Official Rythmik Audio Subwoofer thread - Page 7

Thanks Brian -- making me think, hurts! Too long since my grad acoustics classes...

The LF corner (per Magnepan) is around 35 Hz, but you are relating the shift to the baffle size rather than the LF corner (curious, I am trying to learn this stuff)? Makes some sense to me. I was planning to run the subs in parallel with the main amp (not using the AVR's sub output) and cross over ~40 Hz, around the Maggie's LF corner, with the steep roll-off (to limit bleed into the mains), and then check the response. I started on that today but got sidetracked and haven't finished yet. And, I really wish I had an audio VNA to generate phase! With a sweeper, natch, instead of test tones, an SPL meter, and hand recording. My old (old, old) cheapie handheld SA is not sensitive enough. All I can do now is play with the amplitude, a relatively hit-and-miss proposition.

My general plan was/is to test the sub around 25 - 30 Hz and match the amplitude to the mains at some midband frequency, maybe 400 Hz. That is, match the amplitude where the mains are fairly rolled off to the amplitude of the mains in their lower midband. Then, measure at the crossover point (around 40 Hz) and adjust the delay to match amplitudes at that point. Pretty rough, but all I've thought of for the moment. I value your advice as a sanity check on where the delay ends up.

I also need to revisit the inversion. The AVR (a Sony 3400ES) simply said the mains were "inverted" during its cal cycle and suggested I flip the speaker wires to correct (I did and got rid of the warning.) The AVR could well be reading them wrong (due to the reflections etc.), or the amp could be inverting (have not checked). I assumed a true inversion, not a 180 phase shift, thanks for keeping me honest! The amplitude rises pretty monotonically as I increase the delay, making me suspect the AVR lied and I need to flip the wires back.

I have also picked up some noise/hum, probably due to the extra 10' lines from the splitter hanging on the back of the AVR now (one set to the mains, the other to the subs). It might be unrelated, e.g. it's been there and I haven't noticed before. Turning the subs on and off has a slight impact but they are clearly not the cause. I may have to get better-shielded cable than the $10 Radio Shack specials I was able to scrounge today. I also need to revisit the rat's nest behind the AVR and pay more attention to cable dressage -- stereo was a lot simpler, and I didn't have digital and video feeds running around the audio cables!

My experience in the primordial past was that spiking the mains sometimes helped, but had virtually no impact on the sub, probably due to its limited bandwidth. I was curious as to your thoughts, thank you!

The good news is that even with the very limited testing I have done so far your subs (mine now!) blow away the Infinity PS212 I had been using since my old servo sub died, and do indeed seem to match well with the Magnepans, speakers traditionally very intolerant of lesser subs. Hopefully I'll be able to dial things in tomorrow.

Thanks again,
Don

The Rythmik website curreently lists the D15SE sub as being on back order, with a reference to the A370PEQ2 amp. Is this a new amp? If so, what's different?

Its actually been discussed in some detail within this thread in a couple of different postings... go back and read posting #122 in this thread, you should find it helpful.

Still hoping to get an answer between the F12 or F15. I even left a message for Brian but no return call.

Which would be the best size for a 22' L x 13' W x 10' H (Average since it is peaked) which equals 2,860 cubic foot sealed room with one doorway.

I am 100% HT and presently using two REL Storm III subs. They have a 10" Driver with a 150 W to 300W peak amp. As you can see in the attached picture I now have them co-located. This is the best spot in the room at present.

I can have it fire the short width of the room adjacent to the couch end or fire from the corner towards the couch.

Would like to have one sub in the corner if possible.

Well I had a single F12 in a sealed ~2200Cu-ft room for a short while this past summer and found it more than capable of pressurizing the room for movies... since then I've purchased another F12 and am now running duals (one on each side of the room). The F15 will provide at least another 3dB over the F12 so you really couldn't go wrong since the price difference is really quite minimal. If you want my opinion, I would suggest you go with the F15 if you intend to cross over below 80Hz... if you are intending to cross higher, I would suggest you continue to seek Brian's input... but might want to consider two F12s (w/ GR drivers).

My two cents, especially given you are using it for home theater, the 15" is a no brainer given the small additional cost.

The Storm V when tested by Ilkka was putting out 96 db at 40 hz, 92 db at 30hz, and 85 db at 20 hz. So using two co-located would give 102 db at 40hz, 98 db at 30hz, and 91 db at 20hz. The 12" Rythmik sub tested in the same manner by Ilkka gave 105 db at 40hz, 104db at 30hz, and 96 db at 20 hz. By going with the Rythmik 12" you will see anywhere from a 3-6db increase in output capability over you current setup (same as buying two more REL Storm's). This is a decent increase and probably fine if you were never stressing the output of the REL's. Going to the 15" will give you another 3-5 db's across the board (more than 6 dbs over your current system as as much as 12 db), a nice increase in headroom for home theater.

Apparently with the new PEQ2 amps, crossing over higher than 80hz isn't a problem.

The difference in the PEQ2 amp is in an earlier post:
http://www.avsforum.com/avs-vb/showt...6#post18215646

I wish to thank you for such a great response.

This helps me tremendously in my decision.

A quick follow-up to my posts after installing and a little listening to audio and video today, fwiwfm:

1. Calibrating with a test CD and SPL meter is painfully slow but revealing. Among the things revealed are that I need to get going on room treatment...

2. Putting the two 12" subs in parallel with my main speakers works just fine and the AVR appears to handle the set-up OK (I am not using the AVR's sub output, but tapping off the preamp outputs so the subs are driven as a stereo pair in parallel with the main L/R speakers). Except that...

3. I still have a bit of hum/noise that I think is cable-related. I have fairly long (10') cables from the AVR to the main L/R power amp, and another pair of long cables to the subwoofers. Line dress helped some but I am going to have to work on it a bit more. I did prove it is not the subwoofers themselves. Blue Jeans Cable is in my future...

4. Using the two Rythmik subs absolutely blows away the relatively inexpensive Infinity 12" sub I was using. The image is much better now, the bass deeper and much cleaner, and even after AVR cal (which ran the Infinity a little too "hot" for me) the sound is clean and the subs do not sound like separate speakers. The blend with my Maggies is very good, no mean feat. It has confirmed my long-ago experience that two subs are far better than one.

5. I tried flipping the limiter on and off and am not sure I ever heard a difference at moderate to fairly loud levels on a variety of musical source material. I meant to do it on the video, but got lost in the movie...

Bottom line: These subs are incredible! Having had good subwoofers in the past (commercial and custom) I knew my Infinity sub, while good enough paired with Infinity mains, was not working that great with my Magnepans. I was not prepared for just how much better the Rythmik subs sounded, and how large a jump in performance my whole system would take. I still have some tweaking to do, but I am very impressed. Kudos, Brian!

System:

Sony BDP350 BluRay player (CDs and BD; I have an Oppo 83 sitting in a box ready for installation)
Sony 3400ES AVR (processing and rear speakers' amp; I have a Pioneer SC-27 on the way)
emotiva XPA-3 (main L/R/C speakers' amp)
Magnepan MG-IIIa L/R mains
Magnepan CC3 center
Magnepan MC1 rear surrounds

Primary source material included a couple of old but familiar CDs: Flim and the BB's Tricycle, and Amanda McBroom/Lincoln Mayorga's Growing Up in Hollywood Town. I watched the new Star Trek movie for video. I used to have pretty good ears but have been out of the scene for a while, which perhaps only reinforces the improvement from the Rythmik subs since they (and the whole system) was so dramatically better to my aged ears.

To bed, gotta' work early tomorrow - Don

A question. My F-15 should be here this week. The way my room is configured, I only have one power outlet behind the entertainment center where all my gear is. My Monster Power HTX3600 MK II power center gizmo is plugged into one of the receptacles and TV, BR, cable box, M&K sub, and receiver run thru it. My XPA-5 is plugged into the other receptacle as it is required to run it directly plugged into the wall. Should the F-15 be plugged into the power center or the wall directly? If it needs to be into the wall, then that will require a minimum 30 foot RCA cable run to the sub (it does not have XLRs nor does my receiver. Brian had indicated that I shouldn't use a longer run than 15' for the RCA cable. Any input? Thanks folks.

I think power wise you can plug it in to whatever outlet you like. As for RCA cable this is what I'm using to connect my sub wirelessly to my AVR. It's a bit pricey relative to the price of the sub. I think there's a similar product out there for $99 or so, but I can't remember the name of it.

http://www.aperionaudio.com/catalog/...utions,84.aspx

With that wireless, there is no signal loss/degradation at all?

None that I could gather from the reviews. And there's a free 30day money back gaurantee. It's not any different than products like sonus streaming an entire audio signal over the airwaves.

http://www.aperionaudio.com/Products/Reviews.aspx

The other day I read a PDF from Bossobass where he maintained that you could not build a sub that's optomized for both music and home theater. That you have too make consessions for one or the other. He then goes on to state about using a musica sub with an ICBM for redirected bass and a home theater sub for the LFE channel.

Two question. Since the article is somewhat dated, is the basic premise still valid?

If it is, which of these subs would be the most musical? My mains are Atlantic Technology 8200 system with 8" woofers and my sub that will be used for the LFE channel is a SVS PB Ultra 13.

I agree that the power strip can probably handle it, but you might want to add up the Watt ratings from the back panels and see how close to the limit you are getting. The XPA-5 draws 1500 W max and the plate on the back of my F12 (370PEQ2 amp, probably same as you are getting) says 750 W. That's already over the limit of a standard 15 Amp outlet (15A x 120V = 1800W max). That said, I had a dedicated 20A line run to our new media room to cover my bases, and with an XPA-3 and pair of F12's I'm over that limit as well (knew I should have gone for a 30A circuit but too late now; at least I have an extra standard 15A line for lights and such I could tap into). You will rarely if ever use all that power, and a brief transient will (almost always) stress but not pop a breaker so you are probably OK. I did not look up the specs on your power strip, but make sure it can handle the load; I'd probably use 50% power in the amps as a starting point. Why? No real good reason, just seems a reasonable place to be on average power with margin, and it's easy to divide by two. The add up the rest of the power (if the receiver has amps you can derate the back panel rating from that as well since you won't use all the power all the time, and with the emotiva virtually none in the AVR's amps).

HTH - Don

Alrighty... I'll do the math. Thank you for that good info. Being a colorblind person - electrial stuff has never been my forte. Another reason to stay away from explosive ordinance disposal... "don't cut the blue wire"

While fairly new to the details of HT (though been a design engineer -- not audio -- for ages and used to be deeply embroiled into all things audiophile) this touches on a topic I have recently been researching. The LFE channel has fairly high frequency content, up to 120 Hz per the THX spec. That is well above what many (or maybe just me) consider the point at which you start to localize the subwoofer (i.e. high enough in frequency that it becomes directional). That's also pretty high if you have good full-range speakers for your L/R mains. Thus, a mono sub under your AVR's bass management is potentially going to "squash " the image at lower frequencies. Does it matter? Dunno' for you, but I can say that replacing my single sub with dual F12's sitting next to my mains solved an image problem I had, though this was partly due to the aforementioned high AVR crossover (again, THX standard is 80 Hz, leaving plenty of content in the sub even when I had full-range mains). So, I think it's still valid, as the required frequency response of the sub for HT is much higher than typical (or desired) for music.

In the past I had one sub centered and it worked OK. In my latest HT room I had to place the sub off to the side, compromising the image, and LFE wouldn't let me set the crossover low enough. Possible solutions are to set your sub up manually, if your receiver lets you do that well enough, or get a pair of subs, run them in parallel with the mains, and not use the AVR's sub output. If you have small mains, you'll need a HPF (high pass filter), either from the sub or externally, which could be a problem with an AVR (no place to break the loop and insert an external HPF without affecting the sub as well). Or, just get three subs, two near your mains for stereo, and a third for the LFE channel...

Can't help on the other question since I haven't heard them, sorry. - Don

Ah yes, Flim and the BB's. "Tricycle", "Tunnel", "Neon" and "Big Notes" - some of the highest quality recordings ever, they're always part of my demo material. Of course, these days I use FLAC rips rather than touch my precious disks. My F12 really helps to hear all the glorious dynamic range in these recordings.

Don,

You raise an interesting question.

If you use only your receiver/prepro for bass management, does it apply only to bass or does it also apply to the LFE channel? In other words, if you set your crossover to 80 hz., does a 110 hz LFE signal still reaches the sub?

I think there may be a test tone for the LFE channel only on Avia. When I get a chance, I'll try it.

Crossover in the pre/pro/avr is for bass. LFE is seperate and there is usually a (mis)labeled adjustment for LFE. If you have your speakers (bass management) set to cross at 80Hz, then bass content below 80Hz will be redirected to the SW.

All LFE content always goes to SW (if enabled/detected). You can choose (usually) where that content rolls off. It is generally recommended to set the LFE filter to 120Hz. If you do that, then all LFE content up to 120Hz will go to the SW - regardless of where your speaker (bass management) crossovers are set.

There is often LFE content above 80Hz, but it dwindles down significantly at 100Hz. The spec for the LFE channel content,I believe, allows content up to 120Hz - hence the recommendation to set the pre/pro/avr LFE filter at 120Hz.

As I said,this is often mis-labeled as a "crossover",which is confusing and wrong.

Brian, those are the two bass management diagrams on page 35 of PDF you linked to in your previous post?

The first bass management method sums the low frequencies from all 5 main channels into the subwoofer, where it is combined with discrete LFE content. The second bass management method sums the filtered low frequences from the centre and surrounds into the front L/R channels, where it is combined with discrete LFE content (use of a subwoofer down stream is optional).

Assuming you choose appropriate crossover points, why would the first method cause loss of signal?

Jim, I think you should listen to Brian over me on this any day... And, study those two figures he referenced very closely (ooh, pictures!) The document is a very good read overall, but Brian zeroed in on two key figures (no surprise!) Note the Dolby Digital Only boxes, though I have noticed several AVRs use a similar block diagram to manage the bass from any source.

In the first scheme, everything (all 5 channel inputs) is summed with the LFE signal, low-pass filtered (LPF), and passed to the subwoofer (after the gain block to compensate for the difference in LFE amplitude). High-pass filters (HPF) are applied to all the other channels (L/R mains, center, and surrounds). In this case, with 80 Hz cut-off (and ideal filters), all LFE content above 80 Hz is lost as Brian says because it is filtered out everywhere (HPF to the mains and LPF to the subs means the LFE signal above 80 Hz is lost; this may or may not matter in a practical sense).

In the second case, only the center and surrounds are initially summed (no L/R signals) with the LFE, filtered (LPF), then this signal is passed to the L/R channels (with gain adjustment) and the final L/R signals are sent out. There is no filtering on the L/R mains; the center and surrounds have HPFs. At the outputs, the L/R signals are summed again and passed through another LPF to an optional subwoofer. In this case, the L/R mains get full-range L/R signals plus the LFE content and all low-frequency content from the center and surrounds, great if you have full-range mains. If the LFE output filter is set high enough, no LFE content is lost since it also goes to the mains. And, you can set your sub's crossover to 80 Hz, minimizing directionality while preserving the higher LFE content.

In either case, there is a LPF (or two) in series with the sub so if you tell it to use an 80 Hz cutoff, that's what it will be. Note that the filters will still allow some upper-frequency content dictated by their roll-off. A 12-dB (second-order) filter will put a 160 Hz signal about 12 dB down, or below the half-loudness point.

A long winded way of saying "no" to your second question, but look at the figures Brian called out to see how your AVR is handling bass for the other channels in answer to your first question.

HTH - Don

edit: I was writing as Sanjay posted; I think I might have answered his question... Note that the THX spec calls for 80 Hz roll-off but content to 120 Hz so they must have been thinking of the second scheme.

My understanding is that whenever you are summing LFE back into a main channel, or even when you divide a center channel into L/R when running a "phantom center", you necessarily run into some level of compression. Are you looking at page 34 of the PDF you posted? Neither of those diagrams show the LFE being mixed back into the mains, but it's highly possible that I don't know how to read the diagram.

Don, I can see where a THX set-up could lose LFE content from 80-120Hz IF those frequencies aren't re-routed to the main channels. But in most cases, crossing over your main channels at 80Hz would mean that content below that frequency would end up in the subwoofer along with the entire LFE channel (up to 120Hz). To lose LFE channel content, you'd either have to set the LFE low pass filter on the receiver below 120Hz or set the crossover knob on the back of the subwoofer below 120Hz.
OK, so you lose dynamic range. But that's not the same as losing content (losing a portion of the soundtrack).

just got my F12SE in yesterday Quick iPhone picture...

I'll take a stab at this, but Brian's the expert. I am a hairy-knuckled design engineer and my day job involves much higher frequencies than subs put out...

@ vantagesc: Figure 3.3 on page 35 of the paper shows the LFE signal fed into the main L/R outputs. As for compression, the LFE signal is recorded at a lower level than the rest of the channels, then boosted at the end into the sub. There's more to it than this (and I am still reading about LFE in general) but this was done to prevent excessive compression that might otherwise occur with a very high-level bass signal. That is, a large bass signal could "use up all the bits" so there aren't any (or few) left for the important upper frequencies riding on the large bass signal. The LFE spec was designed to prevent that, and thus the various gain blocks sprinkled around the diagrams.

If you are talking about routing low-frequency content to your mains and they (L/R main amp and speakers) don't have the dynamic range, then yeah you could get compression, but that's a problem anytime you head for 11 on the gain knob...

@sdurani: As stated, you are exactly right and I agree. However, the dozen or so AVRs I was able to find out about (reading the literature and/or measuring) in the $1k'ish range and below tend to use the first diagram for "small" fronts and second for "large". They set the HPF at 80 Hz for the "upper" speakers and LPF at 80 Hz to the sub automatically for you ("it's a feature" -- especially with the lower-end receivers). Thus, since the LFE signal is sent only to the sub if you select "small" mains, LFE content between 80 and 120 Hz is lost. (Not completely because the filters have finite roll-off but you get the idea.) Some, but not all, of the AVRs had the ability to tweak the subwoofer setting independently of the mains, and the higher-end AVRs offer much more flexibility in setting both points. So, if you have the control you can correct the issue just as you say, assuming your sub has high enough bandwidth (higher than I care for, but that's a personal thing). Of course, that same control means you could lose information but setting them wrong... Disclaimer: Some of the AVRs I checked are older ones I am using at home, so it could well be all the newer ones allow you to set the sub's LPF to 120 Hz. I have noticed some do.

I much prefer full-range L/R speakers but am also much more music- than video-oriented (so far, anyway). As for my kids, well, the opposite, natch!

Again, Brian or someone with more experience/knowledge will hopefully step in and correct my mistakes. - Don

Hey Bigred, are you going to change to "Bigblack" now? Gorgeous sub, btw.

Aside: I was born and went to college in Columbia, MO -- small world! Still go back to visit the inlaws in Columbia and Fulton every year.