My first build. Need XO help.

Ironhead

Member
2007-12-10 5:43 am
Hi,

I have searched the forum and I haven't found what I was looking for. There is just so much info to poor through and I get tired of looking at the screen so long so I figured no one would hate me if I asked.

I have been wanting to build my first two way speaker for a few weeks and I get confused about crossovers. I don't understand how to choose a crossover frequency. Out of everything I've read there seems to be no exact way to do it which is the way I like to do things. Choices just confuse me more. I like things to be one way.

I chose the cheapest speakers I could because I didn't want to spend a lot on something I did for the first time. I will probably use these as computer speakers. I chose this woofer:

http://www.partsexpress.com/pe/pshowdetl.cfm?&Partnumber=295-330&CFID=15014910&CFTOKEN=84176090- and this tweeter:

http://www.partsexpress.com/pe/pshowdetl.cfm?&Partnumber=275-030&CFID=15014910&CFTOKEN=84176090.

So, from what I understand the crossover would be at about 7k Hz. How wrong or right is that? Seems too high to me but what do I know. Please help.
 
These are not really well matched drivers as the woofer should be crossed much lower due to its break-up modes. You would need to build a rather complex, high order crossover which will add significantly to the cost.

I use the DA135-8s in my center channel speaker for HT but it is crossed at 1450 Hz. I also added bucking magnets to video shield them - necessary also if your computer monitor is CRT.

The DA135-8s are a quality woofer but consider a different one to mate with that tweeter, or perhpas go with a single wide range driver, with no or minimum filter.

As to where to choose the crossover point - lots of variables there and this requires quite a bit of experience and also access to design software. I would recommend reading up at www.zaphaudio.com, and consider these two designs as possibilities for your computer:

http://www.zaphaudio.com/ZBM4.html

http://www.zaphaudio.com/audio-speaker18.html
 

Ironhead

Member
2007-12-10 5:43 am
Many thanks to the both of you. Until now I didn't realize the importance of having drivers that matched well. I think I'll try the ABM4's from Zaph for my first 2-way build. I also have the wood cut for a single driver full range project I started before this using the W3-871.

One more question. Should I try to completely design my own speakers next time, I should choose two drivers that crossover around 2,000 Hz right? Maybe within 500 Hz?
 
The crossover frequency is dependent on the drivers chosen, and varies widely. Usually the crossover point is the same frequency for both drivers, but it can overlap with a low order slope, which is better than a gap in between, where an audible dip (relative quietness) in speaker frequency response can occur. Some people like this however - a "laid back" midrange is what is often described.

My preference is an even response across the performance range of the speaker - it is representative of reality.
 

jnb

Member
2006-12-30 11:55 pm
You will do well to go with an existing design for your first project. Don't forget to modify it extensively and learn from it.

Your initial concerns with choosing drivers are the tweeter resonance (Fs) and the woofer's rough top end. Keeping 1 to 2 octaves (2 to 4 times) above Fs for youe crossover and 1 to 2 octaves below the woofers breakup, is a simple rule of thumb.