Brahma 15 Linkwitz Transform Check

[Raoul]

I have a Brahma 15 MKI that I plan I using in a sealed box with a Linkwitz Transform. This is the first time I have used a Linkwitz transform, and I wanted to see what you guys think of the design.

The box is 60 liters. Attached is the WinISD model of the SPL with 250W. Above 250W I reach max excursion.

[Raoul]

And here is the group delay without high/ lowpass filters...

[Raoul]

Here is the SPL with a L.R. lowpass at 50Hz and a second order Butterworth highpass at 16Hz...

[Raoul]

Cone excursion with highpass, lowpass, and Linkwitz transform...

[Raoul]

And lastly, group delay with highpass, lowpass, and Linkwitz transform...

[Raoul]

One thing that bothers me is the group delay when I apply all the filters. WinISD predicts 32.8m/s at 20Hz. I plan on running on my filters actively, but my understanding is that the phase shift will cause group delay even when using active filters. Is this correct? Any suggestions?

[mike.e]

yes group delay is related to phase shift
Dont worry about phase graphs,not many people can even interpret them.

Worry instead about how to integrate it with your room!

Also,regarding power input,your amplifier must be capable of providing the power demanded by the EQ. So if 250w input is correct,if your amplifier can handle the ~9dB EQ you may have applied [2000w]

www.sound.westhost.com describes it.

[Raoul]

Thanks mike.e,

What is interesting is that the phase response calculated by True Audio's page looks much different than WinISD's...or maybe I am one of those who can't interpret phase graphs, which is quite possible .

I have a BK Electronics OMP1000 (http://www.bkelec.com/Diy/mf1000.html) that delivers 1050W into a 2ohm load. It is currently powering a 1ohm load and seems to be holding its own, but I don't know what kind of power it is putting out.

True Audio's spreadsheet calculates a 12-13dB gain at 20Hz (see attachment). Ouch. However, Rod Elliot's page implies (as I read it) that the amp will not be required to crank the full EQ power RMS as much of the signal demands appear as transients and much of the low bass in music occurs at a lower volume. Unfortunately, he doesn't expand on this as far as I can tell, so it has left the actual power requirements as a bit of a mystery to me.

Also, I plan to use this sub strictly for music, as I have a ported Brahma 12 that I use for home theater. The Brahma 12 models a group delay that climbs steeply into the upper 30's m/s at 20Hz. I wanted to build this sub partly to compare a low group delay sub to the relatively high group delay of the Brahma 12. That is why I was so concerned about the GP and phase shift.

Do you have some tips on integrating the sub into the room?

[simon5]

Originally posted by mike.e
Also,regarding power input,your amplifier must be capable of providing the power demanded by the EQ. So if 250w input is correct,if your amplifier can handle the ~9dB EQ you may have applied [2000w]

I read the whole article and didn't see it, can you point us a bit better?

He's using 250W and the Linkwitz Transform is before the amplifier so if he's using 250W of amplification, he's using 250W, not 2000W...

[CBFryman]

i dont know wtf you did in your WinISD but in my WinISD you dont reach 28mm one way untill 2000w in a 60l box....even if you forgot to hit one of the 0's, ie 600l box (HUGE) untill a 500w input and you only reach that at 10Hz..... at 20 you need 800w...but then agian WinISD is Ghey.....