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Author Topic: Prosound Shootout 2007  (Read 43533 times)

Les Webb

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Re: Prosound Shootout 2007
« Reply #120 on: October 24, 2007, 09:29:15 pm »

I don't think there were any suprises in the tests, most of the cabs had been tested before. I hate that Jeff's prototypes didn't do what he wanted, many of us have been through that before, they still looked really nice.  

Impedance sweeps are the end all for telling air leaks, Leland was surely not unaware of this, just caught without something to fix the leak, for which he was really glad that Jeff let him borrow some Very Happy . Thanks Jeff.

The t48s tested like we expected, they were optimized for 40hz up.  When adjusted for impedance and pack space I think they faired very well with the larger boxes.

Thanks once again Wayne for putting on a top notch shootout.  I WILL be there next year with some T-36s and maybe some other Fitz designs.

Les
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Wayne Parham

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Re: Prosound Shootout 2007
« Reply #121 on: October 25, 2007, 01:25:41 am »


Les Webb wrote on Wed, 24 October 2007 20:29

The t48s tested like we expected, they were optimized for 40hz up.  When adjusted for impedance and pack space I think they faired very well with the larger boxes.


There's no need to adjust for impedance because we measured it.  We ran sweeps at a constant 28.3v, and also at 100w, 200w, 400w and so on.  Compare charts at constant power and there is no need to adjust for impedance.

Looking over the charts on the Fitzmaurice website, I'd say they are pretty close on SPL but somewhat off on response shape.  They're smoothed like what I'd expect to see in groups of six to eight, even when a single horn is shown.  The Fitzmaurice flare shape seems to result in a pretty consistent response curve, and that is not apparent on the Fitzmaurice website.

The Tuba 36 we measured had a similar curve as I recall.  Some have said it was because the driver chosen was not right for the horn, and that may be.  But I do see some similarity in the response curve shape of all the Fitzmaurice basshorns we've measured.

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Pascal Pincosy

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Re: Prosound Shootout 2007
« Reply #122 on: October 30, 2007, 12:59:03 am »

I really wished you had tested 2 boxes at a time like you did the first year and last year. Measuring one single horn cabinet with is a very poor indication of what the boxes will do in the real world.
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Wayne Parham

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Re: Prosound Shootout 2007
« Reply #123 on: October 30, 2007, 01:58:29 pm »


I wished we had measured groups of horns too.  At least two, maybe four or more.  We just flat ran out of time.  Next time, we'll probably reserve two hours per exhibitor rather than just one hour.
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Grant Rider

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Re: Prosound Shootout 2007
« Reply #124 on: November 01, 2007, 01:20:35 am »

Wayne Parham wrote on Tue, 30 October 2007 17:58

I wished we had measured groups of horns too.  At least two, maybe four or more.  We just flat ran out of time.  Next time, we'll probably reserve two hours per exhibitor rather than just one hour.


Judging from previous shootouts, I think you can just add 3db to the charts to calculate for two boxes. 6db if you don't correct for the parallel connection cutting impedance in half. The charts get a little smoother too.

By the way, nice job. Thanks for doing the shootout. Kudos on the push pull idea too, it definitely drops the distortion waaaay down.

http://srforums.prosoundweb.com/index.php/m/257706/25195/0// /15858/#msg_257706
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Wayne Parham

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Re: Prosound Shootout 2007
« Reply #125 on: November 01, 2007, 10:58:19 am »


Grant Rider wrote on Thu, 01 November 2007 00:20

Judging from previous shootouts, I think you can just add 3db to the charts to calculate for two boxes. 6db if you don't correct for the parallel connection cutting impedance in half. The charts get a little smoother too.


That's true.  We would have liked to measure pairs and groups of four, but we were pressed for time.  This lets us see response in groups, which is a little different than just increasing SPL.  Basshorns are almost always acoustically small, so grouping them helps make them more efficient.  It not only increases SPL but also tends to reduce response ripple.

We were going to measure with voltage constant, so that would have added 6dB.  In other words, when measuring pairs, we would send 28.3v to each box, then 100 watts to each box, and so on.  Sending 100 watts to a pair of boxes is 200 watts total, of course, which is 3dB greater than 100 watts total.  If a person wanted to compare a single cabinet to a pair of smaller cabinets, they could easily view the data in many ways, say comparing charts measured with 200 watts on a single cabinet against 100 watts per cabinet for a pair.


Grant Rider wrote on Thu, 01 November 2007 00:20

Kudos on the push pull idea too, it definitely drops the distortion waaaay down.

  http://srforums.prosoundweb.com/index.php/m/257706/25195/0// /15858/#msg_257706


It does reduce distortion, that's for sure. A basshorn with two woofers should always be configured push-pull, in my opinion.  This configuration has proven to be extremely effective at reducing distortion, as you can clearly see from the measurements.  The biggest improvements are in the bottom octave, where distortion of most subs goes off the charts.  Most subs (even basshorns) have distortion that rises above the fundamental down near cutoff.  The 12Pi basshorn subwoofer doesn't do this, in fact, distortion at the low cutoff is no higher than anywhere else on the response curve.  It's down near the noise floor level all the way across the curve, even at very high output levels.
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Wayne Parham
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Grant Rider

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Re: Growler Prototype
« Reply #126 on: November 02, 2007, 10:07:00 pm »

I noticed the Growler tested at the Tulsa Shootout was different than other models. There seems to be a 2007 model and a 2008 model, and then a third version was taken to the Tulsa Shootout.

Charts in the road test forum show the 2007 and 2008 models
Charts on the prosound shootout website show the third version

What is the difference between each of these three models? Does each have a different woofer inside? Why were the changes made? What are the strengths and weaknesses of each version?
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Tom Danley

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Re: Prosound Shootout 2007
« Reply #127 on: November 04, 2007, 08:18:03 pm »

Hi Wayne

I have to take a small issue with a statement here, as it is misleading.

“This configuration has proven to be extremely effective at reducing distortion, as you can clearly see from the measurements.”

Technically speaking one couldn’t possibly draw that conclusion, in order to see how effective the push pull arrangement is, one would have to compared the same horn shape but not in push pull.  Comparing different horns with different drivers tells you nothing about the value of push pull vs standard mounting.
As you might be aware, at the Michigan subwoofer shoot out, where the labs were measured, they had the lowest distortion of all the speakers there. (look up the curves on line).   That same driver linearity is how people have been able to use them in living rooms eq’d to extend the bottom.

Have you built and measured a 12 pi that wasn’t in push pull to see how much difference it actually makes when “that” is the only thing different? (The proper way to isolate and evaluate the effect)
Keep in mind, P/P doesn’t reduce the distortion that sounds bad, only the 2nd Harmonic produced by the driver.  

Tom
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Wayne Parham

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Re: Prosound Shootout 2007
« Reply #128 on: November 04, 2007, 10:37:01 pm »


Tom Danley wrote on Sun, 04 November 2007 19:18

Comparing different horns with different drivers tells you nothing about the value of push pull vs standard mounting.


I wouldn't say it tells me "nothing" but I would agree that it would be best to compare a horn made exactly the same as a 12Pi but without push-pull drive.  I will say that with all the horns we've measured, the 12Pi has consistently shown much lower distortion, especially at frequencies near horn cutoff and below.

Tom Danley wrote on Sun, 04 November 2007 19:18

As you might be aware, at the Michigan subwoofer shoot out, where the labs were measured, they had the lowest distortion of all the speakers there. (look up the curves on line).   That same driver linearity is how people have been able to use them in living rooms eq’d to extend the bottom.


Could you please provide a link to that data?  Was it done at power levels like what we did in Tulsa?  Was it done outdoors?  I hope so, because I'd like to see more measurement data on a LABhorn.  All I've seen was one chart that shows SPL at a very low drive level.  I keep thinking someone will bring a LABhorn to one of the Tulsa shootouts, but so far no one has yet.

I expect the distortion characteristics of a LABhorn to be similar to other basshorns, which is to say they will rise as frequency drops, and that at high power levels they'll be louder than the fundamental near cutoff and below.  For the LABhorn, what I'm calling "high power" would be about 40v, which is roughly 800 watts.  Even at just 20v, I'll bet LABhorn distortion at 30Hz is only about 10dB lower than the fundamental, which is 30% distortion.  I'm also sure distortion is actually higher than the fundamental at 20Hz.  I can find nothing to make me believe otherwise.

What do you expect from a LABhorn, with regard to distortion?  Do you have any measurements to quantify distortion performance at various power levels?

You mentioned EQ'ing the LABhorn to extend the bottom.  Are you still suggesting that this be done to use the LABhorn below 30Hz?  Do you think LABhorn distortion will be low at frequencies below 30Hz?  Or do you just think that people won't know the difference, that they can listen to the second and third harmonics and be happy?

Tom Danley wrote on Sun, 04 November 2007 19:18

Have you built and measured a 12 pi that wasn’t in push pull to see how much difference it actually makes when “that” is the only thing different?


I plan to do that in the next few months.  I'm actually making a new horn prototype, and in the process of doing so I'll be able to take parts of it to do the exact test you're talking about.  I can make the equivalent of a 12Pi without push-pull drive from it.

Care to place a wager with me on the results?  I'll bet it confirms once again how the 12Pi push-pull drive is what is responsible for its ultra-low distortion at low frequencies and high power levels.
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Wayne Parham
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Wayne Parham

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Re: Prosound Shootout 2007
« Reply #129 on: November 05, 2007, 03:57:03 am »


Tom Danley wrote on Sun, 04 November 2007 19:18

As you might be aware, at the Michigan subwoofer shoot out, where the labs were measured, they had the lowest distortion of all the speakers there. (look up the curves on line).   That same driver linearity is how people have been able to use them in living rooms eq’d to extend the bottom.



I did a quick search of the internet to find the distortion measurements from the Michigan shootout in 2003.  There are some differences between the Tulsa data and the Michigan data that make this less than an "apples to apples" comparison, but I think it is still good information.

The graph below is distortion of four LABhorns measured with "9-12 volts input".  I'm not sure why the voltage wasn't recorded more precisely than that, but in any case, that's less than 40 watts.

Since the LABhorn presents about 4Ω load impedance, 9 volts is 20 watts and 12 volts is 36 watts.  We're only talking about 10 to 20 watts per woofer being sent for the distortion measurements.  I wouldn't expect much distortion at these power levels, because they're so low.

Having four horns is an advantage too, since loading is better at low frequencies than what you would get having just one horn.  So again, this comparison heavily favors the LABhorn, with the very low drive voltage and the use of four horns instead of just one.

http://www.audioroundtable.com/misc/LABhorn_quad_10v_distortion.jpg


As you can see, even at just 10v, distortion at 25Hz is already at 10%, rising rapidly at frequency falls.  As one would expect from a basshorn, it is lowest in the passband, but rises rapidly at the cutoff frequency.   From 35Hz down, distortion ramps up heavily, already above 3% at 30Hz even at the low drive level of 10v.  By 20Hz, it is at 30% distortion, again, at only 10v input signal.    

These figures aren't unexpected.  If you double the drive signal, you'd see that distortion would be louder than the fundamental at 20Hz, probably also at 25Hz.  At 30Hz, distortion might be about equal to the fundamental, or maybe slightly less.  If you increase drive even more, nearing maximum power, distortion of the LABhorn would be even worse.  This is no slam of the LABhorn, all basshorns are like this.  They work best when used in their passbands, and as you get close to their lower cutoff frequency, distortion rises rapidly.  That's just the way it is.

Except for the 12Pi with its push-pull drive.  Look at the charts below.  The blue line is SPL and the violet line is distortion.  This is a single horn, run at 28.3v - three times the drive voltage as was used to test a group of four LABhorns.

http://www.prosoundshootout.com/Measurements/2007/12Pi28v.jpg


Notice that distortion doesn't rise at low frequencies like it does on other basshorns without push-pull drive.  This makes a cleaner, tighter sounding bass.  Everyone notices it right away.  The distortion is so low at this 28.3v drive level that we really can't see it - it's mostly below the noise floor.  

The distortion curve is shown in decibels, and to convert these values to percentages use the chart at the link below.  The noise floor was about 70dB, so anything below that is indeterminate.

Now the real nut cutter.  How does it perform at higher power levels?  See the link below:

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Wayne Parham
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