Beyma 18P80Nd in sub horn: Am I missing something?

[Thijs666]

Hi all,

I've been lurking around here for quite some time now and I'm very enthusiastic about the subhorn designs you guys come up with. Encouraged by the possibilities, I started playing around with Hornresp. With the help of some excellent tutorials (thank you lilmike form AVS), I am starting to get the hang of it.

Now for the reason I started this thread: lately I had the chance to buy a smoked Beyma 18P80Nd for a nice price. I still have to receive it (eBay purchase ), but a recone kit can be ordered for €110, so it's quite a bargain if it all works out, I guess. I really would like to come up with a solution for using electric drums on stage (I'm a drummer) and I hope to work out a subwoofer integrated in a drum riser/stage/E-drum set, so I would be able to set up in the blink of an eye.
This drum riser can be as large as 155x94x70 cm, but that would included the e-drum set as well, so I'd like the height to be limited to around 50 cm (or so), otherwise I won't be able to get the whole rig into my car...

So I started working on some horn designs using the 18P80 and the (15.5x9.4x5.0 dm) ~ 700L available. I came up with these. Please tell me what you think about it, as I am wondering if these numbers are to good to be true ...

Tapped horn 700 L:

800 watts:

Front loaded horn 650 L:

800 watts:

Front loaded horn 700 L:

800 watts:

Measurements of the final build here: Measurements: Keystone vs Titan 48 vs Drumriser (homebrew)

 

[epa]

hallo thijs
the sims look ok.
but there a difference between simulated volume ,and actual(bild)volume.
this can be 25~35% bigger .
so a sim of 500 ltr could turn out to be a huge 750 ~850 ltr cab.
other then that the beyma seems to work verry nice in a th.
what are you going to use for mid/high frequentie?

 

[Thijs666]

hallo thijs
the sims look ok.
but there a difference between simulated volume ,and actual(bild)volume.
this can be 25~35% bigger .
so a sim of 500 ltr could turn out to be a huge 750 ~850 ltr cab.
other then that the beyma seems to work verry nice in a th.
what are you going to use for mid/high frequentie?

Hoi Eric,
Isn't the compression ratio of the first fl a little too high (3,59:1) for an 18"?

I did realize there would be a difference in volume, but that big !? I am contemplating to build with 12mm BB on the outside and 10-12 mm underlayment on the inside, with lots of internal bracing and save a little on volume as well as weight. I have 2 T48s in 21" width (they are built with 12mm BB sides and 10mm underlayment internals) that work quite good, but I don't really have a reference since I'm not a pro. I know this probably isn't recommended, but the underlayment is cheap as sh*t, so it practically only costs me my free time.

Yes, the th seems to have the edge in spl. But since xmax (linear) is 'only' 7.5mm, wouldn't the flh with its lower diaphragm displacement values be less prone to power compression and thus ultimately be able to approach the simulated spl?

And how about the dip in the th between 100~200 Hz? Would the flh be able to play higher? Or is that going to sound really 'boxy'? (I know my T48's don't sound very nice above 120Hz)

I'm not sure yet on the mid/high. Any suggestions ? For the time being I think I will use my DR200s.

 

[epa]

taking a closer look,yes it th cr is a bit high for an 18". 2:1 is reccomended for 18"
working with 12 mm ,and not use angled corner pieces,wil help getting the total volume down.
ofcourse it al depends on the layout.

lower diagram displacement also means less cooling from the pole piece.
id say the th is x-max limited ,and the flh power limited.
both need a highpass filter.
the th hpf can be set lower then the flh hpf in your examples.

the flh wil play much higher.
the th, if you make the th s2 area smaller the dip wil be smaller.

if i understand corectly you wil be using this only as a backline for drums?

 

[Thijs666]

lower diagram displacement also means less cooling from the pole piece.
id say the th is x-max limited ,and the flh power limited.
both need a highpass filter.
the th hpf can be set lower then the flh hpf in your examples.

the flh wil play much higher.
the th, if you make the th s2 area smaller the dip wil be smaller.

Thanks! The way I interpreted the displacement figures was that the flh's -in theory- wouldn't need a high pass filter, since 26mm is never reached with 800 watts... (not that I wouldn't implement one!). But I didn't think of the cooling factor. Good one!

Adjusting S2... something like this? (cr raised to 1.90:1)

800 watts:

if i understand corectly you wil be using this only as a backline for drums?

Yes . And perhaps I will allow the bass player to plug in if he needs some back up on the lows, but I think it'll be difficult to get a balanced sound without a sound guy.
Of course with proper PA it won't be needed, but that has practically never happened where I played up to now (mostly cafe's).

 

[epa]

yes this looks nice
if you look at the excursion plot ,you can put the hpf at 35 hz and boost 35hz with 6 db with a q of 2.
that way you can extend the sound to a nice 35 hz f3
do you want me to model something like that.
specify the outher dimensions.

erik
edit 155x94x50cm?

 

[epa]

here is a scetch
simple design.
easy tuneable by cutting off the front bafle (red)eg mouth gets bigger and the hornpath shorter.

 

[Thijs666]

Wow Erik! That's easy indeed . I must be the millionth one asking which software you use (or is recommended)? I tried looking for it on the forum, but for some reason it doesn't come up in the results. I must be using the wrong search term . I found a thread with spreadsheets for laying out the horn though. Haven't had the time to read through it though...hopefully tomorrow.

I'll save your design locally, just in case. Thanks again .

 

[epa]

hoi thijs
i use autocad,
but people on this forum sugest sketchup.
i wil check the exact measurments and a detailed drawing.

 

[Thijs666]

Finally I think I was able to translate this design into akabak. Here's what I've come up with:

|DATA EXPORTED FROM HORNRESP - RESONANCES NOT MASKED

|COMMENT: Beyma 18P80/Nd Tapped horn 700L EPA

|~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

|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 = 2.83V 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 = 252.00e-4; |Horn segment 1 throat area (sq m)
S2 = 833.00e-4; |Horn segment 1 mouth area and horn segment 2 throat area (sq m)
S3 = 1095.00e-4; |Horn segment 2 mouth area and horn segment 3 throat area (sq m)
S4 = 1571.00e-4; |Horn segment 3 mouth area and horn segment 4 throat area (sq m)
S5 = 1190.00e-4; |Horn segment 4 mouth area and horn segment 4 throat area (sq m)
S6 = 1761.00e-4; |Horn segment 5 mouth area and horn segment 4 throat area (sq m)
S7 = 2570.00e-4; |Horn segment 6 mouth area and horn segment 4 throat area (sq m)
S8 = 1999.00e-4; |Horn segment 7 mouth area and horn segment 4 throat area (sq m)
S9 = 2047.00e-4; |Horn segment 8 mouth area and horn segment 4 throat area (sq m)
S10 = 3046.00e-4; |Horn segment 9 mouth area and horn segment 4 throat area (sq m)
S11 = 2245.00e-4; |Horn segment 10 mouth area and horn segment 4 throat area (sq m)
S12 = 2475.00e-4; |Horn segment 11 mouth area and horn segment 4 throat area (sq m)
S13 = 2951.00e-4; |Horn segment 12 mouth area and horn segment 4 throat area (sq m)
S14 = 3998.00e-4; |Horn segment 13 mouth area (sq m)

L12 = 30.00e-2; |Horn segment 1 axial length (m)
L23 = 40.00e-2; |Horn segment 2 axial length (m)
L34 = 10.00e-2; |Horn segment 3 axial length (m)
L45 = 10.00e-2; |Horn segment 4 axial length (m)
L56 = 85.00e-2; |Horn segment 4 axial length (m)
L67 = 21.00e-2; |Horn segment 4 axial length (m)
L78 = 21.00e-2; |Horn segment 4 axial length (m)
L89 = 10.00e-2; |Horn segment 4 axial length (m)
L910 = 21.00e-2; |Horn segment 4 axial length (m)
L1011 = 21.00e-2; |Horn segment 4 axial length (m)
L1112 = 1.20e-2; |Horn segment 4 axial length (m)
L1213 = 38.00e-2; |Horn segment 4 axial length (m)
L1314 = 33.00e-2; |Horn segment 4 axial length (m)

Ap1 = 1225.00e-4; |Throat chamber port cross-sectional area (sq m)
Lpt = 1.80e-2; |Throat chamber port tube length (m)

Vtc = 2200.00e-6; |Throat chamber volume (cubic m)
Atc = 1225.00e-4; |Throat chamber cross-sectional area (sq m)

|Parameter Conversions:

Sd = 1225.00e-4; |Diaphragm area (sq m)

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-Segment-13-Segment-14-Segment-15-Segment-
|16-Segment-17-Segment-18-Segment-19-Segment-20-Segment-21-Radiator

|~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Def_Driver 'Driver'

Sd=1225.00cm2
Bl=21.90Tm
Cms=1.93E-04m/N
Rms=2.34Ns/m
fs=30.00Hz |Mmd = 121.16g not recognised by AkAbak, fs calculated and used instead
Le=1.90mH
Re=5.10ohm
ExpoLe=1

System 'System'

Driver Def='Driver''Driver'
Node=1=0=5=20

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

Duct 'Port'
Node=4=9
SD={Ap1}
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=12=11
STh={S5}
SMo={S4}
Len={L45}
Conical

Waveguide 'Horn segment 5'
Node=12=13
STh={S5}
SMo={S6}
Len={L56}
Conical

Waveguide 'Horn segment 6'
Node=13=14
STh={S6}
SMo={S7}
Len={L67}
Conical

Waveguide 'Horn segment 7'
Node=15=14
STh={S8}
SMo={S7}
Len={L78}
Conical

Waveguide 'Horn segment 8'
Node=15=16
STh={S8}
SMo={S9}
Len={L89}
Conical

Waveguide 'Horn segment 9'
Node=16=17
STh={S9}
SMo={S10}
Len={L910}
Conical

Waveguide 'Horn segment 10'
Node=18=17
STh={S11}
SMo={S10}
Len={L1011}
Conical

Waveguide 'Horn segment 11'
Node=18=19
STh={S11}
SMo={S12}
Len={L1112}
Conical

Waveguide 'Horn segment 12'
Node=19=20
STh={S12}
SMo={S13}
Len={L1213}
Conical

Waveguide 'Horn segment 13'
Node=20=21
STh={S13}
SMo={S14}
Len={L1314}
Conical

Radiator 'Horn mouth'
Node=21
SD={S14}


I tried to take the corner bends into account, but I'm not sure I did it correctly .

Here's the graph:

Any suggestions are welcome

 

[Thijs666]

Oh, and by the way, I took a shot at Autocad... not my kind of program . I'm ok with Photoshop, but autocad...

And Sketchup doesn't seem to be able to do any sort of complicated calculations.

Of course what I'd really like to be able to do, is set up a design and let the program determine the optimal horn layout . But that's not gonna happen .

 

[epa]

hi thijs
i'm not an akabak guru,but is see some flaws.
vtc should be about 6000 and atc 600,from L45 on,all segments are labeled "4"
but somehow the graph seems right.
i think in reality the low knee is giong to be closer to 40hz.

there seems to be a horn spreadsheet floating around on this forum.
but there's always a human brain drawing program interface needed

 

[Thijs666]

Oops, forgot to correct the labels (you can see which part I copy-pasted ).

vtc 6000? Isn't this 18mm (baffle thickness) x Sd?

And atc isn't equal to Sd? So the baffle cutout should be smaller than Sd? I thought both values were supposed to be the same as I put them in hornresp? What am I missing?

I've found that horn spreadsheet and fiddled around with it. This is as far as I've gotten with it (see zip).

 

[epa]

hr see's a driver as it were a flat piston,if this was the case your inputs were correct.

Volume Throat Chamber of an 18"(volume of the cone)=aprox 6 ltrs(6000cm<3)
Averidge Throat Chamber is about 600 ,so the lenght Throat Chamber wil be about 10 cm.

vtc/atc=ltc


you use lpt1/ap1 for bafle opening wright,i normaly ad the volume of the bafle to the vtc.

so vtc of 8000 and atc 700 comes closest to realety,without the ap1/lpt1 inputs.

it wont make a difference in the spl graph

 

[Thijs666]

Volume Throat Chamber of an 18"(volume of the cone)=aprox 6 ltrs(6000cm<3)
Averidge Throat Chamber is about 600 ,so the lenght Throat Chamber wil be about 10 cm.

vtc/atc=ltc

you use lpt1/ap1 for bafle opening wright,i normaly ad the volume of the bafle to the vtc.

so vtc of 8000 and atc 700 comes closest to realety,without the ap1/lpt1 inputs.

Ok, thanks. Got it

So this would be correct? :

Ap1 = 1225.00e-4; |Throat chamber port cross-sectional area (sq m)
Lpt = 1.80e-2; |Throat chamber port tube length (m)

Vtc = 6000.00e-6; |Throat chamber volume (cubic m)
Atc = 600.00e-4; |Throat chamber cross-sectional area (sq m)

That's with the use of Ap1&Lpt .

I have to admit I don't like it that the sensitivity now is down from about 104dB to just over 100dB per watt . And there's a 3dB dip at 108 Hz. The T48's (of which I own two) claim to do the same and even more starting from 50 Hz in a lot less space using a 15"... Back to the drawing board .

 

[epa]

you got it

I have to admit I don't like it that the sensitivity now is down from about 104dB to just over 100dB per watt

Wel hofmans law says pick any 2 of the 3 low,loud and small.
in you sim it extends down to 35 hz,shortening the horn/bigger mouth wil tune the boxer higher ,resulting in a higher efficientie.
changing layout wil not give you more eff.
however whe could try to decrease the dip.
edit/if you would inverse the driver dip gets smaller.eg make s2 ~550 and take away the throat chamber and port
decrease s3 ,s4 and s5 -250

 

[epa]

increase the mouth to 6000

 

[Thijs666]

increase the mouth to 6000

Already did that. I also reduced S2-S5 (easy to do by modifying the angle of the baffle). The blue graph represents the latest alterations, the bottom black graph is the starting point.

Still a quick & dirty sim, I haven't recalculated the lenghts of the horn segments...

 

[Thijs666]

here is a scetch
simple design.
easy tuneable by cutting off the front bafle (red)eg mouth gets bigger and the hornpath shorter.

Hi Eric,

Since the summer has finally arrive here in holland, I'd like to start building. I have to work outdoors, so my progress will depend strongly on the weather.
I think your design above is the best possible with this driver and the available space I have, so I'd like to build it. Since it's not a particular difficult design, I hope to be able to finish it quite quickly .
I can (and will probably will) take SPL measurements afterwards, but for now, I still need to translate the design into real world wooden panels, which is something I could use some help with .

What I've got so far:
Inner height of the horn = 50 cm
S1=252 -> width of horn (woh) = 252/50 = 5 cm (speaker baffle starts 5cm+thickness of panel from the right side)
Speaker is mounted with center 30cm from the front, measured along the baffle.
S2=835 -> woh = 16.7 cm (woh at center of baffle = 16.7 cm)
Baffle panel is xx(?)cm long. help very much appreciated
S3=1765 -> woh = 35.3cm ('center' panel ends at 35.3 cm from the back panel and about 40cm from the left side panel. that 40 cm is my best guestimate...
Experimenting with the front panel for best performance is needed.

Would you be able to help me a little with the measurements?

 

[epa]

hi thijs
ill put some measurements in the drawing.