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Old 23rd March 2008, 10:56 AM   #1
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Default 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.
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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Old 23rd March 2008, 10:57 AM   #2
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And the SPL plot:
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Old 24th March 2008, 01:56 AM   #3
GM is offline GM  United States
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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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File Type: gif ambiorix 14.14-109.51 hz conic th.gif (13.3 KB, 823 views)
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Old 24th March 2008, 04:51 AM   #4
pkm is offline pkm  New Zealand
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Perhaps talk to this guy

http://www.speakerplans.com/forum/fo...TID=12356&PN=5

Click the image to open in full size.

I see in your input page, that its a small design. Have you checked that excursion isnt exceeded with that input power? Id consider going slightly larger/larger woofer for shorter path length.
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Old 24th March 2008, 09:27 AM   #5
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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. ) 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.
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Old 24th March 2008, 09:32 AM   #6
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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.
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Old 24th March 2008, 10:32 AM   #7
pkm is offline pkm  New Zealand
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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.
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Old 25th March 2008, 05:37 PM   #8
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Quote:
Originally posted by pkm

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/p...em/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!
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Old 25th March 2008, 06:57 PM   #9
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Quote:
Originally posted by pkm
Perhaps talk to this guy
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.
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Old 25th March 2008, 11:08 PM   #10
pkm is offline pkm  New Zealand
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Quote:
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.
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