Backloaded horns, do we want delayed bass, and how do we want it? - diyAudio
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Old 22nd January 2014, 02:32 PM   #1
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Default Backloaded horns, do we want delayed bass, and how do we want it?

Context: trying to make a 3-way horn on a budget. To learn more about horns, not to make the “best” speakers ever. I am aware of the compromise i am taking which this approach. More bandwidth from the midbasshorn is what i am after just to make crossover to the mid easier. I know exta bandwidth and high spl is a contradiction.

I have been reading up on backloaded horns. And have found several methods of handling the delayed backwave coming out of the horn. Some questions arise, there seems to be no general agreement on how to handle the backwave. It would be nice if we somehow could end up with a rough guideline for handling the backwave in a backloaded horn in this thread.

Click the image to open in full size.

Method one. Replikon horn / Horn reflex
– the delay of the backwave is a problem, backwave pathlength should be under 1.4 meter

the bends in the horn should be as smooth as possible
– the crossover between horn output and woofer should be as low as possible.
– the backchamber should be big, to create a lowpass for the backwave.
– high Qes woofer, massloading close to a ported design.


Click the image to open in full size.


Method two. Cumulus 2 Hobby Hifi, Fostex etc.
– the delay of the backwave is not a big problem. (lenght above 2 meters)
– the bends in the horn act a lowpass and should be “boxy” to cutoff the backwave. Difraction in the horn is welcome and positive. See the Fostex reflectors.
– the crossover between horn and woofer output matches the need for bafflestep
– there should be no backchamber.
– 2 x Fs/ Qes (25 Hz & 0.15 Qes) = 344 Hz massloading point where the backwave should begin to fallofff.
(Cumulus 2 horn, Thiel coincident).

Click the image to open in full size.

Method three. Carfrae/ Hedlund
– the delay of the backwave is no problem. (lenght around 2 meters)
– the bends in the horn should be as smooth as possible
– the crossover between hornoutput and woofer should be as high as possible
– there should be no backchamber or it should be really small (magnet depth)

2 x Fs/ Qes (45 Hz & 0.23 Qes) = 393 Hz (Lowther)

Here goes. There is probably a relation between the length of the hornpath and the amount of midrange hornoutput that is usable. Would it be possible to use 1/3 offset placement of the driver in a backloaded horn to shorten the pathlength (reduce phase differences). Set the driver back in regard to the hornmouth (imagine the driver in the right upper corner of below horn) and get more usable bandwidth? What would be the delaytime / hornlength that would work this high up in the 5 – 600 Hz range? I found numbers from 2 to 6 milliseconds. The Haas effect is our friend i asume, but how far up in the midrange can we push this?


Click the image to open in full size.

What i have seen from measurements, even horns that use "difraction" to smooth out the peaks as above, have output high up into the 400 Hz region.

On a side note. I would appreciate some thought before using abbreviations. I found quite some older Diyaudio post unreadable due to the extensive use of VB, IB, WG and DT.


Last edited by Phenoholic Anonymus; 22nd January 2014 at 02:37 PM.
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Old 22nd January 2014, 07:29 PM   #2
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These picture will probably better descibe my delusion Both horns use the same Fostex FW208N driver; Re 5.8 Ohm, Fs 31 Hz, Qes 0.26, Vas 12 liter, Sd 204 cm2, Le 0.51 mH, Xmax 6.5mm.

Click the image to open in full size.


Blackline; classic Fostex BK201 horn
Hornlenght 1.70 meter, Vb (compression chamber) 7.3 liter, exponential, throath 155 cm2, mouth 750cm2

Redline; back loaded horn with driver placement offset.
Hornlength 2.50 meter, driver offset 0.865 meter from start of horn, Hyperbolical flare. No compression chamber, throat 70cm2, mouth 750cm2. Driver offset from end of horn -0.31 cm.


Let's pretend we can we shorten the “redline” horn to below 2 meters and thereby shorten the pathlenght in the horn. Making it more usable in the midrange...? Less delay...? Use a lower Qes driver etc?

Click the image to open in full size.


Left fostex BK201 horn, right offset driver horn.

Last edited by Phenoholic Anonymus; 22nd January 2014 at 07:45 PM.
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Old 22nd January 2014, 07:47 PM   #3
tinitus is offline tinitus  Europe
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some like the sound of backloaded better when mouth opening is backwards

gosh, you learn fast, considering you apparently had no clew about delay just one week ago
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Old 22nd January 2014, 07:59 PM   #4
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Thanks, I am a NOOB at horns, not speakers in general

The hornopening to the back preference is interesting. Could be extra delay, could be damping of "garbage" peaks... Oh i forgot, the speaker placement on top with the basket up is only ok upto a certain diameter driver. The Fostex 208N would still be 180 degrees directive at +- 800 Hz.

There's an old thread at the Audio Asylum about backloaded horn delay. High efficiency speaker asylum. Re: How do we hear (if we hear) a lag of 0.016 sec at low frequencies?

Last edited by Phenoholic Anonymus; 22nd January 2014 at 08:14 PM. Reason: Added link to delay discussion
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Old 22nd January 2014, 08:07 PM   #5
DrBoar is offline DrBoar  Sweden
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Mass rolloff really does not work. I used a bass driver in a short horn similar to the Klipsch La Scala. According to Fr and Q it should roll off above 180 Hz or so, in practise it was quite flat up to 1200 Hz!
In the Jericho 08 horn they calculate that bass horn should fill in below the baffle step of the driver. Then there is the trade off between deep bass/long horns and time delays. The idea is to match the lowpass of the horn with the frontradiation aided by the baffle step coming in.
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Old 22nd January 2014, 08:20 PM   #6
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Thanks, i toyed around with the edge to place the FW208N asymetrical on a 55 x 45 cm wide (top) baffle. I am curious about "shooting" far over the horn output meets driver output point, with a low Qes speaker. But need some more input, don't like to waste expensive Birch plywood.

Last edited by Phenoholic Anonymus; 22nd January 2014 at 08:40 PM.
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Old 23rd January 2014, 05:16 PM   #7
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Could someone point me out to a horndesign with a smooth backhorn and a very low Qes driver? Still curious about what amount of mid is coming out of the horn
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Old 23rd January 2014, 05:26 PM   #8
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Default frugal-horn

Quote:
Originally Posted by Phenoholic Anonymus View Post
Could someone point me out to a horndesign with a smooth backhorn and a very low Qes driver? Still curious about what amount of mid is coming out of the horn
Try search herein Diyadio for Frugal-horn or Planet 10's site. F-H looks easy to construct and the drivers will not break the bank. ...regards, Michael
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Old 23rd January 2014, 06:04 PM   #9
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Thanks,

I have a fine >90 dB fullrange speaker at home. Would like to step it up to >100 dB, the Frugal horn looks are stunning.
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Old 24th January 2014, 11:39 AM   #10
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Quote:
Originally Posted by Phenoholic Anonymus View Post
Context: trying to make a 3-way horn on a budget. To learn more about horns, not to make the “best” speakers ever. I am aware of the compromise i am taking which this approach. More bandwidth from the midbasshorn is what i am after just to make crossover to the mid easier. I know exta bandwidth and high spl is a contradiction.

I have been reading up on backloaded horns. And have found several methods of handling the delayed backwave coming out of the horn. Some questions arise, there seems to be no general agreement on how to handle the backwave. It would be nice if we somehow could end up with a rough guideline for handling the backwave in a backloaded horn in this thread.

Click the image to open in full size.

Method one. Replikon horn / Horn reflex
– the delay of the backwave is a problem, backwave pathlength should be under 1.4 meter

– the bends in the horn should be as smooth as possible
– the crossover between horn output and woofer should be as low as possible.
– the backchamber should be big, to create a lowpass for the backwave.
– high Qes woofer, massloading close to a ported design.


Click the image to open in full size.


Method two. Cumulus 2 Hobby Hifi, Fostex etc.
– the delay of the backwave is not a big problem. (lenght above 2 meters)
– the bends in the horn act a lowpass and should be “boxy” to cutoff the backwave. Difraction in the horn is welcome and positive. See the Fostex reflectors.
– the crossover between horn and woofer output matches the need for bafflestep
– there should be no backchamber.
– 2 x Fs/ Qes (25 Hz & 0.15 Qes) = 344 Hz massloading point where the backwave should begin to fallofff.
(Cumulus 2 horn, Thiel coincident).

Click the image to open in full size.

Method three. Carfrae/ Hedlund
– the delay of the backwave is no problem. (lenght around 2 meters)
– the bends in the horn should be as smooth as possible
– the crossover between hornoutput and woofer should be as high as possible
– there should be no backchamber or it should be really small (magnet depth)

– 2 x Fs/ Qes (45 Hz & 0.23 Qes) = 393 Hz (Lowther)

Here goes. There is probably a relation between the length of the hornpath and the amount of midrange hornoutput that is usable. Would it be possible to use 1/3 offset placement of the driver in a backloaded horn to shorten the pathlength (reduce phase differences). Set the driver back in regard to the hornmouth (imagine the driver in the right upper corner of below horn) and get more usable bandwidth? What would be the delaytime / hornlength that would work this high up in the 5 – 600 Hz range? I found numbers from 2 to 6 milliseconds. The Haas effect is our friend i asume, but how far up in the midrange can we push this?


Click the image to open in full size.

What i have seen from measurements, even horns that use "difraction" to smooth out the peaks as above, have output high up into the 400 Hz region.

On a side note. I would appreciate some thought before using abbreviations. I found quite some older Diyaudio post unreadable due to the extensive use of VB, IB, WG and DT.

None of those are really 'horns' tho are they? Top is more a BVR the second is an offset TL. Slightly pedantic but I was under the impression true horns were defined by pretty specific maths.
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