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Old 13th September 2012, 08:24 AM   #1
imagios is offline imagios  Czech Republic
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Default Beginers questions to speaker designing and building

Hi,
I would like to design and build my self new simple budget speakers, for tv and listening.
I took a look around and as a first project it seems that the B20FU20-51FW would be the right choice, decent quality and listenable performance. I would as well ad a tweeter or something to help with the higher frequency.
S far I downloaded the WinISD to design a simple box.
Out of that I played around and got this:
A 7Ol box with a 40hz at -3db and 32hz at -8db
here comes my question, I know the box volume and can calculate the dimentions, but ISD gives me a tuning freq. how do I achieve that? As that is something I can influence in design, but dont know what it is.
To make it simple, I attach a screen shot of the situation:
Click the image to open in full size.
I would as well need to get the line more "stable between 50-100Hz"
but for now I just would like to know how do I in real influence the tuning freq. and as well the ISD gives me the dimentions, but says nothing about the position of the driver... how do I find out the right position of the driver?
Any one who can advice?
Thanks,
Daniel
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Old 13th September 2012, 09:13 AM   #2
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Download WinISD Pro.

Try looking at the "Vents" tab - play around with port area and length, see how tuning changes.

Lots of reading here - scroll down to "Baffle dimensions and diffraction"

Arpeggio Loudspeaker

Chris
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Old 13th September 2012, 10:24 AM   #3
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A few general points.

Firstly, the Pioneer B20 was discontinued several years ago, so you'll either need 2nd hand, or to find somewhere with some gathering dust on a shelf.

Since I get rather different results for the same 70 litre Vb and 36.57Hz Fb indicated in the WinISD shot you attached, I suspect you are using different driver data. I used the ones published on the PartsXpress site, and assuming these, you should get somewhat better results than what you have indicated, although I would be inclined to tune a touch lower, to 33Hz. A fractional response peak as you can see, since the box is a little smaller than the driver prefers, but nothing to cause major problems. As Chris mentions, WinISD Pro, though not without bugs, is preferable to the stock WinISD.

In practice, you don't want a flat response in the LF; that's a quasi-anechoic simulation which does not take into account baffle losses (not necessarily a huge issue in all situations -depends on where the boxes are placed relative to room boundaries), or room-gain. The latter will tend to cause excessive peaking on the bottom end if you model for a flat response, so in practice, it's usually better to employ a more damped output, for e.g. the attached, from my prefered Unibox.

There have been many designs using the B20 discussed on this forum; if you run a search you should find quite a few. These may help give you some additional ideas.
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Old 13th September 2012, 11:28 AM   #4
imagios is offline imagios  Czech Republic
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The paremeters I use are the ones in the tool Click the image to open in full size.
I will try the PRO version and come back to you with the result...
so far thanks for the advise
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Old 13th September 2012, 11:50 AM   #5
imagios is offline imagios  Czech Republic
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hmmmm i downloaded the WinISD Pro and I try to enter the GRS 8FR-8 Full-Range 8" Speaker Pioneer Type B20FU20-51FW 292-430
since the preivous is really out of stock and it gives me a error on consitancy with the driver parameters...
If nothing works a fall back plan is to use the Alpair 10.2, its more expensive and I thought to set it up as my second project, bud should I have problems with the Pioneer, I might skip them, but anyway I will still have the same questions
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Old 13th September 2012, 02:22 PM   #6
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That will be because it calculates some parameters derived from others which you have entered. This is rather useful because nine times out of ten, the specifications on data sheets are inconsistent with each other since they are typically average values for a batch. You can do the same thing manually of course, but it saves time to let the software do it, and this is probably what I use WinISD for most (quickly checking driver specs.)

Here's one way: enter Qe, Qm, B*L, Sd, Re, Xmax & max. power handling if available, and let it calculate the rest. Alternatively, enter Qe, Qm, Sd, Mms, Re, Xmax & max. power handling. Same deal.


Incidentally, those specs. you picture above are far removed removed from the ones on PE, which are TTBOMK reasonably representative of the last B20s. I've certainly never seen a B20 with a 0.2 Qt or an Fs of 29Hz, so IMO they are way out.

GRS against Alpair 10.2? The latter is smaller, but it's a much more expensive & ultimately much higher quality product, with a reasonable number of cabinet designs available.
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Old 13th September 2012, 03:30 PM   #7
imagios is offline imagios  Czech Republic
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So I managed to put the Pioneer into the WinISD Pro, here is the simulation...
Click the image to open in full size.
it delivers a -3db at 34Hz and -8db at 29Hz, in a 72 litre box... for sure just a simulation...
Regarding the Alpair, sure there are a lot of box plans out, but its hart for me to verify them... the main idea of designing them by my self is to understand it, more than to make the "perfect box"
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Old 13th September 2012, 03:51 PM   #8
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That looks more like it. I suggest tuning a couple of Hz lower which will damp the LF output slightly.

Excellent. In that case, I strongly advise you to aquire a few books on the subject. Vance Dickason's Loudspeaker Design Cookbook, and Martin Colloms's High Performance Loudspeakers are currently in print, and a very good starting point.
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Old 13th September 2012, 06:05 PM   #9
imagios is offline imagios  Czech Republic
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well thanks a lot for the advice, is there a way how to set up the height/position of the driver? And how is done the tuning freq.?
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Old 13th September 2012, 07:40 PM   #10
tvrgeek is offline tvrgeek  United States
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About ten times: follow Scottmoose. READ a little. I also recommend Testing Loudspeakers by D'Appolito. It will tell you what you are looking at in the sim. Simulations and measurements are only truly useful when you know what they mean.

You also might read the help pages for the tools you are using.
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