Can the /excessiveness/ of the 8361A be better utilised?

[Tovarich007]

A sealed loudspeaker will have more output than a ported one, below the port tuning frequency. Since we're looking specifically for increased output down there, sealed is about the only option.

NB - the other option is to extend the length of the port, which will decrease the tuning frequency. This is much more difficult to do well than simply sealing the port. Ideally, you'd increase the cabinet size to maintain a somewhere-near flat response. Playing around in WinISD or Hornresp will be educational for those following along.


Chris

Yes of course, due to the gentle progressive roll off of a sealed design, I never said the contrary, but a sealed design doesn't go lower in absolute terms than a ported one. But the more progresive roll off and thus the relative higher output under the tuning port frequency has a price in SPL, power requirements, distorsion, and that's not so easy to fix properly without a simulation, tests and measurements, for a speaker not originally designed to be sealed.

Genelec has always released ported speakers. it doesn't mean they can't do other types of designs if they will, because this company has the expertise to design any type of design. But they consider it's the best compromise, and they don't do so only because a ported design is less subject to thermal overheat risks, being opened, even if they surely have taken this criteria into account.

Whatever can be the more or less satisfying results of such a transformation, It will certainly cancel the constructor warranty and services in case of problem.
For many reaons, I'm not sure it's a good idea to suggest to make such a modification for a person like 8361AM, who is quite sympathic but evidently not an expert or a technician.

 

[ChrisG]

a sealed design doesn't go lower in absolute terms than a ported one.

We're arguing over semantics, I suppose, but I'll always argue this is false. A sealed box has more output at 1Hz than a 36Hz-tuned ported box. The ported box is an acoustic short-circuit below its tuning frequency, while a sealed box has some output all the way down. Not as much output as the ported box within its power bandwidth, sure, but we're talking specifically of LF extension here.


I did note the caveats of trying to EQ a sealed-up 8361.


Chris

 

[8361AM]

Many thanks for the additional feedback.

I'll aim to respond later today but for now I wanted to share what I believe could be progress...

Using GLM, I can set a substantial negative high pass filter at a low frequency point (e.g., -10dB at 40Hz). According to GLM, this tilts up the low end frequency response so that the speaker extends flat much lower (e.g., flat to 30Hz rather than 36Hz). The downside is that the ~30-90Hz range is boosted above a flat response, thus reducing accuracy. However, the GLM custom notches can then be edited to re-flatten the response. It's possible to go even further so that, for example, a negative 18dB filter at 40Hz reports flat extension down to 24Hz. Hopefully, this is clear, but I'll share an image or two later showing this as I suspect this will be more useful.

I'd be keen to know if what I've done here gets round some of the concerns raised here. It seems to me that what I've done is "safe", because I've cut rather than boosted and SPL remains in abundance. However, similar to what some others have shared, I'd be keen to measure the result so that I can determine whether the changes made in GLM have actually resulted in the kind of response GLM reports. I don't know how to do this but will look into this later unless someone would like to make a recommendation...

 

[ChrisG]

You've "cut" until you reach for the volume control and apply 18dB more gain.

Then, you've essentially boosted the LF range.


Pushing a ported speaker hard below tuning is a great way to mechanically damage them. Trust me on this - I've folded more than a few cones. One of them was a Beyma 15P1200Nd. Woops!


Chris

 

[Tovarich007]

We're arguing over semantics, I suppose, but I'll always argue this is false. A sealed box has more output at 1Hz than a 36Hz-tuned ported box. The ported box is an acoustic short-circuit below its tuning frequency, while a sealed box has some output all the way down. Not as much output as the ported box within its power bandwidth, sure, but we're talking specifically of LF extension here.


I did note the caveats of trying to EQ a sealed-up 8361.


Chris

Your reply is "right" but purely theorical acoustics and maths, who cares about 1 hz ? There is absolutely nothing to hear.
BTW, the best trained and sensible human ears can't hear something lower than 16 hz. At such low frequencies, we're in the infrasonic vibrations domain, that's not audio anymore, what we could perceive is not these frequencies by themselves, but eventually harmonics generated by the infrasonic frequencies and vibrations.

 

[Old_School_Brad]

You've "cut" until you reach for the volume control and apply 18dB more gain.

Then, you've essentially boosted the LF range.


Pushing a ported speaker hard below tuning is a great way to mechanically damage them. Trust me on this - I've folded more than a few cones. One of them was a Beyma 15P1200Nd. Woops!


Chris

The "clack clack" sound is one of those distinctive noises that stick with you, much like the "tick tick tick" of a engine's failing connecting rod bearing. The harder you push to the limit, the more likely you are to hear one of these sounds.

 

[Tovarich007]

Many thanks for the additional feedback.

I'll aim to respond later today but for now I wanted to share what I believe could be progress...

Using GLM, I can set a substantial negative high pass filter at a low frequency point (e.g., -10dB at 40Hz). According to GLM, this tilts up the low end frequency response so that the speaker extends flat much lower (e.g., flat to 30Hz rather than 36Hz). The downside is that the ~30-90Hz range is boosted above a flat response, thus reducing accuracy. However, the GLM custom notches can then be edited to re-flatten the response. It's possible to go even further so that, for example, a negative 18dB filter at 40Hz reports flat extension down to 24Hz. Hopefully, this is clear, but I'll share an image or two later showing this as I suspect this will be more useful.

And such low bass extensions and further corrections are not enough for you ? What do you want more ?
Have you eventually tried these GLM settings and re-flattening corrections in your room with real music and soundtracks, at your desired output level ?

IMO, you're looking for the moon (as we used to say in french) if you're unsatisfied with that.
This is my last contribution to this thread. I can't see what i could say more which could be practically useful.

 

[8361AM]

You've "cut" until you reach for the volume control and apply 18dB more gain.

Then, you've essentially boosted the LF range.


Pushing a ported speaker hard below tuning is a great way to mechanically damage them. Trust me on this - I've folded more than a few cones. One of them was a Beyma 15P1200Nd. Woops!


Chris

Thanks, Chris.

Understood and keen to take good care of my babies...

It seems there's some potential to EQ as I've suggested to achieve what I hoped to but also that there's a point at which I risk damaging the speaker. So, at what point am I putting the 8361A at risk when stressed; for example, negative 1, 3, 5, 7, 10, or more dB? I sense that no one here will know specifically for the 8361A, but keen to be corrected, and so it seems a follow-up question would be how to determine what's feasible (furthermore, we'd need to be specific about SPL and content, since I'm sure a -18dB cut as described above would be fine when at low SPL and with minimal bass content). Relating to this, I also wonder if there are ways to reduce the stress, such as reintroducing a steep drop at ~20Hz or otherwise.

 

[8361AM]

So, at what point am I putting the 8361A at risk when stressed; for example, negative 1, 3, 5, 7, 10, or more dB?

It's just occurred to me that we may be able to answer this based on the speakers specifications...

Here's what Genelec states:

Peak SPL: ≥124 dB
Short term max SPL: ≥118 dB
Long term max SPL: ≥109 dB

It seems to me that the kind of content that will stress the 8361A most is the audio from movies and further that this content is not constant. Thus, the short term max SPL might be the better metric to consider here (rather than long term max SPL).

If I were to go down the extreme route of an -18dB shelving filter (not that I'm suggesting this but as a case in point) but the speaker would be limited to SPL at 100dB or lower, this would seem to be within the speakers limitations. Of course, this isn't quite the case, because the shelf I've suggested tilts up the bass and this will put greater stress on the speaker, but I think it's useful nonetheless. Thus, might it be reasonable to suggest that if SPL is limited to say 90-95dB (as a safety precaution), that the speaker should not be at risk?

EDIT: It seems this could be calculated; for example: short term max SPL (e.g., 118dB) - shelving filter (e.g., -18dB) - tilt (e.g., 3dB) - safety (e.g., 3dB). Based on these example figures, SPL should be limited to 96dB. Based on my above -18dB filter example, the 8361A could trade 22dB for an extra 12Hz extension (flat to 24Hz rather than 36Hz). Of course, this is based on the actual response matching GLM...

 

[JustJones]

The 118dB max SPL is derived from a sine wave averaged 100hz - 3khz at 1 meter. I doubt you would get flat to 24hz using your weird shelving before the driver protection limit circuitry kicks in. You're better off using room boundary or subwoofers.

 

[Randyman...]

Seems like a potentially expensive experiment, but hopefully the amp/DSP will prevent any mechanical damage.

 

[ChrisG]

Your reply is "right" but purely theorical acoustics and maths, who cares about 1 hz ? There is absolutely nothing to hear.
BTW, the best trained and sensible human ears can't hear something lower than 16 hz. At such low frequencies, we're in the infrasonic vibrations domain, that's not audio anymore, what we could perceive is not these frequencies by themselves, but eventually harmonics generated by the infrasonic frequencies and vibrations.

The guys over on AVS Forum would disagree with you. They're chasing tactile response down to the single-digits, and some of them manage it. A pair of 18" long-throw subwoofers is "just getting started". Yes, really. Measurements here: https://www.avsforum.com/threads/fo...-riser-curved-screen-custom-software.1507428/

Having experienced such LF extension a couple of times, I can understand the appeal. You can't "hear" it with your ears, but your body can still detect such air movements.

Based on my above -18dB filter example, the 8361A could trade 22dB for an extra 12Hz extension (flat to 24Hz rather than 36Hz).

Perhaps, but you're still applying boost below the port tuning frequency. As I've written several times, this is a No Go for speakers. Best case, you hear the drivers distorting and turn it down. Worst case, you actually damage the drivers. The Beyma 15P1200Nd that I've damaged previously was hit by less than half its AES power rating, but it was well below the tuning frequency. NB - it's not a cheap driver. In fact, it's one of the better 15" PA subwoofer drivers on the market. They're remarkably abuse-tolerant and can keep up with mid-tier 18"s in much larger cabinets. Still, hitting it with a few hundred Watts of below-port-tuning was enough to cause mechanical damage.

I don't know if Genelec has built excursion limiters into their design, or if they're just expecting reasonably-sensible inputs. If it's the former, you'll hit those limiters first, and quickly. If it's the latter, I must stress that what you're planning is not a "sensible input".
Blocking the port is how you can prevent the acoustic short-circuit and give the drivers some protection from over-excursion.

Finally, I'd like to note that the maximum SPL ratings are typically mid-band (say, 100Hz-3kHz) or perhaps The Loudest Sound This Speaker Can Produce... Once. You can read more on that subject here: https://www.prosoundweb.com/spec-wars-looking-inside-loudspeaker-spl-specifications/
Which I wrote back in 2017 after spending some time with some members of the industry that should really have known better.


Chris

 

[Randyman...]

Expecting 2x 10"s to dig down in the 20's at moderate (read that "feelable") SPL's are not what that speaker/driver was engineered to do. Your THD is going to go through the roof (not the worst thing in the world at sub frequencies), and you will be asking for excursion many times the speaker's capabilities below f3 port tuning/loading - even at low SPL. It's basically an IB once you get 1/2 octave below the tuning frequency, and I guarantee the 10" drivers are not optimized to be run unloaded (and with the port cancellations shooting you in the foot). Then you have the admitted issues in the linear pass-band that also have to be corrected. You spent $10K on mains that can be VERY flat in their passband, you surely have a few grand for some descent subs that are designed flat to 25Hz or lower?

 

[Tovarich007]

Just 2 last answers on this thread to ChrisG and randyman.

Chris : Of course, you can feel the infrasonics ! that's for instance what you feel when you experience a begnin earthquake, or a shaking when a large truck passes by very close.

But I don't recommand to stay exposed a long time to infrasonics, as spectacular as it is. That could be dangerous. I worked a long time ago in the control domain of health and safety in working environements, and experts and medical ear and neuro specialists all agree about that.

Do you know that subject people to ultra or/ and infrasonics has been used (maybe still used yet) has a form a "clean and scientific" -sic- method of torture ?

Randyman : the 8361 bass drivers are elliptic, there're smaller than real classic10" drivers, so this could be even worse than you wrote, they're robust and reliable, just like Genelec is reputated for, but not designed to go very low. Their classic monitor 1237 with its 30cm (12") has probably better capability in these frequencies, within limits anyway.

 

[sigbergaudio]

But I don't recommand to stay exposed a long time to infrasonics, as spectacular as it is. That could be dangerous. I worked a long time ago in the control domain of health and safety in working environements, and experts and medical ear and neuro specialists all agree about that.

Do you have references for this? Unless we are talking extreme levels, I don't think this is true.

 

[GXAlan]

Do you have references for this? Unless we are talking extreme levels, I don't think this is true.

Negative Effect of High-Level Infrasound on Human Myocardial Contractility: In-Vitro Controlled Experiment - PMC

Human exposure to infrasound is increasing due to man-made factors, such as occupational conditions, wind farms and transportation. The concern among the public regarding the safety of infrasound exposure is growing. To evaluate whether exposure to ...

pmc.ncbi.nlm.nih.gov

 

[sigbergaudio]

Negative Effect of High-Level Infrasound on Human Myocardial Contractility: In-Vitro Controlled Experiment - PMC

Human exposure to infrasound is increasing due to man-made factors, such as occupational conditions, wind farms and transportation. The concern among the public regarding the safety of infrasound exposure is growing. To evaluate whether exposure to ...

pmc.ncbi.nlm.nih.gov

Based on this I wouldn't be too worried about listening to music or watching movies.

 

[Tovarich007]

Of course, like every harfmful phenomenon, it's dangerous if you're exposed to high levels ! It depends of thresholds and duration of exposition as for any other harmful phenomenon.

But the effects of prolonged high level exposition to infrasonic vibrations on inner ear, neurologic and psychics have been studied and documented for more than 50 years.
I don't have anymore the documentation that has been given by our teachers more than 40 ans ago. I'm retired now.
And use of infrasnics and ultrasonics as torture have been proven true, alas !

I'll search more recent documentation on the net. You can do it also.

Nowadays, the problem is this crazy quest for "ultra realism" in sound and image. It seems that the louder and the lower is the better.
I recenly was in a movie theater in Paris. During the advertising and previews of two or three upcoming block busters (I don't remember their titles and I don't give a damn about it anyway), the sound was way too loud and way to low in frequency, it was ear bleedind and shaking and vibrating. I felt not at ease and wasn't the only one to feel the same in the venue. Fortunately, it didn't last long and the main movie was much more peaceful.

So when I read on this forum or elsewhere people who want to experience at high level ultra low frequencies, I'm a bit scary.
Our technological world is pushing the game too far sometimes.

 

[Digby]

Still something of a mystery WHY the op wants to do this, for what practical purpose? To make your 8361s function as stand in for subs, down to 20hz?....Sorry, that will never happen and you risk damage to a pair of expensive speakers.

Can you boost the bass frequencies above port tuning somewhat...yes, provided you account for reduced SPL (which you may not need).

 

[dshreter]

Still something of a mystery WHY the op wants to do this, for what practical purpose?

I think ‘why’ is obvious. OP bought a super expensive pair of speakers that are doing little more for him than the smaller pair could have done. He wants to know if he can somehow squeeze a subwoofer out of them so the expense wasn’t a waste.

OP has also received about 20 thoughtful replies explaining this isn’t a good idea, but doesn’t seem to want to acknowledge any of them, considering the points unhelpful.

OP’s idea makes sense, but it is not practical due to the port design of this speaker.