OTop8 dispersion angle and Bi-amping

[Keryn O'Shea]

Good evening everyone,
I hope you guys are well, so I'm removing the woofers from a pair of TLAPs to build 6-8 OTop8s. The TLAPS were brilliant while hung in my shed..

However after changing premises I've found moving them around or using the pole mount is difficult, they're awkward & heavy to carry by yourself, & also recently finding the DR280 has better performance for much less power, they're now kinda redundant for outdoors use. I'll re-load these with a lighter driver and find them a home.

I thought I could try the OTop8s for easier setup, so I whipped up an operational pair to have a listen... was not disappointed
Just running off a HT receiver in the pool room with a Lab12T30 and very minimal EQ they are excellent

I was wondering what the dispersion angle of these cabs is? Being able to set these up in 3-4 cab spiral array each side will be very handy I reckon!
I also found that the HP filter coils for the CD are hideously expensive here... so the successive cabs will be bi-amped. These first two cabs have the filters and will always be the top cab in the stack, so out if it's two speakon connectors, one will be wired to the filters for single cab use, and the other will be used when bi-amping with multiple cab set up. When connecting wires from the bi-amp connector to the CDs and woofers, do I need to fit a switch to break the filtered circuit? I'm thinking yes.. but where?
You may notice the lower CD horn has a better finish, this is my first time working with Baltic birch... and it has spoilt me, it's soo nice to work with

[Keryn O'Shea]

Would the horizontal dispersion be 90 degrees?
If I need to break the filtered circuit when bi-amped, would I wire a recessed 10A rocker switch on the back between the positive out of the woofer filter and the positive terminal of the woofer?

[Seth]

Keryn, dispersion is directly related to the width of the cab (or diameter of the driver in a standard PA cab) and depends on the frequency. I'm having a little trouble pulling the information up from memory (uh-oh! Just turned 50. Has it begun already?!?!)

Bill, I'm having a brain fart... what's the cab width rule?

[Bill Fitzmaurice]

The wider the horn mouth the narrower the dispersion. It's 180 degrees when the radiating plane is 1 wavelength, where it's less than that it's wider than 180 degrees. From there it narrows as you go higher in frequency. It's different at every frequency, so any quoted angle is a broadband average.

BTW, inductors at wagneronline.com.au/ and www.theloudspeakerkit.com don't seem all that high priced. Twice that than the US, but everything down under is.

[Keryn O'Shea]

Thank you for your responses regarding dispersion.
The 1.8mH inductor with the right DCR starts at $65au here, and for the complete filters in the OT8 its $140au each cab.. plus shipping, so $1120au nearly buys me a PA2. For the cost of this one inductor for all 8 cabs buys me the 8x4 core leads for these cabs. Also the stock availability for the inductors alone is low nationally. If I move to bi-amping everything (except piezo)
It's less time sourcing things that don't exist here, and building filters which is my least favorite job.
I have enough 1016s to build a pair of J10Ls (which I already have the filters for) and 20 spares for the DR280s, after that it will be all CDs and bi-amping as the GT1016s landed here are $8au each, and the Daichi equivalent is not the same quality.
If what I'm trying to achieve with this OT8 with dual circuits is more trouble than it's worth, I'll just bi-amp them too. But it would be nice to utilize the filters installed for 2-way operation.

[Bill Fitzmaurice]

https://speakerbug.com.au/index.php?rou ... uct_id=853

Took me three minutes to find these.

[Keryn O'Shea]

Excellent, thank you for taking the time to look Bill! I wasn't aware I could substitute air core inductors for P-Core, it's not mentioned in the plans & I'm not educated enough about filter components to make those decisions.
I'm still going to move to bi-amping from now on, and still curios regarding dual circuits in these particular cabs..
I'm sorry if my questions are annoying, I wish I knew more so I didn't have to bug you guys.

[Keryn O'Shea]

To isolate the 2 circuits, switches were fitted to both + between the filter and drivers, and - between woofer and filter, attached to the woofer baffle accessible through the port so l didn't have to fit and try sealing the switches on the back panel.
You probably wouldn't set out to build 8 OT8s from the start, but l like the narrow height and look when spirally arrayed.

I fitted 8.5" strips to the top of each cab to help stability when set up that way.

[Keryn O'Shea]

These 4 cabs are ready for paint, l'm trying not to give into the temptation of fitting drivers and wiring to the 2 Bi-amp only cabs to see how they perform, as l've moved into this century with a PA2 and RTA-M, and keen to use it's features!
I just know I'll have to spend more time pulling them apart when it comes to painting..

[Seth]

...l'm trying not to give into the temptation of fitting drivers and wiring to the 2 Bi-amp only cabs to see how they perform, as l've moved into this century with a PA2 and RTA-M, and keen to use it's features!

You're a better man than I am. Ida had those suckers wired up and wailing first chance I got! Your patience and perseverance is admirable. And they're looking darn good Keryn! Well done sir, well done.

Soooo... paint tomorrow and a tuning party Sunday?

[Seth]

Cripes! I forgot, you're already eating lunch on Saturday while I'm cleaning up my Friday dinner.

[dlv]

That OT8 tower is a thing of beauty Karyn!

[Keryn O'Shea]

Thank you very much for the kind words guys!

..Ida had those suckers wired up and wailing first chance I got!

For a pair.. yes mate, l know I'll regret it when it comes to pulling apart 8 though!

Soooo... paint tomorrow and a tuning party Sunday?

I wish, I'll just have to pull my finger out and get them done. Assembling No.5 Horn & cutting parts for 6-8 this weekend.. won't be long.

I'll be taking them out to a friend's 150 acre farm for a couple of days for tuning, looking forward to that.
I will need more subs though, another 4xT48s would do it, but then I'll need a truck for transport..!

[Keryn O'Shea]

G'day legends,
Hope you guys are well, the OT8s are getting closer to painting and l'm contemplating a lighter colour in the horn area, like a medium or gunmetal grey tinted white Duratex, as once the horn was painted black on my DRs, it's depth and detail seemed diminished.
I was thinking of the CD horn, phase plug and supports being flat black, the horn area grey, and the outer cab black. The flat black will be first on, but l don't know which colour to paint next?
The CD horns are removable.
This paint scheme will add quite a bit more work!
Also would an SLAP trump an OT8 in any way?

[Seth]

Yeah baby! Check those out!

On pro gear, the cabs are done in black so they disappear along with the rest of the rigging in a show. But, I agree it's a bit of a shame to hide all the interesting angles and for some shows you don't need or even want the speakers to disappear into the darkness. Sometimes they're the star of the show and I can't think of a good reason not to do 'em up in a way that accents, highlights, and showcases the unique appearance of these cabs... in a way that maintains the professional look of a commercially finished cab. I think grey would pull it off. Oddly, I find some of the loud colors like orange and plum crazy purple to be delightful accent colors too, if not overdone. Grey is safe, neutral, goes with a lot of other color schemes, and I think it would look really good.

Can't wait for you to fire the system up with these!

Only benefits I can think of for the SLAP is the size and it's really easy to build. Other than that, it takes more amplifier to get to the same SPL, costs more, and doesn't stack as well.