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06-30-2010 Post does not mapped to Knowledge Tree
skushino
Seattle, WA
Posts 93
Joined on 07-07-2004

Post #: 1
Post ID: 13892
Reply to: 13892
Mitigating Undesired High Freqs in Midbass Horns
fiogf49gjkf0d
One of the challenges I see for my midbass horns is to minimize hf output.  The goal is to operate the horn in a bandwidth where it can cross to the higher horns, and have each horn function in their best sounding manner.  My drivers are Altec 515-16Gs, and they will cross to the upper bass around 200 - 240hz.   There are three options under consideration, in order of preference:

1) aim off axis - unlike the main horns which are aimed behind the listening seat, aim the midbass horn straight back.  this should allow the 'beamy' hf to shoot straight past the listening position.

2) hf absorbing liner - I was wondering if anyone tried lining the inside of the horn with a material with high coefficient of hf absorption?  Perhaps something like a thick, luxurious velvet liner.  Imagine an entire listening room lined with velvet or something similar.  In my mind that room will sound very dead, because the hf is being swallowed by the textured material.  If you have tried this, did it work?

3) higher order low pass crossover - this should help to control the output, but has all the downsides of high order crossovers on phasing.

I'm most interested in learning if anyone has tried lining their horns with an hf absorbing material, and your results. 
06-30-2010 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 9,366
Joined on 05-28-2004

Post #: 2
Post ID: 13894
Reply to: 13892
It is all depends….
fiogf49gjkf0d
There are a few other ways to roll off HF: shaping and extending front chamber, playing with damping of the driver cone and so in. The Altec 515G at 220H, what the channel above? When you say that you have too much HF then how do you methodologically conclude 300Hz is better to be reproduced from lower MF Chenal?

Anyhow, the off axis is fine method but it helps only in very with a few dBs. Also, if you toe off your midbass horns then the sides of your room need to deal with that HF.

The HF absorbing material is a bit complicated as to control the absorbing rate is very difficult. I think the combination of off axis with absorbing is more promising. Still, the absorbing not ONLY rolls off the HF but do a lot of other things (overtone and harmonics). So, you need to be VERY accurate what you do with absorbing. I use to use absorbers in mouth before but I feel that if I can then I would not do it as it is very hard to mange.

Higher order low pass crossover or moving the crossover to the left is the most controlled way to do the thing. It all about the degree. You can get a bit from crossover, a bit from off axising and so on. Do not forget that off axising midbass horn you minimize the listening spot…

The Cat


"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche
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