Experiments with M2 horns.

[Don C]

I thought that this kind of fooling around should have it's own thread and not go into the M2 thread, as these cannot be called M2s.
I mounted the 2452Hs to the horns and set them on top of my PS1400s. It surprised me how much they look like they belong there right off the bat. They look more at home than the PT800s ever did. The compression drivers are resting on an inch of styrofoam, itself resting on the same stand previously used for the PTs. The horns are upside down, so that they don't rock on the rounded part.
My early impression is that they sound breathy, that is, I'm hearing the singer breathe on the mic more than I used to. I like that I can walk around and the sound doesn't change a lot. My listening chair is a little off center in the room, and I'm hearing more from the opposite speaker than I used to. They sound pretty neutral, not as big of a change from the PT800s as I expected. I have a lot of adjustment left to try though.
The crossover is the same JBL SPP-AC1 that I have been using with the PT800. There are no filters left in the woofer cabinets. I Set the crossover frequency to 800, and they sound better to me with the phase invert on. I set the horn eq to 4K, just going by ear. I don't have any protection filter on the tweeters, so I have to be careful. I could live with this setup forever as it is, but those boxes sitting on the chair contain 1500FEs, for future use.
I know that I'm not the only one here who bought these horns, and I want to see what you guys are doing with yours now.

[Don C]

My experience so far is that they sound wonderful on one CD and awful on the next. When they are good, they're very good. Larry Carltons Sapphire Blue CD sounds absolutely amazing. But I'm having some frustration getting the level matched between the horn and woofer. With no padding on the tweeter, the tweeters level control on the crossover is turned down to near it's minimum. Making a tiny rotaion to the level pot makes a huge diference to the sound. Fine adjustment is impossible. I'll get some resistors installed into the driver circuit and continue later this week.

[pos]

Hi Don

My experience so far is that they sound wonderful on one CD and awful on the next.

That is probably a hint that the EQ settings you are using do not give a flat response.

FWIW, here is what it gets to make it flat with the D2 driver:

[Don C]

OK, saying they sounded awful was too much exaggeration. A Steven Wilson concert earlier this month has robbed me of some of my hearing and left me prone to listening fatigue. Tonight, Fleetwood Mac made them sound awesome again.

[ivica]

Hi Don


That is probably a hint that the EQ settings you are using do not give a flat response.

FWIW, here is what it gets to make it flat with the D2 driver:

Hi,

But with 2450H driver, EQ curve would be different, I would expect, especially if Ti-ribbed diaphragm is used, so only after some measurements more realistic EQ can be get, not to mention the bass-to-VHF driver sensitivities differences.

regards
ivica

[pos]

Yes of course, but the horn would still require very specific EQs.
The idea was just to stress the fact that this horn require more complicated EQ settings than say a PT waveguide (ie it is less smooth by nature).

[Don C]

I haven't told the full story about the drivers and diaphragms here, it involves me screwing up. When I saw the horns at Speaker Exchange, I also saw the drivers, 2452H, and brand new at better than half off, looking like a bargain. I suspected that I really wanted 2451s, but looking around, none were for sale, at least not at prices that I wanted to pay. So I got the 2452s. Right after the 2452s were delivered some used 2451s showed up on ebay, pretty cheap. (2451SL-16) I debated with myself for a while and then ended up buying those too.
When I got the adapter plates I knew that they would need to be modified to take both styles of driver. After imposing upon a friend who spent 45 minutes setting up a fixture to mill out the slots, this was done. We set a bit to just kiss the inside diameter of the original holes, then moved it out from center .375, making the slots long enough for a four inch circle. I was sure this was correct. I was wrong. The 2451s need a 4.5 circle, and I'm a bonehead.
So more work is needed but it has to wait.
What I did do, was this. After I listened to the uncoated 8 ohm ti diaphragms for a few hours, I removed them and borrowed the -SL diaphragms from the 51s. They fit right into the 2452s. You just have to move the terminal posts from the old diaphragms to the new ones. These are a big improvement, immediately it was obvious that something had changed for the better. I thought that I would be adjusting the levels up by 3db, to compensate for the impedance change, instead I ended up with 5db more, and they are less harsh even at that level. I'm still fooling with the settings too much though. I set the horn comp down to to 3Khz and have played with the levels endlessly. One CD seems to have too much treble, the next not enough. It's probably a sign that the horn levels are correct and my music selection is the problem. I also have some Truextent diaphragms that 4313B sold me. But I'm not going to install those until I get the resistor network straightened out. And those slots elongated more. And then I'll probably put them into the 2451s.