Trial Balloon: 3-way project using Coax 12"?

charlielaub

Thanks to all who have shown interest in the Driver Diaspora. This is helping me out a lot! In the meantime I have started to think about a project that might make use of some of the leftovers:
Cerwin-Vega 12" Coax with 1-3/8 threaded CD mount
Selenium D250x midrange CD
Top mounted or sit-on tweeter, perhaps GRS RT3.0-8
Cabinet: left-over 2.0 cuft MDF subwoofer cabs

Initially I was hoping I could come up with a 2-way coax project with the CerwinVega woofer and a CD tweeter. The problem with this is that the horn formed by the C-V woofer cone starts to show some nasty behavior around 4k-5k Hz and up. If that only happened above 10k I would chance it, but 4k is too low for that sort of garbage. This means using a CD tweeter is out. Also the woofer breakup starts IIRC around 1.5kHz, and this would have required a really steep filter or low crossover point, maybe too low for the CD.

But if I forget about the idea of a 2-way and instead move to a 3-way concept there is an interesting possiblity: to use the threaded CD mount for the Selenium midrange CD driver. This can be crossed over lower. I made a couple of quick measurements just now to confirm (see attached). The D250x is not bad in terms of distortion performance and could cover 700 to 3k or maybe 4k Hz. Then I would hand off to the tweeter.

I could call it something like the "SourcePlop-123", a SourcePoint-10 inspired, 12 inch coax 3-way. Take THAT, Mr A. Jones! So, assuming this works I could bring it to InDIYana and demo it. The big question is: can I accommodate the two giant cabs in my car in addition to all the drivers I am bringing???

.

jhollander

I'd check the CD in the C-V woofer off axis to see if the 5.5K dip goes away. Might be usable as a 2 way depending on what you do for BSC on the C-V woofer. The 2-way might be a valid Indy entry which could be more fun.

charlielaub

Here ya go. I did a couple of off axis angles (22 and 45 degrees). See below.

I am pretty sure that the 5kHz dip is the horrible performance of the horn formed by the woofer cone. I saw this same kind of thing (without the HF droop) with a CD tweeter I tested last week. Initially I thought the project was dead, but if I move to a 3-way and cross over to a tweeter below that first dip I think it will work.

Wolf

@jhollander said:
I'd check the CD in the C-V woofer off axis to see if the 5.5K dip goes away. Might be usable as a 2 way depending on what you do for BSC on the C-V woofer. The 2-way might be a valid Indy entry which could be more fun.

Cabs would be too big, and the theme is now closed with 20 entries.
By all means, he could still bring it...

PWRRYD

Not to veer off too far but Ben, would you still like me to bring those 70's Sansui speakers? Bone stock or with an external baffle step LR comp circuit? My car is getting pretty full since I'm buying some stuff from Charlie and transporting JR. Thanks.

ugly_woofer

Shit Craig, JR is tiny now, you have plenty of room.

charlielaub

@Wolf said:
Cabs would be too big, and the theme is now closed with 20 entries.
By all means, he could still bring it...

Correct, I should have made it clear that I wasn't planning to make it a theme entry, just loosely following the theme after finding some inspiration from it. I quickly realized weeks ago that there was no way I was going to make any sort of decent passive crossover even if I could find drivers that played well with each other! I read online that you have to use these things call "inductors"...

PWRRYD

"Inductors" lol!

Wolf

Craig, it's your call. I'd like to hear them one way or another, but do what you need to. The speaker exposure I had in the 80s (My folks did not purchase better stereo until then) were through a pair of Lloyd's 8" 2ways that had dual cone woofers and cone tweeters, until my dad smoked the woofers playing 'Drag City'.

Steve_Lee

"Inductors"

Are these the people that get you into the speaker building Hall of Fame?

charlielaub

No, these folks just create some hysterics while circling around their tightly wound core. That is a type I want to avoid. Too complicated, but you only realize it after you get to know them for awhile...

charlielaub

I just finished a quick set of measurements of the drivers for this system. I took these indoors with the cab on its back elevated up on a table in a room with a high vaulted ceiling, and managed to get pretty good resolution.

For a reference about the SPL level (SPL levels in plot are arbitrary), the tweeter is rated at about [email protected]. Even with some baffle step on the woofer I should be able to reach [email protected] above 100Hz or so, although for an active system this is not critical. The tweeter was simply placed on top of the cab, centered, and with the faceplate touching and overhanging the front baffle. Since its a ribbon, it will be easy to remove and pack away from transport that way. This should reduce the risk of damage to the ribbon element. The effective baffle is kept very small, being only the width of the tweeter faceplate itself.

Wolf

I'd say that looks doable.

charlielaub

I did some massaging and got a decent first attempt at a crossover, below. I have to finish putting together the cabs and then I can do some listening and voicing. Rinse and repeat.

jr@mac

LMT

Steve_Lee

@charlielaub said:
No, these folks just create some hysterics while circling around their tightly wound core. That is a type I want to avoid. Too complicated, but you only realize it after you get to know them for awhile...

Sorry for being off-topic but this ^ response of yours was utterly brilliant and funny. Thanks.

PWRRYD

@jr@mac said:
LMT

Great!

Wolf

I was seeing 700 and 3-3.5k for likelihood, so that reflects my thoughts.