THAM15 - a compact 15" tapped horn

[Brian Steele]

Originally Posted by soho54

Are you going to explain your "Dog Food" method, or just wait for us to guess?

LOL. I was spending a bit more time trying to research the effect, empirically .

It's simple, really. Remember when I did my experiment to demonstrate that modifying the bends in my tapped pipe had little or no effect on the passband if the cross-section around the bend was not significantly altered?

Well, after doing that, I just messed around with the cards a little at other locations in the pipe to see if they would produce any significant response changes at other locations. I noticed that, at one particular point in the pipe, if I adjusted them to have a significant effect on the cross-section in that area, the "notch" started to fill in, without significantly impacting the rest of the passband. The effect would significantly reduce, if not disappear, if I moved the obstruction caused by the cards only a inch or two forwards or backwards in the pipe. I also placed the mic *in* the pipe in that location, and set TrueRTA to Rel mode, the graph started to show a peaked response around the same frequencies that the notch appeared in the tapped-pipe's response curve. Coincidence? Perhaps.

I thought that perhaps I could remove the notch even more if I used something more solid than the matt-board cards to act as an obstruction. But what to use...?

Then I saw the cans of dogfood that my eldest daughter left on the kitchen counter.

The pictures below are self explanatory .

One shows the change to the tapped-pipe that seemed to produce the best results, and the other shows the change to the tapped-horn that seemed to produce the best results also (luckily I didn't permanently attach that particular panel!). In both cases, I'm pretty sure the effect can be modelled in Akabak as constrictions in the path at those points (no "horn voodoo" involved).

In the case of the tapped-pipe, the pipe is being constricted about 2/3rds of the way along its length. In the case of the tapped-horn, I'm not sure what would be the best way to model the effect - the 2/3rds point appears to occur right on the bend - maybe the arrangement of the cans converts that area into a resonant chamber that notches out the frequencies that cause the cancellation measured at the mouth. In any case, it seems to work.

In both cases, shifting the cans just an inch or two back and forth results in the effect being greatly diminished. It's VERY position dependent.

This weekend, if I get the opportunity, I'm going to try to replace the cans with something else a bit more fitting to see if I better the response graphs I previously posted.

Tuning horns with dogfood cans - who knew?

[soho54]

I figured it was this. I was wondering if you were using cans, or shaping it with your hands.

My question is what happens as you turn it up? I would expect the lowend to continue to possibly suffer more and more attenuation. Can you check without upsetting the neighbors?

[Brian Steele]

Originally Posted by soho54

I figured it was this. I was wondering if you were using cans, or shaping it with your hands.

My question is what happens as you turn it up? I would expect the lowend to continue to possibly suffer more and more attenuation. Can you check without upsetting the neighbors?

Had a simple test sim going earlier based on the one I posted in your spreadsheet thread.

System 'DEMO1'

Def_Driver 'Driver'
dD=26cm dD1=11cm tD1=6.5cm |Cone
t1=1.1cm
fs=39Hz Vas=92L Qms=7.5
Qes=0.31 Re=5.2ohm Le=0.37mH ExpoLe=0.618


Def_Const
{
S1 = 4.8e-2;
S2 = 6.3e-2;
S3 = 8.2e-2;
S4 = 9.6e-2;
S5 = 10.9e-2;
S6 = 10.1e-2;
S7 = 10.1e-2;
S8 = 11.8e-2;
S9 = 13.1e-2;
S10 = 12.1e-2;
S11 = 12.1e-2;
S12 = 14.5e-2;
S13 = 17.1e-2;
S14 = 16.1e-2;
S15 = 17.3e-2;
S16 = 15.8e-2;
S17 = 13.6e-2;
S18 = 13.6e-2;
S19 = 14.8e-2;
S20 = 13.4e-2;
S21 = 11.8e-2;
S22 = 13.6e-2;
S23 = 16.3e-2;
S24 = 15.3e-2;
S25 = 16.3e-2;
S26 = 17.7e-2;


L1 = 20e-2;
L2 = 26.7e-2;
L3 = 2.5e-2;
L4 = 3.3e-2;
L5 = 2.0e-2;
L6 = 33e-2;
L7 = 3.0e-2;
L8 = 3.9e-2;
L9 = 2.5e-2;
L10 = 30.5e-2;
L11 = 4.0e-2;
L12 = 5.2e-2;
L13 = 3.7e-2;
L14 = 4.0e-2;
L15 = 5.4e-2;
L16 = 4.0e-2;
L17 = 17.0e-2;
L18 = 3.0e-2;
L19 = 4.7e-2;
L20 = 4.0e-2;
L21 = 4.2e-2;
L22 = 4.8e-2;
L23 = 3.4e-2;
L24 = 13.9e-2;
L25 = 20.9e-2;
}


Driver Def='Driver''Driver'
Node=1=0=100=3

Duct    'Dogfood'  
Node=101=102
dD=10cm  Len=1.8cm




Waveguide 'Horn segment 1'
Node=3=2
WTh=41.4cm HTh={S1}
WMo=41.4cm HMo={S2}
Len={L1}

Waveguide 'Horn segment 2'
Node=3=4
WTh=41.4cm HTh={S2}
WMo=41.4cm HMo={S3}
Len={L2}

Waveguide 'Horn segment 3'
Node=4=5
WTh=41.4cm HTh={S3}
WMo=41.4cm HMo={S4}
Len={L3}

Waveguide 'Horn segment 4'
Node=5=6
WTh=41.4cm HTh={S4}
WMo=41.4cm HMo={S5}
Len={L4}

Waveguide 'Horn segment 5'
Node=7=6
WTh=41.4cm HTh={S6}
WMo=41.4cm HMo={S5}
Len={L5}

Duct 'Duct segment 6'
Node=7=8
WD=41.4cm HD={S6} Len={L6}

Waveguide 'Horn segment 7'
Node=8=9
WTh=41.4cm HTh={S7}
WMo=41.4cm HMo={S8}
Len={L7}

Waveguide 'Horn segment 8'
Node=9=10
WTh=41.4cm HTh={S8}
WMo=41.4cm HMo={S9}
Len={L8}

Waveguide 'Horn segment 9'
Node=11=10
WTh=41.4cm HTh={S10}
WMo=41.4cm HMo={S9}
Len={L9}

Duct 'Duct segment 10'
Node=11=101
WD=41.4cm HD={S10} Len={L10}

Waveguide 'Horn segment 11'
Node=102=13
WTh=41.4cm HTh={S11}
WMo=41.4cm HMo={S12}
Len={L11}

Waveguide 'Horn segment 12'
Node=13=14
WTh=41.4cm HTh={S12}
WMo=41.4cm HMo={S13}
Len={L12}

Waveguide 'Horn segment 13'
Node=15=14
WTh=41.4cm HTh={S14}
WMo=41.4cm HMo={S13}
Len={L13}

Waveguide 'Horn segment 14'
Node=15=16
WTh=41.4cm HTh={S14}
WMo=41.4cm HMo={S15}
Len={L14}

Waveguide 'Horn segment 15'
Node=17=16
WTh=41.4cm HTh={S16}
WMo=41.4cm HMo={S15}
Len={L15}

Waveguide 'Horn segment 16'
Node=18=17
WTh=41.4cm HTh={S17}
WMo=41.4cm HMo={S16}
Len={L16}

Duct 'Duct segment 17'
Node=18=19
WD=41.4cm HD={S17} Len={L17}

Waveguide 'Horn segment 18'
Node=19=20
WTh=41.4cm HTh={S18}
WMo=41.4cm HMo={S19}
Len={L18}

Waveguide 'Horn segment 19'
Node=21=20
WTh=41.4cm HTh={S20}
WMo=41.4cm HMo={S19}
Len={L19}

Waveguide 'Horn segment 20'
Node=21=22
WTh=41.4cm HTh={S21}
WMo=41.4cm HMo={S20}
Len={L20}

Waveguide 'Horn segment 21'
Node=22=23
WTh=41.4cm HTh={S21}
WMo=41.4cm HMo={S22}
Len={L21}

Waveguide 'Horn segment 22'
Node=23=24
WTh=41.4cm HTh={S22}
WMo=41.4cm HMo={S23}
Len={L22}

Waveguide 'Horn segment 23'
Node=25=24
WTh=41.4cm HTh={S24}
WMo=41.4cm HMo={S23}
Len={L23}

Waveguide 'Horn segment 24'
Node=25=26
WTh=41.4cm HTh={S24}
WMo=41.4cm HMo={S25}
Len={L24}

Waveguide 'Horn segment 25'
Node=26=27
WTh=41.4cm HTh={S25}
WMo=41.4cm HMo={S26}
Len={L25}

Duct 'Du1' Node=100=26
WD=41.4cm HD=30cm Len=1.7cm

Radiator 'Horn mouth' Def='Horn segment 25'
Node=27

That looks pretty good, however the "Dogfood Duct" is perhaps a little bit longer, there are actually two with different effective cross-sections in POC#2, and their lengths should be subtracted from the waveguide sections in those areas.

Pity AkAbak doesn't have an optimization routine to determine the best size and location for the ducts .

Good point on possible power compression. My neighbours seem to be out, so I may get an opportunity to do some SPL tests this weekend. To reduce the effects of compression, perhaps rounded ducts (think half-pipe sections placed tangential to the path) could be used. Think I'll pay me a visit to the hardware store tomorrow...

[soho54]

That looks pretty good, however the "Dogfood Duct" is perhaps a little bit longer, there are actually two with different effective cross-sections in POC#2, and their lengths should be subtracted from the waveguide sections in those areas.

That was just me playing around earlier today trying to see what you could be doing with dog food.

I figured you were either creating a restriction, or using the can as a stencil to add some tuning holes. The holes reduce a resonances output, and the restriction can help a null.

Looking at your pictures I would do something more like this to mimic it, quickly:

System 'DEMO1'

Def_Driver 'Driver'
dD=26cm dD1=11cm tD1=6.5cm |Cone
t1=1.1cm
fs=39Hz Vas=92L Qms=7.5
Qes=0.31 Re=5.2ohm Le=0.37mH ExpoLe=0.618


Def_Const
{
S1 = 4.8e-2;
S2 = 6.3e-2;
S3 = 8.2e-2;
S4 = 9.6e-2;
S5 = 10.9e-2;
S6 = 10.1e-2;
S7 = 10.1e-2;
S8 = 11.8e-2;
S9 = 13.1e-2;
S10 = 12.1e-2;
S11 = 12.1e-2;
S12 = 14.5e-2;
S13 = 17.1e-2;
S14 = 16.1e-2;
S15 = 17.3e-2;
S16 = 15.8e-2;
S17 = 13.6e-2;
S18 = 13.6e-2;
S19 = 14.8e-2;
S20 = 13.4e-2;
S21 = 11.8e-2;
S22 = 13.6e-2;
S23 = 16.3e-2;
S24 = 15.3e-2;
S25 = 16.3e-2;
S26 = 17.7e-2;


L1 = 20e-2;
L2 = 26.7e-2;
L3 = 2.5e-2;
L4 = 3.3e-2;
L5 = 2.0e-2;
L6 = 33e-2;
L7 = 3.0e-2;
L8 = 3.9e-2;
L9 = 2.5e-2;
L10 = 25.5e-2;
L11 = 4.0e-2;
L12 = 5.2e-2;
L13 = 3.7e-2;
L14 = 4.0e-2;
L15 = 5.4e-2;
L16 = 4.0e-2;
L17 = 17.0e-2;
L18 = 3.0e-2;
L19 = 4.7e-2;
L20 = 4.0e-2;
L21 = 4.2e-2;
L22 = 4.8e-2;
L23 = 3.4e-2;
L24 = 13.9e-2;
L25 = 20.9e-2;
}


Driver Def='Driver''Driver'
Node=1=0=100=3

Duct    'Dogfood'  
Node=101=102
WD=24.84cm HD={S10} Len=5cm

Waveguide 'Horn segment 1'
Node=3=2
WTh=41.4cm HTh={S1}
WMo=41.4cm HMo={S2}
Len={L1}

Waveguide 'Horn segment 2'
Node=3=4
WTh=41.4cm HTh={S2}
WMo=41.4cm HMo={S3}
Len={L2}

Waveguide 'Horn segment 3'
Node=4=5
WTh=41.4cm HTh={S3}
WMo=41.4cm HMo={S4}
Len={L3}

Waveguide 'Horn segment 4'
Node=5=6
WTh=41.4cm HTh={S4}
WMo=41.4cm HMo={S5}
Len={L4}

Waveguide 'Horn segment 5'
Node=7=6
WTh=41.4cm HTh={S6}
WMo=41.4cm HMo={S5}
Len={L5}

Duct 'Duct segment 6'
Node=7=8
WD=41.4cm HD={S6} Len={L6}

Waveguide 'Horn segment 7'
Node=8=9
WTh=41.4cm HTh={S7}
WMo=41.4cm HMo={S8}
Len={L7}

Waveguide 'Horn segment 8'
Node=9=10
WTh=41.4cm HTh={S8}
WMo=41.4cm HMo={S9}
Len={L8}

Waveguide 'Horn segment 9'
Node=11=10
WTh=41.4cm HTh={S10}
WMo=41.4cm HMo={S9}
Len={L9}

Duct 'Duct segment 10'
Node=11=101
WD=41.4cm HD={S10} Len={L10}

Waveguide 'Horn segment 11'
Node=102=13
WTh=31.05cm HTh={S11}
WMo=31.05cm HMo={S12}
Len={L11}

Waveguide 'Horn segment 12'
Node=13=14
WTh=31.05cm HTh={S12}
WMo=31.05cm HMo={S13}
Len={L12}

Waveguide 'Horn segment 13'
Node=15=14
WTh=31.05cm HTh={S14}
WMo=31.05cm HMo={S13}
Len={L13}

Waveguide 'Horn segment 14'
Node=15=16
WTh=31.05cm HTh={S14}
WMo=31.05cm HMo={S15}
Len={L14}

Waveguide 'Horn segment 15'
Node=17=16
WTh=31.05cm HTh={S16}
WMo=31.05cm HMo={S15}
Len={L15}

Waveguide 'Horn segment 16'
Node=18=17
WTh=31.05cm HTh={S17}
WMo=31.05cm HMo={S16}
Len={L16}

Duct 'Duct segment 17'
Node=18=19
WD=41.4cm HD={S17} Len={L17}

Waveguide 'Horn segment 18'
Node=19=20
WTh=41.4cm HTh={S18}
WMo=41.4cm HMo={S19}
Len={L18}

Waveguide 'Horn segment 19'
Node=21=20
WTh=41.4cm HTh={S20}
WMo=41.4cm HMo={S19}
Len={L19}

Waveguide 'Horn segment 20'
Node=21=22
WTh=41.4cm HTh={S21}
WMo=41.4cm HMo={S20}
Len={L20}

Waveguide 'Horn segment 21'
Node=22=23
WTh=41.4cm HTh={S21}
WMo=41.4cm HMo={S22}
Len={L21}

Waveguide 'Horn segment 22'
Node=23=24
WTh=41.4cm HTh={S22}
WMo=41.4cm HMo={S23}
Len={L22}

Waveguide 'Horn segment 23'
Node=25=24
WTh=41.4cm HTh={S24}
WMo=41.4cm HMo={S23}
Len={L23}

Waveguide 'Horn segment 24'
Node=25=26
WTh=41.4cm HTh={S24}
WMo=41.4cm HMo={S25}
Len={L24}

Waveguide 'Horn segment 25'
Node=26=27
WTh=41.4cm HTh={S25}
WMo=41.4cm HMo={S26}
Len={L25}

Duct 'Du1' Node=100=26
WD=41.4cm HD=30cm Len=1.7cm

Radiator 'Horn mouth' Def='Horn segment 25'
Node=27

This is still pretty ruff, but it is closer to what you have done there. Did the restriction end up at about halfway in both horn paths?

[soho54]

Playing with it some more it seems like you are countering the dip between the 5th and 7th harmonics, or your third impedance peak depending on how you want to look at it.

This is where the horn is changing over from 1/4WL to 1/2WL operation.

Using some horns I am more familiar with it seems 1/2 the horns acoustic length is the place to start. So physical length + mouth correction, and divide by two. Looks like placing the initial resistance as close to this as possible, and them moving towards the mouth to dial it in for the flare rate used seems to work pretty well.

As power is increased I would expect a non-linear increase in overall SPL, and more a pronounced reduction on the lower end SPL with a drop in Fc. Maybe you will get to test it out this weekend. If it goes well with your setup I'll get it added to some testing to be done in the spring with some monster horns.

[Djim]

(Big sigh) Many many thanks guys!!! Finally I’m getting some answers! Btw Soho, do you have some pretty diagrams of those horns in your collection which you are willing to share? Don’t see them around here.

But then again it still doesn’t answer or rule out the possibility that a section within the horn can produce harmonics as side effect of ‘rough’ bendings, is it?

(Brian, next time if you want to throw off a bite call it the old "brick method" for instance cause fish only take a bite in rocks they recognise… Lol, I really didn’t catch that although I admit it drove me bunkers; first mouth measurements, fluffy cards and then Dogfood?!?!)

[Brian Steele]

Originally Posted by soho54

Playing with it some more it seems like you are countering the dip between the 5th and 7th harmonics, or your third impedance peak depending on how you want to look at it.

This is where the horn is changing over from 1/4WL to 1/2WL operation.

Using some horns I am more familiar with it seems 1/2 the horns acoustic length is the place to start. So physical length + mouth correction, and divide by two. Looks like placing the initial resistance as close to this as possible, and them moving towards the mouth to dial it in for the flare rate used seems to work pretty well.

Eyeballing it, it seems to be closer to 2/3rds down the path, but it's quite possible that my approximation may be off a bit. In the case of the tapped-pipe, it looks definitely like 2/3rds, as the constriction's best location is in the second half of the box.

Originally Posted by soho54

As power is increased I would expect a non-linear increase in overall SPL, and more a pronounced reduction on the lower end SPL with a drop in Fc. Maybe you will get to test it out this weekend. If it goes well with your setup I'll get it added to some testing to be done in the spring with some monster horns.

It may be possible to achieve something similar by using instead an external chamber that resonates at the center frequency of the notch (in the case of the THAM15, this could be a chamber at the bottom, or even one on the 1st 180 degree bend, as I've found that even filling up almost half the bend with cans really didn't do much damage to the passband response. This should avoid any potential compression problems caused by putting a constriction in the path. Of course this is more difficult to test quickly .

[jbell]

I prefer an approach (voodoo or not) that works at 2.83v AND at 28v and louder.... and doesn't require a can opener and a pet to make modifications.

My ss15 for example has a dip exactly where hornresp predicts... but it's only 2HZ wide... not nearly what hornresp predicts. In fact it's such a narrow dip that smaart completely misses it at 1/24oct resolution. If I didn't make it a practice to listen to sine waves at every 1hz increments -- I'd never known it was there.

Considering 1/2 steps are 10hz apart at that frequency... a 2hz wide dip, that is halfway between notes will never be noticed.

The whole point (to me anyway) in this discussion, is to be aware of what path lengths 'can' create issues and at what frequency, and how to avoid making mistakes in the folding process. However, if you make a cabinet and have something you can't live with. (like my 2x2x4 cabinet) Knowing what to look for in trying to salvage a cabinet, gives you options to make it 'better.' In the case of that cabinet... 2 small reflectors made things better.

[Brian Steele]

Originally Posted by jbell

I prefer an approach (voodoo or not) that works at 2.83v AND at 28v and louder.... and doesn't require a can opener and a pet to make modifications.

...and I prefer an approach that depends on known theory (no "horn voodoo"), and can be simulated by software that allows me to optimize the design before cutting a single piece of wood.

BTW, if it wasn't obvious, the dogfood cans (which were full btw, no can-opener required!) were only deployed temporarily, to determine the effect of changing the horn's topology at a particular point to see if the THAM "notch" can be effectively dealt with without significantly altering the design. As I fully expected, the effect can also be modelled (and optimized) via Akabak - no voodoo involved .

Next step is to replace the cans with something a bit more permanent, and I can use Akabak to model the effect before ever cutting a piece of wood.

Whether or not the modification has any significant impact on the horn's response @28V remains to be tested.

[tb46]

Hi,

Interesting stuff Brian, I think we're all waiting for your high SPL results.

As an aside, I compared the THAM15 to the SS15:

Regards,