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Old 14th May 2007, 09:56 AM   #371
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Quote:
Originally posted by 316a
What about multiple drivers or a clamshell pair of drivers or both ? What would happen to the TS of a pair of drivers in a clamshell ? [/B]
Sorry for my bad english, what is a clamshell? Do you mean two drivers in a compound/isobarik way mounted onto each other?
Then, for the resulting "virtual" speaker:
- BL rises
- VAS halves
- Mass doubles
- fs changes slightly
- One of the Q-faktors changes as well...

Have to scam through my papers if I find the exact equations for this. There are some on the net with simple "double here, half there" rules of thumb, but since one of my old modeling-software (LASIP) does a fine job of calculating this, I allways use it and donīt have the equations in my head

You could PM me with the TSP, Iīll calculate it for you, if you like.
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Old 14th May 2007, 12:21 PM   #372
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Clamshell mounting makes little if any sense. There is no real advantage. The SD remains the same, BL and moving mass is doubled, thermal power handling is doubled, but the power requirement is also doubled, hence the efficiency is reduced by 3 dB. The cost is doubled!

More sensible is push pull mounting both drivers. Output is increased by 6 db, and distortion is reduced because it is push pull. The size should also be increased.
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Old 14th May 2007, 04:13 PM   #373
freddi is offline freddi  United States
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I'd like to know subjectively the general effects of stretching William's 30Hz TH a bit taller (-assume only l2 needs to be changed in the script-?)

also, wheres that vertical mark on qwerty that looks like a "l" appearing in front of horn deifinitions, etc?

what other woofers besides 830847 are cool for 4.4M pipe of this cross-section?


3.5M vs 4.1M 803500
http://img174.imageshack.us/img174/3...035v41lwi8.gif

4.1M 803500 vs 830847
http://img174.imageshack.us/img174/4...0830847ov7.gif

4.1M (~84inch tall) vs 4.4M (~90inch tall)
http://img174.imageshack.us/img174/4...4mvs41men8.gif

here's Z and spl up close of the 4.4M XXL TH
http://img230.imageshack.us/img230/3...44msplziv0.gif

here's Z - minimum and dips
http://img402.imageshack.us/img402/4...4mzdipsae4.gif
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Old 14th May 2007, 07:47 PM   #374
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Hello,

Getting into Akabak is very fun, especially trying to model a tapped horn.

I think the real power in a tapped horn design is the reduction
in cone excursion. Having a flat response with minimum cone excursion wil be the goal in the design, allowing maximum electric power without reaching the xmax (less distortion ) is the final goal.

Like i write a couple weeks ago; akabak does a summation of two soundsources dependent of the distance/phase their are related from each other. What it doen`t calculate (automatically) is the influence on each other (it`s like that they don`t feel the radiation of a other soundsource, which is the reduction in cone excursion). Especially in the case of a tapped horn, where the summation of the front and back cone happens in a real small portion of the horn.

You could check this by simulating in Akabak;

Put 2 direct radiators in a closed box. Shift one of the two about 100cm backwards. Check the summation. You should see the first notch at about 170Hz and every 180dgr. phase shift. Every 0 and 360dgr. phase shift you see the 6dB rule.
Now put the 2 loudspeakers parrallel and look to the excursion of the cone with one speaker driven and with both speakers driven. You don`t see any difference in the excursion.

I can image that pratical you should see some difference. Just if you put 2 loudspeakers very close together with only one driven you can feel the restoring force on the cone that is not driven.

Does anybody know something about this "mutual coupling" effect? and are there some good reading papers that deal with this effect?

Cheers,
Marcel
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Old 14th May 2007, 08:16 PM   #375
aceinc is offline aceinc  United States
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Patrick,

I have thought about using two of these in a TH as a test. I have a number of them laying about that I could use for testing.

My idea for using two drivers is to mount the drivers at 90 degree angles to one another such that they fire into the resulting triangle. This assembly is mounted over a slot for the sound to enter the throat of the horn. If push pull is desired mount one of the drivers firing in, the other firing out.

I would be willing to build this as a test bed, if someone would provide some design ideas that have a reasonable chance of making decent noise

Paul
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Old 14th May 2007, 08:39 PM   #376
freddi is offline freddi  United States
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daydreaming I put a pricey but good looking RCF with 6.5mm and 59Hz fs into a 2.1M version of William's 50Hz TH. Can one just change the length input when investigating different heights when the TH width, depth and mouth do not change???


RCF L12 P540 in 2.1M TH 28.3vrms
http://img404.imageshack.us/img404/3...p540th1bh4.gif

1951 Karlson reduced cone excurtion by maybe a factor of 2-3 compared to reflex equivalent to their rear chamber volume and tuning - I don't know if its mainly bandpass but the K-slot helps dynamics when running them high
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Old 14th May 2007, 08:47 PM   #377
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Quote:
Originally posted by Marcello
I think the real power in a tapped horn design is the reduction
in cone excursion. Having a flat response with minimum cone excursion wil be the goal in the design, allowing maximum electric power without reaching the xmax (less distortion ) is the final goal.
Thatīs what Tom Danley describes in his paper and as far as I understand it, this seems to be the case. Can you confirm my assumption that akabak plots peak-peak in the excursion analysis? If so, the excursion reduction somehow is seen in Akabak, even when mutual coupling is not really taken into account. Hm... confused...
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Old 14th May 2007, 09:47 PM   #378
316a is offline 316a  England
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Quote:
Originally posted by freddi
daydreaming I put a pricey but good looking RCF with 6.5mm and 59Hz fs into a 2.1M version of William's 50Hz TH. Can one just change the length input when investigating different heights when the TH width, depth and mouth do not change???
Thats what I've been doing . No idea if it's correct , have a look at the horn length l2 in these sims . I've been using a rule of thumb where the throat is Sd divided by 1.5 and the mouth is 3 x Sd . The main parameter changed has been the length , the rest of the parameters have just had a slight fiddle . Drivers singled out this evening are as follows :

Eminence Delta Pro 12A

Quote:

| Tapped Horn

Def_Const |Horn Dimensions

{
a1 = 354e-4; |Area at throat (cm^2)
a2 = 360e-4; |Area at rear of driver (cm^2)
a3 = 1050e-4; |Area at front of driver (cm^2)
a4 = 1055e-4; |Area at mouth (cm^2)
l1 = 15e-2; |Distance from throat to rear of driver (cm)
l2 = 280e-2; |Line distance from rear of driver to front of driver (cm)
l3 = 30e-2; |Distance from front of driver to mouth (cm)
}

Def_Driver 'Dr1'

| Eminence Delta Pro 12a xmax 4.6 (flat)

Sd=532.4cm2
fs=51Hz
Qes=0.37
Qms=7.56
Vas=81.7L
Re=5.71ohm
Le=0.84mH



system 'S1'

Driver Def='Dr1' 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
Fane M412LF

Quote:
| Tapped Horn

Def_Const |Horn Dimensions

{
a1 = 354e-4; |Area at throat (cm^2)
a2 = 360e-4; |Area at rear of driver (cm^2)
a3 = 1050e-4; |Area at front of driver (cm^2)
a4 = 1055e-4; |Area at mouth (cm^2)
l1 = 15e-2; |Distance from throat to rear of driver (cm)
l2 = 220e-2; |Line distance from rear of driver to front of driver (cm)
l3 = 30e-2; |Distance from front of driver to mouth (cm)
}

Def_Driver 'Dr1'

| M412LF Fane xmax 5.5mm (fairly flat)

Sd=532.4cm2
fs=62.7Hz
Qes=0.479
Qms=11.1
Vas=45L
Re=6.26ohm
Le=0.84mH



system 'S1'

Driver Def='Dr1' 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
Beyma 12br70

Quote:
| Tapped Horn

Def_Const |Horn Dimensions

{
a1 = 354e-4; |Area at throat (cm^2)
a2 = 360e-4; |Area at rear of driver (cm^2)
a3 = 1050e-4; |Area at front of driver (cm^2)
a4 = 1055e-4; |Area at mouth (cm^2)
l1 = 15e-2; |Distance from throat to rear of driver (cm)
l2 = 350e-2; |Line distance from rear of driver to front of driver (cm)
l3 = 30e-2; |Distance from front of driver to mouth (cm)
}

Def_Driver 'Dr1'

| Beyma 12br70 xmax 6mm

Sd=540cm2
fs=35Hz
Qes=0.44
Qms=1.85
Vas=135L
Re=5.6ohm
Le=1mH



system 'S1'

Driver Def='Dr1' 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
Beyma SM112/w

Quote:
| Beyma Tapped Horn

Def_Const |Horn Dimensions

{
a1 = 354e-4; |Area at throat (cm^2)
a2 = 360e-4; |Area at rear of driver (cm^2)
a3 = 1050e-4; |Area at front of driver (cm^2)
a4 = 1055e-4; |Area at mouth (cm^2)
l1 = 15e-2; |Distance from throat to rear of driver (cm)
l2 = 250e-2; |Line distance from rear of driver to front of driver (cm)
l3 = 30e-2; |Distance from front of driver to mouth (cm)
}

Def_Driver 'Dr1'
|Beyma SM112/w 5.5mm xmax (flat)

Sd=530cm2
fs=42Hz
Qes=0.36
Qms=4.92
Vas=90L
Re=5.8ohm
Le=1.1mH



system 'S1'

Driver Def='Dr1' 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
...currently trying to find the specs for 12SW , Ciare's website is down

cheers

316a
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Old 14th May 2007, 10:16 PM   #379
freddi is offline freddi  United States
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hi 316a - (I'll look at those later) lets hope we get an answer regarding more TH length when width, depth and mouth are fixed and some more modeling input.

with short TH, doe's William's 50Hz configuration with mouth at "top" always make better use of bulk as there's more length?-- in some situations mouth at "front/bottom" as on William's 30Hz horn might be more practical.

I assume Akabak's excursion prediction is one-way (?)
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Old 15th May 2007, 12:00 AM   #380
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G'day all

If you're locking several variables in your model then you will never come up with an optimum result. Several people seem to be using the line areas I used in some of my horns. Remember, at the time these horns were designed, the dimensions were little more than educated guesses on my part. With a bit of fiddling it is possible to get very flat response curves (+/-1dB), but that is not always an ideal solution. Other factors such as size, weight and timber usage must come into play alongside F3, efficiency/power handling and driver choice. It's a bit of a silly exercise trying to find a good driver for an expo horn with an "x" mouth and a "y" throat. Several people here are doing essentially the same thing with their tapped horn models.

Cheers

William Cowan
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