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Old 31st October 2008, 08:12 PM   #21
MaVo is offline MaVo  Germany
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Join Date: Jan 2006
Quote:
Originally posted by screamersusa
A funny thing happens to horn loaded speakers as they age, the cones explode. The same pressures that help the box get louder also rip the cones apart if they get wet or dry rot. Too much compression is a bad thing.
There is no "pressures that help the box get louder" as sound itself is a periodical pressure change.

As i see it, the only force that is applied to the cone is due to its movement, which is the same in every possible alignment. A horn only couples a speaker better to the air, so the available power isnt lost due to the impedance mismatch between cone and air. I really cant see a relation between compression factor and cone stress here.

Look at the worst case, a speaker with a closed box on one side and another one with an infinitesimal small hole in it on the other side. This should instantly kill a cone if the high compression theory is correct, but i cant see this happen. Its just two spring forces opposing the cone movement, thus lowering the theoretical output.
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Old 31st October 2008, 08:27 PM   #22
JLH is offline JLH  United States
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I know how all you guys feel. It took quite a bit of time to figure out my double TH. Physics can be very cruel to us speaker designers. Sometimes I find it very difficult to make certain compromises. The thing I had to give in on was sensitivity for the double TH. With the chamber volume and the T/S parameters of the W8-740 woofers, the mouth had to be small to get a reasonably flat response. These woofers also like a small throat.

Just as MaVo mentioned, a woofer will only tolerate so much compression before the cone shreds. However, this is where the compression chamber becomes a very good friend. Due to the low frequencies of interest and airís compressibility, the torture experienced by the cone is lessened to a good degree. The compression chamber lets you get away with a little higher compression ratio than usual.

Just as a side note I did some experimenting with my double TH in an effort to determine how successful the push-pull configuration canceled distortion. I reversed the polarity of the outside woofer to see what would happen. What I was expecting was near complete silence because the woofers were now out of phase with one another. What I ended up hearing was still a surprising amount of bass coming from the TH. Reason told me that any bass coming from the TH had to be the non-linear portion because anything in common should have been canceled. This revealed two very important things: 1.) the Tang Band W8-740 might have lots of excursion, but is not all that linear. 2.) For the highest purity and fidelity in bass reproduction, push-pull is a requirement. Of course this does not directly apply to this thread because Iím not talking about Live sound, but home audio. However, I thought I would still share this with you guys.

Rgs, JLH
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Old 31st October 2008, 08:30 PM   #23
JLH is offline JLH  United States
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Quote:
Originally posted by MaVo


There is no "pressures that help the box get louder" as sound itself is a periodical pressure change.

As i see it, the only force that is applied to the cone is due to its movement, which is the same in every possible alignment. A horn only couples a speaker better to the air, so the available power isnt lost due to the impedance mismatch between cone and air. I really cant see a relation between compression factor and cone stress here.

Look at the worst case, a speaker with a closed box on one side and another one with an infinitesimal small hole in it on the other side. This should instantly kill a cone if the high compression theory is correct, but i cant see this happen. Its just two spring forces opposing the cone movement, thus lowering the theoretical output.

Compressable volume is what saves the woofer from destruction. With the compressibility or air the short periodial pressure change the cone avoids damage.

Rgs, JLH
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Old 31st October 2008, 11:11 PM   #24
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Location: Fort Collins Colorado
Why the nexo 18 (very expensive) scoopy design blows woofers without warning...... The woofer is sitting in the middle of the box and vents out in both directions. There is no compression, there is no air pressure resistance in the box at all.... The wofer can run out of xmax and smash the voice coil in a millisecond and you won't hear it coming. In the Meyer and EV subs, there is restriction in the ports due to size, strong spiders in the suspension of the drivers and a pressure "LAG" acting like a spring inside the cab. When you get a big inaudible peak the combination of spider and cabinet air pressure act like a shock absorber. It's not much but enough for a good engineer to realize there is a problem before he or she toasts all the subs.
Scoops don't give you much if any warning either.
Air pressure, compression and decompression , can be your friend as well as your enemy. Live sound is a BIG compromise to get volume at the cost of frequency response or power. Home and studio sound can be as perfect as you can get because it doesnt need to make 100 db 200 feet away for a thousand people.
Some compression and HPF work on the tapped horn will probably help keep woofers from dying. My TH gets that soft compressed sound some of us are familiar with so you know where to stop. The Bulldog without compression has already taken one 3015 out of comission with LESS POWER!!!!!.
Lovely smell. 3015 will smell before it blows.
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Old 5th November 2008, 08:49 PM   #25
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Default Here is the HTH15 to play with

The HTH15 is a reverse mounted hybrid tapped horn.
I'm sure someone will find this interesting. It uses a ported chamber. The woofer faces out into the mouth, the port feeds the horn side. This version fit in a 31x39x21 casing. It had very good mid bass response well above the hornresp prediction.
100 db at 100 hz, from 102db at 95, 106db at 70, 104db at 60, 99db at 50, 98db at 45hz and drops like a rock past that.
Since the woofer is flush with the horn mouth top, you can use a standard 15 dollar grille to protect the driver. The upper bass sounds clearer than the reverse tappeds so I think it might be a good choice for non drum heavy bands who only need two.

|DATA EXPORTED FROM HORNRESP - RESONANCES NOT MASKED

|COMMENT: corrected final HTH15 chambered reverse internalmount mouth adj

|================================================= ================================================== =====

|REQUIRED AKABAK SETTINGS:

|File > Preferences > Physical system constants:

|Sound velocity c = 344m/s
|Medium density rho = 1.205kg/m3

|Sum > Acoustic power:

|Frequency range = 10Hz to 20kHz
|Points = 533
|Input voltage = 2.80V rms
|Integration = 2Pi-sr
|Integration steps = 1 degree ... 1 degree
|Integration method = Cross

|================================================= ================================================== =====

Def_Const |Hornresp Input Parameter Values
{
|Length, area and volume values converted to metres, square metres and cubic metres:

S1 = 40.00e-4; |Horn segment 1 throat area (sq cm)
S2 = 649.67e-4; |Horn segment 1 mouth area and horn segment 2 throat area (sq cm)
S3 = 840.00e-4; |Horn segment 2 mouth area and horn segment 3 throat area (sq cm)
S4 = 2150.00e-4; |Horn segment 3 mouth area and horn segment 4 throat area (sq cm)
S5 = 2575.00e-4; |Horn segment 4 mouth area (sq cm)

L12 = 17.20e-2; |Horn segment 1 axial length (cm)
L23 = 4.00e-2; |Horn segment 2 axial length (cm)
L34 = 169.60e-2; |Horn segment 3 axial length (cm)
L45 = 22.00e-2; |Horn segment 4 axial length (cm)

Ap = 344.40e-4; |Chamber port cross-sectional area (sq cm)
Lpt = 2.00e-2; |Chamber port tube length (cm)

Vtc = 30420.00e-6; |Throat chamber volume (cc)
Atc = 1521.00e-4; |Throat chamber cross-sectional area (sq cm)

|Parameter Conversions:

Sd = 881.00e-4; |Diaphragm area (sq cm)

Ltc = Vtc / Atc;

I'll post build pics in a few days. For now someone can try to tweak it to go lower without making the box bigger, but maybe wider. Cheers
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Old 5th November 2008, 08:54 PM   #26
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Location: Fort Collins Colorado
Default Here is the PATH15

This is the cabinet I am probably going to use. I like the sound of the HTH15 better but it's not low enough.
It fits in a 40x31x25.5 casing. Wheels and handles on the back like the Danley Box. Rumbles pretty good, especially in pairs.


|DATA EXPORTED FROM HORNRESP - RESONANCES NOT MASKED

|COMMENT: Smallest possible actual build translate 1 fix to try version 2 pathagain

|================================================= ================================================== =====

|REQUIRED AKABAK SETTINGS:

|File > Preferences > Physical system constants:

|Sound velocity c = 344m/s
|Medium density rho = 1.205kg/m3

|Sum > Acoustic power:

|Frequency range = 10Hz to 20kHz
|Points = 533
|Input voltage = 2.80V rms
|Integration = 2Pi-sr
|Integration steps = 1 degree ... 1 degree
|Integration method = Cross

|================================================= ================================================== =====

Def_Const |Hornresp Input Parameter Values
{
|Length, area and volume values converted to metres, square metres and cubic metres:

S1 = 367.00e-4; |Horn segment 1 throat area (sq cm)
S2 = 708.82e-4; |Horn segment 1 mouth area and horn segment 2 throat area (sq cm)
S3 = 710.00e-4; |Horn segment 2 mouth area and horn segment 3 throat area (sq cm)
S4 = 2247.44e-4; |Horn segment 3 mouth area and horn segment 4 throat area (sq cm)
S5 = 2456.00e-4; |Horn segment 4 mouth area (sq cm)

L12 = 33.80e-2; |Horn segment 1 axial length (cm)
L23 = 0.10e-2; |Horn segment 2 axial length (cm)
L34 = 202.70e-2; |Horn segment 3 axial length (cm)
L45 = 21.00e-2; |Horn segment 4 axial length (cm)

Ap = 424.10e-4; |Chamber port cross-sectional area (sq cm)
Lpt = 9.80e-2; |Chamber port tube length (cm)

Vtc = 1843.00e-6; |Throat chamber volume (cc)
Atc = 900.00e-4; |Throat chamber cross-sectional area (sq cm)

|Parameter Conversions:

Sd = 881.00e-4; |Diaphragm area (sq cm)

Ltc = Vtc / Atc;
}
|================================================= ================================================== =====

|Network node numbers for this tapped horn system:

| 0-Voltage-1
| |
| -Port-4-Chamber-5-Driver-
| | |
|8-Segment-9-Segment-10-Segment------11-Segment-12-Radiator

|================================================= ================================================== =====

Def_Driver 'Driver'

Sd=881.00cm2
Bl=18.60Tm
Cms=1.40E-04m/N
Rms=3.90Ns/m
fs=42.4464Hz |Mmd = 85.40g not recognised by AkAbak, fs calculated and used instead
Le=4.90mH
Re=5.30ohm
ExpoLe=1

System 'System'

Driver Def='Driver''Driver'
Node=1=0=5=11

Duct 'Throat chamber'
Node=4=5
SD={Atc}
Len={Ltc}
Visc=0

Duct 'Port'
Node=4=9
SD={Ap}
Len={Lpt}
Visc=0

Waveguide 'Horn segment 1'
Node=8=9
STh={S1}
SMo={S2}
Len={L12}
Conical

Waveguide 'Horn segment 2'
Node=9=10
STh={S2}
SMo={S3}
Len={L23}
Conical

Waveguide 'Horn segment 3'
Node=10=11
STh={S3}
SMo={S4}
Len={L34}
Conical

Waveguide 'Horn segment 4'
Node=11=12
STh={S4}
SMo={S5}
Len={L45}
Conical

Radiator 'Horn mouth'
Node=12
SD={S5}

...........................
Tweak away
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Old 5th November 2008, 09:10 PM   #27
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Location: Fort Collins Colorado
Default What I found....

To contribute a few things I seem to have discovered with and without help:

Compression in a tapped does help a great deal.

Getting upper bass to sound good is a pain in a th.
So I wouldn't consider a DIY TH if you have top boxes that are weak at 100hz. If you have 15" tops you should be ok. Otherwise
stick with a double 18 or 15. Especially if you only want two subs.
If you are one of those rare quiet acts (especially midi) you might like the path15.

You have a very limited bandwidth to work with.

While not as loud as a typical folded horn, TH boxes sound better for live use. (I gave away my one folded DIY...empty).

A couple of cm makes a BIG difference in a PA type cabinet.

Folding certainly causes issues that I'd love someone to point me at information on how to solve them.

Considering I've spent almost a month, almost every day building and unbuilding boxes, I've cleaned out my horn resp database 3 times, I gone through countless styrofoam and plywood boards, done close to a hundred tests, I'll say this.....
If you have the money....Dont cheap out, go buy the Danley.
My goal was to get to 103db from 45 to 120, couldn't do it.
Although for a DIY the HTH might be interesting as it pushed
up to 106db at 70hz due to compression and the chamber.
For the rest of us who probably won't be able to afford new subs... we'll keep plugging away at it.
Cheers
Scott MacAuley
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Old 5th November 2008, 10:10 PM   #28
FlipC is offline FlipC  United States
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Screamer :
Quote:
My goal was to get to 103db from 45 to 120, couldn't do it.
Is this due more to you using a cheap driver?
(Eminence 3015lf )


One thing I am having issues with is modeling
for high SPL. I can get good flat responses at 1W@1M but when I start pushing the power up the curve goes a muck. How can one model more than a single TH cabinet in HR?
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Old 5th November 2008, 10:12 PM   #29
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One more thing..

The HTH was designed to work with omnitops as they are rather whimpy at 100hz. . I still needs some work in the upper range as it has a phase issue at 122hz. It sounded the best with the Omnis as it has the forward firing woofer resulting in better mid bass intelligibility.
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Old 6th November 2008, 02:24 AM   #30
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Location: Fort Collins Colorado
Quote:
Originally posted by FlipC
Screamer :

Is this due more to you using a cheap driver?
(Eminence 3015lf )


One thing I am having issues with is modeling
for high SPL. I can get good flat responses at 1W@1M but when I start pushing the power up the curve goes a muck. How can one model more than a single TH cabinet in HR?

Not exactly, and they're not that cheap.
I tried the 4015 and teh 15btx in the sims. Similar issues with all 3. The 4015 would be better, the 15btx is the most expensive.

I try Jbl 2225H drivers as well just to see what they'll do at lower volumes. I like the sound of the JBL much much better. I'm guessing the BTX would probably be best, 4015 second then maybe the 3015lf. The other eminence offerings don't have the xmax. The HTH15 looks like it may be able to take other drivers since the horn is actually just a giant port.

In max spl, yes the waveform goes to hell..as it should. Speakers are not linear.
If you are using the new max spl option in the wizard here's how I use it. (nice addition there David!).
Set your xmax, adjust your power level until something starts CLIPPING. Go to your chamber or horn and tweak away in the chamber section or s1 and 2 to try to minimize the clipping.
Then raise the level a little and try again.
Also look at the displacement as well, the 3015 runs out of xmax
very quickly below 40. I have not figured out how to set a hpf in hornresp. It's a big balancing act.
I basically try to get it so the tops of the waveforms peak at max spl at about the same time. For example if I have a peak at 45hz and 65hz, I try to get them to max out at the same level.
At 400w and 9.0 xmax on the 3015 those two peaks look about the same at 126-130 db if I get it right.
The end result is a cabinet that sounds fairly loud and full versus a loud sounding box with no...balls .

I can tell you that if you want 94 db at 100 feet full blast...you need at least two diy TH horns coupled together, and you'll be pushing the hell out of em.. Personally I believe one should consider all subs in pairs where ever possible. Saves a ton of amp dollars and prevents blow ups. That 20,000 watt amp isn't much good if the speaker can only take 1200 watts .
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