High pass filter for mains... or not?

[PingWine]

Before I start I wanna say that I love this site! I have been trying to find objective discussions about audio for a good while and you seem one of the most competent people who actually follow research and don't blindly follow the masses. I really hope you don't mind me "spamming" threads now that I can actually have meaningful discussions rather than having some delusional audiophile recommending expensive power cables...

Now that out of the way my question is about subwoofer integration. The general way of doing it seems to be to have a crossover somewhere near 80Hz-120Hz. The reasoning behind this is that the mains now have more dynamic headroom as they don't need to push out all that bass.

I, for a long time, thought that of course this is the way until I saw the presentation by AV NIRVANA on how "you should excite as many modes as possible" and that includes having mains with no high pass.

Now I'm left pretty clueless as to which advice to follow. The first one seems logical for higher SPL as the "excite as many modes as possible" seems logical for more smooth and uniform bass response.

 

[DonH56]

I would not run the mains full-range but opinions vary. Below is what I wrote years ago about the advantages of subs.

HTH - Don

I use subs, and have for decades, for all the usual reasons:

- Very (perhaps extremely) few "large" speakers actually play well below 40 Hz let alone 20 Hz. They distort heavily when presented with large bass signals (which most are -- see Fletcher-Munson) and driving them down low robs headroom for higher frequencies and causes distortion well above the fundamental signal frequency (harmonic and nasty intermodulation). Subs typically enable the mains to operate with much lower distortion.

- Very rare is the room setup such that the best place for stereo imaging and soundfield is the best place for the subs (or deep bass drivers) to counter room modes and such. Having independent subs provides placement options to smooth the in-room response. It is almost impossible to counter a null without subs (typically must move the MLP or change the room's dimensions though there are purpose-built panels that can also work). This is one of the things that led me to subs despite having quite capable mains.

- Powered subs offload the main amplifiers of the need to provide deep bass energy, providing more headroom and cleaner sound from the amplifiers.

- Music (let alone action movies) often contains deep bass content even if it is not real obvious. Kick drums, tympani, organ, sure, but also piano hammer strikes, plucked strings, beat patterns from instruments playing together, etc. May not really notice when they are there but usually obvious when they are taken away. Having subs fill in the bottom octave or three can make a difference.

- Purpose-built subs can provide high output cleanly at relatively low cost. The amplifiers and drivers need only cover a fairly limited frequency range so have fewer constraints upon them than woofers in a full-range system.

I do prefer main speakers with fairly deep bass and always have. Crossovers are not brick walls so a fair amount of energy still comes from the mains an octave below the crossover frequency. Higher-order crossovers allow you to reduce the overlap, but I still like having the capability. I have never really understood the idea of running "passive" bi-amping as implemented by an AVR (sending full-range signals to multiple channels and letting the speaker's crossovers separate frequency bands -- wastes amplifier headroom and seems to me of little benefit). Nor do I agree with the "plus" setting putting subs and mains in parallel; again, my idea has always been to isolate the two for the reasons above.

My first sub was a DIY design using an Infinity IRS woofer with my own control box to provide the crossover and a servo circuit using the second voice coil of the woofer. I had a Hafler DH-220 around so also incorporated a circuit to bridge it for use as a subwoofer amp. It worked well and the -3 dB point was ~16 Hz. I now run four small (F12) Rythmik subs using a similar (but updated) servo design with my Revel Salon2's and am happy with the result.

FWIWFM/IME/IMO/my 0.000001 cent (microcent) - Don

 

[Jon AA]

I, for a long time, thought that of course this is the way until I saw the presentation by AV NIRVANA on how "you should excite as many modes as possible" and that includes having mains with no high pass.

That's a very legit way of doing it. In my opinion the "proper" way to integrate subs is so room and setup dependent, I think any generalizations or telling people they're doing it "wrong," is misplaced without a ton of information about their setup. The exception (a pretty big one though) is for lower information users that don't have measuring equipment, EQ ability, etc. For those cases I say sure, cross them at 80 and hope for the best.

 

[RayDunzl]

There's a similar discussion recently: https://www.audiosciencereview.com/...r-lower-the-needed-power-for-a-speaker.13779/

My conclusion: The speaker driver may be relieved of bass load but the high-passed amplifier may see an (unexpected) increased peak signal demand.

 

[MickeyBoy]

Matt Poes has written that he usually runs his main speakers full range.

I think the question really amounts to what high-pass should we use for the mains? (1) Their natural one - running them wide open. Archimago has written that he added a small second sub that made a big difference. Why couldn't the mains in some situations do the same? (2) Or a high-pass filter that can be tuned from null up to the point where the subs' low-pass kicks in. Even an overlap from 60-80 Hz might be helpful. As in my situation with a killer 60-65 dip.

 

[pjug]

I run main speakers full range and just LP filter subs, but that's mostly because I don't have an active crossover. A lot of powered subs have a built-in passive crossover. I always assumed it would be a bad idea to drive main speakers through an extra passive filter. Whenever I see these discussions I think it is assumed that crossover would be active, but I think it is helpful to be clear what kind of crossover is used.

 

[RayDunzl]

I run main speakers full range and just LP filter subs, but that's mostly because I don't have an active crossover.

Me too (well, I don't have a crossover set up).

But my mains go lower than the subs, so that is a consideration.

My experiment is with cheap subs (4) that permits a 9dB drop in signal for each bass driver (as compared to a single bass driver on each side) while achieving the same SPL as an experiment in reducing low frequency distortion.

It does sound nice and full and differentiated down low, so I'm satisfied.

 

[Sal1950]

I think you'll find a lot of good arguments on both sides.
IMO, it depends on how capable your mains are, how deep they go.
If your running stand mounts with 5-8" woofers I believe that's an automatic choice to run a LPF
If you had some monsters with 1 or 2 12" woofers and are reasonably flat down to 40hz or lower you might start thinking about full range.
Since the end results have so many variables I'm afraid the only solid answer is to do some in-room measurements and try things both ways
looking at main speaker distortion levels and the severity of the room modes.. Then decide which compromise gives the best results of your needs.
I just switched from standmounts for reasonably capable mains and haven't even began to try and work things out.
With the stands I rolled them off at 80hz and use dual subs in radically differnet positions to try and level thing out, then DRC to get them a bit better yet.

 

[aarons915]

A lot of good points and IMO it depends on how capable your mains are but I also think whatever your crossover point, all your speakers should be set to the same so that the bass sounds identical in all channels. Many people make the mistake of crossing their large mains over at 40-60Hz when the center and surrounds need an 80Hz crossover, for example. I think all speakers should be crossed over at the highest frequency of the least capable speaker so that the bass is seamless across all channels.

Wanted to add that people like me with smaller mains (LS50) want to keep as much bass out of our mains as possible to reduce distortion and play loud cleanly so that just reiterates the importance of your mains when making the decision on your crossover point.

 

[richard12511]

I disagree with Matthew here, and I usually agree with him. He's a lot more knowledgeable than me, though, so maybe ignore me

The first one seems logical for higher SPL

This is probably true. You're gonna be listening to much less distortion this way, though it's arguable how important distortion really is in the bass. Very few mains are truly full range. I wouldn't consider Matthew's mains (Geddes Abbey) to be full range speakers. My 170lb tower speakers are certainly not full range. @DonH56 's Salon 2s are very close to full range, though they still only have a -6 of 23Hz, and can play much louder when not run full range. Maybe something like the JTR 215RT that has 2 15" woofers in a 6ft tall box? Even still, you're limiting its headroom by running it full range.

as the "excite as many modes as possible" seems logical for more smooth and uniform bass response.

This can be true, but is most often false(ime) due to the placement of the mains/subs, and inability of the user to get them properly integrated. For the second point to be true, you really have to know what you're doing, have the right tools, and have the right room/placement options.

I have a minidsp 2x4hd that I can use to independently adjust sub delays, and I have 100% placement flexibility(live alone in a big house and don't care about aesthetics). I spent 100+ hours moving things around, adjusting phase, making tiny delay adjustments on both subs, and still I was unable to get a smoother response by running my mains full range. No matter what I did, trying to run my mains full range messed up my smooth frequency response by adding 1 or 2 extra nulls. That was the measurement part, but it also sounds horrible in comparison when I switch them to full range.

So yes, it might be true, but you've gotta have the right situation(I don't), and you really gotta know what you're doing.

My advice would be to (if you haven't already) get a mic, install Room EQ Wizard, and measure it both ways. Spend time playing with placement and delay and see if you can get a smoother response by running your mains full range. Nothing to lose by trying, and maybe potential for gains. If you can get a smoother response, then you can weigh that against the advantages of high passing them and decide what you want.

Also, be sure to listen and see which way sounds better.

Also also, play around with listening to (and measuring) various crossover points to find the optimal crossover.


Finally, @Matthew J Poes is a member here, so maybe he can give you some more insight. Heck, he might convince me to give it another go

 

[Jon AA]

Many people make the mistake of crossing their large mains over at 40-60Hz when the center and surrounds need an 80Hz crossover, for example. I think all speakers should be crossed over at the highest frequency of the least capable speaker so that the bass is seamless across all channels.

I disagree with that. I do agree many do it improperly though--boosting the sub to provide the "Harman preferred" rise in the base, which may sound great with mains crossed at 80, but completely bloated for surrounds or center crossed at 120 (for example). When done correctly (every speaker including the subs following the same target curve at low frequencies before the crossover is applied) such that the bass managed response of each speaker is the same, bass should sound seamless for all channels.

 

[aarons915]

I disagree with that. I do agree many do it improperly though--boosting the sub to provide the "Harman preferred" rise in the base, which may sound great with mains crossed at 80, but completely bloated for surrounds or center crossed at 120 (for example). When done correctly (every speaker including the subs following the same target curve at low frequencies before the crossover is applied) such that the bass managed response of each speaker is the same, bass should sound seamless for all channels.

The target curve should definitely be the same but what I'm saying is if you crossover your mains at 40-60Hz and your surrounds at 80-100Hz, it's very unlikely that the bass is going to sound the same since your mains will be playing 40-80 and the subs will take care of that range in the surrounds. There is also no point in going under 80 regardless of your mains capabilities in my opinion, since it isn't localizable anyway. Of course this is a 1st world problem anyway and doesn't really matter if you know what you're doing but theorycrafting is always fun.

 

[DonH56]

My mains are reasonably capable in the bass region but crossing them over higher allows me to place the subs to manage room modes. Dr. Toole has the same mains and also chose to cross them over at 80 Hz so I feel I am in decent company.

I do't see why a crossover would "unexpectedly" raise power above the crossover -- at worst it should stay the same, but in general will be lower power in the mains with subs crossed over to carry the deep bass.

 

[Sal1950]

My mains are reasonably capable in the bass region but crossing them over higher allows me to place the subs to manage room modes. Dr. Toole has the same mains and also chose to cross them over at 80 Hz so I feel I am in decent company.

Thanks Don, I was wondering where to start with my new JBL's

 

[Slare]

Subjective or not I prefer 60hz when my fronts are capable towers in an ht setup. But I also prefer straight 2.0 for music. My mains have 14” low end drivers and I also have capable 15” subs. Regardless of how well I get my subs tuned I still prefer 2.0 for music in my room. I’m sure the room interactions have a lot to do with it but things like kick drums just never sound quite as clean to me from big subs handling everything below 80hz. I’ve debugged this room after room, with sub after sub, and AVR upgrades with these fronts and always end up feeling the same way.

Only exception would be for very bass heavy music at high volumes, like for a party. And I‘m sure I wouldn’t have the same opinion with weaker fronts. Systems with the subs above 80hz drive me crazy as well. I think I just naturally prefer things flat in that ~100hz zone. Back in the old school eq days that 100 or 150hz slider was always a couple db down.

 

[richard12511]

My mains are reasonably capable in the bass region

I'd say they're more than "reasonably capable" One of the few speakers(that I know of) that I'd consider close to truly full range.

but crossing them over higher allows me to place the subs to manage room modes. Dr. Toole has the same mains and also chose to cross them over at 80 Hz so I feel I am in decent company.

This has been my experience. It might be possible to have "better" bass with full range mains, but it's incredible hard not to make it sound worse(unless you don't care about imaging/soundstage).

@PingWine , really the best thing you can do is to measure and try both and see which you like better. Can't stress that enough. It really, really depends on your room, so there's no true answer to your question. I would say high passed is usually smoother and better for output, and that's what Floyd Toole uses(who has Salon 2s), but it's not always the case.

Also, don't underestimate playing around with the crossover. A lot of people just default to the 80Hz default, or go lower because they have big mains and think it will be better, but that's a huge mistake, imo. Crossover should be set based on what measures and sounds best in your room, not by how big the woofers in your mains are. Crossover can have a huge impact on the overall sound quality. My friends and I setup a blind test to find the best crossover for my room, and it was one of the easiest blinds I've ever done. Everyone agreed that

120Hz = 100Hz >>>>>> 80Hz >> 60Hz > 40Hz = Full Range

120Hz actually measured slightly better than 100Hz, but none of us could hear the difference, so I just went with 100Hz. It will be different for your room, but you wont know until you try.

 

[richard12511]

Subjective or not I prefer 60hz when my fronts are capable towers in an ht setup. But I also prefer straight 2.0 for music. My mains have 14” low end drivers and I also have capable 15” subs. Regardless of how well I get my subs tuned I still prefer 2.0 for music in my room. I’m sure the room interactions have a lot to do with it but things like kick drums just never sound quite as clean to me from big subs handling everything below 80hz. I’ve debugged this room after room, with sub after sub, and AVR upgrades with these fronts and always end up feeling the same way.

This could be a time alignment issue. I recommended a couple PSA subs for a friend, and he ended up not liking them for music either, and I agreed with him when I heard it. It ended up being a time alignment issue. The bass from the mains and subs were hitting at slightly different times, which was smearing the bass notes, making them sound less "tight". We fixed it by adding a minidsp 2x4hd(super cheap). If you're not already using something like that, you may wanna try it. Not a huge loss if it doesn't work(you still have 14" mains ), and it has the potential for huge gains.

Systems with the subs above 80hz drive me crazy as well.

You would hate mine, I use 100Hz for my crossover(and sometimes 120Hz)

I think I just naturally prefer things flat in that ~100hz zone.

No reason why subs should be less flat in the ~100Hz. If anything, they'll generally be more flat, as they have more placement flexibility. In that frequency range, you're not even really hearing your speakers, you're hearing your room, so placement flexibility is paramount.

 

[AudioJester]

Are there any measurements to support the theory that full range mains will perform "better" with a high pass filter?

 

[richard12511]

Are there any measurements to support the theory that full range mains will perform "better" with a high pass filter?

It depends so much on the room that I imagine it would be difficult to provide data that could apply to any one individual's own room. I could show you my measurements, but it wouldn't mean that a high pass would work better in your room.

Maybe if you get enough people to post both their with and without high pass measurements, maybe you could start to give some sort of generalized probability? It would be tough.

 

[AudioJester]

So is the concept based on uproven theory? Subjective corroboation?
Curious to see how it works.

I have always run the mains full range with subs - assuming the multiple bass source theory. Maybe I am doing it wrong.