The truth about subwoofers

[GordonW]

I've really never met a passive subwoofer crossover, that was better than an active one. Passive crossovers lose dynamic range, woofer control, and output capacity. In short, they waste power in a pretty significant fashion, due to losses in the components required to create those crossover frequencies.

That's been my experience, over the last four decades of building, repairing and installing speaker systems.

The only benefit to a passive crossover, has sometimes been in the minute degrees of tuning variability that is available, when the crossover topology is completely arbitrary. In short- a passive crossover can readily be built to any slope, damping, combination of tank circuits, shelving circuit, and such- limited only by the amount of time the designer has to tune it all. Active crossovers- unless you're building them from scratch- or more recently- you have a DSP with enough tune-ability in order to accommodate the driver responses, exactly- can be harder to make exactly match the transfer function needed- especially in the mids and highs, where breakup modes are a big thing. Fortunately, that's not nearly as much of an issue in the bass- topologies can be much simpler- so DSP and other active crossover technologies do a great job in the lows...

Regards,
Gordon.

 

[Tube Radio]

I always either run an active sub or a passive with a dedicated amplifier.

My current second system uses two 15" Cerwin Vega woofers in 3 cu ft sealed boxes (one per woofer) as subs powered by a Carver TFM-25 amp with a pair of DIY three way speakers sitting on top driven by a Carver TFM-15 amp. I use DBX 234XS crossover which is fed from my computer's pro audio sound card.

Sounds great as is.

Will eventually get two more 3 cu ft sealed boxes and a pair of proper subs for them then the vegas will be for midbass/midrange duty while the new subs will be driven by a Carver TFM-35 amp

 

[Grenadeslio]

I've really never met a passive subwoofer crossover, that was better than an active one. Passive crossovers lose dynamic range, woofer control, and output capacity. In short, they waste power in a pretty significant fashion, due to losses in the components required to create those crossover frequencies.

That's been my experience, over the last four decades of building, repairing and installing speaker systems.

The only benefit to a passive crossover, has sometimes been in the minute degrees of tuning variability that is available, when the crossover topology is completely arbitrary. In short- a passive crossover can readily be built to any slope, damping, combination of tank circuits, shelving circuit, and such- limited only by the amount of time the designer has to tune it all. Active crossovers- unless you're building them from scratch- or more recently- you have a DSP with enough tune-ability in order to accommodate the driver responses, exactly- can be harder to make exactly match the transfer function needed- especially in the mids and highs, where breakup modes are a big thing. Fortunately, that's not nearly as much of an issue in the bass- topologies can be much simpler- so DSP and other active crossover technologies do a great job in the lows...

Regards,
Gordon.

passive crossovers seem to work just fine in speakers lol

again just subjective opinion with no basis in fact

 

[Tube Radio]

But not quite as good as active crossovers and separate amplifiers for each driver.

I've experienced that myself.

 

[Grenadeslio]

But not quite as good as active crossovers and separate amplifiers for each driver.

I've experienced that myself.

agreed, passive with outboard amps and active crossovers are the endgame, and the norm in custom car audio. As I stated in the beginning of this thread, in the middle, and now at the end, I've been running every kind of sub setup for 5 decades, beginning with car audio back in the 70's.

There's more than one way to skin this cat.

Ciao

 

[Tube Radio]

Agreed.

I've had both passive and active crossovers and both can indeed sound good.

My big system which has two 12" subs two 12" midbass drivers and two Altec 811B horns is all actively amplified and sounds amazing.

My three smaller systems use passive crossovers and powered subs and they sound amazing as well.

I mainly prefer active amplification because there's so much more tuning that can be done to make them sound their best.

One of the three smaller systems is at work and it's not practical to go with multiple amps.

 

[GordonW]

passive crossovers seem to work just fine in speakers lol

again just subjective opinion with no basis in fact

I'm sorry- but it is readily possible to definitively measure the hysteresis, resistive losses, and saturation effects in large inductors- especially the metal-core ones that are usually required to do subwoofer frequencies,without breaking the bank.

It is also readily possible to measure the dissipation losses, hysteresis, and distortion caused by large value caps- usually electrolytic, to get the values needed for subwoofer frequencies.

All of these things act to change the waveform being fed to the woofer (a.k.a distortion and non-linear time delay effects)- never for the better.

This is something that ANY decent speaker builder or designer knows about, pretty much as an unavoidable part of speaker construction. It doesn't even take any real
research to find plenty of references to these effects. It's scientific fact, not subject to dispute.

https://www.electronics-tutorials.ws/electromagnetism/magnetic-hysteresis.html

https://www.sciencedirect.com/topics/engineering/dielectric-absorption

At their best- about the most that can be hoped, is for a passive subwoofer crossover to be as good as an equivalent arrangement of active crossover and amp, in terms of performance vs. cost. Usually, though, in the vast majority of cases- a passive subwoofer crossover will be built of components with all of the compromises mentioned just above- with all of the performance losses inherent thereof. In those cases, it is not hard at all to exceed their performance with active crossovers.

Regards,
Gordon.

 

[imral3]

 

[kfa888]

"Where necessary, the subwoofer will break that is urine: considerably leaning forward, like a sling diffuser produces a hefty bass kernel space."

That's been my experience with subs as well.

 

[spark1]

That's been my experience with subs as well.

Totally agree.

 

[kevintomb]

Lest anybody think speaker-level is "fringe audiophile" stuff -- and frankly I would mostly suspect that prior to having direct experience -- it's not fringe stuff. I discovered it by accident, long before I ever thought about or read about it sounding better because the sub signal matched the mains.

I had a small JVC executive system (all-in-one receiver/CD/speakers) -- it was a $500 mini system -- so it was fairly high quality for what it was, but definitely nothing like a high-end system. At the time I bought it, I didn't happen to have an RCA cable for the JVC sub output, so I begrudgingly connected the sub via speaker-level. I honestly felt pretty icky about using speaker-level because it seemed crude and I was certain it would be worse (especially since the JVC amp was not a powerhouse - I think 15-20wpc). Nonetheless, I was anxious to hear the system with the sub, and this was pre-amazon Prime one-day delivery for an RCA cable, so I just used speaker wires as a temporary solution. It sounded great.

I used it like that for about a year until I happened to have an RCA cable free, so I switched it to line level and was anxious to hear the results. It didn't sound as good. Specifically the sub sounded more isolated from the mains instead of being a seamless extension of the mains. I left it connected via line level for a while, tweaking the sub controls over a few days to try to get it to sound better, but then I just switched back to speaker level and left it that way. I thought it was an idiosyncrasy of that system, but I've found that to be the same experience with every 2-channnel system I have. It was only much later when reading an article that I understood how and why speaker-level can sound better than line-level it could possibly sound better -- I should have figured it out on my own, but it's pretty hard to even think about the possibility of speaker-level sounding better than line-level, so my brain never went there.

For 5.1/7.1 or mixed theater/music use, I always use LFE and never use speaker-level, but for 2-channel, speaker-level has always sounded more integrated in my systems. Everybody's mileage may vary -- I wouldn't dream of saying speaker-level is better for the general case -- I do encourage trying both and choose what works best in your system (and hopefully report back what you found in your testing so we can all benefit from your experience!).

It is VERY likely the speaker level outputs had active equalization. Almost all systems of that type do. So you were almost surely hearing the effects of the built in dynamic bass boost, and when using RCA outs, there was no active equalization, just the flat signal.

 

[fill35u]

Line level vs. speaker level doesn't inherently matter. The difference is a just a handful of resistors, and whichever is more convenient. What matters are the implications of using speaker-level:

1. High frequency noise should not be an issue. The subwoofer driver (should!) be mechanically incapable of reproducing those higher frequencies, and there's going to be an active or passive low-pass electronic/electrical filter somewhere in the sub chain. Subwoofers simply don't hiss. However, they might *hum*, and shielded or balanced line level connections might be more hum resistant than ordinary twin-lead speaker cable.

2. Speaker-level connection to the sub implies the mains are being run full range, which is usually stressful for them. If the mains are reproducing sub frequencies, they are almost certainly not *located* anywhere near optimally to do so. If speaker-level is being used to feed the sub, the only way the mains are *not* reproducing sub frequencies is if they have a passive high-pass filter. Which, at the frequencies involved, would be large, heavy, expensive, tricky to implement well, typically limited in slope, subject to overload at high power, and annoying to adjust.

3. Passing speaker-level to the sub immediately means that the sound from the mains cannot be delayed relative to that of the sub. So proper time alignment is not a possibility, unless the sub is located closer to the listener than the mains.

4. Using speaker-level connection *implies* that it's going directly into either a powered sub, most of which have only the most rudimentary tools for integration, or directly into a passive sub, which have *no* integration tools.

However, I don't buy that the transfer function of the upstream amp for the mains matters one bit, if it's competently designed for high fidelity. Sure, some archaic capacitor-coupled or (ahem, archaic) tube amps *might* have poor low bass response. The answer there is to not use them where they aren't capable, and to split off the sub signal *before* the incapable amp (i.e., don't use speaker-level). But for the vast majority of amps, any high pass filtering should have minimal response drop at 20Hz, and therefore minimal phase shift.

Frequency response of an upstream amp shouldn't matter, because you *should* have the tools in the sub chain to adjust the sub's response anyhow. The sub doesn't have flat anechoic response, let alone however it will perform in the room. If you don't have the tools to measure and adjust, well, thanks for playing...

Phase response of the upstream amp doesn't matter, because again, no sub has flat anechoic phase response, let alone how it performs in the room. Neither do the mains speakers it's integrating to. Any changes made to frequency response, by any means, will change the phase response (well, except FIR digital filters). Again, if you don't have the means to measure and adjust, thanks for playing...

Gain/level matching is trivial, either passive or active.

*Below* 20Hz is anybody's guess, there you really have to measure the entire chain. "Chasing the dragon" of ULF is a very expensive obsession, with every precious Hz lower won only by increasing effort, and with diminishing prevalence in source material.

The overwhelmingly important factors, for those going the quick, easy, simple, and cheap route (who don't want to measure, and/or lack tools to integrate):

1. The room
2. The capabilities (frequency response and distortion *at different volumes* ) of the sub(s)
3. The location of the sub(s) in the room
4. The location of the listener(s) in the room
5. The number of subs
6. Demands of the source material

Proper integration measurements and tools can make a vast difference. But they are what you use *after* you optimize the above.

 

[fill35u]

FWIW, I have eight 18" subwoofer drivers in my system, which integrate with the four 18" high-sensitivity woofers in my mains:

 

[kfa888]

much of what we base our decisions on in this hobby are theory, but which is the cleaner signal is not. whether we will hear the difference is subjective, I choose to err on the side of a cleaner signal, if others don't that's their choice.

And as you, I'm having fun spinning records on the theoretically superior design of my Well Tempered Lab Turntable lol.

You are so worried about a cleaner signal you will argue for pages about it and then spin records, one of the dirtiest and most destructive method of getting the music reproduced. Love it. Make sure your rumble filter is on, your records are brand new and you stylus is the best or... dirty signal!!!

 

[fill35u]

Make sure your rumble filter is on

That's an excellent point. I would think *any* rumble filter would exactly counter the effort to reproduce frequencies handled by subwoofers. And that the use of subwoofers at high volumes would preclude a turntable?
For those of you spinning vinyl, how do you resolve rumble with subwoofers? What type of rumble filtering/arm damping/turntable suspension works for you? Have you found volume limits before rumble feedback occurs?

 

[motorstereo]

For those of you spinning vinyl, how do you resolve rumble with subwoofers?

Spiking my sub cured that issue for me.

 

[Grenadeslio]

You are so worried about a cleaner signal you will argue for pages about it and then spin records, one of the dirtiest and most destructive method of getting the music reproduced. Love it. Make sure your rumble filter is on, your records are brand new and you stylus is the best or... dirty signal!!!

six weeks to come up with a response lol?

 

[Grenadeslio]

That's an excellent point. I would think *any* rumble filter would exactly counter the effort to reproduce frequencies handled by subwoofers. And that the use of subwoofers at high volumes would preclude a turntable?
For those of you spinning vinyl, how do you resolve rumble with subwoofers? What type of rumble filtering/arm damping/turntable suspension works for you? Have you found volume limits before rumble feedback occurs?

Absolutely no issues running a turntable with subs, been doing it for decades, no rumble filter applied either.

There was a time when one of my tables wasn't optimally located in one room and some acoustic feedback had to be dealt with, but no subs with that system at the time.

The issue was only at high volume, once the cure was in place....



This reading was taken with a record as the source.

 

[fill35u]

Absolutely no issues running a turntable with subs, been doing it for decades, no rumble filter applied either.

Thanks for the info! Some more questions, if you don't mind:

What record/song were you playing when you took that dB reading?

Have you found any rolloff at the lowest frequencies, through the overall turntable/preamp chain? Have you measured for it?

What do you use as a test record? Does it have tones down to 20Hz or below? Are they cut at reference level?

 

[peterp1]

It is VERY likely the speaker level outputs had active equalization. Almost all systems of that type do. So you were almost surely hearing the effects of the built in dynamic bass boost, and when using RCA outs, there was no active equalization, just the flat signal.

That's a good point and very possible for my JVC example because the amp and speakers in "all-in-one" systems can have built-in EQ to compensate for what are always bass-challenged mains, but it's not the case for any of my other systems using speaker-level -- those are analog 2-channel only with no active EQ.

Again, I would never recommend speaker-wire for theater use, but I prefer speaker-level for analog 2-channel in my direct experience. I only recommend that people try both (for 2-channel only) and determine what works for them.

For those who believe that all amps sound the same, its easy to see why they also believe speaker-level can't have any benefit. For those that don't believe all amps sound the same, they don't really have a leg to stand on to say the using speaker-level can't be beneficial (<- that doesn't mean it "will" be beneficial, it only means the amp can make a difference in how the sub sounds when connected by speaker wire). There are no "absolutes" about which is better -- that will depend on individual room acoustics, the specific system components used, and the types of music played (e.g. techno with ULF content vs jazz). The best approach is to try both for 2-channel, and stick with the one you prefer (and report back so we all benefit from your experience! ).