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Old 31st December 2013, 02:59 PM   #81
DHAA is offline DHAA  United States
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O.K., it looks like you guys are sleeping in today. I will take a stab at the first question "If I was to explain acoustic impedance to my six year old grandson, what would I say?" The kids is actually very smart, so there may be hope.


"Now listen boy, there is something called electrical resistance, and something called acoustic resistance, and they are very different.

Electrical impedance is like a resistance or opposition to the voltage that is passing through the driver. Now that driver right there that says 8 ohms on the back, but is only actually an average of 8 ohms. If you picked two different frequencies and tested it, it would likely be vastly different measurements.

Now acoustic impedance is based on what is going on inside of the cabinet that driver is in. At certain frequencies, certain things will happen to cause more resistance or opposition, and that will effect the way the cabinet sounds and behaves. In a tapped horn, the sound has a long way to travel, so acoustic impedance is something you better pay attention to.

So boy, don't ask me any more questions right now, and how about you go outside and shovel some snow."


SO IS GRANDPA TELLING LIES AGAIN?

Last edited by DHAA; 31st December 2013 at 03:04 PM.
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Old 31st December 2013, 04:00 PM   #82
tb46 is offline tb46  United States
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Hi Y'all,

I know all of you know better, but just to keep things from getting confusing, Post #77: "...When it comes to the L34 distance, or the L45 distance (driver acoustic center to throat)..." That should read, driver acoustic center to mouth (not throat).

As to impedance measurements, I know I was, and I think littlemike and epa were also referring to the driver's electrical impedance when installed in the enclosure.

Vance Dickason's Loudspeaker Design Cookbook would be very helpful here, and should be on every speaker builders book shelf: Loudspeaker Design Cookbook 7th Edition Book | 500-035 I highly recommend it, he describes the methods used for measuring impedance, as well as measuring and calculating Thiel/Small parameters of your driver. Then there are various test and measurement systems: SPL Meters / Audio Analyzers in the Speaker Components Department at Parts Express | 337 (I'm lusting for the OmniMic Precision Measurement System, but, sofar have been to cheap. :-))

Brian Steele has a nice page/example on using impedance graphs in a tapped horn: The Subwoofer DIY Page v1.1 - Projects : Using Impedance Graphs

As to acoustic impedance for your 6 year old grandson, maybe the simple air resistance when moving paddles of different size (e.g.: 6"x6" and 18"x18"), and seeing how fast he can move them?

Regards,
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Old 31st December 2013, 05:42 PM   #83
GM is offline GM  United States
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Quote:
Originally Posted by DHAA View Post
So boy, don't ask me any more questions right now, and how about you go outside and shovel some snow."


SO IS GRANDPA TELLING LIES AGAIN?
Depends on the locale......... around here it's 'rake the leaves'.

GM
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Old 31st December 2013, 05:52 PM   #84
DHAA is offline DHAA  United States
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O.K. Oliver - It looks like I was telling lies, propagating ideas that have no basis in reality. Bad Grandpa.

The good news is that I believe I actually may have an early edition of The Loudspeaker Cookbook stashed away in the basement. I bought a bunch of books when I was younger and I think that was one that was too scientific for me at that point in my life. And since I have become interested in speaker design more recently, I never bothered to find it - I had assumed it had outdated info. I will try and dig that out tonight, it may be the source of information that will clear up my confusion in numerous areas. Thanks for the recommendation.

I actually have some speakers testing equipment already. I have never done much subwoofer testing though, I have used it manly for PA tops and home stereo speakers. I really like building crossovers and tweaking them to perfection, and that is what I have used it for up to this point.

Thanks for the Brian Steele article too. That is exactly what I need. Thanks for your help.

Last edited by DHAA; 31st December 2013 at 05:54 PM.
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Old 31st December 2013, 06:13 PM   #85
GM is offline GM  United States
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Quote:
Originally Posted by littlemike View Post
Impedance measurements are as valuable as (if not even moreso than) SPL.
+1

Dayton PA385S-8 TH simmed example:

GM
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File Type: gif Dayton PA385S-8 TH impedance example.gif (17.1 KB, 55 views)
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Old 31st December 2013, 08:12 PM   #86
DHAA is offline DHAA  United States
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Quote:
Originally Posted by GM View Post
+1

Dayton PA385S-8 TH simmed example:

GM

GM, I had already imported your HR file from post #45. When I check the Electrical Impedance, I get a very different graph than the one you just put up in post #85. Any idea what I could be doing wrong?
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Old 1st January 2014, 01:49 AM   #87
GM is offline GM  United States
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Sorry, it's a different alignment meant to 'prove' that the impedance sim trumps its SPL sim, but changed my mind in midstream only to find I had inadvertently posted what I'd started. I'm always in a hurry with little time for the forums or PMs anymore, so anything longer than a one-liner from me has usually been done in bits n' pieces over time.

Since it's up though, its a good one to reverse engineer.

GM
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Old 1st January 2014, 02:43 AM   #88
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Quote:
Originally Posted by tb46 View Post
Hi Y'all,

I know all of you know better, but just to keep things from getting confusing, Post #77: "...When it comes to the L34 distance, or the L45 distance (driver acoustic center to throat)..." That should read, driver acoustic center to mouth (not throat).

As to impedance measurements, I know I was, and I think littlemike and epa were also referring to the driver's electrical impedance when installed in the enclosure.

Vance Dickason's Loudspeaker Design Cookbook would be very helpful here, and should be on every speaker builders book shelf: Loudspeaker Design Cookbook 7th Edition Book | 500-035 I highly recommend it, he describes the methods used for measuring impedance, as well as measuring and calculating Thiel/Small parameters of your driver. Then there are various test and measurement systems: SPL Meters / Audio Analyzers in the Speaker Components Department at Parts Express | 337 (I'm lusting for the OmniMic Precision Measurement System, but, sofar have been to cheap. :-))

Brian Steele has a nice page/example on using impedance graphs in a tapped horn: The Subwoofer DIY Page v1.1 - Projects : Using Impedance Graphs

As to acoustic impedance for your 6 year old grandson, maybe the simple air resistance when moving paddles of different size (e.g.: 6"x6" and 18"x18"), and seeing how fast he can move them?

Regards,
Oopsies...

I even proof-read it, still missed that. Sorry if I caused any confusion, I meant "mouth".

And - I was referring to electrical impedance.
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Old 1st January 2014, 12:19 PM   #89
DHAA is offline DHAA  United States
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Quote:
Originally Posted by GM View Post
Since it's up though, its a good one to reverse engineer. GM
O.K GM, I will accept your challenge. Let's make sure we are on the same page though.

Is the chart you made in post #85 created from the HR export you attached to post #45, with some changes to it? If that is correct, I believe I have replicated the what you did to achieve that result. After playing with the different parameters, all I had to do was shorten L23 to 80cm, and the results appear very similar. But that had a drastic effect on the SPL chart. The results are posted below.
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File Type: png SPL.png (25.1 KB, 46 views)
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Old 1st January 2014, 01:36 PM   #90
GM is offline GM  United States
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Well, I did mine using a [T]horn design routine, so it's different in detail, but not the alignment concept. Since it looks way too under-damped, it would likely not be considered a viable alignment, yet the impedance plot indicates otherwise.

GM
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Last edited by GM; 1st January 2014 at 01:48 PM.
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