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FLH Qtc

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Keen View Drop Down
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    Posted: 24 July 2018 at 2:52am

Hi all, 

 

Aiming to identify Qtc of FLH x, using driver x. 

 

Any correction most appreciated. Can't find an example and it's out of my depth tbh...

 

Using data from hornresp:

...assuming Fc is the final resonant frequency of the box/system. i.e. frequency of peak impedance [???]

Calculate the ratio between the DC resistance (Re) and the maximum impedance, call it Rc. Find the two frequencies on either side of the resonant frequency, f1 and f2 where the impedance is Re * sqrt(Rc).

Side query here; is the DC resistance of the driver present in the impedance peak or does it need to be added to the magnitude? 

Calculate Qms as:

Qms = Fc sqrt(Rc) / f2 - f1

[note: the standard calculation for Qms is; Qms = Fs sqrt(Rc) / f2 - f1. However, I have swapped Fs for Fc because the calculation is for a FLH, not a sealed direct radiator and needs to consider how the volume of air in the horn and rear chamber will affect the compliance of the driver. It's perhaps also worth noting the dimensions of the horn and rear chamber can effectively be tuned so that Fc = Fs]

Calculate Qes as:

Qes = Qms / (Rc -1)

 

Calculate Qts as:

Qts = Qes * Qms / Qes + Qms

 

Calculate Qtc as:

Qtc = (Qts x fc) / fs 




Many thanks,



Edited by Keen - 24 July 2018 at 9:53am
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Keen View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Keen Quote  Post ReplyReply Direct Link To This Post Posted: 24 July 2018 at 3:25am
Interestingly, when Fc = Fs, Qtc = Qts (Qts of the box not the driver). Understanding this allows observation of FLH Qtc in an identical way to observation of sealed direct radiator Qtc and helps identify what drive unit parameters are required to achieve a desirable Qtc factor in a FLH. It also obviously raises the question of what is a desirable FLH Qtc for the user and does it differ from that of a direct radiator used in the same application?

Make sense much? WackoWacko


Edited by Keen - 24 July 2018 at 10:00am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote fatfreddiescat Quote  Post ReplyReply Direct Link To This Post Posted: 24 July 2018 at 9:30am
Have you had a look at 'hornresponse' software?
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Keen View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Keen Quote  Post ReplyReply Direct Link To This Post Posted: 24 July 2018 at 9:45am
the whole thing is based on data from hornresp, as stated in the OP.
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Elliot Thompson View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Elliot Thompson Quote  Post ReplyReply Direct Link To This Post Posted: 24 July 2018 at 12:01pm

Horn Response will offer a simulation. If you are going to the trouble of wanting to know the Qtc it must be measured literally in the actual box to get accurate results. ARTA or Room EQ Wizard (REW) has the capability of giving accurate results under real world conditions as they are classed as Loudspeaker Measurement software.

 

Loudspeaker Measurement software literally sends voltage to the loudspeaker in order to give accurate results under real world conditions. This is why Loudspeaker Measurement software can measure TS Parameters of a loudspeaker when the TS Parameters are not accessible. Simulation software estimates what to expect in a perfect world and cannot measure TS Parameters of a loudspeaker.

 

 

 

 

Best Regards,    

Elliot Thompson
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Keen View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Keen Quote  Post ReplyReply Direct Link To This Post Posted: 25 July 2018 at 4:17am
fair point Elliot, but Qtc is often calculated and used as a guide for how a direct radiating enclosure will sound. One of the aims of the topic is to confirm the same can accurately be done with a FLH. 
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Keen View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Keen Quote  Post ReplyReply Direct Link To This Post Posted: 25 July 2018 at 4:36am
The main point is to perhaps allow a more accurate understanding of how driver-x will behave in a horn, and why. There’s a lot of opinions and suggestions about what drivers are suitable for bass horns but not a lot of unddrstanding as to why. 


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Keen View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Keen Quote  Post ReplyReply Direct Link To This Post Posted: 25 July 2018 at 8:54am
Here's some links about system Q for infinite and open baffle environments......

http://www.acenindia.com/concept%20of%20q%20of%20loudspeakers.htm

https://volvotreter.de/downloads/what-is-Q.pdf

please forgive me if this comes across as a sermon, I lack tact at the best of times and just wanna get this out, to if nothing else, at least be corrected. 

This may be completely wrong from what I can tell, but in two horns of the same rear chamber volume, throat size and length, the one with less volume in the horn (i.e. less expansion) will yield a more damped (lower Q) response curve at the expense of sensitivity. 

Q is derived by the relationship between the mass of the moving parts, compliance and electrical damping of the system. The volumes of air in the rear chamber and horn are effecting the mass of the moving parts and compliance of the system. The Qms is derived from these two factors and obviously skyrockets compared to the driver Qms in free air because of extra loading produced by the horn and rear chamber. 

A high system Qms produces a very sharp impedance peak and high Q (under damped). Not sure why.... 

That leaves one factor to provide damping and lower the Q in a horn system, electrical damping. Damping is considered important in a loudspeaker system because it limits the activity of the driver at the resonant frequency of the system. The resonant frequency of the system is the frequency when the moving parts are creating the most force? Picture the woofer has to then stop, and immediately go the other way. So maybe it does become reasonable why damping is important if you want articulate bass frequencies? Considering mechanical damping is drastically reduced in horn, the electrical damping capacity of the driver would appear to become very important if you're going for articulate bass in a FLH. 

Wacko










Edited by Keen - 25 July 2018 at 10:06am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote snowflake Quote  Post ReplyReply Direct Link To This Post Posted: 25 July 2018 at 7:14pm
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Elliot Thompson View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Elliot Thompson Quote  Post ReplyReply Direct Link To This Post Posted: 25 July 2018 at 11:52pm
Qtc is a good indicator for sealed enclosures but, not used for reflex enclosures.


When one measures the TS Parameters of a loudspeaker, the VAS is determined by using one of the following,

Some means of pressure on the cone such as placing coins on the dust cap

Inserting the loudspeaker in a sealed cabinet

----------------------------------------------------------------------------------------------

Since the sealed cabinet does not differ (other than size) of the sealed cabinet of the folded horn, you can scale the driver in the sealed chamber of the folded horn to get an estimate of the Qtc.    

As the enclosure gets larger the Qtc figure will decrease and, when the enclosure becomes smaller, the Qtc figure will increase.

The above can be created using a loudspeaker simulator. Accuracy would still be up in the air. However, if one needs to get an idea on what to expect, such a method would be a quickest way to find out.

From a Horn perspective, you may want to read the papers written by dB Keele.

www.xlrtechs.com/dbkeele.com/papers.htm

Best Regards,

Elliot Thompson
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Keen View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Keen Quote  Post ReplyReply Direct Link To This Post Posted: 26 July 2018 at 3:36am
awesome links, they're of particular interest. 

ps....frothing after just the intro snowflake, this is the one haha, thank you so much!


Edited by Keen - 26 July 2018 at 7:20am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Keen Quote  Post ReplyReply Direct Link To This Post Posted: 26 July 2018 at 8:23am
just fantastic Snowflake, truly! It’s all there...Thumbs Up
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