Big OB fun. Come hear!

[Pano]

For you fans of the open baffle - here is a rig that may tickle your fancies. And you can hear it next month in Dallas at Lone Star Audio Fest - LSAF May 14, 15, 16
This is real DIY - all done from scratch.

Photo courtesy of Positive Feedback Magazine

This belongs to my buddy John, but it will be in my room at LSAF. Please drop by for a listen. This speaker was a big hit at LSAF 2008. Don't know what room I'll be in yet, but will post when I know. LSAF is still small enough that it's easy to find anyone.

Basically it's an Altec 605 coax with an 18" Eminence helper woofer. The 605 section is passive, the 18" Emmy is active. See the crossover schematic below.
The 18" is no longer made, alas, but it's a low Qts pro 18. Used here on the open baffle it's crossed at ~40Hz, 3rd order. This low x-over point fights the rising response this driver has on open baffle. 3rd order blends best with the 15" Altec cone above it.

Being a coax -and an Altec Alnico - of course it has tone and vocals to die for. Imaging is top notch, too. The crossover was tweaked for best in-room response in the Embassy Suites. I will probably tweak it further this year, and will report the results.

The idea here is to have a big, but not gigantic, baffle that is very musical with great vocals and imagining - but also has some real grunt. Thus the division of passive mid/high and active woofer. The mid/high section can be driven with a nice little flea amp.

Speaking of amps, I'll have a few there - I like amps - but the star will be a Grant Audio SET amp. Their A-534B 300B integrated. Should really sing with the Altec coax!

I hope you can stop by for a listen and a chat. always fun to meet other DIYers. And it will give you a chance to hear a nice OB rig. One with no secrets.

[CLS]

Well done!

It looks a well-proportioned baffle and beautifully made. Pity I can't hear them.

40Hz 3rd order LPF is steep! Is that 18" hungry for power?

[jerome69]

a 2.5 OB. I made one fully passive.
This loudspeaker should give a big sound (2400cm² of area)

[Pano]

Well the 18 is going to be a bit hungry. Much more so than the mid. But that's the nature of Open Baffle. You have to do something to fight the loss of bass - so power is the solution.

Electrically a 3rd order low pass at 40Hz is steep. But acoustically it works out much higher and somewhat less steep. I will try to measure it in-room in Dallas.

It is a big speaker with a "big as life" sound. I like the powered bass. John likes all passive rigs, so he built another. It will be there, too. I'll post pics.

[a.wayne]

a.wayne asked here about imaging with the wide baffle, but somehow his post got mangled.

[Pano]

Here is another, even bigger, OB rig that will be at LSAF.
Photos below of the front & back under construction. It's 2x18" + 1x10" + tweeter. All passive crossover. Plays deep and clean. Nicely efficient, too.

It should be up at the Nor Cal DIY meet on the 24th.
diyAudio - Nor Cal DIY Audio Group Spring 2010 Meeting

Drivers are:
2x Goldwood 18" for bass. Run in parallel for a 4 ohm load.
Goldwood GW-1858

1x 10" Seas
Seas Prestige A26RE4 (H1411)

Dome tweeter TBD. (John has a lot to choose from)

Anyone going to the Sacramento event, please let us know what you think.

[StigErik]

Very nice!

No dipole peak EQ there... I would expect that is necessary?

[Pano]

Hey Stig. Thanks! I know you do a lot of great work on OB.

The dipole peak EQ is hidden in the woofer to mid crossover. That's part of the reason for the low freq, 3rd order filter. It all kinda works out. If I get a chance in Dallas, I'll do some measuring. But as you know, in-room measurements are hard down that low.

[CLS]

Hi,

Forgot to ask, the 605, in the first post, is the rear cap of the compression driver removed?

And, why not give hi-Z amp a try? Maybe it can surprise you

[Pano]

No, the rear cap is in place. I might try it off just to hear what the back splash will do. Good idea.
Hi-Z amp. Got one?