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What is the science behind this?
- Thread starter MrCash
- Start date
The slot gives wider dispersion at high frequencies. This applet shows how that works:
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The slotted second baffle also creates a chamber in front of the cone, and that chamber turns the speaker into a band pass, which boosts the lows. But if narrow enough to boost lows its it also kills highs, and you can't get wider dispersion of highs that the speaker can't produce. To work well over a wide range the slot shouldn't be less than half the speaker diameter, the Trace slot is too narrow. The biggest problem is that they left the slot visible. If they covered it with a full grille the cabs might have sold a lot better, but they didn't, and bass players don't have a natural tendency to gravitate to technology that's foreign to them. They're as bad as anyone where listening with their eyes is concerned.
Link Removed
The slotted second baffle also creates a chamber in front of the cone, and that chamber turns the speaker into a band pass, which boosts the lows. But if narrow enough to boost lows its it also kills highs, and you can't get wider dispersion of highs that the speaker can't produce. To work well over a wide range the slot shouldn't be less than half the speaker diameter, the Trace slot is too narrow. The biggest problem is that they left the slot visible. If they covered it with a full grille the cabs might have sold a lot better, but they didn't, and bass players don't have a natural tendency to gravitate to technology that's foreign to them. They're as bad as anyone where listening with their eyes is concerned.
The cab exploits the quantum duality of sound - waves and particles.
- Feb 12, 2006
- 60,989
- 5
- 220,787
- Disclosures
- Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
The slot also acts as an acoustic high pass filter, in addition to the diffraction of high frequencies. Not the best approach for a bass amp IMO.
The original approach for this was used in early horn loaded cabinets from the 40's and 50's (Altec for example) for the purpose of lowering distortion and improving phase coherence in LF sections such as the A2, A4, A7 cabinets.
The original approach for this was used in early horn loaded cabinets from the 40's and 50's (Altec for example) for the purpose of lowering distortion and improving phase coherence in LF sections such as the A2, A4, A7 cabinets.
Ah yes now I understand.
However I don't understand there thinking on this one.
Perhaps they thought it would squeeze some extra performance out of a little combo. Although from what I've heard people's opinions are divided. I've also heard some people flipped the driver and got a. "Supposidly" better result.
They stuck a tweeter on the front of later ones.
Interesting concept nonetheless.
However I don't understand there thinking on this one.
Perhaps they thought it would squeeze some extra performance out of a little combo. Although from what I've heard people's opinions are divided. I've also heard some people flipped the driver and got a. "Supposidly" better result.
They stuck a tweeter on the front of later ones.
Interesting concept nonetheless.
- Nov 24, 2008
- 4,343
- 7,163
- Disclosures
- Owner & designer, AudioKinesis; Auth. mfg, Big E (Home Audio only)
Imo that is where the configuration starts to get interesting.
You have the narrow slot acting as an acoustic (instead of electrical) low-pass filter to roll off the top end of the woofer, while simultaneously improving dispersion. If the tweeter is a wide-dispersion unit (not common in bass cabs, but possible), ideally with a radiation pattern matching that of the slot-loaded woofer in the crossover region, then at least theoretically you have the building blocks for a cab with much wider and more uniform coverage than normal.
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- Feb 12, 2006
- 60,989
- 5
- 220,787
- Disclosures
- Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
There's a lot more going on with the slot, the slot (especially when very narrow) actually acts like both a low pass and high pass filter, but on the high end the diffraction effect is one factor that alters the low pass response. The slot dimensions relative to the driver diameter affects a variety of performance parameters.
If you go back to the original Altec (and others) application, the slot also added some air mass loading which changed the coupling or acoustic impedance matching between the driver and horn throat. The slot was nowhere near as narrow as in the Trace example.
One disadvantage of a narrow slot is the loss of average sensitivity, and probably the impact on voicing would not be suitable for today's player too.
Here's an interesting discussion of this theory (though different application): Acoustics/Filter Design and Implementation - Wikibooks, open books for an open world
This shows the schematic representation of an acoustic low pass portion, the initial transition from slot to open represents the first order equation (which is what the slot by itself is).
In actuality, this is all pretty imperfect stuff, and significant assumptions are made to make it somewhat conform.
If you go back to the original Altec (and others) application, the slot also added some air mass loading which changed the coupling or acoustic impedance matching between the driver and horn throat. The slot was nowhere near as narrow as in the Trace example.
One disadvantage of a narrow slot is the loss of average sensitivity, and probably the impact on voicing would not be suitable for today's player too.
Here's an interesting discussion of this theory (though different application): Acoustics/Filter Design and Implementation - Wikibooks, open books for an open world
This shows the schematic representation of an acoustic low pass portion, the initial transition from slot to open represents the first order equation (which is what the slot by itself is).
In actuality, this is all pretty imperfect stuff, and significant assumptions are made to make it somewhat conform.
EdwardofHuncote
I Still Dream of Jeannie
- Aug 21, 2013
- 6,652
- 2
- 16,421
- Disclosures
- I privately own and operate a local musical instument repair shop.
I design audio gear for a living, and have a degree in Acoustical Physics. There might be a narrow range of frequencies where slot loading like that helps a bit, but I'd bet over most of the frequency range, you'd get better results without it.
If you like how it sounds, great, but it's not the audio equivalent of curing cancer. It's probably more effective at getting your wallet out of your pocket than improving anything.
There was an enclosure promoted by Karlson many years ago that had an exponential slot in it. It may have worked better, as it obscured the driver less. Despite having its patents expire, nobody makes those today. Ported enclosures, those are popular. Survival of the fittest at work.
If you like how it sounds, great, but it's not the audio equivalent of curing cancer. It's probably more effective at getting your wallet out of your pocket than improving anything.
There was an enclosure promoted by Karlson many years ago that had an exponential slot in it. It may have worked better, as it obscured the driver less. Despite having its patents expire, nobody makes those today. Ported enclosures, those are popular. Survival of the fittest at work.
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These statements depend on my faulty memory: Back in the day I happily used an Ampeg V4B folded horn cab. I seem to remember replacing the drivers and wondering why the speaker opening was slotted about four to six inches wide. I ASSumed it was a structural reason.
Uh, yes. What Aged Horse said. I don't understand any of it, but I love my Genz Benz so what Aged Horse said.
My brain hurts.
My brain hurts.
Wow! And here I thought they just ran out of grill cloth with only 2" left to go. 
No -its not! The EV 1502 is just a simple vented enclosure with a horn-style LF section. It was designed that way to help make it a little more efficient.
Same here with my horn loaded 15" Peavey FH-1's. I found it odd that the woofer baffle was a slot instead of a round hole roughly the size of the cone area. I was very young when I encountered this, so I assumed it had to do with compression loading. FYI: The enclosure was rated at 8ohms but used a 4ohm woofer. I did a Google search, and that seems to be common for what are called "W" horns.
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- Feb 12, 2006
- 60,989
- 5
- 220,787
- Disclosures
- Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
The main reason for the use of the slot on horns (and especially folded horns) is to improve phase coherency by eliminating path length differences in areas of the woofer that don't contribute as much to overall SPL. They also function as a LPF which is tuned by the dimensions (width) of the slot adding to the electrical filter of the crossover. Ideally it would match the crossover frequency and thus increase the slope by one order. Rarely were the results ideal, but every improvement back then was welcome.
I am going to need more mushrooms to finish this thread. Outstanding brain matter going into this!
