Sealed versus Ported Bass, can the difference be measured?

[Paul McNeil]

Well, I've done, I hope, the measurements requested by Keith_W.

I think that the problem is with Dirac and the subs.

Key to combined data set attached: 1) Stereo both subs; 2) left subs only; 3) right sub only; 4) all subs OFF; 5) left speaker only; 6) Dirac OFF

I got an error message trying to measure the right speaker only about a timing issue, so that's not included.

Impulse response looks good with both subs OFF. Turn either sub on, and it goes South. The impulse response looks best to me with Dirac OFF!

Any thoughts are appreciated!

 

[Paul McNeil]

Whoops the combined file is too large.

So here they are separately

 

[Paul McNeil]

Yes..

Would you like to elaborate?!

 

[Hayabusa]

Would you like to elaborate?!

Yes: It can be measured.
take the SVS ported once that can be put in sealed mode.
Many measurement are there.
on example : https://data-bass.com/systems/5b11c1e3a201f10004e39d67

Clear influence on FR, distortion, and group delay.

 

[levimax]

Well, I've done, I hope, the measurements requested by Keith_W.

I think that the problem is with Dirac and the subs.

Key to combined data set attached: 1) Stereo both subs; 2) left subs only; 3) right sub only; 4) all subs OFF; 5) left speaker only; 6) Dirac OFF

I got an error message trying to measure the right speaker only about a timing issue, so that's not included.

Impulse response looks good with both subs OFF. Turn either sub on, and it goes South. The impulse response looks best to me with Dirac OFF!

Any thoughts are appreciated!

When you updated DIRAC did you remeasure everything or just update the filters? If you didn't start fresh I would try that. Also what delays did DIRAC set? Do they make sense compared to a sanity check of distance from LP plus 6 ms DSP delay (decent estimate for SVS subs).

It is possible to over ride DIRAC delays but you need to know whst the right ones are

 

[Keith_W]

I had a look at your measurements.

Just so you know, this is how you determine what is responsible for what peak in the step response.

Step 1: Import all measurements of individual speakers into the same MDAT.
Step 2: SPL and time align all of them.
Step 3: Open "Overlays" and go to "Step Response".
Step 4: Display the reference curve (this will be the curve with ALL speakers and subs playing together) and fix your eyes on that huge late arriving peak at 100ms.
Step 5: Click on/off each measurement and see which speaker is responsible for that peak.

In this case, red is the reference. It's from that SEALED MDAT that you posted a few days ago. Purely for illustration, the purple curve seems to match the shape of the previous measurement. I said "purely for illustration" because the measurements you took are incorrect.

Firstly, if these are measurements of the subwoofers alone (from MDAT labelled "SVS 13 only" and "SVS 17 only") why does the measurement extend up to 20kHz? This is clearly a measurement of the subwoofer with the speaker.

You see that double peak at the start of the Energy-Time Curve? That means that you measured both main speakers together. This is supposed to be a measurement of the "SVS 13" by itself. I can even tell how off-centre your microphone is. The time discrepancy between the peaks is 220 us, meaning your mic is 75mm off-centre.

How can I be so sure that you measured both speakers together? Well, in pink we have "L speaker only" and in blue we have "SVS 17 only". The "L speaker only" measurement does not have a double peak. Sometimes, double peaks can be caused by very very bad mic placement (e.g. a mic which is 37.5mm away from a wall can create a double impulse with 220us delay). But anyway I digress.

TO BE CLEAR, these are the measurements that need to be taken:
- L subwoofer ALONE, with timing reference
- R subwoofer ALONE, with timing reference
- L speaker ALONE, with timing reference
- R speaker ALONE, with timing reference
- Both speakers with both subs, with timing reference

 

[Paul McNeil]

I had a look at your measurements.

Just so you know, this is how you determine what is responsible for what peak in the step response.

Step 1: Import all measurements of individual speakers into the same MDAT.
Step 2: SPL and time align all of them.
Step 3: Open "Overlays" and go to "Step Response".
Step 4: Display the reference curve (this will be the curve with ALL speakers and subs playing together) and fix your eyes on that huge late arriving peak at 100ms.
Step 5: Click on/off each measurement and see which speaker is responsible for that peak.

View attachment 463020

In this case, red is the reference. It's from that SEALED MDAT that you posted a few days ago. Purely for illustration, the purple curve seems to match the shape of the previous measurement. I said "purely for illustration" because the measurements you took are incorrect.

View attachment 463021

Firstly, if these are measurements of the subwoofers alone (from MDAT labelled "SVS 13 only" and "SVS 17 only") why does the measurement extend up to 20kHz? This is clearly a measurement of the subwoofer with the speaker.

View attachment 463022

You see that double peak at the start of the Energy-Time Curve? That means that you measured both main speakers together. This is supposed to be a measurement of the "SVS 13" by itself. I can even tell how off-centre your microphone is. The time discrepancy between the peaks is 220 us, meaning your mic is 75mm off-centre.

View attachment 463023

How can I be so sure that you measured both speakers together? Well, in pink we have "L speaker only" and in blue we have "SVS 17 only". The "L speaker only" measurement does not have a double peak. Sometimes, double peaks can be caused by very very bad mic placement (e.g. a mic which is 37.5mm away from a wall can create a double impulse with 220us delay). But anyway I digress.

TO BE CLEAR, these are the measurements that need to be taken:
- L subwoofer ALONE, with timing reference
- R subwoofer ALONE, with timing reference
- L speaker ALONE, with timing reference
- R speaker ALONE, with timing reference
- Both speakers with both subs, with timing reference

Thanks for the clarification, I didn't realize that you wanted subwoofers alone, and speakers alone. Won't the timing reference be lost without the mains (treble) in play? I had a problem measuring one speaker alone, I only got the mid/tweeter region (speakers are bi-amped), and an error message about the timing reference. Something must be wrong. Back to work...

 

[Paul McNeil]

When you updated DIRAC did you remeasure everything or just update the filters? If you didn't start fresh I would try that. Also what delays did DIRAC set? Do they make sense compared to a sanity check of distance from LP plus 6 ms DSP delay (decent estimate for SVS subs).

It is possible to over ride DIRAC delays but you need to know whst the right ones are

No the settings for the subs are totally out of line with those for the L/R. I put this down to DSP delay in the subs. Also the back surrounds and height surrounds make no sense.

Front L/R 10.0 ms whereas the subs (no more then 0.5 M further distance) are 0.00 ms and 4.6 ms. The back surrounds, at least 4M more distant than the fronts, are set to 2.4 and 3.0 ms.

I didn't start with a fresh set of measurements when I updated the filters. I was waiting before I changed anything else to remeasure as directed by Keith_W.

Of course I can measure distances, but with DSP in the subs, that will not be accurate.

 

[Paul McNeil]

Step 1: Import all measurements of individual speakers into the same MDAT.
Step 2: SPL and time align all of them.
Step 3: Open "Overlays" and go to "Step Response".
Step 4: Display the reference curve (this will be the curve with ALL speakers and subs playing together) and fix your eyes on that huge late arriving peak at 100ms.
Step 5: Click on/off each measurement and see which speaker is responsible for that peak.

I actually did do this. And from the data I collected it is clear that with either sub (playing with mains) the offending, delayed peak will appear in the step response. If the subs are off, the Step Response does NOT have this peak.

 

[Paul McNeil]

- L subwoofer ALONE, with timing reference
- R subwoofer ALONE, with timing reference

When I try to measure the subwoofers alone, I get message waiting for the timing signal, as I expected. I'm missing something...

 

[3ll3d00d]

When I try to measure the subwoofers alone, I get message waiting for the timing signal, as I expected. I'm missing something...

when using an acoustic reference, the timing signal has to be routed to a speaker that can play high frequency (it's a 5-20kHz sweep iirc) so route that to one of your mains

 

[Paul McNeil]

when using an acoustic reference, the timing signal has to be routed to a speaker that can play high frequency (it's a 5-20kHz sweep iirc) so route that to one of your mains

That's what I thought but Keith_W wants sub only measurements. Maybe he'll explain how to do this...

 

[Paul McNeil]

Here is the step response of the L/R only (no sub playing), GREEN, and L/R plus one SUBwoofer, MAGENTA. It's clear what the sub adds to the response, which I think is problematic, large positive and negative peaks at around 100 ms. If I use the other subwoofer the result is nearly identical. If I used both the peaks are larger. Doesn't this tell us something? Of course, but what?

 

[Keith_W]

That's what I thought but Keith_W wants sub only measurements. Maybe he'll explain how to do this...

To measure the LEFT sub:

1. Optional: Ensure that the microphone is properly centred. To do this, do a sweep of the LEFT speaker using the RIGHT speaker as acoustic reference. Then sweep the RIGHT speaker using the LEFT as acoustic reference. If you see a negative time delay, this means the acoustic reference has arrived before the actual speaker measurement. Move your mic towards the speaker that you are measuring (i.e. away from the speaker you used as acoustic reference). When the delay is the same (0ms) your microphone is properly centred. We don't need actual 0ms (perfect centring), but it should be better than the 8cm discrepancy (0.25ms) evident in your current measurements. The reason we centre the microphone is to allow proper timing comparisons.
2. Disconnect or mute the LEFT speaker.
3. Using the RIGHT speaker as acoustic reference, sweep the LEFT sub from 20Hz - 200Hz.
4. Repeat the measurement for the RIGHT sub.

In any case, I had another look at your measurements. It is evident that the timing of your subs is very very off.

Blue: both speakers only with no subs, Green: both speakers with both subs.

The question is whether the latency of the subs is simply horrible or whether it is an acoustics issue causing that peak at 100ms. You need to know when the subwoofer impulse starts, this is why you need to measure the subs by themselves. Also, whether it is one sub that is creating this issue, or both subs.

FWIW, I don't have much faith in REW's acoustic timing measurement because I find that the results are inconsistent, PARTICULARLY for subwoofer measurements, and PARTICULARLY for noisy environments. Subwoofer impulses are too low amplitude and time stretched for REW's automatic impulse detection to work reliably. It is more reliable for tweeter measurements. You should run the sweep a few times and see if you get the same delays each time. I have better procedures for determining subwoofer timing, but whether you can use these procedures depends on your system.

 

[Paul McNeil]

To measure the LEFT sub:

Thanks, would never have figured that out...monkey with typewriter...will give it a try when possible.

 

[Paul McNeil]

In any case, I had another look at your measurements. It is evident that the timing of your subs is very very off.

I a posted similar data above. And it's both subs.

 

[Keith_W]

BTW, if your speakers and subs are on separate DAC channels, you can simply tell REW to measure the sub alone which makes things a lot simpler. This is the procedure:

1. Set REW Preferences to send output to the sub
2. Set REW Preferences to use a speaker as acoustic reference (use the same speaker as acoustic reference for all subsequent measurements!)
3. Go and measure.

I am assuming that your subs and speakers are on the same DAC channel which is why I gave you the instructions earlier.

 

[Paul McNeil]

BTW, if your speakers and subs are on separate DAC channels, you can simply tell REW to measure the sub alone which makes things a lot simpler. This is the procedure:

1. Set REW Preferences to send output to the sub
2. Set REW Preferences to use a speaker as acoustic reference (use the same speaker as acoustic reference for all subsequent measurements!)
3. Go and measure.

I am assuming that your subs and speakers are on the same DAC channel which is why I gave you the instructions earlier.

I use a MacBook and the output is via the headphone channel, RCA into the pre/pro. So no, I don't think that will work, though of course via the pre/pro output they are on separate channels.

 

[3ll3d00d]

The question is whether the latency of the subs is simply horrible or whether it is an acoustics issue causing that peak at 100ms.

it looks like just his sub continuing to play without barely decaying, you can see it in the spectrogram and the decay view

 

[levimax]

I use a MacBook and the output is via the headphone channel, RCA into the pre/pro. So no, I don't think that will work, though of course via the pre/pro output they are on separate channels.

With your setup I think you will need to create the sweep file with REW "Generator". On the Top set of tabs on the "Generator" chose "Sweeps" and on the second row of tabs chose "Measurement" then fill in information the same as what you used before. On the third set up tabs chose "Save to file" and set up the channels and timing reference as before and click the "WAV" button. This will create a file you will use to measure. On the main REW Measurements Icon for Playback chose "from file" and navigate to and select the file you just created. Then load up the file into whatever "player" you are using then go back to REW click "Start" and then back to you player and start playing the file. REW will "listen" for the timing reference and when it plays will start the measurement process. You will probably have to create two files, one for the right with the left reference and one for the left with the right reference. Before you do the measurement make sure you have the volume on your player where you want it or you might be surprised. I usually use -20 dB when I Generate the sweep files to help prevent too loud playback accidents.