Car horn question
 

I decided to put some of my holiday spare time to good usage.
I've been playing with Hornresp for a bit trying to simulate a decent horn for a hatchback car but don't seem to be have a huge amount of luck.

The attached pics are what I've come up with sofare. I had a look at other threads and kinda guessed the driver side of the specs (besides the cone area). To be honest I don't have the thiell-small specs for this 15 inch driver which makes it a little harder.

Firstly.... will it sound alright? (by usual car doof doof standards :xeye: )

second... can anyone see a way to improve the design?

and the Hornresp data...
another quick thought.... will a simple enclosure be just as good?

It's not a bad curve, as cabin gain will fill it in below 40 Hz. Howver, using a fifteen is absolutely unnecessary. Large drivers and small horn cabinets don't mix. Use no more than a ten. And where is your rear chamber? A rear chamber volume of zero is only seen with high frequency compression drivers, and even they have some rear chamber volume, if only a cc or two.

I don't know how you're gonna fit that under the hood. I would go with a 1 1/2 inch driver maximum.


Sorry, I couldn't resist :rolleyes:

Horns with small mouths compared to the wavelengths they are going to reproduce will always have a rollercoaster frequency response or else they have way to much damping.
Yours is not the worst one, approximatly pluss minus 5dB from 40-100 Hz. Not unusual for subs at all, and like Bill said, you'll get some gain below 40.

But the good news is that I have tried a similar horn in cars, and if you have enough free air inside your car it will have an unbelievable impact. If you have <2 cubic meters of free air, you should concider building a rear chamber or a regular box instead.

Horns with no rear chamber (like yours at this stage) work best with a lot of free air around them:
If you have >3 cubic meters of non occupied air, this would be a nice project. You just have to be careful with your ears....doof doof....:D

Re: Car horn question
 

Doesn't all this guessing make the design or any comments on it a waste of time? Surely better to have all the required TS parameters before attempting to design a horn? Or am I just being a killjoy?

I read in another thread that having it at zero means your only rear loading the driver which I did to save space and the response curve was better.

By 'free air' are you refering to the the boot (which is only seperated from the cabin through a carpet/cardboard parcel shelf) or the entire car?

Your half right. Although I am missing a large chunk of driver specs, I tested with different dirver specs and the varience was not overly huge. At worst the dips in the response curve went down to 100db but the peaks stayed as is. I assume alot of the charactoristics of a horn speaker are from the horn and not the driver.... but I could be very wrong.

If it sounds terrible I'll just tear out the middle and make the box *gasp* normal :D

By free air I'm referring to non occupied air in the space where the side of the driver which is not loaded by the horn is facing.

If this side is in the boot, you can calculate the volume and subtract everything you put in there including the box;)

There is a lot of guessing when you do not know S&T parameters, but the ones you choosed are pretty typical for a car driver (not the real good ones) so I guess your sound will be quite similar to what you have calculated.

Good luck with your project, and please tell us how it sounded when you're finished...

Zero rear chamber volume is correct for a rear-loaded horn. And you're correct, with a horn 90% of the result is from the horn, 10% from the driver. But you're still not taking advantage of a horns potential with that big driver. This is what you can do with a 14x14x32 inch horn using an eight.
http://billfitzmaurice.com/plans/images/autotuba.jpg

Not to threadjack, but I think this is relevant...

Bill,
Your designs appear to be quite impressive. Are your freq. response graphs free air? Are they measured or simulated?

I have definite interest for a home sub.

Marc