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High Bl, BR enclosures, and port damping?
High Bl, BR enclosures, and port damping?
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Old 10th July 2018, 04:20 AM   #1
Cableaddict is offline Cableaddict
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Default High Bl, BR enclosures, and port damping?

My current subwoofer plan is still a big foggy, but most likely I will be build some kind of BR design (likely PPSL) and then immediately afterwards, building a TH design. - Then comparing them.

As I will be using he best components possible ($$$) and also because I will be very interested to compare the two designs as accurately as possible, I hope to use the same drivers in each cabinet type.

- if there is no compromise involved, and hence this thread / question.


I've read many times that a horn-loaded sub should use a driver with a very high Bl, because there is a lot of compression to overcome. Since high Bl also offers several important benefits (efficiency & driver control) I of course am glad to read this.

HOWEVER, I have recently read that with BR enclosures, sometimes it's best to have a slightly lower Bl. The reason given is something I don't understand:

The article said, quote: "Really high Bl can cause problems with the reflex ports being under-damped and requiring modification. A slightly lower Bl can yield a more balanced result."
-------------------------------------

1: Do you agree with this?

2: If it is true, then let's discuss that "modification."

The part I don't understand is what he means by an under-damped port.
Can someone explain this?

I assume that this problem can be minimized by either going with larger ports (and thus a larger enclosure) or smaller ports, yes? Or perhaps slot ports vs tube ports, or vice-versa?

Thx.
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Old 10th July 2018, 06:07 AM   #2
Cableaddict is offline Cableaddict
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FWIW, someone might glean something from the following article, even though it's discussing sealed enclosures. Maybe some of it still pertains in some way?

http://citeseerx.ist.psu.edu/viewdoc...=rep1&type=pdf


I can't seem to find anything directly related to my specific question.

Last edited by Cableaddict; 10th July 2018 at 06:13 AM.
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Old 10th July 2018, 06:22 AM   #3
wonderfulaudio is offline wonderfulaudio  India
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A BR enclosure does not load the driver in the same way as a horn. The very high BL driver may cause a peak at tuning but that can easily be overcome by Eq.

In horn the driver loading is far higher and the very high Bl should not cause the peak that is seen in BR case, just SIM it.
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Old 10th July 2018, 07:07 AM   #4
Cableaddict is offline Cableaddict
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Thanks, WA.

I'm just learning software, so can't sim it yet with confidence, but even if I could:

Would Eq'ing the peak work for all volume levels? If so, then heck, no problem.

If not, and port modification was deemed a better answer, does that then mean smaller ports or larger? Or something else?

I'd really like to understand all my options.
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Old 16th July 2018, 01:53 AM   #5
bentoronto is offline bentoronto  Canada
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High Bl, BR enclosures, and port damping?
Bl is just like motor strength. If you have a speaker that suffers when the driver you install has too much motor, something is whacky*.

What the linked AES paper (by a local guy....) says about BR is that if you sim that high Bl driver in a BR and the sim says to start adding damping to the port, either (a) you're wasting your money on that great driver or (b) pretty silly using a BR with a high Bl driver.

I'd go with b. Instead, I'd favour the sealed boxes also shown in the article where the advantages of a strong motor are put to good use. Given the real-world parameters of drivers and human hearing, you may need to tweak the speakers with EQ. But if you want a good system, far smarter to tweak EQ than to diddle with a BR until you get an tolerable compromise.

Sim users should know when a sim is doing its business perfectly correctly yet coming out with stupid answers.... like when recommending tiny sealed boxes.

B.
*as an automotive enthusiast, I favour sporty cars and motorcycles with proper sized motors because there are various trade-offs such as engine weight and location. For some vehicles, efficiency matters. But in audio, efficiency hasn't been much of an issue for 50 years although a unit that shows high efficiency (like a high Bl driver) is admirable. Cost and weight aside, the high Bl driver isn't trading off anything you want.
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Last edited by bentoronto; 16th July 2018 at 02:03 AM.
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Old 16th July 2018, 07:36 AM   #6
freddi is offline freddi  United States
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High Bl, BR enclosures, and port damping?
read this collection of notes from the late DJK dealing with the assisted 6th order bass reflex case. Qts = 0.312 is optimum. Without the 6dB/q= 2 boost at fb, the alignment is SSB4

Low Qts - djk - High Efficiency Speaker Asylum
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Old 16th July 2018, 08:21 AM   #7
chris661 is offline chris661  United Kingdom
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Cableaddict, I was reading into the Radian super-subs that you've posted about, and came across this - Radian Audio Engineering's 2218 Neo Driver: Absurd Claims or Not?

Granted, it's the 18" version, but it might be worth testing one of the Radian 15"s before ordering a few of them.


With regards to your question, sometimes high-BL drivers (which often have very low Qes and therefore Qts) are at their flattest when used in an extremely small ported cabinet tuned quite high up.
The simulators will usually recommend a "textbook" alignment, ie, aiming for a Butterworth rolloff, and will play with the cabinet's properties to get there, regardless of where the low-end rolloff actually ends up.
You'll find that using a cabinet that's larger than recommended by the textbook alignments gives a frequency response that isn't perfectly flat, but it'll usually only be a touch of EQ away, and will go much deeper into the bass.

For the reference of the other posters, is this still for your PA system?

FWIW, try WinISD Pro (Alpha) to get to grips with some simulation software.

Chris
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Old 16th July 2018, 08:44 AM   #8
KSTR is offline KSTR  Germany
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A BR is just a Helmholtz resonator exited by the driver. Like any other resonator it has a Q factor that dermines how strong it resonates and how long it takes to settle to any change of input exitation and how narrowband the range of frequencies is where it actually can be exited. This Q factor is specified with no driver installed, replaced by a rigid baffle on the opening.

A driver with extremely low Q does not add any damping to the Helmholtz and if its a good rigid build the resonator Q will be too high to be useful (tried it, and as predicted in the "High BL" paper it doesn't work well and you can't fix it with EQ). We want to use the driver to damp the resonator, and this is done by choosing a driver that isn't a brick wall and has enough "give", that is, has controlled moderate electrical damping itself which means moderate Qes. You can always increase Qes by using an amplifier with a synthesized higher output impedance, which is an excellent way to use otherwise unsuited drivers.

One can also try damp the enclosure mechanically to reduce the resonator Q with stuffing material etc but this is usually not well defined and hard to dial in to a proper value.
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Old 16th July 2018, 04:31 PM   #9
whgeiger is offline whgeiger  United States
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Default Optimal Sub-Woofer Design Stratagy.

The use of servo controlled drivers, particularly when cost is no object, will deliver superior performance in a small footprint enclosure as well. This reduction in size permits deployment of at least 3 units in a well designed listening space for reasons given by Geddes and others. Such an approach makes all the issues addressed here, at best, nominal. In this setting a stronger BL product may be put to good use by forcing diaphragm excursion to faithfully follow the drive signal. However, if the listener has been conditioned by repeated exposures to the output of boom-box designs, then the initial impression will be characterized as a too-weak bass response, which is due primarily to the pronounced absence of overhang and the missing response peak centered somewhere between 40-60 Hz found in conventional designs. Of course, when the cannon shots occur while listing to 1812 Overture [1], that impression will be changed forever if not before.

[1] Boston Pops
YouTube

WHG

Last edited by whgeiger; 16th July 2018 at 04:42 PM.
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Old 16th July 2018, 04:47 PM   #10
whgeiger is offline whgeiger  United States
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Default Optimal Sub-Woofer Design Stratagy.

The use of servo controlled drivers, particularly when cost is no object, will deliver superior performance in a small footprint as well. This reduction in size permits deployment of at least 3 units in a well designed listening space for reasons given by Geddes and others. Such an approach makes all the issues addressed here, at best, nominal. In this setting the stronger BL product may be put to good use by forcing diaphragm excursion to faithfully follow the drive signal. However, if the listener has been conditioned by repeated exposures to the output of boom-box designs, then the initial impression will be perceived to as a too-weak bass response, which is due primarily to the pronounced absence of overhang and the missing response peak centered somewhere between 40-60 Hz. Of course when the cannon shots occur while listing to 1812 Overture [1] that impression will be changed forever if not before.

[1] Boston Pops
YouTube


WHG
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