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Old 5th April 2011, 10:12 PM   #891
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Quote:
If you are using a dB meter that has only “A “and “C” scale, the “C” scale is better for measuring LF, but is still down about 2 dB at 40 Hz.
I am using a PAA3 meter for the testing and the weighing is off. Its a pain to read the meter from behind the speacker. I am going to try and hook it up to a lap top for further testing. Andy
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Old 5th April 2011, 10:53 PM   #892
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Quote:
Originally Posted by 4pyros View Post
The testing was not perfect and the mesherments may not be exact. I know my pyro box should go slightly lower than Jim's SS15. I need to come up with better ways to test it and repost the results. Coming soon. Andy
Andy,

Other than a (possible) difference in meters, was there any difference in the way you tested your cabinet than the way Jim tested his?

What "better" way do you have to test it?

By the way, it is no easier to dial in 28.3 volts than it is to dial in 2.83 volts, they are just 20 dB different in level, one watt or 100 watts into an 8 ohm nominal load. It is easier to set the level if you turn down the amp gain in either case.

Get the voltage correct at 60 Hz, don't mess with it at different frequencies, chances are your meter will be most accurate at 60 Hz, and may be "off" at other frequencies.
Set the level without a load to get it close, then trim it out with the load (speaker). Some amps won't change in output voltage at all between no load and loaded, others do change, especially with lower impedance loads.

At 28.3 volts, you will be able to see the speaker move a bit, but it will still have more than six dB of headroom left down to 45 Hz or so.

If your cabinet has a longer path length than the SS15, it may have a slightly lower Fb, or Fc.

Speaker excursion in standard horns just increases as frequency decreases.
Fc (horn cutoff) is the normal term used for the LF corner with horns, but TH actually behave more like BR than regular horns at the low corner, there is a pronounced excursion minima, followed by a very rapid increase in excursion.

A lower Fb with the same box volume reduces LF efficiency.
A lower Fb in a smaller box volume (space taken up by corner ramps, etc.) reduces LF efficiency further.

As long as the speaker does not run out of excursion, you can use EQ to make up for the lesser output down to, and slightly below Fb.

With EQ, you may be able to squeak a few Hz more bottom extension (at a lower maximum SPL level) out of your box than a "standard" SS15.

Art
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Old 5th April 2011, 11:08 PM   #893
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Originally Posted by 4pyros View Post
I also had some problums with my test waves. I downloaded the the test CD that Jim had suggested and put it on a stick. My player would not play the files so I put them on a CD.
I started testing at 10 to 20Hz and was getting some high numbers. Than when I whent to 20-30Hz the DBs dropped by 10 or so and steady rose again from there. I am not shure what that was about but I will take a look at the CD in Gold Wave and try to convert the files for the stick that can work on the player. Andy
At 10 or 20 Hz your meter will mostly be reading wind noise, the cabinet response drops at around 24 dB per octave below Fb.

If you don't have a wind screen for your meter, you will often have to wait a long time between gusts. Even with a wind screen, using the Magnitude Response with Smaart, I spend far more time waiting than measuring, but at least I can look at the Coherency trace to see if the measurement has suffered from wind contamination.

If the wind is steady, (never is here in Madrid, NM ) with a dB meter, it is hard to tell how much LF is wind noise, and how much the speaker is putting out.
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Old 5th April 2011, 11:21 PM   #894
Djim is offline Djim  Netherlands
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Pyros, you need a detailed drawing from your ‘custom’ SS15 otherwise all this good help is for nothing. That way you can translate your cab back to a corresponding HornResp prediction and find the points in your design that can benefit from a little re-arranging. Also from a corresponding HornResp you can calculate exactly the max power you can use and as long your amplifier doesn’t go over that max you can eq as much as you like at any point in the bandpass!
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Old 6th April 2011, 04:48 AM   #895
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i finished the building/painting. since this is being used on the beach for a beach radio, i decided to paint the sub to look like a cooler. it kinda looks like one from far away
Click the image to open in full size.
Click the image to open in full size.
Click the image to open in full size.
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Old 6th April 2011, 04:58 AM   #896
Djim is offline Djim  Netherlands
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And we Europeans already make a lot of fuzz about those 'tiny mini' ghetto blasters on our beaches ;-)
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Old 6th April 2011, 02:21 PM   #897
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Quote:
Originally Posted by Djim View Post
Pyros, you need a detailed drawing from your ‘custom’ SS15 otherwise all this good help is for nothing. That way you can translate your cab back to a corresponding HornResp prediction and find the points in your design that can benefit from a little re-arranging. Also from a corresponding HornResp you can calculate exactly the max power you can use and as long your amplifier doesn’t go over that max you can eq as much as you like at any point in the bandpass!
The maximum safe power that can be used can more accurately be ascertained by measuring cone excursion in the actual cabinet rather than relying on a simulation.
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Old 6th April 2011, 03:35 PM   #898
Djim is offline Djim  Netherlands
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Originally Posted by weltersys View Post
The maximum safe power that can be used can more accurately be ascertained by measuring cone excursion in the actual cabinet rather than relying on a simulation.
True, but give me an example where excursions in a TH was higher then predicted, just one Art?! Which means the calculated excursion is safe. But I would agree with you if you say in reality some TH's can be powered way beyond predicted max safe power.

Nevertheless, it still doesn't matter how much and where you EQ as long you don't feed your cab with more watts then its max safe power (from predictions or real life measurements).
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Old 6th April 2011, 03:47 PM   #899
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Quote:
Originally Posted by Djim View Post
True, but give me an example where excursions in a TH was higher then predicted, just one Art?!
That's probably the case for every alignment simulated by a program that doesn't take BL nonlinearity into consideration. Most assume that the driver behaves at large signal levels the same way it does at small signal levels, which is simply not true.
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Old 6th April 2011, 05:19 PM   #900
FlipC is offline FlipC  United States
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Dave NonZero -
Well the cabients have a -7 to -10 DB drop at rear to rear off axis. Plus some cancellation. And being 15' off rear wall I wasn't getting any real reflections. IE none of that boom room node going on. BUT if you notice there is also have a pair of 12x1" 2 way's as monitors. So cutting through wasn't a problem.
My ears weren't ringing at all afterward. Though I only went out in front maybe 3 times the whole night. And only in front of the speakers for the last song. To get a quick massage!
Salz - no those arent DIY tops. JFL210's.
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