloff
...And so on, with each order equaling 6dB/octave faster rolloff than the previous order. ------------- It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."
Posted By: jetmech_jt8
Date Posted: April 20, 2009 at 1:37 PM
Just what I needed, more complexity, oh well, something new to learn that's all. Now where would I start with trying to figure out what resistor I want? Are these just standard resistors that go in line with the cap? I'd like to drop the volume by 50% to the dash speakers.
Posted By: jetmech_jt8
Date Posted: April 20, 2009 at 2:08 PM
Ok, I looked up an L-Pad, it appears to basically be a reostat. The one I found is a 15 watt stereo L-Pad with 3 connections on it. How do I go about hooking this up? I assume both the dash speakers will tap into this and the one volume knob will turn them both down.
Posted By: haemphyst
Date Posted: April 20, 2009 at 2:22 PM
Well, in simplest terms, 50% is 3dB. A 3dB drop on a 4 ohm driver would be a 4 ohm resistor. This is the fixed resistor value.
The rheostat, if it is a stereo rheostat, would be able to adjust both speakers, yes. If it is not, then you must have one for both speakers - one each. You said it has 3 terminals; I am going to guess (fairly safely) that this is NOT a stereo 'stat.
Your amplifier positive will go on one of the outside terminals. Your amplifier negative AND the speaker negative go on the other outside teminal. The speaker positive then connects to the center terminal - the wiper. If you turn the knob in the "up" direction, and it gets quieter, you need to reverse the three wires (the amp positive, and the amp/speaker negative) on the outside connections, but leave the center one alone. Connect them first, without soldering, to make sure you can move wires easily after testing.
-------------
It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."
Posted By: jetmech_jt8
Date Posted: April 20, 2009 at 10:05 PM
Thanks, great explanation. It could very well be a four point unit, I was looking at a stock photo. As far as frequencie goes, if I want to cap at 500 Hz, would I just add that in the positive wire after the Pad?
Posted By: stevdart
Date Posted: April 20, 2009 at 10:10 PM
The pad is directly before the speaker; the crossover occurs before the pad. That's the usual scenario, anyway, in a passive design.
-------------
Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.
Posted By: jetmech_jt8
Date Posted: April 20, 2009 at 10:42 PM
This is a great site, the info and explanations are second to none. Does this L-Pad have to be 4 OHM specific? I'm hooking up to a 75 Watt RMS per channel amp. I've got a set of components and one 4x6 speaker running off each channel. The 4x6 is run right off the amp as is the components as well.
Posted By: jetmech_jt8
Date Posted: April 21, 2009 at 2:48 PM
I found 8 ohm 15 watt L-pads. I've been researching this but can't quite find what I'm after. I can wire the 8 ohm Pad for 4 ohms, but can't find the proper diagrams on how to do this
Posted By: haemphyst
Date Posted: April 21, 2009 at 3:30 PM
You may not get adequate attenuation with an 8-ohm l-pad on a 4-ohm speaker. Either that, or your amplifier will see an 8-ohm load, and make less power, accordingly.
Best to find a 4-ohm l-pad. They exist...
-------------
It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."
Posted By: stevdart
Date Posted: April 21, 2009 at 10:28 PM
When I was a rookie I was bound and determined to get more out of the amplifier than it was designed to deliver. I, too, searched for Lpads and was lucky (I guess) to find a couple at a now defunct web house, and it wasn't easy, as you have seen, finding the 4 ohm variety. I hooked up the rear speakers that way so I could turn them down lower than the fronts. Well it wasn't long after that I got the amplifiers I needed for two component sets, two rear coaxials and one sub...just a four channel and a mono amp. Now I don't need those Lpads but they're installed and staying in that car for the last four or so years, and they are still being used but not needed, as I could have used the deck's attenuation for the rears at that point. It was a matter of me wasting money for something I should have done something differently about. But I always look on the brighter side and consider it a learning experience ;) You said you are hooking up a set of components and a coaxial to each channel. "I'm hooking up to a 75 Watt RMS per channel amp. I've got a set of components and one 4x6 speaker running off each channel." It looks like you are trying to get too much out of that amplifier. One channel should power one component set or one coaxial, not both. Advice is to get the amplifiers you need to do the job right. You'll be upgrading to what you should have had to begin with sooner than later. Unless, of course, you are in it for the learning experience.
-------------
Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.
Posted By: jetmech_jt8
Date Posted: April 22, 2009 at 10:52 AM
It's a 4 channel amp. The rear channels are powering the rear speakers. The front is as I mentioned, a 4 ohm component and a 4 ohm 4x6 . I figured I be ok with this set up as the amp is rated for 2 ohm stereo. I'm not trying to build a competition system by any stretch. Just want something that sounds good and has a bit of kick to it for the summer car thats rarely driven. Some of the posts mentioned using a plain 4 ohm resistor as well. Will this setup really over tax my amplifier?
Posted By: stevdart
Date Posted: April 22, 2009 at 9:20 PM
I didn't mean that the amplifier would be overworked. I meant that you have to go to extraordinary measures because there aren't enough channels for the speakers you want to power. But you could use resistors and if one doesn't attenuate the speaker enough, add another in series. Use the tools found to the left in the blue help area, "parallel and series" resistance calcs to help with configuring resistors to give you the attenuation you want. ------------- Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.
Posted By: jetmech_jt8
Date Posted: April 22, 2009 at 11:47 PM
I want approx a 50% drop in volume and and cut everything below approx 500 Hz. So I guess I'm looking at a 4 ohm resistor on each channel. Are these just the standard resistor? One you would find on a circuit board? I would add them in series in order to increase resistance correct? This is just spliced in on the positive line? The amp would see an 8 Ohm load form the dash speakers? Would this effect the 4 ohm components in terms of volume output or do they remain unchanged? Thanks for your help
Posted By: i am an idiot
Date Posted: April 23, 2009 at 12:03 AM
You will need a high wattage resistor. Radio Shack sells an 8 Ohm 20 watt resistor for 2.49USD. You can parallel 2 of these to make a 4 ohm 40 watt. You will have to monitor them for heat. You may need to mount them to a heat sink.
Posted By: jetmech_jt8
Date Posted: April 23, 2009 at 9:42 AM
I's there a wiring diagram for this? I'm searching this site for it now. Does the positive from the amp go to one side of both resistors, then off to the positive of each speaker and vice versa for the negative as well?
Posted By: jetmech_jt8
Date Posted: April 23, 2009 at 3:41 PM
Just wanted to thank everyone for there help. I found four 10 ohm 25 watt resistors that are built right into heat sinks. I paralleled them for a little over 5 ohm's, popped them into the positive line and tried it out. It's exactly what I'm after. I now have a soft fill on the dash speakers that smooth everything out. There's no need for a cap as my amp is on 100 Hz high pass and the resistors are creating enough of a volume drop that the 4x6's are not trying to pop through the windshield.
Thanks again
|