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TOPIC: Home Theater Equalization and Crossover with 8x8

Home Theater Equalization and Crossover with 8x8 6 years 5 months ago #13462

  • kwcouch
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This is a summary of home theater project using the Mini-DSP 8x8. I purchased this unit to replace two Behringer DCX 2496 units which were causing me several problems: (1) I needed 8 outputs and each Behringer only supports 6, thus I needed two boxes and (2) the 2496 units use PA level inputs and outputs which was limiting my ability to use the full range of the A/D and D/A processing. Not to mention the PEQ processing is very limited due to the available amount of processing power. I would be lucky to get 2 PEQ settings per channel if you use steep roll off filters (48dB).

First I will describe my system so you will understand what I am trying to accomplish. I have attached various pictures to show the system build. My front channels speakers are actually comprised of 8 different speakers:
Front Left and Right speakers are comprised of two speakers each. I have two PA 12” speakers with in wall cabinets (see photo) for each side that are crossed between 40Hz and 180 Hz. These provide a superior drum kick sound at very high SPL and also relieve the other front speakers from trying to reproduce the punch achieved used PA speakers. These are used in combination with two Gallo Acoustic Reference 3.1 speakers which have amazing sound and imaging. These are crossed from 180 Hz to >20kHz.

The center channel is comprised of 4 individual speakers. Three are JBL Professional Audio PA speakers. I have added an Air Motion Transformer (AMT) tweeter to the middle PA speaker as an experiment to improve the sound quality while still being able to handle good SPL levels. The AMT tweeter and PA speaker is crossed at 4k Hz.

Why PA speakers for the center channel? For home theater use, many home based tweeters cannot handle the dynamic response of movie content at high volume levels without distorting. Compression tweeters can blow your ears out before they distort. Thus, when a crash scene happens in a movie, the sound remains ultra-clear and provides a superior impact. The center channel is probably the most important channel in a home theater as it reproduces a high percentage of the sound content, especially voice. If you go to a concert or movie theater, the voice is being reproduced by a PA speaker, generally with a 12” or 15” driver. It seems strange that the 300Hz to 3k Hz sound is reproduced by a large driver, but these are PA drivers, not home speaker drivers. The voice reproduced by these speakers is a much fuller and forward sound than what a home speaker can deliver. In my opinion after many A/B tests between the PA and my Gallo Acoustic speakers, I think the PA speaker produces a better sounding voice range. I would qualify that this is only for Home Theater applications. For critical music listening, home theater speakers win every time. Why 3 PA speakers instead of one? I have to cover a large listening area (17 feet wide) at a distance of 12 feet from the screen. One of the drawbacks of using a 12” driver for higher frequencies is they are more “beamy” or they have a poor sound dispersion as compared to a 3” driver. Normally this is not a problem for PA speakers at a concert or band where the primary listening audience is more than 12 feet away. The problem is solved using 3 speakers which are already designed to be used in an array which gives very even sound levels across the entire listening area. The sound at the end seat is now just as good as the middle. The speakers are driven using an Outlaw 770 (200W /channel), except for the tweeter which is driven with an Emotiva XPA 100 (250W/channel).
For the very low end, I have 6 subwoofers: Two SVS tube subs, One 18” dual passive custom built sub using the TC sounds driver, Two 15” TC sound subs with in-wall cabinets, and a 15” earthquake sub. These are powered by either built-in plate amps (SVS and Earth Quake) or 4,000 Watt PA amps (Crest Audio CC4000). I can hit 140 dB at 20Hz. My subs are crossed from 15 Hz to 75 Hz.

So… now you may have a fair idea of the room calibration challenge. I need to make sure all the speakers are crossed properly, have the correct phase delay to time align them, level them to have the same SPL, and then EQ them to my room. Enter the 8x8 mini-DSP which does all of this and does it well. Well, except for the 2x4 Mini DSP I use to EQ my subs and adjust the output levels to drive my PA amps.
The process I used to do this was to position a microphone (Dayton Audio EMM-6) at my main listening position and calibrate each set of speakers individually. The only exception was for the two center channel speakers that are positioned to hit the end seats of the listening area. In these cases, I positioned the mic at each end seat. The general adjustments I made included:
-Adjust input gain levels to maximize A/D conversion for the three input channels (FL, Center, FR)
- Use crossover matrix to split the 3 input channels to the 8 channel output: 2xFL, 4xCC, 2xFR
- Adjust the gain, crossover, PEQ, and delay for each of the 8 channels. I still haven’t messed around with the threshold settings). This was done with one speaker set at a time. One of the keys was to make sure the PA 12” speakers were properly matched with my Gallo speakers in crossover, SPL, and delay. The resulting frequency response for each of the speakers is shown in the pics. I did the same thing for my subwoofers using the 2x4 mini and made sure to balance the levels with the overall system.
The final step was to do a final frequency sweep using all the speakers. I did just a bit of PEQ tweaking using the input PEQs to make final adjustments. The frequency response flatness is not perfect… which I could do. I issue is that if I over correct for one listening position, it tends to have larger offsetting effects for the other listening positions.
The result? The mini-DSP gave me all the controls I needed to balance this complex set up… all in one box using a great graphical interface. The sound is amazing. Better than the Behringer could ever get me (without doing the mods). I’m very happy as the 8x8 solved my A/D, D/A level optimization issue and provided plenty of PEQ adjustments for every channel without the limitations I had in the Behringer. Movie theaters can’t even come close to the surround experience I get with this system. (I also have Butt kickers in every seat, just in case the slam from the 6 subs and 4 12” PA speakers wasn’t enough )

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Last Edit: 6 years 5 months ago by kwcouch.
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Home Theater Equalization and Crossover with 8x8 6 years 5 months ago #13543

  • devteam
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Nice! Yet another very neat step by step application on how you used the 10x10 for your setup.

Thanks again for sharing!
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