High Bl, BR enclosures, and port damping?

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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."
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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.
 
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.
 
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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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
 
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.
 
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
 
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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
 
I have no experience with TH designs but with high-BI (actually high BI^2/Re product) drivers and when money is no object I'd prefer multiple drivers in small sealed boxes. I hope we are talking about domestic conditions? I don't know whether you consider active system with some DSP magic or not but resulting benefits for domestic listener from such combination are obvious.

- Direct radiator design - maximally controlled response. Sound excitated purely with driver itself without relying on non-linear behaviour of resonant air column.

- High motor strength will result with critically damped boxes. Total control over radiation time domain.

- Highest possible ratio of radiation area to volume occupied - saves cost of materials and workmanship.

- Sealed box is ultra-easy for equalization, especially with DSP.

- Multiple radiators around typical listening room can eliminate most of room modal resonances.

- Any sealed driver design has inherently high WAF.


Amplifier power is so cheap nowadays that I would't take efficiency upon consideration anymore.
 
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I have no experience with TH designs but with high-BI (actually high BI^2/Re product) drivers and when money is no object I'd prefer multiple drivers in small sealed boxes.
I hope we are talking about domestic conditions? I don't know whether you consider active system with some DSP magic or not but resulting benefits for domestic listener from such combination are obvious......
.

Nah, I'm primarily talking about live band / DJ subs.

- Bit all data is useful, so thanks. Also, I agree that two smaller drivers per sub offers several benefits, but of course this also adds complexity & has trade-offs. I think the best overall idea s to se a driver that is rated for way more watts than you need, and not drive it hard. The trade-off there is that most such drivers are less sensitive than their lower-wattage cousins.

Amplifier power is so cheap nowadays that I would't take efficiency upon consideration anymore.

Yes, but available current is typically a huge problem for a small band or mobile DJ. It doesn't matter what mondo amps you carry, if all you have is a single 15a circuit. (and you also have to run computers, lights, etc. Believe me, I've made a hobby of melting Lab Grupen Fp6400's, and circuit breakers run for cover when they see me pull up t the gig.
 
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.... 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.

Chris, are you saying to err on the side of a larger enclosure, despite what the software recommends, in order to lessen the impedance against the driver? (Sorry, I may be using the wrong terminology.)

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

Yes. I would like to try both some kind of BR design, and then also a TH, using the same drivers so I get as "fair" a comparison as possible. But of course, if no driver is actually optimum in both designs, then this idea goes out the window. I'm working on the assumption that a high compression ratio horn works best with a high Bl driver. - Something I've read multiple times.
 
Chris, are you saying to err on the side of a larger enclosure, despite what the software recommends, in order to lessen the impedance against the driver? (Sorry, I may be using the wrong terminology.)

What I'm saying is that a high-BL driver will typically give a textbook Butterworth response shape at a frequency that's higher than we'd want for a PA subwoofer. It's a small box, tuned quite high.
So, we go off-piste just a little by making the box bigger and tuning lower. It'll give a response that slopes down a little, but at least then the LF extension is there.

For what it's worth, the Faital Pro 15HP1060 drivers I use in my (approximately) ported cabinets have also been used in THs around here, with good results on all accounts.

I think you'll be able to put them in either just fine.

Of course, the best way to learn is to play with simulators, and then build them. I think you'll be able to answer a lot of your own questions if you set off with WinISD Pro and then graduate to Hornresp.

Chris
 
you can't fix it with EQ

http://www.xlrtechs.com/dbkeele.com/PDF/Keele (2003-10 AES Preprint) - Nom vs True Eff High BL.pdf

Quoting from the above paper
"When the true efficiency of the driver is considered,
it is clear that increasing the Bl factor will directly
result in higher efficiency values at all frequencies.
Unfortunately, the constant-voltage-drive low frequency
response may suffer, but this only means
equalization must be used to flatten the frequency
response."
 
wonderfulaudio;5491409 [url said:
http://www.xlrtechs.com/dbkeele.com/PDF/Keele%20(2003-10%20AES%20Preprint)%20-%20Nom%20vs%20True%20Eff%20High%20BL.pdf[/url]

Quoting from the above paper
"When the true efficiency of the driver is considered,
it is clear that increasing the Bl factor will directly
result in higher efficiency values at all frequencies.
Unfortunately, the constant-voltage-drive low frequency
response may suffer, but this only means
equalization must be used to flatten the frequency
response."

Some bad confusions there.

KSTR was not wrong in saying you can't use EQ... to fix resonances. But you can fix freq response if by FR you mean plots like the basic REW sweep*.


I found the Keele article disturbing. Yes, you can make an FR-sweep go lower by using a worser driver. Or a driver with a ½ lb cone assembly. Maybe that kind of "logic" appeals to commercial sound contractors.

Anybody like those kinds of thoughts?

B.
* but not perceived tonal balance which I think would be influenced by resonances differently than an REW plot.
 
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No choice

Given venues close to this

Yes, but available current is typically a huge problem for a small band or mobile DJ. It doesn't matter what mondo amps you carry, if all you have is a single 15a circuit. (and you also have to run computers, lights, etc. Believe me, I've made a hobby of melting Lab Grupen Fp6400's, and circuit breakers run for cover when they see me pull up t the gig.

a tapped horn implementation is what you need. The driver chosen must have parameters that meet horn requirements. BL product is only part of it.

Alternatively, invest in a generator set, for these wimpy venues, and charge extra for its use. Otherwise observe, that there are some (non-) business opportunities that you should simply walk away from.

WHG
 
Hi, What do mean 'melt a Fp6400' ? Just that you tripped a breaker?

From what I can tell, he's literally destroying those amps. Until recently, he had 4x Bag End 18" sealed subwoofers with their processor. Sealed subs aren't efficient at the best of times. Add in the compression in the processor and I'd expect the amp (and speakers) to be working very hard.

I wouldn't expect a Lab Gruppen amp to blow (ever), but that's where we are.

Chris
 
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