I'm going to be adding a sub next week and was wondering if anyone has had experience with high-passing their monitors with a passive filter? I understand the theoretical benefits, but am looking for opinions based on personal experience. My Harbeths go down to about 50Hz and the filter begins at 85Hz. Would be driven by a MC275IV.
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Passive High-Pass Filter with Monitors?
- Thread starter Bill C
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william.keith
Super Member
Bi-amping monitors provides a significant sonic advantage. I have written much herein as has others. An electronic filter is much better than a passive filter.
Could you explain why an electronic filter would be better than a passive? Also, are there any you would recommend? thanks,
-Bill
I ran my Harbeth C7 ES3 full range and crossed over the sub using its internal crossover at about 45 Hz. Sub is an ACI Force XL. I think that while theoretically the high pass route makes sense, in practice it's a little more tricky. Matching Q, phase ambiguities, interface considerations for additional cable, raising the noise floor, are all potentially introduced into the system. Running the Monitor 30s full range should not be an issue at all.
The trick with a sub is for it to be unobtrusive sonically. Most people tend to turn it up too high. When you think you have it dialed in, back it off a smidge. Anyway, the main point I'd make is that with the C7s in my fairly small room the sub probably wasn't all that necessary, but it was nice having that extra horsepower down low for movies and bass heavy music. There were more than a few times when I forgot to power the sub back on after electrical storms here in FL and I'd go days before realizing it wasn't even on.
william.keith
Super Member
Bill, a question. By passive, I assume you mean that the sub does not have it's own amp/preamp section? In other words, your main amp will power both the monitors and sub? And you plan to run the monitors full-range?
Sorry for the confusion. The sub is powered. (ACI Force XL). ACI offers passive filters to go between the preamp and amp so that you can relieve the amp of low frequency duty as well as the speakers.
Love it! It's a great fit in my room, 13'5"x18'8"x8'. I toyed with getting another one to have stereo subs, but using ACIs test disc I can rattle the windows and door in here pretty easily
Used it with Harbeth C7s for about 7 months (using Magnepan 3.6 now), based on that experience I'd say you're in for some good sound with your M30s. One thing that is really cool is the C45 preamp has a separate 2channel sub output and I can control that level right from the remote. So no bouncing back and forth to the sub in the corner to adjust level just right for any given movie. I can be a lazy slug and adjust it right from the listening chair.Have nothing but good things to say about ACIs customer service. I've actually used the ACI owner discount on DH Labs cables several times. One time I ordered some interconnects and they were drop shipped from the DH Labs factory on the east coast of FL and I received them by UPS the next day!
william.keith
Super Member
Setting the hi-pass filter at say 80Hz on a powered sub increases the power handling and efficiency of the main amp and reduces distortion in the main speakers.
A powered sublike the Force XL uses an integrated low pass filter (it does also have a HP filter but even ACI recommends against using it). The connection to the sub is via low level line connections, in this case a full bandwidth line output from the C45 or other model pre, in parallel with the signal going to the main amp and speakers. In this configuration there is no bandwidth limiting of the power amp or main speakers.
Inline HP filters or an external crossover between the pre and main amp are how you'd achieve BW limiting. But I still question the overall benefit of inline HP filtering, I think there is a real potential there for causing more problems than you'd solve. Especially with high power amps like Mac and full range speakers that are designed to go down to the low 30s or high 20s. I think you'd get a better integrated and more cohesive signal running full range, at least that has been my experience. Using an external active crossover is a different approach entirely, implying bi or triple amping.
As for those subs that do have a built in high pass filter I just don't see it making sense to run long interconnects to the sub from the preamp, go through what is probably a pretty low performance crossover/filter circuit, then run long interconnects back to the power amp. Way to many added variables and opportunities for noise and other impacts on the signal.
My intent with a sub was to augment low freq extension of my Maggies (and Harbeths when i used them) while running them full range. The key consideration for me was musicality, not sound effects for movies. A long time went into dialing in the sub just so, especially given the flexibility of the ACI LP filters. I've found that once I got them set right I haven't fooled with them except for boosting the sub output level occasionally for movies via the C45 controls. A sub is defintiley one of those things where there can be too much of a good thing.
william.keith
Super Member
I obviously take a totally different position. The electronics in a McIntosh powered sub are the same quality as separates. A sub powered with it's own amp is optimized to produce low bass better than a large 3-way floor standing speaker and certainly better than a 2-way stand mounted speaker. By using a hi-pass filter, the main amp only has to provide power at say 80Hz and up. Therefore, the amp is much more efficient and runs cooler since most amp power is used to produce low signals. In addition, smaller power amps such as the MC275IV can produce higher SPL levels if desired. The added benefit is that small (6-7") mid-woofers used in 2-way stand mounted speakers do not experience nearly as much harmonic distortion trying to produce signals as low as 30-50HZ and as high as 1.2-1.5kHz, all at the same time. As a result, sound is cleaner and more natural.
You're free to visit and listen to my system anytime.
william.keith
Super Member
You have a very nice system. You should be very pleased. I am also very pleased with my all McIntosh system utilizing a pair of LS320 mains and PS112 subs hi-passed at 80Hz.
If you get the ACI sub they also sell aat a discount DH Labs cables. They make some subwoofer specific RCA interconnects, I can't remember the name but the info is on the ACI site. I've actually been pretty impressed with DH Labs cables, have used both interconnects and speaker cables from them. A lot of folks here also recommend Guerrilla, they are an AK sponsor and there should be a link at the bottom of the page.
The most important benefit of electronic filter (active crossover) over passive is that it devides the audio frequencies ahead of the amplification stage at a low signal domain. The passive crossover does the same but after amplification stage.
Dividing the signal ahead of the amplification has considerable benefits, the most significant is the use of dedicated amps for specific frequencies meaning huge gain in system efficiency and headroom along with considerable reduction in distortion at higher volumes.
Vahe