I'm assuming you mean 'by not using a relay'?
Low amp dual horns will work. If you don't use them often, should be ok.
Having said that, it is recommended you use a relay.
One is that you could blow a fuse and have no horn.
2nd is there are a few cases where the higher amps ruin the horn button.
I don't use the horn often and have avoided the relay. My brother uses his a bit more and has paid the price.
I have just replaced my horn with the Freeway Blaster and used no relay. Sounds good, but not as loud/powerful as the dual or air horns like the stebel.
Be aware that the fuse for the horn does also feed other electronics for the engine. Blow the fuse and you affect other things as well. I found that the factory horn even sounds a bit louder when fed by dedicated power direct from the battery through a relay and using heavier 16ga wire rather than the thinner wire the factory uses. I pulled the factory horn wire pair up under the top shelter and used that pair to trigger the relay (the easiest relay trigger source ever) and put an inline fuse just off the battery on the way to the relay. I then also added a 132db low tone Blaster horn from Autozone (they let me test it on the bike in the parking lot before buying it) so I now have 2 horns. The low tone penetrates the cab of cages better than high tones. The factory horn is higher tone than the Blaster so the discord of the two also improves the effectiveness even though the factory horn is not quite as loud.
Both horn brackets are mounted at the factory horn mount point, one angled forward to the right and the other back and to the left. Both horns face down and forward. The Blaster has a coil trumpet.
See some details with wire diagram HERE in post 2 & 3. also see the relay location in post 1.
I used a 15 amp fuse since I also use this relay to switch to the 15 amp 12 volt socket under the seat. It's wired so either the socket has power OR the horns, but not both at once. This is possible with a special relay that has pin 87A for normally off power.