peniku8

The driver was designed for the IPAL feedback loop system, which meant is was basically overengineered, especially in terms of motor force. That happens to make for a really good driver which works great in usually undersized cabinets. You need the amp and the sensor to take full advantage of the IPAL system, but you don't need the amp to take advantage of the driver.

Specs are specs, so you can pretty much compare apples to apples here.

Unless you're after the low Fs, the 18IPAL would probably be your best bet. More Xmax, more power, much lower Qts...

The Loadbank

While a bucket might've been the easiest solution, I wanted something rack mounted (for easy storage) that at least somewhat resembled something store-bought.
I figured I could fit everything into 3 rack spaces, so I bought a 3U case from Amazon.

As with everything I do, I first made a 3D model in Inventor. That always proved to leave very little room for errors. This is the front plate I made:

After I was happy with the design, I generated some G-Code with Inventor HSM and made the front plate on my cnc router.

I used a 2mm end mill to cut the holes. I have since bought a 3mm end mill specifically for sheet metal, which is much better suited for the task obviously, but the results were decent nontheless.

For the hardware I used regular Neutrik connectors, heavy duty (30A) switches and busbars for easy wiring. I glued the busbars to the front plate.

The heavy gauge wires were a pain to solder with my tiny soldering iron... I have 12 heating elements with the blue cap on the back and 4 without (went out of stock). The elements without the cap have a slightly lower impedance (~0.4 Ohm less).

I cut a hole into the rear case wall and made a mounting bracket for the heating elements with some acrylic. The plan was to screw the elements into the acrylic (has been tested with scrap pieces before) but that didn't work out and I didn't want to try myself out on thread milling just yet. I used my favourite stepped drill bit to make the holes a little larger and glued in the elements that wouldn't fit with silicone. Everything else came together nicely.

A quick sanity-check revealed that everything works as intended, which was a small surprise to me because I did all the wiring from the back of my head without a wiring diagram.
With the current setup I can do 4x8, 4x4, 2x2 and 1x1. And of course various useless impedance combinations.

The device is quite heavy fully assembled. I haven't weighed it yet, but it's probably around 40lbs. And it's sturdy.
This is what the back looks like now:

At first I thought I could get away with air cooling, but after one of those elements almost exploded into my face after plugging it into the wall in free air, I decided to go with a basic water bin. I still have lots of spare acrylic, which came in handy here.

I trimmed the edges with a flush trim bit and even made a roundover. I never planned on doing any experiments with hot-forming or welding. The glue I used basically welds plastics anyways. The container was made to slide into the case. You basically fill it up with water (to the point I marked to avoid overflow) and put the loadbank over it. The loadbank then rests on the container, with the heating elements being surrounded by at least an inch of water at all sides.

The case has enough room to accomodate the container as well. Without water preferably when stowing it...

That about wraps up my build, which I'm pretty satisfied with. I tested one amp already and it worked like a charm. The banana sockets are connections for my Pmillet Soundcard Interface (or basically any oscilloscope).

The font I used for the text on the front plate is called Elixia!

I built a loadbank to bench-test audio amplifiers on a resistive load.

The loadbank consists of 16 3KW 220V heating elements, which allows me to test any combination of 8 8Ohm clusters for up to 4 channels.
More on the loadbank in this post.

Results:

• Sanway FP-13000 (MKI)
• t.amp TSA-1400
• t.amp TSA4-300

Testing methodology:

1. Calibrating the signal chain without an amp in the loop
2. Getting a frequency response measurement of the amp
3. Determining the amp's maximum unclipped output voltage (Vmax@1khz) with no load connected
4. Adjusting my audio interface's input gain to scale the input signal at Vmax to -12dbFS (optional, just for convenience and consistency)
5. Doing a reference recording at Vmax@1khz (any other known uncompressed output voltage would work as well) with no load connected
6. Feeding the amp various sine waves and recording the maximum signal levels generated into various loads
7. If clipping (>0.5%THD) was observed during step 6: Scale back the signal level in 0.1db steps until the THD drops below 0.5%
8. Calculating the power into a given load with the level difference between the calibration recording at Vmax and the under-load recording Vmax'

To 3:
I used REW to do this. I sent the amp a 1khz sine wave and monitored the signal return with REW's RTA. I increased the level until THD exceeded 0.5%, then scaled it back by 0.1db. For amps with built-in soft limiters I approached the maximum possible outut voltage for the minimum possible input voltage in 0.1db steps.
The generator in REW fades in, which results in 3.5 cycles (@1khz) being between -6db and 0db. That is equivalent in power to 1.75 cycles at 0db, which is why I generally add 2ms to the duration charts for the results. Not that it really makes a difference, but hey, I'm doing it.

To 5-7:
I record all the signals with Cubase 10 Pro. Vmax is determined through the Pmillet's voltage meter readout. I compared it against my HoldPeak TrueRMS meter and both were always within 1%. You can see my test environment in Cubase below. I checked THD of the recordings with MathAudio's THD Meter and noticed that as soon as the sine wave started looking clipped, it approached 0.5% THD. A very convenient way to quickly see if I need to reduce the output for a certain load (I did so in 0.1db steps if needed). I check all results with the THD meter notheless.

To 8:
I export the recorded files and open them in Adobe Audition. Audition can display peak levels under the cursor, which makes my life much easier.
I use Microsoft Excel to do the calculations for me and plot the charts with. I feed it the reference dbFS(RMS) value and its corresponding RMS voltage, the recorded db value and the load it was connected to. Excel calculates the generated power and plots it over the user defined time axis.
This is what my excel table looks like, with the Sanway FP-13000 into 1x4Ohm and 1x2Ohm as an example:

Everything in green is user input for easy navigation.
Power numbers posted will be the 100ms value. If any value within the 10s window deviates from that value by more than 5%, the power over time graph will be posted as well.
Default time stamps are used when the changes are linear (left example above). I will adjust the time stamps when the default time stamps wouldn't represent the actual power over time plot accurately (right example above).

The whole setup looks like below. The supply line is 6mm² (9AWG) 3x230V 32A. I log the voltage and current readouts of my power distributor. Speakon cables are 4mm² (11AWG). Even after several back-to-back full duration tests (2 minutes each) with ~2KW dumped into the loadbank, it was still completely cold to the touch from the outside. The tank holds about 15l of water.

Got an impedance sweep outside today. And gave them some music. They have lots of headroom for a cab this size for sure.

I just saw that the Eminence driver is also available in Europe now. I'd get three 21DS115 for its price here and even the 21IPAL is still cheaper 😐

Observations:

Actual Frequency response vs Simulated HR+Edge Output:

I didn't expect the native frequency response to be +- 1db from 35 to 100Hz, that is very nice. Average sensitivity is 89db at 2.83V @ 2m groundplane outside from 35-100Hz.

The HR response here has been scaled down by 4.5db, the measurement was 1m, normalized to 2m (-6db). I don't know how the sensitivity ended up 1.5db higher than the sim, but I ain't complaining.

Feeding the cab a 28.3V sweep showed zero compression between 40 and 80Hz. I didn't get a louder sweep yet, but the cab started to produce wind noise with 70V signals between 30 and 50Hz.

It was hard for me to make out a tuning point as there wasn't a clear excursion minimum, but it seems to be 37-38Hz. I will get an impedance sweep tomorrow.

Conclusion:

I'm not entirely sure if this is actually the case, but it seems like the shaped port made the peak from the port loading a bit broader, which is why the peak is much smaller compared to the sim and the sensitivity around the peak is a bit higher. Maybe this is also the reason why I had trouble finding the excursion minimum.
The tuning is quite low for a 12" 85L (3cuft) PA cab. The back chamber is about 50L (2cuft). I might go for a slightly higher tuning in v2, making the port entrance flare a little bigger and maybe adding some port area. The average port area is 120cm². It wouldn't hurt (ergonomically) if the cab was like 1cm wider. F6 is 31Hz, which is a good 10-15Hz lower than most PA subs this size.

And most importantly: I like the sound!

Colour me impressed, whatever I throw at it, I can't get the ports to make excessive noise.

Tuning came in at around 38Hz and even 35Hz sines at Xmax produce very tolerable wind noise. The results are very impressive and they also sound great without a dsp dialed in yet.

I designed them to have increased sensitivity where excursion is low (slightly rising response towards the top end plus a bump around tuning), which will be corrected via dsp, since those subs were never intended to be used on non-dsp amps. I will get a free field measurement tomorrow. Unless it rains.

They weigh just 19kg (42lbs or so) and have an external volume of 85L. I designed them to realize smaller shows alone (weddings etc.).

They're also surprisingly stable when I pole-mount my EV ZLX12 on top. This is a great compact setup. I was going to do like 5 weddings with em next month, but the current health crisis delayed those by a few months. No actual gigs in the near future 😞

Finally! Measurements coming soon. If the weather is on my side.

2 hours ago, pazo said:

I have 2 pieces RCF 21n401  .Any suggestions?

That is a fairly high Qts driver, which is not ideal for "small" cabs like this. The sims don't look good either. Voltage sensitivity is really rough and hornresp says it has 5db less headroom than a 21DS115.

5 hours ago, Ricci said:

I can't hear much past 16kHz anyway these days

Blame those rough raw gigs back in the days..! At some point I started wearing ear protection for rehearsing and don't even know how I could endure playing the drums without em pretty quickly.
I'm so happy that our band uses a full blown IEM system now, so I don't have to kill my ears with every gig. That nasty china cymbal...!

6 minutes ago, Droogne said:

The DE360 only goes down to 1200hz, and my synergy stops at 700hz.

Yea I'll likely cross it at around 1.5k. I think a three way will be the better choice if your crossover will be that low.

6 minutes ago, Droogne said:

What would you recommend for inside EQ (in a 'chaotic room'). Just EQ down to 500hz?

You'll need to get rid of all reflections which make its way into the mic. Since the mic is omni, you basically have to eliminate all reflections ideally (resulting in an anechoic chamber).

Your horn is quite big so the mic distance should ideally be at least twice the largest dimension of your baffle (the diagonal in most cases which results in a mic distance of over 2m for you), but the closer your mic is to your sound source, the louder it is in relation to the reflections. I think you'll get decent results if your mic is between .5 and 1 meter away from the speaker and you hang blankets on the sides of the speaker and the mic. Carpet on the floor and another blanket ceiling should do the trick.

The blankets should not be touching the speaker or they will mess with the edge diffraction.

And EQ the drivers after the crossover if that's possible with your hardware. My next DIY project will be driven by a Hypex FA123 per speaker which has more than enough dsp for the task!

Cool topic, I wonder why I haven't discovered it yet.

For speaker measurements I'd recommend doing those in a anechoic room (outside for us plebs). I think speakers with a native flat response over ~500Hz sound better than speakers which have been EQ'd flat indoors. Our brain basically filters out reflections to a degree, which the measurement mic does not. Even if you end up measuring a spike and EQ'ing that away, you might percieve it as lacking in that region then.

If you have enough amp channels/dsp channels you could go with the B&C DCX464 as alternative to the BMS. It will have higher dynamic range (111db sensitivity+almost 400W power handling?! dear god...) and probably have a wider operating range due to the dedicated mid. It's priced similarly. I'm planning on doing a build with those and possibly something like a 12NDL88 or some 10" drivers.

I'll also play around with the DE360. It won't go ultra loud but the HF response is super smooth with the new diaphragm material. Plus that one is only like 60€!

3 hours ago, Ricci said:

I've heard that as usual for a 2" exit cd the air above 14 or 15kHz isn't as good as a smaller cd or a Be unit but the midrange is supposed to be very good.

B&C have optimized phase plugs inside their CD's to help with that issue and if you built some into your horn throat it should help. Would probably be too much effort for a single DIY project thou and I have no clue what those would look like.

11 hours ago, klipsch said:

@Ricci Instead of the "8 point star" design as the throat braces, would a "tic-tac-toe" pattern work as well?   Something very rough like this?

 

 

Nice joints there! 😊

39 minutes ago, Droogne said:

Yup yup, all "non-essential" stores will be closed from tomorrow on. So I will not be able to buy the wood I need. Will have to shelve the project. I'll finish up the design, focus on tweaking my mains (of which I will be starting a large thread on AVS/diyAudio/both), study, and hope I have the time to build the subs before my event in june. 

That's what I have an emergency stock for..!

I staple gunned foam to the sides to reduce distortion, especially out of band distortion when running at high output levels. Any sort of filling will reduce maximum output capabilities.

PA subs usually don't use filling for that reason. If you have a very nasty resonance resulting in a bad waterfall plot, using some (lots of) filling will enhance SQ, but reduce sensitivity and efficiency. I'd line the sides with foam and only add some actual filling if I notice anything problematic when measuring/listening.

It was +75% of the shorter dimension in my case, since the port opens to the side of the longer dimension in my cab.

It's a guess, but the tuning of yours will probably come in between +50% and +75%.

What are you trying to achieve with the filling?

It will drop the tuning, but probably not by a noticeable amount. The cab will still be like 3cm off the ground and there are no side walls in addition to that.

Also, the air pressures outside the cab and inside the cab differ, which probably also has an affect on how the geometry behaves, which is probably also insignificantly small. 
With my cab, I got the tuning spot on when I added 75% of the vent width to the length, with a vertical port. But that‘s only due to the weird port entry geometry and the fact that the port is only about two port widths from the rear wall. And the handles...

Your port is pretty long to begin with, so the difference will be like 1Hz or so. I‘d not care much.

Keep in mind that the video above is one channel of the FP-13000 running full tilt into the impedance minimum of the 1/3 vent SKHorn there, which basically feeds it like 5KW since the two 21DS115-8 are in parallel. I never run into audible port chuffing during regular use, since I roll off the below 20Hz stuff usually.

39 minutes ago, klipsch said:

I have experienced this with orbital shifters. There are videos with sheets waving in front of them from the air velocity. Looks cool, sounds like...

To each their own. 

Gotcha. No I haven't done anything custom with extruded aluminum profiles yet. All aluminum components you see came with the machines and are not off the shelf profiles.
They've been sturdy enough for me to never break anything. All moving parts on the table saw are aluminum and everything else is steel. The machine is over 2000lbs, but using it feels pretty easy.

I thought about doing the CNC stand with Bosch/Item profiles but my dad offered to make one from wood, which is what you see there. I wish I had welded a steel frame. The wooden construction moves too much for my taste.

1 hour ago, klipsch said:

Haha exactly. 

Using the room simulator in REW really helped me when I was designing / building my room. 

I originally had my first row of seating in a massively bad null area. Moved it forward 12 inches, got better... Moved it 18 inches and all nulls were basically removed. Moving the speakers did nothing in the simulation as that spot in the room was just a bad room node spot based on dimensions. Adding different treatments helped that original location's response, but why start with something poor like that if you don't have too? 

I have not come across that feature yet. So you'd say it's reliable? Did it predict the actual room response/dispersion well enough?

If you reverse the butterfly layout on both subs, you could join the two volume boxes to a simple case. Brace it a little and add some PE foam and you have a mixer case or case for mic stands w/e you're carrying around with you

On 3/11/2020 at 1:20 AM, klipsch said:

How well has the extruded aluminum worked for you?  I've heard good things...

What exactly are you referring to? The T-Slot table?

Well if he is using the cab at home it's probably the room. I have a null at exactly 63Hz in my room, so I also feel like the SKHorn is lacking something.

When there are nulls, there are peaks somewhere else. If I stand in the 63Hz peak it feels like I'm in a fist fight with Mike Tyson.