Best Open-Back PA Speakers?

[tbryanh]

I plan to make an open-back pa speaker enclosure.

It will be similar to a cabinet for a fender twin reverb, but the amp will be a pa amp, not a guitar amp.

I haven't seen any pa cabinets that are open back.

What speaker would work best for this?

[TransLucid]

The reason you don't see open-back pa cabs is that they have poor bass response. Ported enclosures provide better response and efficiency in the bass.

Also, pa speakers should have wide, flat frequency response and controlled dispersion, which means you should probably include a HF horn.

You can make a ported cabinet similar in size to a twin reverb cab that will work well.

[Enzo]

Ever stand behind an open back guitar amp cab and listen to it? Why would you want all that sonic energy coming out the back of your PA cab? Wouldn't you rather it went out the front?

[tbryanh]

In medium to large venues, closed back is probably best.

In small venues, I heard closed back can be a little directional and might not fill the room with sound as well as open back does.

I am really anxious to try an open back pa as described, so any help I can get on speaker choice will be appreciated.

Thanks

[Chuck H]

In that case I suppose cabinet design becomes quite critical. Figuring for the response at different points in the room (and it will always be a different room) with different phase angles and cab dimesion as it relates to the uber port size (open back... and not phase corrected) etc. Not to mention that you will still only get directional output from any horn or tweeter you might use.

Consider that any open back guitar amp sounds different in different rooms. You can work around this for a guitar, but not for a reference amplifier.

Since it's small venues in question, you may do well a pair of small front loaded cabs. Almost like old school stereo console speakers. Still directional but perhaps a little less so.

[riz]

Well, yes it'll be inefficient, so I say throw some high-powered EVs or something like that in there an let it rip. When I was younger we used to do a lot of "wharehouse/garage"-type shows using whatever we could cobble together as a p.a.--ANY amp or cab that could make sound, all in a big pile! Some of those rigs sounded WAY better than they should have... So, go for it, and don't get too science-y. You already said Twin Reverb, so, start there, and figure making it a bit larger to fit in a horn, and go have fun. That's what I say. I feel you on the small room thing. Too much directionality kills the vibe in the small room setting, with any real volume involved. But who knows, it'll work great for your application, or you may discover "why" what everyone else is talking about...

[pdf64]

The way forward depends on what the PA is intended for, material wise. If it's just vocals in a small to med venue, then open back cabs may be ok. It would be beneficial if the speakers were more linear, not as peaky a frequency response, than regular guitar speakers.
If that's the case, then the bigger the baffle is, the better the bass will be.
Efficiency? My understanding is that given the same driver, the mid range efficiency of ported, infinte baffle and open back will be basically the same, so for vocals it doesn't really matter.
If the input signal is full range music, or may include a bit of kick drum etc, then open back may result in the bass being turned up (to compensate for low frequency cancellation) and the amp overloading.
Tony McPhee used to play solo blues gigs in pubs with just an AC30 for mic and guitar - it sounded great!
YouTube - ‪Tony McPhee - Write Me A Few Short Lines‬‏
Pete.

[riz]

My assumption was it would be for vocal and light instrumental reinforcement in low-ish volume smaller room situations... But those conditions change from night to night now, don't they!

[tbryanh]

Here are some youtube links to some open baffle designs for the home.
YouTube - ‪Open Baffle Visaton Eminence speakers‬‏
YouTube - ‪Open Baffle Speakers‬‏

Maybe I can put a woofer and a subwoofer in the twin reverb cab and then sit a self contained horn on top.

The pro audio industry makes lots of different speakers, but most are probably for acoustic suspension (closed box or ported) systems.

Probably the biggest difference between acoustic suspension speakers and non-acoustic suspension is the stiffness of the surround.

If non-acoustic suspension pro audio speakers cannot be found, it might be that high wattage acoustic suspension pro audio speakers, when used at low wattages, would have stiff enough surrounds.

[Jot]

Or if you're willing to consider possibly the lowest-tech solution to the problem: I've sometimes turned PA speakers around to face the rear wall (in places with a hard-surface back wall, of course). Eliminated the directionality problem. At reasonable small-venue amplification levels, no feedback problems, either, surprisingly, and often no need for monitors. I do that with my guitar amp sometimes, too, on small stages.

[tbryanh]

It looks like it is very common to put a pair of Eminence DELTA PRO-12A speakers into a Fender Twin Reverb cabinet. They have a 52Hz - 4.5kHz frequency response.

If I feel I need more bass, I will add a Horn Loaded Subwoofer cabinet filled with a pair of Eminence Lab12 speakers, and if I feel I need more treble, I will add a self contained treble horn cabinet.

I haven't tried it yet, but at this point, I think a Fender Twin Reverb cabinet loaded with a pair of Eminence DELTA PRO-12A speakers will do everything I need.

[pdf64]

Re directionality, another couple of ideas; in the 60's & 70s, for PA vertical line arrays of speakers were used to improve horizontal dispersion (side by side speakers will make the horizontal dispersion worse); and smaller drivers have better high frequency dispersion than 12" types.
So how about sticking 4 http://www.eminence.com/pdf/Delta_Pro_8B.pdf in a vertical line cab. They don't have the steep cut off after 5kHz of the Delta Pro 12A. Pete.

[tbryanh]

I might try the Eminence BETA-12LTA. It has a frequency range of 48Hz - 8kHz.

Good things are being said about it.

It doesn't have as flat as a response as the Eminence DELTA PRO-12A.