Effect of using dampening in rear horns?

[Geek]

Hi all,

I was using Horn Designer looking for the ultimate backhorn. The "flattest" curve for the driver was this spikey one so attached.

I would like to know the effects of partial lining of a backhorn.

1) will it smoothen out these spikes?
2) what effect does lining have on efficiency?
3) will it affect the tuning by acoustically lengthening the horn?
4) what material should I use?

TIA

[Geek]

Uh...errr...right. Here's the attachment

[MJK]

Geek,

The mouth is too small, you really have a TL response. Increasing the mouth size will damp the peaks.

[BillFitzmaurice]

In mu experience McBean predicts a far more ragged response than what it ends up measuring in the final product, so I wouldn't be too concerned.

Fully lining the rear chamber, but not the pathway, is critical to prevent midrange reflections that don't particularly affect the backhorn output but will really mess with the front wave.

Lining has no effect on sensitivity.

Making the horn longer will tune it lower, but without a commensurate increase in mouth size will also roughen response.

The best damping material is high density rigid fiberglas but it's hard to find and nasty to work with; inch thick high density polyester furniture batting is a good inexpensive second choice.

You'll get considerably better response from the horn if you align it to take advantage of boundary loading via the rear wall or a room corner, both of which will serve to increase the effective pathlength and mouth area.

[Geek]

Thanks, I shall do some experiments

I messed up my first post, too tired I guess. It's a rear-loaded front-firing horn, not a backhorn. My bad

@MJK: I already have the mouth area at 2 metres square, can't physically go much bigger in my house (a 400 sq. ft. trailer).

[BillFitzmaurice]

What space did you model in? That response is not very good for a horn with a mouth that large. You should be modeling in half space or even quarter space to get a reasonable idea of how the horn will work in room. My 18" cubed Tuba 18 gets a far better response in room corner loaded than what your sim shows. It's a front loaded sealed rear chamber sub, so the comparison isn't totally valid, but still it points out that your sim may be too conservative.

'Backhorn' is a synonym for rear loaded, but you should have the horn mouth facing the wall for boundary loading; this will enable you to get 1/4 space loading. The mouth should only face forward with a horn that passes directional frequencies.

[Geek]

I modelled in 1/4 space. You should see the 1/8 space response!

Mouth face the rear, huh? Ok, thanks.

/me tube guru, horn n00b

[BillFitzmaurice]

In 1/4 space with that large a mouth that response is pretty unimpressive. How long is the horn and what Fc are you trying to get? What driver?

[Geek]

Folded horn, total 3M long, Fostex FE206E. I want the bottom to be ~45Hz, with a cutoff of 38Hz.

[BillFitzmaurice]

Try modeling in 1/4 space, throat 110cm sq., mouth 10000 (1 sq meter) length 300 cm. F3 is 46Hz, F10 40 Hz, but room lift will pick things up below 50 Hz anyway; if you must go lower another meter of length or corner loading will do it.