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Old 16th August 2003, 10:30 AM   #11
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Well, it looks a little more than I would expect for new drivers, but for well used 7 year old ones I am not surprised. Just think of them as properly run in!

The differences are likely due to manufacturing tolerances being exagerated by time and positioning. For instance, was one driver more in the sunlight than any others, or maybe one speaker was nearest to a radiator or an indoor plant, leading to slightly different levels of humidity. All will have a slight effect over time.

I would suggest that if you use them, you pair them up so the lumped parameters even out.

However, on reflection, I would suggest you just mod the existing system. Using SW, you can work out the system response, and upgrade the tweeter and crossover. You could possibly even add a sealed back dome mid driver as well, such as the Vifa DM75. Don't worry about the chipboard box, as they are TLs, the stresses on the box are not nearly as great as a sealed or ported design. That way, you get the excellent bass of the originals, and clean up the mid highs.

edit- here is the link to the DM75 datasheet, thoughon second thoughts they may not fit in. Hmm
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Old 16th August 2003, 12:35 PM   #12
Vikash is offline Vikash  United Kingdom
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Ello pinkmouse,

Quote:
All will have a slight effect over time.
One of the bass drivers and one tweeter has been replaced over the period as well. Result of underpowering on a drunken birthday.

I guess I should model the drivers based on the mid-measurements of all four?

Quote:
However, on reflection, I would suggest you just mod the existing system
I see your point, but I kinda want to get my feet wet ,and this seems a good place to start since I have the drivers to spare. Kinda like a test run before I take on my expensive Seas design.

I want to use this material for the enclosure.

Quote:
Don't worry about the chipboard box, as they are TLs, the stresses on the box are not nearly as great as a sealed or ported design
Well I had a feel around in the cabinet, and I can't see anything that classes them as TL's. Just seems like a rectangular box with a vertical brace in the middle. It might need closer inspection.
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Old 19th August 2003, 05:01 PM   #13
Vikash is offline Vikash  United Kingdom
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HELP! I just tried modelling the drivers using the t/s params derived using SW (haven't done the VAS yet - using current Moncaor SPH-175 VAS = 48l, xmax=2mm)

fs=32
re=10.9
qms=9.11
qes=0.82
sd=137cm
le=0.44

Unibox Standard Designs:
Sealed
Vb=1760.8l
fb=32.86Hz
f3=32.87Hz

Ported
Vb=750.6l
Fb=16.92Hz
F3=12.95Hz

LOL. Can anyone shed some light on the suspect qms and qes values?
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Old 19th August 2003, 06:04 PM   #14
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Hmm, just used the online version of winisd with your numbers for a quick check, and it comes out with the following recommended sizes.

Ported - Volume 97l, F3 at 25Hz, Fb 26Hz

Sealed - Volume 48l, F3 at about 45Hz

Both of these seem reasonable, within isd's usual limitations on tuning, and from what I remember of the drivers. Maybe you have found a flaw in the Unibox curve fitting routines. I would suggest trying the above volumes in Unibox to see how they work out.
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Old 19th August 2003, 06:19 PM   #15
Vikash is offline Vikash  United Kingdom
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I should have mentioned that I was modelling 2 units in parallel, but the results with one driver is equally unrealistic.

I've just tested in WinISD online and i'm getting different results to you. Something's not right...
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File Type: gif winisdonline.gif (9.0 KB, 836 views)
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Old 19th August 2003, 06:31 PM   #16
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Eek, calculated Qts wrong!!

Doing it properly by hand it comes out as 0.747, near enough your result. Hmm, I will have to think about this some more...

How closely do your measured results with SW come to the published data on the Monacor?
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Old 19th August 2003, 06:41 PM   #17
Vikash is offline Vikash  United Kingdom
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Way out. But ignoring even the SW measurements, the Re=10.9 (published = 5.7) which could mean it's a different driver.

If I change the Qms to something more sane, everything seems to look better. I've measured each driver a number of times, trying different ways of supporting them just to rule that out, but the measurements are relatively consistent.

SW measures my sub closer to its published specs (after 4 years use), so it's not an obvious SW setup error...
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Old 19th August 2003, 06:55 PM   #18
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The Re thing suggests a 16 ohm driver, does this agree with your curves on SW?

The high Qms is strange, but I once measured an Audax 5" driver that had a Qms of about 12, but the Qes was much lower, at about 0.3.

I wish I could remember the exact designation of the Monacor driver, perhaps it had significant differences to the current model. Maybe even it was a driver modded by TDL, that they then released in their general range, but is now discontinued.

I would check the Vas as a priority.
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Old 19th August 2003, 06:55 PM   #19
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I've had a thought. I questioned the high impedence at fs and then forgot about it. Now i don't know how the qms is calculated, but perhaps this is related somehow. I guess it's feasible that a bad SW setup could result in increasing error of impedance measurement as it gets higher, thus being realistic for my sub (~35R at Fs) but not so for the Monacor (~130R at Fs).

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Old 19th August 2003, 07:00 PM   #20
Vikash is offline Vikash  United Kingdom
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Quote:
The Re thing suggests a 16 ohm driver, does this agree with your curves on SW?
Yes.

I questioned it as I don't see Monacor offering multiple impedances as an option for their drivers.

Quote:
I would check the Vas as a priority.
I agree. Off to the garage then...
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