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Guide to WinISD Pro and Hornresp

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mobiele eenheid View Drop Down
Young Croc
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    Posted: 30 January 2005 at 8:00pm

Hi all,

I?m working on the English version of my small guide for WinISD Pro. By translating it into English it should be able to help a lot of people out there starting with speakerbuilding-simulating. Any advise-point outs are welcome as well.

Scroll down for the Hornresp guide.
 
Johan


Edited by mobiele eenheid - 07 February 2008 at 2:40pm
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Young Croc
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mobiele eenheid Quote  Post ReplyReply Direct Link To This Post Posted: 30 January 2005 at 8:06pm

WinISD Pro

 

Frequently I encountered questions about how to work with WinISD, or people that think that they have to let WinISD do all the calculating. And build the cab WinISD comes up with right after starting up.

That's why I've written these pages that should explain the meaning off the most important tabs/pages from WinISD.

ATTENTION: A lot of people are still working with WinISD 0.44. De explanation given is about WinISD Pro (a6 and a7). It's mostly that WinISD 0.44 doesn't have the pages these explanation is about and by that's not giving the information necessary to make a good cabinet.

To make things more clear for the reader/practicer I've added a few examples based on the 18sound 18LW1400.

I used the following Thiel/Small-parameters (to avoid the use of other parameters and thus different results):

 

18LW1400

Qes: 0,31

Qms: 7,2

Qts: 0,297

Fs: 31 Hz

Vas: 297 ltr

Mms: 190 g

Re: 5,0 ohm

Bl: 24,7 Tm

Le: 2,3 mH

Xmax: 9 mm (it's actually 5 mm, but that's an other story, I'll use 9 mm here anyway)

Pe: 700 W (that's the W RMS value, nowadays it's specified as 1000 W AES).

Sd: 1228,5 cm^2

Z: 8 ohm

 

The other parameters are calculated on the hand of these, by WinISD Pro. The Help-function of WinISD Pro should give you the basic knowledge to fully understand this slightly advanced explanation. The explanation is about making a basreflex sub, since this is one of the easier things to build.

The standard calculation done by WinISD Pro after start up is leading up to confusion amongst many users. The only thing the program does is calculating a frequency response as flat as possible., with as much low end extension possible as well. The program doesn't bother with the powerdip created, groupdelay, etc.


A bug that can be encountered in a7 is that the tuning will be suddenly be resetted to 0.00 (zero). If you're having problems inputting T/S-parameters (and getting them accepted) turn of the auto-calculation, see also the updates sectio below.

WinISD Pro a7 is surely not the best program out there. But since it's freeware (that's how LEAP started ;) it's a good start in understanding how the parameters influence the function of a loudspeaker, furthermore to avoid the "rotten apples".

 



Edited by mobiele eenheid - 12 March 2010 at 4:15am
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Transfer function magnitude

 

This is the so called frequency response. Here the amplification or weakening (in dB's) is put against the frequency. This is where you usually try to get a response/ line as flat as possible, without getting into problems on the other pages. Small holes or peaks won't matter to much (up to about 2 dB). The response doesn't necessarily have to be flat, tho it's common to try so.

 

WinISD Pro standardly calculates a frequency-response as flat as possible and as much low-end extension as possible. The program doesn't keep the groupdelay nor the Maximum Power in mind. Sometimes the volume and tuning will get extreme values, sometimes it's very useful.

Designing a loudspeaker is about finding a compromise between all those values. It's person/application depended what's most important to be correct. Luckily there are some standards to keep in mind.

 

If you are using your basreflexsub for PA don't try to get as much low end extension as possible. For most parties a f3 or f6 of about 40 á 42 Hz is useful enough. This doesn't mean that the frequencies below 40 Hz will not add to the sound. In most cases they will, especially for Home Theater-applications. But when used for most types of music it's not necessarily. Also low frequency production is very energy and space consuming and therefore quite the opposite of having a small soundsystem. If you're convinced you need better low frequency reproduction, tune at the Fs of the driver or higher.

 

For PA-applications you'll get most times more low end extension with an 18 inch then with an 15 inch. This is not just because the 18" is bigger. The bigger size will give it (in principle) changes in T/S-parameters that will make it more useful for low frequency reproduction. But these changes can be made in more ways than just increasing the diameter.

Actually a lot of speakers optimized for low frequencies are 12" but due to the low Fs of these speakers, necessary to get good low frequency reproduction, they're also less efficient and thus need (much) more power to get to the same SPL-levels as an average 18" would need.

 

There is a physical law that correlated size of the cab, efficiency and low end extension. For instance you can make a relative small cab to go very low (below let's say 20 Hz) but this will result in a inefficient model. On the other hand you can make a cab of the same size go much louder due to it's efficiency. But then you won't get the same amount of low end extension.

Thus the reason why for most PA-applications 40 Hz is low enough. You could make it go lower but the cabs would increase in size accordingly. In the end it's your personal choice and application that will make most choices for you.



Edited by mobiele eenheid - 06 July 2009 at 10:58am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mobiele eenheid Quote  Post ReplyReply Direct Link To This Post Posted: 30 January 2005 at 8:18pm

Maximum Power Chart (aka Powerdip)

In the "Maximum Power" window is showed how much power the speaker can handle without exceeding the Xmax. A graph with on the Y-Axis the maximum power and on the X-Axis the frequency.

To make it easily understandable it's best to simulate a basreflex cab (br-cab) with the 18LW1400. With a volume of 200 ltrs and tuned to 40 Hz. If you look at the maximum power you'll see a straight line (with a value of 700 watt). Below 34,5 Hz the maximum power drops down fast. This indicates it's best to use a low-cut at 34,5 Hz.

Next simulate the cab with a volume of 400 ltrs, still tuned to 40 Hz. Now there is a small dip created in the straight line. This is the so called powerdip. Around 49 Hz the maximum power is only 615 Watts.

The bigger you make the cab or the lower you tune it, the bigger the powerdip will be. The smaller the volume or the higher the tuning the smaller the powerdip will be.

This simulation uses a sine-wave to do the maximum power calculation's, music however isn't a sine-wave. The dynamic range of a sine-wave is 3 dB. Low frequencies mostly have a dynamic range of about 3-6 dB. Meaning that in some cases (6 dB) you can double the amount of power as showed by the simulation, depending on the style of music/sound. Mid and high frequencies will usually have an even bigger dynamic range into the signal (say 9 -12 dB).

It's still best tho if a speaker doesn't has a powerdip (unless off course the powerdip is out of the represented frequency range). With most subs/woofers the powerdip is somewhere around the 40 á 60 Hz area. Those frequencies are of great importance to most types off music. Also a speaker will frequently be used at a higher power than the rated rms-powerhandling.

By raising the powerhandling you can see where the powerdip is, in case it's not visible at maximum power (parameters, double click on the Pe-number and type the new {higher} number, changes will not be stored).

With some cabs/loudspeakers the lower powerhandling created by the powerdip will be significantly lower than the rated powerhandling. Some speakers show this lowered powerhandling even on a very "friendly tuning". In most cases the lack of Xmax is to blame. Sometimes it just shows the speaker not being intended for use in a br-cab or the intended application. You can make the volume of the cab less or the tuning higher, but in some cases you'll just have to sacrifice to much.

Guitar loudspeakers are often designed to exceed Xmax. In those cases the "sound" of the guitar speaker/combo is partially created by the distortion formed. Most speakers that are advertised as being guitarspeakers will have a very tiny Xmax. Because the Xdamage (Xmech) is several times higher, the speaker will not be damaged. The sound however, so useful for a guitar will ruïn the sound of a good PA.



Edited by mobiele eenheid - 12 March 2010 at 4:16am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mobiele eenheid Quote  Post ReplyReply Direct Link To This Post Posted: 07 February 2005 at 12:28pm

Cone excursion

 

Directly related to the maximum power and powerdip is the cone excursion. In this graph the movement of the speaker (in mm) is shown in respect to the frequency.

In the case of WinISD Pro a6 it's the Xmax p-p (peak to peak). This is somewhat confusing because the maximum allowed excursion is now 2 times the Xmax (or Xmax p-p = Xmax times two).

On the "Signal" page, under "Power", you can type the amount of power that you would like to give to the speaker. Now you can see how much excursion the speaker will have, with respect to the frequency.

 

Give the cab a volume of 400 ltr and tune it to 40 Hz with 700 Watts of power going to it.

Around 49 Hz the excursion is now about 19 mm/ 0.75 inch. Xmax times 2 (=Xmax p-p) is 18 mm/ 0.71 inch. So the speaker will exceed Xmax but only around this frequency.

If you would use an equalizer to lower that frequency-band enough than the Xmax would no longer be exceeded. This is off course not very practical, especially because a lot of "energy"  is housed at that area..

 

When a speaker exceeds the Xmax it will loose control over the movement of the cone. Instead of moving only back and forward the cone will also start to move sidewards. In basreflex cabs this is usually noticeable because the quality of the sound is being reduced.

If the cone exceeds Xmax too far it will hit the pole-piece and thus starts to destroy itself. In that case the speaker exceeds the Xmech. Xmech is usually around 2 times Xmax (guitarspeakers generally have a Xmech several times larger than Xmax). And some speakers like the Ciare 12.00 SW have a Xmech quite close to Xmax.

Not every speaker will loose control at the same rate. The 18LW1400 for instance won't loose control quickly when it's exceeding the actual 5 mm/ 0,2 inch. Also Xmech is 25 mm/ 1 inch.

 

Using basreflex cabs both hearing and eyesight are useful tools to "see"  if Xmax is exceeded. Exceeding Xmech the speaker will produce a ticking sound which you will hopefully never hear.



Edited by mobiele eenheid - 06 July 2009 at 11:08am
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Rear port- Air velocity

 

On this page the airspeed in the basreflex port(s) is showed. Either in m/sec. or ft/sec. For Hifi-applications 17 m/sec. (or 56.7 ft/sec.) is an useful limit. For PA-applications 34 m/sec. (or 113.3 ft/sec.) is more useful.

If the airspeed in the port(s) is to high it becomes hear-able, even at SPLmax. It's also called "Port noise".

 

A round port has a slight advantage over square or rectangular ports. By rounding of the corners with a router the port noise can also be reduced just a bit more.

The rounded corner is still part of the length of the port. Sometimes a flair is used.  Making the surface of the ports larger or using more ports, reduces the airspeed in the port but the length will increase.

A port that's to long won't work correct either, this also depends again on the diameter/surface of the port.

 

A rule of thumb is that the port surface has to be at least 1/9th of the surface of the cone.

The more power the speaker will get, the higher the air velocity in the port will become. That's why the air velocity in the port will often look to be nothing at all, since the Power on the "Signal-page" is standard 1,0 Watts.

By raising the power, you'll also raise the air velocity in the port. Off course you should use the amount of power in the simulation that you'll use in practice or the amount of power that the speaker can handle.

The lower the frequency the higher the air velocity get's (up to a certain point).

I've found the limit of 34 m/sec (113.3 ft/sec) to be rather correct. Therefore personally I prefer 30 m/sec. (100 ft/sec.) as the upper limit for PA-applications.

With 6th order bandpass designs there is also a front port. For this port the same rules apply as written above.



Edited by mobiele eenheid - 06 July 2009 at 11:12am
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Groupdelay

 

On this page the groupdelay (in miliseconds) is shown in relation to the frequency (Hz). A high groupdelay will result in a boomy/muddy sound. The groupdelay is created by the basreflexport and is thus one of the downsides of using basreflex cabs.

Most people however are used to this sound since basrelfex is used widespread in daily live.

Not only the highed of the groupdelay is to be considerd. The shape is also important. It's better to have a slowly forming round peak then a sudden needle-like peak that's there for just a few frequencies..Generally the groupdelay will reach it's maximum around the tuning frequency

 
A rule of thumb coming from Hifi is: frequency x groupdelay = 400 (max). Less being preferable. At 40 Hz that would be 10 miliseconds. A little bit higher (up to 600) around the tuning frequency can be overcome.

From this rule of thumb you can clearly see that the highed of the groupdelay becomes more important at higher frequencies and less important at lower frequencies. This is because the sensitivity of your ears increases as the frequency rises.

A high groupdelay in the 80 Hz and up area for instance will ruine the "kick'. Making it sloppy having less impact. Making the volume bigger or tuning the port lower, will increase the groupdelay. As you lower the tuning frequency the groupdelay will shift down along side with it.

 

You could lower the tuning frequency that much that the tuning will be beneath the lowcut (aka highpass) your using. The downside to this is that the output of the port will be lost as well.



Edited by mobiele eenheid - 06 July 2009 at 11:15am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mobiele eenheid Quote  Post ReplyReply Direct Link To This Post Posted: 24 February 2005 at 7:42am

- Your add could be here -

(reserved for updates) 
 
Update:
 
Ones every while people experience problems uploading new drivers to WinISD Pro. The main issue is that WinISD Pro standardly calculates the unknown T/S-parameters from the ones given. As soon as your input doesn't correspond with the mathematical coherence between the T/S-parameters a driver will not load.
 
The easiest way around this is go to the bottom of the "Driver Editor" and click-off the "Auto Calculate Unknowns".  An other way around is to only load those T/S-parameters that do not mathematically correspond to other T/S-parameters: The input sequence should be:
 
Qes, Qms, Fs, Vas, Re, Le, Sd, Xmax, Pe (leave the rest open).
 
Best regards Johan


Edited by mobiele eenheid - 12 March 2010 at 4:17am
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Post Options Post Options   Thanks (1) Thanks(1)   Quote Elliot Thompson Quote  Post ReplyReply Direct Link To This Post Posted: 24 February 2005 at 10:48am
I got a gig today, tommorrow, and, Saturday. If no one shares
their thoughts, I will offer mine on Sunday.

I could've sworn, WinSID Pro offered an English version?
(I haven't looked at it since 2000)

You could always, paste your info in Microsoft Word, and,
let the program modify the grammar.

PS: How About "Maximum Power Chart" or "Maximum Power Graph".

Best Regards,


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Hornresp Kickstart

 

Introduction

The Hornresp program, written by David McBean and based on Olson's horn model, is a very easy to use horn simulation program. David wrote the original version in the early 1970's in Fortran IV and ran it on a room-sized IBM mainframe computer. Some people call it a bass horn simulation program as it does not have enough input information to always simulate higher frequencies accurately, but the model is accurate for predicting power response at higher frequencies as well (more on this later). But if it's so easy, why write a guide? While it's easy to use, it has some abbreviations and terms which will remain a mystery to many, even after reading the built-in help file. Furthermore Hornresp's abilities keep growing steadily. Hence the reason for this guide.

 
 
Entry guide
 
 
ANG:
 
Here you indicate where the horn is located. In a nutshell, enter 0.5 for optimal hifi corner loading, or 2 for PA outdoors use where you will have a floor but may not have a rear wall.

INPUT INPUT DENOTES SPACE DESCRIPTION Typical Application Comments
0.5 Corner loading 1/8 space Placed in a corner Hifi Horn can be made smaller
1 Floor & Wall 1/4 space On floor with one wall Hifi
2 Ground only 1/2 space On ground outdoors or middle of room Typical PA Sub/bass cabinets
4 Full space Full space Suspended high over the ground Large PA Mid/high cabinets

Low-frequencies are omni-directional, radiating in all directions. This full sphere is known as 4 Pi space. When placed on the ground, the sphere is cut in half and the ground forms an acoustic mirror which effectively doubles the size of the horn mouth compared to full space. As a result you can make the mouth smaller when placed on the ground. This is called half space. When the horn is against another wall, the hemisphere is divided in half again, quarter space. Where there are two walls and a floor, we have a corner, 1/8 space. Each time the radiation angle is cut in half, the required mouth size is halved, hence it is recommended to place the horn in a corner to reduce the necessary physical size of the horn.

In most cases, except very large PA, subs are ground stacked and thus are best simulated in half space. Tops are usually flown or placed upon standards or subs (to get the high frequency drivers horn mouth above the crowd). As the height of placement and/or the frequency rises, loading will go from half space towards full space. This is accelerated by the horns increased directivity at higher frequencies (they aren't strictly omni-directional any more and thus are less affected by boundary loading). PA tops in general therefore should be simulated in full space.
Note: Loading into half the previous space (i.e. 4 Pi --> 2 Pi) gives a maximum increase of ~ 5 dB according to Hornresp (6 dB in theory), this is however based upon a very solid boundary. Thin/ wooden walls, ceilings or floors might not present such a solid boundary and thus show a smaller actual increase in SPL then predicted.
In worst case scenario's (often high SPL/low frequencies) a wooden floor/ wall might actually act as a bass-absorber as it vibrates (converting sound energy into movement and heat).
 
VEL / DEN:
 

Note: In later versions of Hornresp VEL/DEN were replaced with EG and RG

The velocity of sound in air at a given temperature and pressure (at standard conditions) / Density of air at a given temperature and pressure - Unless you know the precise conditions of the location your horns will be used at, keep this at the default value (VEL - 34400 cm/s / DEN – 1.205 g/litre)

EG:

Amplifier RMS Voltage (Volts) - Effectively the input power, when it's squared and divided by impedance (see the electrical impedance tab). In Hornresp you're not working with Watts (like WinISD Pro) but with voltage. This tab will influence the SPL and cone excursion and enables you to get an indication of the maximum SPL performance based on the excursion limits of the driver.
Hornresp has a calculator (appearing upon double click in the tab) that can "translate" the amount of Watts, on a specific load (impedance), to the Voltage required in the tab.

2.83 Volts translates into 1 Watt @ 8 ohm. 2.83 would also be 2 Watts into 4 ohm. For instance if you need 200 Watts into a 8 Ohm load, Hornresp calculates 40.00 Volts.

U = I x Z --> 40.00 / 8 = 5 A --> P = U x I --> 40 x 5 = 200 W (= U^2 / Z) {U = voltage, I = current, Z = impedance, P = power}

 
RG:
 
Amplifier output resistance (ohms) - This includes the resistance from the cables (from amplifier to speakers) too. The next values ought to give you a start: Cable from amplifier to speakers (10 meters long, 2.5 mm^2 on average) ~0,3 Ohm, amplifier itself ~ 0,04 Ohm.
 
CIR:
 

Free space normalised horn mouth circumference in flare cut off frequency wavelengths - CIR is only visible when either the last horn segment is Exponential or the first and only horn segment is either Exponential or Hyperbolic-exponential. If this is not the case CIR is replaced by FTA (ahead).

As you might know, Hornresp simulates the horn (mouth, throat and segment) area's as if those are circular. To give optimum efficiency at the cut off frequency of the horn, the circumference of the circular mouth area needs to be the same length as the wavelength, corresponding with that cut off frequency (in 4.0 Pi). You have achieved this when CIR is 1.0
For 2.0 Pi you can get optimum efficiency for a certain cut off frequency with a smaller mouth area. In 1,0 Pi this mouth area can be made smaller again, etc.
In most modern horn designs the actual mouth area is smaller than the optimum mouth area (most often a compromise between gigantic size and actual performance needed). About the reasoning behind this you can find more information in the Speakerplans FAQ's and general horn theory found on the www. In short you can get away with a CIR smaller than 1.0 without degrading performance to much if designed correctly.

 
FTA:
 
Flare tangent angle (in degrees) – Only visible if CIR is not (see CIR).
When the FTA is zero, the horn is a straight tube, the 90 degree maximum is a (close to infinite) expansion/ flare rate: I.e. S1 is much smaller than S2 and/or L12 is very small. See also the schematic diagram.
 
S1:
 

This is the area at the beginning of the horn (or throat area), the end closest to the driver. It's ratio to the driver's area sets the compression ratio for normal horns.

Compression ratio

The compression ratio is Sd/S1 (except for tapped/offset horns). So if Sd is 1220 cm2 and S1 is 610 cm2 the compression ratio is 2. What the compression ratio will be is up to you, but there are some boundaries you should take into account. 10:1 is what some high frequency compression drivers use - this is considered high for midrange and bass horns. 4:1 is more typical of the range used in midrange and mid-bass horn, with 2:1 to 6:1 being pretty standard. Because there is no published parameter yet for the strength of the cone (hint to manufacturers ;), it’s not easy to figure out what a safe compression ratio is other than figuring it out in practice (too high a compression ratio could cause the cone to break due to high pressures generated at the throat of the horn). If you are designing for home hi-fi use, this is usually not as important. If you are designing for pro-sound levels, it becomes much more important.

 
S2:
 
This is the horn segment 1 ending area and horn segment 2 beginning area. So you don’t have to type this again in S2 at the beginning of the second horn segment (because S2 = S2), Hornresp will do this for you.

Footnote: For tapped and offset horns Sd/S2 sets the compression ratio.
 
L12:
 

The (axial) length of horn segment 1 (in cm). You can choose CON (conical), EXP (exponential), HYP (hyperbolic-exponential), TRA (tractrix) by typing c, e, h, or t while your cursor is in the length box.
Many horns are built out of several conical segments, which together can come close to approximating the shape of an exponential expansion (for example). Keep this part in mind when designing your horn. It’s not easy to build a true exponential (and still solid) sub/bass horn. This is the main reason why most horns consist of multiple conical parts.
Mid/high and band pass horns can be made much shorter and frequently consist of just one horn segment. With a band pass horn the throat and rear chamber become more important (more on that later). However, all horns are band pass devices - the importance of sizing the front and rear chambers depends on the exact characteristics you are trying to design for.

 
F12:
 
Horn segment 1 flare cut-off frequency in Hz (for exponential, hyperbolic and tractrix).
 
T:
 

Note: In earlier Hornresp models this parameter was known as FLA.

Hyperbolic (-exponential) horn flare parameter - This controls how fast the horn flairs as you get towards the mouth. Press H when the length tab is highlighted. You can only use the input boxes for the first segment now (S1, S2 and L12).

 
T = 0
 
The horn flare will be catenoidal, this type of horn flare is really nice to integrate in a design since the horn will almost not expand till it’s close to the horn mouth, where it will expand very quickly. You will find that this way it’s easy to fit a long horn in a relative small folded horn enclosure.
Of course there is a downside to this: To get a nice and deep output, you want the horn to expand more quickly like with:
T =1 (exponential)

An exponential horn will give more gain in the low-frequency reproduction of the bass horn than a catenoidal horn. However as you might aspect, it’s much harder to fit it nicely into a compact folded horn enclosure.
Luckily you can make it anything in-between 0.00 and 1.00 so that you will get a compromise you’ll like.

These aren’t the only possibilities though, with:

T = 99,999.99

You will get a conical horn. A conical horn will be totally straight, from S1 to S2 it will go in a straight line. Conical horns often have a small "hump" (few dB's gain on small frequency-band) before they fall off downwards. In some cases you can use this hump to extend the low-frequency response.



Edited by mobiele eenheid - 12 March 2010 at 4:19am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mobiele eenheid Quote  Post ReplyReply Direct Link To This Post Posted: 13 May 2005 at 10:17am

T/S-parameters

Hornresp can calculate BL, CMS, RMS and MMD out of other T/S-parameters. Just double-click on the tab and a calculator will appear that will calculate the mechanical parameters from the T/S-parameters (Fs, Qes, Qms. Vas).

SD:

Driver diaphragm piston area (in square cm / cm2) - Table: Typical Sd values for different diameters. Footnote: 1 sq inch = 6.45 cm^2.


DIAMETER SD (cm2)
5" 85
6.5" 130
8" 230
10" 330
12" 500
15" 780
18" 1200
 
BL:

Driver's force factor, a measure of motor strength - This is equal to the magnetic flux density in the gap (B) times the length of voice coil wire in that flux (L), and thus the units are Tesla-meters. Sometimes it's stated as Newton/ Ampere's, read here why that's the same but different.

CMS:

Driver diaphragm suspension mechanical compliance (m/Newton) - Compliance is the inverse of stiffness. If you double click on the CMS box, the calculator will ask you if the {VEL}, {DEN}, and SD values are correct. Then it will ask for the driver's Vas in litres (cubic dm / dm3).
Footnote: 1 cubic ft ~28.32 litre.

RMS:

Driver diaphragm suspension mechanical resistance (Newton.sec/m) - For this parameter to be calculated you need CMS (so calculate this first if necessary), Fs and Qms.

MMD:

Driver diaphragm, voice coil, and other moving parts dynamic mechanical mass - Mms also takes the weight of the air displaced by the driver into account. Therefore Mms is higher, but usually not by much. Note: How Mms is derived might differ amongst manufacturers, Mmd can be calculated.

LE:

Driver voice coil inductance (Milli-Henry's / mH) - This parameter can't be calculated from other T/S-parameters. The Le will have a large influence on the high frequency roll-off of the horn in some cases. A higher voice coil inductance will limit upper usable range, however in a bass horn other compromises such as bends in the horn and the front chamber volume could impose a more significant limit.
An Adire Whitepaper demonstrates an impact on transient response which may be a more significant effect.

RE:

Driver voice coil DC resistance - For an "8 ohm driver" this will generally be around 5 - 6 ohms, for a “4 ohm driver” around 3 ohm.

... end of T/S-parameters

ND:

Number of drivers in the loudspeaker enclosure - Input parameters --> Tools --> Multiple drivers. As Nd doubles so should horn parameters such as S1, S2, VTC, VRC, AP, ATC, etc. to keep the horn(s) the same as before. The horn length will remain (approximately) the same.

VRC:

Rear compression chamber volume (litres) - This is the horn's rear chamber (in case of a front loaded horn). In most cases it's a closed chamber with the speaker mounted into one of its walls, like in a standard sealed box system.

  • A horn sub that is meant to be used in singles generally has a large rear chamber to get a decent output on low frequencies. The downside of a large rear chamber is the accordingly lower mechanical power handling (Xmax is reached with a lower power input).
  • A horn sub that is meant to be used in stacks generally has a smaller rear chamber. These kind of subs trust more on the horn loading of the stack to get decent output at low frequencies. If a horn like this is used on its own, it will have a relatively large dip in the frequency response (like the LAB horn). By stacking multiple horns together the mouth area will be enlarged. The lower the frequency, the bigger the mouth area needs to be to give good results.
  • Band pass Horns (BPH) generally also have large rear chambers, mostly combined with a large VTC (throat chamber). It's hard to define a specific number here but a rear chamber above 80 litres (for an 18" or smaller) would be considered quite large. BPH are also typically meant to be used in multiples. The horn length is too short to be a true horn. By stacking the horns together, the virtual horn length will increase slightly due to a larger end correction from the larger mouth area, thus lowering the cut-off frequency of the horn compared to a single one.

LRC:

Rear compression chamber average length/depth - If you mask the resonance of the rear chamber, this has no influence (Tools, Options: Throat chamber and rear chamber resonances), so you can put here any number you like (i.e. 20 cm). If you don't mask the resonances this parameter can influence where notches and peaks in the high frequency response occur, but in most cases these will be out of the frequency area you will use the sub for. As the LRC becomes larger, these resonances will be lowered in frequency. When you're new to Hornresp you can mask it but keep it in mind when you are finishing up a design that will actually be built (and off course it will).

FR:

The airflow resistivity of any stuffing / damping material used in the rear chamber - You can leave it at default if you're using stuffing but don't know any values for it. More typically, stuffing is not necessarily used in sub horn rear chambers, so you can change this to zero.

TAL:

The thickness of the used isolating material - You can leave it at default or zero depending once again on whether or not you want to use stuffing.

AP:

Rear chamber port cross-sectional area (sq cm) – Ap and Lpt (see next) characterise the port dimensions (Helmholtz resonator) in the rear chamber. On default FR and TAL are shown, upon double click on either the VRC, LRC, FR or TAL tab, FR and TAL make place for Ap and Lpt (and vice versa). The tuning frequency can easily be spotted in (amongst) the SPL response and diaphragm displacement-window as the bottom of a steep/sharp dip in the response.
For the combined frequency response of the driver and port, use Tools --> Combined Response --> (Difference in cm) --> Enter. See also Port assisted horns (ahead).

Ap en Lpt can also be used to specify a port in a tapped horn system with throat chamber. The port enters the tapped horn at S2, whereas the throat chamber is located between the driver and the port.

LPT:

Rear chamber port tube length (cm) – See AP (above) and Port Assisted Horns (ahead).

VTC:

Volume Throat Chamber (in cm3) - The volume of the front chamber. Notice that you'll have to use a factor of 1000 here to get the number in litres. In principle you will almost always have a front chamber because the volume of the air in / directly in front of the cone is acting as a front chamber. The front chamber is the volume of air that is compressed when the cone moves forward as opposed to the air that moves down the horn. Sometimes it is hard to know where the boundary between these two areas is, especially with low compression ratio designs.

A large VTC will limited the upper frequency response. In high frequency drivers it's downsized by using a phase plug /phase bung. In a BPH the VTC is generally quite large (making the BPH look like a 4th order band pass, hence the name).

ATC:

Throat chamber average cross-sectional area normal to the axis of the horn (in sq cm) - In case you choose to mask resonances (see the LRC comments) this parameter will not influence the results. In the schematic diagram it's easy to see what the ATC is by comparing 2 different value's. In case you don't mask the resonance, you can keep the ATC the same as the Sd of the driver by default, or change it to move the resonances around.


Some handy tools:

The tools that you can use/pick depend on the current Window you're viewing. The tools listed below are the ones I used/needed most frequently in the first months (and still). Tools are listed per Window.

Window 1 (Input parameters):

Driver arrangement (multiple drivers) - Normal: With this Hornresp calculates the new T/S-parameters as they would be for a single driver when you replace multiple (of the same) drivers. For simulating multiple driver subs like the Labhorn or mulitple horns when stacked.
Driver arrangement – Offset: Newer feature to calculate a horn where the drive isn't firing straight down the horn but rather starts further down the horn from the sides. I.e. the 1850 horn, CV-style fold, Punisher, etc. S1 – S2 = horn before (the middle of the) driver, S2 -S3, etc. = horn after driver. Compression ratio = Sd/S2.
Driver arrangement – Tapped Horn: For simulating tapped horns (no prompt before calculating). See also Tapped Horns (ahead).
System design (hypex-designer) – With driver: For calculating the optimal hyperbolic exponential horn based on the T/S-parameters of the driver and the needed low-and-high frequency roll-off. Subs calculated these way for PA use aren't very functional in handling, size and weight (and the name “monster horn” quickly comes to mind). The normal route for PA use is to design 4 or 6 cabs that in total will have the same mouth area and horn length as one of these monsters. This way it does show that you need to have realistic demands when it comes to both SPL and low frequency response.
With the use of the "compare"-function (ahead) you can easily reverse engineer this “monster horn” to a more usable size and weight.
System design – From specifications: Newer option, S1 and VRC are fixed, nice for a quick mid/topdesign.
Find: Easy to find a record if you have too many already (you'll), just select and close (or double click). For an easy way to keep the active record list short, see Hornresp Merge (Updates).

Window 4:

Multiple speakers: For calculating the response from multiple cabs (stacked).

Impulse response: Calculate the impulse response. A good impulse response shows a sharp peak with little dips and peaks afterwards.

Window 3,4,5,6,7:

Sample: Depended on Window-type this gives a sample at a certain frequency. For example at Window 6) it will tell you the excursion the driver has to make at a specific frequency, so you can see what power your driver will handle.

Window 4,5,6,7:

Compare: Compare the current calculation with the previous. This way you can find the horn parameters that will suite you, by comparing each step with the previous while changing one (or more) parameters each time. Also enables you to compare the influence of the drivers T/S-parameters. You can also use Control + C, to capture the current result.

Window 1 t/m 7:

Options: Throat chamber and rear compression chamber resonances: Here you can tell Hornresp if it should mask the resonance coming from the VRC and VTC or not, it can also prompt you for each calculation.
Options: Default result window: SPL response (4) is regular.



Edited by mobiele eenheid - 07 May 2009 at 7:21pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Pinheiro Quote  Post ReplyReply Direct Link To This Post Posted: 13 May 2005 at 1:09pm

Thanks very good

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