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Author Topic: Prosound Shootout 2007  (Read 43532 times)

Jeff Permanian

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Re: Prosound Shootout 2007
« Reply #110 on: October 20, 2007, 05:18:29 pm »

What a disaster! We brought out some untested prototypes and they measured very poorly, decreasing 50hz and increasing 70hz.
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Leland Crooks

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Re: Prosound Shootout 2007
« Reply #111 on: October 20, 2007, 10:59:26 pm »

I'm breaking my rule about posting here to thank you for your assistance Jeff.  It seemed to be day of unexpected problems.  It was a pleasure to meet you.  I owe you a tube of liquid nails.  I'll catch you for it next year. It was still a good time.

Leland
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Wayne Parham

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Re: Prosound Shootout 2007
« Reply #112 on: October 21, 2007, 01:34:21 pm »


I didn't think Jeff's speakers measured poorly at all.  I've measured a lot of small basshorns, and I thought the Growlers did well.  Hoffman's Law tells us you have have extension, efficiency or size, but you can't have all three.  A small basshorn is usually either peaky or sacrifices extension, some sacrifice efficiency.  The thing is, Growlers are small enough to be easy to carry and you can group a bunch of them together to bring the efficiency up and smooth the response.  It's actually about half the size of a typical double 18" sub or a medium sized basshorn, probably a quarter the size of the biggest ones.  So you can get more Growlers in the same real estate.

Leland's horns measured pretty well too.  I think he is used to seeing smoothed response curves, which hide the bumps on basshorns and the "grass" on top boxes.  Leland's horns are Fitzmaurice designs, and they have a characteristic Fitzmaurice curve, sort of a pipe/horn.  When measured in groups, they smooth out.  That's how most people use horns anyway.

Leland had a leak in one of his subs, but fixed it before response was measured.  He actually discovered it when we did the impedance sweep.  This is one of the benefits of measuring impedance rather than depending on "advertised impedance" - It tells us things about what's going on inside the box and how our horns are operating.

I thought everyone was a winner this year.  I don't say this in a "kumbaya, let's all hold our hands and get along" way - I'm saying that each horn showed specific strengths and all they all sounded good.  The Growlers thumped pretty well for a small box, and were easy to carry by hand.  The Fitzmaurice horns were larger but did't weigh too much and were easy to roll on built-in castor wheels.  They had deeper extension, and would be able to make use of it when grouped.  The BassMaxx horn thumped real well, as you would expect, and would handle a lot of power.  I was very proud of my 12Pi too, as it did well.  It definitely hits the low notes.

We only measured singles, and that's a worst case situation.  It really shows the characteristics of each basshorn.  When used in groups, ripple smooths out and the bottom end response comes up to match the top.  Efficiency comes up too.

We need a full hour to do all the tests we do on LMS.  We measure impedance, then sweeps for SPL and distortion at 28.3v, 100w, 200w, 400w and 800w.  Some we do at 1600w as well.  That's about a dozen sweeps per box, so even if we can get setup and run each test in just a couple minutes, the hour goes quick.

To measure groups, we probably need two hours for each exhibitor.  That allows us another hour to move in additional boxes and do the sweeps for them.

Anyway, I've uploaded all the response charts and am now making links to each of them.  I'll write back when everything is up online.
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Wayne Parham
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Wayne Parham

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Re: Prosound Shootout 2007 - RESULTS
« Reply #113 on: October 21, 2007, 04:36:00 pm »


http://www.prosoundshootout.com/Prosound_Shootout_Banner.jpg



Measurement results from the 2007 Prosound Shootout are available now on AudioRoundtable.com and ProsoundShootout.com.





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Wayne Parham
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Wayne Parham

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Growler Prototype
« Reply #114 on: October 21, 2007, 09:50:34 pm »


Jeff Permanian wrote on Sat, 20 October 2007 16:18

What a disaster! We brought out some untested prototypes and they measured very poorly, decreasing 50hz and increasing 70hz.


I thought your Growlers did pretty well.  Glad you came out!  Good hanging out with you.

You said the new woofer had 21mm xmax, didn't you?  That's cool, I know you liked the extra excursion for operation under horn cutoff.  But I wonder if it might have been better to use a woofer with about half that xmax.  The long voice coil required to get the extra excursion spreads the flux over a wide area.  A shorter coil would concentrate it more and could bring the efficiency up.  Through the pass band, the limit would still be thermal even with half the xmax.  Just a thought.
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Wayne Parham
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Jeff Permanian

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Re: Prosound Shootout 2007
« Reply #115 on: October 22, 2007, 10:33:27 am »

Leland Crooks wrote on Sat, 20 October 2007 21:59

  It was a pleasure to meet you.  I owe you a tube of liquid nails.  

Leland


Great meeting you and everyone else.


p.s. The Growler was still +3/-3db 44-120hz.
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Wayne Parham

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Re: Prosound Shootout 2007
« Reply #116 on: October 23, 2007, 02:36:07 pm »


Jeff Permanian wrote on Mon, 22 October 2007 09:33

The Growler was still +3/-3db 44-120hz.


Yes it was.  We measured a couple other subs about the same size on previous years, namely Cerwin Vega L36 and Fitzmaurice T24.  I think each of these is about 8ft3.  Check 'em out for comparison:


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Wayne Parham
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DAVID_L_PERRY

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Re: Prosound Shootout 2007
« Reply #117 on: October 24, 2007, 03:41:09 am »

Can you point me in the direction of what equipment is required, and how to carry out a loudspeaker impedance sweep, and what to look out for....

I have a pair of Titan 48's and although I cant hear any leaks, (tested with a 25hz source) I am interested in a more accurate test method.

Many thanks, Dave Perry
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Iain_Macdonald

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Re: Prosound Shootout 2007
« Reply #118 on: October 24, 2007, 10:16:52 am »

David,

There are a number of different ways. I don't know what test gear you have. But this ProSoundWeb educational article is a good start.

 http://www.prosoundweb.com/install/sac/n26_4/zrta/zrta-1.sht ml

Iain.
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Wayne Parham

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Re: Prosound Shootout 2007
« Reply #119 on: October 24, 2007, 11:23:48 am »


Impedance is actually pretty simple to measure with a sine wave generator and an oscilloscope or good AC voltmeter.

If using a meter, be sure it is one that is accurate at frequencies other than 50/60Hz.  If you don't have a tone generator, you can download a sine wave generator that works with most sound cards.  Here are some examples:

Connect the speaker to the sound card through a fixed series resistor.  You'll probably want a value between 100Ω and 1kΩ, although other values can also be used.  You should know the value of the resistor very precisely.  The more accurately you know the value of the resistor, the more accurate you'll be able to calculate the value of your speaker's impedance.

Set the tone generator for a specific frequency and measure the voltage across the resistor.  Using Ohm's Law, calculate the current flowing through the resistor using the known values of resistance and voltage across the resistor:

I = E/R

Now measure the voltage across the voice coil.  Knowing the current through the circuit, you can calculate the impedance of the voice coil:

Z = E/I

You can make a plot of impedance values at various frequencies in the passband.  Just take your time and step through some frequencies, measuring voltage and calculating impedance for each one.

Note:  Do not depend on the voltage across the voice coil to be the difference between source voltage and the drop across the fixed series resistor.  It will only be that when the impedance of the voice coil is purely resistive, which only happens at a few frequencies at best.  Most times, the voltage across the voice coil and the voltage across the resistor are out of phase, and so cannot be added as a scalar.

Phased voltages are vector values, so adding them together as scalars doesn't make sense.  To demonstrate, let's say you have two 10v signals that are 180
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Wayne Parham
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