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Old 8th April 2008, 01:42 AM   #1491
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Default Tapped horns vs front loaded horns

Quote:
Originally posted by dwk123
judtoff - William is spot on. For a given size, a tapped horn will outperform a Tuba if we're only worried about use as a sub. The 'problem' with Bills Tubas is that they're wider band devices, and the sub frequencies are at the lower-efficiency end of their passband. For example, the Table Tuba holds ~95dB efficiency down to 30 Hz, but needs 9 cu ft. My models show a tapped horn holding 95dB down to 25Hz in about half that size.
Just a quick question, are there any disadvantages with going for a tapped horn instead of a front loaded horn enclosure? I know the front loaded will be larger than the tapped but front loaded also tends to have very little or no harmonic distortion which is nice. Do tapped horns do this also?

Another thing, would there be any difference in performance between front loaded and tapped below the frequency where the horn unloads?

Right now I'm torn between building a front loaded and tapped...
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Old 8th April 2008, 10:14 AM   #1492
iand is offline iand  United Kingdom
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Default Re: Tapped horns vs front loaded horns

Quote:
Originally posted by MikeHunt79

Just a quick question, are there any disadvantages with going for a tapped horn instead of a front loaded horn enclosure? I know the front loaded will be larger than the tapped but front loaded also tends to have very little or no harmonic distortion which is nice. Do tapped horns do this also?

Another thing, would there be any difference in performance between front loaded and tapped below the frequency where the horn unloads?

Right now I'm torn between building a front loaded and tapped...
Tapped horns have the same distortion as a front-loaded horn with the same excursion -- which means better than a small front-loaded horn (loading is poor) but not as good as a huge one (excursion peaks are larger). Tapped horn distortion can be worse if a harmonic hits one of the out-of-band resonant peaks which can amplify it by 10dB or so (see below).

Below where the horn unloads you've only got the stiffness of the driver suspension (no rear chamber), so it won't take much to bottom the driver unless you use a driver optimised for a tapped horn which has higher Fs -- the ideal total compliance is the same as a front-loaded horn driver with sealed rear chamber, which typically means Fs<Fhorn for a normal horn and Fs>Fhorn for a tapped horn.

I'd say that the only significant disadvantage is the big high-Q peaks just above the passband, which don't get attenuated enough even with a 24dB/octave crossover and can amplify harmonic distortion.

To remove these you need either a *very* fast rolloff crossover (which means almost certainly digital), or to null out the peaks with quarter-wave resonator pipes like in the DTS-20 (which need tweaking and damping), or notch them out electronically using a parametric equaliser.

Of course a front-loaded horn with similar cutoff and ripple is much *much* bigger, it's not really a fair contest :-)

Ian
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Old 8th April 2008, 02:50 PM   #1493
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Default Re: Re: Tapped horns vs front loaded horns

Quote:
Originally posted by iand


Tapped horns have the same distortion as a front-loaded horn with the same excursion -- which means better than a small front-loaded horn (loading is poor) but not as good as a huge one (excursion peaks are larger). Tapped horn distortion can be worse if a harmonic hits one of the out-of-band resonant peaks which can amplify it by 10dB or so (see below).

Below where the horn unloads you've only got the stiffness of the driver suspension (no rear chamber), so it won't take much to bottom the driver unless you use a driver optimised for a tapped horn which has higher Fs -- the ideal total compliance is the same as a front-loaded horn driver with sealed rear chamber, which typically means Fs<Fhorn for a normal horn and Fs>Fhorn for a tapped horn.

I'd say that the only significant disadvantage is the big high-Q peaks just above the passband, which don't get attenuated enough even with a 24dB/octave crossover and can amplify harmonic distortion.

To remove these you need either a *very* fast rolloff crossover (which means almost certainly digital), or to null out the peaks with quarter-wave resonator pipes like in the DTS-20 (which need tweaking and damping), or notch them out electronically using a parametric equaliser.

Of course a front-loaded horn with similar cutoff and ripple is much *much* bigger, it's not really a fair contest :-)

Ian
A couple more advantages:
- It's generally agreed that a tapped horn "tolerates" a driver with a higher FS. If you have two drivers of equivalent parameters, the one with the higher FS will have a higher sensitivity. This is often overlooked, and can add an additional DB or two to the overall output. One trend I've noticed in sealed box subwoofers is to use drivers with an FS in the teens. A driver like that almost invariably has a sensitivity in the low 80s. The tapped horns we've seen in this thread are sometimes using drivers with sensitivity ratings in the high 90s. That fact alone can contribute FIFTEEN db to the base efficiency of a tapped horn vs a sealed sub.

- It's damn near impossible to get a front loaded horn to go down to 15 or 20hz. Even the vaunted Lab Horn rolls off well before that. If you want to get bass at 20hz or lower, you're basically limited to bandpass, sealed, vented, tapped horn, transmission line and acoustic lever.
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Old 8th April 2008, 04:06 PM   #1494
MaVo is offline MaVo  Germany
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Default Re: Re: Tapped horns vs front loaded horns

Quote:
Originally posted by iand
To remove these you need either a *very* fast rolloff crossover (which means almost certainly digital), or to null out the peaks with quarter-wave resonator pipes like in the DTS-20 (which need tweaking and damping), or notch them out electronically using a parametric equaliser.
electric filters wont get you rid of the distortion amplification, which those peaks cause, since the filter happens before the distortion is generated. so the resonators win, as they are placed after the distortion generation and also filter those.

btw, has someone tried to sim a TH for around 10-40hz? i wonder which drivers would suite those frequencies. i get good results with lab12, but i need lots of drivers and lots of horns, meaning 2-4 m of volume
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Old 8th April 2008, 08:14 PM   #1495
kstrain is offline kstrain  Scotland
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Default Report: PD1550 tapped horn

Today I eventually dared to measure my PD1550 tapped horn. The only possibilty was a near field measurement with an ECM8000. I measured in 1 Hz steps from 20 to 56 Hz. There is a (roughly) known 20 Hz high pass in my mic/preamp response and a crossover low pass around 50 Hz, left in for the measurement.

The measurement tracked the Hornresp/AkAbak model (next post) within +/- 1dB over the measured range (with the mic and crossover response filters included). The peak of the response was at 36.5Hz rather than 41.5Hz, but the difference at both frequencies was just 1 dB.

Comparison with a 100l reflex shows the TH has much lower unwanted output for the same level (when relatively loud for domestic music use). The dullness (if that is the right word) of low frequency souds is refreshing. The 90 or 160Hz (approx) pipe resonances have not been troublesome with 50 Hz 6th order low pass. (Other things in the room produce far more unwanted noise.)

Thanks again to all who encourage the building of tapped horns. Anyone who is hesitating, I encourage it too. If you happen to have a Pd1550 spare there are worse things you could do (or a similar fs~30Hz, low Q, 15").

Model to follow. I could provide the measurement data on request, but they don't tell much.

Ken
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Old 8th April 2008, 08:24 PM   #1496
kstrain is offline kstrain  Scotland
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Default AkAbak PD1550 Tapped Horn

Here is a stripped down model of the PD1550 tapped horn described in my previous post. Actually Hornresp was used more, but I played around with extra cavities and reflectors in AkAbak. This model has all the extras stripped out for clarity and the AkAbak version posted as plain text. I've also removed the microphone response model and the crossover filters which were in for comparison with measurement.

Predicted cone displacement still to be measured, sometime.

Ken


| 20 Hz - 50 Hz Tapped Horn
| Single fold in box approx 2.4 by 0.4 by 0.4m uniform taper, not conical (but probably
| does not matter much for mild taper used)

Def_Const |Horn Dimensions
{
a1 = 320e-4; |Area at throat
a2 = 344e-4; |Area at rear of driver uncertain due to geometry
a3 = 1100e-4; |Area at front of driveruncertain due to geometry
a4 = 1120e-4; |Area at mouth
l1 = 20e-2; |Distance from throat to rear of driver
l2 = 440e-2; |Line distance from rear of driver to front of driver
l3 = 20e-2; |Distance from front of driver to mouth
}
|moderately insensitive to division of length among l1/l2/l3
|checked using Hornresp

Def_Driver 'pd1550'
SD=890cm2 dD1=10cm tD1=3.5cm
fs=31Hz Mms=123g Qms=5.55
Qes=0.22 Re=6ohm Le=2mH ExpoLe=0.618
|driver run in for a couple of weeks prior to measurement
|Le guess, not critical


system 'S1'
Driver Def='pd1550' Node=1=0=3=4
Waveguide 'W1' Node=2=3 STh={a1} SMo={a2} Len={l1} Conical
Waveguide 'W2' Node=3=4 STh={a2} SMo={a3} Len={l2} Conical
Horn 'H1' Node=4 STh={a3} SMo={a4} Len={l3} Conical HEdge=40cm WEdge=240cm


edit: tidied commets

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Old 9th April 2008, 03:11 AM   #1497
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Default Re: Re: Re: Tapped horns vs front loaded horns

Quote:
Originally posted by iand
Tapped horns have the same distortion as a front-loaded horn with the same excursion -- which means better than a small front-loaded horn (loading is poor) but not as good as a huge one (excursion peaks are larger). Tapped horn distortion can be worse if a harmonic hits one of the out-of-band resonant peaks which can amplify it by 10dB or so (see below).

Below where the horn unloads you've only got the stiffness of the driver suspension (no rear chamber), so it won't take much to bottom the driver unless you use a driver optimised for a tapped horn which has higher Fs -- the ideal total compliance is the same as a front-loaded horn driver with sealed rear chamber, which typically means Fs<Fhorn for a normal horn and Fs>Fhorn for a tapped horn.

I'd say that the only significant disadvantage is the big high-Q peaks just above the passband, which don't get attenuated enough even with a 24dB/octave crossover and can amplify harmonic distortion.

To remove these you need either a *very* fast rolloff crossover (which means almost certainly digital), or to null out the peaks with quarter-wave resonator pipes like in the DTS-20 (which need tweaking and damping), or notch them out electronically using a parametric equaliser.

Of course a front-loaded horn with similar cutoff and ripple is much *much* bigger, it's not really a fair contest :-)

Ian
Well I was planning on using a DCX2496 for filtering, which has 48db/octive filters which should be good enough (i hope)... Plus having a smaller enclosure (than a front loaded horn) is always good.

I'm gonna give hornresp a go with a Eminance 4012, and see if I can get any good results...

Also, I've heard that folding a front loaded horn filters out harmonic distortion, I'm guessing this is true with TH's also?
Quote:
Originally posted by Patrick Bateman


A couple more advantages:
- It's generally agreed that a tapped horn "tolerates" a driver with a higher FS. If you have two drivers of equivalent parameters, the one with the higher FS will have a higher sensitivity. This is often overlooked, and can add an additional DB or two to the overall output. One trend I've noticed in sealed box subwoofers is to use drivers with an FS in the teens. A driver like that almost invariably has a sensitivity in the low 80s. The tapped horns we've seen in this thread are sometimes using drivers with sensitivity ratings in the high 90s. That fact alone can contribute FIFTEEN db to the base efficiency of a tapped horn vs a sealed sub.

- It's damn near impossible to get a front loaded horn to go down to 15 or 20hz. Even the vaunted Lab Horn rolls off well before that. If you want to get bass at 20hz or lower, you're basically limited to bandpass, sealed, vented, tapped horn, transmission line and acoustic lever.
I think i've pretty much decided on tapped then, My 4012's have a Fs of 45Hz, so I'll have to see what hornresp and Akabak make of it.
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Old 9th April 2008, 10:31 PM   #1498
iand is offline iand  United Kingdom
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The DCX2469 is an excellent solution, both from the point of view of rapid rolloff crossover and parametric EQ to notch out the peaks. The big advantage is that it becomes trivial to make changes, especially if you're using the free PC control software instead of the front panel.

As was pointed out this doesn't prevent the distortion being picked out by the peaks, resonators are the best solution but I suspect a lot of experimentation tweaking is needed to get the diameter and length correct, to get the centre frequencies right with just the right amount of damping to get the correct Q.

Ian
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Old 10th April 2008, 02:21 AM   #1499
tb46 is offline tb46  United States
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Default references

Hi Naudio: have not had a lot of time lately, well what else is new, here are some links that may be helpful:

Post #1139/1146/1175: MaVo shows pictures of the interior of the DTS20; Post #1140 explanation by cowanaudio.

In Post #1147: Marcello provided a link to the tapped horn patents.

In Post #1174/1183: jnb shows the effect of a resonator in an AkAbak simulation, with and without damping (e.g.: polyfill stuffing in a PVC tube).

In Post #1187: Cordraconis presented his AkAbak for Dummies script with explanations for the individual elements.

Have fun!
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Old 10th April 2008, 02:40 AM   #1500
tb46 is offline tb46  United States
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Default TH Eminence 4012

Hi MikeHunt79:

Here is an attempt at a Hornresp model with extended low frequency response for the 4012. Looking forward to see what you come up with.
Attached Images
File Type: jpg th_eminence 4012_extended lows_small.jpg (64.0 KB, 924 views)
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