myn's Tuba HT Review (LLT vs THT) - Page 5

I use sine waves for output vs distortion testing, because I have found that if you can play a sinewave at the dB level you need with less than 5% or less than 2% (even better) THD, you can play any program material at that level without any problems whatsoever to my ears....even maybe a few dB louder without any problems....sine waves are a torture test, any flaws in a sub's clean output capability will be found....

My THT plays sinewaves at 110dB at the seating position 11 feet away with less than 2% THD from around 18Hz on up to crossover at 120Hz. Below 18Hz, I get a less output, but I have it eq'ed/highpassed so that I never get more than 5% THD.....sounds awesome.


JSS

holy crap. whose build is that? waf is a 9.5

Hey edge make sure to take a ton of pics during your build please!!!

Good luck!

Dbl

They probably won't be as good as myn's, but I will try to get good pics, after the I get the adhesive off of my fingers of course.

I have rolls and rolls of that tubing in my basement, I am a professional aquarist.
MOST of my questions will be answered by your wonderful build thread, but you will be the first one I ask if I have a question! Thank you for offering the help so willingly!

Good way to heat up your voice coils and perhaps damage them.

Why not just do a standard sine wave sweep at various levels and checkout FR and where compression sets in? Less strain on your drivers with a sweep.







Jsut wondering, what is your HP frequency set to?

Actually it's not a whole lot easier on the system depending on the scenario. Still a lot of heat going on if you are getting to the level where compression sets in noticeably during the sweep. You could also have excessive distortion starting well before the compression got glaringly obvious. Either way be careful with sweeps or sine waves.

With never more than 15-20V in, I've had no damage. I don't ask the impossible out of the box...the sine tones are only kept at high volume long enough to calculate THD. I haven't tried to use holmimpulse yet for THD testing, because it does so with sweeps, which would be better for the driver. I currently use the spectrum function of REW to calculate THD, and as soon as 10% or more THD sets in, I turn it down....10% THD is a rough approximation of Xmax, so my sub runs at much lower excursions.

I have never found any power compression with my THT, but I have never run a sweep through it at higher than 15-20V (45-80 Watts). No need to. Even with it's small rear chamber, You can reach excursion/distortion limits at low voltages at frequencies below 15Hz.

My high-pass? That's complicated by the fact that I run Audyssey and a plate amp with a built in hipass and low freq boost, and a Reckhorn B-1. Audyssey inadvertently 'boosts' frequencies below what it detects as your subs -3dB point (I can show you graphs how it does this) by about 9dB. I also run Audyssey's DynamicEQ, which boosts the lowend by a varying amount based on the volume level you are listening at to account for equal loudness curves.

With all that taken into account, my Reckhorn is set at ~13Hz. My plate amp is set at 16Hz. The freq response curve for the plate amp is at:

http://www.oaudio.com/docs/manual_v1_6.pdf

If I set my plate amp to the 20Hz setting, I lose clean dBs from 15-20Hz, so I set at 16Hz, and the addition of the Reckhorn controls distortion down below 15Hz. My receiver sets my sub out at -12dB, with my plate amp's volume knob at 10 o'clock.

I listen at -10 on the volume dial, but recently I have learned that DTS usually does not use dialnorm (except for Transformers 2); because of the dialnorm (and it's absence in some movies) my system is actually capable of clean output at a higher level than I initially thought, though I rarely use it as such. I always thought some movies were just mixed hotter, until I learned more about dialnorm. It would be nice not to have dialnorm, just a single reference level standard on bluray/DVD.

EDIT:

Here's a quote from the article found here:

http://www.hometheaterhifi.com/volum...on-6-2000.html

"Myth #2: Dialnorm reduces everything by 4 dB, altering reference level playback of a movie.

A common criticism is that Dialogue Normalization "normally" reduces the level of the soundtrack by about 4 dB. Reduces it as compared to what? You have to compare it to something else first, and then the question becomes: is the Dolby Digital soundtrack 4 dB too low, or is the other material 4 dB too high? Follow me on this one.

A lot of home theater enthusiasts are concerned with what is called "reference level playback". In a nutshell, you use test-tones (as may be found on such DVDs as AVIA) to set the volume to the same standard levels used in cinemas. The reason to do this is to hear the soundtrack at the level the movie makers intended. A concern naturally arises that if volume is being altered by Dialnorm, the sound engineer's vision is compromised. Reference level playback is in practice very very loud in the relatively small acoustic spaces of home, and we must caution you against it at this point. Not only do most find it uncomfortably loud, but as we noted in our article explaining the LFE channel, it can quickly bring a subwoofer to its knees. But for the record, let's press on.

The default power-on setting for Dialnorm on Dolby's professional AC-3 encoder, the DP569, is -27 because as we noted, that value is a perfect fit for movie soundtracks. True, this value calls for your decoder to attenuate its output by 4 dB. Fact is, the two most common reference DVDs, Video Essentials and AVIA, were encoded with the same -27 Dialnorm value, so their test noises are also being attenuated by 4 dB, making them a perfect reference for Dolby Digital movies. If you've set-up a system with either of these tools, then any movie you play will not be "reduced" by 4 dB as compared to the reference.

DTS soundtracks, unlike Dolby Digital, are not attenuated by 4 dB by your decoder. This means that if you've set up your system using AVIA or Video Essentials, the DTS soundtrack is actually going to play 4 dB too high. Yes, that's right. You read it right: On a system calibrated for reference level playback with Video Essentials or AVIA, DTS soundtracks play 4 dB too loud. Conversely (and to be fair), if you set up a system using DTS test noise, the Dolby Digital soundtrack will be 4 dB too low. Yet what is important here, and what I really want you to take away from this, is that regardless of what actual level you watch a movie at, relative to one another, there exists this 4 dB difference between DTS and Dolby Digital movie soundtracks played over consumer equipment. If at any time you are comparing soundtracks, you must turn your volume down when listening to the DTS track and/or raise it when listening to the Dolby Digital track (as the case may be) in order to hear the same level from both.

We should note that most THX-certified receivers and processors address this by attenuating DTS material by 4dB after the decode stage, effectively putting everything on level ground."


JSS

JSS

Max, I understand the complications of the low end as you have it setup. Have you ever done an electrical sweep of the electronics chain as setup?

REW will easily do that. REW output into the R main channel, REW input at the end of the subwoofer output chain. The only item that will be missing is the subwoofer amplifier. Audyssey On, B-1 ON, perhaps Audyssey EQ OFF and ON.



Regarding your statement "I also run Audyssey's DynamicEQ, which boosts the lowend by a varying amount based on the volume level you are listening at to account for equal loudness curves". There are a few people who claim that the entire concept of Dynamic EQ is bogus. My opinion is that the concept seems valid and quite valuable.

The bottom line is, does it work as advertised? No EQ is used at normal loud volume levels, but does it sound "better" at low playback levels?

DTS does not use Dialnorm for DVD encoding even though it was part of the DTD DVD specification. However, that old article was written before BlueRay. BlueRay DTS does now use a Dialnorm value.

As usual, the Dialnorm value varies disk to disk on both DD and on DTS. Sometimes a Dialnorm volume reduction value is used, and sometimes the volume is not reduced at all.

Regardless, all that Dialnorm does is reduce volume levels of everything. Same as lowering the master volume control a bit.

J Cass,

I had to sweep the electronics with REQ to find my problems with Audyssey....

It went like so:

Response curve of receiver with Audyssey off:



Note the decreasing response below 10Hz, typical of most audio equipment.

Now engage Audyssey:



Note how it places cuts where needed. Also note how it does not place any cuts below 20Hz, or above 250Hz. Of significant note, the overall level has been increased, to make the apparent overall volume equal between Audyssey on and off.

Both traces together:



You can see that below 20Hz, there is a SIGNIFICANT 'boost' happening because of the level change, which was causing my sub to distort. Hence the purchase of the reckhorn.

Now, to see that it is just a level issue, I move the Audyssey on trace down by 10dB:



10dB is the same as 10x the power. SVS uses an amp similar to mine, and some SVS owners were also complaining that Audyssey was 'boosting' the extreme low end too much. What I did with my amp/reckhorn combo is essentially fill in the dip between 20 and 15Hz with my amp's freq response, and used the Reckhorn to eliminate the sub-15Hz 'boosting' Audyssey was implementing.

As for Dynamic EQ, I really like it. It reads volume frame by frame and adjusts eq according to equal loudness curves. Louder passages get less eq, softer passages get more, and the level of eq varies not only by source content but by master volume setting. At 0dBMV, no eq is added to anything. Many terabytes of data implementing equal loudness contours as well as pro mixers' input was used to make the algorithm. Dynamic EQ alters the levels of the surrounds, boosting them a little as the volume is decreased. It is a prominent effect. Switching between Dynamic EQ on and off listening at -15dB, with DynEQ off, everything collapses to the front 3 channels. My one complaint is that at very low volume levels (-20dB or lower), there is too much bass. I think the algorithm is great for listening down to -15dB, but lower than that and it sounds strange, too much low end.

I have measured the boost, and at -10dBMV, with a -3.0dBFS sinewave sweep, it applies a maximum of 3dB of low end boost, more boost as you delve lower in frequency.

Why I HATE dialnorm is that it changes the Dynamic EQ algorithm. For movies that have the -4dB offset, to get equal level, I turn up to -6dBMV. That means Dynamic EQ is applying less changes, less low freq boost. The difference became apparent with the two versions of TF2. I bought the standard version, not knowing the big screen version existed. When I got the big screen version, it seemed to lack authority, due to the dialnorm. When I turned it up to -6dBMV to match, Dynamic EQ did not apply as much changes, and while it was close to the same level, the low end had slightly less punch and depth, because DynEQ was applying less change...it is noticeable....less kick, less shake, less rumble. And we are only talking about a few dBs here...it seems tactility of bass freqs is highly dependent on level.

Dialnorm now explains why movies like the Hulk are the loudest I own, no dialnorm offset on that one or Master and Commander...

JSS

Max, you followed a nice and solid procedure. Did you finish up with an in room sweep (or equal) from 1 to 10 kHz or so to checkout your system's complete frequency balance?

I look at a lot of speaker combinations playing together, but I prefer to look at the R & L mains plus the subwoofer playing together for starters. I have used TrueRTA, REW, and Spectrum Lab at different times and they all give similar results.

I'd be interested in trying something like this THT. But I'd want something that fits under my projector screen.

Something like 96" wide x 18" tall x 18" deep.

I'm one of the many who don't feel a center channel speaker is necessary if you have good front mains. Anyone know of anything that would fit in about the space I mentioned above?

Bill's AutoTuba at 14x15x32 inches would work if I used two of them. But I have a huge room and I doubt a pair of 10" drivers is going to make me forget my current two 15" Tempest-X tuned to 16hz.

JCass,

I don't have any fullrange sweeps of the current setup, but here are previous ones:

Stereo pair, Ausyssey in light green:



Center, Audyssey in blue:



These are old sweeps with the RS meter that is only good to a few kHZ before peaking....I don't have any saved with the Galaxy meter...but they do look OK...

Not bad for $800 spent in speakers (LCR+sub) + plate amp....and they play at less than 5% THD at 10dB under reference...

If I were to do it again (maybe someday), I'd build CBTs or something like augerpro's No Quarter for mains/center/surrounds and either multiple horns (THTs or otherwise) or multiple sealed boxes for subs. With horns, you use less drivers, but are generally limited in LF extension to a certain extent when compared to the equivalent in sealed boxes (usually 3-4 sealed boxes per one horn, depending on the horn)....

MK Theater's comparo of 8x18 sealed subs vs 2 DTS-10s should be very interesting...I sincerely hope he does output vs distortion tests for each setup....

JSS

Looks (sounds) nice! What amp is he running those off of, do you know?


dbl

Not bad. I use the RS Digital SPL meter for the mike for my charts. As we both know we end up with a C scale rolloff at both end of the scale.

Here is a Spectrum Lab FR chart of my stereo pair, JPC MBM plus the subwoofer(s). No smoothing or averaging applied, bin size is about 0.7 Hz per bin. The green line (peak average) in the top spectrogram is the line to follow.











I think that he is making a mistake in changing. However, he did not ask me for my opinon!

The on site soundtrack was clipping all the way though the demo. The recorder probably can not take the SPL's.

I got my Dayton 15" woofer for the THT today! I will put together a build thread soon. Here it is sitting on top of my Klipsch SUB-12

Haha. That's going to be huge step up in output and sound quality!

No kidding, it is gonna be pretty sweet going from this middle of the road Klipsch Subwoofer to this THT beast.

This thread has convinced me I need to try a horn for my next project - nice job on that THT.

Not sure if I'll try this design though... I kind of want to learn these for myself. That, and I want to see if I can horn load a Mach 5 MJ-18M. Still not sure if that driver is right for the job.

Designing horns isn't easy. Even the majority of professional acoustical engineers don't have a thorough understanding of how they work or how to make them. As for your eighteen, horns and large drivers are a bad match. Horns work based on the length of the horn, and the larger the driver used the less horn length one can fit into the box. Even for pro-touring sound I don't use eighteens in any of my cabs.

Thanks for the input - I kind of thought as much about the Mach 5, that it would need a big horn to be useful. A friend of mine used 18" JBL horns for school dances back in the day - he only had four of them, each with one woofer, but those boxes were massive. I had to help him load them onto the truck - that was not fun.

The fact that it's not easy is probably why I want to learn horn design so much. I currently can't get my head around them too well, and that drives me absolutely nuts. When it comes to something I'm interested in, I just can't leave it alone until I know how it works... my brain won't let it go

maxmercy,

Do you have a link to your THT build?


dbl

SOrry for my bad english - just a Dane....


Oh my G...... THT is maby just what i've been looking for

Currently been running these fun babyes
-hometheatershack.com/forums/exodus-audio/19261-tempest-x-2-300l-br-17hz.html-

And did just get my last 2 of the tempest gen 1.....so have 4 of these drivers......hmmmm what would 4 of these in 4 THT do for the ht

Just working on my new woodworkshop, and it should be up and running by jan 2010.......

Sorry if i disturb this thread, but i really like to get som help on the THT.....also been looking at Danley's spud's the 10's and so on, but that means new drivers....and that is not possible at the moment.....hmmm THT - not good i've found this thread........

My THT build thread was on the Bill Fitzmaurice forum, but it has since been deleted due to lack of posting activity on the thread. If you have questions, I can answer them.

Please remember that there are many ways to skin a cat. The THT allows skinning of said cat at a low cost but significant time investment, but as with any single subwoofer solution in a small room, you can't have more than one seat with great response unless you get lucky. It is also a very large box.

Consider your budget, your sound goals, and the space you have available before you decide on a low freq solution for your room. THT is awesome for output vs cost, at the sacrifice of space and build time (compared to a sealed box). If you have the space for 2 or 4 THTs (and the time to build them), you'd have a formidable system that could provide very good low freq sound for a seating area. For every THT, you'd need approx 3 sealed 15" drivers to keep up. The three 15" sealed drivers would have more extreme low end than a single THT, but you'd have to buy 3x the drivers....and need 3x the power of a single THT....


JSS