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Old 10th October 2010, 02:59 PM   #1
Sella is offline Sella  Finland
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Default Full range in a front loaded horn

In my new project I am going to use full range driver in a front loaded horn. With hornresp program I can calculate theoretical frequency response with knowing horn geometry and driver's T/S-parameters. The problem is that I would like to add drivers hf response to the analysis. Then I could optimize the horn to match driver's hf-response.

I have measured the driver's frequency to half space (ie fitted to infinite baffle). It isn't clear to me how to add these two responses together. I was thinking following:

1. It is an 8" driver so, frequency response start's to roll off when wavelength is over 4" and about 3400 Hz in frequency. It is my intention to use driver's response from here on upwards and add a roll of 6 dB/oct downwards to the measured response.

2. This response is add to simulated response.

My idea is to divide the response to two subsystems: the horn system and approximating that from 3400 Hz upwards the driver behaving same as radiating to half space. The goal is to make sure that horn's upper cut off frequency matches driver's rising response (Fostex 206) and not causing a remarkable dip or peak.

I am making any sense with this?

Last edited by Sella; 10th October 2010 at 03:10 PM.
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Old 11th October 2010, 03:48 PM   #2
Sella is offline Sella  Finland
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Yeah, I tackled down that problem as I noticed that hornresp is also able to add the piston response to the horn's response (trough: tools - directivity - response)

But how the **** you guys get any sense to this front horn + full range thing? I tried to model Azurahorn 204 and Oris 200 and I always get the frequency band which the horn horn amplifies to play about 5 dB louder than the hf-range (according to the manufacturer's measurements and my own).

I think there is some piece missing from the puzzle..

I posted as an attachment my hornresp simulation of the Oris 200 horn and Fostex 206 driver. According to Fostex driver's spl is somewhat 100 dB up from 2k Hz. So without horn it is 5 dB supressed and with 5 dB attenuated.
Attached Files
File Type: pdf Fostex206e.pdf (14.7 KB, 174 views)
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Old 11th October 2010, 08:11 PM   #3
Ivo is offline Ivo  Netherlands
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I built a number of tractrix horns for Lowther drivers a few years back. I had a lot of contact with Bert Doppenberg of BD-Design/Oris horns. Hornresp only simulates the predictable behaviour of the driver and horn combination. It won't be able to simulate the cone break up for you, so Hornresp cannot predict what happens in the higher frequencies. The horn also won't let through the higher frequencies unaffected. In an Oris-like configuration, it forms a a mild low-pass filter, rolling off the highs at about 3 dB/octave (if I remember correctly).

So what you have been doing is roughly right, the horn-response is dominant in the horn pass-band, above that you eye-ball the response from the graph and the expected roll-off. And then measure to see what you've got. Bruce Edgar had some tips about acoustically modifying response in his midrange horn article (see Volvotreter's website, the download section). Playing with the backchamber can also be helpful to adjust response.

The Fostex FE206 is used with success in front horns, so you have a good chance of succeeding.
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Old 12th October 2010, 06:42 AM   #4
Sella is offline Sella  Finland
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Thank you for a good answer. It always gives confidence knowing that is heading to right direction.

That SPL pump still worries me. Has anyone ever posted any measurement of Oris or Azurahorn with any full range driver? I could not find any.. if there is they must be buried deep in some thread.
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Old 12th October 2010, 10:08 AM   #5
CLS is offline CLS  Taiwan
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I got rough RTA measurements by the built-in function of Behringer DEQ2496.

My Oris 150 is loaded by a Focal midrange Audiom 7K rated 98 db/w, and xover'ed to a waveguide loaded tweeter Eminence APT50 rated 105 dB/w.

The overall pink noise response of my system shows downtilt - bass/mid are higher than the treble, i.e., sensitivity of Oris 150 + Focal is higher than 105 dB, I'd say by 2~3 dB in an overall shallow slope. If comparing both ends of spectrum, the total drop on the top might approach 10dB. I tuned it that way on purpose, I like warmer balance, and often listen quietly.

Interestingly, I once briefly tried Lowther PM4 in Oris. It played obviously louder than the Focal (even though their rated efficiency is the same at 98db/w). I didn't have APT at that time, so no direct comparison.
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Old 12th October 2010, 10:12 AM   #6
CLS is offline CLS  Taiwan
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Oops, it's not 10dB drop, but 20.

Click the image to open in full size.
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Old 12th October 2010, 12:58 PM   #7
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There are frequency response graphs for the Azurahorns here:

Azurahorn -Le Cleac'h Acoustic Horns - Products

For the Azurahorn 160, the graphs are ruler-flat with compression drivers, less so with Lowther's (as you would expect).

I'm using a Fostex 206E in the Azurahorn 160 and it sounds fantastic, though I have yet to measure it (but will at some point).
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Old 12th October 2010, 03:48 PM   #8
Sella is offline Sella  Finland
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Thank you for your kind answers. I have tought this matter quite a lot lately and I think I will go to coaxial driver instead of full range. I think that full range drivers poor hf would need a super tweeter in any case. Currently I am running PHY-HP KM30 in IB and I think that I would take a step down that way.

I have tought of these drivers:

BMS 12CN680 (12")

and

Beyma 8CX300Nd (8")

Both drivers employ a compression driver and a waveguide for the hf-range.

Here are some initial simulations with Beyma driver with closed back chamber. I guess cross xo-points would be somewhat 300 and 1000. With vented rear chamber It is able to go down near 200 Hz.

I also started to wonder where I could find 12" coaxial driver which fs would be near 30 Hz? I was thinking to go Avantgarde Solo and do a full active system with larger front horn, back chamber tuned near driver's fs and the slope taken care with active xo.
Attached Files
File Type: pdf Beyma.pdf (14.7 KB, 47 views)
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Old 12th October 2010, 04:02 PM   #9
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Don´t know about the 200Hz, as factory specs can be a lot of smoke and mirrors...but a coaxial driver can be a bagful of fun.
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Old 12th October 2010, 06:00 PM   #10
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Quote:
Originally Posted by Sella View Post
...and I think I will go to coaxial driver instead of full range. I think that full range drivers poor hf would need a super tweeter in any case.
I'm listening to a coaxial in a 160Hz Azura.
It can sound quite nice IMHO.
Using 10" Tannoy Reds, w/ 15" 60Hz front horns below.
no crossover used on top or bottom of the Tannoys, or on the 60Hz horn.
A pair of Tapped horns for the very bottom, and super tweeters crossed in @ 10k.

Definitely not a "full-range" system (so doesn't go on this forum), but I don't know how else to actually get full range.
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