Mt-121 simplified plan

oops, just found the thread... can be closed ( dont know how.. )

smoore wrote: I found the original horn played more in the 80-200hz region compared to the simplified. I have built both (however the simplified version was 12mm MDF and the original version I made was 15mm birch ply all around) and preferred the original. However, the difficulty to build is a lot higher!

No i did mean 80-200 region. Or even up to 300hz I never ran mine higher than 800hz so thought I would cross them lower. I often use a 12db filter at 100hz or so. Its total nonsense in my opinion that people say it 'won't go lower than 120hz'.. Of course it will. Its just x-max is a lot higher when you push the driver and it may not sound as it was designed to. I much preferred the sound of a reduced slope filter at a lower frequency, compared to a higher, ie 24db or 48db filter. Sounded much more natural and fuller

It is just case of how loud you are going to play. With efficient design like MT121, power levels are more likely to be quite low so you can get away with shallower slopes.

Extreme example: you can listen to pretty much any compression driver with 100hz HPF, you just need to keep levels REALLY low.

The two part flare will load the low range better. Not too suprised to hear it sounds fuller.

Some recommendations for drivers in MT121, that can play down to 130hz, at upto 400W power input would be great.

Low end frequency response is pretty much dictated by the horn. All the typical quality drivers used in this design seem to share similar low end. Frequency response will be down by the time you go down from 200hz to 120hz, but pretty much every driver should be able to handle the excursion.
To flatten the response, some shelving EQ could be used along with the HPF, this would come at the expense of overall sensitivity when either the amp of the driver will run out of its capabilities sooner.

Quick sim of MT121 with BMS 12N610, Fane Colossus 12MB and B&C 12NWL76  indicate that all should be able to handle 120hz crossover with ease. At least with 24dB slope the crosspoint will be -3dB or -6dB down already, so from full 400 watts that would be half or quarter power. With 400 watts all three give excursion around 4,5 to 4,8mm at 120hz. BMS's Xmax spec is lower than other two but they publish absolute "pure" Xmax with full amount of turns in the gap, so no worries there.

B&C 12PE32 is the only modern driver I would have tiny hesitation of using with 120hz HPF, but most likely it would handle it easily too. 12PE32 sim gives little bit over 5mm of  excursion at 120hz with 400 watts.

edit: I meant to say that my verdict is that any driver that is able to handle 4-5 millimeters of excursion and 400 watts should be able to work in that box with that crossover frequency with no problems.


Edited by pfly - 21 June 2014 at 10:38pm