Discussion in 'Subwoofers' started by JIT, Apr 11, 2004.
Finally got round to charting my Servo 15's response.
That dip at 40hz is HUGE or did you want it like that?
I know, this is with the Servo placed in the front left corner of my room behind and to the left of my front left speaker. When i get a chance i'll move it more towards the centre between my fronts and see what readings i get there.
I'm not using any EQ on the sub and have the crossover on my receiver set at 80Hz.
What did you use to get your measurements, I have Avia and the sub sweep is just to fast for me to get accurate measurements.
I know from the spl readings that I have a few dips, but charting them would seem a nightmare at the moment.
I have downloaded some test tones but these are in mp3 format. I have aslo mislaid these and can't remember where I aquired them from.
Even with the dips it sounds and FEELS excellent.
Look here - http://www.snapbug.ws/bfd.htm
There are links for tones and the Excel chart plus information on how to do everything.
Thanks JIT, more experimentation for me.
I will post my chart once I have carried it out.
It will be interesting to see what your dual Servos produce.
Here we go, quick test done with kids running in and out. Amp set to -21db to get spl to read 75db on first signal, if that is understandable.
I have tried to attach an image here
I know the dips are all over the show, but it still does feel good with movies.
A few more tweeks and a BFd should sort it out, hopefully.
The subs are in a open plan living area, can't be bothered to work ou the volume, it does measure 28ft x 32ft roughly.
Both subs are located between the front two speakers.
And It was a quick test, i didn't unplug the main speakers, just done the test with all speakers. I just scanned the instructions from the site you pointed me towards JIT.
The graph is with the adjustments made for the SPL.
Keep in mind that it is always better to reduce peaks by moving the sub than trying to do it all through a BFD. "Room-boom" isn't just increased SPL of a certain frequency range, it is also distortion. The echo's causing the increased SPL arive later in time.
Is it just concidence that you have a big trough at 80Hz?
Are you crossing over just there?
Try making phase adjustments and retest
Spot on Nimby, I have moved the subs aprt by 17ft and the graph pattern is pretty much the same.
I have plotted a graph for one sub and the pattern is the same, for both dips and picks in each case.
Will try phase adjustments, x over at 40 and set my mains to large. keep the others small.
Am also moving the subs back in between the fronts as the pattern doesn't really change.
how the hell do some people fet such staright lines. By the way the only phase adjustment i can do is on the amp, i do not have an x30.
JIT, I did a similar exercise a while back with my Rel Q200 and posted my charts. I was told by a certain member that the dip i had at 40hz was robbing me of a lot of 'punch', 'slam' whatever you like to refer to it as.
It may be worth having a look to see what you can do about yours as that is quite a hole you have there. Mine was relatively easily fixed by changig the amps settings to set the main speakers to small. I also moved the sub into the corner.
Changed crossover to 60, it has helped, the dip is not as pronounced, but is still there. It gets slihghly worse as it reaches 100.
I will say I have pitched ceiling in the part of the room the subs are situated, could this be causing it.
It is all wooden flooring and wooden blinds, I suppose some form of room trestment, rug etc, will probabaly be better.
sorry to jump onto your thread JIT.
When you say you moved them a further 17ft apart do you mean equidistant to each other as before. IE if you were to place a sub in the mid point between the two at the first locations and the second locations would this central ghost sub be in same spot?
The dip at 80Hz looks too big to just be a phase error due to xover. I think there is more than that happening.
Gordon, I just moved on of the subs 13ft to the left.
I have attached another graph, wityh the servos back to the original positions, the red line shows xover at 60 and the blue line xover at 40, these settings done on the amp.
You said "The dip at 80Hz looks too big to just be a phase error due to xover. I think there is more than that happening."
What do you mean or think is going on?
Because I have no idea
Oops, in my haste I forgot to attach the file, here it goes, hopefully iwth the file this time .
Supra: Can you email me a word doc with a line drawing of the room layout. I want to know where your speakers are (subs) and where your seats / listening measuring positions are.
Going shopping but if you get me this I can have a think.
Also can you measure the response in a corner for me (ie put microphone in corner and do your sweep
Will do Gordon, just popping out in 10 mins for a bit, I will then do measurements and email them, thank you very much for your assistance
Hi gordon, i have sent you e-mail, with attachments.
What do you think, the readings taken in the right hand corner seem better, no dip, at 80. But a dip at 45 anfd t5he spl readings are a lot higher.
Ihave no idea what to make of this, brain ache time
That's ok about the thread.
I'll move it about a bit and try to fix that dip.
Would a good exercise be to place my Servo where i sit and then take SPL readings at various places in the room where the sub could be placed and where the response is best that is where the sub will sound best?
I moved one of my subs and took readings, the dips were still there. i haven't got a lead long enough to try them out at the back of the room.
I have read somewhere else that even when you move subs about the pattern always seem t o stay the same.
Let us see your graph after you have moved your sub.
i did consider stacking my two subs, but they just look silly like that in my living room.
Good luck in fixing thta 40hz dip
That is not true. My room is fairly good but I can walk around the room and hear the peaks and dips in the response in different parts of the room. If I placed the sub in one of those areas of peak or dip, the response would be completely different.
You may find that even moving the sub through 90 degrees will have an effect, though I am not sure if a dip of that magnitude will be fixable by simpy just moving the sub, though it probably can be improved slightly.
The main factor in my room measurement was the changing of settings on the amp.
Ian I have moved my sub about,within the limits of the leads(need to borrow some long lead) and the pattern has stayed the same.
Mind you I moved one sub by 13ft, along the same wall, the pattern after taking spl readings was still the same. I didn't locate where the dips were before doing this though.
Whilst I have these dips on my graph, when watching films the lfe effects are still excellent. I am just trying to improve upon the current performance.
I will try later it later on and walk round with the spl, to find the dips and see if I can position a sub there. then take measurements, probabaly won't be today. It was just something I had read. Will try and see for myself.
So far changing the settings on the amp has made adiffernce, however, the pattern still remains the same.
I have my amp's crossover at 80Hz with all speakers to small as i find this to be best.
The key to getting best reponse is.
Move sub or seats.
Presuming you have set the electronics up correctly in first place.
I will post a little in a mo to explain why moving sub makes a difference.
From one of my posts in another forum:
"Here's is an analogy for you to consider.
Imagine a swing in a park. You are standing behind the swing.
You are the subwoofer the swing is the pressure wave.(mode)
If you push forward when the swing is at the top of its backswing all your energy is transfered in to making the swing...swing and it goes higher (louder) If you push the swing with the same force when it is still moving backwards you reduce the movement (less loud).
So it is with moving subs around. If you place the sub in the wrong area you add to the excitation of the swing(mode). By careful positioning of the sub you can flatten out the room modes at your listening position or possibly several listening positions. Of course it may not be possible to deal with all the modes in this fashion in which case you can try room eq.
Hope this is of some use,"
After much persuasion I changed my mains to small too and this did give a better response Have a look here and you will see my room response graphs.
At the end of the day if you are happy with the sound you are getting then it's not worth beating yourself up about it, and i'm not suggesting in any way that you should be displeased by the way. I am sure that I could have improved things further by moving the sub about, putting more slabs on top of it, hanging it from the ceiling on the finest fishing line available but there comes a point where the room has to be aesthetically pleasing as well as performing to it's optimum, it's a compromise, it depends which is more important as to how far you go.
The reason 80Hz crossover sounds better is that it is easier to manage the speaker/room interaction if you just have one source of sub 80Hz signal.
If the main speakers are excieitng room modes then moving sub is not going to fix the problems they are creating. They would need positionsed as well. Of course as Steve says this starts to become a bit of a nightmare in a domestic environment
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