New Push-Pull 15"

MarjanM wrote: Can you measure the boxes without any HPF? That way we can see how low it really goes. It does look to me that the back chamber can do a little bit better under 55Hz. Can you put the mic right on the round port exit so can see where the back chamber is tuned? Front one seems to be spot on where it suppose to be.

Zoost, thats a new one 

Steve_B wrote: MarjanM wrote: Can you measure the boxes without any HPF? That way we can see how low it really goes. It does look to me that the back chamber can do a little bit better under 55Hz. Can you put the mic right on the round port exit so can see where the back chamber is tuned? Front one seems to be spot on where it suppose to be. I thought that this was a reflex box with a B6 alignment??? I'm not sure what you mean by the tuning of the rear and front chamber. If I remember correctly the box is tuned to the same frequency as the drive unit and the box is 4 times Qt^2 times Vas. The box then requires a boost of 6dB at 1 point a bit the resonant frequency, which is also the -3dB point; 38Hz I would presume from the OP.

Marjan,  The design is based on my Q15 box and all I have done is put 2 drivers in a PP arrangement to make use of the lower distortion that this gives.

Edited by Tony Wilkes - 23 July 2013 at 12:09pm

Marjan, Max X is at 55hz and is 9mm,  At Fb it is around 4mm at max power (600 per driver)

The B6 alignment is supposed to have good control over cone excursion both in and out of the operating bandwidth. It was documented in Thiele’s Loudspeakers in Vented Boxes paper, and Keele wrote a paper on variations of this alignment.

With modern software I don’t see the point in sticking to specific alignments as the programs give full response plots for every possible combination of box volume and tuning.

With regards to using electronic eq to achive the desired response I am all for it. The easiest thing is to give an example.

The plots below are for an Eminence Delta 12LF. As a comparison the pink plot is a BMS 12.

The green plot is the default winisd box. This is 129 litres

Keeping the same tuning, but reducing the box volume to 36 litres gives the blue plot.

Using the above tuning but adding some electronic eq results in the red plot (+8dB at 40Hz and -4dB at 100Hz. Remember this is in a box 3.5 times smaller than the green plot. So what is the catch, because everyone knows you can’t get much bass out of a small box.

Well the next plots show the max SPL. Again the pink plot is the BMS 12” sub speaker in a 36 litre box.

Apart from some loss at the port resonance, the max output is exactly the same for the big and small boxes. If you are after a flat response both boxes will give 114dB down to 40Hz. The BMS puts out a couple of dB more.

Lots of eq probably means lots of phase shift. The next lot of graphs show the group delay. There is not much to choose between them above 40Hz. The red peak is caused by the fact I added a high pass filter to that design.