Crossover challenge

[Ty_Bower]

Here's an episode of "Can it be made to work?"

Here's what I've got with which to work. The budget has been spent. I don't think it would be worth it to buy any extra parts, unless they're unbelievably cheap. The goal is to make something at least fit for garage duty:

One pair of enclosures, about 1.25 cu ft each.
One pair of Radio Shack 8" poly woofer (RS 40-1024)
One pair of Dayton DC28F tweeters (PE 275-075)
Two 4.7 uF caps
Two 8 uF caps
Two 10 uF caps
Two "universal crossover" coils, 0.6 / 0.47 / 0.3 mH
Two wirewound potentiometers, ?? ohms (RS ??-????)

I built these as a teenager. I recently bought the Dayton tweeters because they were inexpensive, and I thought they might help salvage these otherwise unlistenable speakers. Then I realized my crossover was probably all loused up and half responsible for the bad sounds coming out.

I downloaded Speaker Workshop. It appears to be a powerful tool with an equally powerful learning curve. I think I've figured out how to import the frequency and impedance curves for the Dayton. I've got nothing for my 8" woofer, so I imported the data for a different woofer (just so I could learn how to use SW).

I'll admit I don't have a lot of parts, but I'd like to layout the best I can with what I've got. Any hints where I should start? Is there any chance I'll find any data anyway for my Radio Shack woofer? Can I even begin to think about building a crossover with the pitifully small number of components I've got? Should I just pitch the thing in the dumpster and cry?

[Dave Bullet]

I wouldn't give up. If you don't mind spending a few hours, you may not be able to get a perfect speaker but something possibly more listenable with the parts you have.

First - you really need to get a frequency response and impedance measurement for the woofer. Without it, you will be software modeling in the dark.

Have you googled for your woofer?

Assuming there are no FR / impedance plots on the web. If you can't take the woofer (preferably in the cabinet you plan to keep) around to an associate to measure, can you get hold of an SPL meter? An SPL meter would be a manual and laborious way, but with time you can get enough points to build a set of frequency response points.

If you can get me the raw data - I am happy to model a crossover given the components you have. I won't guarantee the results, but will at least give you a picture of what is possible.

Cheers,
David.

[Dave Bullet]

Found these specs for the 40-1024 at RS:

SPECIFICATIONS
Nominal Impedance .....................8 ohms
Frequency Response .......35 Hz-3000 Hz
Free Air Resonance (Fs) Frequency .................... 35 Hz
Infinite Baffle Resonance Frequency ................... 33 Hz
Piston Area (SD) ..................... 0.0214 m2
Power Handling 50 W RMS
Maximum Power...... 100 W
Flux Density (BL).........6.77
DC Voice Coil Resistance (RE, ohms) ............6.6 ohms
Voice Coil Inductance (LVC at 1 kHz) .............. 0.93 mH
Equivalent Air Volume (Vas).... 2.7 ft3/76 l
SPL........ 87ð ±2 db/1W/1m
Moving Mass (Mms).....................18.38 g
Electrical Q Factor (QES)..................0.57
Mechanical Q Factor (QMS)..............3.46
Total Q Factor.............0.49
Equivalent Acoustic Volume (VAS)..76.3 l
Mechanical Suspension Compliance (CMS, UM/N)..........1174.63 UM/N
Mechanical Mass of Cone Assembly and Free Air Load..............18.35 g
Mechanical Mass of Cone Assembly Only .........16.55 g
Peak-to-Peak (Maximum) Linear Excursion.....2.35 mm
Cutout..... 7 Inches/17/8 cm
Depth.... 31/8 Inches/8.0 cm
Magnet Weight ......9.97 oz.
Speaker Weight.....33.3 oz.

Looks like with a higher Q it may be more suitable for an open baffle.

The 2.35mm xmax limit is a concern though... you won't be able to get any serious bass at any reasonable volume with these.

I cannot find a frequency plot

There is however another thread discussing options with the 40-1024 here:
SPECIFICATIONS
Nominal Impedance .....................8 ohms
Frequency Response .......35 Hz-3000 Hz
Free Air Resonance (Fs) Frequency .................... 35 Hz
Infinite Baffle Resonance Frequency ................... 33 Hz
Piston Area (SD) ..................... 0.0214 m2
Power Handling 50 W RMS
Maximum Power...... 100 W
Flux Density (BL).........6.77
DC Voice Coil Resistance (RE, ohms) ............6.6 ohms
Voice Coil Inductance (LVC at 1 kHz) .............. 0.93 mH
Equivalent Air Volume (Vas).... 2.7 ft3/76 l
SPL........ 87ð ±2 db/1W/1m
Moving Mass (Mms).....................18.38 g
Electrical Q Factor (QES)..................0.57
Mechanical Q Factor (QMS)..............3.46
Total Q Factor.............0.49
Equivalent Acoustic Volume (VAS)..76.3 l
Mechanical Suspension Compliance (CMS, UM/N)..........1174.63 UM/N
Mechanical Mass of Cone Assembly and Free Air Load..............18.35 g
Mechanical Mass of Cone Assembly Only .........16.55 g
Peak-to-Peak (Maximum) Linear Excursion.....2.35 mm
Cutout..... 7 Inches/17/8 cm
Depth.... 31/8 Inches/8.0 cm
Magnet Weight ......9.97 oz.
Speaker Weight.....33.3 oz.

No rock on open baffles?

Cheers,
David.

[Ty_Bower]

Originally posted by Dave Bullet
Have you googled for your woofer?

...can you get hold of an SPL meter? An SPL meter would be a manual and laborious way, but with time you can get enough points to build a set of frequency response points.

There doesn't seem to be much data for this woofer, other than the TS parameters. I do have a SPL meter, as well as a PC with a sound card and a microphone. I'm not sure the response of the microphone is good enough to get any useful measurements, but I'm not against doing it by hand with the SPL meter. How many data points do I need? How far should the meter be from the driver when taking measurements?