| mrlots2do |
I don't have Mathcad or BLH worksheet and frankly don't understand how to use it. Well anyway!
I was messing around this weeked thinking of using a HiVi A2S as a back loaded folded horn. I'd like a small BLH similar to FE84E enclosure. Loaded the 2" driver into WinISD as a 1 liter vented enclosure, tuned 60 hz and .5"x4.5"x53" tappered vent.
The tappered vent (horn) is 1/16" per 1" for about 45" and (horn mouth) 3/8" per 1" for last 8".
Do I use the drivers 1 liter volume for the compression chamber size?
If not 1 liter volume what would you suggest would work best?
Noob, could use your assistance and suggustions.
Phil |
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| Nelson Pass |
When I don't have an existing design already worked out,
I make the chamber larger than I will probably need and
then fill it, either with rocks or packing foam / peanuts. |
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| mrlots2do |
| quote: | Originally posted by Nelson Pass
When I don't have an existing design already worked out,
I make the chamber larger than I will probably need and
then fill it, either with rocks or packing foam / peanuts. |
Hi Nelson
Love your horns. Good idea above.
How do I know when the compression chamber is near correct volume? Normally I use WinISD and deside on the best compromises.
How do I know what size the horn mouth should be? I made this horn mouth outlet nearly same as the FE84E drawing but I tappered the horn mouth.
My thoughts are to build the horn length based on port vent needs of the enclosure.
Please look at my horn drawing.
Thanks for your assistance
Phil |
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| Nelson Pass |
Of course you know it's the right size when you get the
best sound. I use measurements to help out, but they
don't quite cover the territory, so I let my ears have the
final say.
From my experience in this regard, the performance is just
as sensitive to the stuffing in the chamber as the volume
itself, so you have two degrees of adjustment freedom. This
will tend to keep you busy for a while.
:cool: |
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| mrlots2do |
Sounds like a plan.... lol, not much different than my other projects.
Thanks, Phil |
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| Cortez |
By backloaded horns, is there any reason to use a compression chamber at all ?
How does it work ? It just decrease the efficiency cause the air compressed here
wont go to the horn. Or not ? |
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| mrlots2do |
| quote: | Originally posted by Cortez
By backloaded horns, is there any reason to use a compression chamber at all ?
How does it work ? It just decrease the efficiency cause the air compressed here
wont go to the horn. Or not ? |
I can't answer these questions, I'm a noob to BLHs.
My believe is to reduce the drivers vented enclosure volume some (don't ask me by how much). This should increase flow thru vent port (the horn). The expansion of air within the horn due to taper restricts air flow back to vented enclosure chamber.
Please, can anyone explain any of this? |
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| mwmkravchenko |
Download the article on the J-Low and you will have a clear explanation of what a rear chamber does on a back loaded horn. It attenuates the high frequencies at a rate of about 6db/octave. The volume can be calculated but as Nelson pointed out it is better to err on the larger side and pad pr fill it in the get the responce that you want.
MArk |
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| Cortez |
I know that it acts like a low-pass filter, like a reflex enclosure, but what is does with the efficiency ?
The compression of the air particulars doesnt decrease the main sound energy ?
And what about using more then one compression chamber in series ?
The first chamber would be right behind the speaker with a small size, and then a reflex-tube-like
narrow section and then an other chamber with bigger volume, and at the end of this chamber
would start our horn with a small cross section.
This arrengement should have more "low-passing" character, and
due to air-compression the phase shifting wolud be also better.
And the efficiency would be the same cause of the horn ending.
A meditate often about hybrid type enclosures to combine the benefits of these types.
What do you think, is there a chance to achieve this ?
My basic principles: there are 3 ways to improve the bass response:
- BR: both the rear and the front radiation is working is phase
- TL: an open air column resonator helps us to enhence bass
- Horn: we improve the acoustic joint between the low freqs and the radiating area |
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| Colin |
If it helps, I came across this in an article by John Crabbe in HiFi News a few years ago:
horn decoupling equation, cavity volume for capacitive shunt reactance to equal horn throat resistance at frequency f, where At = throat area
V(cu in) = (2150 At)/f [where At is in sq ins]
V(cu cm) = (5550 At)/f [where At is in sq cm]
(JC developed a number of horn designs for the magazine in the 50s and 60s.)
Colin |
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| mwmkravchenko |
THe horn length, flare rate, and mouth size dictate the overall response. In a front loaded horn the rear chamber also has alot to do with the response helping to null the reactance that is part of the driver unloading the horn as it reaches Fh ( horn cutoff frequency ). In a backloaded horn you are as you have stated introducing a lowpass filter by creating a volume directly behind the driver inbetween the driver and the horn throat. WHat it does and how it behaves is a function of it's size and it's lining and or stuffing density. The size and the stuffing or lining the walls has to be played with and the results listened to or measured.
Mark |
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| pieterv1 |
I have two points to make within the framework of this thread.
In the last months I am looking for a diy implementation of a 10 cm fostex fullrange. This thread is interesting because it is discussing some fundamentals as a consequence of positioning of some kind of horn against or very near to a wall.
In my view the most commonly choices (when one wants to use a 4 inch full range) narrows to a dedicated fostex cabinet or a buschhorn mkII (may be an updated Cheap Trick 164). And this in combination with a fostex FE103E of a FE108EZ. The last one's are for the 'normal' diy worldwide the easiest available and the most recent incarnations of this sort of fullrangers.
I for myself favours the concept of the buschhorns mkII because of 'looks' and expected performance in combination with my listeningroom (16 square meters, medium damped). I have the possibility to play with speakerpostioning, hotspot and roomboundaries. In my view alike dipole speakers (electrostats f.e) it is principally needed to use horns of this kind with enough space around it, gain by the way of roomboundaries and room for integration of the sound perceived at the listeningposition. Otherwise you end with very uneven sounddispersion and a tiring presentation.
In my opinion and expierence (mostly with very good electrostats, even in small rooms and with small two way bookshelf speakers) a horn implementation will stay difficult with a cabinetposition fully against the wall. In my view a dedicated two way bookshelf, may be helped by a adjustable sub, will give a nicer result.
Only, when the 10 cm unit is comming out of the front of the wall-framework (not so nice to see and for persons with another level of acceptance quite awfull) there is may be a way out. On the net there are some cabinets that have a sort of neck. When you mount the neck horizontal and pace the mouth of the horn as near as possible to the corner walls you can may be accomplish a good result.
This requires quite another form for a horn cabinet than the buschhorn, fostex or CT164. And a good implementation wil require quite some woodworking expierience and motivation to tuning the endresult in a given room.
My advise would be: look again into the possibilities of a rather freestanding little horn so that you can get the most out of this sort of instrument for music retrieval. When you stick to a against the wall implementation go for another way to reach nearly the same, only by another way to load the air in the room for your own enjoyment.
The second point I want to make to the more experienced in maths and computersimulations is the following. In the last threads on diy audio there are several concrete questions on hornparameters such as size and form of the CC, throatsize, hornlength/deployment and mouthsize. I have tried for myself to make some calculations of especially CC size and throatsize. The goal was to get some insight in these parameters in relation to some popular cabinets for the forstex FE108EZ. I came to the conclusion that I am too inexperienced to make thrustfull calculations.
Is it possible to present in this or in a specific thread some theoretical/computersimulated parameters for enclosures around the Fostex FE108EZ? I think that several prospective diy ers have the same question, because they will choose this (relatively new) type according to worlwide availability and their desire to make a one shot approach in line with expected performance.
Not that that theoretical parameters are the end in the discussion or experiments, but they can give some quidance for constructiondetails (fe enough room to make cc and throat somewhat smaller from the start).
In the end we have all to experiment to get the best results out of the chain 'source, amp, horn, room and personal sound preferences'.
Although it helps a lot to know some indicatitions for the parameters for the FE108EZ, because the specs of this type differ quite a lot from those for the older types! And the most discussed horncabinets are at their time develloped specifically for that older types.
I am looking forward to some more information on the critical parameters.
Greetings. |
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| mrlots2do |
| quote: | Originally posted by mwmkravchenko
It attenuates the high frequencies at a rate of about 6db/octave. |
The 6db attenuation on top end per octave occurs as result of low end extension. Then the more low end I attempt to extend may make a need for tweeter to fill in the lost high end in frequency response. Guess I shouldn't try to get to much low end out of a 2" driver. Is tuning to 60hz to much? Fs is 153hz
| quote: | Originally posted by Colin
horn decoupling equation, cavity volume for capacitive shunt reactance to equal horn throat resistance at frequency f, where At = throat area
V(cu in) = (2150 At)/f [where At is in sq ins]
V(cu cm) = (5550 At)/f [where At is in sq cm] |
Not sure this formula works or I may be using wrong values.
Hornthroat= 94 sq"
Hornmouth= 43.5 sq"
Hornthroat & Hornmouth= 137.5sq"
Fs= 153hz or Ftuning= 60hz
Best I calculate volume as 1932 cu". This is huge, I was using WinISD at 62 cu" (.9 liter) vented enclosure.
Could you maybe show me my error. |
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| mrlots2do |
| quote: | Originally posted by mrlots2do
Not sure this formula works or I may be using wrong values.
Hornthroat= 94 sq"
Hornmouth= 43.5 sq"
Hornthroat & Hornmouth= 137.5 sq"
Fs= 153hz or Ftuning= 60hz
Best I calculate volume as 1932 cu". This is huge, I was using WinISD at 62 cu" (.9 liter) vented enclosure.
Could you maybe show me my error. |
Hornmouth in quote is not the opening of the mouth but really a second Hornthroat area.
This is the entire Hornthroat area.
Hornthroat & Hornmouth= 137.5 sq" |
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| Cortez |
I know the basics about acoustical RLC filters, but i have some uncertainties too.
When we decrease the throat, we must decrease the chamber too, cause when the
throat's impedance is too high, the air will just compressed in the chamber,
instead of going to the horn, like by a BR enclosure, when the port is too long.
But the horn's efficiency depends on the starting throat area, if i'am right.
Therefore have i asked, that why we need a big rear chamber. Theoritacally when the
rear chamber would be 0 size, the air could nothing else to do, like go to the horn,
and therefore should be the efficiency at the maximum, that we can reach with our horn.
My other question: why the horn's length does matter. I understand the need of the
expansion, cause of acoustic transformation, but why we need to create a horn with a
long line ? Whats the different between a shorter and a longer type horn, when the
Mouth/Throat rate is the same ? By a back-loaded horn its maybe logical, cause when the line
is too short, the acoustical shortcut will eliminate the SPL with the front waves.
But why does it matter by a front loaded horn ?
An example:
Why is the straight section so long ? Maybe this acts like a TL too ? :eek:
(If you want, read my post here too: http://www.diyaudio.com/forums/show...2166#post702166) |
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| GM |
| quote: | Originally posted by Colin
If it helps, I came across this in an article by John Crabbe in HiFi News a few years ago:
horn decoupling equation, cavity volume for capacitive shunt reactance to equal horn throat resistance at frequency f, where At = throat area
V(cu in) = (2150 At)/f [where At is in sq ins]
V(cu cm) = (5550 At)/f [where At is in sq cm]
(JC developed a number of horn designs for the magazine in the 50s and 60s.)
Colin |
Greets!
Thanks for sharing! FWIW, I compared the (cu in) formula to a couple of proven BLH designs and one was ~3.7x too large and the other was ~100x!, so without knowing more about his horn designs I recommend these not be used.........
GM |
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| GM |
| quote: | Originally posted by Cortez
I know that it acts like a low-pass filter, like a reflex enclosure, but what is does with the efficiency ?
And what about using more then one compression chamber in series ?
The first chamber would be right behind the speaker with a small size, and then a reflex-tube-like
narrow section and then an other chamber with bigger volume, and at the end of this chamber
would start our horn with a small cross section. |
Greets!
Like any vented design, efficiency varies depending on the alignment. Remember, a typical 'HI-FI' BLH is nothing more than a BR with a huge flared vent. For this reason having multiple gain stages doesn't make any sense to me since this is accomplished by the flare rate ('M', aka 'T', factor). If this doesn't yield enough gain, then use different flare rates in series (aka Klipsch's 'rubber' throat), which would provide better performance overall.
GM |
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| Cortez |
> Remember, a typical 'HI-FI' BLH is nothing more than a BR with a huge flared vent.
Why ? With a small rear chamber it should act as a horn, should not ?
> For this reason having multiple gain stages doesn't make any
> sense to me since this is accomplished by the flare rate.
What do you mean exactly under "multiple gain stages" ?
> If this doesn't yield enough gain, then use different flare rates
> in series, which would provide better performance overall.
Could you write more about this "rubber throat" ?
Why it helps us to improve the bass radiation ? |
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| GM |
| quote: | Originally posted by Cortez
> Remember, a typical 'HI-FI' BLH is nothing more than a BR with a huge flared vent.
Why ? With a small rear chamber it should act as a horn, should not ?
> For this reason having multiple gain stages doesn't make any
> sense to me since this is accomplished by the flare rate.
What do you mean exactly under "multiple gain stages" ?
> If this doesn't yield enough gain, then use different flare rates
> in series, which would provide better performance overall.
Could you write more about this "rubber throat" ?
Why it helps us to improve the bass radiation ? |
Greets!
Why 'what'? It's the physics of the situation and I don't know how to further simplify it, so if you can't grasp this concept then I don't know how you're going to ever understand BLH design. Anyway, read my response here, maybe it will help: http://www.diyaudio.com/forums/show...2815#post702815
Each one of your multiple compression chambers would be a 'gainstage', i.e an amplification chamber, if properly designed of course!
Not too much to write about. I mean it's my understanding that PWK coined the term around 1940 to describe the multiple flare rate of his corner horn. He may also have been the first to do it since I've never seen one before Altec Lansing developed the 811 sectoral lens in the late '40s. Both these used fast initial expansions to control their HF response, then slow down to the Fc flare rate.
This yields less gain near Fc though, so for more gain you'll need a much slower initial flare rate, then speed it up to keep it a semi-reasonable length/BW. Or not, as the case may be as is done with the B*** AWC, which is a long straight pipe, relying on loading the back side of the driver with another one. It yields a rather underdamped response, but used as a true sub this may not be a 'big deal' depending on your room design/performance goals and you can't beat it for simplicity: http://www.diyaudio.com/forums/show...=&threadid=9501
GM |
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| Cortez |
> Why 'what'?
You said, that a classic hifi horn is just a BR with a huge port.
And I said to this, that when we have a very small (0 size)
rear chamber, it cant be act as a BR, cause the air cannot be
compressed and therefore it can just go to the horn.
> Each one of your multiple compression chambers would be a 'gainstage'
How ? imho a chamber only shifts the phase end increase the speed of air in the output port.
A horn would gain, cause of acoustic transform, but a simple chamber how ?
I'am still curious, that how we should size a horn, when we want
to include our room's size to the calculations. I think when a horn
operates indoor, the acoustical conditons are quite different, cause
in a smaller, closed air-space we need a little more power to compress
the rooms' air related to an open air environment, where we
do not have this problem, and can concentrate only to the transform.
So in a little room maybe a smaller mouth would be better.
The flare could be the same, but the throat, and the mouth size
should maybe decreased, shouldnt ? |
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| GM |
Greets!
Once the filter chamber is deleted, it's no longer a typical HI-FI BLH, but a zero compression horn (expanding TL, aka Voigt pipe) that can be either considered a dipole front or back loaded depending on its configuration.
If each gainstage was smaller than the previous one then it would act as a very resonant stepped reverse tapered TL, applying additional pressure on the back of the driver. If the last gainstage were attached to a horn lens throat......... So why not just shape the horn flare to do this? Look at the RCA's catenoid flare: http://home.att.net/~lkalin/fabrication.html
Yes, in a typical HI-FI room the acoustics are indeed quite different than in a very large one or especially outdoors. Down low the room dominates, so for best performance the room's gain curve should be measured and the horn's response designed to have ~the inverse of it. IOW, where the room has a peak, the horn should have a null and vice versa down to the point where the room's gain begins climbing, so yes, the mouth would need to be somewhat smaller than optimum to get this 'ripple'. At this point you want the horn to be rolling off at about the same rate it's rising.
This all sounds good in theory, but tough to achieve in practice, so most folks just make the horn as long/big as can be tolerated and the response is what it is, with some using digital EQ to smooth it out.
GM |
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| Cortez |
| quote: | | Once the filter chamber is deleted, it's no longer a typical HI-FI BLH, but a zero compression horn |
And what is your view about a design like this ?
| quote: | | This all sounds good in theory, but tough to achieve in practice, so most folks just make the horn as long/big as can be tolerated and the response is what it is, with some using digital EQ to smooth it out. |
No, not the ripple was the point, but the inertia of a closed airspace.
A horn, designed to outdoor use (huge sizes with ideal flare, etc...)
cant work properly in a small room. It isnt enough strong to compress the air.
But if the horn (maybe the throat and the mouth too) is smaller, it would have more power against the walls. |
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| bobhayes |
Decreasing the mouth size in this manner is defeating the object, you're going to end up with a transmission line.
When you say 'inertia of airspace', are you referring to the acoustic impedance of the room as seen by the speaker and enclosure?
The whole point of a back loaded horn design is to create a great deal of gain in the bass region for drivers that are highly damped, by coupling a small moving cone to a large volume of air. This is the requirement even if your room is only small, it's much bigger than the cone displacement volume). Look at the response curves of the fostex driver range, note their Q values and then see what fostex recommend as enclosures. The lower the Q value (damping factor), the more gain the cabinet will have. If the Q of the driver is higher than about 0.3, then a horn isn't really required for hi fi use, unless it's part of a multi way system, as the bass output from the horn will be too high in comparison to the directly radiated middle and high frequencies (unless these too are more efficiently coupled to the listening area).
Outdoor, stadium, Nightclub, theatre and concert P.A. type horn speakers are large, don't usually go very low, and have very high sensitivity over a small bandwidth compared to hi fi horns, and are used in arrays with lots of differing driver/enclosure combinations to cover various frequencies, with active filters and multiple dedicated amplifiers to suite their application.
Most single driver hi fi back loaded horns will perform over a greater bandwidth, with a compomise in efficiency, but this isn't a problem, as the bass horn output only needs to match the sensitivity of the driver in the unassisted mid and treble regions for a balanced overall respose. As a back horn design is a compomise between bandwidth and efficiency, and the efficiency doesn't need to be great, the bandwidth is quite broad and usually performs well into the higher frequencies that are not required from it, where the drivers sensitivity has increased, hence the compression chamber.
Take away that cusion of air, and you'll and up with a big hump in the mid bass and beyond, possibly emphasised by the room modes of your listening environment.
A back loaded horn needs to balance:-
Efficiency (Sd to throat ratio and flare) to match the mid and high frequencies,
Bass extension (length and flare),
Low pass filter (compression chamber) to remove excessive mid bass etc. and of course domestic acceptability.
Typical successful designs balance these variations in a manner that is generally approved by many people, and versatile enough to be located in many sized rooms.
If you're building a bass horn speaker for a smaller room, make either a small one like the cheap trick or fostex recommended 103 or 108, of a larger one with a little less efficiency, to tame overall gain in the confined room volume.
By the way, a PA bass horn will perform exactly the same indoors (near field response), but the enclosed airspace, reflected sound waves and room modes would create a dangerous place to be without ear defenders if fully driven!
:) :bawling: :bawling: |
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| Cortez |
| quote: | | Decreasing the mouth size in this manner is defeating the object, you're going to end up with a transmission line. |
I didnt say to decrease it to a straight line.
Rather throat: Sd/3, mouth: Sd*8
| quote: | | When you say 'inertia of airspace', are you referring to the acoustic impedance of the room as seen by the speaker and enclosure? |
Yes.
| quote: | | The whole point of a back loaded horn design is to create a great deal of gain in the bass region for drivers that are highly damped, by coupling a small moving cone to a large volume of air. |
I know, but note, that already a BR with a little size port can help a lot in bass.
Relate to this, 8*Sd is enough large, isnt ? :) |
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| bobhayes |
Rather throat: Sd/3, mouth: Sd*8
With most full range drivers, a throat this small and a mouth this large would be very efficient (depending on flare type and length), increasing the risk of over powering bass in relative to the upper frequencies.
I once made this mistake with a 12cm driver enclosure- throat being Sd/2 and mouth at a massive 25*Sd with a hybrid flare and around 1/4 Fo in length. The efficiency was too high for the room I had intended to use it (due to the Sd/throat ratio not mouth size), the resulting bass output was overpowering the other frequencies greatly.
It sounded far better in a much more damped room with lots of soft furnishings and a deep pile carpet, but still bass heavy.
The problem was that the Q value of the driver was higher than stated in the documentation provided, so the bass gain of the horn was not required.
You mention that a reflex enclosure greatly enhances bass output, but the way in which the port resonates is unlike a horn system.
The port/enclosure volume is tuned to resonate at a specific frequncy and contributes to the overall output of the system over a very limited frequency range, and the maximum linear output from the port is directly related to its size, unlike a horn.
P.A. bass systems often have very large ports or multiple ports so that they remain linear even at high S.P.L.'s.
Shove a sock in the port of most home reflex speakers and you conceive a drop in bass output at normal listening levels. However, lower bass frequencies will usually raise a little, due to blocking up the short circuit, and making the speaker aa acoustic suspension type.
At high levels with a small port, you probably wont notice much of a difference when the sock goes in, due to the port output being comparatively low in relation to the cone output.
I'm still rather partial to acoustic suspension systems for this reason, as well as the superior transient response.
:) |
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| Cortez |
> With most full range drivers, a throat this small and a mouth
> this large would be very efficient (depending on flare type and
> length), increasing the risk of over powering bass in relative to
> the upper frequencies.
Well, i'am not afraid of this. :) The bass isnt enough for me now.
My horn is ca. 2m long. What length do you advise ? |
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| GM |
| quote: | Originally posted by Cortez
And what is your view about a design like this ?
No, not the ripple was the point, but the inertia of a closed airspace.
A horn, designed to outdoor use (huge sizes with ideal flare, etc...)
cant work properly in a small room. It isnt enough strong to compress the air.
But if the horn (maybe the throat and the mouth too) is smaller, it would have more power against the walls. |
Greets!
It has its uses when done properly, but it's not going to compete with either type of BLH unless you accept its highly resonant response.
Like I said, you want the horn to be rolling off with increasing room gain so it doesn't increase room 'compression'.
GM |
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| Cortez |
I concentrate in general to the low end, aside from the other resonants above.
My main goal is to build an enclosure wich works effectively in a 30-100Hz region
as wide and as smooth as possible. That's why i'am interested in Karlson designs too,
because there the widerange operation can be achieved. And against the wavy FR
is will i plan to use acoustical filters like a muffler, that low-pass up to 100-200Hz.
With smaller horn sizes adapt to the room size, i meaned for: lets take a big horn,
with relative big rear chamber, and big throat and mouth area. Now lets keep the
length and the flare rate from this horn design, but lets decrease it (the rear chamber too)
proportionately. Wath would happen, what would be different now ?
(Because you sais all the time, that the rolloff depends on the mouth size) |
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| bobhayes |
Ok, so for example (2m length) you decrease the throat area. This will increase the efficiency of the horn, and decrease it's active bandwidth.
Now you have a mid bass hump.
You also reduce the mouth area. This shifts the lower cutoff frequency and you loose lower bass tones. It also increases the 'comb effect' as the flare rate is reduced causing a more uneven response through the active range.
Now you decrease the compression chamber. This will filter out less of the upper frequencies from being loaded by the horn. Now the mid bass hump is bigger and wider.
If by chance, one of the reinforced harmonics in the mid bass output corresponds to a room mode in your smaller room, you will conceive a loud single note bassline, with lots of missing bass notes.
If you could expect reasonable performance by doing this, I should think you might see more enclosures built like this.
If you want to experiment with the effects of playing with the horn geometry, try the applet at www.ishtek.com/software_ts.html
I've built a pair of horns based on the results from this applet, and the program seems quite accurate.
:) |
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| Cortez |
Ok, thx, i will try this program!
Otherwise can you tell me, how the horn's long defines the operation ?
Lets fix the rear chamber's volume, the throat area and the mouth area too.
Now just our horn's long is variable. I'am curious specially for the operation, not just the results.
Isnt there a site somewhere on the net about horns with FEA ? (Final Element Method) |
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