please help with this TQWT modelling with corals flat 8 - diyAudio
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Old 12th October 2004, 03:52 AM   #1
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Default please help with this TQWT modelling with corals flat 8

hi!

i have some vintage full rangers and am interested to listen to it in a tqwt cabinet. ala http://www.t-linespeakers.org/projec...QWT/index.html

i have input the t/s parameters and done the simulation here.
http://diyparadise.com/flat8_tqwt.html

or let me link everything here.

Click the image to open in full size.

Click the image to open in full size.

appreciate any advice to lower the bass "bump". we loves boomy bass?

thx!

donjuan
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Old 12th October 2004, 11:24 AM   #2
MJK is offline MJK  United States
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donjuan,

I just checked the consistency of your T/S parameters and they do not look correct. Did you measure the drivers yourself? A Qts of ~0.5 should not have a hump in the infinite baffle response curve (blue dashed line). I think the problem is the driver input data.

Hope that helps,
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Old 12th October 2004, 12:50 PM   #3
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hi martin

thx for replying. i didn't measure the parameters myself but 2 of my friends who did so found their measurements to concur pretty well.

donjuan
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Old 12th October 2004, 01:57 PM   #4
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Hi DonJuan,

The T/S parameters input into MathCad represent a redundant set of values, In other words, if you have some of the T/S parameters you can calculate the remaining parameters. This is what I do with any T/S parameters I see on the Internet, or on a manufacturer's data sheet, to assess the accuracy of the reported parameters.

For your Coral Flat 8 driver I used :

fs = 51.5 Hz
Re = 7.06 ohms
Sd = 324 cm^2
Qms = 5.391
Qes = 0.5518
Vas = 69.558 liters

to calculate the remaining parameters :

Qts = 0.501
BL = 9.244 N/amp
SPL = 94.2 for 1 w/1 m

The value of BL is significantly different fomr the one you used. Something looks to be in error in your input data. If I had used your value of BL to calculate Vas, I would have ended up with a different set of parameters. I recommend rechecking your measurements.

Hope that helps,
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Old 12th October 2004, 03:21 PM   #5
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Hmm, I wonder where my response from around 5:45am EST went? Oh well, here it is again:

GM



First things first: either BL is way off or one or more of the other specs are. Based on some other Coral 8" drivers specs and the fact that the drivers were measured, I assumed BL was much too low, so I used 9.1898 calc'd based on the WS's p0 = 1.21/c = 342. If you look at the infinite baffle response plot it's obvious since the response has a >0.7 Qts hump in it Vs the ~0.5 Qts 6dB/octave roll off it should have.

I also made Lvc = 0.8 mH since this is the average of the other 8"ers.

WRT SAF, the specs are such that making it small will keep it from performing anywhere near it's potential.

Anyway, here's three good looking alignments that you can input and adjust to hopefully meet your performance/SAF goals:

T/S max flat ML-TL:

L = 40.25"
CSA (w x d) = 209.429"^2
eta = 0.4288 (17.25")
density = 0.25lbs/ft^3
rp = 2.75"
Lp = 0.75"

ML-TL extended to 30Hz, yielding a nice TL-like response:

L = 56.125"
CSA = 178.645"^2
eta = 0.3869 (21.7")
density = 0.25lbs/ft^3
rp = 2"
Lp = 0.75"

Alpha TL - ~traditional end loaded stuffed pipe to mimic an infinite baffle response, so it will have to be folded to get the driver at a decent level:

L = 61.53"
CSA = 251.926"^2
eta = 0.065 (4")
density = 1.415lbs/ft^3 (assumes polyfil)
rp = 8.955"
Lp = 0.0001

GM
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Old 13th October 2004, 02:53 AM   #6
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hi martin

yes. i goofed!

i didn't input B1 parameter, thinking that it isn't important. clearly it is!

the sensitivity of the flat 8s are reputedly 95db so your value is very close.

one thing though, how do you determine sd? although it's said to be an 8-incher, i measured surround edge to edge, it's only 18cm. it's only 8" if i include the gasket at the edge as well.

is it coincidental that even using your fostex 164 enclosure, the coral flat 8s also give quite a respectable freq response?

hi gm

thx for your simulation!

CSA (w x d) = 209.429"^2
eta = 0.4288 (17.25")

sorry i don't understand what is "csa"?

also eta means measured from the top or from the bottom?

with regards to the port, how do we determine where to place them?

with regards to stuffing, where do we determine where to place them? up to which point?

thx gentlemen for your help. as you can see, i'm still very green here. without your help, i'll still be struggling as i'm off a wrong path.

donjuan
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Old 13th October 2004, 05:23 AM   #7
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Greets!

Quote:
Originally posted by DonJuan
hi gm

thx for your simulation!

CSA (w x d) = 209.429"^2
eta = 0.4288 (17.25")

sorry i don't understand what is "csa"?

also eta means measured from the top or from the bottom?

with regards to the port, how do we determine where to place them?

with regards to stuffing, where do we determine where to place them? up to which point?

donjuan
You are welcome!

CSA = cross sectional area, i.e. width (w) x depth (d).

eta is the distance down from the top.

The vent should be near/at the bottom when the driver is positioned at the proper point along the pipe's length, but as you shift it upwards, the vent needs to shift upwards also, then adjust its length to get the desired response.

WRT stuffing, I prefer to line the walls as required, but using fluffy polyfil or Miraflex from the top down to the bottom of the driver works well once the amount is right, though I have noticed that they usually prefer less than what looks good in a sim.

GM
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Old 13th October 2004, 10:00 AM   #8
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hi gm

thx for the prompt reply. ok, here's more dumb questions.

how does csa relate to sd, s0 and sl? asking this as i'm trying to model your recommendations in the mathcad spreadsheet. got to see how it "looks" and learn from there.

finally if we specify s0 as 1.sd and sd is say 100cm2, then this means we make s0 100cm2 right? up to us to define width and depth?

finally making some progress (i hope!)
donjuan
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Old 13th October 2004, 11:10 AM   #9
MJK is offline MJK  United States
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Hi DonJuan,

Quote:
one thing though, how do you determine sd? although it's said to be an 8-incher, i measured surround edge to edge, it's only 18cm. it's only 8" if i include the gasket at the edge as well.
I measure from the mid point of the surround to the mid point of the surround. It is not uncommon for an 8" driver to have a diameter of about 6" which produces a Sd of approximately 200 cm^2.

Quote:
is it coincidental that even using your fostex 164 enclosure, the coral flat 8s also give quite a respectable freq response?
It is a nice coincidence, if it looks like a good fit that produces a nice SPL response then I don't see any reason for not considering the ML TQWT enclosure for your Coral drivers.

Hope that helps,
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Old 13th October 2004, 07:27 PM   #10
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Greets!

Quote:
Originally posted by DonJuan
hi gm

thx for the prompt reply. ok, here's more dumb questions.

how does csa relate to sd, s0 and sl? asking this as i'm trying to model your recommendations in the mathcad spreadsheet. got to see how it "looks" and learn from there.
You are welcome!

Right, this stuff does not make much sense if you can not 'see' the results.

CSA is strictly a function of the pipe's net Vb (internal volume after the driver, vent, bracing, Vb is deducted from it) divided by its longest dimension. Using some multiple of Sd is just MJK's way to define it and has nothing to do with Sd per se. Indeed, you can input any Sd you like and as long as you adjust BL to suit using these formulas, the sim will still be the same except for the woofer displacement scale, so is not necessary for doing 'quickie' sims.

Cms = Vas/(Sd^2*rho*c^2)

where:

Vas is in m^3 (liters*0.001)

Sd is in cm^2

c is in meters/sec*0.0001 to get Cms in mm/N

then:

Mms = 1/[(2*pi*Fs)^2*Cms]

BL = SQRT[(2*Pi*Fs*Re*Mms)/Qes]

Look at the top of the WS to see what MJK is using for 'rho' (air density) and 'c' (SoS).

Quote:
finally if we specify s0 as 1.sd and sd is say 100cm2, then this means we make s0 100cm2 right? up to us to define width and depth?
Correct. Yes, once I figured out how to change the WSs, I originally listed CSA using golden ratio dimensions, but between so many folks wanting to know if they could change them and MJK/Bob Brines saying it had no sonic benefits (I disagree, but have done no testing to prove it so YMMV), I quit doing it unless asked.

GM
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