Ported EBS alignment preference

[Masterp2]

Which of these alignments would produce more robust, clean, flat performance, mostly for HT. It will be a non-corner-loaded application. Sub will be located behind sofa. Up to 1000W available. Disregard port constraints. They are not an issue. Only ported suggestions, please.

volume,Fb
a.)140l, 22HZ
b.)160l, 20HZ
b.)180l, 20HZ
c.)220l, 18HZ
e.)"here's my suggestion"


Driver is an HE-15


Qts .326
VAS 3.768ft^3
Fs 29
Re 1.5 Ohm DVC
Le 3.7
xmax .9 inches, 23 mm
Z 2.0 Ohm
Qms 6.0
Qes .345
SPL 89.42
Pe 2000W
Bl 13.5
Dd 11.92
Sd 740cm^2, 111.6 in^2

Thank you to all who model it.

Michael




Michael

[ThomasW]

Extended Bass Shelf", or EBS, systems are ported systems that are usually characterized as follows:
The volume of the box is larger (sometimes significantly larger) than that of a maximally flat ported system using the same driver.
The tuning frequency of the enclosure is at or close to Fs, the driver's resonance frequency
The power handling of the EBS is lower in the midbass frequencies when compared to the maximally flat systems. However, the power handling at lower frequencies is usually better.
As with the standard ported systems, almost any driver can be used. However, the best results will be obtained with drivers of Qts <0.35.
One of the main reasons given for using an EBS system instead of the usual "maximally-flat" systems is to take advantage of "room-gain", the increase the bass response at lower frequencies, starting at around 1dB at 30 Hz and increasing to 9dB at 20 Hz, that you get in most rooms. This "room-gain" can tend to produce a boomy response with speakers designed to maximally flat to frequencies below 30 Hz.

To design an EBS system, use any box frequency response modelling software (like my spreadsheet) and model the response of a system using your driver, where the box size is 160% to 180% the volume suggested for a maximally flat response. Then, set the tuning frequency to near Fs for the driver.

If the cabinet is too large, the frequency response curve will be peaked below the shelf. Too small, and the shelf will be attenuated. Adjust the cabinet size to suit.

If the tuning frequency is too low, the shelf will roll off prematurely. Too high and the response peaks at the bottom of the shelf and the premature rolloff occurs again. Adjust the tuning frequency accordingly.

When tuned just right, the shelf level is not too low, and reasonably extended, with a smooth low end rolloff. Note also that if the box is very big compared to what's called for in a maximally flat alignment, there's a loss in midrange efficiency that may be more important than the small increase in low frequency output.

The above notes are based on correspondence sent to the BASS and DIY Loudspeakers Mailing List by the contributors listed below. You may wish to contact them for further details and assistance.

Roger Andersson
Peter Basel
Aaron Bohnen
Dan Wiggins
Mike McCall

That's the technical low down an EBS from the DIYsubwoofers site

Since all the alignments you listed are significantly lower than the drivers Fs, it's your call on how big a box you want to live with.

Obviously my choice was 160L @18-19Hz that keeps the 6" port under 30" long, thus avoiding pipe resonances.

AS-15 is the largest and heaviest subs I've ever built, and I certainly wouldn't want to own anything bigger or heavier.....




theAudioWorx
Klone-Audio

[Masterp2]

The main physical constraints I have is the minimum cabinet size to adequately house the HE-15 and 2-25" long powerports, 6" diameter. 160 l is doable and 140 l is a squeeze.

In your final result with the AS-15, is there an EQ benefit to a smaller cabinet, even if extension is sacrificed? In other words, in your opinion, what EBS alignment would require the least EQ aside from the inductance hump, taking into account if port length were not a constraint?




Michael

[Masterp2]

Second question. Would there be any harm in adding 100g of mass to this driver? It seems it would aid in flattening the response curve some.




Michael

[ThomasW]

The AS-15 was designed and built to obtain the maximium performance from a HE-15 in a ported cabinet. Believe me I spent a LONG LONG time researching the design before building it.

I wouldn't recommend a smaller cabinet. The AS-15 was designed to be the smallest cabinet that could be used to give the best performance. Regarding a bigger cabinet IMO the payback just isn't worth the work.

I certainly can't speculate about the EQ needed for a different box size. The amount of EQ needed is much more a function of the room than any minor differences in box size.

I don't recommend adding any mass to that driver. It's real easy to damage metal cone drivers, Also the efficiency is going to plummet with a ~40% increase in weight. And finally you're creating a Mms that the drivers suspension isn't designed to handle. .

Just use an adequate amount of EQ to get the performance you want and forget about all these other 'tricks'.




theAudioWorx
Klone-Audio

[Hank]

And finally you're creating a Mms that the drivers suspension isn't designed to handle. .

Ahhh...there's the rub!