Can I place subs in all these locations without issues? - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 14 Old 02-11-2017, 01:20 PM - Thread Starter
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Can I place subs in all these locations without issues?

I don't really understand how to read a room mode readout from a calculator in totality but have followed along with all the best practices as far as sub placement options- 4 corners, 1/4 wall points, 4 mid wall points etc...

But my question is would it be bad or good to actually place subs in ALL of the above locations in one room? My plan is to line the perimeter of the walls with subs and since I want to keep the cabinets 12" deep they will need to be long so in all actuality the subs would end up being placed closer to each of these points. Obviously I could make sure they are all exactly in the specified location or try to squeeze an extra cabinet in on some walls. Either way is doable- every corner, every 1/4 point, every mid point or just squeeze as many as possible around the perimeter. Controlling each set of symmetric subs won't be an issue as the Altitude32 can handle each pair as its own sub.

These would be sealed 18s and larger drivers for LFE and as far down into the ULF zone as possible. I'm choosing my equipment chain carefully for my HT2.0 upgrade and low frequency rolloff is a major determining factor for the equipment. My PrePro is down .5 from D.C.-20khz so that's a start.

If the perimeter sub design works and ends up giving me great output down to 3-4hz then that will be great but if not I could do overhead IB manifolds for the super ULF no problem. I'm just wondering how the system will perform laid out like this? I honestly want overhead subs too but just figure if go that far might as well let them be IB if the cabinets are already in the attic.

Anyone know if having subs laid out like this will cause issues that will be worth going in a different direction? I could always try to manage a way to stack subs in multiple locations but the acoustical plan pretty much takes up all the wall space above where the cabinets would be laid on the floor in most places.

I can't do a SBA or DBA because of all the space being taken up by the screen channel speakers.

Any thought?

Thanks all!
Alex
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post #2 of 14 Old 02-11-2017, 01:32 PM - Thread Starter
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My plan as of now is to use my FTW and MAL 21s on the screen wall and rear wall since there won't be the 12" depth constraint on those two walls. Then for the rest of the room perimeter I'm wanting to use the most reliable, high excursion drivers that will work with the 12" deep cabinet design.

Mark has a new slim cabinet in the works so that is right at the top of my list if we can work around rack mounted amps. If that option doesn't work out then there are some Dayton options that could work; although, I'd rather have drivers a tad more brutal. Some Fosgate 19s have crossed my mind in a half MAUL cabinet for the screen 1/4 points but thinking mixing those two vented/loaded cabs with all the other sealed cabs could just cause Walter more issues than they are truly worth during tuning or I could use them for the low end on my 5 way active LCRs way when listening to music I could totally run an insane house curve which would be fun. But that too would just make total system tuning more difficult just for headroom basically.

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post #3 of 14 Old 02-12-2017, 03:44 PM - Thread Starter
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Anyone?

What I'm curious about I guess is cancelations from the speakers being placed in the same locations on the opposing walls kinda like in a DBA configuration even though none of the walls would be creating a wave like that. If placing the cabinets offset on each wall like most designers spec fill-in subs would be better I could do that as well but wouldn't be able to place cabs in all four corners if offset.

Basically two good options in my mind with possibility of IB in ceiling with either of them.

1. In all the locations stated above. Corners, 1/4, mid points

2. Offset like a checker board as many as possible around perimeter


The rear and front wall may use more than just the cabs located on the floor. Stacking in a few places is doable so might incorporate that once the drawings are complete but am stuck on arranging the subs right now because I don't understand if the physics would help/hurt in my planned designs.
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post #4 of 14 Old 02-12-2017, 04:07 PM
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Not trying to throw a wrench in your plan I am just going by my own experience nothing more. When I first finished with building my first sub ( Marty Cube ) I had the perfect spot picked out and once I got everything arranged so it looked good and I turned it on it sounded pretty bad. Sometimes people get lucky but more often then not what you think is the best spot for a sub might be the worst. The best way to figure out where to put the sub or subs is to buy a mic. from minidsp or Parts Express ( approx 100 with shipping ) down load REW from Home Theater Shack turn on the RTA function make sure you have long enough cable and push the sub around the room and look for the best response should be fairly flat. Yes its a pain but once its done you do not have to worry about moving the subs around again. Me being hard head took several failed attempts of doing it my way before I decided to get the mic and do it right.

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post #5 of 14 Old 02-12-2017, 04:56 PM - Thread Starter
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Quote:
Originally Posted by Cichlid109 View Post
Not trying to throw a wrench in your plan I am just going by my own experience nothing more. When I first finished with building my first sub ( Marty Cube ) I had the perfect spot picked out and once I got everything arranged so it looked good and I turned it on it sounded pretty bad. Sometimes people get lucky but more often then not what you think is the best spot for a sub might be the worst. The best way to figure out where to put the sub or subs is to buy a mic. from minidsp or Parts Express ( approx 100 with shipping ) down load REW from Home Theater Shack turn on the RTA function make sure you have long enough cable and push the sub around the room and look for the best response should be fairly flat. Yes its a pain but once its done you do not have to worry about moving the subs around again. Me being hard head took several failed attempts of doing it my way before I decided to get the mic and do it right.
Yea I have a mic and understand how to find the optimal position for a single or few subs but what I'm concerned about is their interaction with one another once placed equally on all sides. It may be a non issue and be totally fine but wanted to get some input before moving forward.
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post #6 of 14 Old 02-12-2017, 05:34 PM
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Hard for people to tell you if it will work as planned. Put up some room pic's. This will be very helpful.
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post #7 of 14 Old 02-12-2017, 05:51 PM - Thread Starter
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Originally Posted by derrickdj1 View Post
Hard for people to tell you if it will work as planned. Put up some room pic's. This will be very helpful.
Standard rectangle room with one door no windows. 18'x30' from baffle to rear wall. 18'x35' total room excluding baffle wall.



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post #8 of 14 Old 02-17-2017, 08:47 AM - Thread Starter
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Nobody has ever thought about this or seen it done?

I can obviously take measurements of the locations but there's no way to take measurements of the final design until they are all in place so just trying to get some nods or shaking of heads. I wouldn't think there would be enough cancelations to merit anything note worthy especially since there will be seating and full room treatments covering the walls above all the cabinets along with modex plates in the corners and traps at ceiling/wall intersections.

Guess I can just draw it all out and sent it to an engineer and pay for their thoughts as well. I want Shawn and Walter both to look at it anyway when get some consulting from them.
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post #9 of 14 Old 02-17-2017, 09:07 AM
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From looking at the room 4 large subs in the corners. Two NF behind the second row. A couple under the riser if possible. I can't see a need for subs lining the side walls. More cost effective would be an IB or tactile transducer. No real need to try and get to 3 or 4 Hz IMHO. There is plenty of shaking in the 10-20 Hz range.
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post #10 of 14 Old 02-17-2017, 09:24 AM - Thread Starter
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Quote:
Originally Posted by derrickdj1 View Post
From looking at the room 4 large subs in the corners. Two NF behind the second row. A couple under the riser if possible. I can't see a need for subs lining the side walls. More cost effective would be an IB or tactile transducer. No real need to try and get to 3 or 4 Hz IMHO. There is plenty of shaking in the 10-20 Hz range.
This is a three row theater so no can do behind second row.

Riser can't be used as a cabinet.

I'm already down to that range but am tearing the theater apart for HT2.0 with the subs spread out. That is the reason for side wall filler subs. I have pro room layouts that call for subs in these places but not in all of them at the same time- e.g. A filler sub on left wall at rear 1/4 point plus a filler sub at front right 1/4 point and rear wall center point. I'm wanting to use them all at the same time though. The space is being taken up regardless if a sub is placed there or not and the amount of subs will be similar regardless of which way I go.

Reaching 145db+ 20hz-120hz is hard to do which I am pretty much at right now but when I split the subs up from the front wall I will need to add a bunch more in order to keep that output plus extend the FR lower into the ULF range. All my gear that rolls off at 7hz is going out the window so this will be possible. And if an IB ends up being necessary after adding all the other subs then that will be easy to do directly above all the seats. The side perimeter subs should fill the FR across all seats equally which is the goal. Right now I'm filling the two middle seats equally across the three rows. The room will be 18' wide minus 1' on each side wall for cabs/treatments leaving 16' wide for seating which I'm only going with 3 wide so every seat gets the most from the Altitude32 40ch capable setup.

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post #11 of 14 Old 02-17-2017, 07:15 PM
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Once you get beyond four subs around the room the FR will not change much, extension may get better. You do know anything over 115 plus redirected bass of 122-128 db., you will be clipping in the digital domain for movies. Getting more spl is fine for short demo's but, it will be distortion for the most part. I would do the IB first and that will tell you how many additional subs may be needed.

I have 8 large subs and anything else is overkill. You may be over doing this since you should not watch movies at those extreme spl.
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post #12 of 14 Old 02-18-2017, 07:10 AM - Thread Starter
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@derrickdj1 Why is anything over 128db clipped in the digital domain? I run songs and demos all the time well into the 140s but have never noticed any distortion or other funky stuff. I set my signal chain up optimally and it still allows me to play that loud.


And why wouldn't the signal just go past the (theoretical) 0dbFS like normal with a WAV file since I have changed it in my optimization? I have just never heard clipping and I play at levels well above 128db just like many others here do. Heck most of us run a 20db house curve and still crank it well past MV reference (125db on subs). I just don't get it as long as the system's gain structure is setup to max out the amps? That is how I set it up and never an issue.

I just find that statement incorrect especially when mixing pro and home audio gear.

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post #13 of 14 Old 02-19-2017, 11:44 PM
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Quote:
Originally Posted by audiovideoholic View Post
@derrickdj1 Why is anything over 128db clipped in the digital domain? I run songs and demos all the time well into the 140s but have never noticed any distortion or other funky stuff. I set my signal chain up optimally and it still allows me to play that loud.


And why wouldn't the signal just go past the (theoretical) 0dbFS like normal with a WAV file since I have changed it in my optimization? I have just never heard clipping and I play at levels well above 128db just like many others here do. Heck most of us run a 20db house curve and still crank it well past MV reference (125db on subs). I just don't get it as long as the system's gain structure is setup to max out the amps? That is how I set it up and never an issue.

I just find that statement incorrect especially when mixing pro and home audio gear.
I'm not the best person to fully explain this but, I will give it a try. Our avr's will produce a maximum signal a 0 db. Any thing less for the digital signal is a -4 or -6 db for example. In other word the gain control is telling how close to reference we are producing the signal. In theory we can't exceed 0 db. unless something happen.

Boosting above reference the signal has to undergo alteration. In hard clipping the signal is squared of and any info that is not clipped is just lost. Soft clipping, re-quantization can occur to fill in the missing signal. This were avr's may differ in their processing ability This should sound OK. Beyond the soft clipping several things start to happen, the amp produces excessive current and power, VC damage, XO damage or amp damage can occur or, there will be an increase in harmonic distortion.

This is one of the reasons some of the guys have mega systems and so many subwoofer. In essence, they are compensating for each of the above problems to run their system safely. In short, you can't produce what is not there and movies are based off a reference standard digital signal. Quantiztion of the signal is different from reproducing the pure signal. A signal meant to produce 70 db at reference is clipped beyond 70 db but, it not as likely to cause problems.

Because the signal is digital, this can be thought of as an independent variable other than just the spl. This was the way I interpreted things from my readings. Maybe someone else will chime it with some more info on the topic.

All clipping is not bad and can allow us to push our systems beyond reference. This does not mean care should not be take and equipment damage is possible. WAV files that undergo quantization cab exceed 0 db and not be overtly distorted. This is not the same with movies and I don't know if there is a rock solid number to hang your hat on.
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Last edited by derrickdj1; 02-19-2017 at 11:51 PM.
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post #14 of 14 Old 02-20-2017, 05:53 AM
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You are confusing digital signal level and a notion of movie reference with the analogue waveform that ends up moving a driver. 0dBFS could come out as any voltage (and hence SPL) in the end, the actual value just depends on how you setup your system.
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