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Hornresp Diaphragm Displacement

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DMorison View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote DMorison Quote  Post ReplyReply Direct Link To This Post Posted: 24 January 2018 at 4:49pm
Originally posted by snowflake snowflake wrote:

also, the length of the rear chamber is not 86cm. if you want to model resonances in the rear chamber it should be the average distance from the back of the cone to the wall behind it (in this case the side of the speaker). to model the interaction of the front and rear output I thought you would want the chamber length to be the average distance from the rear of the cone to the centre of the rear vent. this would enable modelling of phase differnces and interference between the horn and vent outputs. However, trying it now, with the 'masked' option selected, the depth of the rear chamber does not seem to have any effect on the combined output implying that the rear path length is not being used to model the combined output.

Perhaps David can clarify how this works?

Originally posted by snowflake snowflake wrote:

Originally posted by mobiele eenheid mobiele eenheid wrote:

Quote However, trying it now, with the 'masked' option selected, the depth of the rear chamber does not seem to have any effect on the combined output implying that the rear path length is not being used to model the combined output
That is what the mask resonances option is for. Do not mask resonances for the influence on the frequency response (which is usually out of the pass band of a sub woofer). 


yes, but there are two effects. one is the resonances which occur in all speakers with a rear chamber - sealed, FLH etc. the other is the interaction between the front and rear outputs. I thought that the masked option only disabled the first one.

It's been a while since I read any of the tech info on Hornresp, but I don't recall anything saying that the resonance masking only affected part of the resonances - I'd agree with Mobiele Eenheid to leave them unmasked.

Most of the effects of the rear chamber length are, as stated above the passband we're interested in so I wouldn't expect it to make a huge difference. Regardless, I think that it should always be the distance to the back wall that is used wherever possible.

Originally posted by snowflake snowflake wrote:

if the drivers are facing each other you need several litres of front chamber volume to represent the air inside the speaker cones. has a small effect on response.

This should only be the volume within the cones themselves, as modelling the entire enclosure as SWCNC is doing uses the "horn" part of the model for the majority of the plenum between the drivers.

I use a rough rule of thumb of 3-4x SD for that volume, perhaps as these are 21" drivers that should be increased a little, I wouldn't expect it to be more than 6 or 7 litres per driver anyway.

Again, while it's good to model as accurately as possible, I don't think it's going to make a vast difference.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Xoc1 Quote  Post ReplyReply Direct Link To This Post Posted: 24 January 2018 at 9:12pm

I looked at the cabinet spec. sheet carefully and there is the added complication of a parametric bass boost of 2db at 33hz Q 0.8 that pushes the cone excursion even more.
So Run the sim with the recommended 141 Volts & add all the filters with the filter wizard - the only thing that you cant sim is the low pass being L R instead of Butterworth - But we are more interested in the LF performance.
Excursion  is under 25mm at recommended power
X mech is 35mm so still another 10mm to go, and we are probably well into non linear excursion and compression that will reduce this more.
Also at 48hz it stays around X max at 141 volts.
I suppose there is no point in having all that cone movement if you never use it. Rock & Roll!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote SouthwestCNC Quote  Post ReplyReply Direct Link To This Post Posted: 25 January 2018 at 12:27pm
Thanks xoc1. Reassuring stuff. -10db @ 30Hz these play low :)

just to clarify. When you say chamber length you always measure to back wall, in this case do you mean the 86 or side directly behind driver?

I don't suppose anyone can explain why the filters increase group delay?

Much appreciated guys

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Post Options Post Options   Thanks (0) Thanks(0)   Quote snowflake Quote  Post ReplyReply Direct Link To This Post Posted: 25 January 2018 at 4:45pm
Originally posted by SouthwestCNC SouthwestCNC wrote:

Thanks xoc1. Reassuring stuff. -10db @ 30Hz these play low :)

just to clarify. When you say chamber length you always measure to back wall, in this case do you mean the 86 or side directly behind driver?

I don't suppose anyone can explain why the filters increase group delay?

Much appreciated guys



chamber length is perpendicular to the driver so in this case meausre to the side wall. looks like about 30cm. model with 30cm and it will show an resonances high up in the response. If there are no alarming spikes you can forget about the resonances and use the chamber length to accurately model the path from the rear of the driver to the start of the vent. average distance from the back of the driver to the centre of one of the vents is probably about 25cm.

the reason for this confusion is that if you look at the schematic, the hornresp model always assumes that the vent begins at the rear wall of the rear chamber. in this case the two distances are the same. however in most real speakers they are going to be different and should really be defined by two different values.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote SouthwestCNC Quote  Post ReplyReply Direct Link To This Post Posted: 25 January 2018 at 4:59pm
Originally posted by snowflake snowflake wrote:

Originally posted by SouthwestCNC SouthwestCNC wrote:

Thanks xoc1. Reassuring stuff. -10db @ 30Hz these play low :)

just to clarify. When you say chamber length you always measure to back wall, in this case do you mean the 86 or side directly behind driver?

I don't suppose anyone can explain why the filters increase group delay?

Much appreciated guys



chamber length is perpendicular to the driver so in this case meausre to the side wall. looks like about 30cm. model with 30cm and it will show an resonances high up in the response. If there are no alarming spikes you can forget about the resonances and use the chamber length to accurately model the path from the rear of the driver to the start of the vent. average distance from the back of the driver to the centre of one of the vents is probably about 25cm.

the reason for this confusion is that if you look at the schematic, the hornresp model always assumes that the vent begins at the rear wall of the rear chamber. in this case the two distances are the same. however in most real speakers they are going to be different and should really be defined by two different values.


Well explained snowflake. I now follow you. You were close at 27cm vent to rear of driver. No real change in this case.

Can anyone advise why using filters in horn resp you see group delay increase, like to understand this better instead of face value tia
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Post Options Post Options   Thanks (1) Thanks(1)   Quote snowflake Quote  Post ReplyReply Direct Link To This Post Posted: 25 January 2018 at 10:05pm
group delay is the gradient of the phase response. filters have frequency-variable phase shift so changes the group delay.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote citizensc Quote  Post ReplyReply Direct Link To This Post Posted: 03 June 2020 at 12:24pm
Sorry to dig up an old thread, in general what should I be aiming for with Xmax, its difficult to know if a design in hornresp is viable when you don't know what is an acceptable amount of diaphragm displacement. 

In a FLH it seems unreasonable to try and stay with in xmax in hornresp. None of the successful designs I have simmed are close. Here are some examples, both 89.44v at 8 ohm. 

Punisher with 12.00sw (11.5mm xmax)

WSX with L18P300 (8mm xmax)


Would it be reasonable to subtract 3db for power compression and 6 db for the fact that a real signal isnt a 40hz sign wave? 


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Post Options Post Options   Thanks (0) Thanks(0)   Quote JulianDA Quote  Post ReplyReply Direct Link To This Post Posted: 03 June 2020 at 1:37pm
Hey, try using the "Filter Wizard" in Hornresp and put in the correct HPF. That should lower the excursion a lot :)
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Post Options Post Options   Thanks (0) Thanks(0)   Quote odc04r Quote  Post ReplyReply Direct Link To This Post Posted: 03 June 2020 at 5:42pm
Your graphs are broadly agreeing with the acoustic impedance discussed in the other thread. If a driver is not loaded then there is no volume of air pushing on it as it moves (beyond suspension in free air) and its displacement is going to skyrocket.

You can make allowances for the average musical content in the unloaded region to be lower than that of above it but it will only get you so far and it might not be true in all situations.

I think probably there is something fundamental in the horns you are simulating that does not match your expectations for one reason or another.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Xoc1 Quote  Post ReplyReply Direct Link To This Post Posted: 03 June 2020 at 8:22pm
Almost any speaker will require a high pass filter to be driven to anything like its power rating. The FLH horn that you are developing in the other thread is quite interesting in that with a high pass filter it will almost be power limited not excursion limited. With a decent high pass it will be safe with massive amounts of transient power. The actual high pass you need to be safe will depend on the transient power that you have available.
However x-max has another parameter sometimes used  that it represents approximately 10% distortion. Excessive excursion = Excessive distortion!
Any speaker will become very non linear after x-max and actual excursion will be dependent on the mechanical properties of the driver, Will it hit the end stops and destroy its self, or will it restrict movement with the suspension? Who knows, are you brave enough to find out?

I would ignore the power compression effects with most designs in that is compensated for by just delivering more transient power to the driver.
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