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<blockquote data-quote="drew gandy" data-source="post: 42450" data-attributes="member: 880">Re: Virtual SMAART training: HPR122IBack when this thread really got going I decided that I wanted to borrow an HPR box at some point to measure.&nbsp; I was finally able to put my hands on one this past week. Unfortunately it was the 12&quot; model which is obviously a little different on account of the woofer size but also because the HPR122I uses a round waveguide horn thing as compared to the rectangular horn in the HPR152I that Phil started this thread with.&nbsp; Nevertheless, I took some measurements and have decided to share them.&nbsp; As these were done in [ghetto] ground plane fashion at a very close distance the coherence was pretty much &quot;at the top&quot; over the entire useful range of the box although in one measure I did find some drops in the coherence right at the big notch at the crossover point.&nbsp; First I started off almost on axis with the horn. [ATTACH]150140[/ATTACH] Then I went down to a lower angle that might better reflect where a listener would be when the speaker is on a stick.&nbsp; At around 15-20 degrees down I got a curve that I think started to resemble what Phil posted. [ATTACH]150141[/ATTACH] But, figuring that was unrealistically steep I moved up to around 5-10 degrees down from on axis.&nbsp;&nbsp; [ATTACH]150142[/ATTACH] &nbsp;Then, based on my curiosity about the polarity of the tweeter I swapped it and measured in the same position and angle.&nbsp; [ATTACH]150143[/ATTACH] &nbsp;To my amazement, the phase was remarkably flat.&nbsp; Here&#039;s a shot where I reversed the polarity of my reference so the phase is right up the middle around zero. [ATTACH]150144[/ATTACH] I&#039;m not certain if my test setup carries correct polarity or not but it is generally a little easier to see the phase when it doesn&#039;t wrap.&nbsp; One of the take aways that I was hoping Phil would comment on is that 2khz is really too high to crossover a 15&quot; cone.&nbsp; (And a 12&quot; or 10&quot; as well for that matter).&nbsp; There are a few reasons as to why but the one that stands out from these measurements is the significant lobing that occurs around crossover throughout the supposedly useable vertical range.&nbsp; Because there is a difference in the arrival times of the woofer and tweeter for each different angle that we might be listening at, there is a different combined response.&nbsp; If the crossover point were much lower we would typically see much smaller changes in response.&nbsp; The Meyer CQ boxes or the Geddes Summa are examples of designs with a much lower crossover point.&nbsp; So, why are these [much cheaper] QSC speakers designed such as they are?</blockquote>

[QUOTE="drew gandy, post: 42450, member: 880"] Re: Virtual SMAART training: HPR122I Back when this thread really got going I decided that I wanted to borrow an HPR box at some point to measure. I was finally able to put my hands on one this past week. Unfortunately it was the 12" model which is obviously a little different on account of the woofer size but also because the HPR122I uses a round waveguide horn thing as compared to the rectangular horn in the HPR152I that Phil started this thread with. Nevertheless, I took some measurements and have decided to share them. As these were done in [ghetto] ground plane fashion at a very close distance the coherence was pretty much "at the top" over the entire useful range of the box although in one measure I did find some drops in the coherence right at the big notch at the crossover point. First I started off almost on axis with the horn. [ATTACH=CONFIG]150140.vB5-legacyid=2728[/ATTACH] Then I went down to a lower angle that might better reflect where a listener would be when the speaker is on a stick. At around 15-20 degrees down I got a curve that I think started to resemble what Phil posted. [ATTACH=CONFIG]150141.vB5-legacyid=2729[/ATTACH] But, figuring that was unrealistically steep I moved up to around 5-10 degrees down from on axis. [ATTACH=CONFIG]150142.vB5-legacyid=2730[/ATTACH] Then, based on my curiosity about the polarity of the tweeter I swapped it and measured in the same position and angle. [ATTACH=CONFIG]150143.vB5-legacyid=2731[/ATTACH] To my amazement, the phase was remarkably flat. Here's a shot where I reversed the polarity of my reference so the phase is right up the middle around zero. [ATTACH=CONFIG]150144.vB5-legacyid=2732[/ATTACH] I'm not certain if my test setup carries correct polarity or not but it is generally a little easier to see the phase when it doesn't wrap. One of the take aways that I was hoping Phil would comment on is that 2khz is really too high to crossover a 15" cone. (And a 12" or 10" as well for that matter). There are a few reasons as to why but the one that stands out from these measurements is the significant lobing that occurs around crossover throughout the supposedly useable vertical range. Because there is a difference in the arrival times of the woofer and tweeter for each different angle that we might be listening at, there is a different combined response. If the crossover point were much lower we would typically see much smaller changes in response. The Meyer CQ boxes or the Geddes Summa are examples of designs with a much lower crossover point. So, why are these [much cheaper] QSC speakers designed such as they are? [/QUOTE]

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