phase?...first build

[ZeNmAc]

I'm planning to build some small OB bookshelf sized speakers. I have some old woofers from an alpine component set that I just refoamed. My initial rough measurements looked pretty good, so I'm planning on buying a cheap tweeter and sticking it in an open baffle since I don't know the specs. On a side note, would you recommend OB or sealed for woofers with unknown parameters? They're going to be for a computer, so near-field with a wall fairly close behind them.

Here's my question. The woofers originally had grilles on them so they have permanent 'flanges' that stick out about 1/4 to 1/2'' around the circumference of the woofers. I'm guessing that would do horrible things as far as diffraction so I'm planning on rear mounting them.

If the woofer is rear mounted and the tweeter is surface mounted or flush with the baffle, how do I compensate for the difference in distance (1/2-3/4'' thick baffle). Should I get a waveguide or something so the tweeter is even with the woofer?

One last question, I forget what the rule is for determining phase for passive xovers. I'm planning on 2nd or 3rd order.

Any help you can give is greatly appreciated. I'll probably get frequency response graphs of the woofers up later.

tl;dr version: rear-mounted woofer, surface mounted tweeter, passive xover, how do I make sure they are in phase?

[ZeNmAc]

Here's my rough measurements. It's not entirely accurate since I don't have a sound treated room with an infinite baffle laying around .

It was actually measured with my dayton emm6 about an inch away from the dust cap. Don't pay attention to bass and upper treble. It was't that far away from other objects in the room. I was actually holding the driver's magnet with my hand . Upper treble is rolled off either by the laptop or cheap amp I was using.

Distortion of each driver

dist1.PNGdist2.PNG

Frequency response of each driver

fr1.PNGfr2.PNG

Thankfully they seem to be pretty close.

here's one last one using sine sweep instead of pink noise (unsmoothed).

FR.PNG

I think I've decided on using the aurasound nt1-204-8d for the tweeter.

[PeteMcK]

You'll need an impedance plot to design xovers,
xover order - even orders are phase inverted
'OB' & 'small' are mutually exclusive...

[speaker dave]

Originally Posted by ZeNmAc

Here's my question. The woofers originally had grilles on them so they have permanent 'flanges' that stick out about 1/4 to 1/2'' around the circumference of the woofers. I'm guessing that would do horrible things as far as diffraction so I'm planning on rear mounting them.

If the woofer is rear mounted and the tweeter is surface mounted or flush with the baffle, how do I compensate for the difference in distance (1/2-3/4'' thick baffle). Should I get a waveguide or something so the tweeter is even with the woofer?

One last question, I forget what the rule is for determining phase for passive xovers. I'm planning on 2nd or 3rd order.

You are off to a good start because you can measure frequency response.

Rules for phase vs. network order are primarily for electrical networks alone: without drivers. Not only will drivers have delay from front mounting/rear mounting but the total depth of the woofer (approx to voice coil) will add delay not compensated for in the simple networks.

For that reason it is hard to predict what xover order and polarity will add.

Don't add a waveguide for the sake of phase shift. Some network will work with the relative depths that you have. Since you can measure response (can you measure phase?) just start with networks that give response corners at the right place and see how they add. Try the tweeter polarity both ways and if one way is great and the other cancels with a deep notch, you are done. If both ways add poorly then try a different order on one or both drivers and repeat.

Herre is a long thread that goes through 1st, 2nd and 3rd order networks for a system and how they impact summing. It tells you all you need to know.

Crossover mods for the AR4x - The Classic Speaker Pages Discussion Forums

I would start with a damped 2nd order for the woofer (series L and shunt C and R, try 0 to 3 ohms for the R) and 2nd order for the tweeter. Simple networks but they will give a lot of response versatility.

Get a variety of crossover parts to experiement with. Don't be afraid to pull turns of an inductor or parallel a bunch of small capacitors to see what different values do. Get a feel for how crossover values effect crossover frequency and especially how L to C ratio impacts corner shape. Understand this and you are well on your way to being a system designer.

Regards,
David S.