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

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
 
the bass from an 18" Audiobahn AW1805Q in a 12cf vented enclosure

FYI,

No need to use fudged numbers:

b:)
 

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Audiobahn AW1805 port lenght in a 340l box

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


 
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.
 
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
 
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

Member
2006-01-09 7:04 pm
Texas
Tuning a BR enclosure

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,
 
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
 
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.:eek:

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

Again thanks

Philip
 
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.



Thanks Oliver for the info.

Just wondering, did you ever try the winISP program, and if you did how would you compare it with Boxplot?

From the same data as you have supplied (25Hz in an 11.75cf box) the winISP reports a very strong peak of +4.575db at 26.07Hz, however it also states that the 2x 4” ports should be 6.33” long which is very different from the lengths Boxplot described of 2x 8 inches with 4" diameter vents.

When I forced the winISP to use 8” ports the box tuning shows a peak of +3.388db at 23.95Hz. In both cases the peaks are higher than the value your software defined of +2.5db. This is where the numbers between different software packages starts to get interesting!!:confused:

I have ask; in your setup did you use the voice coils (2x 4ohms) wired as parallel (total 2ohms) or series (total 8ohms), as this plays a strong roll with the BL parameter.

Thanks for the effort it’s very much appreciated.

Philip

 
This is where the numbers between different software packages starts to get interesting

Don't get too hung up on the small differences between programs; the real life margin of error is going to be even greater.

IMHO, your box in far too big to get a clean flat response. Group delay will be atrocious.

If I had that driver, I would stick it in a 1cu.ft sealed box with LT equalization. Clean, low, and relatively small; what more could you want.
 
If you have tuned the box to 20Hz, you will never get any power handling at any frequency below 20Hz no matter what driver you use. Ported boxes should not be operated below resonance as the driver unloads.


Hi Richie00boy
It is normally true that the power handling will drop below resonance however the compliance of the cone’s support plays a very big roll in this matter as to which driver will be more or less effective at very low frequencies.

In the case of the JBL 2245 this is very obvious as the power handling drops to 18watts at 10Hz, mostly due to the very loose compliance of this woofer. Whereas with the Audiobahn AW1805Q I can partially stand on the cone :eek: (figuratively speaking) and I doubt that I would be able to exceed its mechanical limit. This is also evident by the winISP reporting that this sub can handle 470.071watts at 10Hz (more than 25 times the capability of the JBL), and the AW1805Q has an FS of 23Hz meaning that it is further below its FS (at 10Hz) than the JBL which has an FS of 20Hz. Note, the box was tuned for 20Hz for both drivers. Therefore your argument that I will “never” get any power handling below the box tuning is not exactly accurate, it’s more a matter of degree as to which driver will misbehave more than the other depending upon its construction. This is also very evident by examining most (Home Theater) manufactured sub-woofers sold now-a-days and you will see many operating well below their box resonances, and without the drivers hitting their mechanical limits.

So my question to you would be, “What decent (price is important) 18” sub would you suggest for a 12^3 foot box tuned to 20Hz or lower?

And would you consider the use of passive radiators tuned to something like 15Hz?

Thanks for the comment.

Philip

 
.... Therefore your argument that I will “never” get any power handling below the box tuning is not exactly accurate, it’s more a matter of degree as to which driver will misbehave more than the other depending upon its construction.

Forget power handling and how it "behaves" below tuning; what will it sound like? I know........

CHUGGA-CHUGGA-CHUGGA-CHUGGA-CHUGGA-CHUGGA!

Port and mechanincal suspension noise will dominate and it will sound like garbage.

And would you consider the use of passive radiators tuned to something like 15Hz?

You would gain nothing by using passive radiators. Ports at least have the advantage of using air as the resonating mass; meaning it has no excursion limit and you can't break it . ;)
 
Don't get too hung up on the small differences between programs; the real life margin of error is going to be even greater.

IMHO, your box in far too big to get a clean flat response. Group delay will be atrocious.

If I had that driver, I would stick it in a 1cu.ft sealed box with LT equalization. Clean, low, and relatively small; what more could you want.

Hi theAnonymous1

Thanks for the info.

Yes I agree with you knowing that this sub was originally designed for the auto sub market meaning that it was meant for a relatively small enclosure, and using it in a large box will definitely extend the group delay. But recall my original goal was to design something that will generate sub-sonic frequencies (below 25Hz) as my modified ESS monitors are producing more than enough audible deep bass. It’s the earth shaking rumble that I am looking for, those frequencies between 10 and 25Hz that shake the foundation. And at these frequencies a small box will not cut it, unless I use multi-kilo-watts of power in a sealed enclosure (reference: Sunfire).

Personally I don’t believe the longer group delay will have any noticeable negative affect on the total sound balance at these sub-sonic frequencies, as they are meant to be felt rather than heard.

Seeing how I already have the space for the 12^3 foot enclosure and it has an unobtrusive location (it’s sitting under my and my wife’s common computer desks), and more importantly it does not offend my wife sense of aesthetics;), what sub would you suggest I use in this situation that will generate the deep frequencies I’m looking for?

Again Many Thanks for the comments.

Philip
 
Seeing how I already have the space for the 12^3 foot enclosure and it has an unobtrusive location (it’s sitting under my and my wife’s common computer desks), and more importantly it does not offend my wife sense of aesthetics;), what sub would you suggest I use in this situation that will generate the deep frequencies I’m looking for?

Can't think of anything off the top of my head; search for a driver with Vas >10cu.ft and Qts <0.4.

EDIT: Check out the Aurasound NS18-992-4A. It's not cheap, but it looks like it will do well in a 12cu.ft box tuned to ~17Hz.
 
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Forget power handling and how it "behaves" below tuning; what will it sound like? I know........

CHUGGA-CHUGGA-CHUGGA-CHUGGA-CHUGGA-CHUGGA!

Port and mechanincal suspension noise will dominate and it will sound like garbage.



You would gain nothing by using passive radiators. Ports at least have the advantage of using air as the resonating mass; meaning it has no excursion limit and you can't break it . ;)


Hi theAnonymous1

To say that there is nothing to gain form the use of Passive Radiators (PR) is not as clear cut as you make it.

The advantage of passive radiators is that they don’t “CHUGGA-CHUGGA-CHUGGA-CHUGGA-CHUGGA-CHUGGA!” and they don’t consume valuable internal volume from the enclosure, note 2x 6” ports (to reduce the CHUGGA) tuned to 20Hz will have to be 27.5 inches each, and if I tune the enclosure to 15Hz the vents would have to be 52.2 inches long each :eek: that’s a lot of space taken from the enclosure to house the vents which will push the enclosure resonance way up!

Moreover PR’s are very easy to tune and re-tune as necessary, something that is not so easy with ports. Just mount them backwards on the enclosure and add mass to the cones:cool:. When satisfied with the results invert them back into the enclosure and the results will be nearly the same.

As you have mentioned excursion limits may be an issue, and for this reason I always use at least two times the PR diameter as that of the driver they are mated to, as I did with my ESS monitors where I have 3x 12” PR’s for my one 12” driver. The original ESS monitor had only one PR. For the AW1805Q I would contemplate using 2x 18” high excursion PR’s.

The only remaining issue would now be the “mechanical suspension noise”, however from the very stiff compliance of the AW1805Q, it does not move very easily nor does it move a lot even at high power levels. As a result of this the noise produce by the suspension is almost totally inaudible. I have tested it at 1Hz and at 10Hz with 400watts and all I could hear was 3rd and 4th harmonic distortions and only when operating above 10Hz (it’s not a great driver by any stretch of the imagination unlike the JBL 2245 & 2242 drivers).

Recalling the points I made in and earlier tread about the sonic effects of the group delay at sub-sonic frequencies, I now ask, in your opinion do you still think this combination would sound like “garbage”, :)

Regards

Philip