Hello, while trying to take quasi-anechoic for some of my test speakers for a variety of drivers, I noticed that non of them exhibit, the usual behavior, of sharp SPL drop from the woofer around the port tuning frequency. Also, when measuring the impedance with REW and a DIY jig, there aren't two separate and define spikes of impedance (the middle of which is usually the port tuning frequency). The measurements show relative agreement with models made with WinISD show I suspect it's something with my designs.
How should I utilize drivers like this in vented enclosures? The ND90 supposedly should be able to provide good and linear results, but the other two either give a huge output spike if the tuning frequency is near the Fs or the response ripples near the roll off.
Driver's I've used:
ND90 8ohm
TEBM35C10-4
Aliexperss 3inch T/S parameters acquired with manual measurements.
(measurements not baffle diffraction corrected)
How should I utilize drivers like this in vented enclosures? The ND90 supposedly should be able to provide good and linear results, but the other two either give a huge output spike if the tuning frequency is near the Fs or the response ripples near the roll off.
Driver's I've used:
ND90 8ohm
TEBM35C10-4
Aliexperss 3inch T/S parameters acquired with manual measurements.
(measurements not baffle diffraction corrected)
What are the IR window settings? Is your mic in the middle of the woofer and very close for the measurement? Is the mic in the middle of the port and in line with the vent opening for the measurement?
On further review, you seem to have tuned the ND90 really low for a 3.5" driver with an FS of 71Hz. How big is the cabinet and port?
These aren't gated measurements so I havent touched IR.
Yes the mic was in the middle of the cone and port with just enough clearence so that it doesn't come into contact.
The ND90 is in 4L box with a 65hz port.
Though judging from the graph the actual port tuning might be lower than I thought...?
The other two are in 1L Boxes with 120hz and 100hz port tuning.
The ND90 with its 0.65 Qts is severely under damped, requiring in theory this T/S max flat alignment:
Vented net volume (Vb) (L) = 20*1.77*.65'^3.3 = 3.5942 L
(Ft^3 = (Vb)/~28.31685)
Vented box tuning (Fb) (Hz) = 0.42*70.7*.65'^-0.96 = 44.9 Hz
F3 (Hz) = 70.7*0.28*.65'^-1.4 = 40.7 Hz
So from this we see that with an even larger box tuned higher this is why you're not seeing the second spike because you're squelching it, an early prosound mid-bass alignment made popular for DIYers by Wayne Parham/Pi Speakers IIRC, but his White Paper has apparently been scrubbed from the net and only found the Word doc, which I no longer can open; regardless, I used it just as you have by happy accident to get excellent results venting high Qt drivers.
Vented net volume (Vb) (L) = 20*1.77*.65'^3.3 = 3.5942 L
(Ft^3 = (Vb)/~28.31685)
Vented box tuning (Fb) (Hz) = 0.42*70.7*.65'^-0.96 = 44.9 Hz
F3 (Hz) = 70.7*0.28*.65'^-1.4 = 40.7 Hz
So from this we see that with an even larger box tuned higher this is why you're not seeing the second spike because you're squelching it, an early prosound mid-bass alignment made popular for DIYers by Wayne Parham/Pi Speakers IIRC, but his White Paper has apparently been scrubbed from the net and only found the Word doc, which I no longer can open; regardless, I used it just as you have by happy accident to get excellent results venting high Qt drivers.
i finished a 2.1 system with a corner placed low tuned 80l reflex box and a cheapo noname 20cm bass with certainly high q (unknown thiele small parameters). Reflex heading right into the corner. And driver close to it.
Cannot complain about the bass it does - reaching low down to 30hz listening to a sweep. In room response at listening point is good.
I tried no damping at all inside and the active filtering at 100hz is good enough suppressing the mid frequencies. Amp is mini class d: Zk mt21 with cs8673 chips.
Was prepared to add damping and an extra magnet to the driver if bass is boomy but its not.
Also prepared a second driver for isobaric clamshell built but no need for this as it reaches low.
I am really fond of now building corner placed subwoofers aiming for max efficiency.
It is this "quality" of drivers, in this case only one sided with alu foil.
Cannot complain about the bass it does - reaching low down to 30hz listening to a sweep. In room response at listening point is good.
I tried no damping at all inside and the active filtering at 100hz is good enough suppressing the mid frequencies. Amp is mini class d: Zk mt21 with cs8673 chips.
Was prepared to add damping and an extra magnet to the driver if bass is boomy but its not.
Also prepared a second driver for isobaric clamshell built but no need for this as it reaches low.
I am really fond of now building corner placed subwoofers aiming for max efficiency.
It is this "quality" of drivers, in this case only one sided with alu foil.
Some Fotos with better light.
Already one sided with alu tinfoil there is a great stiffening effect. Will be added as bass for the Beyma 8agn speakers. Used for an outdoor Bluetooth speaker.
Current driven amp with Lm1875 will be used as amplification.
Already one sided with alu tinfoil there is a great stiffening effect. Will be added as bass for the Beyma 8agn speakers. Used for an outdoor Bluetooth speaker.
Current driven amp with Lm1875 will be used as amplification.
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So in essence when you say it's underdamped, you mean the total Q of the system is too low for this driver? This makes the second spike very weak and hard to distinguish in the impedance graph for example(it's just a hump)? But then again a lower tuning wouldn't really make sense for such a small driver? This is what i struggle to comprehend.
Does this give a flat alignment, because when I use this numbers in winISD the response is indeed a smoother roll off with an extended low self. The issue is the cone excursion below 35hz, and the fact that max power and max SPL is severely lowered compared to the alignment I used.
I know that by no means what i used is "flat" the opposite for that matter, there is a wide 4db bass-boost.
This issue is even bigger with the two other drivers that are even smaller in size (2 inch and 2,5 inch), it seems counter intuitive, you either shouldn't use them in a vented enclosure, or you have no other option that to underdamp them? All I get is a chebychev-like response with a high Q.
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Simulation of the ND90 and the underdamped box in Basta (with the appropriate port dimensions though the real word port has a slight conical shape) shows the characteristic drop in SPL in the driver response as well as the two impedance spikes. Maybe the software isn't able to simulate this?
Here are the T/S parameters for the two other drivers (I've taken the average of a couple of measurements because the repeatability of my jig was pretty bad):
TEBM35C10-4
TS Parameters file
Room EQ V5.20.9
Dated: Aug 31, 2024 7:07:41 PM
From measurement Tectonic Free air B2
Zmin 4.25 ohm
fmin 949 Hz
f3 6999 Hz
Le(f3) 0.065 mH
Motional impedance parameters
R0 15.15 ohm
CMES 256.8 uF
L0 3.426 mH
beta 0.0000
omega0 1585.5
Blocked impedance parameters
RDC 4.00 ohm
dR 0.09 ohm
Re 4.09 ohm
Leb 5.1 uH
Le 0.119 mH
Rss 23862.9 ohm
Ke 0.0271 S-H
Thiele-Small parameters
fs 169.7 Hz
Qms 4.147
Qes 1.121
Qts 0.882
Fts 192.3
Mms 1.06 g
Cms 0.831 mm/N
Rms 0.272 kg/s
Vas 0.14 litres
Bl 2.031 Tm
Eta 0.06 %
Lp (1W/1m) 79.73 dB
Dd 3.74 cm
Sd 11.0 cm^2
Added mass measurement: Tectonic Mass B2
Added mass 0.700 g
Air temperature 29.0 C
Air pressure 1013.25 mB
Air density 1.1682 kg/m^3
Speed of sound 348.5 m/s
Aliexpress driver
TS Parameters file
Room EQ V5.20.9
Dated: Sep 1, 2024 4:04:08 PM
From measurement JBL Free air A3
Zmin 3.65 ohm
fmin 798 Hz
f3 3730 Hz
Le(f3) 0.114 mH
Motional impedance parameters
R0 43.35 ohm
CMES 233.0 uF
L0 2.423 mH
beta 0.0744
omega0 1948.5
Blocked impedance parameters
RDC 3.50 ohm
dR -0.03 ohm
Re 3.47 ohm
Leb 5.6 uH
Le 0.199 mH
Rss 100000.0 ohm
Ke 0.0418 S-H
Thiele-Small parameters
fs 206.8 Hz
Qms 6.840
Qes 1.051
Qts 0.911
Fts 227.1
Mms 2.00 g
Cms 0.296 mm/N
Rms 0.381 kg/s
Vas 0.13 litres
Bl 2.932 Tm
Eta 0.10 %
Lp (1W/1m) 82.09 dB
Dd 4.70 cm
Sd 17.3 cm^2
Added mass measurement: JBL Mass A3
Added mass 0.700 g
Air temperature 28.0 C
Air pressure 1013.25 mB
Air density 1.1721 kg/m^3
Speed of sound 347.9 m/s
Here are the T/S parameters for the two other drivers (I've taken the average of a couple of measurements because the repeatability of my jig was pretty bad):
TEBM35C10-4
TS Parameters file
Room EQ V5.20.9
Dated: Aug 31, 2024 7:07:41 PM
From measurement Tectonic Free air B2
Zmin 4.25 ohm
fmin 949 Hz
f3 6999 Hz
Le(f3) 0.065 mH
Motional impedance parameters
R0 15.15 ohm
CMES 256.8 uF
L0 3.426 mH
beta 0.0000
omega0 1585.5
Blocked impedance parameters
RDC 4.00 ohm
dR 0.09 ohm
Re 4.09 ohm
Leb 5.1 uH
Le 0.119 mH
Rss 23862.9 ohm
Ke 0.0271 S-H
Thiele-Small parameters
fs 169.7 Hz
Qms 4.147
Qes 1.121
Qts 0.882
Fts 192.3
Mms 1.06 g
Cms 0.831 mm/N
Rms 0.272 kg/s
Vas 0.14 litres
Bl 2.031 Tm
Eta 0.06 %
Lp (1W/1m) 79.73 dB
Dd 3.74 cm
Sd 11.0 cm^2
Added mass measurement: Tectonic Mass B2
Added mass 0.700 g
Air temperature 29.0 C
Air pressure 1013.25 mB
Air density 1.1682 kg/m^3
Speed of sound 348.5 m/s
Aliexpress driver
TS Parameters file
Room EQ V5.20.9
Dated: Sep 1, 2024 4:04:08 PM
From measurement JBL Free air A3
Zmin 3.65 ohm
fmin 798 Hz
f3 3730 Hz
Le(f3) 0.114 mH
Motional impedance parameters
R0 43.35 ohm
CMES 233.0 uF
L0 2.423 mH
beta 0.0744
omega0 1948.5
Blocked impedance parameters
RDC 3.50 ohm
dR -0.03 ohm
Re 3.47 ohm
Leb 5.6 uH
Le 0.199 mH
Rss 100000.0 ohm
Ke 0.0418 S-H
Thiele-Small parameters
fs 206.8 Hz
Qms 6.840
Qes 1.051
Qts 0.911
Fts 227.1
Mms 2.00 g
Cms 0.296 mm/N
Rms 0.381 kg/s
Vas 0.13 litres
Bl 2.932 Tm
Eta 0.10 %
Lp (1W/1m) 82.09 dB
Dd 4.70 cm
Sd 17.3 cm^2
Added mass measurement: JBL Mass A3
Added mass 0.700 g
Air temperature 28.0 C
Air pressure 1013.25 mB
Air density 1.1721 kg/m^3
Speed of sound 347.9 m/s
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125ms left
500ms Right
Changing them doesn't seem to affect it
The port is a 3.5cm by 13.5cm circular port, faired on one end with a slight conical shape.
A "high" valley between two peaks (or no real valley at all) may be a sign of air leaks or eventually overdamping/too much damping between driver and port.
Have a look here for some suggestions to find air leaks.
Have a look here for some suggestions to find air leaks.
During Construction i use a small flashlight in a dark room that i place in the box to check for light bleed through the joints to check for air leaks. Also in my experience, air leaks have a resonant frequency, so if you play a sinewave and increase the frequency slowly it's easy enough to hear them.
I am pretty confident that there are no air leaks.
Too much dumping between driver and port ? You mean with damping material ? I have tried with staffing and without stuffing. The only difference i saw was the higher port resonances and a slight increase in port tuning frequency:
Green with damping material
Red without damping material
I am pretty confident that there are no air leaks.
Too much dumping between driver and port ? You mean with damping material ? I have tried with staffing and without stuffing. The only difference i saw was the higher port resonances and a slight increase in port tuning frequency:
Red without damping material