P.O.C. #2 - Compact Tapped Horn

[Brian Steele]

Hi Everyone:

Please critique, thanks:

Driver params:
Sd: 855.30 cm^2
Cms: 1.73 E-04
Mmd: 88.63
Re: 6.20
BL:20.50
Rms:3.92
Le:2.49
Xmax=6mm

Tapped Horn:
S1=550 cm^2
S4=2000 cm^2
L12=22 cm
L23=239 cm
L34=22 cm

Folding: similar to http://www.diysubwoofers.org/project...struction.html
Net depth works out to about 72 cm or so. Height and width depend on what dimensions I choose for the cross-section, but should be somewhere around 80 * 64 cm (net)

First two folds stuffed with polyester fiberfill. Speaker mounted with magnet facing into mouth (but I will experiment)

Predicted Result ~ 120dB @ 100W from 40 Hz to 100 Hz without exceeding Xmax. Stuffing should actually improve the response above 100 Hz (based on P.O.C. #1 results). Will likely experiment with the amount used - the removable side panel gives me access to all sections of the "horn".

Use - stacks of 2, 4 or even 8 , to provide everything below 100 Hz . Small club, or back of truck, LOL. Will likely adjust dimensions to be able to get 4 across back of a flatbed truck, if possible.

Note: vented 3.6 cu.ft. will get a dB or two higher above 60 Hz, but at double the power (and I'm going to bet that power compression is going to remove that advantage anyway).

Any suggestions welcome (including "you idiot - don't do that!, LOL)

[bjorno]

Originally Posted by Brian Steele

Hi Everyone:

Please critique, thanks:..

Any suggestions welcome (including "you idiot - don't do that!, LOL)

Hi Brian,

You won't get any negative critique from me other than a reminder that 12 dB HP filter is needed at 30 Hz.
This TH, easy to integrate to most main speakers would work IMO nice at 70 W input producing more than 117 dB SPL above 40 Hz.

The driver brand?

b

[Brian Steele]

Originally Posted by bjorno

Hi Brian,

You won't get any negative critique from me other than a reminder that 12 dB HP filter is needed at 30 Hz.
This TH, easy to integrate to most main speakers would work IMO nice at 70 W input producing more than 117 dB SPL above 40 Hz.

The driver brand?

b

Thanks..

The driver brand? I'm going to keep that secret for now - but will disclose later, if this project goes forward. It's a reliable brand - I'll leave it at that .

I forgot to mention that I'm considering implementing this as a "stepped" horn, i.e. four sections of constant cross-section, rather than a conical taper from S1 to S4. If I've understood things correctly, this would likely introduce response abberations, but above the TH's cutoff frequency (I hope!). To do this, I'll basically be dividing the box into 4 segments of increasing volume from throat to mouth, like indicated in the diagram below (ignore the dimensions given).


I'm not sure how to model this in HornResp though.

[GM]

No way to model it in HR, it doesn't have enough segments to create the transitions, but AkAbak can AFAIK plus it can do stuffing effects. Anyway, even with only two usable octaves, IME you'll need at least five pipe segments, three for the ~120-60 Hz octave and two for the ~60-30 Hz one.

Then again, my experience is with higher BW compression horns where our hearing acuity is better, so looking forward to your results.

GM

[Brian Steele]

Originally Posted by GM

No way to model it in HR, it doesn't have enough segments to create the transitions, but AkAbak can AFAIK plus it can do stuffing effects. Anyway, even with only two usable octaves, IME you'll need at least five pipe segments, three for the ~120-60 Hz octave and two for the ~60-30 Hz one.

Then again, my experience is with higher BW compression horns where our hearing acuity is better, so looking forward to your results.

GM

I'm unfamiliar with Akabak - looks like another tool I'll have to start getting familiar with

Each segment in this "horn" is going to be around 71 cm. Some notes from Danley (copied here - http://techtalk.parts-express.com/sh...d.php?t=212802) suggest that 1m segments start having a serious impact around 200 Hz, so I'm thinking that the impact of these 71 cm long "steps" might occur a bit higher - and out of the TH's passband.

I've run into another "issue" though - it looks like a simple EBS design in a smaller box (~ 5.5 cu.ft.) with the same driver can produce the same low-end response at similar theoretical SPL levels, albeit at lower efficiency (220W needed).

I might still build P.O.C#2, but I'm now wondering about its practicality....

[Don Hills]

Here's an Akabak script and SPL graph for your design, for both the theoretical (conical) model and the stepped model with 4 segments. There's not a lot of difference at the frequencies of interest. Note the deeper notches at high frequencies in the stepped version, as predicted.



Def_Driver 'Driver'

Sd=855.30cm2
Bl=20.50Tm
Cms=1.73E-04m/N
Rms=3.92Ns/m
fs=37.7004Hz |Mmd = 88.63g not recognised by AkAbak, fs calculated and used instead
Le=2.49mH
Re=6.20ohm
ExpoLe=1


System 'Conical'

Driver Def='Driver' 'Driver_C'
Node=1=0=12=14

Waveguide 'W1'
Node=11=12
STh=550cm2
SMo=912.5cm2
Len=71cm
Conical

Waveguide 'W2'
Node=12=13
STh=912.5cm2
SMo=1275cm2
Len=71cm
Conical

Waveguide 'W3'
Node=13=14
STh=1275cm2
SMo=1637.5cm2
Len=71cm
Conical

Waveguide 'W4'
Node=14=15
STh=1637.5cm2
SMo=2000cm2
Len=71cm
Conical

Radiator 'RC'
Node=15
SD=2000cm2


System 'Stepped'

Driver Def='Driver' 'Driver_S'
Node=1=0=22=24

Duct 'D1' Node=21=22
SD=550cm2 Len=71cm

Duct 'D2' Node=22=23
SD=1033.3cm2 Len=71cm

Duct 'D3' Node=23=24
SD=1516.6cm2 Len=71cm

Duct 'D4' Node=24=25
SD=2000cm2 Len=71cm

Radiator 'RS'
Node=25
SD=2000cm2

[GM]

Originally Posted by Brian Steele

Some notes from Danley........

I've run into another "issue" though - it looks like a simple EBS design in a smaller box (~ 5.5 cu.ft.) with the same driver can produce the same low-end response at similar theoretical SPL levels, albeit at lower efficiency (220W needed).

I might still build P.O.C#2, but I'm now wondering about its practicality....

His example is a much faster expanding expo flare whereas yours is very slow expanding, so kind of surprised that AkAbak predicts minimal variance in the intended pass-band.

Yeah, driver specs dictate different optimal pass-bands for different loading schemes, so if it performs best overall in an EBS........... Still, less power = lower distortion if the intended app requires high SPL and once damped, the TH will have a flatter phase response which may/may not be a plus depending on the details of the app.

GM

[Brian Steele]

Originally Posted by Don Hills

Here's an Akabak script and SPL graph for your design, for both the theoretical (conical) model and the stepped model with 4 segments. There's not a lot of difference at the frequencies of interest. Note the deeper notches at high frequencies in the stepped version, as predicted.



Def_Driver 'Driver'

Sd=855.30cm2
Bl=20.50Tm
Cms=1.73E-04m/N
Rms=3.92Ns/m
fs=37.7004Hz |Mmd = 88.63g not recognised by AkAbak, fs calculated and used instead
Le=2.49mH
Re=6.20ohm
ExpoLe=1


System 'Conical'

Driver Def='Driver' 'Driver_C'
Node=1=0=12=14

Waveguide 'W1'
Node=11=12
STh=550cm2
SMo=912.5cm2
Len=71cm
Conical

Waveguide 'W2'
Node=12=13
STh=912.5cm2
SMo=1275cm2
Len=71cm
Conical

Waveguide 'W3'
Node=13=14
STh=1275cm2
SMo=1637.5cm2
Len=71cm
Conical

Waveguide 'W4'
Node=14=15
STh=1637.5cm2
SMo=2000cm2
Len=71cm
Conical

Radiator 'RC'
Node=15
SD=2000cm2


System 'Stepped'

Driver Def='Driver' 'Driver_S'
Node=1=0=22=24

Duct 'D1' Node=21=22
SD=550cm2 Len=71cm

Duct 'D2' Node=22=23
SD=1033.3cm2 Len=71cm

Duct 'D3' Node=23=24
SD=1516.6cm2 Len=71cm

Duct 'D4' Node=24=25
SD=2000cm2 Len=71cm

Radiator 'RS'
Node=25
SD=2000cm2

Thanks for this Don.

I've got two questions though....

1. How did you come up with the equivalent duct sizes? I just averaged the volumes for each section, and came up with the following: S1=731.5 cm^2, S2=1093.75 cm^2, S3=1456.25 cm^2 and S4=1818.75 cm^2. Your method looks like it's obviously more accurate, as the resulting response looks pretty close to the unstepped horn.

2. The low frequency response predicted by AkAbak seens a bit different to the HornResp model - see attachment. Any ideas why, and if so, which is more reliable? If it helps, I'm using 2*Pi for the HornResp model.

Thanks again...

[Brian Steele]

Originally Posted by GM

Yeah, driver specs dictate different optimal pass-bands for different loading schemes, so if it performs best overall in an EBS........... Still, less power = lower distortion if the intended app requires high SPL and once damped, the TH will have a flatter phase response which may/may not be a plus depending on the details of the app.

GM

I'm having a hard time deciding what's best here. The actual subs, if they actually ever get built, and I'm thinking of building several, will be used to provide bass for small club (type of music played is typically hip-hop, R&B, that sort of thing). Not sure of the floor space, but it can fit up to 350 people comfortably. There's also a good chance that they'll be dragged onto a flatbed truck at least once a year for a more, um, "mobile" experience .

I like the idea of a lower Pe requirement. OTOH, the TH takes up about 13 ft. net - enough space to use two of these 15" drivers in an EBS alignment. The driver in question is about $140 US, to it might make sense to just spring for the extra $140, ramp up the watts (and watts are cheap these days) and enjoy 6dB more output capability in something that not only takes up less space than the TH, but has a greater bandwidth as well.

[Don Hills]

Originally Posted by Brian Steele

Thanks for this Don.

I've got two questions though....

1. How did you come up with the equivalent duct sizes? I just averaged the volumes for each section, and came up with the following: S1=731.5 cm^2, S2=1093.75 cm^2, S3=1456.25 cm^2 and S4=1818.75 cm^2. Your method looks like it's obviously more accurate, as the resulting response looks pretty close to the unstepped horn.

2. The low frequency response predicted by AkAbak seens a bit different to the HornResp model - see attachment. Any ideas why, and if so, which is more reliable? If it helps, I'm using 2*Pi for the HornResp model.

Thanks again...

1. You said 4 sections. Throat is 550cm2 and mouth is 2000 cm2.
Therefore first section is 550cm2, last section is 2000 cm2. Middle 2 sections:
2000 - 550 = 1450
1450 / 3 = 483.3
550 + 483.3 = 1033.3cm2
2000 - 483.3 = 1516.6cm2


2. Ah, you spotted my deliberate mistake - well, that's my excuse anyway. I messed up, I put the driver 71 cm in from the ends instead of 22 cm.
Here is the revised script and SPL graph:

Def_Driver 'Driver'

Sd=855.30cm2
Bl=20.50Tm
Cms=1.73E-04m/N
Rms=3.92Ns/m
fs=37.7004Hz |Mmd = 88.63g not recognised by AkAbak, fs calculated and used instead
Le=2.49mH
Re=6.20ohm
ExpoLe=1


System 'Conical'

Driver Def='Driver' 'Driver_C'
Node=1=0=12=13

Waveguide 'W1'
Node=11=12
STh=550cm2
SMo=630.29cm2
Len=22cm
Conical

Waveguide 'W2'
Node=12=13
STh=630.29cm2
SMo=1854.85cm2
Len=239cm
Conical

Waveguide 'W3'
Node=13=14
STh=1854.85cm2
SMo=2000cm2
Len=22cm
Conical

Radiator 'RC'
Node=14
SD=2000cm2


System 'Stepped'

Driver Def='Driver' 'Driver_S'
Node=1=0=22=26

Duct 'D1a' Node=21=22
SD=550cm2 Len=22cm

Duct 'D1b' Node=22=23
SD=550cm2 Len=49cm

Duct 'D2' Node=23=24
SD=1033.3cm2 Len=71cm

Duct 'D3' Node=24=25
SD=1516.6cm2 Len=71cm

Duct 'D4a' Node=25=26
SD=2000cm2 Len=49cm

Duct 'D4b' Node=26=27
SD=2000cm2 Len=22cm

Radiator 'RS'
Node=27
SD=2000cm2


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