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Discussion Starter · #1 ·
It seems that Max SPL is calculated using 8 ohms and not the actual resistance of the driver. As a result, the power limited SPL is too high. The problem is worse the lower the actual resistance of the driver.


Example:


On the main data page, I enter 500 watts and 2.8 ohms. The voltage is 37.42. Press calculate and the SPL shows about 122 db for the horn I have in front of me. Then go to Tools > Max SPL, and enter 500 watts and 15 mm. Press OK and Max SPL is showing power limited at 127 db at the same frequency.


Then go back to main data entry page and enter 500 watts into 8 ohms and get 63.25 volts. Press calculate and the SPL shows 127 db.


If others confirm this bug, I'll drop a note to McBean.
 

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Good to know. I'm feeling a tad lazy after a day in the workshop, so I'll take your word for it! What I tend to do is use max SPL for a quick idea, but then enter in the actual power I have in mind, then check excursion.
 

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Discussion Starter · #3 ·
that is what i do as well and how i came to notice the bug.


i'm just looking for a second confirmation before i bug mcbean just to be sure that i haven't missed something.
 

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I'd just ask him anyway, he's a really nice guy and very proactive in keping the software developed. It may be a bug or something you're overlooking and will probably take him no time to explain if it's the latter, and something he will want to correct if it's the former.


If you're not a member at diyaudio, I'll post a link to this thread if you like.
 

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Take a look at your cabinet's impedance plot.


It is my understanding that the Max SPL tool does not look at a real-world amplifier, but rather pours voltage into the load until either the driver's thermal limits or excursion limits are reached.


The "power" numbers quoted are calculated with the impedance of the load taken into account, so you can get some strange behavior at impedance peaks.


Mine seems to be working as I expect it to, but I don't use Max SPL all that often.
 

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Quote:
Originally Posted by lilmike /forum/post/20902036



It is my understanding that the Max SPL tool does not look at a real-world amplifier, but rather pours voltage into the load until either the driver's thermal limits or excursion limits are reached.

It doesn't consider the thermal limits either, it only gives displacement limited power, totally different than WinISD Pro, for example, which does consider both xmax and Pe. It could consider Pe if Pe was one of the input parameters, but it isn't.
 

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Discussion Starter · #7 ·
"If you're not a member at diyaudio, I'll post a link to this thread if you like."


alpha niner, i don't really spend any time over there. is that where mcbean would be contacted/reply? if you could make a post, that would be appreciated.
 

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This isn't a bug. Hornresp uses the impedance curve to determine the maximum voltage the driver can take at a given frequency, so the voltage is not constant.

When you put it in the voltage, it stays constant.
 
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