ohms, crossovers
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=126355
Printed Date: April 29, 2024 at 3:37 AM
Topic: ohms, crossovers
Posted By: p40whk
Subject: ohms, crossovers
Date Posted: February 28, 2011 at 11:32 AM
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!
Replies:
Posted By: DYohn
Date Posted: February 28, 2011 at 4:32 PM
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? ------------- Support the12volt.com
Posted By: oldspark
Date Posted: February 28, 2011 at 5:56 PM
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...
Posted By: p40whk
Date Posted: February 28, 2011 at 6:57 PM
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: https://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.
Posted By: i am an idiot
Date Posted: February 28, 2011 at 9:56 PM
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
Posted By: p40whk
Date Posted: March 01, 2011 at 6:23 AM
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.
Posted By: DYohn
Date Posted: March 01, 2011 at 11:33 AM
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. ------------- Support the12volt.com
Posted By: p40whk
Date Posted: March 01, 2011 at 2:48 PM
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!
Posted By: DYohn
Date Posted: March 02, 2011 at 10:35 AM
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? ------------- Support the12volt.com
Posted By: p40whk
Date Posted: March 02, 2011 at 11:34 AM
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.
Posted By: DYohn
Date Posted: March 02, 2011 at 6:11 PM
You want to build a custom sound reinforcement system. That's cool. Let me look at the drivers you've picked out and make a few suggestions... ------------- Support the12volt.com
Posted By: DYohn
Date Posted: March 02, 2011 at 8:42 PM
OK, here's what I'd suggest. Since you like the Selenium high frequency driver, buy two of those. You'll also need a screw-on horn for each one, such as Parts Express part number 270-300. Make the system a 2-way not a 3-way. Purchase four of the Eminence Alpha 8A woofers.
Build your enclosure so that there are two chambers with approx. 1.5 cubic feet of space inside for each set of woofers. Mount two woofers and one tweeter for each side. Port each side at about 41Hz, which is most easily accomplished using a piece of 4" ID PVC pipe cut to 10.5" long. The port can face any direction that is convenient
I suggest building a second order crossover at 2.2KHz. Wire the two woofers in parallel (a 4-ohm load) and the crossover will consist of one inductor of 0.58mH in series and one poly cap at 9 uF in parallel. Use an air core inductor of at least 16 gauge.
In series with each tweeter will be a cap of about 4.5 uF and in parallel an inductor of 1.16 mH. This cap should be a high quality poly or film/foil cap, and this inductor can be a cheap one with iron core. I also suggest using an L-pad such as parts express part number 260-265 for each tweeter as they are about 8db more sensitive than the woofers in parallel. NOTE that since this is a second order network, the tweeter must be in reverse polarity in relation to the woofers. The negative speaker terminal connects to the positive input terminal through the l-pad and in-series cap.
This system should be quite musical and will hit about 120db with 125 watts of power, with sufficient long-throw characteristics to be used outside. ------------- Support the12volt.com
Posted By: p40whk
Date Posted: March 02, 2011 at 9:39 PM
Great! Thank you DYohn,
If I'm understanding you correctly, it should look something like this:
I was considering upgrading to the better Selenium Drivers (the D220Ti 264-270) if you think that's worth the extra $13 a driver, it's still within my budget?
And am I reading correctly when you suggest four inch inside diameter PVC? I'll have to get to work on designing a shape that will house that big of pipe.
Thanks again. I'm going to start drawing things up.
Posted By: p40whk
Date Posted: March 03, 2011 at 6:19 AM
I realized last night after shutting my computer down that I forgot about the L-Pad in my drawing. Will have to draw that up today.
Posted By: DYohn
Date Posted: March 03, 2011 at 8:37 AM
Yes, your schematic is correct for the Xover layout, just missing the L-pad. Using the higher end compression driver is a good thing as it has better frequency response and power handling. It has higher sensitivity numbers so you'll REALLY need to pad it down. If you can't add a vent to the enclosure it will still function as a sealed system. You'll just lose low-frequency output level. ------------- Support the12volt.com
Posted By: p40whk
Date Posted: March 03, 2011 at 8:45 AM
Ok, redrew the schematic (need to get out of rookie status so I can edit my posts). The L-Pad in the drawing is just a representation as I'll use the adjustable one from parts express. They also have an adjustable flared 4" port as well which I may use to pretty up the enclosure but that would add an additional inch to the length using flared ports.
I think you've set me on the right track! Thank you sir!
Below is the schematic, parameters, and speakers (showing the D220's because the Seleniums weren't listed in X-Over Pro)
Posted By: DYohn
Date Posted: March 03, 2011 at 8:50 AM
Cool. It's actually a second-order Linkwitz-Riley network, not a Butterworth. But that's not really important. You can use a lower gauge than 16 for the parallel inductor which will save you some money, but do use at least 16 for the air core. Plus as you say, the specs given for the tweeter are not the same as what PE lists on their web site... Looks like you're ready to go for it!
edit: If you can't find the exact values for the caps and coils, you can be within 5% to 10% and not alter the function significantly. If you need help with suggested parts, let me know. ------------- Support the12volt.com
Posted By: p40whk
Date Posted: March 03, 2011 at 9:34 AM
Posted By: DYohn
Date Posted: March 03, 2011 at 11:29 AM
Great. Be sure to post build pics and to give us your impression of how it sounds. ------------- Support the12volt.com
Posted By: p40whk
Date Posted: March 03, 2011 at 11:50 AM
DYohn] wrote:
Great. Be sure to post build pics and to give us your impression of how it sounds.Â
Will do and I just can't thank you enough for helping me out. Ended up going with the better Selenium HLCDs so the total was right at $450.
Parts-Express is only 40 miles from my house so I'll probably have all the components tomorrow. Will start the build this weekend an post pics.
The only quest I have is, does it matter what order I Place the speakers? I was thinking of putting the tweeters on the outside with the port in between each woofer like this:
Tweeter Woofer Port Woofer (o O∙ O) ( O∙ Oo) Woofer Port Woofer Tweeter
Thanks again
Posted By: DYohn
Date Posted: March 03, 2011 at 3:34 PM
That should work great. ------------- Support the12volt.com
Posted By: stevdart
Date Posted: March 04, 2011 at 10:50 PM
Looks like a great project. You've got interest in this build. Good luck!
-------------
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: p40whk
Date Posted: March 05, 2011 at 8:50 AM
stevdart wrote:
Looks like a great project. You've got interest in this build. Good luck!
Thanks! Most of the components were on my front porch when I got home yesterday, I was 3 woofers short but they should ship Monday.
I'm headed to Home Depot to pick up the MDF today and will begin laying everything out.
I picked up the Dayton
H110 Horns based on DYohn's recommendation but I should have checked the dimensions before I ordered them, They're huge! They're too big for what I want to do so I'm trying to figure out what to replace them with.
I'm leaning towards the Selenium HL14-25 but that's a completely different horn shape and not sure how it will affect the performance.
My other option is the Slenium HM17-25 but the throat depth is only 4 inches where as the original horn suggested has a 9-5/8" depth. The first Selenium horn I have listed above is closer in depth (10") but it has a narrower dispersion pattern (which may not be that bad for my application)
Honestly don't know what the difference between Constant Directivity, Exponential, and Bi-Radial horns are. I do know that all the specs given for the Selenium driver I'm using D220Ti, are based on the HL14-25 horn.
Posted By: DYohn
Date Posted: March 05, 2011 at 8:59 AM
Conststant directivity means the horn will produce a more even soundfield. There is less "beaming" like you get with a round or radial horn. CD horns are much more effective outdoors. Yea, they are a bit large, sorry about that.
The horn does not require an enclosure. Here's an idea: build your enclosures for the woofers and just mount the horns on top with a layer of fiberglass over the drivers to protect them from the elements.
Here's a nice looking but smaller CD horn, although the PE site seems to be out of stock at the moment. ------------- Support the12volt.com
Posted By: p40whk
Date Posted: March 05, 2011 at 9:12 AM
I've only got about 11 inches to work with between the top of my Bimini and the bottom of the tower that the pod will mount to. I can't mount anything on top of the tower because I trailer the boat through some pretty low tunnels.
Here's a pic of the boat showing the Bimini, tower, and current Polk speakers:
My ultimate size will be right at 58" wide by 11" high by 14" deep.
Posted By: DYohn
Date Posted: March 05, 2011 at 9:19 AM
Hmm. That's a very small area to work with. Here's a simple drawing of what I had in mind, but that won't work in your mounting location.
------------- Support the12volt.com
Posted By: p40whk
Date Posted: March 05, 2011 at 9:28 AM
Yeah, I'm kind of limited. Would the other horns really sound that bad? Shape and size wise they solve my problem. If they were closer to 8" square I would have no problems with the H110's but they're almost 12" square and I couldn't find anything (at parts express) any smaller.
I'll do a bit of web searching to see if there is anything else out there
Posted By: DYohn
Date Posted: March 05, 2011 at 9:56 AM
They won't sound bad, no. The only down side of them is they are simply more directional. I say go for it, use the design that fits into your system best and see what you end up with. Be sure you order a horn that is designed to screw onto your drivers. 1 3/8-18 thread I believe. ------------- Support the12volt.com
Posted By: p40whk
Date Posted: March 05, 2011 at 10:15 AM
DYohn] wrote:
They won't sound bad, no. The only down side of them is they are simply more directional. I say go for it, use the design that fits into your system best and see what you end up with. Be sure you order a horn that is designed to screw onto your drivers. 1 3/8-18 thread I believe.
Great! That's a relief. I've been laying everything out on paper and trying to fit everything in and it looks as if the two horns I have as options are the only things that will fit. Even the flared vent port I bought is too big so I'm going with PVC as you originally suggested.
Will document and post pics as I go.
Posted By: DYohn
Date Posted: March 05, 2011 at 10:18 AM
If you can't return the horns and the flared port, let me know via PM. ------------- Support the12volt.com
Posted By: p40whk
Date Posted: March 05, 2011 at 11:30 AM
DYohn] wrote:
If you can't return the horns and the flared port, let me know via PM.
I talked to P.E. last night and they'll take them back but thanks.
On another note; I was laying this out with cardboard cut outs to get an idea of the shape trying to fit it to the maximum dimensions I have available and that big 4" hole for the port just seems to get in the way (It'll work fine I'm just thinking aesthetics).
I thought to myself; "what about a slotted port?" then did some research and found this calculator: Port Size Calculator that allows you to calculate a rectangle port.
With a 1.5 cubic feet box, at 41Hz and 8" wide by 1.5" high port is 5.97" deep. I could use the 264-308 Square Horn with the slotted port underneath it built into the bottom of the enclosure and this would give me a very symmetrical look.
Is my thought process correct here?
Posted By: DYohn
Date Posted: March 05, 2011 at 11:53 AM
That's correct. A slot port is often the choice for pro-line speakers. I only suggested round because it's easier to build. :) ------------- Support the12volt.com
Posted By: p40whk
Date Posted: March 08, 2011 at 9:23 AM
Posted By: DYohn
Date Posted: March 08, 2011 at 11:40 AM
Looking great so far! ------------- Support the12volt.com
Posted By: p40whk
Date Posted: March 08, 2011 at 8:21 PM
Posted By: p40whk
Date Posted: March 09, 2011 at 7:51 AM
Quick question, Other than adding more internal bracing, is there another way to decrease the volume of the enclosure?
I filled the box with packing peanuts then measured the peanuts using a 6"X6"X6" box and it seems I've got too much space (better than too little I guess).
I was wondering if there was something easy I could put in like some of that "Great Stuff" expandable foam?
Posted By: DYohn
Date Posted: March 09, 2011 at 9:23 AM
How much space is too much? 6X6X6 is only 1/8 cubic foot... But to answer your question, use a block of MDF or 2X4 to fill space. And don't forget the space that will be occupied by the drivers and the crossover takes away volume. ------------- Support the12volt.com
Posted By: p40whk
Date Posted: March 09, 2011 at 9:31 AM
DYohn] wrote:
How much space is too much? 6X6X6 is only 1/8 cubic foot... But to answer your question, use a block of MDF or 2X4 to fill space. And don't forget the space that will be occupied by the drivers and the crossover takes away volume.
I was thinking that 6X6X6 was 1/2 cubic foot! No wonder I did so poorly in math! I should be good to go then, will re-measure again tonight.
Posted By: p40whk
Date Posted: March 13, 2011 at 4:52 PM
A few more pics of my progress.
Bodo applied and rough sanded:
And the crossover components mounted to their boards:
Posted By: p40whk
Date Posted: March 15, 2011 at 7:56 PM
Quick question; since I'm reversing the polarity of the HLCD, will I still be wiring the L-Pad like this?
I'm assuming the Negative now goes to pin 3 and the positive lead will now go to Pin1. Looking at the photo of my crossover above, the positive lead entering the capacitor on the upper right will go to the negative side of the speaker or Pin 1 of the L-pad. It's a bit late so I may be over thinking this.
Posted By: DYohn
Date Posted: March 15, 2011 at 10:48 PM
That will work fine. Polarity through the L-pad really doesn't matter. All you need to ensure is the relative polarity between the woofers and the tweeter is reversed (since a second order crossover introduces a 180-degree phase shift.) ------------- Support the12volt.com
Posted By: p40whk
Date Posted: March 27, 2011 at 8:54 PM
Posted By: DYohn
Date Posted: March 28, 2011 at 11:30 AM
Outstanding! That looks great. Have you connected it to an amp yet to see what it sounds like? ------------- Support the12volt.com
Posted By: p40whk
Date Posted: March 28, 2011 at 11:48 AM
DYohn] wrote:
Outstanding! That looks great. Have you connected it to an amp yet to see what it sounds like?
Not yet, all of the stereo equipment and batteries are out of the boat for the winter and I plan to start putting things back together as the weather permits (Cincinnati weather sucks).
I may try to run it from the amp in my truck though, I could do that fairly easily and may try that tonight. Will let you know what I get.
I did hook up an ohm meter to it and with the L-pad at dead center it reads 2.8 Ohms. Not sure if that's what I should be seeing but it's within the Amps tolerance level.
Posted By: DYohn
Date Posted: March 28, 2011 at 12:21 PM
The DC resistance you read with an ohm meter is different than the impedance it will exhibit in use, which varies depending on the music's frequency. Your system net impedance will be around 4-ohms. ------------- Support the12volt.com
Posted By: p40whk
Date Posted: March 28, 2011 at 12:35 PM
DYohn] wrote:
The DC resistance you read with an ohm meter is different than the impedance it will exhibit in use, which varies depending on the music's frequency. Your system net impedance will be around 4-ohms.
Ok, didn't know that. I'm anxious to hear how it sounds, hopefully will know this evening.
Posted By: p40whk
Date Posted: March 28, 2011 at 5:33 PM
Well, Got home and hooked it up to the truck amp (Kenwood 350 watt) and disconnected all the truck speakers so I only heard my box.
At lower volumes it sounds great but the bass gets a bit muddy and slightly distorted when I turn it up. The HLCD definitely overpowers the eminence drivers and I had to turn those down quite a bit with the L-Pad.
I'm thinking the Eminence drivers probably need to be broken in a bit before they really sound good. I have a bag of Acousta-Stuf Plyfill that I'll probably put in to see if that helps.
I played a bit with the EQ on my head unit and setting it to deep bass made it sound much better Unfortunately I didn't have time to play too much with it so not sure if it was the setting of my stereo or something else. It'll have a dedicated EQ (WS420) that I can make sure the levels are right.
It did sound much better the further away from it I got so that's a good sign and what I intended the unit for, probably just needs some tweeking.
Posted By: p40whk
Date Posted: April 07, 2011 at 6:50 AM
The box is complete, everything is hooked up and it sounds great! I finally was able to listen to it with a clean source so I think my problems before was the Amp in my truck. Bass is tight and the highs are very crisp.
I hope to have it installed in the boat this weekend weather permitting so that I can hear it in it's intended environment.
Thanks for the much needed help. Couldn't have completed this project without it. I learned a lot making this and may end up re-doing the enclosure to save a little weight, it's pretty heavy. But that's only after I get a chance to put it through it's paces.
Thanks again DYohn for your help. This was a fun project, one I'll probably repeat.
Posted By: DYohn
Date Posted: April 07, 2011 at 12:24 PM
Having fun and ending up with something the looks and sounds good - a perfect ending! Please post a picture of the finished system once it's installed on your boat.  ------------- Support the12volt.com
Posted By: p40whk
Date Posted: July 13, 2011 at 4:42 PM
Posted By: DYohn
Date Posted: July 13, 2011 at 6:45 PM
You did a really fantastic job. Good work! ------------- Support the12volt.com
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