- Thread Starter
- #21
half a metre. Can't really go back any more than that.
The phenomenon that is causing these dips and peaks is called Speaker Boundary interference response (or SBIR). basically at the low frequencies the speaker is omnidirectional and is radiating towards the back wall, the sound reflects from the backwall and arrives back at the listening position at the opposite phase and cancels the frequency. It can also arrive with indentical phase and cause a peak instead.
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at 1/4 wavelength you get a null, at 1/2 wavelength you get a peak, and so forth.
seems to match up quite nicely with your results. this effect can be minimized with bass traps (absorption panels) behind the speakers or by pushing the speakers further into the wall (preferably even in-wall mount them).
Note: same thing happens with the listening position, but it's called LBIR instead. people try to 'stack' the nulls of the SBIR with the peaks of LBIR. it can work to your advantage.
I'm having issues level matching my mains to my subs but thunder and lightning has stopped play here so I'll have to leave it here for now.
Ill post back soon.
don't level match them, gain match them .
otherwise either the subwoofers or the mains will be overdriven.
I don't understand the difference?
I'll explain what I did and maybe you can pick it apart?
Before running GLM, I set my SHD to -30 volume as I feel that would be a good 75db starting point.
I then ran GLM as full range and as independent speakers.
I saved the calibration.
I then ran an SPL calibration and set it to 75db and confirmed it.
Uploaded the results to my speakers and removed GLM from the system.
I set up SHD routing as was suggested on page one.
Set all sliders to zero and ensured no crossovers or PEQ was active.
I then set up my umik1 with REW.
I then tested SPL using my umik1 and REW and it was down at 69db.
I checked the subwoofer SPL and that was down quite a bit too!
Bear in mind, I've had these two subs for years and have previously set their individual levels with the gain dial on the rear.
I'm not sure what happened but it isn't right.
Can't do anything with it right now though.
I would start by getting everything restored to defaults, and then try to get the speakers to generate 75 dB @-30 dbfs (I'm sure one of the sliders on the back do that or via GLM). Use pink noise @ -30 dBFS (80Hz to 20KHz) for the calibration via the generator function. Make sure that the VU meters on the outputs in the MiniDSP show -30 dBFS as well during this procedure (it's actually -22 dBFS in REW generator for me on the 2*4 HD).
then what you would want to do is match the gain of the speakers to the gain of the subwoofers. Start by doing an SPL sweep on one of the Genelecs, then pick up one of the subwoofers and temporarily swap locations with the genelecs, keep doing sweeps and fidling with the gain knob of the subwoofer till you get the same exact curve as the genelecs (same dB / loudness).
when everything is gain matched do the alignment, then do Dirac calibration. and voila! reference quality system.
Just a quick question.
The image below is a measurement taken of both my mains playing together.
Why does it look so awful? Huge peaks and dips everywhere whereas the individual speaker measurements look fairly good.
Is this what I'm hearing or is it not accurate?
This is a single point, full range measurement taken at the MLP.
I thought the GLM software is supposed to fix things like this?
Using the alignment tool in REW, I was able to flatten it out quite significantly but is this something I should be doing?
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You may have a phase alignment issue around the crossover. I’m not at my computer at the moment, but Google “REW phase alignment tool”. There are YouTube videos showing how to do it. Watch a couple of those. Basically, you measure sub(pair) and left or right speaker with sweep, then tell REW where your crossover is by clicking on the line in the graph. REW will then give you a delay in ms to add to the miniDSP that will phase align your two subs to the monitor you chose at the crossover frequency.
That is the one big benefit of the otherwise-overpriced GLM subs. They eliminate all complications(for stereo configurations, at least).
Any guidance for a total NOOB would be great!!
Sorry for all the questions!
So, I haven't used a miniDSP and I can't answer your questions about specific steps in their UI. However, you're aware they have a bunch of step by step tutorials on their site right?
eg: single sub with REW/Dirac, dual sub with Multi-Sub Optimizer
I would consider GLM a separate optional step entirely, as REW/Dirac will just see the GLM-corrected response and as far as it's concerned that's just the speaker's normal response.
I'm not intending to use DIRAC as I want to keep things as simple as possible. DIRAC came "free" with the SHD otherwise, I wouldn't have paid for it to be honest.
Used DIRAC before and wasn't a fan of it.
I'm not intending to use DIRAC as I want to keep things as simple as possible. DIRAC came "free" with the SHD otherwise, I wouldn't have paid for it to be honest.
Used DIRAC before and wasn't a fan of it.