Bossobass Dave

Here are the drivers I'm using:

 

http://www.bcspeakers.com/products/lf-driver/21-0/21ipal

 

They have a DC resistance of 0.7ohm, and I also measured 0.7ohm with my meter.  

 

 

 

 

In Josh's measurements of the Othorn cabinet with the 21sw152-4 (DC resistance of 3.3ohm), the impedance minimums are at about ~28hz and ~59hz

 

 

 

 

 

28hz: 3.8ohm

59hz: 3.9ohm

 

 

 

21sw152-4 specs:

 

 

 

Josh also tested the 21-IPAL in the Othorn cabinet and stated the impedance between 25-30hz to be ~1.1ohm.  

What mains? Do you have measurements of the current draw while playing a 29 Hz sine tone?

The K20 roll off is the same as the K10 FWTW.

Gotcha. I have the K-10 FR graph, thanks.

Anyone have the SP FR?

I did post the FR of the PS amps and also the SP amp in comparison in the electronics FR thread I believe. You can use the comparison with the PS to derive the SP FR. It is pretty good below 10Hz.

Nope. I see the K-10 but no FR for the K-20 and no FR I can find for any SP amp. Mic'd sweeps are not reliable FR measurements of amp rolloff.   

Dave, what are you trying to say here?  You talk about the lack of bridge capability like it's a flaw, when in fact the amps are already bridged internally.  And in fact, they bridge into 2 ohm loads, unlike most amps that need 4 ohms to be operated bridged.  Or, is there something special about delivering your power into 4 ohm as opposed to 2 ohm?

 

The power supply capabilities are especially impressive.  That long duration sweep likely drains all the reserves, so it really measures what the power supply (and the AC supply line) can provide up to the point at which current limiters kick in for thermal protection or to prevent circuit breakers from flipping.

 

As for efficiency, I am fairly certain that the efficiency advantages of class D do not have to do with recycling of back EMF energy, and in fact, the presence of back EMF is a nuisance that appears in their design that is most adequately quelled by bridging the outputs.  To have not one but two fully-bridged outputs is an advantage, not a disadvantage.

 

It looks like the SP2 and K10 probably have very similar roll-off characteristics.  The signal chain measurements thread shows the K10 down about 3.5 dB down at 5 Hz and 7.5 dB at 3 Hz.  That doesn't look too bad at all, of course, assuming the K20 and K10 have identical roll-off.

What I'm saying is that it is not a proper comparison of amplifiers to compare a single channel that is a full bridge configuration amplifier of amplifier A to a single channel that is a half bridge configuration channel of amplifier B. The 'flaw' is in the test methodology and, therefore, the results. I would have thought that was obvious in looking at the comparisons page of the SP site.

The roll off characteristics of either of the amplifiers is not apparent from any data presented and in that respect I assume nothing.

How many bridged channels an amplifier may have is not relevant to my comment.

I don't think Dave believed me when I was telling him how powerful the sp2-12000 was, but these tests shouldn't leave any question.

 

As you know, I'm running mine to loads very close to 1ohm per channel, and it never complains. I've seen the fans skin up maybe twice in the last year I've had it.

I haven't doubted the raw output data, but I do question the 1 ohm operation claim. Again, I don't doubt certain situations permit that sort of stupid-high current draw, but I don't think your system presents such a situation. I don't believe you operate anywhere near 1 ohm.

If you have any data to the contrary, please post it.

Thanks for this. I like Brian and his products but have never liked his comparison data because I believe it is heavily biased toward his product.

To be more specific, his amplifiers are all full bridge configuration. The SP 2 channel amplifiers are the equivalent to 2 full bridge amplifiers and thus cannot be bridged. Comparing a full bridge amp to a single channel of a half bridge configuration is like comparing 2 dual VC drivers with one of the drivers using only one of it's VCs. Although interesting, it's not relevant data.

The SP amps weren't running 2 ohms in stereo.

With Class D the efficiency is increased by feeding the back EMF to the PS to recycle the power that is otherwise lost to heat. That's why the 2nd channel cancellation is the cure for bus pumping at <100 Hz amplification, but the FR is pertinent. Class D amps that offer half bridge channels usually have a relatively high FR roll off and aren't intended for use to reproduce content to 3 Hz at maximum output. Also, combined with a higher, steeper roll off, a large enough cap reservoir could also prevent bus pumping in a half bridge configuration.

This ^^^ is why I also would love to see the FRs of the amps. It's a simple procedure and roll off characteristic is imperative data in any sub amp comparison for obvious reasons. Amplifiers enter a quantum dimension proportional to frequency as frequency decreases.

Sweet! Thanks for posting, Dave.

 

Hey, I have a question/critique.... are those shadows in the back supposed to be rear surrounds and the other side surrounds for 7.1 audio? Are you finally going 7.1? If so... please, do NOT place them like this. You might as well stay 5.1 if so. I can help and suggest other spots but I know space is tight in your room.

 

Thanks again for posting.

The only speaks placed like the scaled drawing are the dual sub stacks and the CC. I just randomly grabbed a Dolby 7.1 plot and copied it for the drawing and the SBR and SBL are future when I move to 7.2.4 with 4 ceiling speaks. I'll post then and you can spill the beans. It will, as always, be much appreciated.

I have got to make it down to Dave's one of these days.

Man, this visit and reciprocal visit thing is so far overdue I'm embarrassed to even mention it. It's gonna get cold soon. I'd love to get to your place before then and you're always welcome here in the Shahlit Town.

Layout before build to scale to make sure everything would fit:

Section to make sure riser would work:

Signal chain hardware:

Speakers:

Seating and monitor:

Dudes, I'm like so put off you are clogging up this thread with decoder noise. I had to wade through a page to get to nuthin'....

Where's da BASS???

I'd love to see some measurements that have been.. umm... ported.

 

More low end, yo.

Haha we do love dem low end ported measurements. Actually I need to watch some damn movies. Gotta get caught up. 

Dudes, if he ports the graphs, the <5 Hz content will be below tune... <poof> content gone.

He just forgot to tilt the graphs.

He should port them.

Just watched The Gunman with Sean Penn. Good flick. Usual gunshots and explosions and one scene out of the blue with unexpected ULF.

Big hit at 16-22 Hz with a spread from 3 to 60 Hz. Chapter 18, no spoiler:

Niiiiiice.

Hi Maxmercy,

 

My name is Eric Flament and I work for Eminent Technology.  We produce the TRW-17 rotary woofer.  Your post is really great.  I am working on updating our web page and I stumbled across this website.  Do you mind if I link to this post on our website: http://www.rotarywoofer.com?

It's about flippin' time!

I've stopped referencing your site because of the lack of updates. Please pop in and keep us informed of any progress and let us know if we can be of any assistance. Also, pop into the GEAR side of the forums and start a thread. Should produce memorable quotes, usable graphs and a great list of titles for you guys to use and reference.

Hey I checked this scene out after you posted and at reference with the subs 15db hot I still got nothing from this scene. I have roll off below 10hz and although the content was there just nowhere near anything to feel it. My amp was barely flickering too which means it didn't see much there. Curious what gear you were running and how hot your subs were to feel that?

Must be a different mix/disc than the rental I used when it was first released. I would have noted it and probably graphed it. Even the peak hold Nube graphed doesn't show that content.

I took the 2 screen caps from the club scene and combined them onto one graph. You're right, Aj, this scene is over 3 minutes of full bandwidth transients. I'll also reiterate my previous observation about the background drone of every even numbered frequency from 4 Hz through 114 Hz... awesome stuff. I enjoyed it. Actually, the sound elevated the movie from ho-hum to excellent, IMO.

Any budget.  I'd like to know my options. 

 

I've very seriously considered Dave's A14K, but I think the noise and current draws might be a bit much for my living room, sitting 6ft from the amp and running off a 20A circuit.  It's pretty much the toast of the town in its price class, from what I can tell from his specs and the info on customization.

As you all know, you'll only be able to draw wattage according to the mains outlet, a dedicated 20A = 2400W and a dedicated 30A = 3600 at 120 Volts, long term.

30A is brutal current for any amplifier I've ever tested... except one.   Transient requirements to the bottom of the signal chain is what matters with soundtrack reproduction (see Adam's thread re: HTTYD Red Death dragon crash scene, et al, measurements) during which we've measured 33+ amps peak draw from a dedicated 120V-30A home run.

I believe it's the secret to accurate playback, assuming the subwoofer at the end of the line can handle the input signal. Others' opinion may vary. C'est la vie.

In any case, this amplifier is badass in any book on the subject:

I think that most of the time when the system errs on extension, it tends to give a higher rating that is deserved.  "The Equalizer" (TE) seems to be a rare case of a movie that got a worse extension rating than it probably deserves.

 

Bossobass reported excellent bass for TE when listening (presumably at theatrical reference) with his subs at +6 dB.  Without a doubt, he's hearing more ULF (potentially a lot more) than he would have if he ran his subs calibrated equal to his mains.  Does this mean that he overrates the bass in TE?  I don't think there's a straightforward answer there at all because we all listen differently!  Even in the studio, as we've found out, tracks are rarely monitored with enough low-end capability to hear everything that's present, and we have reason to suspect that much monitoring happens at lower-than-reference playback levels in order to compensate for the reduced playback levels used in common theaters.

 

Now, one could point out that if Bossobass plays "Pacific Rim" (PR) with subs at +6 dB, it's unlikely he will hear nearly as much ULF as he did in "The Equalizer".  PR has a steep filter compared to the modest roll-off seen in TE, so arguably TE should have a much better extension rating.  On the other hand, PR with BEQ gets rave reviews, so given that PR has good sounding ULF content underneath a steep filter, perhaps it should get a good extension rating too?  As a thought experiment, what happens if you cancel the 20 Hz filter and boost the sub by 30 dB on HTTYD2?  It might sound awesome!  Clearly (looking at the PvA) there's a nice 10 Hz hit buried in there, just waiting to be EQed and boosted out.  Or maybe it'll wreck the score and make it sound bad.

Rare case or not, the ULF is relative and not dependent on MVL. Pac Rim is filtered. Running it at +10dB will not reveal anything that isn't there in the first place.

EQ vs Pac Rim:

There are cases where the DVD vs BR and/or the 5.1 mix vs the 7.1 mix are vastly different in content and/or level and that has resulted in some wowing a soundtrack that I thought grossly anemic.

Prometheus and Thor are 2 examples. Thor BR is +10dB louder than Thor DVD and Prometheus 5.1 is +10dB louder than the 7.1 mix. Master & Commander is the first one that alerted me to a possible reason for huge differences in subjective opinions being that there is a huge difference in content between DVD and BR, etc.

Transformers is one disc that I always bumped the sub during playback because it's level is low and bumping the SW trim brought out the ULF and low end overall.

But, playback level doesn't add content.

I hear ya, Max... loud & clear.

To be clear as crystal, my recent comments regarding EQ were sparked by Nube's subjective comments that the low end was mid-bass with droning 29 Hz content, which is bullshit, plain and simple, and needed to be clarified, IMO.

The problem really is that no one caps scenes using the waterfall/waveform features of SL. Those will ALWAYS separate the facts from the subjective comments and certainly eliminate the need for alterations of the peak hold/average graph, IMO.

The average is taken over the entire length of the movie, so soundtracks with more content will show a higher average even if the content is identical.

I gave this movie top honors for 2014. Not a chance I would do that if it's extension is 23 Hz.

Yes, you can clearly see the big spike at 54 Hz (actually, it's a dual spike at around 52.X & 53.X Hz), but when the floor ripples, there's plenty of <20 Hz content.

The low end effects in this movie rival any movie in my collection for originality, variety and extension. It just isn't a constant drone of low end like some enjoy more, but there is no category for minutes of LFE per minutes of length of movie. Plus, the scene in ch 13, worth the price of admission in itself, is nearly a minute of mayhem.

For comparison's sake, the FOTP scene that makes it a 5 star movie lasts 1/2 as long. It has some content below everyone's radar and a spike at 32 Hz, but not much else in the scene or in the rest of the movie.

I understand that metrics and anomalies co-exist. I'm just sayin' don't let the ratings fool you on this one. It has the goods and it's a tad better movie to watch than the FOTPs of the cinema world.

Has anyone graphed the Equalizer? Thinking of picking this up today, but not if it is filtered.

I just have 2 scenes. We loved the flick and Denzel pulls it off yet again. Man On Fire reprise. It's a def buy for me:

I have no way of telling, one way or the other, how much distortion is present in your system from the spectrograms you posted.  They actually look quite different to me, but I'm assuming the differences I see are mostly due to room-response and maybe some limiting in the case of HTTYD.  Measuring actual distortion with live source material may be quite difficult.  One approach that could work would be to deconvolute the mic response with the room impulse response, measured at a low enough level that distortion can be neglected.  Then, deconvolute this result with the source itself.  In theory it should work, but I imagine it might be messy to do in practice.

 

As for why distortion does not appear in spetrograms, I can propose a few reasons.  It must be emphasized that distortion results from non-linearity of the subwoofer's mechanical components among other things.  Nothing about the signal changes the physics of the situation.  Without some kind of specialized correction, non-linearity will lead to distortion.  Why would this not appear in a spectrogram comparison?

Actually, harmonics appear in SpecLab the same as everything else the mic pics up does, including noise to -60dB. My point is not that SL doesn't detect it, but rather, it simply isn't generated by the subs when the signal is complex vs steady state.

Frequency response non-linearity explains the differences you see in the comparisons, as you guessed. But, there are no differences in the area focused on in the HTTYD scene (they are virtually identical) and yet there is an obvious difference in the Irene scene which clearly shows 2HD that does not belong there (and 3HD is obviously masked by the effect).

In both effects, the fundamental is the same, the system is the same, the levels are the same, the mic position is the same, the room is the same... in fact, only the input signal is different.

I've found this phenomenon to hold true in countless examples of comparison of complex effects vs Irene, and now EOT.

My own theory is that this is related to IMD in a way no one has suspected. In fact, when I finally post the theory, backed by measurements, I have no doubt about it's reaction from pretty much everyone. I may conclude that my theory is unfounded and just accept the phenomenon as a good thing and leave it at that.

Ilkka concluded that IMD exactly tracked THD so he eliminated the spectral contamination portion of his battery of tests as redundant. I tried to persuade him otherwise, but Ilk rarely followed mu suggestions and it was he who had to do the extra work or not, so I let it go. But, I have used the spectral contamination data from the tests he did conduct and post the results of using the same drivers in 2 of the cases.

This is just a curious result in my data. But rest assured, if there is no harmonic distortion in the spectrograph, then there is none being generated. The ACO Pacific rig is accurate and SL graphs what is being fed into it without discrimination.

If there are pure sine sweeps as LFE in various soundtracks, can you post the speclab of one here, as I'm not aware of any?

Some years back, Axiom conducted a listening test focused on what the threshold is for audibility in the subwoofer range. The results were surprising to most and caused a lot of howls and jeers.

Link: http://www.axiomaudio.com/distortion

Conclusion notes:

The Results

While it is has been recognized for years that human hearing is not very sensitive to low bass frequencies, which must be reproduced with much more power and intensity in order to be heard, what these results show is that our detection threshold for “noise” (made up of harmonically related and non-harmonically related test tones) is practically non-existent at low frequencies. (The “noise” test tones are noise in the sense that they are not musically related to tones commonly found in musical instruments.) In fact, the “noise” tones at 20 Hz and 40 Hz had to be increased to levels louder than the music itself before we even noticed them. Put another way, our ability to hear the test frequency “noise” tones at frequencies of 40 Hz and below is extremely crude. Indeed, the results show we are virtually deaf to these distortions at those frequencies. Even in the mid-bass at 280 Hz and lower, the “noise” can be around -14 dB (20% distortion), about half as loud as the music itself, before we hear it.

Conclusion

Axiom's tests of a wide range of male and female listeners of various ages with normal hearing showed that low-frequency distortion from a subwoofer or wide-range speaker with music signals is undetectable until it reaches gross levels approaching or exceeding the music playback levels. Only in the midrange does our hearing threshold for distortion detection become more acute. For detecting distortion at levels of less than 10%, the test frequencies had to be greater than 500 Hz. At 40 Hz, listeners accepted 100% distortion before they complained. The noise test tones had to reach 8,000 Hz and above before 1% distortion became audible, such is the masking effect of music. Anecdotal reports of listeners' ability to hear low frequency distortion with music programming are unsupported by the Axiom tests, at least until the distortion meets or exceeds the actual music playback level. These results indicate that the “where” of distortion—at what frequency it occurs—is at least as important as the “how much” or overall level of distortion. For the designer, this presents an interesting paradox to beware of: Audible distortion may increase if distortion is lowered at the price of raising its occurrence frequency.

I'm positive that I've conducted the largest body of comparison spectrograph measurements off the disc compared to mic'd at the seats from the subwoofers ever. As I've mentioned before, curiously, there is no detectable harmonic distortion found in any of those results with the exception of sine wave-based effects.  Here are some examples that should show harmonics with even cursory examination, if they were present:

Plane Crash Scene in WOTW:

Red Death Crash Scene from HTTYD:

Neither THD nor IMD tests have ever been conducted using program source. But, I know this: If I input a 5 Hz sine wave @ 0dBFS, like the low end burst shown in the HTTYD scene , I'll clearly see the 2HD distortion at 10 Hz in speclab, whereas none shows up when the entire effect plays. That phenomenon needs to be examined, IMO.

I've scoured dozens of these comparisons using different SL settings over the years and have never found a calculable trace of harmonic distortion.

Regarding the EOT effect, it really appears to be a sine wave that was sent through an effects processor. Otherwise, it makes no sense. But, it follows a similar pattern of effect creation in that it consists of a fundamental with odd-order overtones, like the chopper blades in Irene and others.

Bosso,

 

While I agree mostly with what you are saying, I still think anyone should have enough system to playback what is on the disc with less than 5% distortion.  To reach for that 5Hz more extension at the price of a 10-20% bump in THD is not at all ideal.  A system should be run to reasonable limits.

 

That being said, when you get under 5Hz, the 3rd harmonic is still essentially undetectable even at 80dB, and you can 'cheat' a little.

 

But 2pi space graphs for sealed enclosures will always look bad under Fb.  Room gain really helps remedy that.  It only can do so much for higher order alignments.

 

 

JSS

The curious thing, IMO, is that all of the complex sound effects show no harmonic distortion in my scrutiny of the digital v mic'd versions in speclab. It's only in the extended and relatively very high level sine wave effects like EOT and Irene that show harmonics that don't belong.

For example, comparing the Red Death dragon crash in HTTYD digita v mic'd, I saw zero harmonics of the big 3-5 Hz hit and which portion should have shown harmonics that don't belong if there had been any at 2HD. Yet, I saw 3% 2HD of the 6 Hz fundamental in Irene at reference level.

Although I find that result curious and worthy of examination, if anyone is ever gonna try to convince me that they will detect harmonics that don't belong at 10% THD ('T' for TOTAL) in effects like those found in the MWB we all crave...

...I'm gonna have to stick with "Ain't gonna happen"

All enclosures fall prey to their native responses in 2pi space.  I would at least build one sealed enclosure and see how it measures in room (to see room gain profile, as it will cut down on those harmonics seen in 2pi).  Now that REW can do distortion calculations with a regular sweep, it should be quite easy to see if you could do sealed, or if a quasi-IB or LLT will allow you the SPL/distortion needed and still hit the <10Hz goal.

 

You are absolutely correct about harmonics when playing back ULF.  They can easily be detected, and the fact that you are taking it into account in the planning phases is quite good.

 

JSS

Although I'm sure there are a few effects that are comprised of a single sine at 'x' Hz < 20 Hz, they are rare and I haven't experienced any to date.

The important things to remember in anticipating the audibility of harmonic distortion in-room are 1) the effect of room gain on harmonic distortion as a percentage and 2) the masking of harmonic distortion by the sound design result.

A good example is the recent EOT opening scene effect. The 10 Hz fundamental is simultaneous with a 3HD tone at 30 Hz @ -10dB, or 31.6% harmonic distortion, a 5HD tone at 50 Hz @ -20dB, or 10% harmonic distortion, etc.

If, as an example, your sub generates 20% 2HD harmonic distortion at 10 Hz and you have typical +15dB room gain at 10 Hz and +5dB at 20 Hz the harmonic distortion drops as a percentage to around 5% with odd order harmonics being completely masked by the design of the effect. I submit that it is impossible to audibly detect that.

Adam recently posted his speclab cap of that scene mic'd at the seats and it looks like he's around 10% 2HD at 20 Hz from the 10 Hz fundamental, but that's running the subs at 5-10dB above reference level and I will still question whether anyone could audibly detect that amount of distortion. At reference level, the distortion level would be <5% and absolutely inaudible.

Back in the day it was the Irene scene from BHD and when comparing the mic'd at the seats version to the looped version it was easy to see the distortion drop to <5% with room gain and with odd order harmonics being completely masked by the fundamental structure of the effect.

Yes, playing a single sine makes it simpler to detect audible harmonic distortion but there are no pure single frequency sine waves in nature nor in sound effects. In fact, as a general rule, ULF sound effects contain an incredibly wide array of frequencies. Neither is it possible to know exactly what the original version of a star ship going to warp should sound like vs the final version presented to the seats by your system.

The bottom line is that, based on many years of listening and measuring tests, filtering out the bottom half of soundtrack effects because of the possible audibility of added harmonics based on projections derived from ground plane test results of a single driver version of a subwoofer would be a tragic mistake without very specific tests done in-room with actual program source.

Marchand BASSIS and Bossobass SEQSS MKII:

OPPO BDP-105 & Bossobass SEQSS, both with 100 Hz low pass filter in line: