DIY bDEAP experiences anyone

From the Colaborative Tapped Horn thread some people will already know that I'm seriously looking into converting my oversized vented sub into something more efficient.

After coming to the conclusion that my driver is not suited for a Tapped Horn, I started looking into a compromised back loaded horn.
Eventually I ended up with a bDEAP, which gave the 5dB rising slope I wanted over the passband to compensate for room gain (is this correct?) and had less ripple over that band than a regular BLH of the same size. By altering the flare of the external airpath it can also be more "dialled into the room" than other designs.

After searching the net and this forum for DIY bDEAP attempts, I found suprisingly little ... Hence my question for people their experiences with this and most important their in-room responses.

Also I read about a bDEAP-R that was designed for HT use and that was in the making but doesn't seem to have made it outside of SPL Labs basement. :D
Anyone can fill me in on that? I think what I have cooked up comes rather close to a HT-optimised bDEAP, but with less SPL capability (Danley gets all the fun!)





With Leach' math I came up with the basic parameters and then I adjusted some according to HornResp's trial-and-error. I'll see to post my findings tomorrow after work.
Final adjustments will be made with AkAbak *after* I tried the folding work maybe later this week.

Volume is 125L and the second segment is the External air path of 90L (70% extra horn!)
Design goal is to have flat in-room response from 30-80Hz (I have a variable low pass <150Hz on both the plate amp and my PC) and to get 115dB ref level output over that band.
 

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In theory, room gain is 12 dB/octave below the 1st mode, but it varies quite a bit in the real world, so you really need to measure yours if trying to design a complementary speaker response. For instance, in my room there's little gain in the audible BW other than boundary gain and even then I'm only getting ~half the theoretical due to a floating floor and the so-so construction builders can get away with down here in the Deep South.

WRT a HT B-DEAP, all I recall is stacking two spaced near a corner for a client.

Hmm, a B-DEAP uses dual 12" drivers, so it seems reasonable that it would make more SPL and be smoother than your single 8"? driver variant.

Anyway, your driver looks OK for a TH to me:

GM
 

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Hi!

I recall the +-5dB rising slope from somewhere in the TH thread, but indeed it should be best to measure the room behaviour.
The only measuring equipment I have right now is a RadioShack-like SPL meter available here in Europe. Guess I could see for a good calibrated mic to hang on my sound card someday ...
The sub I have now is dead flat till 30Hz (simulated) and deep down low there is to the ear more output in-room, probably due to room gain and/or room modes. (I find it not too disturbing, but a friend of mine said it sounded like the amp didn't had the cone under control. Since his system's output stops at 60Hz I recon he just never heard anything lower than that.)
Anyway, having a gentle slope will make it blend in the room better than a maximally flat one methinks.

It's indeed an 8", as this was what I bought 2 years ago. The plate amp that I purchased with it, has a rumble filter at 25Hz, so no point in going below 30Hz like with your TH GM. It's also a LOT larger than my bDEAP, even with the external airpath included. (If I'm moving out of the house in the future, I want something more manageable than my current 4 feet tall "Pillar" that barely fits into the car and is *just* portable for one strong man. :xeye: ) What I meant about my TH was that I couldn't get a satisfactory response within the 125L limit. Tapped Horns need a certain size and it seems a good compromised BLH is a better spot in the spectrum in this case. (ie with this driver.)

pkm's comment about the excursion is also a good one: I recall the driver having a 6mm xmax, but on an other site it is rated as only 3mm. Anyway, with both 6mm or 3mm input in HornResp, I still get the 115dB with my bDEAP, while the TH tops out around 105dB. As there are multiple reportings of the limited excursion of TH's Vs simulations, this SPL number could be higher, but still ...

I have seen the 4-driver PA bDEAP you mentioned while googleing around. If I recall correctly, it stops around 45Hz but he hasn't had time to fully test it yet. I shall read the thread again to see which compromises he made to get till that cutoff. I'll post my findings from the HornResp simulations in the next post.
There you'll see why I choose such a large throat area (no larger/more woofer(s) needed for the path length/given volume) and the lower taper to get till 30Hz in such a small package.
 
It's partly in Dutch, but you'll get the point.


****************************
voor 30-120Hz via ML-Util

27 liter back chamber
180 throat
2,3 Liter front
49Hz voor reactance annull
gaat tot 164 Hz
Voor 125L kast: 180-1225 area en 175cm lang (30Hz taper)
--------------: 180-879 area en 217cm lang (20Hz taper) (beste wegens 1/4WL total path))
--------------: 200-901 area en 206cm lang (20hz taper)
--------------: 220-914,43 area en 195cm lang (20hz taper)
--------------: 110-808,38 area en 273cm lang (20hz taper)
--------------: 180-732 area en 240 cm lang (16Hz taper) (beste met XMAXProt filter)
****************************

*Low expansion rate and long pathlength gives a certain minimum lower corner (from the pathlength?), and modifying the external expansion rate only improves the ripples on the upper cutoff. The rising slope over the passband is only slightly modified.
*Higher expansion rate and less pathlength gives a higher cutoff (like a full horn of higher expantion rate) and more sensitivity, modifying the external path lowers the lower knee somewhat but mostly increases ripple on the upper knee. The rather flat slope over the passband stays almost the same, albeit with more ripples.
*So far the best compromise by trial and error is to make sure that the sum of the internal and the external airpath (=height of cabineth) is exactly 1/4 WL of the desired lower knee. To maximise the mouth area of the cabineth - and because of that the external volume of the horn! - we should take a compression ratio of 1:1 and so the path length for a given volume of horn becomes rather short. To circumvent this and to make sure the lower knee specification is met, use a taper of 2/3 of the desired lower responce freq. For 30Hz, this is a 20Hz taper.
All this should give a bDeap subwoofer with about 5dB/octave gently rising slope from the lower knee till about 2 octaves higer up, that complements the average room gain. Cabineth volume is such that the external part of the horn is maximized, and the internal taper+pathlength is so that there is maximum flexibility to adapt the external taper (and the rising of the slope) for more subbass or for better midbass+sensitivity.
 
A rising slope to partly fit in with room gain is sensible. There should be an approximate RS SPL meter calibration chart,since the response is knowningly ruined by some parts on the board(rusty memory)
I remember seeing a site associated with speaker workshop,where components were changed to help fix response.


3mm isnt much - I think that this could be the limiting factor - high harmonic distortion could be interpreted as 'the amp losing control'

Im interested in this - since many car audio 8"-12" subwoofers are very cheap here,and I dont want a 1cubic foot 84dB box.

Certainly,his design is different,being a PA design for 45hz - 150hz.But atleast you can see some one elses results.
 
pkm said:

Certainly,his design is different,being a PA design for 45hz - 150hz.But atleast you can see some one elses results.

His simulation plots are moved in Photobucket, so they are no longer visible in the thread. However I managed to find them in his photobucket archive:

http://s128.photobucket.com/albums/p188/rave-roborg/new system/simulation/

By inputting his area's and length in HornResp's exponential apex designer tool it seems he has a 30Hz taper of 1/4WL long.

I haven't had time to sim one cab to see if his 45-50Hz output from his single-cab tests (his second one is in the making) is also seen in the sim, but from what I've simmed with my design in free space, I think it is pretty much spot on.
So far it seems he'll hit 30Hz when he has all his cabs. Nice!
 
Great work, but after building a set of LABs, I swore I'd never do anything so complicated again.

Nice thing about the thread was the B-Deap drawings drom djk (who always seems to have all the guff on speakers) early in the thread.
agree - woodworking is well above my level of skill

DJK has all the hints and lore.

I think that pic is from the Patent.
 
I reversed engineered a single cab in half space in HornResp:
There is a flat response (+-3dB) from 40Hz upwards, which is what he found out from his test. When simming 2 cabs or more in 1/4th or 1/8th space, one quickly gets CIR>1 in HornResp, which makes me wonder if there will be actual output till 30Hz with his full system. Sure there will be enough, but it starts to descend around 45-50Hz while I would expect it to stay flat till 30Hz.
But I'm nitpicking ... :D

Time to fold my design, stay tuned!

Edit: So the patent for b-DEAP was never awarded? Not that I'm going to build and sell them, but if I want to replace this one later in life, at least it won't end up in a bonfire with the driver and amp gathering dust on the shelf.
 

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Done a first pass of the folding process.

3 bends of 180° and I ended up 12cm outside the bottom of the cabinet, making everything about 19liters larger than expected.
The back chamber (27 liters) takes up quite some drawing-space, so with my next folding attempt I'll go for 20liters and use stuffing to compensate.

I'll search the forum later for some volume Vs stuffing guidelines .
 
Here is one of my previous attempts where I ended up outside the cabinet. Before realizing the first (rectangular) part of the horn took more than 10 liters extra off the volume. After that I made the back chamber triangular and made the front chamber zero liters (about 1L in reality from area under the cone.)

I made an excell/calc-openoffice spreadsheet that calculates the length of a straight piece + the 90° bend after that, based on the cross sectional area's at those points.
You just put in the numbers till the (straight segment+bend) length is equal to the available cabineth width.

Saves ages in recalculating and redrawing once you get the hang of it. I'll post it later if some people want.
 

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It has been a while since I could continue my work, but here it goes:
I translated my drawing into this AkAbak script:

------------------------------

Def_Driver 'Driver'
Sd=218.00cm2
Bl=7.60Tm
Cms=1.21E-03m/N
Rms=2.21Ns/m
fs=27.9192Hz |Mmd = 25.00g not recognised by AkAbak, fs calculated and used instead
Le=0.60mH
Re=6.20ohm
ExpoLe=1

System 'System'
Driver Def='Driver''Driver'
Node=1=0=300=200

Enclosure 'BackChamber'
Node=300
Vb=0,027m3

Waveguide 'Totdrvr'
Node=199=200
WTh=0,22m
HTh=0,065m
WMo=0,22m
HMo=0,08m
Len=0,15m
Conical

Waveguide 'EersteCon'
Node=200=201
WTh=0,22m
HTh=0,08m
WMo=0,22m
HMo=0,12m
Len=0,535m
Conical
Vf=0,001m3 | Onder Cone

AcouMass 'Ma1a' Node=201=202
Ma={1.85/0.12} | 90° bend Ma=1.85/WD

AcouMass 'Ma1b' Node=202=203
Ma={1.85/0.135} | 90° bend Ma=1.85/WD


Waveguide 'TweedeCon'
Node=203=204
WTh=0,22m
HTh=0,135m
WMo=0,22m
HMo=0,185m
Len=0,52m
Conical


AcouMass 'Ma2a' Node=204=205
Ma={1.85/0.185} | 90° bend Ma=1.85/WD

Waveguide 'DerdeCon'
Node=205=206
WTh=0,22m
HTh=0,22m
WMo=0,22m
HMo=0,23m
Len=0,05m
Conical

AcouMass 'Ma3a' Node=206=207
Ma={1.85/0.23} | 90° bend Ma=1.85/WD

Waveguide 'LaatsteCon'
Node=207=208
WTh=0,22m
HTh=0,23m
WMo=0,22m
HMo=0,475m
Len=0,425m
Conical

Duct 'Mond"
Node=208=209
WD=0,295m
HD=0,295m
Len=0,01m



Radiator 'Horn mouth'
Node=209
SD=870cm2

--------------------------------------

I used the AcouMass element for the bends of the folded horn, according to the manual. The formula is for 90° bends with constant diameter, but I guess for 180° bends the sum of two 90° bends with the diameter of the throat and mouth of the bend, gives a good approximation/average.

So far I get lower extension than in HornResp (mass loading of the last segment???) and the high frequenties are much smoother than I tought. (Damping from the AcouMass element? Folding a horn reduces HF output, so this would be as expected.)

I will try again later to add Reflection to simulate the corner loading, as I can't seem to get it right this time.
:dead:
 
AkAbak Vs HornResp in Corners

I simulated the corner loading by adding an extra waveguide for the external airpath and then putting the Radiator Element at the appropriate spot in the corner.

I'm not going to fret about 2-3dB difference, but I clearly get 10dB *less* SPL in AkAbak than with HornResp, while the slope of the curve stays about the same.
Either one of the programs is very optimistic/pessimistic about corner loading or else I forgot something in AkAbak which I think not ...

Time to do some more thinking or get some clues ... :confused:

(Script omitted for the moment, my posts/monologues are getting long!)
 

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Let them be long, hopefully one of these days before I become completely brain dead I want to at least semi-master AkAbak, so will need all the sims and associated supporting data I can round up.

WRT corner loading, none of the programs I've used match up well with rooms I've measured, being somewhat optimistic down low, so assume they are based on a theoretically infinitely massive/stiff construction, ergo maybe AkAbak with rare exception (underground basement, bomb shelter, etc.) is more realistic.

GM