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Old 15th July 2013, 04:29 PM   #31
tb46 is offline tb46  United States
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Hi Bart,

Looking at epa's simulations in Post #25, the sum of S2 and S3 is 2633, you seem to have found additional cross-sectional area in Post #28: S2 + S3 = 2707. Your S4 is only 500, I would suggest not to go below Sd/3 (2x1250/3=833.3). You have the drivers connected in series. It may not make a difference in a HT application, but the example from Post #28 needs a 10Hz LR4 HP with the given Eg.

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Old 15th July 2013, 04:41 PM   #32
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Oliver,
I was hoping not to need a HPF at such a low tuning.
What do you think?

I'll fiddle around a bit more. Thanks for pointing me out on the S value's.
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Old 15th July 2013, 05:00 PM   #33
tb46 is offline tb46  United States
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Default HP?

Hi Bart,

In the home you will probably not reach Xmax, but why risk it? I like the HP (low cut) filter.

Now, in a lot of systems you don't have signal response down to DC anyway, so, if the system already attenuates the low end of the signal, you may not need a dedicated HP.

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Old 15th July 2013, 07:32 PM   #34
epa is offline epa  Netherlands
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a hpf wouldn't hurt,the question is how low can you set it.
your latest sim with 2 drivers look real nice.
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Old 15th July 2013, 08:02 PM   #35
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Yes it looks nice and I don't think in real live usage, I'll need the HPF. I'll just set the limiter and be done with.

I was thinking along the line of building two subs, half the width and each enclosure one driver.
Start with one and hear how that go's. then I still have the choice of leaving it like that, because, let's be honest, a TH like that will shake the house quite a bit with only one driver. (it already does in a BR! )
Besides, I have the opportunity to place a second one somewhere else (room nodes)
Or use the second driver between the L&R channel, tuned a bit higher. These TH will only reach up to 60hz... Still pondering...

At this very moment I'm mailing with mr. Kirchner ([ATB PC PRO]Kirchner elektronik - Onlineshop) about the T&S measurement of these drivers.
I'm about to send him a screenshot of the problem and hope it will get resolved. (updates will be posted on that)
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Old 17th July 2013, 01:47 AM   #36
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Default 2 TH's

Quote:
Originally Posted by ▀art West-VL. View Post
Yes it looks nice...

I was thinking along the line of building two subs, half the width and each enclosure one driver.Start with one and hear how that go's. then I still have the choice of leaving it like that....
Hi there B: Agree, your HR design and graphs for a single TH using 2 Series drivers look exceptional. However, recommend that you redo the HR simulation for a single driver TH enclosure, the sim' may be different (much different is possible) when you cut the width in half (reduce the areas). I've have had the opposite happen, single TH not acceptable and a 2 series driver TH look good. ...regards, Michael
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Old 17th July 2013, 08:30 AM   #37
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j.michael droke,

Both graphs should be the same, whether they are in series, parallel or only one driver at half the surface. Except for the SPL of course.

It's very time consuming for me to use all sorts of programs and I'm struggling with my second driver because I want to use measured specs.
Since this driver is not broken in yet, I suspect that is the reason my measurements are so far off.
I remember when my first BR with this driver didn't sound good at all, until after about 5 hours, then it started to get better and better. I think it's stabilized somewhat now.
I'll try to get a transformer hooked up this afternoon that can drive the sub in free air without smoking either of them.
I was thinking ▒24V. This would be 72W at 8Ω
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Old 17th July 2013, 01:26 PM   #38
epa is offline epa  Netherlands
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hi bart
gona try to draw one 1/2 the width,with the center baffle on an angle,so the driver fits.
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Old 17th July 2013, 02:23 PM   #39
epa is offline epa  Netherlands
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hmmz ,there is no way to fit the driver in a box half the width....
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Old 17th July 2013, 02:43 PM   #40
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Thanks epa, but not so fast! lol. This is still in the thinking jar.

At this very moment, the 18" woofer is getting 43.8V @ 2.75A
That's ▒120.5W and results in a resistance of about 16Ω@50hz
Previously I've put half the Voltage on it and the cone movement P-P was about 6mm
Now it's about 12mm and the air, deep in the magnet vent hole, is about 34░C.

side-note: the transformer pulls 127W from the socket. This means it only looses 6.5W on the way to the woofer. 5.4% loss. This gives me confidence that the transformer won't blow up anytime soon. (it's not overloaded)
I did put it on a cooling fin, with some dishwasher liquid between the two, for heat conduction. Fin is at ▒34░C too.
ambient temp is 23░C

The woofer does make a humming sound of course and a bit of vent hole wind noise, but I don't want to leave the house for the annoying hum and risk a fire.

Another important thing... While trying to measure T&S parameters I realized that my method has a flaw. The woofer is just sitting loosely so it can rock back and forth much more then when it would be mounted in a box. I think this is the reason the parameters don't resemble the factory specs.
At this moment I don't have any good way of mounting the driver tight or don't know how to weigh down the basket in a good and heavy way to reduce the woofer from moving too much. Any tips?

Here's a HD-video ☺
↑click↑
Attached Images
File Type: jpg 23V.jpg (643.2 KB, 23 views)
File Type: jpg 43V.jpg (373.6 KB, 21 views)
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Last edited by ▀art West-VL.; 17th July 2013 at 02:45 PM.
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