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ulf wrote:

Well, it was not really a surprise to us that the horn without the phase plug was dissapointing. Without the plug we had a horn that was a bit too short, had too large front cavity and less compression than we desired.

It is hard to say. I find that it is never possible, at least in my experience, to say what compression would be desirerable. The horns programs and projected compression rate will indicate only pressure level but never indication about quality Sound. I uses never target any compression objectives and always try to make the thing to sound “correct” and then whatever compression it lead to I let it be. As long I have compression as a desire I always ended up with inferior sonic result.

ulf wrote:

So it is nor really fair to say that the plug always is better, but in our design the plug is crucial since it is a part of the horn and helps connetcing a rather large driver to a small throat.

This is why the start pussy is using a sampler driver… :-)

ulf wrote:

Under 500 Hz? With slow rolloff filters we still have some energy rather high upp in the MF range. We wanted to the directivity in the upper region of the midbass be close to what we have in the lower region of the MF. I think that the phase plug could be a way to achieve this.

OK, let forget about the directivity as I fie it is invented problem. Mostly likely you MF horn used a first order crossover and most likely it is crossed hear one octave form the horn rate. If so then when MF driver at it’s minus 6dB then the roll-off from the horn’s bell kicks in. At near 12dB the roll-off from the driver come to the picture and the decay goes even sharper.  So, a typical MF horn dies with second to thong order. Contrary to it an upperbass horn with plug and first order has a loooooong tail all the way up to 4K-5K. Usually the tail has quite a few dBs down and it is good integration tool (the MF and Upperbass works as alone array in this case). I was using this method for years but then I stopped because the “quality” of this tail was not as good as the lower knee of my MF diver.  There is another problem with the long Upperbass tails: it is very default to manage it. The Upperbass driver has inductance that “talks” with inductance of the coil that used for the Upperbass low pass filter. In real world it forces to use coil dot 3-4 times more value then what would be predicted by calculations. Measuring response of Upperbass horn drivers in real time I never was able to get the correct roll off and it always forced me to go for very large coils. (I use air coils with 8 ga wire… so you might imagine how big it was for 6-8mH). Still, the larger coil I went the more it did not sound correct to me. The only solution that worked for me was decoupling the filter’s coil from the Upperbass driver coil – I did it by implementing a crossover inside my dedicated upperbass amplifier. The deprecated toady version is here:

http://www.goodsoundclub.com/TreeItem.aspx?PostID=2762

ulf wrote:

On an other more disturbing matter: How can we use MF up to the region of 10k with a driver that has a 200Hz phase plug?? This will give a large amount of distorsion!

I do not believe in such drivers. A horn channel by the nature of topology must not be a wide range channel.

One more worrying issue: How much overlap should we have in the crossover region. I made a 1100Hz tractrix for 1" drivers and tried it as tweeter HP at 9k. It was easy to hear that it had better bottom than the normal tweeter. So if we want to use MF from 500Hz would a 250Hz horn be enough?? Or should we have to use a 100Hz.

It all depends what driver does , what horn does, what crossover does, where the horn sits in the room, not it positioned relive to other channels and from many other factors. Usually 1 octave between crossover point and horn rate is enough but in some cased it might be more or less. It is very hard to say generally. Look for instance my frustration with my lower MF channel in the “Adding one more spherical to Macondo.” thread:

http://www.goodsoundclub.com/TreeItem.aspx?PostID=2433

I think it should be asses in each specific situation differently….

ulf wrote:

This issue gets even more disturbing when we consider the midbass!

Exactly! It imposable to waste one octave of bottom horn opening juts for crossover compliance. With midbass it usably works differently, although I purely undusted that it is compromise.

ulf wrote:

I have not tried the Fane 8M. On paper it does not look that attractive, but it still might work well as you said. Quite heavy diaphragm though. I tried some Fane tweeters which I found to be aggresive and metallic. Which reminds me....tweeters. Still a problem!

Yes, I know that in the paper Fane 8M does not look impressive thought I do like very little excision, 1.6T in gap and 103dB sensitivity. The T/S parameters I find are irrelevant for horn-loading. The good sound of Fane 8M is mystery to me as well. I have the Studio 5M and Studio 10M driver the sound nothing like the Studio8M. The Studio 8M is some kind of very strange mutant, thanks God! BTW, I also used Fane tweeters and also find them horrible, however what whatever reasons I did head them perfume remarkably good in one (just one) Bruce Elgar’s installation… So, go figure…

Rgs,
Romy the Cat

PS: BTW, Ulf, here is an idea for you how you can minimize the side of your front chamber and get more compression but without extending the unnecessary HF with a phase plug.

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