2.5 way cascaded 3 woofer series parallel

[Jed]

Hi, after evaluating my choice for a higher Xover point at around 3K, I decided that a shallow crossover slope and high crossover point such as 3K would not be optimal for an MTM configuration that I simulated previously. So now, I'm looking at an MTMM 2.5 way with a cascaded X-over network with the ".5" woofers wired in series to eachother and the "midrange" wired in parallel to the .5 woofers. The impedance is very flat at 8ohms, the sensitivity is around 90DB, and the phase is very good- especially in the bass region where it stays close to 0. Since the lower woofers are the .5 in the system, are there any negatives on how I've got the system configured with the midrange-woofer above the tweeter? I've adjusted the Z offset to allow the proper phase, but I'm wondering if wiring the .5 woofers in series would through things off or create some kind of vertical lobing problem, that I'm trying to resolve in the first place by going to a single high frequency midrange/woofer. The system uses a single inductor for each woofer section CA18RNX, and the AMT1 tweeter. Suggestions?

Regards,
Jed

[Dennis H]

Looks to me like the single "midrange" driver will be working twice as hard (twice the excursion at low frequencies) as the series ".5" drivers. Ideally, you like it the other way around to take the bass load off the midrange for cleaner mid frequencies. But then that would be a 3-way.

[Jed]

Looks to me like the single "midrange" driver will be working twice as hard (twice the excursion at low frequencies) as the series ".5" drivers. Ideally, you like it the other way around to take the bass load off the midrange for cleaner mid frequencies. But then that would be a 3-way.

I've simulated in SW designs that have the woofers configured like you suggested, that is MTM".5" but since I'm using the AMT1 sandwiched in between a rather large vertical distance/2 mids, I came up with the idea of this MT".5"".5" configuration since the lower mid woofers cross over around 1,000HZ to the tweeter versus the midrange at around 3500. Everything is basically 1st order. The original designer of the pictured speaker has the midranges crossed over even higher than I'm proposing and had mids spaced like the picture I attached to the first post. I guess they sound excellent, but I'm questioning the validity of having such a high and shallow X-over for an MTM section.

Regards,
Jed

[Dennis H]

I've simulated in SW designs that have the woofers configured like you suggested, that is MTM".5"

No I suggested a true 3-way with a single mid and two woofers.

[Jed]

No I suggested a true 3-way with a single mid and two woofers.

I'll give the true 3-way idea a try, but I really am liking the flat impedance and high sensitivity of the cascaded 2.5way setup. Why do you say the midwoofer section draws more power than the series "woofers," when all 3 woofers share bass duties in the series parallel 2.5way configuration?

[Dennis H]

The way I understand your crossover layout, ignoring caps and coils for a moment, it's:

--M (8 ohms)
--W-W (16 ohms)

The M and the WW are in parallel so each group will get the same voltage at low frequencies. The WW is 16 ohms so half the current will flow through it as the 8 ohm mid. Cone displacement is proportional to current so each of the WW will move half as far as the M at low frequencies. Total SPL from the two WW will equal the SPL from the M at low frequencies. On top of that, you'll be cutting the highs from the WW with a coil. So, bottom line, the Ws aren't working very hard compared to the M. Maybe it will sound great but it seems like the drivers aren't being used to the fullest.

[Jed]

The way I understand your crossover layout, ignoring caps and coils for a moment, it's:

--M (8 ohms)
--W-W (16 ohms)

The M and the WW are in parallel so each group will get the same voltage at low frequencies. The WW is 16 ohms so half the current will flow through it as the 8 ohm mid. Cone displacement is proportional to current so each of the WW will move half as far as the M at low frequencies. Total SPL from the two WW will equal the SPL from the M at low frequencies. On top of that, you'll be cutting the highs from the WW with a coil. So, bottom line, the Ws aren't working very hard compared to the M. Maybe it will sound great but it seems like the drivers aren't being used to the fullest.

Interesting,

So, now correct me if I'm wrong- the system impedance, which dips down to 5.5ohms in the bass would indicate that the M is doing more work than the Ws yet the overal output for both M and W is the same SPL? Isn't this the case for all 2.5ways?

I guess the idea that the drivers aren't being used to their fullest is relative to the end goal, which in this case higher sensitivity and an easy load for the tube amplifier. 3-ways are a lot more complicated for me to design- but I'll do some experimenting.

[Jed]

Another solution would be MMTMM if someone can prove to me that a shallow crossover slope around 3.5K won't yield horrific vertical lobing problems due to the large CTC spacing the AMT1 tweeter provides.