JBL 4641 Subs

[Bobecca]

Hello everybody....

Have a pair of 4641 subs and would like to know what kind of external EQ setting JBL is talking about in one of the features, namely

"Usable response to 25 Hz (-10
dB, no EQ), flat to 25 Hz (-3 dB) with External EQ"

taken from the JBL pro site of 4641.

Can't find any settings at all for these Subs or what is the normal procedure/way of thinking when getting flat to 25 Hz with external EQ means.

Any input appreciated

Thanks

[hjames]

Edit - Grumpy is right ... The DX-1 was for another system!

The BX-63 (and the later BX-63A) were a sub EQ box JBL sold for the B-380 and B-460 Bass subs that you would put between your gear and the Power amp you run the sub with. It provided a boost (bump) at the low end that compensated for the low end roll off of their subs.

With anything like that you can use the proper test tones and a spectrum analyzer or similar equipment, just play test tones through your system and use the EQ to dial up the low end to get a charted response like the JBL brochure.

I had a 1/3 Octave EQ a while back that I had in place to use for full range adjustments for my front mains. Crank up the low end for movies, and bypass it for music. I sold it because I never really used it, plus I was was simplifying the system (got rid of the studio monitors and a whole biamp system). Afterwards I found out the new buyer was using it as a bass boost for his sub. I had never tried using it that way with the sub. Didn't really need it.

I run a single 4641 in my Home theater system with an HK Citation 22 bridged mono (no room for a second!). I figure the amp gives it around 600watts that way. My Integra DTC 9.8 Pre/Processor has a general gain adjustment for each speaker, and I usually run the sub -4.5 to -6 db down in the system settings or the bass gets overwhelming. Front and side speakers are set at 0 dB ...

Hello everybody.... Have a pair of 4641 subs and would like to know what kind of external EQ setting JBL is talking about in one of the features, namely "Usable response to 25 Hz (-10 dB, no EQ), flat to 25 Hz (-3 dB) with External EQ" taken from the JBL pro site of 4641. Can't find any settings at all for these Subs or what is the normal procedure/way of thinking when getting flat to 25 Hz with external EQ means. Any input appreciated Thanks

[grumpy]

BX-63(a) ?

[Bobecca]

Thanks for the inputs........

So it means that if there is a roll of in the bass in that region and in that particular situation one can boost if needed and if it is allready flat down to 20 Hz then one can skip the boost. Is this the way of thinking here?

[hjames]

Thanks for the inputs........ So it means that if there is a roll of in the bass in that region and in that particular situation one can boost if needed and if it is allready flat down to 20 Hz then one can skip the boost. Is this the way of thinking here?

Actually, I think the idea is to boost the 20HZ region in advance, to compensate for that roll-off -
Boost the bass going into the amp so when the driver rolled off the low bass, the overall effect was to make it flatter.

Think of how Dolby on cassette decks worked - they would boost the treble during the recording,
so when they cut back on treble during playback, the treble would go back to normal levels,and tape hiss would be reduced

[Bobecca]

Hello again...

Hjames....the second graph shows what kind of settting it is but my felling is that there is something missing.

Freq is 25 Hz and the Q value is 2 but how many dB boost is there??

Should it be asumed around 4-5 dB.

[hjames]

Hello again...

Hjames....the second graph shows what kind of settting it is but my felling is that there is something missing.

Freq is 25 Hz and the Q value is 2 but how many dB boost is there??

Should it be asumed around 4-5 dB.

I just printed charts from the JBL Pro 4641 brochure
JBL-4641-sub.pdf

[Bobecca]

I just printed charts from the JBL Pro 4641 brochure
JBL-4641-sub.pdf

Thanks for the pdf file but I allready have the charts. Was included in the shipment with the subs

I just wanted to clarify on how the boost can be there without specifying the raise in how many dB it is, from the chart of course.
I have the dbx260 and I will give it a try with freq at 25Hz Q=2 and a boost in dB around 5(my guess) and see how it will turn out. But off course it all depends on how the room interacts with the subs placement. Maybe i don't need it afterall.

Thanks anyway

[rlsound]

This is known as the B6 tuning. Boost of 6 db, at box tuning frequency ( in this case 25hz ) at a Q of 2.

[Bobecca]

This is known as the B6 tuning. Boost of 6 db, at box tuning frequency ( in this case 25hz ) at a Q of 2.

Thanks for the clarification.

So, this is all about box tuning of the sub itself.
So if I want flat down to 25 Hz -3 dB then B6 tuning has to be applied regardless of the support of boundary reinforcement.

As mentioned before, I do have a dbx260, where should this setting be applied. Is it in the pre-crossover or post-crossover EQ section.
I believe that it should be implemented in the post-crossover but what is the general idea here?

[4313B]

The boost is created by a 12 dB/octave high pass filter with a Q of 2 centered at the box tuning frequency, in this case 25 Hz.

What this means is that the acoustic output of the ducted port is increased by ~ 6 dB over a very narrow bandwidth controlled by the filter Q. The low frequency transducer at this frequency is at minimal excursion.

Without the boost the 4641 is a quasi-third order system rolling off at ~ 18 dB/octave. With the boost the 4641 becomes a quasi-fifth order system rolling off at ~ 30 dB/octave, the boost having the secondary effect of enhancing protection of the low frequency transducer unloading below enclosure resonance.

***

I just looked at the user manual for the dbx 260 and it would seem that the section you are interested in would be on page 34.

Type

This parameter selects the PEQ band type. Types include:

•
Bell - All bands are bell-shaped.

•
HShelf - One band is a high shelf, while all others are bell.

•
LShelf - One band is a low shelf, while all others are bell.

•
LHShelf - One band is a low shelf, one is a high shelf, and all others are bell.

Band (1-4) Frequency 20Hz to 20kHz

Selects the frequency of the selected band of the parametric EQ.

Level (1-4) -12dB to 12dB

Sets the level (gain) of the selected parametric EQ.

Q (1-4) 0.20 to 16 dB

Sets the Q or Bandwidth of the selected Parametric EQ.

The following figure shows the constant Q parametric filter.

S (1 and 4, shelf type filters only) 3, 4.5, 6, 9, and 12 dB/Octave

Sets the slope rate when using a low or high shelf type filter.

[Bobecca]

The boost is created by a 12 dB/octave high pass filter with a Q of 2 centered at the box tuning frequency, in this case 25 Hz.

What this means is that the acoustic output of the ducted port is increased by ~ 6 dB over a very narrow bandwidth controlled by the filter Q. The low frequency transducer at this frequency is at minimal excursion.

Without the boost the 4641 is a quasi-third order system rolling off at ~ 18 dB/octave. With the boost the 4641 becomes a quasi-fifth order system rolling off at ~ 30 dB/octave, the boost having the secondary effect of enhancing protection of the low frequency transducer unloading below enclosure resonance.

***

I just looked at the user manual for the dbx 260 and it would seem that the section you are interested in would be on page 34.

Type

This parameter selects the PEQ band type. Types include:

•
Bell - All bands are bell-shaped.

•
HShelf - One band is a high shelf, while all others are bell.

•
LShelf - One band is a low shelf, while all others are bell.

•
LHShelf - One band is a low shelf, one is a high shelf, and all others are bell.

Band (1-4) Frequency 20Hz to 20kHz

Selects the frequency of the selected band of the parametric EQ.

Level (1-4) -12dB to 12dB

Sets the level (gain) of the selected parametric EQ.

Q (1-4) 0.20 to 16 dB

Sets the Q or Bandwidth of the selected Parametric EQ.

The following figure shows the constant Q parametric filter.

S (1 and 4, shelf type filters only) 3, 4.5, 6, 9, and 12 dB/Octave

Sets the slope rate when using a low or high shelf type filter.

Ok, lets see if I get this right.

The High pass filter would be a Link-Witz 12 db/octave and Q=2(bell shape) at 25 Hz and the level gain set to 0dB at the selected PEQ.
I do think that most of the post PEQ is for loudspeaker tuning and pre PEQ is for adjusting the room response curve.

The question still a raise, is this a recommended tuning if one can apply one, so to speak. Should I use it. I think I should as long it is gonna protect the sub.

Do I need to take this into consideration, the bolded part, taken from the spec of 4641?



"Recommended Crossover Frequencies: High-pass: 20 Hz, 24 dB/octave or greaterLow-pass: 80 Hz to 150 Hz, 12 dB/octave or greater"


when B6 tuning is applied.

Thanks for the input.

[4313B]

Because this is a digital device your possibilities are significantly increased. Your best bet might be to simply use the dbx to tune the system the way you want while keeping in mind that any EQ boost below the vented box resonance frequency of 25 Hz would be a bad thing.

You can use a bell PEQ at 25 Hz with a Q of 2 but it won't behave like a conventional high pass bump filter, there will be no roll off below the center frequency. Additionally, the boost might not be 6 dB, it might be a bit more or a bit less and totally dependent on your venue. Therefore you might wish to also use a subsonic filter centered at 20 Hz to protect the low frequency transducer.

If this dbx behaved like a miniDSP for instance, you would probably create a bandpass filter and PEQ as shown. This would somewhat simulate how a traditional high pass bump filter works in an active network such as a BX-63 or 5234/5235 (note that these are 12 dB/octave devices).

In reality you are probably going to use several bells at various frequencies to boost or cut in-room response.

[Bobecca]

Thanks 4313B,

As I understand dbx260 I can apply a Q=x and freq=x but if the gain is set at 0dB then this PEQ is not in use.

I follow you in your example....

My choice of setting would be like this and comments are welcome.

The use of LR 12 dB/octave at 25 Hz as a high-pass.
PEQ settings would be at 25 Hz Q=2 and a Gain of +6dB.

This is to me in line with the recommended settings from JBL except from the missing gain of +6 dB. Or any other gain setting.

I find it very strange that this boost of +6dB is not mentioned in the JBL spec

[4313B]

As I understand dbx260 I can apply a Q=x and freq=x but if the gain is set at 0dB then this PEQ is not in use.

Yes but it won't allow you to do it in the actual crossover filter like you would if you were building an active filter such as a BX-63 or 5234/5235. It will only allow you to do that on the shelf and bell filters.

I find it very strange that this boost of +6dB is not mentioned in the JBL spec

Because when you build a high pass or low pass filter with a Q of 2 it creates the bump at the center frequency. There is no need to specify it. I used to have a chart graphically showing the various Q boosts but who knows where that ended up.

Here's a quick primer to review. There are others all over the Internet as well I'm sure. I just did a quick Google and this popped up first.

http://www.audioholics.com/education...r-loudspeakers

You can arguably ignore the part about poor transient response and ringing because it is highly unlikely that you care about such things at 25 Hz.

The use of LR 12 dB/octave at 25 Hz as a high-pass.
PEQ settings would be at 25 Hz Q=2 and a Gain of +6dB.

That should work.