Originally Posted by thylantyr
For the 3 way;
The pros are;
* Best SQ [subjective of course, but seems obvious to me why)
(issues described in the 2 way con are not present)
* Extra driver
* Extra crossover
* Extra cost
* Bigger speaker box
* May or may not need 2 extra amplifier channels
* Driver availability (sorry, but if you want the best, it may take some hurdles)
Don't forget that because you have another driver in the system, there is yet another issue with phase and time alignment, especially if the mid and tweeter are next to each other. As you move left to right, things will change at the xover point due to the path length difference. The current enclosures are in this alignment:
The current response looks like this, including the effects of the response off the floor and ceiling:
Red is with drivers in phase, yellow with the midrange polarity reversed to check for phase coherence. It sounds good, don't get me wrong, and I'm sure the PHL would be better than the 18sound, but we can't get it. I spoke with Elliot at Zalytron just a few minutes ago. They have 2 PHL1120's held for Nate now. They don't know if they are getting any more in though. They have something on order, but they don't know if it will be the 1120's of some other driver that they end up getting.
For the 2 way;
The pros are;
1. Three drivers MTM, vs. three drivers TMW... ooops my
bad, this is not a pro, it's the same number of drivers
It's actually one less driver as the other is a WTMW as you have seen. Basically just saving the customer the money of the midrange. Nate's plan was for a pair of 12" drivers as he wanted lots of midbass kick. That's what I started working on here first. You could easily do a single woofer, mid and tweeter. But then again at that point, a single woofer with just the tweeter is a viable option as well. Greg from Phat Planet Studios is currently working on a 2way using the TD12M's and the neopro5i ribbon. Either way, getting rid of a midrange is always a driver savings.
2. Simpler crossover
3. Smaller box
The cons are;
1. Nobody does an MTM with 10" drivers with ~ 18" center
to center midrange spacing if both midranges operate in
the same bandpass. See the line array rules of thumb.
Wisdom Audio has one now that people are raving about. www.wisdomaudio.com
It uses a pair of 10" drivers and a ribbon tweeter in a freestanding or inwall mounting configuration. The cost is $2250 per cabinet and you have to buy their amplifier with processing starting at $3500 and going up from there.
You also have to realize that in an MTM, drivers act differently than in a line array as there are only 2. You don't have a 3rd, 4th, 5th etc driver to give you cancellations. When you are between the centers of the 2 drivers they actually sum quite well. This graph was at 2meters away from the large MTM's using the TD15M's along with the 18sound XT1464horn. This is the TD15M's only, measured at the height of the center of the tweeter.
Now if you had another woofer above and one below, you'd see all kinds of comb filtering. Or if you get above the height of the woofers you begin to see this as well.
2. Asking the woofer to play bass and midrange at the
same time will cause audible modulation distortion as
SPL rises. HF playback doesn't like large cone movement
caused by bass playback.
Here's a nice test for you that has been done in the past by Paul Butterfield. You can read about it on the Yahoo Lambda Drivers Group. It's the reason the TD15 phase plugs were made longer. Play a 10Hz tone at high excursion and play a 1KHz tone at the same time. See how much level you need to drive it at before the 1KHz tone sounds audibly modulated. With a driver that has high inductance or non-linear inductance with Xmax, the results will be horrible. The TD drivers do this quite well. With the shorter phase plug, the acoustic loading on the cone was different on the inward and outward stroke. Adding the extra long phase plug kept the acoustic loading the same at higher excursion and eliminated this issue.
Most all studios end up with some large system with dual 15" woofers and a compression driver on a large horn that are crossed between 1KHz to 2KHz. This is what they are listening to during the recording and mastering process. It is not at all unrealistic to do the same type of setup when listening to the same music.
Again, I'm not trying to sway people in any given direction. DIY is about deciding what is best for you. If people want to wait for a PHL driver, they are fully welcome to do so. Whether they do a WMTW system and MTM, a TWM, or just a TW system is fully up to them. My only goal here is to present some measured data, give people a starting point to work from. To me, the simple MTM with the 10's sounds significantly better than this WTMW system. I think raw driver measurments is a good point to start to show why. You can eq drivers to flatten them but you're not changing resonances, etc. The impedance curve on the TD drivers extends much higher in frequency and has much less goofy stuff going on. That would be a big part as well.