XO help on cheap PA drivers

[AdamThorne]

So I've built some cheapo party / garage speakers! Cheap, big, and loud were the design goals, and after hearing the woofer run full range I think I'm on the road to success. The box is together, but I still need the crossover. So here I am looking for help.

Here's what I got:
A big, cheap, MCM 12" part no. 55-1745
12'' Professional Woofer | MCM Audio Select | 55-1745 (551745)
Claims response out to 4.5 khz

Cheapish Pyle compression driver
Tweeter Titanium Horn Driver Threaded Compression 150w RMS | Pyle | PDS221
Fs 800 hz (claimed)

I haven't found any frequency response graphs for these inexpensive drivers. I don't have frequency response measuring stuff, though I can do an impedance sweep.

Dayton 10" waveguide for the pyle
Parts-Express.com:*Dayton H10RW 10" Round Waveguide 1" Threaded | horn lens horn tweeter horn bell horn compression driver DaytonAudioWaveguides070109
loads down to 1,600 hz.

My simplistic plan at this point is to hear from some one what kind of acoustic slope is going to come out of the tweeter / WG combo, then add maybe 2nd order electrical (prolly around that 1.6 khz from the WG) to keep me from toasting the tweeters. Then whatever would match that on the woofer. Plus impedance compensation. BSC will be considered after the woofer and tweeter are playing nicely together.

But this is the first pair of speakers I've built w/o someone else's plan to follow, so maybe someone else will have a better idea. Whadya think?

[elac310]

To stay in the spirit of the project (cheapish, simplistic, no data available), I would just put a capacitor in front of the compression driver to protect it. Any value between 6 and 8uF will probably do the trick (a 63V electrolytic is the cheapishest one can find). The compression will most probably play too loud compared to the woofer so you will probably want to add a resistor before the capacitor; depending on taste, something between 2 to 8 ohms should do (10W if you listen musik gently, 20W or more if you do parties).

Chris.

[Inductor]

They look great.

[AdamThorne]

Thanks for the response! I had just about figured this post for ignored.

I was just slapping some poly on them this weekend, to keep the OSB from getting mushy if the garage gets a little damp. I must say that the 12-inch (running full range ATM) is great fun. Rarely misbehaved, and it has great impact, tho I'll have to finish the speaker before I can give it an unrestrained thumbs up. In the box I made I think the predicted f3 is just a bit under 50 hz. Some people think the xmax spec is a typo (according to a post over at BillFitzmaurice that no longer exists, but google still returns it, so grain of salt). I know the driver takes everything my little cheapy 15 watt garage amp can throw at it on bassy music as if it were nothing.

Here's the thing, tho: the 12" is (as one might expect) real directional by the top of it's frequency range. Moving even a little bit off axis during test listening sounds like a blanket is thrown over it. So I was wanted to cross the tweeter in lower so that the party people can still hear the treble when they move off axis. I was thinking of the 2khz neighborhood.

Sound reasonable? Or am I getting too complex?



Thanks again for the input!

[chris661]

That would be expected from a woofer like that - they'll go reasonably high, so you think "brilliant, I can cross that high", then you learn it beams. I'd try to find out where the beaming starts getting worse, then XO there.

For the Xmax, this could well be correct. It is, after all a music speaker, generally speaking (what I've read), they have low Xmax, but decent Xmech. The non-linear starts early, but you don't notice it until it's really far out. For example, I got a woofer with 3mm Xmax, goes to 12mm p/p then bottoms out. Sounds fine anywhere between.

[SState13]

Really like this project idea. If yours turns out well, i might have to try building a pair of my own.

I would like to second what chris said about the X-max. I have most of my experience with subwoofers (where distortion is less audible), but many of those drivers have the capability to far exceed their given xmax without issues. And given the size of that woofer and by the look of the surround, i would think its be capable of over 1mm of excursion without problems

good luck continuing the build

[Inductor]

Xmax (max. excursion (peak) with 10% distortion)
Xlim (max. excursion (peak) before physical damage)

Should be ok for garage functions...

I was thinking of the 2khz neighborhood. (xover)

Lower xover only with a second/third order xover. Testing that low 1st order, maintain power low on the CD because of low frequencies and burn out.

[AdamThorne]

Well it took a little while to get it together, but now it's done: Simple 2nd order LR at 2khz. Based on this site, 2-Way Crossover Designer / Calculator and assuming that the woofer and tweeter were both simple 8r. Also, an L-pad to bring the tweeter in line with the woofer.

And it doesn't sound bad!

Initially I hooked up the tweeter out of phase with the woofer, b/c I had heard that the cross would shift the phase far enough to justify it. But perhaps I heard wrong, or maybe the physical shift from the wave guide was enough to change the phase relationship. Either way, the drivers sound best in phase.

Based on the driver params I measured WinISD suggested a truly gargantuan box. Maybe because I scaled things down some, or maybe b/c I haven't built in any BSC the setup sounded a bit on the lean side. The XTRA-MEGA-BASS button on the garage portable cd player fixed that, though.

I'll probably play with some BSC (have to figure out how to sim it, so I know where to put it), I've heard the wave guide can use some damping and I'm pretty sure the woofer could as well, and probably a little extra work on the XO might render some benefit. Apart from the BSC, though, the speaker is really already about as refined as my garage can justify.

AND they'll go loud enough to rock the garage on just 15 watts. Dynamic and forceful.

If you decide to try something similar, get on MCM's mailing list and keep an eye out for the woofer for a while. They go on sale for $25 / woofer pretty often. At that price it's pretty easy to call them a bargain.

I'll try to measure out and post what my Lpad settings were, as the l-pads were a significant expenditure in this cheapo project.

[rcw]

This type of driver is intended for guitar type applications and has a suspension that increases in stiffness very rapidly from the rest position, this is to resist the very large d.c. pulsing effect you from playing bar chords for instance.

In essence it is designed to produce and not reproduce music, distortion is part of its sound.

A better option is to use a driver such as a coax intended for fold back monitors, these have a larger linear excursion and a curved cone to smooth out the midrange.
rcw.

[AdamThorne]

Is it just the X-max that tips you off that it's a guitar driver, or is there some other aspect?

The MCM site for the driver lists musical insturment as an application, but also PA and sound reinforcement. Then it compares the driver to an Eminence Alpha, and those get used in some Pi Speakers setups. So that's why I bought 'em.

Having listened to the driver, I can say that it is sufficiently well-behaved for garage and back yard duty. The sound quality requirements here are not particularly stringent.