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Old 18th January 2003, 08:43 PM   #11
Ilianh is offline Ilianh  Canada
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Well, the tuning at 500hz aint THAT important, i get same results with anywhere from 150 hz to infinity, so i have place for error..

I was thinking doing all this into a sonotube.

for less that 10$ for the completed project.. (ehe, im cheap)

a sonotube is 5$ and i got the mdf needed, and ports....

and as i know myself, I'll do the project to work with a active subwoofer amp with mixers/phase inverters/active filters/gain and the main amp that I made.

then see how if it works... and dissasemble it all... to try to make something else out of those things.

I rarely do a project that I intend in keeping.
so esthetics aint that important..

Theres only one thing I'm worried about, the group delay and phase plot show me differet stuff in winisd than in the pro alpha, and i dont think that what i see as a group delay or phase plot is too good. Vented looks a bit better/smoother.

Thanks for the help
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Old 18th January 2003, 08:56 PM   #12
Wizard of Kelts
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Well, a Sonotube would be made to order for something like this.

I just asked about the vent because I plugged some vent lengths into WinISD to tune a .2 cu ft box and got nothing. Thought maybe it was undoable. Hence, the PR talk. But .2 cu ft with 150 Hz is definitely doable.

I wouod say the higher the frequency you can tune it, the better. The crossover will have an easier time eliminating the peak the higher it is.

By the way, I located a spreadsheet for % efficiency to SPL conversion. Your specs say that the Max Pentivent is 0.4% efficient, but gives no SPL rating. According to John Murphy, a physicist and writer on audio topics, that corresponds to an SPL rating of 88.1 @ 1W/1M. Here is the link:
http://www.trueaudio.com/basslist.htm

Just click on the SPL-% Spreadsheet link.

Sounds a little simplistic to me, but I'll let some of this forum's engineers tell me if they agree. If they say it is good, I will post the list in it's own thread.

Remember, the rating is for one watt. So if you have a 4 ohm driver, sending 2.83 Volts to it-the normal voltage level speakers are tested on-will give the 4 ohm speaker 2 watts, not one. This will result in an SPL 3 dB higher than the 1 Watt rating.

Speakers are normally tested at 2.83Volts because that is one watt for an 8 ohm speaker.
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Old 18th January 2003, 09:08 PM   #13
Ilianh is offline Ilianh  Canada
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So the woofer is 85 dB spl.... ugh... that aint too good
any ideas how to calculate the spl of a woofer that you dont have specs for? easiest / cheapest way
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Old 18th January 2003, 09:18 PM   #14
Wizard of Kelts
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Quote:
Originally posted by Ilianh
So the woofer is 85 dB spl.... ugh... that aint too good
any ideas how to calculate the spl of a woofer that you dont have specs for? easiest / cheapest way
No, acording to the chart, the woofer is 88.1 @ 1W/1M, which is perfectly average.

However, if you use the 4 ohm version, when manufactuers test the speaker, they run 2.83 Vots through it. If you run 2.83 Volts through the 4 ohm version of this speaker, you will get 91.1 dB. That is because you will be running two watts, not one watt, through it.

These numbers are calculated through Thiele-Small parameters. Assuming the parameters are reasonably accurate, this is what it is supposed to be. Little tricks of measurement do not enter into the picture at all.

I'll be honest, I have some doubts about this chart. I'll Email some engineer members to check to make sure that it really is this easy. I saw a couple of long, long equations once with a lot of parameters as variables, so I figured this thing is complicated. But if the chart is indeed accurate, then that is your SPL number.
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Old 18th January 2003, 09:26 PM   #15
Wizard of Kelts
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How to calculate the SPL of a woofer you don't have specs for? Did you mention once that you know how to use Speaker Workshop?
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Old 18th January 2003, 09:57 PM   #16
Ilianh is offline Ilianh  Canada
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yhea... still didnt calibrate evrything.. but i'll work on that.

one thing im worried about is the room, I cant measure evrything outside... its cold out there and i got no laptop...

I dont have an anechoic (spelled right?) room :\

thx for all the help

I start college monday (around 40 hours classes / week) i wont have much time to work on stuff... so im trying to use this last week end to test stuff for experience
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Old 18th January 2003, 10:10 PM   #17
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Adire Audio has this paper on their tech site for calculating SPL using Fs, Vas, and Qes.

SPL Calculation

Pete
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Old 18th January 2003, 10:46 PM   #18
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Thanks, Pete, for that page and the general info!

However beneficial Pete's information will be to us in the long run, it definitely throws a monkey wrench into the calculations for this particular woofer.

Fs = 19
Vas = 130 L
Qes = 0.37

Max Pentivent claims a reference efficiency of .4%. Kelticwizard, (who will [i]never[/] be confused with Mathwizard), calculates the reference efficiency as .23%. Unless I made a mistake, we are in trouble already.

Converting .23% to SPL yields the number 85.6 dB @ 1W/1M. Pretty much the number Ilianh specified as being "not too good". Oh well.

The contradictions in the chart supplying the Thiele-Small parameters would indicate that this woofer needs measuring by the owner with Speaker Workshop. I myself haven't learned how to use that program, but Ilianh has.

They say it is a good idea to break in the woofer before measuring.
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Old 18th January 2003, 10:56 PM   #19
Ilianh is offline Ilianh  Canada
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I came to that same conclusion, 0.23% (isnt too good...)

yhea, I'll measure the woofer, and I'll post the specs.

That Max company has some better series, I should check em out one day, the professional series has some stuff thats worth having a look at, but they have a "comming soon.." on their web page.

Anyway.. Thanks to you all for the great help
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Old 19th January 2003, 08:38 AM   #20
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I get these numbers for ported and 6th order...
Attached Images
File Type: gif maxpentivent.gif (21.6 KB, 238 views)
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Best-ever T/S parameter spreadsheet.
http://www.diyaudio.com/forums/multi...tml#post353269
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