newbie question regarding DIY

[bryceman22]

hi, i'm brand new to this site and i'm here mainly cause i can't find any answers.

i have some some of the amazingly good WHITE VAN speakers...lol...that i got from a friend. anyways...the box seems solid and i want to replace the drivers and stuff so i can learn about building speakers. this is on a very tight budget. I would really like to eventually look into building my own crossovers but i'm sure that right now i'll need to buy prebuilt crossovers.

anyways...i'm totally confused how the heck you can put a three way speaker together 12" woofer, 4" woofer, and a tweeter and come out with the cabinet being 6-8Ohm. i'm excited about learning this stuff and any help would really be appreciated.

as mentioned:
12" woofer
4" mid
and i'm not sure what the hole size is for the tweeter.

i'd like to do this right as i'm running a Carver HR-772 receiver and really don't want to blow it. says that if i only run A or B it can handle a 4Ohm load...but i don't want to push it.

 

[bryceman22]

also, i may be totally confused...but wouldn't a 3 way crossover (prebuilt 3 way) be running all three speakers parallel? thus causing a low Ohm load...drawing alot from the amp?

what wouldl be the best way to do this? two separate 2-way crossovers? one to split lows and mid/highs and then to split the mid and high?

 

[Swerd]

Welcome bryceman22

You might want to get a copy of a good introductory book like Speaker Builder 201 by Ray Alden. It discusses crossovers in much more detail that I do below, and it discusses how to design an appropriate sized box to get the best bass performance from a given woofer. I think that will answer a lot of your questions.

also, i may be totally confused...but wouldn't a 3 way crossover (prebuilt 3 way) be running all three speakers parallel? thus causing a low Ohm load...drawing alot from the amp?

Even though each driver in a 3-way, or a 2-way speaker, is wired to the input from the amp in parallel, the various filters in the crossover prevent the all the drivers from “seeing” a signal all at once. For the woofer, a low-pass filter at 300 Hz for example, effectively blocks signals an octave above that, 600 Hz or higher, from getting through to the woofer. Something similar works for the tweeter, where a high-pass filter, at say 3,000 Hz, effectively blocks signals much below 3,000 Hz from getting to the tweeter. For the midrange driver, a band pass filter from 300 to 3,000 Hz only allows signals in this range to reach it. The only time two drivers see the same signal at an equal level is near the crossover frequency.

These filters work gradually, not all at once. For example the 300 Hz low-pass filter begins to roll-off signal at 300 Hz by several decibels (dB) per octave. In this example, let’s say it is 24 dB/octave. So below 300 Hz the signal might be 75 dB, at 600 Hz it is 51 dB, and at 1200 Hz it has fallen to 27 db. A difference of 3 dB is typically considered the smallest change in loudness that the average human can detect. Twice as loud is equivalent to a 10dB change in acoustic output.

 

[bryceman22]

Even though each driver in a 3-way, or a 2-way speaker, is wired to the input from the amp in parallel, the various filters in the crossover prevent the all the drivers from “seeing” a signal all at once. For the woofer, a low-pass filter at 300 Hz for example, effectively blocks signals an octave above that, 600 Hz or higher, from getting through to the woofer. Something similar works for the tweeter, where a high-pass filter, at say 3,000 Hz, effectively blocks signals much below 3,000 Hz from getting to the tweeter. For the midrange driver, a band pass filter from 300 to 3,000 Hz only allows signals in this range to reach it. The only time two drivers see the same signal at an equal level is near the crossover frequency.

so...even though the 3 drivers are wired parallel, the crossover isn't allowing them each to recieve the full signal (i completely understand this, and the breakup in your example 600Hz and 3000Hz, i get this) the speakers then are not each drawing their full Ohms? the resistance from the crossover breaking up the signal changes that? so 3 8Ohm speakers wouldn't be pulling at what 2Ohms because of the crossover? that's the part i'm stuck on.

 

[Gimpy Ric]

Here Ya go, get yourself an audio education from Aperion University! Its free, and all about speakers.

http://www.aperionaudio.com/catalog/Aperion-University,2.aspx

 

[Swerd]

so...even though the 3 drivers are wired parallel, the crossover isn't allowing them each to recieve the full signal (i completely understand this, and the breakup in your example 600Hz and 3000Hz, i get this) the speakers then are not each drawing their full Ohms? the resistance from the crossover breaking up the signal changes that? so 3 8Ohm speakers wouldn't be pulling at what 2Ohms because of the crossover? that's the part i'm stuck on.

I think you got it even if you don't quite think so. If a signal is outside the pass band for a given driver, the speaker draws no current (for that signal) and it essentially doesn't exist as part of the circuit.

 

[bryceman22]

ok...this makes sense. if you're only drawing certain frequencies...your only drawing current for those signals.

i also understand that the 8ohm rating is sort of an average at the tested frequency and that it's not consistantly drawing at 8ohm.

so put together a three way speaker that was a nominal impedance of approximately 8ohm (ie the whole cabinet) would you then have to get into the specifics of the draw in those frequencies that the crossover breaks up?

like the average impedence of a tweeter at (to use your example) 3000+Hz...and a midrange drivers impedence from 600Hz to 3000Hz...and the same for the woofer >600Hz? and if so...how would you use that information?

i guess my question is...how would you know what the draw on the entire cabinet would be?

or do you just assume...that with a prebuilt crossover...designed for 3 8ohm speakers...that the overal current draw on the amp would be safe for an 8ohm amp?



a whole nother question that i just thought of (haven't researched this yet as it just popped into my head while typing) a speaker thats rated 8ohm....but doesn't get the complete 8ohm signal because a crossover has removed highs and lows (for a mid pass), would the speaker still get enough current to power it? or is this what the whole fall-out thing is referring to?

 

[Swerd]

i guess my question is...how would you know what the draw on the entire cabinet would be?

or do you just assume...that with a prebuilt crossover...designed for 3 8ohm speakers...that the overal current draw on the amp would be safe for an 8ohm amp?

I guess you could assume, and you would probably be OK in your situation, but the only way to know the draw of the entire speaker is to measure it and plot it as an impedance vs. frequency curve. I found an example of such a profile for a 2-way speaker, the Ascend Acoustics Sierra-1, which was shown on the manufacturer's web site.

Note how in this speaker the nominal impedance is said to be 8 ohms, but it goes as low as about 5 ohms, and that it varies depending on the frequency. That is a function of the impedance of the raw drivers, the cabinet (sealed or vented) and the crossover.

This speaker is a small vented 2-way. I'm guessing the crossover point is somewhere between 2 and 3 kHz. Note how the impedance gently rises above ~400 Hz. You can tell a woofer is vented by the twin impedance peaks in the bass frequencies, in this case at 30 and ~75 Hz. The vent tuning frequency is where the low point is between these two peaks, just below 50 Hz. A woofer in a sealed cabinet would have only one peak, at the woofer's resonance frequency.

The other small peak, between 2 and 3 kHz is the resonance frequency of the tweeter.

To make such a curve yourself, you would need test & measuring equipment and software.

 

[Swerd]

Good link! Thanks.

 

[bryceman22]

Hey Swerd,
thanks a ton for your help and info. i'll definately look into getting that book to get started actually building my stuff.

and i suppose i should look into a 2way speaker system for my first crossover attempt. this should be fun.

again...appreciate the help and the info.

and your coast to coast thread was very interesting...seeing the charts and everything...i guess the real goal is a very flat line.

 

[billnchristy]

Crossovers are very tricky.

If you want to have an easy success, a single driver full range is the way to go...just research the driver that suits you and build the enclosure...job done!

 

[IonMan]

Just to be sure you dont blow up your tweeter (hehe)

Hi all,
I was just having a quick peruse of the forums and saw this thread. I just wanted to clarify something - just to be on the safe side.

The 3 speakers must never be in parallel. Parallel means that all the +ve terminals are connected together and all the -ve terminals are connected together. That may or may not kill anything depending on where you plug the other end of the cable into - ie if you plug them all into the tweeter output of your xover, you'd be ok, but it wouldn't sound too hot). But its better to assume that you will kill your tweeter and squawker (are they still called squawkers? - midrange) and never wire them in parallel.

Each speaker has a different set of connectors (or posts) to attach to and once speakers are connected to their respective xover outputs, they are then in parallel and or series with resistors, Capacitors, or Inductors (R's, C's or L's) or combinations of these. These components on the crossover distribute the signals to the appropriate speaker, which separates the frewuency bands to the appropriate driver (speaker) as explained in other posts. Around the crossover points there will be identical frequencies passed to different drivers, but it will be reduced in level by the via L, C's or R's which all have an impedance value - resistance that varies with frequency. It is this impedance that separates the speakers from each other electrically and that is the reason they cannot be considered in parallel. Even at the points where equal levels of signal are being fed to different speakers, because those levels are 3 dB down (due to series and parallel impedances that separate the speakers electrically.

My worry was that you might connect the speakers in parallel and then to the xover. That would be a sad loss for you

Enjoy your speaker building, its fun,
Ian

 

[bryceman22]

My worry was that you might connect the speakers in parallel and then to the xover. That would be a sad loss for you

Enjoy your speaker building, its fun,
Ian

thanks...i understand. in the prebuilt crossovers you would connect you +/- from the amp to one end and then the two/three sets of +/- come out the other end. the crossover is where the 'parallel' is split in different ways. i did get this...but thanks for bringing it up...if i didn't understand this it would be real sad.

i picked up Designing, Building, and Testing Your Own Speaker System from the library this weekend and it was a good read...lot of info about crossovers and how they work. I appreciate that it actually had some theory in there behind the idea of crossovers. They have a nice two way system in there that i'm itching to build. (they do have a project with single full range speakers, sort of a simple learn but i don't think that i'd have any use at all for them)

i am thinking though that for my first speakers i may want to use some fairly cheap drivers. i understand that they probably wont sound the best, but if i totally screw up i wont be out alot of money. do you all have any recommendations?

also, i'm kinda torn between a two way system with some 4" drivers or a two way with 6" to 6-1/2" drivers...i understand that the larger drivers will provide a better range of sound...but i'm figuring that 4" drivers at the same price as 6" might sound better than the 6" at the price range.

i appreciate all your help and suggestions.
thanks.

 

[Swerd]

i am thinking though that for my first speakers i may want to use some fairly cheap drivers. i understand that they probably wont sound the best, but if i totally screw up i wont be out alot of money. do you all have any recommendations?

also, i'm kinda torn between a two way system with some 4" drivers or a two way with 6" to 6-1/2" drivers...i understand that the larger drivers will provide a better range of sound...but i'm figuring that 4" drivers at the same price as 6" might sound better than the 6" at the price range.

Hey bryceman

There is a kit sold by Parts Express, the BR-1, that is inexpensive and also is a pretty good speaker. It is a great way to introduce yourself to DIY speaker building. This month, it is at a reduced price of $129 for a pair. You won't find any kit at a better price. It has all the parts you need including assembled cabinets. I am told by people who've bought it, that the kits instructions are a very good primer for DIY speaker building. I think you can download them directly from the web page.

 

[bryceman22]

once again swerd you have helped immensely!

this kit looks like the perfect place to start...it's almost exactly like what i was looking to build. (i was going to have a hard time finding speakers to match in the cabinets, the woofer and tweeters...this solves that problem)

i get paid wednesday...and i'm sure i'll be ordering this soon. what a great way to really get down and dirty putting a crossover together.

thanks for throwing this my way.

 

[IonMan]

hi again Bryceman,

I figured you'd probably have known, but its better to be safe than sorry (and less expensive too .)

THere are a lot of great suggestions in this thread. I suppose it would be best to list the reasons you are doing this project, then put them in order. That might help you decide which is the best way to go.
Perhaps you want a system up and running quickly at a good price - maybe a simple full range would be the go ... All your money is then only going to go into one driver per box and therefore quality will be higher (no crossover too).
Or perhaps you want to try constructing a crossover in the future. There's a lot of experimentation you can do with crossovers if you have the desire.

If you do go the kit way, dont stop studying ... theres always things you can do to improve a kit, over time.

I just stuck my nose in cos I have some professional electronics experience and didnt want to see you get in trouble being a newbie and all.

Good luck with your project ... now I might have to start one of my own, lol.

Ian