Crossover Frequency

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Ironhead

Member
Joined 2007
Hi, I got interested in diy audio a few months ago but kind of dropped it because of some confusion I had about choosing a xo frequency. My interest was sparked again when I came across a pair of older (90's) Polk Audio bookshelf speakers for $4 at a local thrift store. Turned out that one woofer was completely useless and the other was near its end. I decided to remove all the old components and use the enclosures to build my own custom computer speakers. My problem is that I want to choose the right frequency to crossover at. I have read that I should crossover 1 to 2 octaves above the Fs of my tweeter which in my case is 3,000 Hz. I'm not sure how to determine that value correctly. Should the xo frequency be 6,000 Hz?

Here are the drivers I plan to use.
Tweeter: http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=276-025
Woofer: http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=264-817

I don't want buy a kit so please don't recommend that option. I feel that building a kit would be the same as simply tearing apart and reassembling a pair of speakers.
 
Iain McNeill

Iain McNeill

Ex-Moderator
Joined 2007
impaudio.biz
Are you using these speakers because they fit in the existing baffle or are you going to cut a new baffle to suit?

Reason I ask is the tweeter you have chosen will be hard to design a crossover for. The natural response is a 2nd order at 3KHz and so as you say, you need to crossover above this point.

You could add a cap at 3KHz (to protect tweeter from LF) and make it a 3rd order acoustic and design woofer hi pass to match.

Then again, the Tang Band is a really nice speaker. I have some W3-1364's which are great as full range albeit no bass below 80-100Hz.

My recommendation? just use the TB's in you're thrift store cabs with new baffles and then add a sub down the road.
 
I

Ironhead

Member
Joined 2007
Iain McNeill said:
Are you using these speakers because they fit in the existing baffle or are you going to cut a new baffle to suit?
Click to expand...

No they will not fit, I will be making a new baffle regardless of what drivers I end up with in the end.

Reason I ask is the tweeter you have chosen will be hard to design a crossover for. The natural response is a 2nd order at 3KHz and so as you say, you need to crossover above this point.

You could add a cap at 3KHz (to protect tweeter from LF) and make it a 3rd order acoustic and design woofer hi pass to match.
Click to expand...

I chose that tweeter mainly because of price and looks, but if there is another that would work better I wouldn't mind switching.

Then again, the Tang Band is a really nice speaker. I have some W3-1364's which are great as full range albeit no bass below 80-100Hz.
Click to expand...

My enclosures are .162 cu. ft. And the woofer selection chart on partsexpress.com indicates the my selected woofer would be at F3=77 at .15 cu.ft. ported. I'm thinking this will be fine for computer speakers especially if I add some damping material. Like you said, I could add a sub later on. I have seen other tang band and Hi-Vi full range drivers that reach 20,000 Hz, Would it be better to just use one or 2 full range drivers? Or is that more complicated?

My recommendation? just use the TB's in you're thrift store cabs with new baffles and then add a sub down the road.
Click to expand...

Are you recommending to leave out the tweeter and just use the TB's. I would do that but I'm not sure if I would need any type of xo or if it would just be straight wired?

Sorry for so many questions.
 
Iain McNeill

Iain McNeill

Ex-Moderator
Joined 2007
impaudio.biz
exactly. Just use the TB's full range straight wired to the amp. No fuss, no muss, no darned XO to mess things up.

Do a search of the W4's on the full-range forum, I think you'll get a lot of hits.

Your .16cuft cab is a bit small for sealed cabinet and would increase resonance / cut off some bass while reducing distortion. But ported, as you indicate, you should get quite acceptable bass with tuning (at the expense of transient response.)

I think the FR crowd may try to persuade you to go open baffle......
 
I

Ironhead

Member
Joined 2007
Great, because I was starting to change my mind and just spend my money on some brand new speakers from amazon. I was leaning toward 2 way because of bass but I may save that for another day when I feel like building enclosures and all. Also I realized that when comparing tweeters I was comparing the Fs of the audax with the wrong number in other tweeters specs. Therefore thinking the audax tweeter had the lower Fs. lol.

Thanks for the help. :)

edit: Still I would like to know how to measure one octave above any given frequency. If anyone would help me out there. I get confused between different things I have read. Am I correct that its just twice whatever the starting frequency is?
 
O

ocool_15

Member
Joined 2004
Ironhead said:


I chose that tweeter mainly because of price and looks, but if there is another that would work better I wouldn't mind switching.
Click to expand...

I don't see alot of information available but I expect you will get a better result using a driver that can cross over lower.


Would it be better to just use one or 2 full range drivers? Or is that more complicated?
Click to expand...

If you are talking 2 full range drivers per side it would normally be used for a full baffle step design which isn't normally used for near field computer speakers.

For best results you will need to measure the drivers.
From the cone diameter you should crossover no higher then 4050 Hz. From the supplied frequency response graph the peak centered at 6500 Hz will likely show up as a peak F2 harmonic of 3250Hz. If its bad you should cross this driver below that point.
 
I

Ironhead

Member
Joined 2007
Ok, I'm still not totally decided on whether I want to use 1 full range driver per side or a new pair of drivers I think will work much better together. Like I said above my decision on that tweeter was due partly to my not comparing the right numbers. So, if I don't do 1 full range per side I may try this.

Tweeter: http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=270-176
Woofer:http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=297-429

I believe that pair would work much better. Crossed over at 2600Hz. The enclosure will still be too small I think but stuffing it would bring it up to acceptable I think. Yes, it will be ported. I may even save this pair for later and make new enclosures specifically for them. How does this look? Comments? I'm learning a lot so don't stop with the help.
 
Iain McNeill

Iain McNeill

Ex-Moderator
Joined 2007
impaudio.biz
Ahh but where's the thrill in buying a pair of ready mades.

If you want your first taste of success with no risk, just put the TB's on their own in your cabinets - sealed. They'll sound great! Then, once you're addicted like th rest of us, you can play with adding tweeters, sub woofers, ports, crossovers, bi-amps, tri-amps, DSP.............

once you start... You have been warned:cool:
 
T

tinitus

Ex-Moderator R.I.P.
Joined 2005
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