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Old 7th June 2006, 10:32 PM   #1
jwatts is offline jwatts  United States
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Location: Erwin, Tennessee
Default Sub Development

I have been asked by the manufacture to help improve the sub with the parameters listed here. The first thing I plan on doing is increase the stiffness of the surround try to drop the Fs to about 30Hz. I expect the Qts to drop in conjunction with the Fs after I have increased the cone stiffness. Can anybody give me any suggestions on what to change? They are for car audio purposes and are DVC. The measurements below are the coils wired in series.

Revc = 4.1489 ohms
Fs = 35.5216 Hz should be 29 to 31 Hz
Zmax = 35.5411 ohms
Qes = 0.8036
Qms = 6.0807 should be 8.0 to 10.0
Qts = 0.7098 should be .5
Le = 2.3762 mH (at 1 kHz)
Diam = 254.0000 mm ( 10.0000 in )
Sd =50670.7504 mm^2( 78.5398 in^2)
Vas = 51.1113 L ( 1.8050 ft^3)
BL = 12.7749 N/A
Mms = 141.6356 g
Cms = 141.7366 uM/N
Kms = 7055.3384 N/M
Rms = 5.1987 R mechanical
Efficiency = 0.2748 %
Sensitivity= 86.3901 dB @1W/1m
Sensitivity= 89.2417 dB @2.83Vrms/1m
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Old 8th June 2006, 02:04 AM   #2
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I'm no expert, but it seems like by increasing stiffness the Fs will increase, too.
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Old 8th June 2006, 03:05 AM   #3
jwatts is offline jwatts  United States
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Default Fs Calc

Fb = 1/(2pi*(Cms*Mms)^.5)

Calculating Fb

Fb=35(Hz)=1/(2pi*((141.736/10^6)*(141.6356/10^3))^.5)

Assuming the Cms has doubled.

Fb=25(Hz)=1/(2pi*((2*141.736/10^6)*(141.6356/10^3))^.5)

Cms = 1/Kms

Your are correct because I have halfed the Kms.

Am I correct in my thinking or am I thinking to hard?
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Old 8th June 2006, 07:18 AM   #4
Volenti is offline Volenti  Australia
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To lower Fs try using softer/more compliant spiders, higher Mms will also lower Fs but this reduces efficency and should be avoided if possible.

Though a softer suspension conflicts with the desired Qms, which calls for a tighter suspension to raise it, which will raise Fs, requiring you to add mass to lower Fs again (which hurts efficiency).

Your desired parameters remind me of the alpine type-X, which has a very stiff suspension, really heavy Mms (396g) and poor efficiency (81.5db, measured) good thing it can handle a lot of power

What's the intended application for the sub, SPL,street beater,SQ?, and powerhandling?
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Old 8th June 2006, 12:02 PM   #5
jwatts is offline jwatts  United States
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Default Sub Type

Street beat/SQ

500 Watts Max

I added mass to the cone to get Fs down but my Qts went up. I also noticed my voice coil resistance is about 3 ohms per coil as opposed to 2 ohms. If I shorten the coil wire length to reduce my resistance to about 3 ohms should the Qes decrease?
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Old 8th June 2006, 09:37 PM   #6
masaki is offline masaki  Peru
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Default Request help

Hi, I have a friend with a pair of old speaker (coming from a destroyed Altec Lansing Voice of the theatre box A7) I want to buy the speakers, but now I'm not sure what to do with these speaker, I have two ideas, and I don't know which is better idea...

1.-reconstruct the original box (I have the schematic of the A7 VOTT) but I need to find a replace tweeter or the original one

2.- Use the speaker and create two sub-woofer box

any ideas ?

--Sorry if I put this post here, but for some reason I only receive a -please search this forum first- message every time I want to post a new message
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Old 8th June 2006, 09:52 PM   #7
TNT is offline TNT  Sweden
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Default Re: Request help

Tick the box "Have you Searched?" upper left in the "New Topic" window and You should be good to go!

/

edit:clarification

Quote:
Originally posted by masaki
--Sorry if I put this post here, but for some reason I only receive a -please search this forum first- message every time I want to post a new message [/B]
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Old 8th June 2006, 10:18 PM   #8
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As I recently learned, increasing suspension compliance will also raise the the Vas, requiring a larger box. This might not make you very happy in a car.
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Old 8th June 2006, 10:45 PM   #9
Notax is offline Notax  Montenegro
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@ jwatts

When you increase stiffness its lower Cms and you got higher Fs.
I belive you thought lower stiffness and higher Cms (mm/N) value.

First, why you want lower Fs?
When you change Cms and Fs, most of T/S parameters change.
Qms, Qes, Qts, Vas. In the way you got same Vb (closed or bass-reflex) in both cases. Because of that, I dont see purpose for that. For these kind of basses it is not always good to get higher Cms value, because of slower stoping of the cone after the signal is gone. Its the balance.

Now, for Fs=25 Hz, you must increase Cms (lower stiffness) some more than two times. (If you dont add mass to the cone)

Cms=0.286 mm/N
Fs=25 Hz
Qms=4.28
Qes=0.566
Qts=0.500
Vas=103.13L
SPL is same.
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Old 9th June 2006, 12:39 AM   #10
Ron E is offline Ron E  United States
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Default Re: Sub Development

Quote:
Originally posted by jwatts
I have been asked by the manufacture to help improve the sub with the parameters listed here. The first thing I plan on doing is increase the stiffness of the surround try to drop the Fs to about 30Hz. I expect the Qts to drop in conjunction with the Fs after I have increased the cone stiffness. Can anybody give me any suggestions on what to change?
They ask you for design help, and you come here?

Forward them my simple driver design spreadsheet. I can perhaps make them a special version, just for DVC drivers. The spreadsheet can be found at:
Diy dynamic driver
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