Folded Horn Speakers?

I've been looking at what I might do next for a set of speakers and I've never had horn speakers before, so I've been digging into those a bit. Paired with the with the fact that I may DIY the speakers the folded horn option adds extra interest for that aspect.

Unfotunately I don't know anyone in my area that has any type of horn speaker, so I'm trying to understand them better but about folded horn specifically, some say they don't like folded horn because they notice the frequency delay. Can anyone elaborate on that? is that only with certain types of music? Is that you won't know until you try it type of thing?

 

Bingo!

When you spend your time in the speaker forums here (hint: use google search) you will find people who have these and the sound is there discussed.

When you want more specific advice, be prepared to ask more specific questions.
These sort of rounded requests belong to 'the general speaker advice' thread.

Godspeed

 

Folded horn speakers are kind of hard to make compared to a regular 2 way speaker, and their specs are usually lack luster. So from a business perspective, it doesn't make a ton of sense to build them. However they sound good when you get it right and it is worth considering a folded horn for a diy project.

As far as the inner workings of a horn speakers, here is my best shot at explaining it.

A horn will acoustically couple (NOT AMPLIFY) a speaker driver to free air. This helps the speaker driver push against the air more efficiently and raises the overall efficiency of the driver. Think of it as a free air transformer. This process usually increases the speaker's efficiency by 6db.

Horns are usually limited in the frequency response they can produce. It is usually limited to 3 octaves, but this is more of a guideline than a hard fast rule. In any case, they are limited bandwidth devices.

Someone in history had the idea to couple a horn with a full range driver to improve bass response. Most full range drivers have very nice mid and high frequencies, but the low end is almost always lacking.

So the question becomes, "how do we add a horn to the speaker such that we hear the speaker driver for most of the music, but let the horn amplify bass frequencies?". Well we simply add the horn to the back of the driver. Most drivers have a back wave that is out of phase with the audio that comes from the front of the driver. We use this to our advantage. By having a folded horn, we let this sound bounce around and it flips the phasing of this back wave so it will be in phase with the audio coming out the driver.

By coupling this horn to our speaker, we can design the horn to raise the efficiency of the bass frequencies of the driver and this extend the speaker's overall frequency response. (we could design the horn to raise other frequencies as well, but obviously we don't want the horn frequencies to interfere with the driver frequencies, so we focus on the bass)

Depending on factors such as the speaker's free air frequency response, free air resonance, how big you want the speakers to be and so on, can determine the overall performance of the system.

The major downside to a design like this is that because your back wave has to travel a longer distance to get to your ears, there is a time delay compared to the driver. This delay can be very noticeable or not so noticeable. The idea is that the longer and bigger you make your horn, the lower the frequency the speaker can play, but the more time delay there is.

So there is a trade off, and you have to find a happy medium.

The best thing to do when designing a folded horn is to find a driver that covers as much of the audio bandwidth as possible so that you only have to worry about low frequency (say 50hz and below as an example). I find that the lower the frequency the horn is tuned for, the less impact issues like timing and phase distortion has on the experience.

 

I have not heard a folded horn yet but recently got some Fostex 3 inch bass reflex kit speakers and find it amazing what they can do as a full range single driver. I am very tempted to buy the BK-12m kit from Madisound.