Axiom Home Page Forums General Discussion Advice from Axiom Owners Raised Floor question

My HT system is located in my basement. As some of you know from my previous posts, I have issues with lack of Bass in this room, among other things, but lack of Bass is huge.

Yesterday I had an audio "guy" come in, call him an engineer, consultant whatever, to take a bunch of sound measurements. He has built a few recording studios and owns one. He also has recorded / produced some CDs.

Point being, he should know what he is talking about and I get the sense that he does. We took several measurements (real time analyzer)and I was very happy to have the gear confirmed exactly what my ears were telling me.. Huge dip in the 65hz to 90hz range, peaks that have directly matching oposing nulls (in different octaves I think ?) , and a quick roll out of high frequencies, starts at 2K and dies at about 3.5k.

So, his first recommendation is to construct a raised floor with 2x4 on their ends 16in centers, insulate the cavity, put neoprene on the contact surface, glue some plywood and finish with a hard surface ie: hard wood or laminate. Also built a wall to enclose that section of the basement to create a smaller but rectangular room of 12' wide by 17' deep. I would like to have 2 sliding doors so that I can open it up to the rest of the room when required. Once we have the raised floor and wall done, then we would re-measure and address treatment options.

Just wondering if any of you have built raised floors in your concrete basements and if there was a significant improvement in the bass response ? Any "gotchas" or construction advice etc.. would also be greatly appreciated.

Have you put up bass traps in all your corners? This would MUCH cheaper and easier to accomplish and will clean up your bass response quite a bit.

-Robb.

I agree with Hutz, you would be much better off treating your corners with Bass Traps first, followed by a few first reflection panels. You don't have to do the superchunks like I did, you can just straddle the corners with panels (at least 4" thick). Treat the 4 corners first, then if you want, some people also treat the corners where floors and ceilings meet the walls.

Also, I assume you have carpeting on your floor? This makes a world of difference if you add padding/carpeting. If not, you need to at least have some throw rugs down at the first reflection points.

Also, the best position in the room with the least nulls is one that is 38% from the front wall of the total room length. Second best is 38% from the back wall. 50% is the worst, or if your right up against the back wall.

Anyway, it would be much cheaper to just build some panels. I don't see how making the adjustments that tech gave you will help with peaks/nulls.

Now, I did build a riser stage for my speakers to sit on and filled that with thick insulation. Many people don't realize that in some instances, the low bass from the speakers can actually travel through the floor and arrive at the listening position faster than the direct sound.

Yes I have already built and installed Superchunk bass traps in 2 of the corners. Built with Roxul safe and sound triangles from the floor all the way up to the ceiling. Then covered with some black acoustically transparent material.

The impact on the sound was very minimal for me. It slightly improved on the echo in the room, it thighened things up a bit, but it did not improve my lack of bass energy.

I also have my listening position 38% from the back wall, I tried the from the front wall but I was way to close to the speakers, or the speakers were to close to each other so that did not work.

So, I am sitting in the proper spot, I have 2 large superchunk bass traps, and I still have the same issue I always had.. no bass in the 60ish to 90ish range.

I have carpet on the concrete floor, which seemed to be absorbing a lot of my high end, according to the graph anyways. The highs sound ok to me, but they roll off quite early on the real time analysis.

The way I understand it, the concrete floor is the main culprit in sucking out the bass energy and therefore create that huge dip. The raised floor provides decoupling and mass to the floor surface, increasing the bass energy. That's the theory anyways.

I listened to and incorporated a lot of your excellent sugestions and leveraged your experiences, but I was still not getting the results that I am after. I felt that I had tried everything I could and it was time to bring in a pro to get to the bottom of it (pun intended) once and for all.

The cost factor is not really an issue, within reason of course, but I'm not looking to save money, I'm looking to fix the problem so that I can finally enjoy the full capabilities of my equipment.

Steph

Also, room size and sub placement have a lot to do with your issue as well. I found out by just moving my sub a few inches in various directions, dramatically changed my graph using Room EQ Wizzard. Also, the various trim settings like flat, half, etc. change things if you have a smaller room.

Just having 2 superchunk bass traps is not going to resolve the entire room. If you have a thick pad/carpeting that should be sufficient. Bass collects in ALL corners of the room, including floor/wall and ceiling/wall locations.

Treating the 4 corners should be a big help. I used owens corning 703, can't comment on your product. If it was me I would work on your sub placement around the room.

As SirQ mentioned, I would suggest the "sub crawl" technique, place your sub in your primary seating position (move your couch and put the sub there), play some bass heavy music or movie, and crawl along the walls to see where the cleanest and loudest response is, that is where you want to put your sub.

-Robb.

You might want to post a question on Ethan Winers forum on musicplayer dot com, they are the experts.

I have also done the sub crawl a while back and the best position for the sub in my room is halfway up the side wall. That is where the bass response is best.

The issue is not related to my sub but the bass of my mains. When I have my sub engaged, and calibrated at 80db with the rest of the system, the overall bass response is "acceptable". Movies are not an issue, plenty of LFE and Bass to go around in movies. But.. and here is the really crux of the matter, when I disengage my sub, my mains sound incredibly anemic and not just because the sub is no longer playing. There is a bass robbing force at work in that room. The sub powers through it because is has the power to do that. About 2 months ago, I decided that my mains were not up to the task so I started the search to replace them. I have Energy Veritas 2.3s which are comparable to the M80s in terms of size/drivers etc.. sound characteristics is another thing and they probably sound different than the M80s, but for intents and purpose, they are decent floorstanding speakers. A fellow Axiom forum member, Kyle, sugested that I move the speakers in another room and see if they still had a lack of bass. I moved them upstairs in the living room, connected my multimedia player to my 2 channel amplifer and played bass heavy content. I was totally blown away by how much bass these speakers were pumping out. Huge amount of clean and tight bottom end.. brought them back to the basement, bass is gone. So, my experimentation has shown that the speakers are fine, the room is not.

Thanks Randy for the sugestions, I will do that and share what they tell me with you guys.

I would then experiment with the placement of your mains from the back wall, side wall, toeing them in, etc... The drivers should not be the same distance from the side walls that they are from the front wall, for example. Also, the more you pull them out from the front wall, the better bass resonse you will get.

Are you running them as "small" or "large"? I received better results with my sub if it was "in line" with my main drivers and in phase. Sorry for the simple questions, I just find it hard to believe you have to reconstruct your floor, and I don't think that will resolve your problem.

Do you have a picture or drawing of the setup?

I have tried several positions of the mains in relations to the side wall and back wall. Currently they are 2 feet from the side walls, and about 2 feet from the back wall, and are 7 feet apart. I found that the minimum for good imaging and stereo seperation is 6.5 and the max is about 7.5, after that I lose the cohesiveness of the image. Now, I did catch in your post that the same distance from side and back is not a good thing.. I remember reading that, it re-enforces something or other ? anyways, I'll experiment some more with moving them away from the back wall. I don't have much more play in the side walls, but the back wall I can go right into the middle of the room if need be.

It's been many months of tweaking, moving things around, trying every crossover option I have, putting up traps, trying blankets on the wall at different locations like back of room, front of room, frz, floor etc..etc..I have done a LOT of experimentation but alas..hence my call to the pro, but before I head down that path I'm going to want assurances that it "will" fix the problem and not create more !!! my room size will diminish by almost half with the wall..so that may introduce more modes as they are typically more apparent in smaller spaces..I don't know..I did not get "all the answers" from my consultation session that I was hoping to get.

The reason I paid $200 bucks to have that guy in was to stop taking shots in the dark and get someone on site to evaluate the situation first hand. I was expecting more I guess, maybe my expectations were unrealistic.

Randy,

Can you tell me how you measured your room using RoomEQ Wizzard ? I have an SPL meter, which can double as a mic, I have an M-Audio revo sound card in my pc, but I don't know how to connect everything to actually record and map the room. The tech guy had a macbook with an Appogee MiniMe external DAC connected to a mic (xlr) on a stand. The sound was then recorded using a software similar to ETF or others like it. If I could just do it myself and experiment I could really map the entire room up, then I would have intelligent data to converse with you guys

Thank you so much

Stephane, the literature relating to bass reinforcement generally is the opposite of what you were told. Concrete absorbs very little of the bass energy and strictly from that standpoint a room with all concrete surfaces would be optimal. The more flexible the walls and other room surfaces, the more the bass energy is diminished.

I see what you mean, from a sound absorption coefficient point of view, carpet is 0.01 and concrete is also 0.01 for a total of 0.02 Now, 1 being the most absortive and 0.00 the least, it's clear that my thin carpet on my concrete floor is not absorpbing much. Mind you those numbers are at the 125hz frequency. I was not able to find any numbers for the low frequencies ie: 40hz to 90hz.

Typical drywall walls on 2x4 studs are rated at 0.29, quite a bit higher. Again that's at 125hz.

So, what you say makes sense, the floor is most likely not absorpbing the bass energy. I'm going to move the speakers around the room in completely different areas and see if I get different results.

Update.

I went home early, ie: before the rest of the fam, and moved my speakers / listening positions in places that I could never leave it that way, but I wanted to know.

Sound did not improve..BUT.. when I put everything back to the " way it was" my speakers were a bit further from the back wall and it sounded better, more bass.. So I played with that for about an hour and I got them in a position where they produce a very good amount of bass..the overall sound is not perfect, but more bass traps / treatments should take care of that..Point being that moving my mains further away from the wall(s) did produce a much better bass response, very acceptable indeed.. So, I guess I don't need to build a raised floor afterall .

The middle of the transducers are 26 inches from the side walls and 46 inches from the back wall.

I think I am starting to actually see the sound waves paterns of my room in my mind !!!!very scary.

Thanks Guys for all the helpfull advice and sugestions.

That is great Stephane! It is amazing how just moving your mains or sub a few inches to a few feet can make a dramatic difference.

Thanks Randy, I appreciate your feedback as always.

when you get a chance, could you tell me briefly how you did your sound measurements of you room ? I know you used the RoomEQ Wizard software, but I am curious as to which hardware you used and how it was connected together.

Thanks again,

Cheers,

Steph

I've used two products to just give me an idea. Keeping in mind, these are taken only from the primary listening position and would be different from other locations.

1) I downloaded the free test tones from the RealTraps website. The CD starts at `10hz and goes upto 300hz in 1hz increments every 10seconds. It takes some time to complete, but gives you a great idea as it includes all frequencies. Some test CD's like 1/3rd octave cd's don't show you the entire picture as they skip over important freq's.

I basically wrote down my results on a piece of paper, and then transfered them to an excel spreadsheet.

2) RoomEqWizzard - I got this off of HomeTheaterShack's website. You have to have a computer/laptop with a soundcard to run this free program. You basically hook up your RS SPL meters "output" connection to the input on the sound card to take the measurements. There is a little more to it, but that is pretty much all it takes. The instructions on the website and help file in the program take you step by step.

Actually, I need to rerun my tests since I've upgraded.

Thanks Randy,

I will give it a go.

Cheers,

Steph

Riker,

Do NOT spend money on a raised floor. The raised floor will increase mid-bass output (80 to 300 Hz) but it will almost surely give you an undesired boost for frequencies below 80 Hz. Have you tried experimenting with the bass control on your receiver?

Mojo,

I'm running everything flat on the tone controls. I'm trying to fix the issues with treatment and position etc.. before I start tweaking with the tone controls or add a Parametric EQ to the mix. If I can get the room flatter than it is now, that would be a major improvement on overall sound quality, then I could experiment with tone controls / eq if there was still something to take care of.

Cheers,
Steph