Axiom Home Page Forums General Discussion Technical Questions Graphs multiple subs multiple seats.

Ask and you shall receive.

The below graphs were taken using my Velodyne SMS-1 as the visual with no EQ adjustments in place. All speakers were calibrated to 73dB's from the Front Center seat. In addition, each sub was calibrated individually to 73dB's as well.

The EP600 was placed back up front centered below my screen and VP150. One 350v3 was placed along the shorter right side wall 6ft from the front wall. The second 350v3 was placed along the left wall about 16ft back next to my second row of seating.

Before I took the pitures, I played with different delay, phase, crossover settings before I found the best results from the main seat.

The pictures are in the following order from each seat; 600 only, 350's only, and finally all subs running. What I've found in all of this testing is that it is very difficult to satisfy all seats in the room, even with multiple subs, or EQ.



Front Center 600 only


Front Center 350s only


Front Center all subs


Front Left 600 only


Front Left 350s only


Front Left all subs


Front Right 600 only


Front Right 350s only


Front Right all subs


Rear Center 600 only


Rear Center 350s only


Rear Center all subs


Rear Left 600 only


Rear Left 350's only


Rear Left all subs


Rear Right 600 only


Rear Right 350s only


Rear Rigt all subs.

Randy,

Thanks for posting.

It appears that the 350s have the type of response that you would expect from a traditional subwoofer (unlike the DSP subs). If your room was smaller, the 350s would be adequate but because you have such a big room, there is no low frequency room gain and hence with just the 350s on, your bass response suffers below 35Hz or so. That's where the 600 comes in to save the day with its flat response down to 20Hz.

Looking at all your graphs, I don't see a compelling need for the 350s. Put the money towards a pre/pro and/or an A1400-8. Your daisy-chaining problems would go away too.

I dunno. Based on those graphs Randy is clearly getting smoother FR from multiple subs. The SMS graphical display is limited to 1/3 octave spacing so its not really as smooth as it looks. The null at 45hz with the 600 up front would make the single 600 sound anemic for front row seats during action flicks.

I would suggest using the natural rolloff of the 350s to your advantage and corner load the pair up front to boost low bass output and flatten that 45hz null, then either leave the 600 where it is or move it around until you find the best placement. One advantage of leaving the dual 350s up front is less problem with getting them in phase with each other and the mains. Its far easier dialling in one 600 as you move it around. If you can try to keep the 350s at an equal distance from where you are measuring and the 600 at a distance of the 350s less 3ft to get the time delay aligned between the 3 subs. The bass will sound tighter.

Randy,

You need to stay home for the next week and do some blind testing .

Jakeman,

Prior to last night, I did have the 350's up front spread out near my 80's per your original thoughts. This is when I had a terrible HUMP around 35-40 or so HZ, much worse than the null your seeing.

Which picture are you looking at, because the graph with all subs running from the primary seat looks pretty good me, the problem is you can't satisfy all seats in the room.

I tried moving the 600 around to various positions, with the 350's upfront in phase, but the graphs didn't seem to change much either.

I may try the 350's on the back wall spread out if I can figure out how to route the coax around the walk out door, see other thread.

Neener, Neener.... Randy's room sucks too!

Well guys, I've about had it with this stuff.

I don't know if I made a mistake getting the extra subs. Don't get me wrong they are great subs. It has to do with frequency response I'm suppose to see with multiple subs.

I don't know if the SMS-1 is not a true reflection of what is going on.

I don't know if the 350's are even helping at all.

I'm just frustrated as I have tried probably 20 different configurations, placements, phase settings, delay settings, you name it, this weekend and I'm not really impressed with any graphs I'm getting.

Placements tried:
600 up front, 350's spread out on back wall.
350's up front spread out, 600 on back wall.
600 on front wall, 350's on side wall.
I've also tried variations of the above 3 main locations, by sliding the subs in one direction or the other.

To me the graphs just don't seem to be getting better.

Should I assume that things are better, and the SMS-1 is not a true reading, like the ones Axiom uses in the videos?

Sorry, I'm venting, but I had high hopes that I would see some drastic improvements across all seating locations.

Randy, what do your ears and senses tell you? Forget the graphs and just go with that.

Oh yeah and I forgot to mention this dang buzzing I'm getting in all my speakers now, it is more pronounced in the center.

If I have just the EP600 plugged into the receiver sub out, no sound at all, all speakers dead quiet.

As soon as I plug the other subs, either daisy chained, or y-adapter at the receiver, buzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz

Randy,

I'd bet my money on ground loops.

Send them back. That 600 is plenty for your room. And start enjoying your system .

Randy. If you expected that three or more subs would give you a lab like flat FR curve equally at all the seats it ain't ever going to happen.

What adding subs does accomplish though is smoothing those nulls and peaks at each seat which "can" translate into better sound. I qualified it because better sound isn't just flat FR but also depends on proper time alignment with the speakers and each other sub. It takes time and patience to get it right. When you do, the reward is you can take the SMS out of the circuit and get yourself a better processor.

Lab like freq response was not my goal John, it was to help improve the peaks/nulls across each seat. The discussions by Dr Toole and Ian are telling people what can happen by adding 2 or 4 subs in a room, people don't have labs at home.

At this point I am not seeing that improvement in the peaks/nulls, at least with the SMS graph, maybe I need to try my REW again, or the Realtraps tones in 1hz increments. If you look at the graphs from say 50hz and above, there is not much change if any by adding the additional subs. In most cases it is much worse.

What can I say Randy...my experience a couple of years ago confirmed the conclusions of the Harman papers and Ian's current video. However it took me longer than you to tweak and adjust the subs. Also you do have a very large irregular room compared to mine which is always a factor. In any event, it may be worthwhile to invest time tweaking the subs where you had them for the graphs. Which sub(s) are connected to the SMS? Have you used the variable phase function in the SMS to further dial in phase? What about other crossover points? Also, small changes in sub postion often change the picture. considerably.

For those that have a 350v3 and an SPL meter, can you put the dial on 60dB selection and place your mic about an inch from the sub grill cover, I'm getting 60dB's with nothing playing.

This is the buzzing I'm hearing, maybe my ears are sensitive, not sure. Sounds like the buzz you hear from a transformer station.

Change the dial to 40Hz and maybe it will go away .

BTW, I didn't have this problem with the 350 when framer brought it over. Then again, when I wired my basement, I made sure that all my AV equipment was on a single 30 Amp circuit.

John, what I have been trying to do, is find the positions that give me the best response possible without introducing EQ, yet. My subs are all hooked to the Denon, and I'm using the SMS graph to see what happens in various situations.

Hypothetically, if I can find a decent arangement without EQ, then I would not need the SMS. Originally, I did have the 350s going through the SMS, and the 600 as an anchor (as you called it), the problem is that nothing I did with manual EQ seemed to changed the graph, and when it did, it was the opposite affect. I was just trying to reduce peaks, which is suppose to be easier.

When you say corner loading, are you saying in the corners, or stack them? I can't put them outside my 80's, since my corner bass traps are in the way. I've got them now just inside each 80, with the drivers the same distance from the front wall. It sure looks like a roller coaster ride.

What is strange is if I put all the subs out of phase, 180, the graph is better, and the 40hz hump is not as bad. I've got the 600 back along the back wall again, next to the walk out door. Maybe I'll try the side wall again to see what happens.

I'm just getting tired of moving these subs around.

The dials stop at 60 on the SPL meters, I even get the noise out of my 600. All my AV equipment is on the same 20amp circuit as well.

Randy, I can't quite remember what I read that prompted me to move my subs, but I tried mid-wall placement on three walls. Actually, it's more like 2/3 of the way on two walls and almost 1/2 on the other. My thinking is that if all subs are in identical placement along each wall then nothing is really being done to cancel out problem frequencies. Asymmetry seems to be best. Of course, I could be wrong.

I don't have any means to graph my room response, but I did do the SPL thing and I made a handwritten chart. My room is fairly flat in the lower frequencies. Maybe I just got lucky. Or my ears are that bad and the anomolies don't bother me. . .

I know Sean, I think part of my problem stem from that I don't have a rectangular room. I know I keep showing my room picture hoping someone will say, oh, just put your subs there.....

As you can see my theater area is pushed over into the left side corner, so central on my screen wall, is not central of the room. Also, there is a huge hallway next to the bar leading into the other side of the basement.

Maybe I should not be trusting what I'm seeing on the SMS graph?

LOL!

Randy, I wish I had a magic solution for you. I do think you are on the right track. Sometimes I get so caught up with the SPL thing and room response and wondering if I have the phase set correctly and the crossover just right and gain at the right level I stop having fun. I've kinda tweaked the subs so they sound right to my ear and I've left it at that. Sure, there are problems with the system, but there is something in that "ignorance is bliss" saying. . .

I just think Randy's subs need more breaking in.

Yes, he should play the pod scenes from "War of the Worlds" on a continuous loop for 3 months straight. . .

Randy, along with your idea of not trusting SMS, do your ears confirm the results you are seeing on the graph when you move to different seats in the room and compare the same scene/song/etc.?

Is it so bad that it's worth all the hair-pulling you're doing moving speakers around (and the big extra investment you made in the new subs?). I'm sure you've considered all this already, I just feel for you and am trying to offer any tidbit of helpful advice I can that might take away from the frustration I can tell you're going through.

Not a problem guys, sitting on the couch upstairs drinking a beer right now and chilling.

Will head down in a sec to give it some more thought, trial, and error.

May try all 3 subs up front next. Just found a thread on AVS where man have this setup. Here is article as well.

http://www.sonicdesign.se/subplace.html

Just out of curiosity, why 3? I've seen 2, and I've seen 4, but I don't know that I've ever seen 3 before.

Good luck.

No particular reason, was debating over a single 500 or 2 350's, pricewise about the same deal.

Just got done placing the 600 dead center below my screen, and each 350 centered on either side between the 600 and side walls.

Let the graphing commence...

Look at this way. Moving subs saves you a trip to the gym.

Anyway, If it looks better at 180 phase then I'd leave it there. Also you can get more output from the 350s from room gain down low by moving them into the corners in front of the bass traps. It may make the peaks higher somewhere but its worth a try. Given your volume problems I would suggest installing the 600 into the SMS so you can have more control over the input signal gain.

Regarding the hum have you tried XLR cables between the subs or splitting the 600 from the 350s at the Denon to troubleshoot where its originating? Hum is very irritating and it may be worthwhile to attack that problem first.

It seems if I have all three subs plugged into the same outlet, doesn't have to be the outlet the other AV equipment is plugged into, the problem is pretty much not a problem anymore. I should be able to figure something out there, especially if I leave all three near the front stage.

There is not enough room on my stage to put the 350's on the outside of the 80's because of the traps. So I moved them on the floor a couple of feet forward, but clear to the side walls.

All subs calibrated to 73dB's individually, and speakers at 78dB.

With all subs in phase - prett flat from 20-40, big dip at 55 by 10dBs, back up to normal around the 80hz, then another big dip at 110.

With 600 in phase and 350's out of phase - still flat from 20 to 40 with a hump showing at 40ish, dip at 55 raised by 8dB's, dip at 110 still there but maybe a little better.

With 600 out of phase and 350's in phase - still pretty flat from 20 to 40, hump at 40 gone again, however instead of dip I have a valley from 45-63, and still have the dang dip at 110.

All subs out of phase - A little uglier than the previous setting.

I think I forgot to mention I have the 600 dead center up front as well.

Try the 600 out of phase and the 350s in phase but with the 350s pointing to the screen wall instead of facing you.

Since bass nulls usually occur at halway points in the room, and the flattest bass response usually occurs at 38% off a wall, I would try to place the subs against a wall that a red line hits, and try to sit where green lines intersect.

Regards

Thanks,

Actually my drawing is not to scale and my seats are following the 38% rule as defined by Ethan Winer at Realtraps. The regulars around here remember when I spent countless hours building my bass traps and panels and room layout per his suggestions.

And look where that got you

I didn't want to say it but since you brought it up Jason, my bass response is flatter than Randy's up to 100Hz. And we all know how bright my room is.

I checked out your web page from your profile. VERY NICE SETUP QUACK! I see you drew the 38% lines, my bad.

Next step "Tear Down those Traps Mr Porter".

Not sure if you still care, but my 350 also has a 60dB hum with nothing playing. It's on its own outlet on the front wall, Rx is on the back wall.

You're ears are definitely more sensitive than mine; I had to put my ear an inch away to hear it.

I suppose with 2 350's I get a 6dB combined gain. Thanks for checking.

Randy, I think I found your problem. See the ground loops in front of your equipment rack?

ha ha

I got a very similar problem with the SMS, which I was not trusting, or trusting myself using it. I had it in the loop, and by looking at the graphs I got, I thought I lost the money. I had long nights and neighbors pissed by the night tests (after work) until I got some decent EQ, but I am not satisfied.

Interesting to see your findings. We are going to certainly learn from them. Tuning both subs sound more difficult that I initially thought.

I got the SMS and started to play around with the EP500 in several positions on the room and different EQ, and trying to figure out if a second sub will improve my room sub acoustics. I really want the second sub, but until I am positively sure I can get them tuned properly, I am not ready to buy it.

Well, if we're talking about a 5.1 system with speakers which are not full range, then at first I thought, sit each speaker (not the center) atop a nice subwoofer and twiddle with the cross-over frequencies. That should approximate 4 full range speakers.

Then I thought, how long is a 20Hz sound wave? Googled the matter and was surprised to find the answer is 17 meters. Wow. That's larger than most rooms. So, I googled, how long is a 20Khz wave? 2/3 of an inch they say. Zounds.

I suppose the idea behind time corrected speakers is that each frequency arrives at the listener's ear at about the same time. I suppose we could move the subwoofer(s) into the next room. Inconvenient and peculiar.

Maybe a 3 dimensional tesseract type layout would work? What? did someone say audiophiles are peculiar?

Great. Thanks a lot 'Quack. As of today every time a CD ends all I can hear is that damn sub hum.

I'm sure in my post in the water cooler forum, that there is an electrical outlet sold to eliminate this hum. It better in order to justify the cost.

sorry doorman. I did plug my 2 350's into the same outlet and now the hum is much better.

When I was in school we did a field trip up to the U of T Aerospace Institute north of Toronto (well, it's the middle of Toronto now but it was north of the city back then). One of the things that impressed me was a sonic boom simulator -- basically a long tapered tunnel maybe 100 feet long and ~8 feet high at the end, tapering to a few inches at the other end. Your basic horn-loaded subwoofer.

Anyways, there was a metal diaphragm at the small end of the tunnel and the air pressure was cranked up behind the diaphragm until it burst, channeling the pressure impulse down the horn to the other end where we were standing. I think they used Saran Wrap or something similar for the demo (to avoid imploding eardrums) but it was still pretty impressive.

Randy, you have lots of open space around your house, right ?

Yup, 2.5 acres of grass surround the house.

2.5 acres of grass? Now we know how can afford all this equipement!!

Bob?, Bobs not here man.....

Stedenko? Is that you man...

2x6, the speed of sound is independent of its frequency. In still air, like that found indoors, the only thing that can affect it is the ambient temperature and humidity. Some crossover designs can alter the phase of sound differently depending on the frequency, so time correction is important in that aspect. Outside of the speaker's cabinet, however, the only thing that needs to be done is to keep the drivers as close to equidistant from the listener's ear as is reasonable.

The lesson here is that those who live in warmer climates get the news before those who live in colder climates. I wonder though if the news is more distorted in warmer climates due to greater Brownian motion.

Thank you PMB. I can now relax. I thought my next speakers would need the tweeters placed 2/3" from the sweet spot and the 20Hz subwoofer all of 54 feet away in order to get "time coherence."

But, what took you so long?

Mojo, I have to try to collect all my free wandering neurons getting knocked around before I can answer, stand by ....