Could someone help me with modeling this driver

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
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.
 

GM

Member
Joined 2003
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.
 
Last edited:

GM

Member
Joined 2003
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
 

GM

Member
Joined 2003
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
 
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:
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.
 
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.
 
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?

All drivers have the same problem WRT the acoustic XO.........

Already explained it as simply as I know how.

Yes, and no. A horn is like a complex, fully adjustable independent rear suspension system with myriad combinations of adjustments to choose from whereas a port or TL is like a typical solid rear axle with only spring pre-load for tuning it.

Apparently everything, not to mention just basic box loading if you don't know about driver mass corners, etc. that define the limits of typical sealed, vented alignments which you need a pretty good understanding of if you want to design good performing horns without relying on whatever HR or similar auto calculates for you.

GM
 
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.

Yeah, This driver without EQ just to lower its mass corner makes it a so-so choice at best for BLH loading, but if one can tolerate a fairly high ~333 Hz acoustical XO, then it can hit some decent numbers at 40 Hz at the expense of contour EQ to flatten it out all the way to the desired 800 Hz XO.........

GM
 

Attachments

  • B&C 8MDN51 29.40-333.33 Hz BLH - specs.gif
    B&C 8MDN51 29.40-333.33 Hz BLH - specs.gif
    7.7 KB · Views: 111
Maybe I am tackling this the wrong way. First I should better define my goals and then see if I am looking at the right driver.

I want to build a speaker using a backloaded horn design with these goals.

- 2 way design, wave guide + midbass
- I want the midbass to cover from 1000hz down as a front radiator
- As midbass hits its natural front radiating F3 I want horn to crossover and fill in the low end. This seems to be where I was misunderstanding how a horn acoustic XO works. I thought you could design a BLH in the same way you design a ported box. I now see that isn't true
- I want to use a midbass similar to the 8NDL51, ie. 8", high efficiency and great sound

I went with the 8MDN51 because I liked the efficiency. Now that I know how to calculate FHM it looks like the 8BG51 or 8BG51 might be a better candidate.

FHM of 8bg51 = 247hz and 8NDL51 = 322hz.

Are these drivers a better fit? Considering the Fostex FE206En FHM = 473hz I am guessing that these look a lot better for what I want to try.

So what do you guys think?
 
That makes way too much sense! ;)

Well, let's see, we want Fs to be at or below the lowest frequency its likely to have to reproduce at any easily audible SPL, a low Qms since it won't have a compression chamber and a Vas so low it makes for a small throat which in turn makes for a long enough horn to maybe hear a bit of an echo or at least some 'smearing' of the signal through the acoustic XO BW.

At a glance then, seems like neither are suitable.

GM
 
GM I am starting to get an inkling of how the T/S relate to BLH. Seems like most modern drivers are not designed to fit the application.

What is considered a low Vas for this design?

What is considered a low Qms?

If you were to have a compression chamber how does that affect everything? Are their drawbacks to a compression chamber?

Do you happen to know of any drivers that might fit what I am trying to do?

I understand that the compression chamber can act as an airspring and a lowpass filter but I am not sure what else it does or when one is required.
 
Last edited:
Not really, their day in the spotlight is long since done. Good riddance, I say except as scoop bins.

< 1.5 ft^3

< 4

The compression chamber loads the rear of the driver in a FLH to counteract the horn's air mass 'plug' 'choking the driver down around its flare frequency ['tail wagging the dog', so to speak], so there isn't one on a BLH and why drivers best suited for BLHs are a bit different from those optimized for other loadings.

Not in an 8" or 'on the cheap' in any size. If it was just a mid-bass scoop bin, then there's lots of drivers available, but to go low and use most all of the driver's usable BW before handing off to the HF is a tall order usually reserved for small or large drivers, so consider either using multiple smaller drivers with the right specs or step up to a 15" combination cab horn driver.

GM
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.