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New Push-Pull 15"

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overdrive View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote overdrive Quote  Post ReplyReply Direct Link To This Post Posted: 25 July 2013 at 9:21am
Hi Steve, it's also good to post the impedance phase plot. Its the most accurate way to find you tuning freq point(s).
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Steve_B Quote  Post ReplyReply Direct Link To This Post Posted: 24 July 2013 at 8:44pm
With reflex cabinets there is an impedance minimum at the box resonant frequency. It is a useful way to check the tuning of the box. In the plots below I created a box and then changed the tuning from 30 to 40 and then 50Hz.



Edited by Steve_B - 11 August 2013 at 2:28pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote MarjanM Quote  Post ReplyReply Direct Link To This Post Posted: 24 July 2013 at 7:50pm
Steve has already explained it quite well. Since English is not my native language i find it difficult for me to even begin explaining things like this over the forum.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote el_dj Quote  Post ReplyReply Direct Link To This Post Posted: 24 July 2013 at 7:02pm
been following this with interest... gentlemen... looks good..

im a bit of a noob, but can someone point me in the right direction to understand "the problem" with the impedance plot, and how that is related to the tuning. ? and on top of that, why this box does not go lower?

maybe a lot to ask. however i dont mind reading if you can point me to the correct links... whenever i search the subject i mainly get car audio subjects and it is not more ohm's low and what not to do.

thanks. :)


Edited by el_dj - 24 July 2013 at 7:03pm
Old twat, with an interest in light & sound

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Tony Wilkes Quote  Post ReplyReply Direct Link To This Post Posted: 24 July 2013 at 6:17pm
Marjan, it uses the same motor assembly but obviously a standard surround, I find it a lovely sounding driver that is usable quite high.
 
Tony
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Post Options Post Options   Thanks (0) Thanks(0)   Quote MarjanM Quote  Post ReplyReply Direct Link To This Post Posted: 24 July 2013 at 6:11pm
I get this all perfectly Steve. Just never really looked at the 15S330, and somehow was thinking it will be a biffed up 12S330, which clearly isnt. That was the confusing thing to me.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Steve_B Quote  Post ReplyReply Direct Link To This Post Posted: 24 July 2013 at 4:47pm
If you are designing a box to be maximally flat with no eq then the BMS 15 does require a volume of 300 litres. The following graph shows such a box plotted in red.


The green plot is for a 150 litre box with a 4dB boost.

The smaller box does suffer slightly at the bottom end when you look at the max spl plots, but don't forget the green plot is in a box half the size of the red plot.


For the live type bands I do, the smaller box would win all the time. I usually run with a 40 - 45Hz HP filter anyway. I doubt you would hear much difference.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote MarjanM Quote  Post ReplyReply Direct Link To This Post Posted: 24 July 2013 at 2:07pm
Just simmed that driver. It is nothing like the 12S330. Asking for a 300+ lit for a double 15 box. Similar box with 12S330 will get you a better low end. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Tony Wilkes Quote  Post ReplyReply Direct Link To This Post Posted: 24 July 2013 at 11:56am
Steve, I know it was not aimed at me, just reinforcing a point to anyone interested. 

In the Q15 design and this double version I played around with the parameters until I got a box with the extension I needed that also maximised the driver in the smallest practical volume.

I also reckon that the tiny boxes also help to cut down on what I term "Box Talk". Should be self explanatory. :)

Tony
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Steve_B Quote  Post ReplyReply Direct Link To This Post Posted: 24 July 2013 at 11:26am
Tony, I didn't think for a minute you did not understand - (well maybe for a couple of seconds Tongue ).

The response was to Marjan asking about the applied boost.

I previous threads some people people seem to have a hard time understanding that you can make a box that on its own is not flat and then correct it electronically. I thought that the example would explain it more clearly.

For PA work, the most useful graph in winisd is the maximum spl. This is the equivalent of the safe operating area familiar to the electronic guys. If your target response fits under the curve you are good to go. Getting a transfer function that is flat down to 30Hz is useless if excursion limitations restrict the output to 100dB between 50H and 85Hz. It is far better to tune the box higher and get the output up where it is generally more useful. If the resultant transfer function requires eq fine.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Tony Wilkes Quote  Post ReplyReply Direct Link To This Post Posted: 24 July 2013 at 7:40am
Steve, That is why I usually refer to these boxes as "assisted alignment" as I do not stick exactly to the B6 rules.

Tony
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Steve_B Quote  Post ReplyReply Direct Link To This Post Posted: 23 July 2013 at 11:28pm
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.

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