Subwoofer integration help request

[lawnchair04]

That is absolutely bizarre. I have never seen anything like this in my personal experience, nor have I seen it happen to anyone else. It's also suspiciously close to your crossover point. Are you SURE that the REW settings are correct?

I measured the sub with and without timing reference at each LPF setting with the HPF turned off, and that 46Hz point was where the difference was. Measurements with and without a timing reference are grouped with the same respective SPL below 46Hz, and measurements with the same LPF are lined up with each other above 46Hz. Really weird.

One other perhaps notable difference is the appearance of the impulse response of measurements with and without timing reference. When a timing reference is used, there is a bit more activity in the response before the sweep begins. I'm not sure if this is meaningful, though.

With:

Without:

Here are the settings I'm using for the sub measurement. I hope there's nothing wrong here. I'm using "L" for output, with the left speaker unplugged. Again, all of the signal goes through the KEF master speaker (R), then to the slave speaker (L) and subwoofer:

I am not a big fan of how REW uses the timing reference. I asked John about it before, and he said that the acoustic reference is not part of the impulse response so I can't use it to determine the timing manually. So I have my own way of doing a timing reference which ignores REW's method. It's a bit too difficult to describe it in a forum post, but if you are really keen you can send me a PM and we can have a chat on WhatsApp and I can walk you through it.

FWIW, inconsistent subwoofer measurements are a fact of life, but I would not expect them to vary by so much. In my own experience, sub measurements vary by about 0.2ms or so. I prefer to read the impulse peak myself and determine the timing manually, rather than simply have REW report it.

I assumed it was hard to avoid some inconsistency. And the real outlier, 5.9, was also the first one, and the only one with a clock adjustment of -48ppm; all of the others were at or around -24ppm. It also appears that the delay was more the higher the LPF was set. I don't know if that's coincidence or not...

 

[lawnchair04]

You could also try an RTA measurement with REW as another test to see if you can resolve this discrepancy. A link I could find on this is: https://mehlau.net/audio/room-correction-peq/, but you could probably find others by searching.

By the way, I would recommend using Var smoothing in REW, in order to see the correct shape of the room resonances: https://www.roomeqwizard.com/help/help_en-GB/html/graph.html#top

Thanks for the tips. I had actually seen that tutorial a few days ago; it's similar to the MMM tutorial posted here on ASR. I posted the MMM measurements I took like that in my OP above, the only differences being the 64k FFT length and the Hann window. I like the MMM measurements for their simplicity and consistency.

The benefit of the individual measurements seems to be the ability to play with gain and time alignment so the sub is precisely integrated. Interestingly, I found that lining up the t=0 of a non-time referenced subwoofer measurement to the start of the impulse instead of the peak, and then summing that with the summed sweeps of the main speakers, gave me something quite similar to what I got with the MMM measurements.

 

[lawnchair04]

This is for me too!

OP @lawnchair04,
You would please read again carefully my above post #13 and the linked post #3 on the thread entitled "Seeking advice on integrating two subwoofers with full-range stereo speakers with passive radiators".
I now attach the contents under the below spoiler cover.

Spoiler: Summary of critical factors in integration of subwoofer(s) and main woofers in our individual acoustic environments:

We have so many critical factors for crossover (XO) between subwoofer(s) (SWs) and main woofer(s) (WOs) in our audio system for better/best low frequency (Fq) sound reproduction in our own/individual listening environments including room acoustics. Of course, the final goal would be greatly dependent on your music listening personal preferences, and hence there would be no general/standard procedures and approaches, I assume.

The major factors would be;
A1. Room acoustic mode(s) including reflection, dispersion, absorption, standing waves, resonances, etc.
A2. Precision (1 ms precision) time-alignment (a kind/side of phase tuning) between SWs and WOs, at your listening position,
A3. Optimization of relative gains for SWs and WOs, should be flexibly controlled on-the-fly while listening to music,
A4. Optimal selection of XO filter type(s) (i.e. BW, LR, Bessel, etc.), XO Fq, slopes at both side, phase inverse or not, further specific EQs or not, etc.

Before starting your optimization/tuning exploration journey in this regard, you need to know/understand several features/aspects; the major points would be;
B1. "Major" low Fq sound reflective plane/wall in your acoustic environment (not always needed to be fully eliminated),
B2. Be aware of that we always have overlapped Fq zone where SWs and WOs sing together, whatever XO Fq and slopes we would use,
B3. Basic understandings on the physical configuration(s) of SWs and WOs, especially ported or sealed, difference in mass of moving parts, etc.,
B4. Difference in transient behavior (step response?) of SWs and WOs, both kick-up responses and fade-out patterns;
____Damping factor/performance of the amplifier(s) driving SWs and WOs more-or-less do "matter" for transient behaviors.

As you may well aware, many audiophile people use REW and/or similar advanced audio measurement/tuning software tools together with suitable measurement microphone(s) for the optimization. I too used wonderful REW during my early stage in my multichannel project as you can find my posts #17, #18, #20, #21, #22 on my project thread.

Because of various reasons, however, nowadays, I use REW mainly as validation and confirmation tool for my rather primitive but reliable reproducible understandable (to me) validated simpler measurement and tuning methods as shared below; If you would be interested, please read carefully these posts on my project thread;
- Precision measurement and adjustment of time alignment for speaker (SP) units: Part-1_ Precision (time-shifted) pulse wave matching method: #493
- Precision measurement and adjustment of time alignment for speaker (SP) units: Part-2_ Energy peak matching method: #494
- Precision measurement and adjustment of time alignment for speaker (SP) units: Part-3_ Precision single sine wave matching method in 0.1 msec accuracy: #504, #507
- Measurement of transient characteristics of Yamaha 30 cm woofer JA-3058 in sealed cabinet and Yamaha active sub-woofer YST-SW1000: #495, #497, #503, #507
- Identification of sound reflecting plane/wall by strong excitation of SP unit and room acoustics: #498

I believe the above linked my posts well cover almost all the aspects and tunings relating to above A1 through A4 and B1 through B4.

Let me emphasize that the use of rectangular-sine-tone-bust signals (8-wave, 3-wave, and even 1-wave) of various Fq and the analysis of the recorded air sound (by second independent PC) of these tone-burst signals using Adobe Audition (or Audacity) would give you really useful information on optimization of SWs and WOs. Especially the 3D (gain-Fq-time) color spectrum of Adobe Audition showing "3D sound energy distribution" is much useful (at least to me!) for observing and tuning the XO configuration for SWs and WOs (and other SP drivers). You can find typical example case in my posts #503 and #507.

If you would be seriously interested in using the test tone signal tracks I prepared and applied in these my measurements and tunings, please simply PM me writing your wish.

These posts would be also of your interest and reference;
- Perfect (0.1 msec precision) time alignment of all the SP drivers greatly contributes to amazing disappearance of SPs, tightness and cleanliness of the sound, and superior 3D sound stage: #520

- Not only the precision (0.1 msec level) time alignment over all the SP drivers but also SP facing directions and sound-deadening space behind the SPs plus behind our listening position would be critically important for effective (perfect?) disappearance of speakers: #687

- Reproduction and listening/hearing/feeling sensations to 16 Hz (organ) sound with my DSP-based multichannel multi-SP-driver multi-amplifier fully active stereo audio system having big-heavy active L&R sub-woofers: #782

- A nice smooth-jazz album for bass (low Fq) and higher Fq tonality check and tuning: #910, #63(remote thread)


Furthermore, I highly recommend you to establish your own consistent "reference/sampler music playlist" consists of tracks of various genres hopefully fitting well for your/our music preferences.

At least in my case, I have been using my own consistent "reference/sampler music playlist" consists of 60 tracks as I shared here #670 on my project thread, and also I have dedicated thread;
- An Attempt Sharing Reference Quality Music Playlist: at least a portion and/or whole track being analyzed by 3D color spectrum of Adobe Audition

You would please find details of my latest audio setup, well covering all of the above mentioned topics, in my post here #931 on my project thread.
- The latest system setup of my DSP-based multichannel multi-SP-driver multi-amplifier fully active audio rig, including updated startup/ignition sequences and shutdown sequences: as of June 26, 2024: #931
Edit:
- The latest Fq-SPL (re-confirmation) of multiple amplifiers SP high-level output signals and that of room air sound at listening position: all measured by “FFT averaging of recorded cumulative DSP-processed flat white noise” (as of June 8, 2025): #1,009

Thank you! Yes, I did start taking a look through your post(s), and it looks like fascinating stuff! But a lot of it is still well over my head...I'm still learning to use REW with my relatively simple setup (a Wiim Pro connected to an active speaker with a subwoofer out), so it's difficult for me to apply the much more complicated multi-channel, multi-driver, multi-amplifier setup you describe in your post. Still, I really enjoy reading about your project, and it gives me a great idea of some of the fundamentals I need to learn in order to get a more clear understanding of your process.

千葉県なんですね。こちらは世田谷区です。

 

[Keith_W]

Here are the settings I'm using for the sub measurement. I hope there's nothing wrong here. I'm using "L" for output, with the left speaker unplugged. Again, all of the signal goes through the KEF master speaker (R), then to the slave speaker (L) and subwoofer:

Your "subwoofer measurement" is actually a measurement of your sub and main speakers. You indicate that your sub has a low-pass of 62.5Hz, but the measurement goes up to 200Hz in all cases, regardless of what low-pass you have put on your sub. When I said "measure your subwoofer impulse with a timing reference", I meant subwoofer alone with the main speakers only playing the acoustic timing reference. I expect to see a series of curves with different LPF settings.

I was confused enough to look up how you connected your system together. Are you using this subwoofer output to send signal to your subwoofer? If you are, then you have no way of independently measuring your subwoofer.

And even if you can get a subwoofer measurement, your sub has no timing adjustments.

So IMO, when you are measuring your sub with acoustic timing ref, you are measuring your sub together with your main speakers up to 200Hz. Run a sweep and gently touch the cone of your main speakers. It should not be moving.

If you can not manipulate your sub independently of your main speakers, there is no point trying to make timing adjustments with REW. All you can do is decide what XO is better, whether polarity should be inverted or not, and maybe slap a few PEQ's in there to get it more even.

 

[lawnchair04]

I was confused enough to look up how you connected your system together. Are you using this subwoofer output to send signal to your subwoofer?

Yes, that is correct.

So IMO, when you are measuring your sub with acoustic timing ref, you are measuring your sub together with your main speakers up to 200Hz. Run a sweep and gently touch the cone of your main speakers. It should not be moving.

I’m sorry if I’m misunderstanding something here, but when I run the sweep to L, and the Left speaker is not plugged into the power, the sound only comes out of the sub. The only sound coming from the main speakers during the sub measurements is the timing reference before and after the sweep.

If you can not manipulate your sub independently of your main speakers, there is no point trying to make timing adjustments with REW. All you can do is decide what XO is better, whether polarity should be inverted or not, and maybe slap a few PEQ's in there to get it more even.

My original goal was to determine the best LPF and HPF settings and generate PEQs. Learning how to use the alignment tool was a great bonus learning experience, even if I’m not able to use the results. I’m enjoying learning more about my system and how all of this stuff works, and I really appreciate all of the suggestions and guidance.

 

[Keith_W]

I’m sorry if I’m misunderstanding something here, but when I run the sweep to L, and the Left speaker is not plugged into the power, the sound only comes out of the sub. The only sound coming from the main speakers during the sub measurements is the timing reference before and after the sweep.

Well, that extra sound is coming from somewhere. Maybe from your right speaker. If you have a 62.5Hz LPF in your sub and you tell REW to measure 20Hz - 200Hz, you should see the sub roll off at 62.5Hz, period. What we are seeing is the measurement continuing to 200Hz.

 

[lawnchair04]

Well, that extra sound is coming from somewhere. Maybe from your right speaker. If you have a 62.5Hz LPF in your sub and you tell REW to measure 20Hz - 200Hz, you should see the sub roll off at 62.5Hz, period. What we are seeing is the measurement continuing to 200Hz.

In other words, are you saying that in the graph I posted of all the sub measurements above, we'd see a much steeper roll of after the LPF, rather than the gradual roll-off pictured there?

I'm positive the sound isn't coming from anywhere except for the subwoofer. So still not really sure what is going on here...

 

[Chagall]

In other words, are you saying that in the graph I posted of all the sub measurements above, we'd see a much steeper roll of after the LPF, rather than the gradual roll-off pictured there?

I'm positive the sound isn't coming from anywhere except for the subwoofer. So still not really sure what is going on here...

Yes, the sub shouldn't output much after LPF. If you set it at 62Hz it certainly shouldn't have any output at 200Hz. Think there must be something set wrong in your kef connect app?

PS 62 Hz is very low. XO both LPF and HPF should be 80, 90 atleast for such small mains IMO.

 

[lawnchair04]

Yes, the sub shouldn't output much after LPF. If you set it at 62Hz it certainly shouldn't have any output at 200Hz. Think there must be something set wrong in your kef connect app?

But it should still have some output, increasingly attenuated following the slope of the filter used, right? So a Linkwitz-Riley LPF of 24dB/octave (which is what KEF subwoofers use) set at 90Hz would be at -24dB at 180Hz. That appears to be more or less true for the slopes in my post above.

For example, for the LPF=90 sweep, the SPL at 90Hz is 77.2dB:

And down to 48.3dB at 180Hz:

Of course this is a bit more than -24dB, but I think the room response is playing a role there. What am I missing here?

PS 62 Hz is very low. XO both LPF and HPF should be 80, 90 atleast for such small mains IMO.

That's been my impression from what I have read online. I'm still trying to grasp why KEF recommends such low LPFs for its subwoofers. The LPF=62.5, HPF 67.5 setting is the KEF recommendation for my LSX II/KEF Kube 8 MIE combo. Well, that's why I'm trying to get measurements so that I can get a better idea of how different settings measure and make a judgment.