Careful with how you make it 8' smaller, you could be right on or very close to two dimensions sharing integer multiples. That means you will have some very large reinforcement modes at the frequencies where they overlap (or come close to overlapping) room mode wise, like I do where my room shares integer multiples (18' width and 9' ceiling).
You might find this helpful, since you can still make the room any dimensions you want (lucky you...):http://www.acoustics.salford.ac.uk/acoustics_info/room_sizing/?content=best
Chadnliz, pay attention to Jkalman's advice. If you shorten the 40' dimension by 8', you end up with 32', depending on exact wall placement. Then you would have dimensions of 32 and 24, all divisible by 2, 4, and 8. This would not be good for mode distribution. If this leaves you confused, suggest you search archives on AudiogoN and Audio Asylum. Lots of information is available on this subject.
Am going along with the others advise on this one.... Any way you can add on to the room for the tools ;-)
Taking 8' (or so) away from the 40' will not have a big effect (if any) in a room that large...It may help, more than hurt.
Large rooms don't suffer acoustical problems to the same degree that small rooms do, unless they are to large....thats another can of worms though.
I strongly beg to differ... My dimensions are ~33' x ~18' x ~9'. Big rooms definitely can have serious modal reinforcement issues. Chadnliz, I recommend you do some research about acoustics online at a forum such as this one:http://forum.studiotips.com/index.php
And this one:http://www.rivesaudio.com/resources/links/frame.html
And this one:http://www.tonmeister.ca/main/textbook/index.html
Dave's advice may be comforting, but it is incorrect information concerning a room of the size you are planning wall distances that share common integer multiples. Your room is not big enough to be immune from these modal issues, especially when taking those 8' off the longest side. With shared room modes you are going to have very large bumps in your room's frequency response in certain places at the low frequencies where there is overlap. Find out for yourself on those links, or find out after the fact if you ever measure your in-room response as I have.
Here is one last link. It is a room mode calculator:http://klipschcorner.com/Tools/ModeCalc.aspx
It will graph out your problem areas... Keep in mind though, it only does so to 200 Hz. For fun, plug in my room dimensions. You can see in my "System" where I have my low frequency room response graphs, that I have major reinforcement modes right where it predicts at 62.8 Hz. I don't have the higher modes at 125.6 because my room is irregular shaped in the back of the room and it is extremely well treated by an acoustical engineering company, so the smaller waves get broken up because of the shape change and bass traps.
Thanks for the input, I know I can read many threads on this and actually wish far more would read instead of asking the same basic questions over and over and over.
I just wanted to get a quick feel for opinions and thanks!
Will some of these issues be tamed by the Vandersteen 11 band EQ tuning feature?
Sure, you can read all you want....still, I said 8' "or so"...With 40' to work with, I don't see a problem that can't be worked out....thats more than comforting, it's a fact.
Also, with a room that large, you will have the advantage of optimum speaker and listener placement within the space...even better.
All rooms need some amount of room treatment...maybe a touch of EQ'ing as a final sound tweak. Every room is different.
All the reading is fine, everyone should read up...and then, disregard about 50% of what you just read...it does not apply. Experience is the better teacher.
Yeah exactly, "experience is the better teacher" such as my personal experience of general contracting my room and seeing first hand how the room modes effect my room from the before and finished states of the room. As well as locating with meters where the nulls and reinforcements are in my room so I can build Helmholtz resonators to try and lower the harder to treat mode reinforcements.
The problem can be worked out, if he picks good room ratio proportions. If he sticks with the ones he has or takes only 8' off instead of a little more or a little less, then he is going to have some major bass reinforcement modes at certain frequencies that the Mode Calcultor I "linked to" shows. It is so simple for him a this point to partition the room to the right size to get ratios that are good enough for a very even room response, but you are trying to curtly convince him otherwise. Take it from someone who has these issues in a room where he couldn't alter the dimensions, it is better to fix it before hand than to get everything set up and have to deal with it afterwards. EQing is not as good of a solution as making the dimensions right to beginning with, I know this because I have been considering EQing for my space and consequently was researching the options (the only analog ones that look worthwhile are professional studio gear because you can cut out nulls as well as reinforcements thus cutting down on "smearing," otherwise you have to digitize the signal and then correct it). Getting the dimensions right to begin with cuts down on having to use large amounts of treatments or even an EQ.
How about instead of giving comforting generalizations, you give some specifics. You claim you are giving "facts," yet you didn't state any "facts" and you didn't leave any links to proof that you are not full of it. Please do provide some proof. "Because I say so" doesn't qualify as expertise, especially since I can provide proof from respected and scientifically valid sources in the acoustic's field (those links say it all!), and so far your only argument has been "because I say so."
Look at the room mode calculator I put up, and plug in those room dimensions he is thinking of... They make those calculators because these problems really do exist in the real world, not because they don't. His dimension choices of 40 x 24 x 11 will have some serious mode reinforcement, as will his other choice of 32 x 24 x 11. If he alters it a little bit using the calculator, he will have one hell of a room, yet you are trying to convince him not to. Why is that? Do you not want him to have the best sounding room possible? What could possibly motivate you to try to deter him from improving his listening environment in a situation where he can do so, so easily because he is already possibly partitioning the room?
It will sound better than mine if he changes the dimensions properly and treats it well to boot. My room is very well designed by Rives Audio. I couldn't change my dimensions so I'm forced to deal with overlapping room modes that couldn't be treated because they were too low in frequency. He can deal with that problem before he even has it, so I'm hoping he can benefit from my "real world" experience with building and measuring my own room's interactions with ETF5, mics, and SPLs as well as all the time I have spent in the last year researching room acoustics in theory and as applied to my room by Rives Audio (with books like Master Handbook of Acoustics and the online material I posted plus others).
If he uses these dimensions (31 x 24 x 11 or 39 x 24 x 11) for the larger room he flattens his room response immensely. Just look on the room mode calculator and plug those dimensions in... If you don't think it will make a tremendous difference when all is said and done, you have never had to tackle these problems in your own room or measured your own acoustic listening environment (that or you got lucky and already have good dimensions to begin with - in which case, it would explain why you don't know any better...).
He will still have the option of optimal speaker placement no matter what room size he uses, since all room sizes have optimal positions for the speakers and listening position. If he changes the dimensions by 1' (either 1' less than 40' or 1' less than 32') he doesn't lose much space and he gains tremendously in terms of acoustics, eliminating the need for a lot of the band-aid efforts you suggest (he should still treat the first reflection points in the room no matter what he does, as well as add extra absorption/diffusion randomly to kill slap echo and other reflection issues in the room).
You will get bass response issues in a room no matter what you do, the key is to lower the amount and size. If you get large overlapping room mode reinforcements as well as nulls, the 5a sub may not be able to accomodate the full extent of the reinforcments or nulls. By limiting the amount of variances in the response before hand, you enhance your ability to deal with and flatten out the frequency response even better as a whole. I believe the 5a is 11 band? That gives you 11 nulls or reinforcements you can deal with. The flatter you get the room before hand, the flatter you can make it afterwards. This will also give you more leeway in terms of room placement as well.
The other issue to consider, what if you decide to switch to another speaker eventually, one that doesn't have built in sub EQ? You severly limit your options unless you want to spend even more money later on and add an independent EQ device.
If you are already doing the work, you might as well build for good dimensions, since you are already paying to have the work done. If you can afford to and don't mind, taking 1' off that wall, even if you don't plan on building that other room, basically makes your room response good to begin with and for all any future speaker options.
Thanks again, it is an existing space but I will see if my parents are going to bid on it...........thanks a bunch.
That room mode calculator will show you a graph of the "general" locations of where reinforcements will occur in the frequency response and how large they will be (relatively). You can always use that to see about any other room sizes you are considering in the future.
If you have no other choice, you can always do what I did... Have an acoustical engineering group like Rives Audio consult with you and design the room to at least limit the room response as much as possible. I would recommend that no matter what you end up doing. That way you can have your room designed with optimal sound treatment.
I've read his posts before...he is not a total newbee. His question was fairly general...so was my answer. I left the exact placement of the "new" rear wall for him. The other walls, and the ceiling are already fixed in place...yes?
If he does some of your reading, I'm sure he can come up with something, other than the wrong place to build the wall? (40' is a lot to work with)
BTW, I did build my audio room, with a little help from my son...and a few friends that were unlucky enough to stop by at the wrong time....great acoustics, if I do say so myself.
I've looked at your room (very nice!)....I can see why you have a few problems though, and they are not the rear wall....of course you knew that.
I have a group of modes overlapping in the 60s and clustering in the low 70s frequency-wise. I know this because I have tried a couple of different speakers in similar positions in the room. Building a bass trap for those frequencies would require a bass trap way too big to be convenient (or sane).
I'm sort of stuck EQing unless I decide to abandon the Home Theater part of the room and get more liberal with speaker placement. I've been looking at some of the analog pro equipment used by Steve Hoffman in his system as potential solutions I could use. I do need something that can both add gain and take gain away from certain frequencies. Luckily, the pro equipment tends to have options that fall right on my problem areas. Rain has some a nice looking options as well, though I might just spend $300 on a Behringer to play around with first (I do like some warmth in the bass region). Also, it would allow me to change things on the fly, for individual recordings.
He will have a very sweet room if he makes it 39' or 31' on that longest room dimension (39' would be best to maintain room volume). I'm jealous of those 11' ceilings... I had to build all the way up to the joists to get 9'. I had steel beams to deal with, and steal support pipes, and a large iron septic output from the house that I had to enclose in a soffit closet. I can't complain though, because my wife let me have the room to do whatever I want to it.
Here is one I'm heavily considering as well:http://www.rane.com/peq55.html
It is around $800 and gives a very nice spread, as well as balanced I/O. I could even double dip and get two of them so I can PEQ more areas, if I want to later on.
Yes, looking at your Freq charts...your problems do look fairly EQ friendly. Your screen is very large, I can see the placement issues you may have with the side walls.
Still, nothing "that" major to deal with IMO. Aren't we lucky to have a wife that lets us play like this!
Very lucky (I have a lot of friends who have no luck, none at all! Instead their wives have all the luck...).
I decided to buy the cheap Behringer Ultracurve Pro DEQ2496 just to pursue the idea of more expensive analog room correction in the future. The DEQ2496 is significantly cheap enough ($300 or so), considering all the options and features, to be a worthwhile experiment in my system. It also has an analog bypass so if the digitization sounds bad, adds some kind of digital hash noise, or hums, etc, I can just bypass it and only use it to get a sense of whether or not I will like the FR improvements. If everything goes well, I'll consider a permanent solution later on that is higher in quality (if this one has significant short comings) like one of the analog GMLs and retire the Behringer to my recording gear setup.
I can't do anything about nulls without an EQ, so aside from those the only really bad thing is that bass hump due to mode reinforcement. It is around +15 dB... Ouch!