Port tuning measurement

**JonMarsh** · 19 February 2022, 21:27 Saturday

The easiest way to get a nice impedance plot is a low cost tool like the DATS tester from Parts Express. There are similar older and slower ones, but DATS is what I use now. You do have to have a PC and install simple software.

Dayton Audio DATS V3 Computer Based Speaker & Audio Component Test System

https://www.parts-express.com/Dayton-Audio-DATS-V3-Computer-Based-Audio-Component-Test-System-390-807

Dayton Audio DATS V3 Computer Based Speaker & Audio Component Test System Dayton Audio DATS V3 Computer Based Speaker & Audio Component Test System The Perfect Companion for Audio Professionals When designing the DATS V3 measurement device, Dayton Audio took everything customers love about the DATS V2 and improved upon the accuracy, capability, reliability, convenience, and flexibility. Any engineer knows that valid and accurate data is crucial to great results. DATS (Dayton Audio Test System) V3 is the essential tool in any speaker designers or audio engineers toolbox, providing accurate, precise measurement data for any audio transducer or loudspeaker system. Save yourself time, money, and trial-and-error frustration by using DATS V3 to measure loudspeaker drivers, crossover networks, and complete audio systems! DATS V3 is a unique, multipurpose test system that works with your PC and full-featured test software to measure the impedance response of a speaker driver and derive a complete set of Thiele/Small parameters that describe its operation. Its as easy as connecting a driver and starting the test! The DATS V3 measurement module provides the electrical stimulus to the driver, measures the drivers impedance on the fly, and then creates a high-resolution graph (30,000 data points!) with no additional hardware required. Whats better about Version 3? From the outside, the DATS V3 has a completely updated look and feel. The extruded aluminum housing makes DATS V3 durable enough to throw into a toolbox without worrying about damage. In addition, optional mounting brackets give you the option to mount the DATS V3 under a desk or test bench to save space. No more searching for a calibration resistor, it is now integrated into the case, just clip the test leads onto the pins on the front of the housing and run the calibration. Also, the test leads have been upgraded to removable insulated banana plug test leads, giving you the ability to use your favorite test leads and easily replace damaged test leads (test leads are included). Finally, we have added a USB-B jack rather than an integrated USB cable (USB A to B cable included). This allows the cable to be quickly swapped if there is any damage, or if a different length is preferred. The improvements continue on to the inside of the DATS V3. The internals have been completely redesigned and improved to deliver better accuracy and more power. With increased output power, the DATS V3 allows you to take measurements at a higher level to minimize the chance that a high noise floor or vibration could affect measurement results. Dayton Audio has also upgraded many of the internal components with tighter tolerances to minimize the margin of error that is caused by a components value variance. Even the calibration resistor has been upgraded to 0.1% tolerance. DATS V3 software is the true power of DATS. The included software not only measures impedance and parameters of speaker drivers with incredible accuracy, but the addition of the DATS Linearity Test gives you the ability to observe changes in parameters with differing drive levels. The Linearity Test automatically performs multiple sweeps of the driver at increasing (or decreasing) levels while saving each test result to memory making it easy to recall and compare the results. As always, the DATS V3 still has the capability to measure the true value of inductors, capacitors, and resistors, and it also works as a signal generator and scope to let you monitor small electrical signals (line-level only). Even more updates are planned to further set DATS V3 apart from the competition. Features Rugged aluminum housing with detachable test leads and built-in precision calibration resistor Tighter tolerances on internal components for more precise measurements Linearity test allows you to easily observe shifting parameters with different drive levels Increased output capability for greater separation from the noise floor for more accurate measurements Optional under desk mounting brackets to save desk space Precise impedance response measurement for loudspeaker drivers and complete systems Accurate measurement of loudspeaker electromechanical parameters (Fs, Qts, Vas, and many more) Measurement of advanced Wright Model parameters (Kr, Xr, Ki, Xi) for precision simulations Precise, high-resolution impedance response measurements with 30,000 data points (1 Hz to 20,000 Hz) Save and compare up to 20 impedance graphs simultaneously within one test file Integrated quality control feature set provides pass/fail parameter measurement Sensitive rub and buzz detection functionality reveals hidden flaws in individual drivers Software signal generator with selectable waveform, frequency, and amplitude Generates sine, square, triangle, saw tooth, impulse, pink noise, and log sweeps Oscilloscope software mode with dual traces, plus adjustable time and amplitude scales Oscilloscope and generator modes are compatible with other audio interfaces Quality test interface hardware assembled using precision SMT components and automation High-quality alligator clip leads minimize contact resistance for improved consistency Includes method for calculating Vas from specified Mmd Faster-than-ever hardware startup time virtually eliminates warm-up/cool-down Measurements The DATS V3 software provides you with an array of tools that are great for all speaker designers Measures T/S parameters Linearity test Precise impedance measurement Efficient Pass/Fail workflow Calculates VAS from Mmd Resistor measurement Signal generator with 10 different functions Measures advanced Wright model parameters Rub and buzz detection Oscilloscope with dual traces Capacitor measurement with ESR, dissipation factor, and Q Inductor measurement with DC resistance DATS V3 vs. DATS LA:DATS V3DATS LAQuick setup and easy to use✔✔Integrated 100 watt amplifier✘✔Small signal parameter measurement✔✔Large signal parameter measurement✘✔Adjustable small signal level✔✔Adjustable large signal level✘✔Motor symmetry measurement✘✔Suspension symmetry measurement✘✔Measure parameter vs. displacement✘✔Calculates displacement per voltage✘✔Measures capacitors, inductors, and resistors✔✔Oscilloscope and signal generator✔✔USB powered✔✘Compact and readily portable✔✔ A solution like no other DATS V3 is faster, more elegant, more versatile, and easier to use than any other speaker test & measurement device. Get ready for your designs to make a quantum leap, thanks to better data! T/S Parameter Measurement Quickly and accurately measure a drivers T/S parameters. Just attach the test leads directly to a driver's terminals and click "Measure Free-Air Parameters" and the impedance magnitude will be displayed on the graph along with the measured Re, Fs, Qts, Qes, Qms, and Le. Next add mass to the cone or mount the driver in a suitable test box and click "Measure V(as)" to derive the mechanical parameters such as Vas and Mms. Enclosure Tuning Verification Once your driver is mounted in an enclosure DATS V3 makes it easy to verify your system's overall tuning for vented enclosures or Q for sealed enclosures by using the "Measure Free Air Parameters" button. The system will run a quick sweep and plot the impedance magnitude making it easy to verify the actual tuning of your system. Verify Crossover Wiring and Performance Once your speaker system is complete, you can run an "Impedance Sweep" to plot the overall system impedance. A quick comparison of the measured impedance to your modeled impedance makes it easy to ensure that your crossover is wired correctly and performing as intended. Oscilloscope and Signal Generator A software oscilloscope allows you to visually observe the behavior of a circuit when presented with or without stimuli. Used in conjunction with the built-in signal generator, you'll be able to hunt down any strange phenomena, or confirm that your system is running properly. Precision LCR Meter Capacitor Measurements As a capacitance meter DATS V3 is in a league of its own. In seconds, it will measure all of a capacitor's electrical characteristics including capacitance, equivalent series resistance, Q, and even loss angle. DATS V3 is capable of accurately measure capacitance from 0.002 uF to 10,000 uF. Inductor Measurements Measure both the inductance and DC resistance of a coil with just one click. The DATS V3 is accurate from 0.05 mH up to 100 mH. Resistor Measurements Naturally, DATS V3 is also perfect for measuring resistance. As a unique feature, it will also plot the impedance of a resistor allowing you to see just how non-inductive your resistors really are. Resistance measurements are accurate from 0.002 ohms up to 10,000 ohms. Minimum System Requirements:• Operating System: Windows Vista, 7, 8, or 10 • Processor: 500 MHz Pentium III or equivalent processor • Memory: 64 MB RAM • USB Port: One available USB 1.1 or 2.0 port Note: Not compatible with macOS Join Our Speaker Building Community Learn more about DATS V3 from seasoned professionals

OTOH, if you have a signal generator and a AC DVM you can figure out the tuning just by connecting the signal generator through a 100 ohm resistor to your speaker, and sweep the frequency, and look for where you have the minimum voltage in the low frequency area.

Trust me, DATs is easier. I can do it both ways... it will generate a plot like this for a reflex system:

But if you'd rather not spend any money and work out an answer, Unibox for Excel will tell you how to size a port for a given volume box, and you can adjust the port parameters (diameter) and it will calculate the length. But you need to have a PC with Excel. Man, the things I take for granted....

So if you want, post the box size, and your port tube diameter, and the target FB, and I'll calculate it for you. And post the Unibox results. If needed, I can go back and look up the design... that was a few revolutions around the sun ago...

**jquin** · 20 February 2022, 01:32 Sunday

Thanks again Jon.
I will try to rig something up.

**CADman_ks** · 20 February 2022, 08:53 Sunday

I recently built an oversized boom box for use at the lake mainly.

I used WinISD to calculate the port size and length. I don't have any equipment to measure it to see if it's correct, but it sounds good, so it has to be close...

**JonMarsh** · 20 February 2022, 09:58 Sunday

Originally posted by jquin

Thanks again Jon.
I will try to rig something up.

Unibox is very accurate in it's predictions, so if you just give me your enclosure volume, I can do the rest. If you already have a port tube, I can calculate what you need, but I'll also look at what makes sense based on port velocity and length required.

For instance, that plot above was a target design for as passive radiator, which is a much more difficult analysis, and I was shooting for an Fb of 30-32Hz, (with Dayton RS225), and as you can see, I pretty much nailed it. With those kinds of calculation tools, verifying by measurement is pretty much optional.

**JonMarsh** · 21 February 2022, 10:22 Monday

Modula MT enclosure calculations for original PE 22L enclosure

For you and the benefit of anyone else revisiting this design, here are the enclosure parameter calculations for the vented design of the Modula MT using the RS180-4. The RS180 can provide even more extended and flatter response in a larger enclosure, but the 22L nominal original chosen is a good tradeoff between size and bass capabilities.

First, we'll show the more optimal but more difficult to build 3" port version, then the more commonly used 2" port version, and show the tradeoffs.

Note the port inner diameter is 7.5 cm.

The box Fb tuning and the -3dB point are at 34 Hz, and response is fairly flat down to 40Hz, though obviously not at room shaking SPL. This is with an input of 20 watts, which is about the low frequency limit.

Excursion is within the driver capabilities

Port air speed is comfortably below the preferred limits; from this, its likely that a 2-1/2" version would work OK, too, without port compression or chuffing.

But note that the port length is about 17-1/4", not including a port flare, so depending on the enclosure configuration and depth, this could pose a problem for a front or rear venting port; the port opening should be about 3" minimum from any enclosure wall. Possibly a bottom mount if the enclosure is tall enough, or a rear mount if a deep form factor like the Q Acoustics 3030i uses, or the one planned for the Obi-Wan.

**JonMarsh** · 21 February 2022, 10:36 Monday

Now, a 2" ID port version is examined.

This results in a much shorter port, about 7" not including flare.

The tradeoff is port air speed and compression at higher sound levels:

If we look at the 2.5" option, it splits the difference and is the minimum port diameter meeting the port speed requirements.

But this does require a port length of 11", not including flare.

**Reet** · 22 February 2022, 09:57 Tuesday

Originally posted by jquin

Hi All
It's been many years since I have posted about speaker building by my son now has an interested in the topic.
I have built a new Modula MT box that will fit in the corner of the room but when it comes to measuring the port's resonant frequency it has been nothing but frustration.
I dusted off the all wallin jig and speakerworkshop but all the results were a failure.
I can not seem to get an impedance measurement going.

So anyway what is the preferred way to get an impedance vs freq plot in order to tune the port?
I'm getting very close to just measuring the port length on the original box and using that.
It's been over 10 years and I can't remember how I got any of this stuff going. *sigh*.

Any advice would be welcome

You've got everything you need in the Wallin jig, but maybe its time to try some more modern software..ARTA or REW will both do the trick. I personally prefer ARTA, the GUI is a lot less cumbersome I find.

All that is required for impedance & T/S measurement is any functioning sound card and a few resistors. As few as 1 resistor if you want to cheap out and make a low level un-amplified jig, similar to the old DATS/WT.

I prefer to include the amplifier for greater reliability and versatility, it just needs an additional voltage divider at the soundcard input to step down the speaker level signal to line level:

Of course, if you study the guts of the old Wallin jig you will find something rather similar already included. Above images are from the ARTA/LIMP manual, a good reference to get started:

https://artalabs.hr/download/LIMP-user-manual.pdf

**Juhazi** · 22 February 2022, 16:14 Tuesday

" I have built a new Modula MT box that will fit in the corner of the room but when it comes to measuring the port's resonant frequency it has been nothing but frustration."

Do you have a mobile phone? Or your son? Do you have a PC or laptop?

Download some freeware sound analyzer app in the phone. Download some freeware sound generator/analyzer progam in laptop (RoomEQWizard for Win). Install and learn to use them!

Use laptop/REW to generate and play pink noise and connect it to an amplifier and that to the speaker. Open phone's analyzer app and put it at the opening of reflex tube and you will see frequency plot, the highest peak spl is the tuning frequency! Use dB(C) or dB(Z) instead of dB(A) filtering to get valid response of low freq! Headset or webcam microphones usually have fixed highpass filter, so they don't work below 50Hz.

If you don't want to use REW or alike, and you have a FM receiver, tune it between stations (disable off-station mute) to get noise to the amp

Anyway, please invest 100$ on some USB-microphone like Minidsp UMIK-1.

**JonMarsh** · 22 February 2022, 16:20 Tuesday

Or just set the port ID and length per the calculations above! YOU DO NOT NEED TO MEASURE IT!

**Reet** · 22 February 2022, 19:53 Tuesday

If all you want to know is resonant frequency and the rest of the speaker is unknown, you can just lay the speaker face up and use a function generator phone app. Throw some rice on the speaker and use the generator, the frequency with least rice bouncing is the resonance.

Port tuning measurement

Port tuning measurement

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