peniku8

Maybe they defined their 'THD' as the sum of only 5th harmonic and up Manufacturers do all kind of crazy stuff to show impressive numbers. Like Klipsch, defining maximum SPL with  the conditions "2 subwoofers used in 1/8th space".

35 minutes ago, kipman725 said:

With the fireface loopback measurements you have a THD+N vs level graph, is this from REW? how do you do this?

RTA→Stepped Sine→select Step level, like this

And no, I'm not keen on doing more sustained testing. I'm tired of blowing stuff up. It's annoying and costly. If you really wanna test PA amps you could put em into an incubator at say 40°C/105°F to simulate a hot summer day and give it a beating over an hour. Pretty sure most amps will die like that.

New ADC arrived today, mind the new scale.

Fireface in comparison (distortion seen comes mostly from its ADC):

From 98db THD+N to 120db THD+N and dropping the noise floor by 20db, that's something I like to see! This is currently limited by the DAC, which will eventually be upgraded too, but I'm pretty happy with this so far. Certainly did not expect having to increase the graph range to -180db because half of the noise floor would drop off the chart even if it was set to -170! At least I can properly measure stuff now without having to worry about optimizing gain structure in my measurement chain (Fireface was distorting more starting from -10dBFS out and/or in). Pmillett measurements following.

5 hours ago, m_ms said:

I did mean and actually wrote extension and not distortion

I did mean but not actually wrote extension lol, sorry for the confusion. Fixed now

For upper/mid bass a long horn will be better than a single bandpass, since it increases efficiency, and thus decreases relative distortion levels. A simple slot 'loaded' bandpass will do the same, but a bit less overall, emphasize upper bass less and maybe yield better results in mid bass if the resulting front 'chamber' volume is larger. Been some time since I designed my last cab in hornresp and played around with this stuff, but design approaches will be pretty good for music.

Group delay might become an issue if the front slot is very long, I'm not sure. But that's probably talking extreme lengths you'd typically not reach, which would also kill upper bass.

23 hours ago, m_ms said:

Never cared for the Devastator variant(s) as it seems they're going rather blindly after extension, but at what cost in other areas of overall bass reproduction? They also take up more space.

I'd not say the devs are cabs that are blindly going after extension. I'd rather attribute that to simple vented designs like the Marty line for example. The devs are band pass designs, which increase sensitivity and should decrease distortion in the mid-upper bass region, depending on the slot length (there are like half a dozen dev designs that I am aware of). Additionally they bury the driver, which protects the membrane, which is something I like.

Never personally built/heard or dug into the measurements of these, so I can't comment on the design itself, but it theory it can be pretty good. Lately I've been very intrigued and impressed by designs with shaped/heavily flared ports, but these are extremely hard to build sadly, if you want to make everything out of wood (and sturdy).

3 hours ago, SME said:

Is it too much to suggest adding back 20 Hz?  I mean 10 Hz is real important to the ULF crowd, but I believe some amps do start to lose a lot of output by 20 Hz, and this would affect a lot more typical sub applications.  So then it would be 10 Hz (ULF), 20 Hz (Deep bass), 60 Hz (Mid Bass), and 1000 Hz (Mid).

I agree that power testing at 16 kHz is probably not important, and in fact, some amps may activate the protection circuit with high amplitude UHF inputs.  More useful for assessing UHF performance would be frequency responses at different impedances, which will often vary for Class D designs.

Sure, I can do that. It's still 2 tests less than my previous set up.

My Sanway amp actually mutes when given high amplitude HF information (above 10k), and also muted when trying to run full power into 1R, so at least some protections are working there. Just unfortunate that they don't have thermal protection, which made mine blow up. I mean, it was fan modded and on a 1 minute full output test, which was a bit unfair, but still...

On 12/3/2021 at 11:22 PM, Ricci said:

How about removing the 15, 30 and 100Hz results. 

Report something like 8Hz ULF, 60Hz Bass, 1kHz Mid?

Maybe 16Khz Treble?

Yea, seeing how the results on the Hypex amp are barely any different at all, I guess we can safely classify and dumb down application types by a single frequency. 60hz for mid-bass, since that's where the kick drum will sit in most non electronic modern music, 10Hz for the HT ULF crowd and 1khz as general full range guideline, but I'm not sure if 16khz is of any value at all. Music is typically mixed to drop off by 3db per octave and then even more when approaching the last octave, so 16khz demands will already be only a fraction of even just 1khz, unless you're talking long-throw line array applications where you need lots of distance loss compensation, in which case you're most likely using specific system amps anyways (or you somehow need maximum power into a super tweeter!??).

You can call the segments 'Full range performance', 'Bass performance' and 'Deep bass performance' I guess.

On 11/28/2021 at 10:09 PM, peniku8 said:

And the loadbank causes another casualty.. this time it's a Yamaha CR-600. Fuses are done for, but I hope everything else is still good. Measurements of my Hypex FA123 coming soon. Also ordered dedicated measurement equipment, since I already had trouble measuring the true performance of the Hypex amps... Fireface not clean enough. Getting the Cosmos ADC to use with a Topping D10b. Probably also going to get the Cosmos APU once it releases, which includes a 1khz notch and a preamp capable to delivering phantom power with lots of gain.

Amp is up and running again, were just the fuses. 45 year old amp takes accidental 2ohm clipping like a champ and only causes 1$ of damage. I love this thing! And it's actually good THD, even by today's standards (0.007% 4V into 8R).

I fixed some other things and mondernized the amp while I was at it, fitting it with a C14 socket (replacing the fixed cable) and clamp style speaker connectors. There are LED-sized light bulbs (!) inside the panel that lights up the tuner's signal strength, of which one still works. I put it in the middle socket and it lights up both meters now, it's great.

13 hours ago, SME said:

Wow, these are nice!

If I may make a suggestion for the comparisons of power at different frequencies: plot these in units of dB instead of watts!  Use 1000 Hz as a reference, so it's always "0 dB" at 1000 Hz and will typically be small or negative at the other frequencies.  (So maybe use "+1 dB" for the top of the Y-axis.)  I think this will convey information that is much more useful to the reader as it clarifies exactly out much output you lose at some lower frequency.

The formula to calculate this is as follows:  dB(f) = 10 * log10( P(f) / P(1000) ) where dB(f) is the decibels at frequency 'f', and P(f) is the power at that frequency.  dB(1000) should always be 0.

Other graphs may also be more useful in decibel units, but decibel units only make sense when you have a meaningful reference point as above.  When comparing different amps to one another, there isn't a good reference unless you choose one of them to compare everything else to.

What do you think?

I record the amp's output as WAV, so I'm logging the db values in the first place, which I then use to derive the powers from. Changing out the values with db values shouldn't be a problem at all, but like you said, if people wanna compare amps at certain frequencies (say you're looking for an amp for your tactile system, so you look at the 8Hz results), you might be better off comparing absolute powers over relative db loss, which you then have to backtrack to compare.

For me it's easier to make out the db changes in my head (like when I'm seeing 1000W at 1khz and then I see 800W at 30Hz that's somewhere around 1db loss), than to reverse the process and I like dealing in absolutes, because we're comparing different amps in the big picture. I could maybe also display both, but I already had enough trouble with Excel to make this work as I wanted it to (it's a universal file and the graph needs to adapt to mono blocks, 4 channel amps etc...), and I think even more info would clutter the graphs a bit too much.

7 hours ago, chrapladm said:

I will try and do the bracing with the dados in 3mm. Wont do all the panels this way. And as I said since I dont have all the plywood yet I will just make some jigs to do the dados. Will be making one for the hatch anyways. Gives me something to do for now.

What bit will you be using for this? Something like here?
https://www.aliexpress.com/item/32947219454.html

Which of the two styles would you guys prefer? Currently it shows values for 1khz for full range reference and 30Hz for deep bass reference, but I'm not even sure if that's needed. The data table clutters the graph a lot imo

Evaluations will additionally have these:

Which will react like this when they're presented with differing values for bust and peak:

On 11/30/2021 at 8:37 AM, chrapladm said:

 

3mm?. Ok

 

I was thinking most did more than that. Here is dsI1's dado if thats what they are called. I liked how it aids in assembly. I plan to make four so I figured I could make a jig for the "dado's," to help speed things up since I dont have a CNC.

I've build 20 speakers with this dado size now and I see no reason why I'd need them to be deeper.

And tbh, I don't think it's worth the hassle to make them when you don't have a CNC. You'll waste all the time you save on assembly with making the joints, possibly more.

3 hours ago, chrapladm said:

Looked at making a template out of some scrap I have. I was hoping to recess the interior panels but wanted to know the depth others are recessing the panels? 1/4"/ 6mm? More?

If you're talking about the dado joints, I always make them 3mm. That way I can cut them with max feed rates on my machine without worrying about inaccuracies too much. I never felt the need to make them bigger, they're mostly for easier positioning anyways, so 3mm is just fine for that. imo it doesn't matter stability wise, unless you expect to throw the cabs off a balcony often.

Well to be fair, I didn't double check and thought I was testing it into 2x8R, but instead the load bank was set to 4+2 Ohm...

And the loadbank causes another casualty.. this time it's a Yamaha CR-600. Fuses are done for, but I hope everything else is still good. Measurements of my Hypex FA123 coming soon. Also ordered dedicated measurement equipment, since I already had trouble measuring the true performance of the Hypex amps... Fireface not clean enough. Getting the Cosmos ADC to use with a Topping D10b. Probably also going to get the Cosmos APU once it releases, which includes a 1khz notch and a preamp capable to delivering phantom power with lots of gain.

1 hour ago, m_ms said:

What's entailed in "people really appreciating the change" from double 18's to the Skram's? What's their feedback in more detail about any change in presentation here - is it simply about (more?) capacity, or does it come down to a perceived difference in presentation between the two box and driver types? 

@Ricci and others: Earlier this evening I was at local cinema watching 'Ghostbusters: Afterlife' (an amusing and largely successful follow-up to the '84 original), and was quite impressed by the bass impact and overall quality in the some 400 seat auditorium (with Atmos sound). Turns out their speakers are from QSC, and the subs they use are these:

https://www.qsc.com/solutions-products/loudspeakers/cinema/subwoofers/sb-series/sb-15121/

I take it the 21" driver used here is the B&C 21SW152, and I believe I've read only two of them subs are used in this auditorium, though I find it hard to believe given how much the bass shook the whole locale. 

My question here is: how would the QSC sub compare to a Skram, say, with the same driver? Does the Skram make more outright use of both its front and back wave of the cone by comparison, or are they comparable to one another in overall SPL and presentation?

The QSC sub is larger and probably has more vent area compared to the Skram (when you block Skram ports to reach the same ~25Hz(?) tuning), meaning the QSC will be louder in the sub bass. Skram is front loaded, which means it's more efficient (louder) in the mid/upper-bass region. Skram is basically a band pass, which means it also masks some distortion.
That would be the 3 main differences I guess. Skram has a rising native voltage sensitivity, while the QSC is probably pretty flat, going by my gut feeling here.

38 minutes ago, Fink_Newton said:

I have them loaded with B&C 21ds115-4's.   The soundsystem will be primarily used for small to medium sized outdoor parties where we might not always have adequate generator power so i figured the extra sensitivity of the 21ds115's might come in handy in certain cases.  Although from what I understand the 21sw152 will go aprox 2-3db louder before power compression sets in? We also considered the new Eminence drivers however they seemed like they would be even harder to power properly in order to get the most out of them.   The 44m20 amp has been absolutely incredible to use. I reckon it could power 8 Skrams in a pinch. We were using a Morin k30 before and although it had plenty of power it was extremely hard on our generators.  The Linea seems to be much more efficient and also there was a noticeable improvement in the tightness of the bass produced. The linea amp also limits it current draw to match the power source which has been super handy as well as integrating seamlessly with our Linea ASC48 in System Engineer.  Also wanted to say thanks for all your hard work and time you put in to sharing your knowledge and designs with us!  This whole project has been extremely fun and rewarding and wouldn't be possible without resources such as these.

The ds and sw are very similar in maximum output at their respective program powers. Bennett from B&C said you should only really use the sw if you need the higher power handling, otherwise it doesn't really matter which you pick so you should go for the cheaper one. Here is a hornresp of different drivers I've compared in the SKhorn

And I just moved and only have headphones at the moment 😖

I'm just gonna say that I believe that most, if not all difference in tonality between different drivers or these subs vs 'normal' subs in a home setting is due to a lack of EQ/calibration. I've been using the SKHorn in my HT for over a year and calibrated to the same response I could hardly hear any difference to the 12" Klipsch sub I had at lower volumes. The SKHorn integrated into my HT just like any other sub. Electrically. Not physically...
These type of cabs often have a significant bump somewhere between 100 and 200Hz, which means your acoustic crossover will be higher than expected (unless they're on a dsp), which probably is what you're describing as 'Brute-ish' or 'dark'.

Thanks to rona I have 4 unused 21ds115's in my basement right now. It makes me sad not letting them loose from time to time. Maybe I can fit a DO 15TBX100 sub into my new room, but maybe I won't even need it with 4x8" woofers from the mains I will be setting up soon. Okay, who am I kidding, of course I will need more woofage.

@jay michaelI had to mount 4 braked wheels to my cabs. If I don't engage the brakes after they're set up, the wheels will rattle, but it's a downfiring design. How are yours behaving?

20 hours ago, jay michael said:

I haven't man, sorry.  Hopefully someday the Skram will get the full testing treatment, I would think the Skhorn results should be a pretty good representation of what to expect obviously with lower output. The Skram also has larger vents so overall we would expect 2 skrams to outperform a single skhorn. At the end of the day it comes down to cabinet size. The Skrams 36x34x24 dimensions makes it a real compact 21" cabinet, I doubt any diy plan packs as much punch and deep extension in those dimensions. I can move these around on my own but they are at the very edge of what I would call manageable if its just you. If you have a dedicated crew that will help you move them into storage at 5am then perhaps look into larger cabinets

Do you have casters on the back of the cabs? My DIY 21" cabs have slots, which serve as handles inside the horn mouth and wheels on the back (on the hatch, which is almost as big as the entire rear of the cab), which makes them really easy to move around. I imagine the horn mouth of the SKRams would also server as a good handle to throw them onto their backs. I'm sure stacking 3 ain't fun. My back hurts from looking at that stack, the SKRam looks like it's at least 150lbs!

11 minutes ago, kipman725 said:

The level seems quite low.  I would expect the noise to be constant with level so SNR should improve if a larger signal is used.  The Fireface UC is spec: THD+N AD: < -98 dB (< 0.0012 %), THD+N DA: -96 dB (0.0015 %) so you're getting pretty close.

What do you mean by low level? The last measurement was taken at 0dbFS, which produced 6,6V at the Fireface's output.

Here is a direct measurement of the FF without the pmillett in the loop (max output 6,6V as before):

Best THD is achieved at 0.5V output, best noise floor at maximum.

Here is the THD/Noise vs output plot:

Pmillett Sound Card Interface loopback measurements:

Measurement chain is Fireface UC → SCI (Generator input) → Internal loopback → Fireface UC
The SCI converts the balanced signal of the Fireface internally and outputs either balanaced or unbalanced, which can be switched. It doubles the output voltage, so if I input 2V balanced, it outputs 4V balanced or 4V unbalanced. Voltages seen are after conversion (means the Fireface outputs half the voltage displayed).

Measurements are sorted by voltage ascending.

The 1V measurement looks similar to the Fireface loopback, so I guess the pmillett isn't adding too much distortion.
The pmillett started distorting at about 8.6V output (unbalanced). When I switched it to balanced, the distortion increased a bit, but there was more headroom (presumably twice the voltage).
Here is a measurement of the Fireface at 0dbFS, which produced 13,25V at the Pmillett's generator output, which is about 24,6dbU:

I figured out the mains hum, which was a rack power strip mounted above my patchbay in my outboard rack.
The following measurement was taken with the power strip switched off:

THD looks good, but THD+N still pretty bad, I'm not sure why that is, as I can't really see anything that dirty in the rta there...

9 hours ago, kipman725 said:

I did some loopback tests of a presonus firebox, they are ~7dB worse than your results for noise and distortion.  However your distortion is much lower.

https://www.audiosciencereview.com/forum/index.php?threads/presonus-firebox-24bit-96khz-loopback-measurments.24565/#post-828710

should be more than adequate for PA amplifier characterization.

The Fireface had been RMA'd once and ever since it seems to reset the connection to the PC occasionally when a ceiling light (LED or Tungsten) is switched on or off, which is very annoying. I suppose there might be something wrong still, which might also cause the mains hum (50hz here in Germany) plus its 3rd harmonic, which is the reason the THD+N gets tanked. I think I should contact RME customer support to confirm whether these results are expected or not. I ran this through my patch bay in the outboard rack, which meant 50ft of cable, but it was balanced so it should not matter much?

I took some new distortion measurements of the interface and the Pmillet Sound Card Interface I'm using.
I decided to use REW's RTA to take these, as it gave it more flexibility with window sizes and averaging etc. 0dbV is not correct, but I had to 'calibrate' it to zero, since I couldn't find a way to take the fundamental as reference.
Thoughts?

Been doing some tests with my Hypex amps and just out of curiosity I ran them without water in the tank, because I wanted to see how warm the elements got when testing lower power levels.

I put the bank on 8R (two elements in parallel) and gave it 50W for a minute. I could still touch the elements after the test was over. They were probably around 50°C (110°F?) at that point. Good news for me, as that means I can test everything below a few hundred watts without having to fill up the tank. I will give it a bit more power tomorrow to see how much the resistance changes, but it shouldn't be much. It's 8.2-8.3R cold and 8R under full load (3KW per element, which would mean an amp with 6KW into 8R would be required to saturate one channel).