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Multi-Way Conventional loudspeakers with crossovers

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Old 30th January 2018, 08:54 PM   #21
charlie2 is offline charlie2  England
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Quote:
Originally Posted by montana1 View Post
Hi To All,
I finally took the plunge and bought a measurement mic (Umik1) and after some setup headaches, I was finally able to capture my very first measurement. Everything is set up using Room EQ Wizard. My lack of understanding is where do I gate the IR given the attached screenshots. All the examples I have seen, there is a logical spot to gate the measurement around 4-5 ms. Any explanations will help in understanding what I'm looking at or what I should be looking for.

Best Regards,
Rich
I measure rightly or wrongly -12db frequency sweeps at upon check levels (REW)

If signal is distorted a pop up box tells you distortion detected pressing ok and then looking at frequency response graph can show a nice flat response

Click on to distortion and it is terrible
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Old 30th January 2018, 09:02 PM   #22
Sonce is offline Sonce  Macedonia
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R1 must be placed between L3 and S2. Values of the high-pass filter components may need further tweaking.
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Old 30th January 2018, 09:05 PM   #23
montana1 is offline montana1  United States
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Thanks Charlie,
I'm starting to gain somewhat of an understanding of taking measurements and working in REW. Draki, had some great pointers in setting up in REW that was very helpful. Still much to learn but its been a fun pursuit while laid off work for the winter. That all comes to an end in about 3 weeks so I better get busy and finish the projects I've started.

Best,
Rich
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Old 30th January 2018, 09:10 PM   #24
montana1 is offline montana1  United States
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Thanks Sonce,
I'm not sure I follow where to locate R1. What I was looking to achieve was an L-pad before the HP xover to pad the tweeter down some. Am I not going about that correctly?

Best,
Rich
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Old 31st January 2018, 02:55 AM   #25
jf4828 is offline jf4828
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Smoothing and gating are used for completely different purposes. If you want measurements without room effects you have to set your gate time so that the first reflection is not in the measurement. You can calculate this based on speed of sound and minimum path length. It is preferable for me to just look for the obvious reflection as the first large bump following the impulse response. I've designed quite a few speakers and always get better results the first time by measuring at about 6 feet when I can get the speaker far enough away from everything. You should be far enough away that all drivers have summed. 6 feet for most two ways is sufficient. So the accuracy of anything below 300hz or so is not usable using this method. I have tried splicing near field several times but the rigor required to get reliable phase data is hard to pull off. Instead I do a ground plane measurement just to see how 20hz to 300hz relates to the rest of the response. I do NOT splice the ground plane measurement but just look at it while designing crossover in simulation. Some people might have luck with spliced near field but it's not for me. I'm not alone in this...

All that said, there are valid reasons to measure room reflections and consider them in the design of loudspeakers. That is a complex topic that could likely spin off lots of debate

Smoothing is just what it sounds like. If memory serves, psychoacoustics studies say it's hard for humans to detect frequency response peaks and nulls that cover less than 1/3 octave. I usually try to hit my target response at 1/3 octave first and then optimize at 1/12 octave. Any finer smoothing isn't really telling you anything useful toward a goal of a well designed speaker.
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Old 31st January 2018, 03:36 AM   #26
jf4828 is offline jf4828
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Quote:
Originally Posted by montana1 View Post
^Here is the beginning of xover design from measurements above. I used PCD7 to find correct offsets then imported summed response into Xsim and adjusted delay until lines overlayed perfect (1.71 in.). Hope I'm going about this the proper way. I welcome any comments that will help me learn at little more about measurements and xover design.

Best,
Rich
I take measurements with a mic height half way between the tweeter and woofer acoustic centers so that path length is equivalent. In this way you don't need to worry about offset. You can't always do this bit for 2 ways with a single woofer it is easier. This may go without saying but, you should never move the speaker or mic between the tweeter and woofer measurements.
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Old 31st January 2018, 03:42 AM   #27
jf4828 is offline jf4828
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One last point, take a look at the response plots on Troels Gravesen's site. You will notice most of his speakers have a slight downward slope. Flat frequency response or a rising high frequency response is not the goal for me. While Harman group studies by Floyd Toole say users prefer flat response, I can't say crowds favorite speakers at audio shows have linear frequency response....
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Old 31st January 2018, 03:53 AM   #28
montana1 is offline montana1  United States
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Thanks jf4828,
I appreciate your detailed explanation on taking measurements. There has been some great information shared on this thread. I'll take a closer look at Troel's response plots.

Best Regards,
Rich
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Old 31st January 2018, 03:59 AM   #29
AllenB is offline AllenB  Australia
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Quote:
Originally Posted by montana1 View Post
Got some measurements to critique.
Post #19 first impulse. Just after and starting just before 2.5ms there appears to be a blip. I assume your speakers are not 2m wide, maybe it is something to try taking out.
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Old 31st January 2018, 05:28 AM   #30
Sonce is offline Sonce  Macedonia
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Quote:
Originally Posted by montana1 View Post
I'm not sure I follow where to locate R1. What I was looking to achieve was an L-pad before the HP xover to pad the tweeter down some.
R1 should be parallel to the tweeter, after the HP filter. Or, complete L-pad (R3 and R1) should be between the HP filter and the tweeter.
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