Brahma 15 Linkwitz Transform Check

[Raoul]

Hi CBFryman,

Did you apply the Linkwitz transform EQ (20Hz) to your model? The excursion peaks with a lot less power given the huge amounts of EQ at low frequencies.

[bossobass]

The TrueRTA spreadsheet doesn't predict a phase curve. The 3 curves are the natural FR, the EQ curve and the FR after EQ is applied to the signal.

I would not use a HP filter in a sealed design...defeats the purpose of choosing a sealed alignment for it's low GD. The Brahma 15 in 2 cubes won't require protection.

If your L/T boost is 12 dB @ 20 Hz, then at max SPL (about 108 dB @ 1 meter), you'll require 250 watts X 16 (12 dB=16 times), or 2,000 watts to maintain a flat response to 20 Hz.

That's per the computer model, which is only a model.

If the sub is strictly for music, a low 'B' tuned 5 string bass will play just above 30 Hz, so most any music you play through the sub will be easily handled. There will rarely be much content at or below 20 Hz.

Still, if you crank the system and there is content at and below 20 Hz, I think your available amp power will be the problem, not the Brahma reaching Max Excursion.

A Brahma 15 in 2 cubes with 12 dB of L/T boost (and final 'Q' of .5) is an excellent music sub design. I have a couple of them around here and I power them with around 1,400 available watts each. Seems to be a good power plant for the design.

I've never bottomed either of them in this config, but I do have amp clip indicators and have seen clipping in some instances.

The 1KW amp you have will be fine. If you feel the need to push the design to it's limits, you can try a larger amp. I think up to 2KW would be fine in most cases.

Another helpful hint in this design is to take every precaution to eliminate air leaks which will sound like $hit and change the excursion limits. Check for them using a 20 Hz sine wave tone, find them and seal them.

All of the above is just from experience with modeling, building and graphing 1X15 and 2X15 sealed, L/T Brahmas in various sizes of box and with various high powered amps and my humble opinion.

Bosso

[Raoul]

Thanks bossobass,

My True Audio calculations were for a final system Q of .77, which I believe is the default for the spreadsheet. I see a final Q of .5 trades a bit of SPL (about 3dB) for lower group delay. I will give that a shot as well.

[Matttcattt]

Sorry to go off topic. You say your OMP1000 works into a 1ohm load? I was contemplating getting two and bridging them into a Tumult (1.6ohm load per amp).

[BassAwdyO]

Matt, why bridge them? Dual 2ohm coils, and two 2ohm amps, one amp per coil!

[Raoul]

"You say your OMP1000 works into a 1ohm load? I was contemplating getting two and bridging them into a Tumult (1.6ohm load per amp)."

Well, I haven't actually had it bench tested or anything. I sent BK an email asking about the possibility of driving a 1ohm load, and their advice was, "try it and see...start at a low volume." So, that is what I did. I haven't noticed any clipping, etc. so far, but I rarely get to really open it up. So I guess what I would say is that it works for me. I actually thought about running each VC with its own module, as BassAwdyO suggested.

The OMP1000 is a pretty burly unit, with big hardware. One modification you will want to make is to the fan. The one that came with my unit was hella noisy. I replaced it with some small, mag. levitation fans that I power from a wall wart. In my setup I can run the amp with the fans off for casual low level listening, but it is probably not the best idea.

[Matttcattt]

Originally posted by BassAwdyO
Matt, why bridge them? Dual 2ohm coils, and two 2ohm amps, one amp per coil!

Thats another possibility I suppose. I havent looked into it in great detail, not having cash for such a setup.

Originally posted by Raoul
"You say your OMP1000 works into a 1ohm load? I was contemplating getting two and bridging them into a Tumult (1.6ohm load per amp)."

Well, I haven't actually had it bench tested or anything. I sent BK an email asking about the possibility of driving a 1ohm load, and their advice was, "try it and see...start at a low volume." So, that is what I did. I haven't noticed any clipping, etc. so far, but I rarely get to really open it up. So I guess what I would say is that it works for me. I actually thought about running each VC with its own module, as BassAwdyO suggested.

The OMP1000 is a pretty burly unit, with big hardware. One modification you will want to make is to the fan. The one that came with my unit was hella noisy. I replaced it with some small, mag. levitation fans that I power from a wall wart. In my setup I can run the amp with the fans off for casual low level listening, but it is probably not the best idea.

If it didnt overheat or blow up when you tried a 1 ohm load, thats tested enough for me.