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MT121 Horn and Tweeter Considerations

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Category: Plans
Forum Name: MT122
Forum Description: Discussion / Questions about the MT122
Printed Date: 15 January 2021 at 5:20pm
Software Version: Web Wiz Forums 12.03 -

Topic: MT121 Horn and Tweeter Considerations
Posted By: Facedrop15
Subject: MT121 Horn and Tweeter Considerations
Date Posted: 26 August 2020 at 4:14am
Hi everyone,

I'm building a new cab that's essentially an MT121 mounted on top of a cubokick15 trap. I'm tossing up a couple of options for the high frequency section that I'd appreciate any thoughts/feedback on. I live in Australia, and the options for drivers/horns are quite limited/expensive here. So considering this and my budget, I've been leaning away from pricey option of buying 2" throat horn and compression driver. I Happen to have a some 6.5" midwoofer's around, and I found these 6.5" + 1" Horn combos in the style of a Martin for a good price

What are the thoughts on using this in place of the 2" compression driver? Considering it would be on top of a cubokick15 and and cubo15, would this be over complicating things with what would essentially be a 5-way system?


Posted By: citizensc
Date Posted: 26 August 2020 at 7:47am
I would disagree with components being limited and hard to get in Australia, especially when talking about small, easy to ship components like compression drivers. Thomann does flat rate shipping to Australia and will sell you pretty much any publicly available driver from almost any major PA driver manufacturer, there are some exceptions like Ciare. I would look at getting a decent 1.4 inch compression driver if you can afford it. 

As far as the horn flare you linked goes, I cant comment on how well it would work, they have not published any data on it eg. directivity, frequency response, recommended driver. It could be a fun experiment to buy one and try it out but I wouldn't put all my eggs in that basket. The 6.5 inch drivers you have, do you have any info on them? I don't know an enormous amount about mid horns but I do know they are picky about drivers. They like high EBH and the phaseplug needs to be as close to the dust cap as possible with out interfering. 

Lastly I highly doubt the mid horn option would work out cheaper. You would need to make some kind of back bowl for the 6.5 inch driver assuming its not close backed. You would also need two extra amp channels assuming you running the system in stereo. 

Hope that helps

Posted By: Facedrop15
Date Posted: 29 August 2020 at 3:35pm
Based on a couple of threads in this forum, I was under the impression that a 2 inch driver was pretty crucial to cover the frequency range between a 12" driver and a horn. Would a smaller driver suffice?

Yep here's the driver:
I think you might be right though. Taking all the crossover, shipping etc into account. It might not really work out any cheaper going with that option. It might be interesting though Ermm

Posted By: Jo bg
Date Posted: 30 August 2020 at 12:53am
That woofer you posted is not loud enough for this box.
At max power, 120 watt with 88db/2.83V sensitivity, will be less loud than a compression driver with 1 watt. Even horn loading these will not raise enough the level to make it worth in an efficent cab like mt121.
No point in using an heavy horn top if you can't get it loud because one band is limited.

The 2 inch they mention about mt121 is a 2 inch throat compression driver -attached to a horn - and is around 108 - 110 sensitivity.
Modern good 1.4 drivers (18 sound rcf bms...) are strong enough to cross lower enough to mate well with mt121 12" while going higher than 2 inch cds. Keep it wo way, use good components and it will be much easier to make it sound good.

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