Could someone help me with modeling this driver - diyAudio
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Old 12th August 2011, 02:36 AM   #1
JZatopa is offline JZatopa  United States
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Default Could someone help me with modeling this driver

I am curious how you model a back loaded horn for a driver like this.

B&C SPEAKERS

I tried using hornresp but I don't know what half the parameters are. What parameter is the rear chamber? What is s1,s2,s3? How do I calculate the best length and flare of the rear horn?

Could someone post what they think would be the best response?

I can figure out sealed and ported no problem but I am lost on back loaded horns.
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Old 12th August 2011, 05:11 AM   #2
GM is offline GM  United States
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All the info about the various HR fields and how to use them are in its HELP file.

AFA designing with it, there's no info or ability to auto design a BLH in its horn wizard.

This driver has a theoretical ~7.35-666.67 Hz horn loading BW, though of course the lower it goes the quicker it runs out of linear travel, not to mention so large that HR can't calculate it, so with no idea what sort of performance is required to meet the needs of the app or even what the app is.................

GM

edit: I thought I saw someone mention doing compound horns in the loudspeaker wizard, but apparently not.

What you can do though is use the system design tool and to get started, let it auto calculate a FLH, then clear out the rear chamber values. Follow the instructions in the HELP file about using the 'combined response' to see the impact of the driver's output summed with the horn's. Use the horn wizard to try different flare frequencies & factors along with trying different front chamber volumes.
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Last edited by GM; 12th August 2011 at 05:29 AM.
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Old 12th August 2011, 05:55 AM   #3
JZatopa is offline JZatopa  United States
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Thanks I will play with it some more. I want to try a driver like this in a backloaded horn in a 2 way setup. I am looking for in room response down to 40hz or better in an average sized room and I think a backloaded horn will give me the sound I am looking for.
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Old 12th August 2011, 04:36 PM   #4
GM is offline GM  United States
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Unless XO'd pretty low, this driver's BW is much too wide for this app as it will have a high acoustic XO, i.e. mouth output rolling off to blend to the driver's output. Typically, ~250-400 Hz is the upper limit depending on how sensitive one is to timing errors.

Note that adding series resistance will raise the driver's lower mass corner [Flm] and lower its upper one [Fhm] referenced to Fs with a doubling of Qes [Rg = Re] cutting its BW in half [~14.7-333.33 Hz], so this is where I would start as an upper BW design limit.

GM
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Old 12th August 2011, 05:50 PM   #5
JZatopa is offline JZatopa  United States
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This driver will be lowpassed around 1000hz. Is that low enough?
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Old 12th August 2011, 06:06 PM   #6
GM is offline GM  United States
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Again, the horn's acoustical XO point for a typical person must be under ~250-400 Hz to be able to use its forward [driver] radiation up to some higher XO point otherwise it must be within this BW [or lower] for 'best' overall system performance. In short, 1 kHz is much too high if the horn is designed around its Fhm.

GM
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Old 12th August 2011, 06:42 PM   #7
JZatopa is offline JZatopa  United States
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Quote:
Originally Posted by GM View Post
Again, the horn's acoustical XO point for a typical person must be under ~250-400 Hz to be able to use its forward [driver] radiation up to some higher XO point otherwise it must be within this BW [or lower] for 'best' overall system performance. In short, 1 kHz is much too high if the horn is designed around its Fhm.

GM
Ok I am lost, what is fhm? Why can you use a full range driver without a crossover and not have a problem and not use a driver like this with it crossed over below 1000hz. Why must it be crossed over at 400hz or lower? Can't I just use a back loaded horn to extend the low end in a similar way a port or tl does? What part of horn theory am I not understanding?

Last edited by JZatopa; 12th August 2011 at 06:45 PM.
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Old 12th August 2011, 07:44 PM   #8
JZatopa is offline JZatopa  United States
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Quote:
Originally Posted by DJNUBZ View Post
Ok I am lost, what is fhm? Why can you use a full range driver without a crossover and not have a problem and not use a driver like this with it crossed over below 1000hz. Why must it be crossed over at 400hz or lower? Can't I just use a back loaded horn to extend the low end in a similar way a port or tl does? What part of horn theory am I not understanding?
Btw thanks for the help, this is the area of speaker design I know the least about.
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Old 12th August 2011, 10:28 PM   #9
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Fhm = the -3dB frequency, taken as 2Fs/Qe.

What GM is refering to is that a back-loaded cabinet of any type is only useful up to a certain point: 250Hz - 400Hz is about as high as you can take them without running into chronic group-delay & attendant issues. If the driver is rolling off above this point, it's either going to need some form of Eq, be it series resistance or something more complicated, or an additional front-horn to 'fill in' the gap between the gain provided by the horn, and the driver itself reaching it's nominal sensitivity figure. Alternatively, you'd need to cross to another driver at the same point to maintain a balanced SPL.
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Old 12th August 2011, 10:54 PM   #10
Boscoe is offline Boscoe  United Kingdom
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I had a go at modelling but due to the high Fs the 40Hz has harder to hit with a total horn length of 180cm. Acheiving 95dB/SPL at 1W and 113dB at 50W (full power due to xmax). Group delay was a bit excessive at 23ms at 40Hz.
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