Members Anderton Posted October 10, 2015 Members Share Posted October 10, 2015 I was talking to a musician friend who's very knowledgeable about live sound. We were discussing subwoofers and he said a lot of engineers think they need to reproduce frequencies below 60 Hz, but all the lower frequencies really do is suck huge amount of power with questionable benefits. He mentioned playing a club that had a modest PA system but which he felt had the most kick-ass sound he'd ever heard. The guy doing the mixing said that he set his highpass filter around 80 Hz. Now, I realize if you're running a techno club the constraints would be different compared to running sound for a bluegrass quartet, so there's no "one size fits all" highpass frequency. But I'd love to hear some comments on what y'all use as your pet highpass filter frequency... Link to comment Share on other sites More sharing options...
Members dboomer Posted October 10, 2015 Members Share Posted October 10, 2015 Interesting topic! So first let me say I am more or less in agreement with your guy. The devil is in the details of course. So so first we have to agree that all filters are not the same. There are different rates of cutoff (slopes) to consider. For live sound 3rd or 4th order filters 18-24 dB/Oct) perform the best. If you use filters with less slope (6-12 dB/oct) then the turnaround number will need to be higher (so 60Hz needs to become 100-120 Hz). If you use higher degree filters (48 dB/oct) you probably actually start adding power back in due to filter ripple. As as I see it there are two major factors to consider ... Sound quality and system protection. If you are rich and have a system that is 10 times bigger than you ever use then you can go for sound quality as your first priority. But in the real world those systems are scarce. The higher you can cut off, the safer and cleaner your system will be. Hopefully you have all the system you need and your choice will be a compromise between these two factors. All things being equal (and there never are in a good way here) it takes 4x the power to reproduce a tone an octave lower so getting down to 40 from 80 requires 4x the amplifier and 4x the excursion of your LF driver. In the real world it takes even more as the losses start adding up quickly down in this range. So so what sounds better? That depends on how you judge sound quality. Most people greatly mis-judge the importance of extreme low frequencies. Yes, a bass guitar's lowest fundamental is 42 Hz ... But ... Most of the sound that you judge an electric bass by is the second harmonic. So even in a "perfect" system, 80Hz is more important than 40 Hz. So a system with 40Hz down 6-10 dB from 80 Hz probably sounds good to most people. I believe it was Doug Fowler over on PSW that did a survey of big concert systems and found that the new standard for huge EDM systems was in the mid 40's and about 10 Hz higher for typical live band systems. So so in my personal opinion, yes there may be material way down low. But reproducing it usually just clouds up everything else. Again, the details matter. One other factor to mention. A lot depends on the venue you are trying to do this in. If you are indoors you will have standing waves and the level of a perfect system at 40 Hz can vary over 30 dB in level every 3-5 feet if the shortest dimension in your room is less than 25 feet ( usually your ceiling height). There is no way to even this out with EQ. Back when I used to do live sound trainings for Peavey (in a room that would hold about 200 people) we used to play a 40 Hz sine wave and then ask the class as we switched to a 50 Hz sine wave if the sound got louder. About half the class would hear it as louder and about half the class would hear it as lower even though the power was identical. That happened because the nodes of the standing wave moved with frequency. Link to comment Share on other sites More sharing options...
Members Pro Sound Guy Posted October 10, 2015 Members Share Posted October 10, 2015 The guy set his high pass at 80hz with how many subs? With several high quality dual 18" boxes on each side I could see 80hz working ok. Doesnt it depend on the subs and how many, and the space? When you couple subs together the low sub bass frequency increases in output. With one 18" box per side I would not see an 80hz hp that working great. Running a live act is different then running DJ stuff. I use the manufacturer suggested high pass for my subs. HPF=35hz at 24db per octave butterworth/LPF = 24db per octave Linkwitz Riley EAW dual 15" boxes EAW single 18" boxes I use a 30hz HPF Linkwitz Riley. For the bigger shows I run the dual 15s as kick bins and the Single EAW 18s center clustered LPF @ 80hz/24db per octave and HPF@ 30hz @ 24db per octave Link to comment Share on other sites More sharing options...
Members agedhorse Posted October 10, 2015 Members Share Posted October 10, 2015 Most of the time, I tend to set my system high pass filters so the electrical -3dB point is the same as the speaker's -10dB point provided there is plenty of rig for the gig. On the other side of it, I may set the electrical -3dB point to the speaker's -3dB point if there's danger of needing more than the PA can deliver safely. Then there's the whole range of in between. I also tend to use a 4th order Butterworth alignment because I want the corner to be well defined and transition into the slope sharply but smoothly. I am also involved more with the pro level market than the non-pro markets. When designing bass amps, I have to consider the class of speakers than may be used with the amp in general, and for products primarily being used with smaller cabinets (higher tunings) I will look at something between 32 and 40Hz. For larger amps designed to be used with larger or more robust cabinets, I will drop the HPF down between 27 and 35Hz, again 4th order Butterworth. I am also well versed in dynamics control approaches under high level low frequency conditions. The answer is "it depends". Link to comment Share on other sites More sharing options...
Members dboomer Posted October 11, 2015 Members Share Posted October 11, 2015 On the other side of it' date=' I may set the electrical -3dB point to the speaker's -3dB point if there's danger of needing more than the PA can deliver safely. .[/quote'] Thanks Andy, I meant to expand on that in my post. This is a good safety practice for those that want to keep the system safe. In my opinion setting the HP filter below this is the leading cause of woofer failure in systems and is way more critical than 2-4x overpowering in the midband. Speakers can usually handle short term overpowering without any harm. Remember the speaker power testing is continuous for multiple hours. But exceeding the mechanical limits of the speaker (making the cone move too far) by introducing a frequency that is too low can wipe one out in a fraction of a second. Remember the speaker's rating is only if you stay in its range and very very quickly falls off once you go beneath it. Link to comment Share on other sites More sharing options...
Members Pro Sound Guy Posted October 11, 2015 Members Share Posted October 11, 2015 I remember Pink Floyds sub bass live well below 60hz to be a wonderful experience. Link to comment Share on other sites More sharing options...
Members Anderton Posted October 11, 2015 Author Members Share Posted October 11, 2015 Great comments, thanks. Glad I asked Link to comment Share on other sites More sharing options...
Members OneEng Posted October 12, 2015 Members Share Posted October 12, 2015 Lots of speaker specs focus on the -10db points .... which is a little misleading IMO, but hey, you have to play the game I guess. If you look at the -3db point on most bar rig subs, it is around 35-40Hz. Keep in mind that this doesn't mean that the speaker CAN'T produce anything lower, it just means it takes quite a bit more power to do it. When I still used passive subs and my own power amp for my subs, I always set a 50Hz HPF. I found that this not only cleaned up the bottom end, but also kept me out of the red on my sub amp as well. For music that depends on a big kick, I would be hesitant to put the HPF as high as 80Hz. To me, there is a feel to a good kick that gets lost if you pull out the lowest frequencies. YMMV. Today, I just run straight into my JBL 618S-XLF's directly off the mixer without any HPF in the mixer output. I guess my assumption is that the fine boys and girls at JBL have protected me from my own stupidity and put the appropriate HPF and limiter in place accordingly Link to comment Share on other sites More sharing options...
Members agedhorse Posted October 12, 2015 Members Share Posted October 12, 2015 Selection of a particular HPF also depends on who's responsible for the damage. For example, if warranty issues might come up, being more conservative may be a better idea. Link to comment Share on other sites More sharing options...
Members vaughn4380 Posted October 13, 2015 Members Share Posted October 13, 2015 I use high quality self-powered speakers with built in processing so I don't have to think about this stuff. Guys like Aged have already programmed the filters to keep guys like me from damaging anything. Link to comment Share on other sites More sharing options...
Members RoadRanger Posted October 16, 2015 Members Share Posted October 16, 2015 The guy doing the mixing said that he set his highpass filter around 80 Hz.Are you sure he was talking about the high pass on the subs? I've seen rigs where 80 Hz was the highpass on the tops. All my subs start to roll off at ~50 Hz so I normally high pass them at 45 Hz when I need to push them pretty hard to keep up with my tops. If they're not being pushed hard I might drop that to 40 Hz. Link to comment Share on other sites More sharing options...
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