• WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required as is 20 years of participation in forums (not all true). Come here to have fun, be ready to be teased and not take online life too seriously. We now measure and review equipment for free! Click here for details.

SEAS Thor MTM loudspeaker kit - some questions about wiring for 2-way config

OP
M

Music1969

Major Contributor
Joined
Feb 19, 2018
Messages
2,095
Likes
1,131
What I meant was that if you did not want to parallel the woofers, or put them in series, drive them with individual amps, but using the same crossover and EQ settings. THis would require an effective "3 way" active system but operating with only one crossover frequency.

Ah yes. I can do this in the software but I can't find a nice looking 3 x pair speaker binding post plate

It looks from the measurements like the amp would see these parallel wired woofers as approx a 4 ohm load so I'm not concerned.

If it dipped to 2 ohms in the measurement I'd probably use your method
 
OP
M

Music1969

Major Contributor
Joined
Feb 19, 2018
Messages
2,095
Likes
1,131
But I believe Figure 10 was generated while the woofers and their network were not connected with the tweeter network

The woofer spec shows voice coil resistance of 6.1 ohm

http://www.seas.no/index.php?option...08s-w18e001&catid=49:excel-woofers&Itemid=359

I'm curious why Fig 10 then doesn't show a min impedance of 3 ohm for parallel woofers?

Unless Fig 10 does have the passive crossover in play?

Not a major thing for my project but just trying to learn along the way
 

R Swerdlow

Member
Joined
Jun 9, 2020
Messages
66
Likes
100
Maybe it would help if you got used to looking at more schematic diagrams of speaker designs. There are different ways to draw the diagrams and to wire the speakers. But all of them make it clear which terminals are connected to what. Ignore the caps, coils and resistors, and focus on the +plus and –minus termials on the speaker inputs and the drivers.

Here is an MTM where the woofers are wired in parallel
1619055024720.png


And here is another MTM design where the woofers are wired in series:
1619055198746.png
 

R Swerdlow

Member
Joined
Jun 9, 2020
Messages
66
Likes
100
The woofer spec shows voice coil resistance of 6.1 ohm

http://www.seas.no/index.php?option...08s-w18e001&catid=49:excel-woofers&Itemid=359

I'm curious why Fig 10 then doesn't show a min impedance of 3 ohm for parallel woofers?

Unless Fig 10 does have the passive crossover in play?

Not a major thing for my project but just trying to learn along the way
Resistance and impedance are not the same thing, even though they have the same unit of measure, Ohms. Resistance is when a signal is direct current (DC). Impedance is when a signal is alternating current (AC). Audio signals are AC.

In those SEAS W18 drivers, their voice coil resistance is 6.1 Ohms and that is constant no matter what signal is fed to the speaker. It's nominal impedance is said to be 8 Ohms, but in reality, it varies with the audio frequency as shown below. I labled the impedance curve. Read it's impedance values on the right side of the graph.
1619056105003.png


I believe Figure 10 does not have the woofer part of the crossover network in play. It shows the combined impedance of two woofers, wired in parallel, at frequencies higher than the 2.5 kHz crossover frequency.
 
Last edited:
OP
M

Music1969

Major Contributor
Joined
Feb 19, 2018
Messages
2,095
Likes
1,131
Resistance and impedance are not the same thing, even though they have the same unit of measure, ohms. Resistance is when a signal is direct current (DC). Impedance is when a signal is alternating current (AC). Audio signals are AC.

THANKS AGAIN, my really noob level understanding was that resistance is a component of impedance.

So I thought that minimum impedance shown on the curve is likely to be related to the 6.1ohms of the voice coil?

Or not really?
 

R Swerdlow

Member
Joined
Jun 9, 2020
Messages
66
Likes
100
THANKS AGAIN, my really noob level understanding was that resistance is a component of impedance.

So I thought that minimum impedance shown on the curve is likely to be related to the 6.1ohms of the voice coil?

Or not really?
Resistance and impedance are not unrelated, but only impedance matters when it comes to measuring speaker performance or designing crossovers.

You can't expect to calculate impedance correctly. You have to measure it with a frequency sweep. And, you have to do that measurement while the woofers are mounted in the cabinet you intend to use. The cabinet design affects the low frequencies of a woofer. (The impedance curve that SEAS published doesn't show cabinet effects.) That's why that D'Appolito article had so many impedance graphs. He designed both the cabinet and the crossover.

You can't properly design a passive crossover without knowing the impedance of the woofers and tweeter in the frequency range affected by the crossover. I believe the Thor MTM has 3rd order crossover slopes, so that would be 2,500 Hz ±1.5 octaves, roughly 1,000 to 6,250 Hz. If it has 4th order slopes, that range would be narrower, ±1 octave, roughly 1,250 to 5,000 Hz.

For those metal woofers, don't even think about using 2nd or 1st order crossover slopes. You'll hear ugly sounding break up noise from the woofers. See the W18's large break up peak between 3 and 6 kHz. You'll also hear distortion from the tweeter. That distortion might be short lived, as the tweeter might fail.
 
Last edited:
OP
M

Music1969

Major Contributor
Joined
Feb 19, 2018
Messages
2,095
Likes
1,131
Resistance and impedance are not unrelated, but only impedance matters when it comes to measuring speaker performance or designing crossover.

You can't expect to calculate impedance correctly. You have to measure it with a frequency sweep, and you have to do that measurement while the woofers are mounted in the cabinet. The cabinet design affects the low frequencies of a woofer. (The impedance curve that SEAS published doesn't show cabinet effects.) That's why that D'Appolito article had so many impedance graphs. He designed both the cabinet and the crossover.

You can't properly design a passive crossover without knowing the impedance of the woofers and tweeter in the frequency range affected by the crossover. I believe the Thor MTM has 3rd order crossover slopes, so that would be 2,500 Hz ±1.5 octaves, roughly 1,000 to 6,250 Hz. If it has 4th order slopes, that range would be narrower, ±1 octave, roughly 1,250 to 5,000 Hz.

For those metal woofers, don't even think about using 2nd or 1st order crossover slopes. You'll hear ugly sounding break up noise from the woofers. See the W18's large break up peak between 3 and 6 kHz. You'll also hear distortion from the tweeter. That distortion might be short lived, as the tweeter might fail.

Cheers for the tips.

I'm now armed and dangerous to make an attempt with this DIY MTM build :)
 
OP
M

Music1969

Major Contributor
Joined
Feb 19, 2018
Messages
2,095
Likes
1,131
Top Bottom