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Old 17th January 2002, 06:01 AM   #31
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you can try the freeware version of LSPcad that adire (or is it audax?) has for it's drivers ...
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Old 18th January 2002, 03:35 PM   #32
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Hi Navin, I post the answers here because I saw this thread has a lot of hits, so I assume that our discussion is interesting for somebody other.


Q: Response decrease 2 db from 400 Hz to 40 Hz

A: If you like to see a straight line in the simulation, just eliminate the cap on the midrange and use a 7mH on woofer!

Q: sound quality of capacitors

A: the critical ones are those in series to the signal, that is the tweeter and the big 300-400 for the mid.
This caps should be of the best quality possible (that's why I try always to eliminate the midrange high pass cap: 400 micro made by Solen's are bigger than the box and more expensive than the speaker!)
Caps in parallel are not so critical, polyester is of adequate quality.

Q: What about L3=0.43, R1=1ohms and R2=15ohms how will this affect the upper midrange area.

A: According to the CAD simulation, the best combination is L3=.27 , R1=1, R2=15.
With L3=.43 you have an increase of the tweeter response below 2.5 kHz and a DECREASE of 0.5 db of the global response
in the overlapping area with midrange. (the two emissions are not in phase in that range)
Anyway you're right in planning to switch the 2 coils and listen to
what's best: we're talking of small changes in the simulated behavior, too small to trust blindly the CAD.

Q ne advantage of using R1 before the LC combination is that one can adjust the sensitivity of the tweeter without affecting the Q of the crossover. Is there any disadvantage?

A: No, but then we have to recalculate all the simulation of mid-tw x-over: it is not given that the global response stay the same if you move the attenuator before the cell.


Q: The R1/R2 combination brings the sensitivy of the tweeter down by how much db?

A: about 2 db (see fig 1, the output is about 2 db below the zero line)

Q: Given the midrange is 88db and the tweeter is 91db and this is some difraction compensation does the tweeter require more reduction? We have ...only 1 6" midrange and 1 12" woofer...

A: The mid is nominally 88db, but is 90db at 1,7 kHz and 92 at 3kHz
The tweeter is nominally 91, but is 92 in the 2-3 kHz range, 91 @ 4k and 90 above that, with a peak of 92 at 17k
The only meaningful reference to use to balance the level is the freq. response graph, nominal spl is meaningless.

Simply because of the higher than nominal spl of both speakers in the 1.5-3 kHz range, we have to dimension the filter to tune their level.
Just think that to achieve our correct 2.3 kHz ACOUSTIC x-over point, the tweeter filter cuts nominally at 3.5 kHz, and the upper mid cuts nominally at 1450 Hz!

Look the graphs at http://www.d-s-t.com/main/index.htm for your speakers.
And believe me, the Scan's response is extremely flat, a Focal kevlar 7" can sound great, but first you have to deal with a peak of +10 db in that freq range!

Q: BTW I downloaded LSPCad but need LAUD (*.frp) files for the drivers I have.
Do you know where I can get this?

A: I don't know LSP cad, but I think that you can simulate your driver inside the program (reproducing the graphs mentioned above) and then save them as .frp
Or maybe someone in the forum can forward you the files.
With my CAD I can export in Clio, Leap and Ono-Sokki (?) format, plus other formats used by local CADs. Let me know if you can import some of the above.

bye
sandro
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Old 21st January 2002, 05:10 AM   #33
navin is offline navin  India
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yes so we have 2 crossovers to choose from. I'd rather use the 7mh cap and eliminate the 300uf cap from the midrange. If I find the midrange getting strssed I cxna switch to the other corssover.

If was to use 200uf average non polarised cap and bypass it with a 40-50uf polyester and then bypass that with a 2uf wonder cap is thaat good enough. will the 200uf cap also have to be of good quality?

Keep R1 = 1ohms and R2 = 15ohms I can switch inductoers and see the difference in the sound. the room effects might make one sound better.

if R1 before the LC network has nt bad effects why dont most compaanies use this. then they can adjust sensitivy of the tweeter (tweeter level) easily.

so your corssover also inculdes the drivers individual response. i was wondering about that. i saw the graphs and could see the rising response of the midraange and the response of the tweeter at the crossover point. In that case even the impedanace for teh corssover is not the nominal impednace but the impedance of the drvier at the crossover point right?

Thanks again. This is an education. I dint know Scan Speak and Peerless are managed by the same company.
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Old 31st January 2002, 10:16 AM   #34
navin is offline navin  India
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Default zeta

I seem to prefer high zeta corssoves. given the components so far teh zeta is quite low. Can a high zeta version (bigger tweeter inductor) be made?

If I increase teh tweeter inductace from 0.25 to 0.45 then the tweeter cap mus tbe reduced to copensate right? I know it is not that simple but presently my tweeter crossover has 1mh inductor and a 5uf cap.

effectively my present tweeter crossover is:
5uf cap, 1mh inductor, 1ohm series resistor, 10ohm parallel resistor.

The tweeter is used with 2 6" (18W8546) in MTM.

Regards
navin
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Old 31st January 2002, 03:44 PM   #35
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Hi Navin,

how is the project? Already sounding or still in building phase?

About your last post: increasing L and proportionally decreasing C (assuming to keep the same Fc) you lower the electric Q of the filter, that is the respose will decrease around Fc (the knee is smoothered)
For instance, in our last example moving from
C=6.8 L=.33 Fc= 3349 Q = .77
to
C=4 L= .57 Fc = 3333 Q = .45

the tw response will be:
same at 1.2 k, - 2 db @ 1.6k -4/5db from 2k to 5k, -2 @ 8k, same @ 14k.

the system response will be affected accordingly, that means that if you want a very low electric Q on the tw filter you should change the mid-bass x-over to compensate for the level decrease in the crossover range.
I'll try to simulate something with the 'low zeta' input, but at this point why don't simply try a 1st order crossover?
bye
sandro
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Old 1st February 2002, 05:57 AM   #36
navin is offline navin  India
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will a 1st order crossover protect the tweeter or even roll of the midbass fast enough so that teh kevlar resonance is rolled off.

Thanks.
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Old 26th April 2002, 05:47 PM   #37
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one idea....

is there any advatage of making the 12" side firing woofer into a tranmission line?

it is quite simple to do this.

all one needs is to partition the sub box into 3 sections using 2 vertical wood pieces that run top to bottom.

of these the vertical that is closest to the 12" is tapered so that the transmission line is wider at the bottom and less wide at the top. sort of tapering the TL.

if the dimension are 28" deep then the 3 sections would be
14" 7" and 7". The first vertical (closer to the front baffle if one were to look at teh side view) woudl tapered so it is 14" at the bottom but 10.5" at the top the second vertical would be parellel with teh rear wall of the speaker. the TL would then taper from 14" to 7" for about 5 feet and then stay at 7" for the last 2.5 feet.

also one can extend the line so that it fire out of teh top of the speaker (by reducing the depth of the cabinet of teh 6" woofer).

If one needed to convert the cabinet back to a sealed cabinet all one as to do is bore 4" holes in the verticals and close the top.

since the cabinet is about 6-6.5" wide internally a 4" hole in the center of the vertical would work.

is this idea worth the effort?
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