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ohms, crossovers


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p40whk 
Copper - Posts: 50
Copper spacespace
Joined: April 07, 2009
Location: Kentucky, United States
Posted: February 28, 2011 at 11:32 AM / IP Logged  
I know that wiring speakers in Parallel with reduce the Ohms that the amp sees but what happens when you introduce a passive crossover into the mix? Does it change the load?
I'm building a set of speakers for the tower on my boat using Pro-Audio 8 Ohm components and when wired together in parallel I should get a 2.667 Ohm load to the Amp. I'm wiring in a passive crossover and if this will change the load have no idea how to calculate it. The crossover is below and I'll be using the following components:
Capacitors
C1 = 5.68 uF
C2 = 51.21 uF
Inductors
L1 = 0.32 mH
L2 = 2.91 mH
I've been reading as much as I can but still can't seem to find an answer to my problem. If adding the crossover doesn't change the load then I'm good, I just can't find anywhere that talks about this.
Any help would be appreciated!
ohms, crossovers -- posted image.
DYohn 
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Joined: April 22, 2003
Location: Arizona, United States
Posted: February 28, 2011 at 4:32 PM / IP Logged  
A crossover is designed to block speakers during specific frequency bands.  If properly designed, the net load on the amp will always be approximately the impedance of one single speaker in the system.  However, given the values you list above that crossover will include overlaps and impedance dips to the vicinity of 4 ohms in a band at each crossover point, which is not desirable as it will introduce peaks in system response in those bands.  What you list will result in a woofer low pass at approx. 440Hz, a mid range band pass between about 350 and 4400 Hz, and a tweeter high pass at about 3500 Hz..  How did you arrive at those values? 
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oldspark 
Gold - Posts: 4,913
Gold spacespace
Joined: November 03, 2008
Location: Australia
Posted: February 28, 2011 at 5:56 PM / IP Logged  
Ah the fun of resistance versus impedance (aka a frequency-dependent resistance).
The crossover does change the resistance of each speaker, but the resistance depends on the frequency and that is how they work.
It may be that to the amplifier, the total speaker resistance needs to look flat across the entire band, or at least not be lower than what the amp can handle...
p40whk 
Copper - Posts: 50
Copper spacespace
Joined: April 07, 2009
Location: Kentucky, United States
Posted: February 28, 2011 at 6:57 PM / IP Logged  
DYohn wrote:
How did you arrive at those values? 
I used an online calculator (I know, probably not the best thing to do). The calculator was at this site: http://www.diyaudioandvideo.com/Calculator/APCXover/
I plan to use the following components:
Selenium DH200E 1" HLCD
Eminence Beta 8A Midrange
And
Eminence Alpha 8A
I was copying a friends setup using these components as a small PA cabinet. He mentioned that he just crossed the tweeter over at 3500hz with a 12db (second order) crossover and left the other drivers alone.
I actually modified the schematic with a second order crossover on the tweeter with first order on the mid and woofer. The tweeter would have a 4.018 Cap and an added 0.51 inductor.
I am completely new to this and trying to learn as much as I can but most of the info out there is already over my head. I can put everything together with no problem it's trying to understand the electronics of it all that's confusing me.
I really would love to understand what I'm doing here but I feel I need to take a basic course in speaker building to make good decisions. Unfortunately, there's nothing available to me so I came here for some guidance.
I do appreciate any advice I can get.
i am an idiot 
Platinum - Posts: 13,666
Platinum spaceThis member consistently provides reliable informationspace
Joined: September 21, 2006
Location: Louisiana, United States
Posted: February 28, 2011 at 9:56 PM / IP Logged  

Several pages of reading for you.  Scroll down to the bottom of the following page then click the link that reads "Next First Order Filters"  Continue clicking next on each of the following pages.

https://www.the12volt.com/caraudio/cross.asp

p40whk 
Copper - Posts: 50
Copper spacespace
Joined: April 07, 2009
Location: Kentucky, United States
Posted: March 01, 2011 at 6:23 AM / IP Logged  
i am an idiot wrote:

Several pages of reading for you.  Scroll down to the bottom of the following page then click the link that reads "Next First Order Filters"  Continue clicking next on each of the following pages.

https://www.the12volt.com/caraudio/cross.asp

Thanks, I had read the first page of that but didn't notice the next buttons. The more I read the more I think I may have chosen the wrong drivers for what I want to do. I have Bass Box pro and X-Over pro software I bought a few years back that I set aside because it seemed too complicated but I'll have to take another look at it.
Good thing is I enjoy digging in to this stuff. Just hope I don't ask too many stupid questions.
DYohn 
Moderator - Posts: 10,741
Moderator spaceThis member has made a donation to the12volt.com. Click here for more info.spaceThis member has been recognized as an authority in Electrical Theory. Click here for more info.spaceThis member has been recognized as an authority in Mobile Audio and Video. Click here for more info.spacespace
Joined: April 22, 2003
Location: Arizona, United States
Posted: March 01, 2011 at 11:33 AM / IP Logged  

p40whk wrote:
The more I read the more I think I may have chosen the wrong drivers for what I want to do..

Perhaps that's where we should start.  What is it you're trying to do?  I'll be happy to help you design a system but I need to know what you're planning.

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p40whk 
Copper - Posts: 50
Copper spacespace
Joined: April 07, 2009
Location: Kentucky, United States
Posted: March 01, 2011 at 2:48 PM / IP Logged  
DYohn wrote:

p40whk wrote:
The more I read the more I think I may have chosen the wrong drivers for what I want to do..

Perhaps that's where we should start.  What is it you're trying to do?  I'll be happy to help you design a system but I need to know what you're planning.

Well, it's actually going to be hanging from my wakeboard tower on my boat. Currently, I have four Polk Momo's run with a Kicker ZX850.4 and I'm extremely unhappy with it.
We typically pull our boats into a cove, anchor and spend a lot of time behind the boats (up to 80 feet back) in the water listening to music. Since this is outside and we don't have the closed environment of a car, most of the premade setups that do sound good use PA drivers and HLCDs. Unfortunately, these premade units are outrageously expensive. The Wetsounds are $900 for what I'm trying to accomplish Wetsounds Pro485
They use 2, 8 inch drivers flanking 1 inch HLCD. I had planned to build my own enclosure out of fiberglass to hold 2 sets of these or four 8 inch drivers and 2 HLCDs (left and right channels).
Car/boat audio (most 4 Ohm) just doesn't seem to give me the volume I need without it sounding like crap. This is why I was looking to build my own system.
Met a guy on the lake a few years back and he used the components I have listed and it sounded 10 times better than what I have at a reasonable cost. All he told me was that he crossed the horns over at 3500hz and wired everything to show a 4 Ohm load.
I've been driving myself nuts trying to figure out how he did it and the more I look in to it the more confused I get. I've picked up and put down this project too many times and am determined to have something before the summer. I can follow a schematic with no problems and my soldering skills are excellent. But, everything I know about audio electronics I've gotten from the web and I'm not getting to far.
I even purchased BassBox and X-Over Pro software but found that not knowing the parameters I can't even use that.
It's frustrating and I appreciate your offer to help. Sorry for the long post and thanks!
DYohn 
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Moderator spaceThis member has made a donation to the12volt.com. Click here for more info.spaceThis member has been recognized as an authority in Electrical Theory. Click here for more info.spaceThis member has been recognized as an authority in Mobile Audio and Video. Click here for more info.spacespace
Joined: April 22, 2003
Location: Arizona, United States
Posted: March 02, 2011 at 10:35 AM / IP Logged  
OK, well he didn't achieve a 4-ohm load with the drivers you list.  Now I understand what you want, and you're on the right track.  My next questions are what's your total budget for this system, are you sure you want to build it yourself, and how large can each enclosure be?
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p40whk 
Copper - Posts: 50
Copper spacespace
Joined: April 07, 2009
Location: Kentucky, United States
Posted: March 02, 2011 at 11:34 AM / IP Logged  
DYohn wrote:
OK, well he didn't achieve a 4-ohm load with the drivers you list.  Now I understand what you want, and you're on the right track.  My next questions are what's your total budget for this system, are you sure you want to build it yourself, and how large can each enclosure be?
Yeah, I kind of figured that. I've been trying to work out that 4 ohm load for over a year now! Through a lot of the reading I've done here since my first post, I figured I could run at a higher ohm rating without hurting my amp which makes these drivers more attractive.
For everything but the enclosure, I'd like to keep it below $500. I'm at around $370 right now with the components I have listed (this is for both a left and right channel, 6 total drivers). I know there are much better and more expensive drivers out there but the people I know that own these "Wetsound" speaker systems tell me I can't build a system for less. I hate being told I can't do something so keeping the cost down is a goal for me. (I can afford more but it's the point that counts).
I would like to build it myself (I'm a licensed aircraft mechanic by trade and love this kind of stuff). For an enclosure, I plan to model it on what this guy did: Fiberglass Speaker Box He built this for 6X9 coaxials but as you can see it's highly customizable. I can probably go as big as 10" woofers but the 8" just seemed to be the right size. That's why I've been looking at the 8" pro audio drivers from parts express.
I have no problem going bigger or even smaller if the end result is a set of speakers that sound good outside at a distance at volume. And as much as I'd love for someone to just say "use these components like this" I really would like to know why each component is chosen so I can learn from the experience.
Thanks so much for taking an interest and helping me out. I've asked all my friends and friends of friends and haven't been able to find anyone that understands what I'm trying to do.
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