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Old 15th August 2010, 01:09 PM   #21
sreten is offline sreten  United Kingdom
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Hi,

How big is too big ?
IMO any design with Vbox near or > Vas of the driver.
There is always a better choice of driver(s) for that box size.
For most good designs Vbox < ~ 1/2 Vas.

rgds, sreten.
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Old 15th August 2010, 02:20 PM   #22
bjorno is offline bjorno  Sweden
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Quote:
..For most good designs Vbox < ~ 1/2 Vas..
Agree and especially if a closed box is targeted, that is: when Qts is >=~0.29 --- <= ~0.41 ==> then Qtc is held between =0.5 to 0.7.

Look at the sensitivity spread and suggested operating BW for this driver:
This driver seems have a wide T/S spread and should IMO always be measured before any box calculation can be relied on.

Here is a suggestion(Home sub) if the TS data can be relied on that easily can be made to run in default mode = a T-TQWT or as an OD-TL(when removing the driver access lid) and in Closed box mode (removing an access lid and closing the terminus).

b
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File Type: jpg PYLE-PDW21250-_T-TQWT.JPG (544.4 KB, 191 views)
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Old 15th August 2010, 03:00 PM   #23
tb46 is offline tb46  United States
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Default T/S for PDW21250

Hi bjorno, and Hi Y'all,

I found some old notes on different T/S parameters for this driver which seem to make it appear quite different:

-----------------------

Quotes:

"http://www.diyaudio.com/forums/showthread.php?threadid=125773&perpage=25&pagenumb er=2


diyAudio Forums > Top >Loudspeakers >Loudspeakers >New Reference - SG-OB "Stargate

panomaniac, Post #37, 07-07-2008, Pyle (PDW21250) 21" T/S parameters as measured by Magnetar:

Using 250 grams "mass loading" method and LIMP this is pretty much where they all average-

FS - 31.61
RE - 5.59
RES- 59.81
QMS- 4.03
QES- 0.38
QTS- 0.34
L1- 1.88
VAS - 274.29 liters
SPL - 95.4

Magnetar, Post #48, 07-12-2008, answers to:I am curious as to your experience with the Pyle PDW21250 21"...:

I would not use them above 200 hz, they have a rising response to about 1K and a peak around 1.7K that is bad but well down is crossed over below 200 cycles with a 4th order electronic crossover. In this system they filled in below the 12. I don't know the xmax but can say when high passed at 50 cycles (3rd order) with a 275 WPC power they did not strain one bit. Now they are used down to 30 cycles with no sub and are OK. I never like to run my bass without a high pass filter, for sure if it's an open baffle.

Magnetar, Post #53, 07-14-2008:

Originally posted by BHTX: I was wondering this as well. Seems like the Madisons would have worked better for OB, but I know you don't have those anymore.

Answer: They are nearly the same thing cosmetically - I don't doubt they are made in the same factory. I never measured the Madisons but I suspect they would have fallen into the same group as these."

----------------------------------

The large open baffle is another possibility that could be build from these big sonotubes (I'd go with a sealed box though).

Regards,
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Old 15th August 2010, 03:19 PM   #24
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The argument from flat curves is a case of engineers' eyeballs looking at visual graphs, as I've said earlier in different words.

Whether of not some output curve (auditory flat or acoustically flat in music rooms etc) is superior to visual flat or simply nobody today can get as much super low bass as an earthquake or organ music fan demands, there may be other more important considerations. For example, just like many of us want subsomething filters (I don't know what to call a filter at 5 Hz??), we might like having a box that (a) adds linear air compression to linearize the spider (is that believed to be true?) and (b) something to hold back the cone from excess looseness at frequencies below which it isn't really radiating much.
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Old 15th August 2010, 09:52 PM   #25
a.wayne is offline a.wayne  United States
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Quote:
Originally Posted by chris661 View Post
That'd be on an infinite baffle, and notice it's the f3. The f10 is usually of more interest.
Hello,

Yes i'm aware of such , it still seems pretty high for F3 ......
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Old 15th August 2010, 09:53 PM   #26
a.wayne is offline a.wayne  United States
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Quote:
Originally Posted by sreten View Post
Hi,

How big is too big ?
IMO any design with Vbox near or > Vas of the driver.
There is always a better choice of driver(s) for that box size.
For most good designs Vbox < ~ 1/2 Vas.

rgds, sreten.
Vented or seal ? vented needs more than 1/2..........
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Old 15th August 2010, 09:56 PM   #27
sreten is offline sreten  United Kingdom
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Quote:
Originally Posted by a.wayne View Post
Vented or seal ? vented needs more than 1/2..........
Hi,

No it doesn't, you need to start off with a lower Qts than for sealed.

rgds, sreten.
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Old 15th August 2010, 10:00 PM   #28
AndrewT is offline AndrewT  Scotland
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yes,
vented tends to suit drivers with a low Qts, 0.2 to 0.4
sealed tends to suit drivers with a medium Qts, 0.35 to 0.65
open baffle or infinite baffle tends to suit drivers with a high Qts, 0.6 to 1
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Old 15th August 2010, 11:56 PM   #29
a.wayne is offline a.wayne  United States
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Quote:
Originally Posted by sreten View Post
Hi,

No it doesn't, you need to start off with a lower Qts than for sealed.

rgds, sreten.
Yes i know , usually anything with a qts higher than .40 it's better to go sealed....
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Old 16th August 2010, 12:06 AM   #30
bjorno is offline bjorno  Sweden
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Quote:
Originally Posted by tb46 View Post
Hi bjorno, and Hi Y'all,

I found some old notes on different T/S parameters for this driver which seem to make it appear quite different:

-----------------------

Quotes:

"http://www.diyaudio.com/forums/showthread.php?threadid=125773&perpage=25&pagenumb er=2

...

FS - 31.61
RE - 5.59
RES- 59.81
QMS- 4.03
QES- 0.38
QTS- 0.34
L1- 1.88
VAS - 274.29 liters
SPL - 95.4

..

Hi Oliver,All

Thank you for Magnetar’s T/S of the Pyle PDW21250 driver.
The data seems to be consistent, but in fact very different ( a stronger Motor- Voice-coil assembly) when compared to the recent T/S data : See the picture:

b
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File Type: jpg PYLE-PDW21250-_T-TQWT-meas-TS.JPG (389.7 KB, 141 views)
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