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Old 7th April 2011, 06:08 PM   #911
Djim is offline Djim  Netherlands
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Location: 'Ollanda
Quote:
Originally Posted by 4pyros View Post
97db at 20Hz
102db at 25Hz
105.5 at 30Hz
106.5 at 35Hz
105.5 at 40Hz
106 at 45Hz
106 at 50Hz

Thats all I did for now. I will try and rerun the full range agin soon.
Andy
That looks really good there Andy, can't wait to see your 28,3V measurements...
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Old 7th April 2011, 06:23 PM   #912
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Quote:
Originally Posted by 4pyros View Post
My test tone CD was messed up. I converted the MP3s to WAVs that could be read by the player on a USB stick. I used the smallest amp to set the 2.83VRMS.
and stood the meter up so I could read it better from the side.

Not the best day for testing but I knew the box would go lower and boy did it.

97db at 20Hz
102db at 25Hz
105.5 at 30Hz
106.5 at 35Hz
105.5 at 40Hz
106 at 45Hz
106 at 50Hz

Thats all I did for now. I will try and rerun the full range agin soon.
Andy
Andy,

Whether wind made for the higher readings, or you managed to set levels incorrectly, or the file conversion increased the LF content, or you changed the mic or cabinet position your current readings would defy the laws of physics for a half space outdoor measurement.

I think you will find your previous readings, which correlate well with Jim's, are correct.

Not to play the Hoffman's Iron Law record out, but when a lower frequency response is obtained from the same size box, it will be at a reduction of output level, not an increased level.

Cheers,

Art
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Old 7th April 2011, 06:48 PM   #913
wg_ski is offline wg_ski  United States
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Quote:
Originally Posted by Djim View Post
Power compression: Since most PA drivers have less then 5% efficiency almost all of the rest of the input power is converted into heat. The more input power the more this heat will rise and therefore the resistance of the voice coil.
Horns also have significant radiation resistance - and the portion of input power that goes into this is converted to *sound*. Look at the impedance rise (above the AC free air resistance), and this is an indication of how much is converted to sound and not heat. Power compression still sets in, it just takes more power to do it.

Quote:
Dynamic compression: When a PA speaker cone reaches the limit of its excursion the mechanical 'elastic' resistance becomes higher.

Which is why most woofers (and instrument speakers) survive at all. The harder you it it, the more it takes to move it. But when this happens with a horn, you very quickly lose some of the radiation resistance and the temps skyrocket at these excursion levels. There's a sweet spot where power compression is low, efficiency is high, and you're not losing much to suspension nonlinearity. Below that, horns rock. Above that, things fall apart quickly.
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Old 7th April 2011, 07:53 PM   #914
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So the 3015lf can play 25 hz without a problem? I was under the impression (as Jbell said earlier) that a 48db/octave high pass was necessary at 40hz to keep the driver safe.
I'm just wondering what is NECESSARY for the driver not to blow....
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Old 7th April 2011, 08:25 PM   #915
Djim is offline Djim  Netherlands
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Quote:
Originally Posted by wg_ski View Post
Horns also have significant radiation resistance - and the portion of input power that goes into this is converted to *sound*. Look at the impedance rise (above the AC free air resistance), and this is an indication of how much is converted to sound and not heat. Power compression still sets in, it just takes more power to do it.
Which is why most woofers (and instrument speakers) survive at all. The harder you it it, the more it takes to move it. But when this happens with a horn, you very quickly lose some of the radiation resistance and the temps skyrocket at these excursion levels. There's a sweet spot where power compression is low, efficiency is high, and you're not losing much to suspension nonlinearity. Below that, horns rock. Above that, things fall apart quickly.
Sorry Wg_ski if I made it sound for drivers in general cause it was meant for power compression levels in TH's.

The point here is not where efficiency is the highest and excursion the lowest in a Tapped Horn. Here it’s about the point where excursion reaches its maximum. At this point power compression levels are similar to basreflex. You can also read that from the differences between Jbell's 2,83V and 28,3V measurements.

Most low frequency PA drivers have efficiency between 2 and 3%. At the point in TH’s where excursion is max (around 1/3 wavelength) you have an efficiency gain around 3dB. This means you end with 5%-6% efficiency.


I hope this cleared things up...

Last edited by Djim; 7th April 2011 at 08:27 PM.
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Old 7th April 2011, 08:57 PM   #916
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Quote:
Not to play the Hoffman's Iron Law record out, but when a lower frequency response is obtained from the same size box, it will be at a reduction of output level, not an increased level.
Art; It is not the same size box and thats why I was expecting more out of it. Andy
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Old 7th April 2011, 08:59 PM   #917
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Quote:
So the 3015lf can play 25 hz without a problem? I was under the impression (as Jbell said earlier) that a 48db/octave high pass was necessary at 40hz to keep the driver safe.
I'm just wondering what is NECESSARY for the driver not to blow....
I was only testing at 1 watt that low. Andy
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Old 7th April 2011, 09:03 PM   #918
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Quote:
Originally Posted by 4pyros View Post
Art; It is not the same size box and thats why I was expecting more out of it. Andy
Hm... I think it would have to be a LOT bigger for the output to change significantly at low frequencies..

FR measurements can be a b*tch to get right. That's why I prefer to look at the impedance response and compare it to the HornResp predictions. Impedance response measurements are a lot easier to get right, and if they are a very close match to what HornResp predicts, it's likely that HornResp's FR predictions would be a close match as well.
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Old 7th April 2011, 10:46 PM   #919
tb46 is offline tb46  United States
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Hi Y'all,

I went through the drawings, and Hornresp simulations for the 4pyros modified SS15, and the original SS15 in quite some detail earlier in this thread. And I tried repeatedly to maximize the Hornresp output for both enclosures. The results in Post #907 do not seem possible, as Brian Steele says in Post #918: "...it would have to be a LOT bigger...", and I for one would put more stock into the Hornresp results.

Regards,
__________________
Oliver
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Old 8th April 2011, 03:14 AM   #920
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Yes; looking back at the SIMs thay do seem to high. OK back to the testing. Andy
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