First DIY !

[gareth]

I am building my first speaker. It will be a two-way bass-reflex design using an Audax AP210Z0 8inch woofer and an Audax TW025M0 tweeter.
I want to build a simple first-order Butterworth crossover for these drivers. I was thinking of crossing over the drivers at 2000Hz. Looking at the manufacturers data for the tweeter it says that the resonant frequency is 976Hz but looking at the supplied graph there is a resonant peak at around 2700Hz of about 25-27ohms.
Does anyone know if this peak will cause problems and if my design is viable? If not are there any suggestions that can be given?

Thankyou
Gareth

[MaVo]

why not use a design from someone who knows what he does, to build some experience?

for example, http://www.zaphaudio.com/ seems to be well liked around here.

[sdclc126]

Hi gareth,

Welcome and congratulations on your project. There are several issues here, and please take all comments you get as help and not criticism.

First, 2-way designs with an 8" woofer are rare and difficult to pull off - they're out there, but again they are few and far between. They usually require high order (steep) crossovers that can be quite complex, with many components, and thus expensive. This is because the operable frequency ranges of the drivers don't have a good overlap - either the tweeter has to operate at very low frequencies, or the woofer has to operate at very high, or both.

This brings me to my second observation about your design - a first order crossover in this case, especially for the tweeter, seems to be quite inadequate, so I must ask, how did you arrive at this design? Is it something you actually researched or modelled with software, or simply what you want to do? I'm afraid that if you build it as stated you will find the drivers distort and the sound quality will not be anywhere near its potential.

Now, I haven't looked up any data on these drivers - I'm opining on the fly here - so perhaps you could post frequency response curves, etc. for a more scientific assessment, but in lieu of that I have to agree with MaVo that you should consider building an established design for your first project - this is the most commonly given advice here for beginners, and most others too!

If you've already bought the drivers then you should, or have someone, model an appropriate crossover for them, if it's possible.

[Jay_WJ]

sdclc's comment above is right. A first order electrical xover (most likely Likwitz-Riley acoustic 2nd order) won't work with an 8" woofer and a 1" dome tweeter in most cases.

[hermanv]

Madisound will model your design and design a crossover (for a fee unfortunately). Then they will sell you a PCB and parts or even build the crossover for you.

As these things go, the fee is reasonable.

[Jay_WJ]

Originally posted by hermanv
Madisound will model your design and design a crossover (for a fee unfortunately). Then they will sell you a PCB and parts or even build the crossover for you.

As these things go, the fee is reasonable.

I've seen some of Madisound designed xovers. Those were not very careful designs that didn't even consider baffle loss/diffraction and phase tracking between drivers. You get what you pay for. I wouldn't use Madisound's xover design service.

[vdi_nenna]

Try to use drivers that over lap in frequency by at least 1000hz.
If you intend to use a 2-way with an 8" driver, try to use a good 1.5 inch tweeter. I think 2000hz is a low xover point, but it all depends. It's not impossible. You will definiately need a high order slope crossover. Try for 18db in the tweeter section. You won't have to worry about phase issues. If crossingover low, you'll need to protect that tweeter. 18db will help protect from low freqs.

Driver selection and crossovers are everything. A good crossover is the difference between a speaker that makes sound and one that will be very pleasing to your ears. This takes a lot of tinkering and listening to get it right.

The low freq impedance peaks can be smoothed out by a zobel network. It's a capacitor and resistor (usually the impedance of the woofer) in parallel with the + and - connections of the woofer. I could be wrong, but you shouldn't worry as much with the impedance at the higher freq end of the woofer as you do at the lower freq end. Of couse, ideally you'd want it to be as smooth as possible.

Hope this helps some.

Vince

[critofur]

Since you already have those drivers, you might want to consider adding a 3rd small midrange to each?

Starting with a good sized bump at 1.5Khz the rest of the high FR of the 8" drivers is pretty rough:

http://www.partsexpress.com/pdf/296-175g.pdf

Also, HF output will be very directional on a woofer that large.

I couldn't find the FR graph of the TW025M0.

[gareth]

Thanks for the recommendation but there doesn't deem to be anything of relevance for my project.

Thankyou
Gareth

[gareth]

Thanks for you reply. I have chosen a first order crossover simply because I felt that it would be easier to design for someone of limited knowledge. Maybe now I will think again.

Do you know of any (cheap/free) software that could help me?

I have the PDF's for the drivers I wish to use if they are of any use to you.

Thankyou
Gareth