Where's the bass from an 18" Audiobahn AW1805Q in a 12cf vented enclosure?

[Max Caliber]

Hi folks

I’m new to posting new threads so pls excuse any errors I may generate.

My problem is that I have a home made 12 cubic foot enclosure (2 x 2 x 3 foot inside dimensions) that I made originally for a JBL 2245H sub that was designed using winISD Pro built with 1” MDF.

The box sounded absolutely great except for one problem the JBL 2245 is not a good driver for a home theater sub as it runs out of xmax too quickly below 20Hz, as the winISD states it can only support 18 watts at 10Hz. Too bad I didn’t appreciate this fact before I purchased the JBL.

I refused to add any type of filter to limit the power below 20Hz as this would have defeated the purpose of the big box that was meant to get these really low earth shaking frequencies.

So in an attempt to salvage the box I purchased a new Audiobahn AW1805Q sub at a reasonable price and popped it into the enclosure. This sub did not have the xmax limitation of the JBL however it’s not producing any real output bass, it seems to be misaligned!

I have two 4 inch vents on the enclosure (I know I should have more or bigger vents but that’s another issue best told later) where the winISD calls for 11.24 inch lengths for a 20Hz resonance and the AW1805Q calls for 11.24 inch vents so I figured that keeping the same vents should have little impact on the sound. Unfortunately, I can hardly get any deep base out of the system.

So seeing how the JBL is a really efficient driver but was limited to 300 RMS (being pushed by a 450 watt amp) the AudioBahn could handle 1200 watts (not sure if this is RMS or peak), so I purchased a Yamaha P7000 amp which is capable of producing 2200watts into 8ohms bridged (the Audiobahn has 2x 4ohm VC wired in series giving the same impedance as the JBL). But even with this amp the Audiobahn just isn’t putting anything decent out (my 12 inch woofer in my ESS monitors running off of 200 watts is putting this sub to shame!). I’ve tested the driver and it seems fine, both VC’s read 3.3 ohms and the cone moves without any friction although its compliance is very stiff (compared to the JBL). The cone does move properly when driven but there’s not much sound output, thus the misalignment theory seems to be the only possible cause.

From this I question whether the winISD is giving the correct information can anybody out there test what an Audiobahn AW1805Q should do in a 12 cf vented enclosure and compare it to winISD?

The winISD TS parameters for the Audiobahn are:
QES 0.440
QMS 5.270
QTS 0.406
FS 23.20 Hz
VAS 4.697 ft^3
Mms 607.3
Cms 0.775 mm/N
Rms 16.79920 N c/m
Re 3.3 ohms
BL 25.76798 N/A
Dd 14.73 in
Le 2.85 mH
Sd 0.1100 m^2
Xmax 26mm peak
Vd 2860 cm^3
Pe 1200 w
No 0.3671
Znom 4.000
USPL 91.65
SPL 87.80
Voicecoils 1
Connection Parallel

Note I had lots of problems getting the winISD to accept the TS parameters for this driver unless I fudged the number of voice coils and set the connection to parallel, and I believe this may have affected the vent length calculations.

Thanks
Philip

[bjorno]

FYI,

No need to use fudged numbers:

b

[Max Caliber]

Originally Posted by bjorno

FYI,

No need to use fudged numbers:

b

Hi bjorno

Thanks for the nice effort its well appreciated. However, is the software you are using not meant for designing Tapped Horns instead of vented (reflex) enclosures, as some of your graphs seem to display? Also I noticed that you used “1” voice coil in your plots whereas the AW1805Q has “2” voice coils at 3.3 ohms each. When I attempted to enter 2 coils in the winISD program, the software would not accept the TS values, thus leaving me to fudge the program using one coil. This IMO may have led me to use the wrong port length resulting in the bass-less box.

The information I really would like to find out is what would be the length of the 2x 4-inch (or 100mm) ports for this sub using both 3.3ohm voice coils (wired in series) and with the sub placed within a 12 cubic foot (or 340 liters) enclosure.

At this time I am also questioning whether the TS parameters I have are correct, if there is anybody out there that knows the true TS values for the Audiobahn AW1805Q let me know if the values I listed earlier are correct.

Many Thanks
Philip

[Brian Steele]

Originally Posted by Max Caliber

At this time I am also questioning whether the TS parameters I have are correct, if there is anybody out there that knows the true TS values for the Audiobahn AW1805Q let me know if the values I listed earlier are correct.

The quoted Re suggests that those published values are not correct. If each coil is 3.3 ohms, quoted Re should be either half that figure or twice that figure.

[Max Caliber]

Originally Posted by Brian Steele

The quoted Re suggests that those published values are not correct. If each coil is 3.3 ohms, quoted Re should be either half that figure or twice that figure.

Thanks Brian
That's what I was thinking. Would anyone hac a correct set of TS values that would work with the winISP Pro program, or can anyone tell me what would be the correct port lenghts.

Again Thanks
Philip

[theAnonymous1]

This is what bassbox gives for both coils in parallel.....

Fs = 23.2 Hz
Qms = 5.27
Vas = 4.697 cu.ft
Cms = 0.0774 mm/N
Mms = 610 g
Rms = 16.82 mohms
Xmax = 26 mm
Xmech = 39 mm
P-Dia = 14.73 in
Sd = 170.5 sq.in
P-Vd = 0.101 cu.ft
Qes = 0.44
Re = 1.65 ohms
Le = 1.425 mH
Z = 2 ohms
BL = 18.26 N/A
Pe = 1200 watts
Qts = 0.41
no = 0.364 %
1-W SPL = 87.76 dB
2.83-V SPL = 97 dB

The program suggests a 6.8 cubic foot enclosure tuned to 19Hz. Two 4" ports would need to be ~25" each (a slot port would be ideal here).

[tb46]

Hi Max Caliber,

As you already have a ported box with a speaker in it you should be able to run impedance curves, and adjust the duct (port) length, the volume and box lining to see what's going on. It really easy to find the twin peaks (or their absence) that are typical for a bass reflex design, and to make adjustments from that. That way you also get around that pesky Thiel/Small parameter problem.

As to Hornresp: it can be used for a very large variety of enclosures.

Regards,

[Max Caliber]

Originally Posted by theAnonymous1

This is what bassbox gives for both coils in parallel.....

Fs = 23.2 Hz
Qms = 5.27
Vas = 4.697 cu.ft
Cms = 0.0774 mm/N
Mms = 610 g
Rms = 16.82 mohms
Xmax = 26 mm
Xmech = 39 mm
P-Dia = 14.73 in
Sd = 170.5 sq.in
P-Vd = 0.101 cu.ft
Qes = 0.44
Re = 1.65 ohms
Le = 1.425 mH
Z = 2 ohms
BL = 18.26 N/A
Pe = 1200 watts
Qts = 0.41
no = 0.364 %
1-W SPL = 87.76 dB
2.83-V SPL = 97 dB

The program suggests a 6.8 cubic foot enclosure tuned to 19Hz. Two 4" ports would need to be ~25" each (a slot port would be ideal here).

Thanks for the good info

However what would your program report the port length for this sub in a 12cf box with two 4" vents, and preferably with the 2 voice coils in series?

That is where I want to compare the results of winISD with some other program like yours to see if they come up with similar results.

Also can anyone find the real TS specs for this now defunct (Audiobahn) sub-maker?

Again thanks

Philip

[Max Caliber]

Originally Posted by tb46

Hi Max Caliber,

As you already have a ported box with a speaker in it you should be able to run impedance curves, and adjust the duct (port) length, the volume and box lining to see what's going on. It really easy to find the twin peaks (or their absence) that are typical for a bass reflex design, and to make adjustments from that. That way you also get around that pesky Thiel/Small parameter problem.

As to Hornresp: it can be used for a very large variety of enclosures.

Regards,

Thanks Oliver

What size and shape of slot port would you think would be required for this sub within a 12cf box?

I a getting very frustrated with trying to tune this woofer and seeing how my modified ESS monitors that have 1x 12” sub and 3x 12” passive radiators in a 4cf box are so impressive that I am contemplating using 2x 18” passives to solve my dilemma. Any good ideas along this line?

Or another approach might be to use a different sub seeing how the 18” JBL 2245 had the most impressive and efficient bass but unfortunately it is a woofer with a 20Hz FS but with almost no power handling ability below 20Hz (at 10Hz it can handle only 18 watts before Xmax runs out, what a shame!). At low volumes listening to music it was a monster, but watching a movie was a frightening experience.

Does anyone know of a very decent 18” (not too expensive) that could work well in a fairly big box?

Again thanks

Philip

[tb46]

Hi Philip,

If the driver parameters are correct Boxplot gives me a "nice" 2.5dB peak @ 25Hz for 11.75ft^3 with 2 x 4" duct @ 8" long, or 2 x 6" duct @20" long. If you don't get that kind of response your driver parameters are probably way of.

Regards.