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High frequency extension

B

Boostedrex

Feb 24, 2009
688
3
Shreveport, LA
#1
So I have the low end taken care of in my upcoming rig build. But just how high do I need the rig to be able to extend? I figure that even the upper harmonics of the G string couldn't extend much above 5KHz. Am I about right, or do I need to build in the ability for my rig to reach up significantly higher than that?

My current plan was to use the dual B&C 15NW100 woofers in 4.0 ft^3 ported to 38Hz and then to have a seperate sealed chamber to hold a Faital Pro W6N8-120 6.5" midrange that would play from 800Hz on up. I haven't decided if I'm going to do a passive 2 way cab or if I'm going to bi-amp it either. So any input/advice from those who are more in the know is GREATLY appreciated. Thanks for taking the time guys.

Zach
 
#2
It totally depends on the tone you're after. Guys who like a zingy bright slappy crisp etc. tone are actually using harmonics all the way up to 20KHz. Thumpy vintage-tone guys probably don't use much higher than 3K most of the time. You'll have to decide where you fall in that spectrum.
 
#3
The harmonics of a 4 or 5'er can actually reach 20KHz with levels that are audible? I could see that being true at concert levels, but what about day to day playing? I hope I'm not coming off as argumentative, I just want to make sure. Keeping in mind that the majority of people's falls off starting at 14-15KHz, needing extension up to 20KHz for a bass seems odd. Thank you for your time and opinion.

Zach
 
#5
By way of example, the "high" control on a Glockenklang bass preamp is centered at 18 KHz, and I can definitely hear its effect on the tone even when playing at low levels. Audible harmonics extend surprisingly high, as it takes far less energy to project those high frequencies audibly compared to the energy needed to project lows. Even when playing lower notes or using non-bright strings, turning up the 18 KHz adds a certain "air" to the tone, an openness, while turning it down gives the tone a more "enclosed" or "dark" feel, without necessarily deadening the sound or turning into a boomy thump like you get when rolling off a passive tone knob.

Edit: I know you're an expert in this area Bill, but I assure you there is something other than hiss present when I open up that 18 KHz control. :)
 
#6
Thanks Bill, 10KHz is reachable with a 2 way/bi-amp setup. Now the question is arrangement of drivers on the baffle. I was thinking a modified MTM arrangement of sorts. Vertically tall baffle with a 15, 6.5" (offset a bit), then 15 on the top. Or would I be better off with 15, 15, then 6.5" on the top?

Bongo, I hear you about having that "air" in a system from my home audio hobby. I just don't see me needing it for a bass. I'll be sure to play around with some commercially built rigs though so that I can get a better idea of what you're talking about. Thank you for your input and for the info that you have shared.

Zach
 
#7
bongomania said:
Edit: I know you're an expert in this area Bill, but I assure you there is something other than hiss present when I open up that 18 KHz control. :)
Click to expand...
Whatever you're hearing it's not likely at 18kHz. Shelving tone controls operate over a 3 octave bandwidth, and even 1/3 octave EQs have functional bandwidths of a full octave.
 
#8
Those upper frequencies may sound nice when you are playing by yourself, but when playing in an ensemble they don't do anything to help define the pitches of the notes you are playing - the extended highs either get lost, or they just add to the hash of high end on stage (from that guy who's bashing the cymbals). I usually roll the top end off of the bass channel on the console, which then allows me - if needed - to apply boost where it helps the notes stand out without adding to the hash or stepping on something else in the mix. (Said boost is usually between 500 and 1500, depending on the situation.)
 
#10
Scope measurements of electric basses show harmonics close to nothing at 7500 Hz and higher.

What you should be asking yourself is, how well those highs disperse off-axis.
I have an 18" JBL E155 that produces pretty good highs from its chrome dome, but only on-axis.
At 45 degrees, it is pretty thuddy.
 
#11
bgavin said:
Scope measurements of electric basses show harmonics close to nothing at 7500 Hz and higher.

What you should be asking yourself is, how well those highs disperse off-axis.
I have an 18" JBL E155 that produces pretty good highs from its chrome dome, but only on-axis.
At 45 degrees, it is pretty thuddy.
Click to expand...

Agreed. This is particularly bad if the cabinet happens to be pointed directly at someone's vocal mic - the bassist thinks all is well, and the mixperson is wondering where all that s*** is coming from. (Or it's pointed at some poor bugger in the audience, and the clickling/twanking is all he can hear - except for the 4x12 guitar cabinet that's shooting a ton of fuzz past the guitarist's knees into the crowd.)
 
#13
bgavin said:
Scope measurements of electric basses show harmonics close to nothing at 7500 Hz and higher.

What you should be asking yourself is, how well those highs disperse off-axis.
I have an 18" JBL E155 that produces pretty good highs from its chrome dome, but only on-axis.
At 45 degrees, it is pretty thuddy.
Click to expand...

bgavin, the off axis dispersion pattern of the B&C's isn't going to be as much of an issue since I'm going to cut them right around the 800Hz range. (early modeling is pointing towards 800Hz with a 12db/oct slope). The Faital mid will take over from there and it has pretty decent off axis response up to 4KHz or so.

Also, thanks for the info on the scope measurements.

Zach
 
#14
billfitzmaurice said:
Whatever you're hearing it's not likely at 18kHz. Shelving tone controls operate over a 3 octave bandwidth, and even 1/3 octave EQs have functional bandwidths of a full octave.
Click to expand...

Fair enough, that would explain it. In that case I would have been hearing freq.s around that up to 10K realm being boosted or cut within the slope of rolloff with a peak corner nominally at 18 KHz. Makes sense.
 
#17
Quick change of plans. :D

The Faital midrange is out. Twin Eminence Alpha 6C's are now the plan. Since I'm going to have two of them, what would be the best arrangement on the baffle? I'm thinking that this would be the ticket, but what do you guys think? From bottom to top have the 15's stacked one on top of the other with the Alpha 6's above the 2nd 15 and have them sitting on the same horizontal axis. Thoughts?

Also, I've been getting told some some people that I will really need a horn for the top end extension. I just don't see that being the case as the Alpha 6's can easily extend to 5.5KHz. Again, thoughts and justifications? Thanks in advance to everyone for their help/input.

Zach
 
#18
Midrange cones should be one above the other as close as possible. They don't need to be directly above the woofers - they can be offset from them.

I take it you chose the C version to get 8 ohms. As I recall the A version has better sensitivity (or was it a smoother passband?). You might be better off with a 4-ohm load too.

What crossover?
 
#20
greenboy said:
Midrange cones should be one above the other as close as possible. They don't need to be directly above the woofers - they can be offset from them.

I take it you chose the C version to get 8 ohms. As I recall the A version has better sensitivity (or was it a smoother passband?). You might be better off with a 4-ohm load too.

What crossover?
Click to expand...

You're correct about going with the 6C in order to end up with an 8 ohm final load.

As of right now, I'm planning on using the Eminence PXB2:500 giving me a 2nd order 500Hz LP for the 15's and a 3rd order 500Hz HP for the mids. I know that buying a pre-made passive is far from the optimum route, but I have never made my own passives and going active is out at this point in time as I was trying to keep this a fairly budget build.

Why, do you have something in mind? After looking at the plots on WinISD I want to keep the X-over point between 500-800Hz between the woofers and mids.

So arrangement on the baffle is the woofers and mids above each other on a common verticle axis. (with the mids being able to be off center a bit like your 15/6 cabinet of course.) If I were to end up adding a horn, could it just go across from the mids in that open area?

billfitzmaurice said:
Depends on your style. I'm content with 6kHz, most slapper/poppers like it good to 8-10kHz. Thumbstyle flatwounder's will find 2kHz adequate.
Click to expand...

Hmmmm.... My slapping/popping still leaves LOTS to be desired, but that is also something that I'm working on improving. But I'm just not sure if I want to make this a 3 way cabinet. Is there really that much content above 5.5-6KHz Bill?

Thanks as always guys, your input is greatly appreciated.

Zach
 

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