chances of having bad room acoustics?

[Scp53]

i have a ~13x ~15 with 8 ft ceiling but actually ~7 ft ceiling because we have panels(false ceiling). oh, and this room is in a basment with carpeted floors if that matters.

from my experience, the overall response is bad(for the bass). i can place my sub any where in the room and it NEVER sounds good while standing near the middle or in the middle of the room. the response can be ok in spots but the spl is crap(and this atlas 15 can put out serious spl). i mean in some spots the spl is so little that you can hear the woofer moving(normally sound pressure covers up mechanical sounds unless its bottoming,etc). and in others spots theres a ton of build up thats not real equal in response. the room has two openings and has only two "real" corners that are opposite each other. are some rooms unfixable? what can i do? thanks for any help.

scp53

[DrWho]

for starters I'd take your atlas outside and see what kind of SPL's you can get...this will give you your max in an "ideal" situation and should be a good reference point in your room. I recently just finished building my subwoofer (haven't made a thread yet cuz i don't have pics yet) and I get a max SPL of 105dB outside which is a lot quieter than I thought it'd be (bloody F-M curves). I brought it inside and yes there was room gain, but it wasn't as much as I was hoping it'd be. Anyways, my point is that I had a reference point where I found the limitations of the driver and I just have to accept that (for now).

After that, it's possible that some heavy duty bass trapping will help with your problem. One thing you might consider is to remove all the cieling panels and see how it effects your sound. Most cieling tiles that I've worked with are built to absorb midrange frequencies (like in offices and stuff to reduce the noise level...the hum of machines and stuff). It's pretty much standard that every drop cieling acts this way unless you purposely go with something else. The reason I mention this is that it's possible that this is sucking out the attack of the upper harmonics associated with the bass sounds, which ultimately can make the bass sound lacking, even if the low frequencies are there. Though I'm basically just spitting out crap to think about, there was once a situation where I installed a sound system at a workplace (multimedia conference room thing) and removing the cieling tiles totally improved the sound. Granted that was ugly and therefore unacceptable, we were able to change out the tiles and we were all good.

Anyways, your best bet is probably to go with some bass trapping, which could take up a lot of space in the corners. Basically, you want to absorb the bass where it's building up in the room...sounds like you're walking around and already noticing this. If you want a solution that takes up less space, then I would start looking into helmholtz radiators, keeping in mind that they are a narrow bandwidth solution which means you will need a few in order to maintain a broadband solution (unless of course you're going to bust out expensive equipment to know exactly what needs to be done; i don't think this would be an option). The nice thing about helmholtz radiators is that you can stick them in your drop cieling and I don't think they're that expensive to build either. I have no experience at all with them, so I'm simply just sharing what I've seen others reporting (both with measurements and just straight up listening). If you're interested, I can guide you to a forum that can help you out (it's a studio construction place, but it's all the same concept).

[Scp53]

thanks for the info DrWho.,

I think ill take it outside today. Chad(from ascendant audio) clocked 120db+ from 40hz and up at one meter on a cement pad in a field. He said at 20hz it was 110db at 1 meter. Those readings are max so they do have some thd. I would think i could hit 110db peaks in music clean at a meter in my yard. And as for build up, i walk from the middle or near the middle of the room to a corner and the spl goes up by ~10db. I definetly have some acoustic problems. Ill post back later after I have played the sub outside.

scp53

[Scp53]

Well i took it outside yesterday and was clocking 112db at 6ft in my yard on a country song(it had more to go- like 4-5db more of clean output). I played part of another and then i figured that neighbors would get mad soon(even though i told them about my "testing"). So im pretty sure i have a crappy room.

scp53

[formica]

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On 4/17/2005 12:44:16 AM DrWho wrote:

Most cieling tiles that I've worked with are built to absorb midrange frequencies

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You are rightmostly mid range. Given the extremity of the original problem... I don't think it'll make a significant difference with or without the tile... apart from getting rid of rattles.

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On 4/18/2005 1:55:43 PM Scp53 wrote:

Well i took it outside yesterday and was clocking 112db at 6ft in my yard on a country song ... So im pretty sure i have a crappy room.

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Your sub does seem to have some pretty good output.

You may have a large null and/or resonance in your room, but I find it odd (improbable) that it's in all locations at all the frequencies. I think you have some serious testing to do with test tones and mic. Music is too inconsistent.

As a starter... use the old trick of placing the sub in the listening position, play pink noise (sub only), and measure the SPL around the room. What did you find? Do you have a laptop to plug into your system and try out trueRTA?

Rob

[Scp53]

that 112 db reading was not peak. I could have pushed it harder but i have neighbors. When i say i have bad acoustics im saying the only strong output is in the corners. I did do the "old tick" but was using sine waves. Is pink noise better? and no, i dont have the ability to use true RTA. would bass traps be an option?

thanks, scp53

[formica]

Did you use a series of single tones or a sweep?

Given that sine waves will basically excite one frequency at the time (actually more complicated than that but... close enough for this discussion) it will only be checking what the response at that single tone will be in different spots in your room. It will vary greatly from frequency to frequency and position to position.

Pink noise will excite all the frequencies simultaneously... so it'll give you an idea of the position that has the loudest average response. It'll still produce nulls, but the peaks it produces will dominate the nulls.

Since this is an experimental stage... I'd put the sub there even if it's inconvenient to the room usage. If you want then verify that spot with sine wave test tones and plot the response it'll give an idea of you room effects (again more to it, but a good start)...

Rob

[Scp53]

I replied to this post the other day. for some friggin reason it didnt work so sorry for the late reply.

i used a series of single tones when i tested. I walked around all the diff tones and got an idea of what had the most output that was reasonably flat. so is pink noise better? and i did place the sub where i thought it sounded best(with tones, not music content and such) when the sub was in my listen spot in the room. That worked but its still crappy. The output there is about equal to that outdoors at the same distance roughly. And i have a few more questions- 1- will those sine waves "build" if played for very long(like 5+ sec)? i have heard from people that waves can build. question 2- will 112 db output outside sound better than 112 db inside(in a room with NO rattles)? It seemed that outside the output was much cleaner at the same db level. any comments Rob or others?

thanks, scp53

[formica]

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On 4/21/2005 6:22:30 PM Scp53 wrote:

I replied to this post the other day. for some friggin reason it didnt work so sorry for the late reply.

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Only critical for someone who lives by their PC...

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so is pink noise better?

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Yes it will give you an idea of the best average (overall) location.

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1- will those sine waves "build" if played for very long(like 5+ sec)?

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Reflections reach the mic in milliseconds rather than seconds.

I think you a referring to the accuracy of the frequency response curve when measuring pure test tones with a full frequency SPL meter? Well it isn't accurate, but it'll give you a bal park idea of what is going on. For details on room measurements, I'd recommend reading the series of dragonfyr's posts in Technical Questions.

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2- will 112 db output outside sound better than 112 db inside(in a room with NO rattles)?

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It will sound better (flatter) outside as it won't have the room effects playing havoc on the response. These will be in the ±12db range. It will normally sound louder inside.

Rob

[Scp53]

formica, do you think the BEST way to test out equipment is in a non-reflecting area(outside- 1/2 space)? Im thinking that in a few weeks I'll take my sub outside again and do a lot more testing. What do you think? only prob will be finding where to not disturb others.

thanks, scp53

[dragonfyr]

Take a look at:

http://web.archive.org/web/20010605052417/www.headphone.com/EditorialHeadroom/RoomTubes.asp

[DrWho]

Conducting a test outside allows you to eliminate the acoustical issues inside your room. Basically, doing a good test outside will show you the limitations of the speaker you built. It's possible that your bass problem could simply be a poorly performing subwoofer (which gets us back to your amp) I'm not implying that this is the problem, but if it won't perform well outside, then it's not going to sound good in your room.

So some things to test for:

-Max output versus frequency

-relative output from 90dB at 80Hz reference point

(or whatever reference point you choose)

-cabinet leaks and resonations at louder volumes

-port noise

-the tuning of the port (you'll be able to tell where the port is tuned because the cone excursion will be less there...using a test tone CD this might be difficult, but can give you a rough idea where the tuning is)

Just a reminder, conduct the tests with the phase set at 0 with no EQ. Then when you are done you should take the sub into your room and do the first two tests again. The difference between the two response curves will then show you the net effect from your room. Peaks can be tamed a bit with EQ (isn't there a built-in parametric on your sub?) and then nulls will have to be treated acoustically.

[Scp53]

thanks for the replies. DrWho, my amp is still the 250watt. and yes thats enough to drive it. outside, Chad clocked 120+ db at 40hz w/o taking thd into account. that was at 1 meter. at 20hz its 110db. all these numbers are from the EXACT same sub i have(he was using same driver, ports, cab, and amp-250watt). so with that i have reference as to what is should do inside my house. I think in the next month or so I'll be able to take it to a bigger room in the house and/or take it outside again.

Where should i get a sine wave cd(test tone cd)? i use my pc for that right now but if i take it outside or in a different room i need a cd. which ones the best and where should i get it from?

thanks,scp53

[DrWho]

You could always make your own. If you want, PM me your email and I can send you a cd-image file of a CD I use that has 1/6th octave tones from 12.5Hz to 20kHz.

Btw, I'm not doubting chad's claims and all that either. Your sub should totally be able to pound out the sound, but it never hurts to check your actual setup. There could be faulty wiring, a bad amp, something wrong with the driver, a bad outlet, etc etc...all problems I've had at some point in the past when at first I had no clue what was wrong. From all your other threads it sounds like something wierd is going on and I can't imagine your room's acoustics really having that large of an effect. Room modes don't happen at every single frequency.

For the record, have you tried playing with the large/small settings on your reciever as well as the phase dial on the sub? The other day I was tweaking in my subs after a recent change and for the life of me I couldn't get all the phases to line up. I set my mains to small and everything magically fell into place. Some more tweaking and I could set the mains back to large, but it was so akward hearing such a huge difference. I didn't have my meter with me, but it was over a 12dB difference for every frequency.

[Scp53]

yea, go ahead and email me the image. Ill go to a friends house who has broadband and burn it.

email- thejonjon@gmail.com