Crossover question for RoryB or others with design moxie

[Boomzilla]

Mr. @roryb -

May I ask a question? My Pendragons are ported speakers with (I think) a nominal 12 decibel per octave roll off below their port tuning frequency (that seems to be about 35 Hz.). So were the speakers being run full-range with a subwoofer, the sub should (theoretically) be rolled off at that same 35 Hz and at that same 12 decibels per octave slope. And due to the the acoustic interaction at the crossover point, the subwoofer should normally be set to 180 degrees out of phase with the satellites. This scenario assumes 12-dB / octave Butterworth behavior (which is what the sub's plate crossover claims to use - I'll double-check this...).

My goal is to run the Pendragons full-range and use the subwoofer's plate crossover to integrate the subwoofer for lower frequency response.

Now to actualities - The lowest crossover point I can set for the subwoofer (using its plate amp) is 45 Hz. If I cross over the sub "normally," using its Butterworth filter, I'll end up with an additional +3 decibels of sound pressure level centered between 35 and 45 Hz. In my room, this will manifest as a boomy bass.

Now the question - If I were to use the subwoofer at zero phase (rather than 180-degrees), the normal "peak" at the crossover frequency will become an acoustic cancellation.

Making things more complex, the Pendragons are designed to have a +5 decibel peak at 35 Hz. (makes them sound like they go lower than they actually do). The Butterworth crossover would normally add an additional +3 decibels at the crossover point. That would give me a +8 decibel peak at 35 Hz. Not good...

But if I reverse the phase on the sub from 180 degrees to zero, then instead of getting the Butterworth +3 decibel bump at the crossover point, I should instead get a -3 decibel acoustic cancellation. I'm hoping that this acoustic -3dB null at crossover frequency will bring the Pendragon's +5 peak (at 35 Hz.) down to +2 decibels - a tolerable amount!

Is this theoretically correct, and will the sub's 45 Hz. crossover point be close enough to the speakers' peak at 35 Hz. to make this a feasible strategy?

Thanks - Boomzilla

[DYohn]

It's really not the Xover you need to worry about it's room acoustics. You are over relying on published specs, which may or may not mean anything in your room. The proper way to integrate a subwoofer with a full-range loudspeaker system really has nothing to do with math based on specs, it has to do with measuring in-room acoustic response and tailoring Xover, level , phase and position to achieve the room curve you desire (and then listening to music to adjust from there by ear,)

So what you need is to set up your room, get an RTA or spectrum analyzer with a FFT function (or a dedicated room analyzer) do some sweeps and review your FR and waterfall plots, then make adjustments. Do both near field and listening position measurements so you'll also be able to "see" both loudspeaker output and your room mode effects. Then you can start thinking about dealing with group delay and latency or just tweak until you like what you hear and disregard the measurements. That's all that really matters in the end, you are not building a test system you are building something you want to listen to.

Assuming this is for music only and not HT, I recommend an initial subwoofer setting of 60Hz and 0 phase to begin.

[Boomzilla]

OK, DYohn - Thanks - I'll whip out the Umik & take some curves today.

[vneal]

If your speaker goes down to 35hz, I would start at 70HZ crossover setting ( I usually double what the speaker goes down to, this is usually a good reference) set the phase at 0, filter at 12 db.You can experiment with the phase at 180 but why?

My sub has filters of 0, 12 and 24DB. For my system the 10db is a good sound. he 0 setting is too much bass. The higher the filter setting the less the boom boom bass but the tighter the drums are. With the big SVS if you can set to 24 db you might try it. I am more about if the sound is pleasing to me and less about the measurements.

[Boomzilla]

Thanks, vneal - I'll try that too.

[Boomzilla]

Also, a quick question regarding phase on the sub. Most subs have a 0-180-degree dial (or switch) for phase, but my current sub has a "delay" dial calibrated in milliseconds. For a 45 Hz signal, I calculate that an 11.5 ms delay should put the sub about 180 degrees out of phase with the primary signal. Am I close?

[Boomzilla]

Mr.s DYohn & vneal -

You're a pair of GENIUSES! I bow to your experience. I was wrong - you were right.

This afternoon, I tried partially plugging the Pendragon's ports (2 pairs of socks in each port, for those counting). And I then split the full range signal from the DAC to both the power amp (Emotiva UPA-2) and the subwoofer (PowerSound Audio S3201 - a dual-18" sealed monster).

I had to tweak the subwoofer's crossover point, phase, and volume.

But now, I've got the best-integrated, tightest-sounding, and most-accurate bass I think I've EVER had in this room. garbulky should bring Pampers when he comes... So I was highly (HIGHLY) skeptical that I could EVER run the Pendragons full-range and get ANY kind of a reasonable match with a subwoofer. But this is not only good, it's GREAT. Having stumbled into ecstasy, I'm not touching a THING. So thank you for stretching my audio horizons. What a long, strange trip it's been...

Boomzilla

[novisnick]

Jul 16, 2017 17:22:27 GMT -5 Boomzilla said:

Mr.s DYohn & vneal -

You're a pair of GENIUSES! I bow to your experience. I was wrong - you were right.

This afternoon, I tried partially plugging the Pendragon's ports (2 pairs of socks in each port, for those counting). And I then split the full range signal from the DAC to both the power amp (Emotiva UPA-2) and the subwoofer (PowerSound Audio S3201 - a dual-18" sealed monster).

I had to tweak the subwoofer's crossover point, phase, and volume.

But now, I've got the best-integrated, tightest-sounding, and most-accurate bass I think I've EVER had in this room. garbulky should bring Pampers when he comes... So I was highly (HIGHLY) skeptical that I could EVER run the Pendragons full-range and get ANY kind of a reasonable match with a subwoofer. But this is not only good, it's GREAT. Having stumbled into ecstasy, I'm not touching a THING. So thank you for stretching my audio horizons. What a long, strange trip it's been...

Boomzilla

I thought I felt EmoSouth shake, now I'm sure of it! Happy Thrilled for you! 🎶🎶🎶🎶

[Boomzilla]

Can't WAIT to hear this with a movie!

[bootman]

Jul 16, 2017 17:22:27 GMT -5 Boomzilla said:

Mr.s DYohn & vneal -

You're a pair of GENIUSES! I bow to your experience. I was wrong - you were right.

This afternoon, I tried partially plugging the Pendragon's ports (2 pairs of socks in each port, for those counting). And I then split the full range signal from the DAC to both the power amp (Emotiva UPA-2) and the subwoofer (PowerSound Audio S3201 - a dual-18" sealed monster).

I had to tweak the subwoofer's crossover point, phase, and volume.

But now, I've got the best-integrated, tightest-sounding, and most-accurate bass I think I've EVER had in this room. garbulky should bring Pampers when he comes... So I was highly (HIGHLY) skeptical that I could EVER run the Pendragons full-range and get ANY kind of a reasonable match with a subwoofer. But this is not only good, it's GREAT. Having stumbled into ecstasy, I'm not touching a THING. So thank you for stretching my audio horizons. What a long, strange trip it's been...

Boomzilla

Did you measure the before and after so that you now have a good baseline for any future speakers?

[Boomzilla]

Jul 16, 2017 17:34:42 GMT -5 bootman said:

Did you measure the before and after so that you now have a good baseline for any future speakers?

Killjoy! LOL I'm still too busy enjoying!

It's a good idea - I'll do it ASAP.

Thanks - Boom

[DYohn]

I'd love to play with a PSA 3201. Congrats on your choice. And I am happy you like the result!

[KeithL]

Something to keep in mind......

If you have a physical acoustic cancellation you're sort of stuck with it (no amount of EQ can fix a serious null).
However, a simple +8 dB bump is easy enough to tame with a little EQ.

[Deleted]

Boomzilla, it sounds like you got good advice overall.

The +5dB bump in the response of the Pendragons in the bass range is intended to give you the idea that they have insane bass response, but the 'new' quickly wears off and that excess bass response obscures detail elsewhere and throws off the system balance, especially when you put them in a room and position that will most likely reinforce that bump further. That bass bump is not friendly to subwoofer integration, so if you have high pass filtering capability in your preamp or HT processor, it is best that you use it to eliminate that bump by crossing over well above it (so it doesn't sneak back in through the summation of the filtered responses of the speaker and subwoofer), and setting that frequency to 2X the lowest frequency the speakers can reproduce is a good way to achieve that. And plugging the port ensures its contribution won't muddy things up when the whole system plays. You might look for solid pieces of open-cell foam (like what is used in foam padding for camera cases and live sound road cases) that you can use to create more permanent and less improvised-looking port plugs.

Side benefits are reduced distortion and better overall bass control because the main speakers are not being taxed to create that deep bass.

[Boomzilla]

Thank you kindly Mr.s Levkoff & Buszka -

Your advice is sterling! And I agree that, theoretically, the "best" option for the Pendragons IS to use active bass management. However, I'm finding that I can get by with plugged ports and the subwoofer-only roll-off. Now the roll-off frequency for the sub is CRITICAL when running the speakers full range - too high a frequency makes the entire presentation sound thick and boomy. But when it's right, then the result is quite impressive.

As to the camera foam replacing the socks in the ports - anyone looking behind my speakers deserves to see the laundry! LOL

Curiously, the "delay" pot on the subwoofer (aka the "phase" control") does its best somewhere just above zero phase, but not all the way. I believe that this puts the subwoofer (almost but not quite) in cancellation of the satellites' bass (normally, for a second-order slope, the drivers would be wired 180-degrees out of phase for the smoothest transition at the crossover point). I think that this partial cancellation (along with the socks in the ports) is almost completely eliminating the speakers "normal" 35 Hz. bump. As currently configured, a string bass or electric bass-guitar can work up and down their frequency ranges without any discernible changes in volume. This is certainly a lucky synergy, but I'm not looking this gift horse in the mouth...

The low-pass filter on the sub does go down to 40 Hz. (per its marking), but there again, I get the best results with the frequency slightly higher. Had I to guess, I'd say it's maybe at 60 Hz or so. The "overlap" may be what's overriding the acoustic cancellation of the sub with the satellite woofers.

Subwoofer gain is also HIGHLY critical. A breath too much, and the system sounds boomy. A touch to little, and the system sounds anemic. But once the match is found, great things happen.

So for the moment, I'm very pleased with the "no bass management" solution. Should I feel the need in the future to change the setup, I can use the Lyngdorf digital crossover to implement bass management. The only negative associated with that option is that I'd then need to use the Lyngdorf's class-D power amplifier, that sounds somewhat less dynamic and less smooth in frequency response, than either of my Emotiva amps.

Thanks again for the feedback -

Boomzilla

[DYohn]

60Hz and zero. Sometimes my guesses are close.

[Boomzilla]

You sell yourself short, David - MOST of the time your "guesses" are right!

[novisnick]

Jul 17, 2017 12:55:06 GMT -5 Boomzilla said:

You sell yourself short, David - MOST of the time your "guesses" are right!

Ive found that unless its a blind stab in the dark most guesses are based on historical education and experience. 😁

[Boomzilla]

And with the ports partially plugged on the Tekton Pendragon speakers, I'll need to measure, but I'm suspecting that the bass roll-off now begins at about 40 Hz. and with closer to a sealed box slope (about 6dB / octave). If so, then I'd have the option of using first-order slopes for both the sub and the Tektons. Listening will tell...

The bigger question is what are the restricted ports doing to the 10" woofers' response higher in the frequency spectrum? With the ports open, the speakers both sounded (and measured) as having a small dip just below the crossover frequency. With the ports stuffed with socks, the "dip" is no longer audible.

Time to get out the UMIK & fire up "FuzzMeasure" again.