why no sEALed fEARfuls???

[kringle77]

I was going to mention transient response. I have used my fdeck hp filter on all my cabs and while it definitely gets you closer, they still don't really sound sealed. I believe bill is right about the distortions. That and the transient response are the missing factors. Whatever they are, they sound good.

 

[john turner]

could someone please explain to me what this "sounds sealed" means?

i understand the difference between sealed and ported, and the science behind the cabs in general (Designed and built studio reference monitors as a senior design project for my electrical engineering degree at georgia tech back in 91, including plotting their acoustic, mechancial and electrical properties on pspice of all things heh), but i see a lot of folks talking about the "sealed sound" and i'm wondering what exactly you guys are meaning.

thanks

 

[staindbass]

i agree about the distortions. but i dont push mine that hard. if i had to i would get more drivers so they dont reach dynamic compression either. we can bicker on specs all day, but i dont see how you could not notice the difference in a side by side test. ports also huff and chuff and make wind noise. ever see a soundman mic a port?

 

[staindbass]

the sealed sound is from no overhang. it stops quicker. when your cab is jamming at 40 hz, there is a noticable start and stop to each pulse or vibration of the string. you can feel each one like a lawnmower engine, you hear each putt with noticable space in between. a ported cab sounds more like a steady tone, like mush.

 

[billfitzmaurice]

I have used my fdeck hp filter on all my cabs and while it definitely gets you closer, they still don't really sound sealed.

It still boils down to how they were built. If they were made to have the same response as sealed then you wouldn't be able to tell the difference in the low end. If they weren't made to have the same low frequency response as sealed then they won't sound the same.
Another point needs to be made. There's no advantage to sealed cabs with most modern drivers, including those used by Ampeg for the last 20 odd years. But there was also no advantage to ported with many drivers of 1960s vintage, including the CTS ten used in the SVT. If Ampeg had drivers with post 1990 specs back in 1969 chances are the original SVT would have been ported. They didn't, so it wasn't.

the sealed sound is from no overhang. it stops quicker.

Not true. The movement of the cone is determined by the signal from the amp. The force of the amplifier damping factor is magnitudes of order higher than that of the speaker suspension/cab system.

 

[john turner]

the sealed sound is from no overhang. it stops quicker. when your cab is jamming at 40 hz, there is a noticable start and stop to each pulse or vibration of the string. you can feel each one like a lawnmower engine, you hear each putt with noticable space in between. a ported cab sounds more like a steady tone, like mush.

oh, ok, thanks . i understand what you guys are talking about there.

when i built my monitors, they were tuned-ported 3ways, but i used a midrange driver that came sealed in its own enclosure a bit bigger than a coffee can. iirc, this was to, among other things, tailor the response of the midrange driver to the frequencies it was intended to drive (as well as protect it from the internal hurricane generated by the 10" woofer ). i wonder if something of this sort would work with a cab like a fearful (apologies if this is already going on with them, not that familiar with the designs).

 

[staindbass]

martin colloms describes it as "boomy" in the book high performance loudspeakers page 116. yes the movement of the cone is from the amp, but take your ported cab and transient test it by touching a 9v battery on and off the terminals. the connection and break connection should sound the same. if it doesnt (it wont, you will notice the sound on breaking the connection is longer the when making the connection- try it, it will click on making the connection, then boom or bong on breaking the connection.) that means you have overhang (speaker making sound)after the original signal has passed.

 

[staindbass]

then try it on a sealed cab..

 

[billfitzmaurice]

i used a midrange driver that came sealed in its own enclosure a bit bigger than a coffee can... i wonder if something of this sort would work with a cab like a fearful

Sealed midrange drivers are used to obtain higher sensitivity. As a for instance, look at the data sheets for the Eminence Alphalite 6a and Alphalite 6a CBMR. The two drivers share all the same parts except for the closed basket on the CBMR. The closed basket results in an increase of Fs from 126Hz to 501Hz, and an increase in sensitivity from 94dB/w to 100dB/w. Response below 500 Hz is sacrificed to get that sensitivity increase. Response of the sealed basket is also much rougher, but if sensitivity is more important to you than flat response it's a worthwhile trade-off. Putting a woofer in a small cab, sealed or vented, accomplishes the same thing. System resonance is raised, and along with it sensitivity, but at the cost of low end response.

martin colloms describes it as "boomy" in the book high performance loudspeakers page 116. yes the movement of the cone is from the amp, but take your ported cab and transient test it by touching a 9v battery on and off the terminals. the connection and break connection should sound the same. if it doesnt (it wont, you will notice the sound on breaking the connection is longer the when making the connection- try it, it will click on making the connection, then boom or bong on breaking the connection.) that means you have overhang (speaker making sound)after the original signal has passed.

What that mainly means is that the cab is under-damped. That's easily cured by lining the cab with damping material, something that many bass cab manufacturers cheap out on. Under-damping is less noticeable with sealed cabs because the 'boom' frequencies where the effects of under-damping are most noticeable are reproduced with higher sensitivity with ported cabs than sealed, especially with cabs that are tuned too high.
Also, using a battery to compare response is very different from using an amplifier. When the battery is disconnected there is no electrical damping being applied to the voice coil. When an amp is being used there is electrical damping of the voice coil, even if there's no signal content present.

 

[kraigo]

I think it might be worth it. Sometime copious low end just leave the room sound muddy. You certainly know that the fundamental isn't everything in the bass tone. That big warm tone, even with it's diminished true low frequencies can be very worth it.

Mind you, I also know all of this and still geek out over trying to get real low end response.

KO

The only 'advantage', if you want to call it that, to the sealed cab is higher harmonic distortion. THD is directly proportional to excursion. Sealed cabs have higher excursion for equal output, so they have higher harmonic distortion, which is often equated with 'warmth'. When you push drivers past xmax THD literally skyrockets, and since sealed cabs are pushed past xmax at far lower power levels than vented that further raises the 'warmth' factor of sealed. But all that warmth is obtained at the expense of low end output, so consider well if it's a worthwhile goal.

 

[john turner]

Sealed midrange drivers are used to obtain higher sensitivity. As a for instance, look at the data sheets for the Eminence Alphalite 6a and Alphalite 6a CBMR. The two drivers share all the same parts except for the closed basket on the CBMR. The closed basket results in an increase of Fs from 126Hz to 501Hz, and an increase in sensitivity from 94dB/w to 100dB/w. Response below 500 Hz is sacrificed to get that sensitivity increase. Response of the sealed basket is also much rougher, but if sensitivity is more important to you than flat response it's a worthwhile trade-off. Putting a woofer in a small cab, sealed or vented, accomplishes the same thing. System resonance is raised, and along with it sensitivity, but at the cost of low end response.

the mids i used weren't just sealed basket, they actually were in their own enclosure, sorta like this :

although i remember the "can" they were in to have been a little bigger.

 

[kringle77]

Bill, what would the effect be if you doubled the amount of stuffing in a ported cab? I said doubled just to make any calculation easier.

 

[rpsands]

There are two aspects of sealed cabs people are confusing.

1) increased distortion from the box forcing more excursion for the same amount of power

2) smooth, early low end rolloff (depending on box size)

#2 is beyond easy to simulate since it follows very similar rules to normal high pass filters.

Getting the sealed bottom on a ported cab is EASY. I've done this a million times.

#1 is where I think people think the magic is. Personally, I don't find it that hard to get close, but opinions vary.

The transient response stuff has been disproven over and over and over again in listening tests. Most ported boxes are too small and ported boxes are boomier when too small than sealed boxes.

This predominance of content in the upper bass region makes them boom which makes them sound slow.

That combined with what Bill said about the shortage of dampening is the big deal.

 

[billfitzmaurice]

the mids i used weren't just sealed basket, they actually were in their own enclosure, sorta like this :

although i remember the "can" they were in to have been a little bigger.

Same thing, what differs is the size of the can. Hi-fi mids aren't concerned with increased sensitivity, they just seal off the back to make an external enclosure unnecessary, so the can volume is larger.

Bill, what would the effect be if you doubled the amount of stuffing in a ported cab? I said doubled just to make any calculation easier.

That depends on whether it's adequately damped. If it isn't a thicker lining will make it work better, if it is adequately damped it would make it worse. Ported cabs are lined, not stuffed.

 

[R Baer]

Its refreshing to hear this from a guy who works with specs on a daily basis, specially in a forum where many people seem to forget to use their ears when judging equipment...

You might be assuming that engineers don't use their ears as much as non-engineers when judging gear. That's not only untrue, the opposite is the case. Engineers know what causes what they hear, and how to make changes in the gear so that it will sound the way they want. They may do so using data, but the data is only a means to an end, good sound, and not the end in itself. Those who do not understand data can only use their ears. Those who do use both their ears and their eyes, and most importantly, their brains, unfettered by misconception.

Ya know, sometimes a piece of gear, despite all it's "engineering flaws", just works. The SVT/810 imparts a certain color and response I haven't heard from other rigs. I'm not talking about just frequency response. I'm talking about the way that your bass responds under your fingers when playing. The way the notes jump off the neck, all the break up and distortion....just amazing!

That said, I can only attribute the wonderful success of that rig to the engineers who designed it. No doubt they had both the engineering chops and the great ears necessary to create what is probably the most successful bass amplification product in history.

 

[JimmyM]

Ya know, sometimes a piece of gear, despite all it's "engineering flaws", just works. The SVT/810 imparts a certain color and response I haven't heard from other rigs. I'm not talking about just frequency response. I'm talking about the way that your bass responds under your fingers when playing. The way the notes jump off the neck, all the break up and distortion....just amazing!

That said, I can only attribute the wonderful success of that rig to the engineers who designed it. No doubt they had both the engineering chops and the great ears necessary to create what is probably the most successful bass amplification product in history.

Agreed on all counts. I'm all for education and learning what's up as much as I can, but sometimes stuff just works.

 

[Plstrns]

What that mainly means is that the cab is under-damped. That's easily cured by lining the cab with damping material, something that many bass cab manufacturers cheap out on.

Hey, damping material isn't cheap from a manufacturers standpoint either.

$5 you say? (example, I know you didn't say anything about costs) Try loading 4-500 cabs a day with $5 worth of damping then get back to me. Damping material is relatively expensive for what it is, so $5 is a low ball.

I don't think it's acceptable from a buyers perspective, but from a quality point of view I can tell you all about it.

1. Commercial cabs start with the Acoustics guys coming down to the production QA booth to sine wave the newest and greatest. They develope a production standard from THE standard in a less than ideal environment (some mics placed a meter or so from the conveyor belt in an insulated chamber that run through a O scope).

2. Production begins, but the enclosures do not check to the standard. Instead of a fully lined enclosure, there's now only a strip of insulation stapled to the floor and partial back wall. Acoustics comes back down to approve the new specs. Clear sailing for this run.

3. Run no. 2. The speaker specs have changed, god help us if there's a new vendor. No new vendor, but the speakers are different. Acoustics takes a cab back to the lab, then returns with a thumbs up! Production can continue. Just rewrite the curve....

4. In the middle of this 600 PC run, the sine wave varies wildly! Acoustics is too busy to come by, so the production manager calls the QC chief to tell him the line has to run now! So, that's what happens. Turns out some wrong caps where inserted in the crossover assembly... That's what warranties are for.

Remember, business is about making a profit. Though, sometimes it tough to stomach.

 

[rpsands]

Damping material bought in bulk would cost nowhere near 5 dollars per cab, especially if you use cheapo insulation.

 

[Plstrns]

Ya know, sometimes a piece of gear, despite all it's "engineering flaws", just works. The SVT/810 imparts a certain color and response I haven't heard from other rigs. I'm not talking about just frequency response. I'm talking about the way that your bass responds under your fingers when playing. The way the notes jump off the neck, all the break up and distortion....just amazing!

That said, I can only attribute the wonderful success of that rig to the engineers who designed it. No doubt they had both the engineering chops and the great ears necessary to create what is probably the most successful bass amplification product in history.

Sometimes I wonder if they got it right (very, very difficult for a first outing, if not impossible), or if we just enjoy the nostalgic sound. It's difficult to distingish- like a cheeseburger, is it really good or do we just think it is? I personally love it, but what are the odds it's really that good?

 

[Plstrns]

Damping material bought in bulk would cost nowhere near 5 dollars per cab, especially if you use cheapo insulation.

Peavey invented the green movement with their insulation. They told us a $ figure that I don't remember, but was more than $5 an enclosure...all recycled... The insulation was a sheet of green fabric too, really cool for the day.