Backloaded horns, do we want delayed bass, and how do we want it?

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Short recap of the Visaton thread. A low Qes driver does not lead to much more efficiency compared with a high Qes driver. -Sofar so good - the low Qes does have a slightly less peaky output / more control. Interesting point made on the forum there: not Fs x 2 / Qes is responsible for the high cut off but the hornthroath dimension. Not so much the volume of the backchamber but it's throathdimensions. Good to see the Germans take this stuff so serious :), complete with measurements in Visaton's own 7x7x7 meter anechoic messraum. And a seven plus page long discusion without any trolls.

This remark made me grinn, in essence a backloaded horn is a bassreflex enclosure with very, very good port to air adaptation.
 
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From a recent link in a HM art thread i found these numbers for the summation effect. Two sources need to be under 1.5 ms from each other to sum correctly. There is little information (links welcome!) about this effect in regards to Spl and frequency.
Two equidistant sources can be virtually any distance away from the listener and sum properly.

1.5 ms describes a distance sound will travel in time, and proper summation requires the arrival times to be within a quarter wavelength or so.
You can figure the wavelength by dividing 1130 feet or 347.7 meters (the speed sound travels per second at average room temperature) by the frequency.

A 1.5ms time offset is not problematic at around 180 Hz and below, but can be very problematic in the mid frequencies.

If the horn path of the BLH is around a wavelength behind the front output it can reinforce, sum, be in phase with the front output, even though it lags behind in time.

The problem with the BLH is if the upper frequency portion of the "horn" is not reduced enough in level by the folds or damping, the arrival time difference creates a ragged mid/high frequency response, "comb filtering".
 
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I think in this respect, the bend is my friend, to damp some of the mid out of the horn.

The back chamber volume can be used as an acoustical low pass filter, but don't count on much mid reduction from bends, just ragged response :D.

Check out the response of this four fold horn, I tried it with the speaker open also (like a BLH) response was little different.
LHC was a 4" speaker, LHD used an EVDH1A compression driver, LHGM used a sealed back 4".

LHC was the same speaker as LHD, with a couple 1/2" holes cut in the sealed back.
 

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Thanks, very insightfull Graph, same effect as with the Jericho horn 1 page ago, the response seems to fall due to the mass roll off > valley > peaks, peaks, far into the midband. "Mass roll off" get's stranger by the minute. In a straight horn i understand midrange coming out of the horn "i can see", but in a folded horn with a backchamber (Jericho not the graphs above), where mass roll off should prevent or at least damp signal above 500 Hz, weird.
 
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And another example of a backloaded horn with lots of mid output out of the horn. I have come to the conclusion there is no way to stop the midrange coming out of the horn. Mass roll off, small volume behind the driver, damping, nothing will prevent mid coming out of the horn...

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[FONT=Arial, sans-serif]Nelson Pass on the Kleinhorn stuffing (pic above):

[/FONT]
[FONT=Arial, sans-serif][/FONT]I ended up taking out all the stuffing except in the chamber before the throat. The sonic result was considerably improved over that of Part 1. The sound was more dynamic and lively, and I found that my approach of removing delayed higher frequencies from the horn did not improve the tonal
balance, coherence, or even the imaging”

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http://www.firstwatt.com/pdf/art_kleinhorn1.pdf
http://www.firstwatt.com/pdf/art_kleinhorn2.pdf

I will stop worrying and learn how to love the backwave :)
 
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Study up on human hearing perception and you'll find that below ~250-500 Hz [and much higher for a relative few] depending on the person and room conditions that our hearing acuity rapidly falls off, otherwise we wouldn't be able to tolerate the BW below this point in a typical room.

The 'name of the game' then is to use a low acoustic XO point same as the pioneers did, first by using low Qt motors coupled to a very high output impedance to maximize efficiency due to having little power available, then raising the driver's Qt as the amp's output impedance fell and its power increased over time until horn drivers wound up with anywhere from a ~0.5-1.0 Qts depending on the app with high power amps with tiny fractions of an ohm output impedance.

GM
 
Hi,

SQ...but what do you mean by BW? Backwave probably! It's not much of an thread this, in the sense of building, testing, measuring, > building, testing, etc, etc. But from what i have found, i reckon, there is a lot of masking going on. This is the most concrete statement on backwave delay in the 500 Hz range for backloaded horns i could find.

"7 ms. at 500 Hz being audible would be on the edge of what I have read. Higher frequency than that - certainly, longer times - certainly, but 7 ms at 500 Hz would be pushing the limits. It is also SPL dependent.

Earl Geddes"


It's time for building. At least @500 Hz (how classical is that for an x-over :) ) it will work ok. Driver @ 1/3 lenght, horn 2.3 meter. Octohyperbolic 74 cm > 2188 cm2 driver setback from mouth -0.30 meter = 3.45 msec. (for the curious hornresper).
 
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Hi,
This is the most concrete statement on backwave delay in the 500 Hz range for backloaded horns i could find.

"7 ms. at 500 Hz being audible would be on the edge of what I have read. Higher frequency than that - certainly, longer times - certainly, but 7 ms at 500 Hz would be pushing the limits. It is also SPL dependent.

Earl Geddes"


It's time for building. At least @500 Hz (how classical is that for an x-over :) ) it will work ok. Driver @ 1/3 lenght, horn 2.3 meter. Octohyperbolic 74 cm > 2188 cm2 driver setback from mouth -0.30 meter (for the curious hornresper).
I don't know the context of Earl's quote, but regarding audibility, the primary issue will be the ragged response the combination of front and rear waves causes.
If the back wave is 10 dB louder than the front wave, there will be little comb filtering, but the closer in level they are, the more apparent the problem.

Hornresp should give you a reasonable idea of what to expect if you set the driver/mouth termination distance correctly for the combined response.

I don't expect it would be very pretty at 500 Hz, could you post the frequency and phase combined response sims?
 
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Greenline = wall + floor placement
Redline = halfspace
Blackline = halfspace without x-over
Yellow on the x-over input screen = series LCR filter
Driver Oberton 8MB250

No ragged response around 150 Hz, where a normal BLH would have a problem. But there are some problems left around 400Hz. Please note Aj-horn is not very accurate 400 Hz and up, for a basshorn just like Hornresp.

For a rough idea about Aj-horn accuracy, Jericho 1996 sim and measurement:

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This could be of interest. Reduction of distortion in conical horn loudspeakers at high levels.
I am not sure if this thread is the place for it. They seem to have found a way to reactance annul with a variovented backchamber in a tapped horn like front horn. Reduces thd. And impedance peaks (not shown). Interesting and can be simulated in Aj-horn.

It would be great if there would be a library or link list for horn related papers, info on Diy audio. Not a horn design for dummies, but a starting place with the Edgar papers, Kolbrek and some others.



 
They seem to have found a way to reactance annul with a variovented backchamber in a tapped horn like front horn.

No, they didn't nor do we know if any of them were reactance annulled because no design details were given. What was proven was the obvious, i.e. damp the open side of the driver to reduce its out of BW 'noise' [harmonic distortion].

At least now you know how to fine tune your BLH's acoustic XO BW.

GM
 
Ex-Moderator R.I.P.
Joined 2005
from my youth I remember a trick some used on fullrange drivers

simply pulling a ladies nylon stocking over the whole driver, front and back, the whole lot
tie it in a knot behind the magnet
and then mount it as is

I thought it looked stupid
but if nothing else, just think of those crazy colors :D
 
I have used variovents in very small sattelites. First time i see it in a backchamber for a horn. For me it is new. Although not usable in a Back Loaded Horn. Probably obvious, but new for me ;)

On a sidenote, i found the Oberton 8M250 drivers and ordered them. + some Ahuja / Monacor KU 516/ Adastra / phenolic midrange drivers. Hope to have some delayed backwaves and mid noise to listen to soon. The 50-500 <>700 Hz range for a backloaded horn is a compromise. But not an easy to avoid compromise. 400 Hz and up for a midrange needs a 60 cm to 2 foot horn diameter... Big, expensive custommade stuff. I will try a comparison with a good large diameter woofer beneath the midhorn. BLH vs BR in short :) If both fail, the Oberton could work well in a straight front loaded horn. For me hearing the compromises works best. Probably looks stubborn, but it's how i learn.

A lot of the old German fullrange speakers have "socks" on the backside. Could be the same thing. Lol, i thought these where to keep the mice from eating the papercone.
 
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Hello Phenoholic Anonymous,

Several thoughts:

- note that simulations of both hornresp and ajhorn are overly precise with regards to peaks and dips, the measured response of built designs is almost always much smoother (as is regularly demonstrated by the German DIY magazines).

- a backloaded horn is like a transmissionline. There are plenty of transmissionline designs that have very smooth response, the same is possible with backloaded horns. But expect to need all the tricks available, so select the right driver for the right horn, play with damping and placement etc. etc. etc.

- you mentioned the original Jericho horn. There is an updated version, the Jericho 08, which uses tricks to get the response right. It is very tolerant of different drive units, the designer published a number of simulations and the differences were minor. One of the tricks is a helmholtz resonator. You can see a simulation here, again, correlation with measured response was good but the measurement was smoother:

HH082_Jericho.gif


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- finally, now you look into backloaded horns, the project starts to remind me of this. Maybe some inspiration. I don't like the backloaded horn, there are more modern and better alternatives, but it does get good reviews.

BK 201 KH

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Thanks Ivo,

My project is loosely based on what i have seen in Hobby Hifi and elsewhere. Klipsch La Scala is a good starting point for 3-way horns. The BK 201 (red horn) you show is one of the inspirations for the project. And at the same time the red horn is one of the reasons i choose the strange 1 /3 driver placement. It's purpose is to get the timealignment ok. This is at least a full midrange hornlenght off in most 3 way horns. I must admit i have no idea if this is an improvement:

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About the peak at 270 Hz in the Aj-horn simulation. It's too far up to be killed by an Internal Helmholtz Resonator. I can flatten it with an internal resonator but i lost 2 to 3 dB from 50 Hz - 250 Hz :mad: It's my own doing it so far up in freq. brought it there myself with the 1/3 driver placement. Just as you pointed out in the difference between measurement and Aj-horn simulation seen in Hobby Hifi, i too hope reality is a little less harsh. Hope to learn how this all sounds IRL pretty soon :)

As can be seen i have a unhealthy obsession with driver to driver C-C distance. You can get the diy-er out of the fullranger, but you cannot get the fullranger out of the diy-er :rolleyes:
 
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