| AndrewT |
Some horn sub-bass project design thoughts;
Flare constant to suit 15Hz (exponential)
Mouth area to suit 20Hz into corner (pi/2 solid radians)
Throat about cone area/2
Qts less than 0.3
BL greater than 25
Frequency range about 3 octaves (20Hz to 160Hz)
Mouth area and flare constant chosen to give flat response to 20 Hz and total horn length = 6m to 7m, mouth=3.6sqm throat = 0.04sqm (15inch driver)
Q1 What effect does Fs have on lo end response?
Q2 Some horn web sites quote Fh=2*Fs/Qts and Fl=Fs*Qts/2. Are these true?
Q3 how flat is the frequency response between Fl and Fh?
Q4 No box loading on rear of cone- just venting into the loft space?
thanks in anticipation
Andrew T. |
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| slowmotion |
Hi AndrewT, all
Nice little horn you've got there, Andrew,
you live in one of them scottish castles? ;)
Sounds like a great project, if you've got the room for it.
Just make the horn big enough. If you start to compromise on size
you'll never know where you end up.
Seems like you're on the right track, tho, so here goes:
Q1: You can safely put Fl below Fs, other things matter more, IMHO.
Q2: Mostly no, there's much more to it than that.
Q3: Depends on the horn, the driver and the room ;)
Q4: I would absolutely load the rear of the cone.
There are others on this forum who know more about horns than I ,
so there may be other opinions, too ;)
I you haven't allready , get the Hornresponse program.
Use it.
cheers ;)
PS : May I ask what the rest of the system is? :drink: |
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| Tim Moorman |
Andrew,
Quite the project - big enough to walk into!
I'll add a bit to slomo's comments, based on limited experience.
Horn Respose can take you a long way with a minimum of calculation.
The throat area, flare rate, and mouth are all inter-related to create a resonant system. Varying one will have an effect on the others. The throat size will govern compression, and the load on the driver to some extent. Your ratio of cone to throat looks about right. If you model some differing ratios in horn response, you will see the overall effect is balancing efficiency with compression. My advice is use no more compression than necessary to get the job done. Drivers of poor quality may not have strength to sustain compression loading for any length of time under severe conditions (driven hard).
Q1 - It's part of the overall picture. That is, you are really creating a resonant system that will effectively lower Fs of the driver. You do not want the driver Fs below Fc of the horn, but low enough to be useful.
Q2 - Somewhat true, although I've seen Qes substituted for Qts by people like Bruce Edgar. Pre-dates horn response by a large margin, and primarily a guideline. Check Marshall Leach's work for the extreme math solutions.
Q3 - If you keep the pathway length and mouth near ideal, you can get very flat response. But with size compromises, you will see roll-off starting perhaps 5-10 Hz above Fc.
Q4 - The rear chamber is used to basically extend response lower by creating a damping condition that counteracts the reactance of the horn as it starts to unload near Fc. Big impedance swings are evident nearing cut-off. Helpful for better low end response. Also, once unloaded(below Fc), a horn rolls off at 12 dB, or slower than the 24 dB of a vented system.
The odd thing is, I know of people who have built horn subs with a 15" vintage driver in mind, and as part of the modeling program, then switched to another 15" driver entirely (same general characteristics), and it worked equally well.
Tim |
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| mike.e |
Note that the ideal driver may NOT be a high BL low Qts highly damped one. ML util will reveal the mathematically correct driver to use (labhorn)
| quote: | | Q4 No box loading on rear of cone- just venting into the loft space? |
Not ideal.
1-youd have to use atleast 2nd order filtering to avoid destroying the driver below Fc
2-Reactance annulling is impossible
3-The driver,being hornloaded on one side,will give rise to audible distortion on the rarefaction wave. Some people enjoy this sound - scoop owners. Personally I aim for the most high fidelity sound - not the 'happy' sound;)
A large rear chamber of even 200litres is in order
If you require hornresp modeling,or cad help,Im happy to lend a hand.
Regards
Mike.e
labhorn link |
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| AndrewT |
Hi all, usefull replies so far. Thanks
Existing equipment/room
Sources
Sugden CD, Gyro LP, Quad FM.
Amplifiers
Croft valve pre or Conrad Johnson PF1
Sub-bass power Crimson 1704 modded to 4003
Bass power Crimson 1704 modded to 2004
Mid power Michell Alecto mk1
Treble power WAD kel80 (valve classAB) or Sugden Class A
Speakers
WAD kls3gold passive xover just now, eventually active.
Room 7.6m * 4.6m * 3.5m high
loft space above adjacent bedroom reserved for this horn project.
Fc & Fs; if I choose a driver with Fs=40Hz, Horn Fc=15Hz then will the horn work a full octave below this i.e. down to 20Hz?
As the horn unloads below 20Hz and the speaker loses the resistive reactance of the horn, at what rate would you recommend rolling off the bass response? 1pole, 2 pole or 4 pole? and starting at 15Hz or 10Hz or what? or just let the infinite baffle box do it at 2pole?
Where can I download hornresponse and MLutil?
regards Andrew T. |
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| slowmotion |
Hi Andrew,
Hows it going with the planning?
I have a small question, If you don't mind:
You listed your speakers,
but I am sort of ignorant about speaker brands,
so I'm a bit uncertain
if they are horns or direct radiators.
Sometimes it is difficult to get a good result
if one mix the two different speaker types.
cheers ;) |
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| AndrewT |
Hi,
all my existing speakers are direct radiators.
This project will be my first dip into horn technology.
I hope the integration of horn to direct works out. In my favour may be that horn below 120 to 150Hz only will be easier on the ear???
I do not want to ditch all my speakers at present but after I've heard this I might want to convert to horn everything!
regards Andrew T. |
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| Brett |
| quote: | Originally posted by AndrewT
Hi,
all my existing speakers are direct radiators. |
You have my condolences.| quote: | This project will be my first dip into horn technology.
I hope the integration of horn to direct works out. In my favour may be that horn below 120 to 150Hz only will be easier on the ear??? |
Under 60-80Hz will be easier.| quote: | | I do not want to ditch all my speakers at present but after I've heard this I might want to convert to horn everything! |
I did, and couldn't foresee going back to DR's: long term, that is. I'm suffering thru some now because I'm away from home for a period and my horn rig takes up more space than my car, let alone fit into it. |
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| slowmotion |
Yes, but that is also dependent on the walls and windows
of the listening room.
With brick or cement walls there's no problem,
you get support from the walls.
On the other hand if you have a room like mine ,
where the walls are made of wood,
most of the low bass goes right through the walls.
That may be a problem or a blessing,
depends on which way you look at it ;)
cheers ;) |
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| slowmotion |
Hi Bill, all
You prolly know more about this than me, Bill,
but what you're saying goes straight against my own
experience with different room materials?
Care to explain more?
cheers ;) |
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| AndrewT |
Hi all,
The room as stated earlier is 7.6m*3.4m high*4.6mwide. The horn is located above the adjacent bedroom. A little Pythagoras &
C gives a half wavelentgh frequency of 20.6Hz.
I thought that a roll off at 20Hz would match this. Or am I wrong?
The reason for Fc being 15Hz is that the response of the horn with adequate mouth area starts to roll off about half an octave above Fc and reaches -3db at about Fc. Again Is this thinking right? I want to achieve flat response in the sub woofer down to 20Hz and if I gain some room gain to compensate for the partially unloaded driver below 20Hz then all the better. I chose my mouth area to match 20Hz into a corner to minimise the size required and to fit the space available. I do not want significant ripples in the response.
Q a contributor has suggested a lower xover frequency (80Hz to 100Hz) to help matching into direct radiators. Any other thoughts?
regards Andrew T. |
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| BillFitzmaurice |
| quote: | | but what you're saying goes straight against my own |
Room materials influence reflection artifacts. ie, room modes, but not room lift (cabin gain), which is a matter of pressurization and not phase.
| quote: | | C gives a half wavelentgh frequency of 20.6Hz |
Close enough, but then you also have to consider room modes, as alluded to by slowmotion. 20.6 Hz will also be reinforced by a positive room mode at about the same frequency, depending on speaker placement. Bottom line is that there are a lot of factors adding to response from 30Hz on down in just about any room, and when you also consider the dearth of program material down there a 25-35 Hz fc is generally quite adequate. |
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| simon5 |
Don't listen to them, I want you to do a Fc of 15 Hz, they are all jealous that you have the space for it...
You'll get like 95-100 dB efficiency at 20 Hz with one watt, if it's not that flat, you'll have alot of headroom to EQ it.
Good luck! |
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| mike.e |
A labhorn size unit has a 28hz cutoff,putting an extender of 1metre on a box this size will acheive slightly lower bass nearer 22hz.
you might require digital delay,or wierd speaker placements in order to acheive a system without late bass due to hugely long horn.
It might require a low crossover frequency due to high efficiency,it will come down to levels and overlaps of each system. |
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| AndrewT |
Hi,
Mike.e
The labhorn uses multiple units to achieve minimum mouth size. 6 units into half space.
A mouth extender will increase the mouth to get closer to the minimum mouth area for the horn.
Fc is fixed by the taper built into the horn.
Q what minimum delay needs to be added to all the Hi freq info? final horn length about 6m to 7m plus 1 m from horn mouth to main speakers.
Q how do you avoid reducing the quality of all the upper frequencies by adding a delay?
Q do you really need a delay for sub bass?
regards Andrew T. |
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| mike.e |
Andrew-Im well aware of the labhorn design,I archived Toms posts in a txt file which is available from the diyaudio wiki.
What i was saying,is that in order to produce low frequencys with a decent efficiency, a basshorn the size of a labhorn will be required. It cant be smaller.
| quote: | | Q what minimum delay needs to be added to all the Hi freq info? final horn length about 6m to 7m plus 1 m from horn mouth to main speakers. |
You can calculate it. its probably in the 30ms range.
| quote: | | Q how do you avoid reducing the quality of all the upper frequencies by adding a delay? |
If the Delay is correct there will be no effect on quality
| quote: | | Q do you really need a delay for sub bass? |
Depending on the situation(noncritical PA or HIFI /prosound) and horn length,yes. Remembering that a drum kick is not just a fundamental in the bass range-but consists of a smattering of spectral information into the midrange and up! So if the bass is delayed-it will sound slow and aweful.
Remember that delay is the same as distance-closer or further sub position compared to main speakers position means that digital delay must be recalculated.
You could sit right near the basshorn,while the main speakers are about the horns path length away- will produce better results if you dont have digital delay. I guess you could use op amps for delay-but no one seems to do it.(allpass?)
The problem with guessing the delay to be used-is that the EXACT REAL horn path length will never be known,so a measurement system like SMAART can figure it out.
Cheers! |
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| slowmotion |
Mike,
I was looking at the picture for at least 20 seconds,
there was something there, but I didn't realize what it was at first ;)
hehehe
Is this your project, Mike ?
cheers ;)
Edit: Looked at the pictures on your site,
some very nice setups there ;) |
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| AndrewT |
Hi,
To everyone who has responded a big thanks.
Mike.e is that horn for listening out in the garden or does it bend & up thro' the floor of the music room?
Are you prepared to divulve some of the design parameters?
How close is it to reporting on results?
Regards Andrew T. |
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| mike.e |
Im afraid that huge 7metre horn isnt mine-I saw it on a forum,they only had pictures,I asked,they didnt have any info.
Youd think that some one making such a beast would post on a forum!
I hope that by posting it alot,some one might recognise it!
Cheers!
:( |
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| Skramstad |
Hi!
I saw my 7 meter "Gjerstad horn" on this forum and thought I owed you some information about it.
The history behind the horns started last year when they did not have enough low bass on the Mølla festival in Gjerstad (Norway).
The festival boss Knut Magne Valle contacted me and said he had bought two P Audio BM 18LF and wanted to have high fidelity and high efficiency bass cabinets at a maximum length of seven meters. Not quite the dream driver for a large horn, so I used three full days modelling and calculating a special horn for these drivers.
To compensate for the weak motors I ended up with an open back sideloaded design where the horn does all the damping. A closed box behind the driver in such a big horn is not nescessary as long as you use your hp filter correct.
Frequency response is pluss minus 1 dB in the bandpass from 23-250 Hz, and the phase response is pluss minus 10 degrees in the intended bandpass from 23-80 Hz (but it still has quit good efficiency at lower frequencies than 23 Hz;)
The horns was built by Jarle Grimsland and Knut Magne Valle, it took the brave boys a full week to build them. They used 100 meters of 2”x4” to brace each horn, and they are planning to fill sand in each cell of braces.
Just to get an idea of how loud these monsters can play, they made ripples on the ponds just like in Jurassic Park.
Best regards
Rune Skramstad |
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| Tim Moorman |
Excellent! Most entertaining. Glad I don't live next door:bigeyes:
Great design on your part to strech the performance envelope a bit on those drivers.
Tim |
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