Determining Total Potential SPL for multiple Subs - Home Theater Forum and Systems - HomeTheaterShack.com

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post #1 of 11 Old 11-24-17, 09:58 AM Thread Starter
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Determining Total Potential SPL for multiple Subs

Iím trying to determine what the total potential (textbook) output would be at a given frequency for a few different Sealed Subs. They will be optimized with MSO, however I️m trying at this point to determine a total potential SPL

Hereís what I️ have:

All SPL values at 16hz and Max Burst Tested by DB

4 Sealed Subs - 109.8 total (97.8 each)
2 double 18 powered subs total: 111.7 (105.7 each)

What would be the total output realized?
I️ was thinking 115.7?

If you have the answer please share how to calculate the value.

Thx


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post #2 of 11 Old 11-24-17, 12:12 PM
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Re: Determining Total Potential SPL for multiple Subs

It's ~116.8 dB if the sources are coherent per Here.

The formula and a quick calculator is shown there. This requires a common measurement point (as at the LP) and the phase at that point to be identical for each source - very hard to achieve in a normal room situation.

It's ~113.9 dB if we are interested in uncorrelated SPL addition. There is a calculator there for that also.
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post #3 of 11 Old 11-24-17, 01:02 PM Thread Starter
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Re: Determining Total Potential SPL for multiple Subs

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jtalden wrote: View Post
It's ~116.8 dB if the sources are coherent per Here.



The formula and a quick calculator is shown there. This requires a common measurement point (as at the LP) and the phase at that point to be identical for each source - very hard to achieve in a normal room situation.



It's ~113.9 dB if we are interested in uncorrelated SPL addition. There is a calculator there for that also.


Thatís exactly what I️ was looking for. Thank you! Great read as well.

Deciding upon getting out of my multi diy Sealed enclosures (which Iíve been happy with) and investing in a robust low tune vented dual cab configuration, or investing in adding to my Sealed Cabs with similar but more powerful sealed units.

I️ will attempt to achieve phasing with a MiniDSP 2x8 and MSO, but not sure how successful that will be.

Thanks again!


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post #4 of 11 Old 11-26-17, 08:41 PM
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Re: Determining Total Potential SPL for multiple Subs

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SeismicHT wrote: View Post
I️ will attempt to achieve phasing with a MiniDSP 2x8 and MSO, but not sure how successful that will be.
If you use the 2x8. make sure to use a 48 kHz plugin. The reason is that the 96 kHz plugin has large inaccuracies for filters operating at very low frequencies due to the finite precision of the fixed-point biquad coefficients. See this review of the 4x10 for some informative graphs demonstrating the problem (a little more than half way down the page).
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post #5 of 11 Old 11-27-17, 10:20 PM Thread Starter
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Re: Determining Total Potential SPL for multiple Subs

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andyc56 wrote: View Post
If you use the 2x8. make sure to use a 48 kHz plugin. The reason is that the 96 kHz plugin has large inaccuracies for filters operating at very low frequencies due to the finite precision of the fixed-point biquad coefficients. See this review of the 4x10 for some informative graphs demonstrating the problem (a little more than half way down the page).


Very very interesting! The 2x8 isnít an ďHDĒ unit like the 4x10 with Upgraded technology. Iím going to read that link piece. Thank You!!


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post #6 of 11 Old 11-28-17, 03:49 PM
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Re: Determining Total Potential SPL for multiple Subs

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Very very interesting! The 2x8 isn’t an “HD” unit like the 4x10 with Upgraded technology. I’m going to read that link piece. Thank You!!
The "HD" designation of the 4x10 HD appears to be somewhat of a misnomer compared to the distinction between the 2x4 and 2x4 HD. The 2x4 has a 28/56-bit fixed-point DSP chip and a short maximum delay of 7.5 msec, while the 2x4 HD has a 32-bit floating-point DSP and a long maximum delay of 80 msec. The 4x10 "HD" has a 28/56-bit fixed-point DSP chip and a maximum delay of 15 msec with the 10x10 48 kHz plug-in. I'd expect the response errors with low-frequency filters of the 4x10 HD to be the same as the 2x8 (since they both use, or can use, the same plug-in). It appears that they just took the latest revision of the 4x10 and placed "HD" after its name for some unknown reason.
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Last edited by andyc56; 11-28-17 at 03:58 PM.
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post #7 of 11 Old 11-28-17, 05:33 PM Thread Starter
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Re: Determining Total Potential SPL for multiple Subs

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andyc56 wrote: View Post
The "HD" designation of the 4x10 HD appears to be somewhat of a misnomer compared to the distinction between the 2x4 and 2x4 HD. The 2x4 has a 28/56-bit fixed-point DSP chip and a short maximum delay of 7.5 msec, while the 2x4 HD has a 32-bit floating-point DSP and a long maximum delay of 80 msec. The 4x10 "HD" has a 28/56-bit fixed-point DSP chip and a maximum delay of 15 msec with the 10x10 48 kHz plug-in. I'd expect the response errors with low-frequency filters of the 4x10 HD to be the same as the 2x8 (since they both use, or can use, the same plug-in). It appears that they just took the latest revision of the 4x10 and placed "HD" after its name for some unknown reason.


Andy, Thank You! Are you the same MSO Andy? If so youíre timing is perfect! My 2x8 purchase was to integrate several Sealed Subs in the room. Most likely SI varieties. When I get it racked I will begin the process of tuning what 4 I currently have.

I have a question though, regarding Ported. If I had two similar HO subs tuned to 17Hz and then say another four, less powerful in 19Hz tuned boxes, will a 2x8 with its architecture and the MSO algorithms be able to properly use delay and phase and gains (and PEQ of course) to integrate and bring them together? Iíve been told the only way to do this is with Dirac Live because each freq needs delay of the sources not just an enclosure getting delay as a whole? In this case only an 88BM or With Dirac running would be able to handle this? MSO doesnít of course use Dirac... Thoughts there? Iíd like to possibly consider converting my drivers into ported cabs, but the cabs wonít be identical or tuned exactly the same (close within a couple Hz). If not Iíll just stay safe with multiple Sealed boxes.

Thanks


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post #8 of 11 Old 11-28-17, 09:49 PM
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Re: Determining Total Potential SPL for multiple Subs

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Andy, Thank You! Are you the same MSO Andy?
Yes, that's me.

Quote:
SeismicHT wrote: View Post
I have a question though, regarding Ported. If I had two similar HO subs tuned to 17Hz and then say another four, less powerful in 19Hz tuned boxes, will a 2x8 with its architecture and the MSO algorithms be able to properly use delay and phase and gains (and PEQ of course) to integrate and bring them together?
Yes, with the caveat that MSO does not explicitly take into account dynamic range issues. To really do a good job of integrating dissimilar subs, you need to know some information about the voice coil voltage levels at which the subs hit their excursion limits and choose the limits of the gain blocks appropriately in MSO. There's a page about dissimilar subs in the documentation. It's hard to give specific advice at times because there's an unlimited variety of sub configurations possible.

Quote:
SeismicHT wrote: View Post
Iíve been told the only way to do this is with Dirac Live because each freq needs delay of the sources not just an enclosure getting delay as a whole? In this case only an 88BM or With Dirac running would be able to handle this? MSO doesnít of course use Dirac... Thoughts there?
I'm not sure what you mean by this, or what Dirac might have to do with this. Mixing ported and sealed is hard to do well, but not insurmountable. Combining all ported subs with very similar box tuning frequencies as you're looking to do here is not a problem at all. The only concern is with dynamic range considerations due to the dissimilar subs. You want the maximum acoustic output to be limited by the more powerful subs, not the weaker ones. If the subs are all DIY and you have WinISD models for all of them, you can choose relative levels into the subs intelligently. Getting MSO to conform to what you want can be a brain teaser though, as it usually involves a bit of trial and error.

Quote:
SeismicHT wrote: View Post
Iíd like to possibly consider converting my drivers into ported cabs, but the cabs wonít be identical or tuned exactly the same (close within a couple Hz). If not Iíll just stay safe with multiple Sealed boxes.
The difference between 17 Hz and 19 Hz tuning is on the same order as the accuracy to which you can predict the box tuning frequency to begin with, so I wouldn't worry about that.

Last edited by andyc56; 11-29-17 at 08:00 AM.
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post #9 of 11 Old 11-30-17, 06:09 PM Thread Starter
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Re: Determining Total Potential SPL for multiple Subs

Andy Thanks much. I appreciate all that info. Iím planning two high output ported boxes and 4 much less powerful ported boxes nearfield firing into the back of the seats. I have a 2x8 that Iím going to use with your MSO to get these optimized.

As for dynamics, I read the piece on level structure. I should be able to determine voltages for excursion limits in these enclosures, however the entire process seems somewhat confusing to me on concept. Iím sure itís me. When that time comes Iíll need some assistance Iím sure.

As for the Dirac question, I asked as an ID manufacturer told me Dirac was only way to match various tuned ported subs. I didnít believe this to be true having an understanding of MSO.

Thanks Andy.



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post #10 of 11 Old 12-03-17, 11:00 PM
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Re: Determining Total Potential SPL for multiple Subs

Quote:
SeismicHT wrote: View Post
I should be able to determine voltages for excursion limits in these enclosures, however the entire process seems somewhat confusing to me on concept. Iím sure itís me. When that time comes Iíll need some assistance Iím sure.
It's not you. It's a complex problem. When you're ready, ask here, as I'm eliminating support in the main MSO thread.
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