Authentic horn sound

I was always under the impression the Speedster came with two horns. One in a high tone and the other in a low tone. Current horns are sold as a dual-tone horn set. I found these on Stoddard.

https://www.stoddard.com/64463510200.html.html

Looks like your looking for these frequencies. above....

This one has specs of

https://www.hella.com/MicroSite/horns/en/index.html

or another ....

https://www.hella.com/MicroSite/horns/en/index.html

This site will allow you to hear them and the horns are close to the original and can be had on amazoonian site for less.

I have dual trumpets from Hella, and they have a very loud sound you can get them from amazooonian as well for less.

I used the Hella Supertones to replace the VW horn that was on my Spyder when I bought it.
300/500Hz  

HELLA 003399801 Supertone 12V High Tone / Low Tone Twin Horn Kit with Red Protective Grill, 2 Horns https://a.co/d/j1W5m80

I like the idea of the closer frequencies like Ray posted. It’s not the frequency or volume of a single horn that is “heard.” It’s the dissonance between the two frequencies that carrys.

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I post this every time someone asks about horns.

I found these Hella 'disc' horns on Amazon for $20 a few years ago and have been very happy with them — or as 'happy' as you can get about car horns. (It's not like car horns are something exciting like alloy wheels or beehive tail lights.)

To me, they sound very close to the original Bosch horns, cost about $300 less, and are still very decent Hella quality. I use my horns about once or twice a year and have yet to be disappointed by them. If you need something loud, they are a lot louder than the meep-meep that was standard on my VS. They are two-toned and commanding in a strangely teutonic way that would be at home in any mid-century full-sized Mercedes sedan, right up to (but not including) the Grosser limousine.

Here they are on Amazon, where there's a 'video' of what they actually sound like. I found them on Hella's site, too, but that recording doesn't sound at all like my horns.

I think that's all that I can contribute on Speedster horns, although this thread will very likely soon drift towards a discussion of whether or not you need a relay in the horn circuit.

You don't.

Well that is in reality blowing your own horn

You don't need a relay in my opinion. Usage of the horn is intermittent.

I like using relays it just reduces the load on the horn button IMO and if you want to be even safer make sure the db's of the horn is over 110db and it will scream at those around you.  On my car I have two hella trumpets from IM stock then I have a screaming banchee air horn and I also have a circuit that flashes the headlights when I lean on the horn.  You can hear and see me coming  So I need a relay for sure in fact i have two FWIW>

Many years ago I bought the high and low tone Hella set from Sierra Madre Collection; listed as the correct replacement for 356's, even though not Bosch. We did install a relay on the advice of my electrical engineer friend.