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Can you tell me whats the best type of top end to use with a 12 driver?

Can you tell me whats the best type of top end to use with a 12 driver. I have some 12 JBL drivers and need some top ends, I need good dispersion because I will only be using one mid top cab per side and dont need the sound to travel too far. I also don't have much money to spend.

Here is a run down of the different types of HF horn commonly in use.

Diffraction horns are normally called slots. They use a narrow vertical slot with a center wedge or phase plug. They are only for short throw use and most have a very wide dispersion. Dispersions around 120 to 150 degrees are normal for this design and they have a very good sound, I think they are probably the best sounding HF units you can get. They all have the drive unit attached to the horn, so are one unit, rather than a separate compression driver and horn. They mostly use what is called an annular ring diaphragm, this is a round diaphragm with a hole in the middle. The only problem with this design is that they can only be used from around 5 KHz and above. Most have to be crossed over at 6 KHz, but I have seen a few which will work down to 4 KHz and others which need to be crossed over as high as 8-10 KHz. Its hard to get most 12 drivers to go as high as 4 KHz without there upper output starting to beam (become narrow) and the cone not ripping apart from the voice coil when driving it with loads of power. There would not be much of a problem if you were not putting too much power through the 12 driver, but it could start getting a bit directional in the upper mid range. A better way to use a slot is to use a 12 driver up to 500 Hz and then and an 8 driver from 500 Hz up to 6 KHz where the slot would take over. This combination would give you a better result. You could use a 8 driver like the Eminence Beta 8 and then a Fane ST 5022 slot, or Selenium ST 320 slot crossed over at 5 KHz. A suitable passive crossover would be the Eminence pxb3 5k which crosses at 500 Hz and 5 KHz. If you used the Eminence px3 5k which has a volume control on the HF section, you could use it to match the output of the HF to mid and bass. Slot tweeters have very high efficiency, the Fane one is 110 dB/1w/1m, so some attenuation of the HF would be needed. This would be in my opinion the best option for you. You would get a very high quality of sound with amazing dispersion, and slots dont cost that much either. You would have the extra expense of the 8 driver and 3 way crossover but this is not too much and the difference between a 2 way and 3 way design with is greatly reduced distortion would be worth the extra. By the way, JBL still uses slot HF units in a lot of its studio monitors, the quality of the slot is that good.

As to exponential horns, that refers to the rate of the flare expansion. So any horn, be it a radial, bi-radial, slot or constant directivity (CD) horn has an expansion rate. The exponential curve is the least severe and efficient, it has an m number of 1. A hyperbolic expansion rate is a lot steeper and so more efficient, it has horn walls that do not open up quickly and that take a longer distance to open up to the same mouth area as an exponential horn. For bass horns the best expansion rate is about m = 0.6, with an m of 1 being exponential and an m of 0 being hyperbolic.

Radial horns are the oldest horn design around, they are good for long throw applications. They normally have a high efficiency but the very high frequency dispersion starts to drop off quite quick. There a bit old technology now and not used for much. The bi-radial or babies bum, which was a JBL invention so it would seem, has a bit extending from the front of the horn. These horn extensions are normally on the horizontal plane and were a bid to try and make the response a bit more uniform. They will have a wider dispersion than a standard radial horn and will not drop off or lose so much upper HF content with increasing dispersion. There not to bad sounding either, JBL still use them in some of their designs now, normally stage monitors, where there smooth and wide dispersion is useful in this application. A pair of these horns matched to something like a JBL 2226 compression driver with your JBL 12 drivers would make quite a good sound, but one that would be very expensive.

Lastly we have the constant directivity (CD) horn. This is an attempt to keep the very high frequencies that would normally drop of in something like a radial horn intact right to the edges of the horns dispersion. So if its a 90 degree CD horn then all frequencies will be reproduced out to 90 degrees, hopefully. Most do it quite well, others not so well, but all of them offer better HF control over the other horn designs, apart from slots. Slots have very good control over beam width, you can stand at 70 degrees to either side of one and still get most of the very high frequencies. Slots also extend the most out of all the horn designs, most will produce up to 22 KHz and some even to around 25 KHz, which is amazing. The best you will get from a CD horn with 1 inch compression driver is about 18 KHz and then only with a good driver. So the CD horn is a good all round option, it has good coverage, extends quite high, can be compact and is cheap. The Eminence SST 1 is a CD horn I have used a lot, it has a good sound and good coverage. It has 90 degrees wide and 40 degrees vertical dispersion, or 90w x 40v. You will need to partner it with a good compression driver though, the Eminence PSD 2002 is not one of the best drivers, although they very rarely stop working and sound a lot better than a punch of piezos. Drivers like the Beyma CP 380M are very good, but will cost a lot more money. Selenium has a 1 driver called the 205 Ti, its quite good, especially for how much it costs. Also worthy of a mention is the DAS M5 1 compression driver and units from RCF, but again theses are not cheap.

As to the frequency at which to crossover from 12 to HF horn, with a 1 compression driver I would say the lowest crossover point should be 1.6 KHz. It all depends on the compression driver you are using, with very good HF drivers I would say between 1.6 KHz and 2.6 KHz. If using a cheaper HF driver then crossing over at 3 KHz will help take out some of the harshness theses units have around 2 KHz, it will also help out with the power handling. The lower you crossover a compression driver or any HF driver the less power it will be able to handle. So a HF driver that is rated at 40 watts crossed over at 1 KHz will have a power handling of around 60 watts when crossed over at 2 KHz. The driver crossed over at 2 KHz will also be less stressed as you are not asking the diaphragm to travel as far, so less distortion and the unit will last a lot longer. So the higher you can cross over from the 12" driver to the HF driver the better. The 12 JBL's you have and other 12 drivers like it should be ok to up to 3 KHz, maybe 4 KHz just as long as you are not placing too much demand on the system.

Another way of doing it is with the Eminence APT range of HF units. They do an APT 150, which has a CD horn and built in compression driver. The dispersion is nice and wide at 100w x 50v and these units sound quite good. They extend out to 20 KHz as well and are very cheap. You have to cross them over at 3.5 KHz and your 12 driver will be able to get that high. Use one of the Eminence crossovers too, the 2 way pxb2 3k5 is the one to go for. All Eminence crossovers have a light bulb for HF protection as well, this system works very well, I have never heard of anyone blowing up a HF driver with one of these crossovers, the bulb normally goes first. The pxb crossover is the cheaper option and you will have to mount it inside the cabinet somewhere, you might also have to use some kind of HF attenuation as well, although not too much. The other option is the px type crossover which has built in HF attenuation on a volume knob and built in speakon connectors as well, all you have to do is mount it on the back of you cabinet and your away. These Eminence crossovers are really good, I have used most of the passive crossovers on the market and these are the cheapest ones which dont saturate, catch on fire and they last for years. The HF protection is a big bonus as well.

So you know which crossover to use, its down to you or your budget as to which HF you use. Best option is the 3 way with 8 on mid and a slot tweeter doing HF (see if you can find a Selenium ST 320), using the Eminence px or pxb3 5k crossover. Not the cheapest option this, but the best sounding. Not too far behind this would be the Eminence APT 150 horn with their px or pxb2 3k5 crossover. They also do lots of other APT horns as well, ones with different dispersions and also just the HF driver (APT 50) if you want to screw it on to a horn of your choice, although you might as well use the horns that come with the units like the APT 150. The APT 50 driver is good for use on the back of coaxial drivers, where the HF driver sits on the back of the bass mid driver and fires though a hole attached to a horn in the center of the bass mid driver. These APT units are used in many commercial designs from lots of different manufactures. I Know that OHM use the APT 80 with 12 and 15 drivers in their RW range of speakers and they sound good.

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