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

Music1969

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Hi all

I'm interesting in buying the SEAS Thor MTM loudspeaker kit and doing some DIY DSP crossover stuff for fun / learning

http://www.seas.no/index.php?option...as-diy-kits&catid=66:seas-diy-kits&Itemid=250

Speaker measurements: http://www.seas.no/images/stories/diykits/thor/audioXpress_Thor_Review.pdf

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

I'm a noob so please forgive my silly questions here.

Amp is a Denon AVR-4308. I already use this AVR for another 2-way DSP DIY active setup, so the idea of how to setup DSP crossover etc, I'm ok with.

But it's wiring for the MTM config that's new to me.

My understanding (please correct me if I'm wrong with anything):

This SEAS Thor kit a 2-way MTM design with crossover at 2.5kHz, so that is probably a good starting point for me (measurements) playing with DSP crossover.

The individual woofer spec sheet shows a minimum impedance of approx 6 ohms.

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

On wiring the pair of woofers in MTM config, for active setup I want to keep this as a 2-way config, so I would wire both of the woofers together in series , correct?

If each woofer individually has minimum 6 ohms impedance then the pair of them wired in series would mean the amp sees this as 12 ohm (minimum) load ? Is that correct ?

Is wiring this pair of woofers for MTM config as simple as the below crappy quick sketch i made? The pink wire is the series connection between woofers


MTM wiring.png



Any corrections and tips much appreciated !
 

somebodyelse

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Looks right to me. I'd probably include a capacitor in series with the tweeter to give it some protection in case of DSP mistakes, but it's not strictly necessary. Starting with the woofers in series is less likely to cause problems for the amp so is a good choice. Check the amp spec to see if it can cope with the 3R parallel combination.
 
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Music1969

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the 3R parallel combination.

Can you explain what you mean by "the 3R parallel combination" ?

With the Denon AVR-4308, one amplifier would be dedicated to the pair of woofers and a separate amplifier for tweeter.

Tweeter is approx 4 ohms and pair of woofers approx 12 ohms (minimum)?
 
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OP
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Music1969

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I'm an amaateur with understanding circuits but in the original design, below is the passive crossover design.

Are both woofers playing the same frequencies in this design?

This is not a 2.5-way design is it?

1619012745771.png
 

somebodyelse

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Can you explain what you mean by "the 3R parallel combination" ?

With the Denon AVR-4308, one amplifier would be dedicated to the pair of woofers and a separate amplifier for tweeter.

Tweeter is approx 4 ohms and pair of woofers approx 12 ohms (minimum)?
If you connect the 6 ohm (6R) woofers in parallel rather than series then the load seen by the amp is 3 ohm (3R). Some amps are ok with a load this low, but others aren't. If the amp is ok with it, and if you don't get enough volume with them in series (the amp runs out of voltage), then you can try them in parallel which should deliver more power.
https://circuitdigest.com/calculators/resistors-in-parallel-calculator
 

R Swerdlow

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On wiring the pair of woofers in MTM config, for active setup I want to keep this as a 2-way config, so I would wire both of the woofers together in series , correct?
Not correct. The crossover schematic clearly shows those two woofers are wired in parallel with each other. Don't wire them in series.
I'm an amaateur with understanding circuits but in the original design, below is the passive crossover design.

Are both woofers playing the same frequencies in this design?

This is not a 2.5-way design is it?
This is not a 2.5-way design. Both woofers receive the same signal and play the same frequencies. (There will be small differences in the lower frequency performances of the 2 woofers. This Transmission Line design places one woofer in the optimal position and the other woofer in a less than optimal position.)
 
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R Swerdlow

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Look at Figure 17 in the Thor review article. Two of those woofers, wired in parallel, in a properly filled TL cabinet, combined with the tweeter and it's crossover network, generate impedance values that are barely below 4Ω, in the range of ~150 to 300 Hz. In that same frequency range, the impedance phase angles change from about 0° to about +45°. This is a gentle phase shift compared to many other 4Ω speaker designs. Those impedance values may seem low, but with that modest impedance phase angle shift, most amps capable of 4Ω loads should be able to handle these speakers.

D'Appolito says:

"THOR’s impedance magnitude and phase are plotted in Fig. 17. The minimum impedance of 3.6Ω occurs at 180Hz. The impedance peak of 18.3Ω at 1.5kHz is caused by the interaction of the woofer and tweeter crossover networks forming a parallel resonance at that frequency. The maximum phase angle of 45° occurs at 2140Hz, but the impedance magnitude at that point is 10Ω. The system impedance is rated at 4Ω."​
1619020604519.png

Do not be confused when comparing Figure 17 with Figure 10. In that figure, two of those woofers, wired in parallel generate impedance values that are barely below 4 ohms, in the range of 100 to 1,000 Hz. This frequency range is wider than in Figure 17. But I believe Figure 10 was generated while the woofers and their network were not connected with the tweeter network.
1619018991568.png
 

R Swerdlow

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OP is planning on using DSP instead of that crossover.
Understood. Going with DSP instead of a passive crossover is one thing. But altering the original MTM design is something entirely different.

@Music1969 – When you mentioned wiring the woofers in this MTM design in series, instead of in parallel, were you concerned over the 4Ω impedance? I wrote my previous response (post #9) while believing that this worried you. If so, you shouldn't worry. Were you thinking of this, or of something different?
 
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Music1969

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Do not be confused when comparing Figure 17 with Figure 10.

In both cases though, if I wire woofers in parallel with DSP crossover, 4ohm rated will be fine ?

If i wired the woofers in series, will the signal frequencies be identical still for both woofers? Or will one woofer have potential to affect performance of the other woofer when in series wiring?
 
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Music1969

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Understood. Going with DSP instead of a passive crossover is one thing. But altering the original crossover design is something entirely different.

@Music1969 – When you mentioned wiring the woofers in this MTM design in series, instead of in parallel, were you concerned over the 4Ω impedance? I wrote my previous response (post #9) while believing that this worried you. If so, you shouldn't worry. Were you thinking of this, or of something different?

Hi thanks for both your help on this, really appreciated.

The 4 ohms didnt worry me but 3 ohms would.

It's moreso deviating from original design that worried me which is why I thought to share the passive design and ask for clarification if this was parallel or series. Now I know the original design is parallel for woofers.

My main worry with series wiring is in post just above,
if series wiring of woofers would cause one woofer to affect performance of the other. Would frequency response of each woofer be slightly different with series wiring?
 

R Swerdlow

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In both cases though, if I wire woofers in parallel with DSP crossover, 4ohm rated will be fine ?
Yes. Do you have an amp in mind that you plan to use with these speakers? Many decent quality AVRs rated at 100-125 wpc at 8Ω should be able to drive these speakers. Those SEAS Excel drivers are very good quality, and they can easily handle higher power as well.
If i wired the woofers in series, will the signal frequencies be identical still for both woofers? Or will one woofer have potential to affect performance of the other woofer when in series wiring?
If wired in series, the voice coil of one woofer can act as a variable inductor (depending on the music signal). As a result, it can variably affect the signal going to the other woofer. It's simpler to avoid that complexity. If low impedance was your concern, I wouldn't worry.
 
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Music1969

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If wired in series, the voice coil of one woofer can act as a variable inductor (depending on the music signal). As a result, it can variably affect the signal going to the other woofer. It's simpler to avoid that complexity. If low impedance was your concern, I wouldn't worry.

My Denon AVR-4308 is currently driving 4 x 4 ohm drivers at the moment (dsp crossover) without issues at the SPLs I listen.

It sounds like if I wire woofers in parallel for this Thor speaker, the amps of this AVR will see similar 4 ohms loads , so i'll do parallel wiring

I'll start with same DSP crossover point that D'Appollito used with his passive crossover design , as a starting point and measure

I need to figure out how to exactly wire the woofers in parallel too.

I'll sketch something and post here for you guys feedback
 

dougi

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Your AVR seems to have 7 external in channels and amplifiers. Can your DSP support active 3 way? Just use same xover/EQ for each woofer and wire to each. You may need to create more binding posts on the speakers though, but as you are building it not an issue?
 
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Music1969

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Your AVR seems to have 7 external in channels and amplifiers. Can your DSP support active 3 way?

This MTM design with the woofers in parallel, is only 2-way right? Just a single crossover point?

Yes would need 2 x pairs of speaker terminals on the back of each speaker. Just need to use this:

1619051643566.png
 

dougi

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This MTM design with the woofers in parallel, is only 2-way right? Just a single crossover point?

Yes would need 2 x pairs of speaker terminals on the back of each speaker. Just need to use this:

View attachment 125572
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.
 
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