Ports on side and feedback?

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Ports on side and feedback?

#1 Post by AlBrum » Mon Sep 28, 2020 8:40 am


Greetings from Birmingham, UK

Weighing up a build at the moment - for live band , play only small bars.We already have a sub (MTH30) that does what we need in the kick drum department running off Crown XLS1500 and currently run a 1 x 12 Fane 250LT with APT150 in small reflex top (actually repurposed old HK "Compact Classic"- Just blown up one side of a Thomanns 1400w amp we were using for these so new amp must be found I think! The 1 x 12 isn't having it, I guess with good tweeter (to lower - 1.6KHz and purpose built crossover it might be workable but maybe try something a bit different...?

use Sound craft Ui24 for eq, feedback suppression and mixer- great piece of kit. Can even use it for crossovers and time alignment with some fiddling.

We only have limited space so thinner cabs much preferred
I'm thinking maybe either SLA Pro or Omnitop8 (looks like it will go to 120Hz where we crossover to sub??)

With the small spaces we play with sometimes speakers only a couple of feet in front of vocalist - Has anyone had any issues with ports on side of Omni8 (or12 etc.) causing any issues with feedback please?

Or can I move the ports inside the horn at all- I think maybe some old designs of bill might have had port in horn but cannot recall... Old age...

SLA pro vs omni 8 - what would you go for and why...?


Bruce Weldy
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Re: Ports on side and feedback?

#2 Post by Bruce Weldy » Mon Sep 28, 2020 9:22 am

The side ports won't cause you any feedback problems.

6 - T39 4-25" 2-22" 3012LF
4 - OT12 2512 Melded/NSD2005
1 - T24
2 - XF210

"A system with a few knobs set up by someone who knows what they are doing is always better than one with a lot of knobs set up by someone who doesn't."

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Bill Fitzmaurice
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Re: Ports on side and feedback?

#3 Post by Bill Fitzmaurice » Mon Sep 28, 2020 9:58 am

The side ports can't cause a feedback problem because only low frequencies from 80-150Hz exit from the ports. Low frequency radiation has a 360 degree pattern, so the sound is the same be they on the front, back, side, bottom or top.

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Re: Ports on side and feedback?

#4 Post by SethRocksYou » Mon Sep 28, 2020 10:58 am

AlBrum wrote:
Mon Sep 28, 2020 8:40 am
SLA pro vs omni 8 - what would you go for and why...?
Hi Al, I'm Seth.

In your other post you were asking about off axis response. The OTops with a melded array will have better off axis response in the tweeter region than the SLA Pro. Although the SLA Pro should have better off axis response in the midrange.

I'm not clear whether it's stage space or pack space that your trying to limit. The OT8 is slimmer than an OT12 when in use, but the overall dimensions of the OT8 are larger than the OT12, so you may take that into consideration if it's pack space you're after.

The SLA Pro is a fairly easy build and is slimmer, which is also beneficial to off axis response.

I only have experience with the 2x6 shorty SLA Pro and I like them a lot.

In either case, I highly recommend you look into an outboard digital solution for your crossover/EQ/feedback suppression such as a Driverack. Money well spent.
Two 2x6 shorty SLA Pro's
One 16" T39, 3012LF loaded
20" Tall AutoTuba loaded with 2 8" MCM 55-2421
8½" TruckTuba loaded with 2 8" MCM 55-2421

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Strange Kevin
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Re: Ports on side and feedback?

#5 Post by Strange Kevin » Mon Sep 28, 2020 12:32 pm

Having built both, I can comfortably say either option is fantastic!

For pubs and small venues, Id say SLA Pro.
The Otops and SLA are both going to have good horizontal coverage but I believe the SLA will have a little tighter vertical dispersion. (Keeping sound from bouncing off the ceiling and floor as much)

SLA Pro is (much) lighter and easier to handle than the Otop8 and visually less obtrusive. That's not always a big deal but could come in handy on smaller tight stages.

My Otop8s (with delta pro 8 drivers) will get a little louder than the standard SLA Pro but thats really only a benefit at larger venues.

I guess another benefit for the Otop is they could potentially be cheaper to build depending on drivers and availability.
Authorized Builder - Phoenix AZ.
Main Rig - 6 DR200s - 6 T48s (30")
SLA Pros for the smaller stuff.

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