Anyone here use si sql-15 sealed fof theater duty?

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ssmokeyy

Junior Audioholic
So I have built subwoofer boxes before ported and sealed. I like sealed over ported. But I want to hit 19 hz with the thunder. Can the sql-15 hit 19 hz sealed over 105db with out sounding like its stressed out?
 
ryanosaur

ryanosaur

Audioholic Overlord
If your actual woofers measure like mine did, I think trying to hit that SPL while maintaining any sort or SQ will not be possible.
Parameters for my SQL-15s are not even close to what is advertised on his site. My Fs is 39 Hz, for example.
 
S

shadyJ

Speaker of the House
Staff member
If your actual woofers measure like mine did, I think trying to hit that SPL while maintaining any sort or SQ will not be possible.
Parameters for my SQL-15s are not even close to what is advertised on his site. My Fs is 39 Hz, for example.
Did you measure after placing it in a sealed enclosure? His spec would be free air.
 
ryanosaur

ryanosaur

Audioholic Overlord
Did you measure after placing it in a sealed enclosure? His spec would be free air.
Free air for my measurements.

I put off building a mule to test in a box just because cost of material has been so stupid. I've been communicating with a few friends and acquaintances (including a guy who is working in JBL Research down in SoCal) and the general advice at this point is to get it into a box and see how it tracks the model.

My measurements had a hiccough in one number, but generally all looked to be in order. When I bust them out again, I was planning o redoing my tests to see if I can get that last measurement locked down. I discovered in the course of my testing with DATS that the numbers fluctuated a bit for every test but would stabilize after running 2-3 tests.
I suspect this is where I ended up with the off measurement as I didn't catch this pattern until I was mostly through testing.

I'll PM you my measurements, just for kicks.
 
S

ssmokeyy

Junior Audioholic
What about using to 3-5 cubic ft box to dig deeper down.
 
ryanosaur

ryanosaur

Audioholic Overlord
What about using to 3-5 cubic ft box to dig deeper down.
Nick recommended I do either a 4cu.ft sealed or a 10 cu.ft ported cabinet for my goals.
With the measurements of my Drivers... I don't see either being functionally worthwhile.

I sat on my Drivers too long during the Pandemic while Lumber prices were skyrocketing. When I did finally get up the gumption to start, I was well beyond making any claim to Nick about my Drivers.

That said...

If you are serious about DIY, you should have a way to verify the actual measurements of your Drivers. You should Model what you want to build. Build a test box and measure the results, comparing it against your Model. Make any tweaks to the design and repeat the process...

While these Drivers have a lot of room for excursion, it is also well known that they don't do very well when pushed that far. The excursive capability vs the linear performance capabilities don't seem to match well.

I could find I am completely wrong, and truly hope that my measurements and understanding of how they will apply to the build will be proven pointless. ;) There is a growing case for the old school rules of Driver/Speaker design being off. But I am not the person to discuss this with.
Keep in mind that we are talking about a Driver being advertised at using 1000-2000w vs more conventional Driver designs... and the world of extreme Subwoofers is breaking the T/S Parameter conversation somewhat.
I'm not arguing one side or the other, but the more cats I talk to about it, the more play between two paradigms seem to exist.

However, when I model the Drivers I have according to their measurements... the models do not stack up favorably for my goals.

Truthfully, I'm expecting that I will have some "OK" Mid-Bass Modules on my hands when I'm done. Not the Subs that will perform strong at 16Hz for Pipe Organ that I was told I would have.
 
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ssmokeyy

Junior Audioholic
So I'm getting that these subs specs listed are not correct. That's kinda sad.
 
ryanosaur

ryanosaur

Audioholic Overlord
So I'm getting that these subs specs listed are not correct. That's kinda sad.
Not the two I tested.
*shrugs

I agree... but remember this is the case with most Drivers, too.
 
TLS Guy

TLS Guy

Seriously, I have no life.
So I'm getting that these subs specs listed are not correct. That's kinda sad.
You have to do an accurate model before you build any sub.

That driver is a high sensitivity driver, and has an Fs of 23.8 Hz, so 24 Hz rounding it off. Now drivers will roll off quite quickly below F3 which is usually a bit above Fs in an optimal ported box. However in a sealed box f3 is usually around an octave above Fs. At that point you have to add Eq at 12db per octave below F3. At the point the driver reaches xmax then you need to high pass it at that frequency to prevent driver damage.

The bottom line is that low end extension and especially output is much greater with an optimally designed ported box, than a sealed design.

The specs, known as the Thiele/Small parameters if honest, are not sad, but essential for designers like myself to accurately model and design for the driver. The numbers are for designers and not for people who buy a driver, throw it in a box and expect thunderous bass. That is not the way it works.

My hunch is you do not understand the physics and principles of loudspeaker design..
If you are patient you can learn a lot on this forum. I have guided a number of members here to build excellent subs.
 
S

ssmokeyy

Junior Audioholic
I understand some about the numbers. The part I have real problems with is understanding port flow and port tuning correctly. All this software out there and not one talks about port flow. I would love to understand more about it.
 
lovinthehd

lovinthehd

Audioholic Jedi
I understand some about the numbers. The part I have real problems with is understanding port flow and port tuning correctly. All this software out there and not one talks about port flow. I would love to understand more about it.
You mean port air velocity? Software for ported boxes would cover that....what software are you looking at?
 
S

ssmokeyy

Junior Audioholic
Bass box pro lite. I keep jacking up winisd. Also I have a guy on avsforum telling me sealed will play loud in a sealed box with room gain. Not saying much more than. That. Thats why I have been asking g about sealed. Than I found some other post stating this subs spe s to be off. O
 
TLS Guy

TLS Guy

Seriously, I have no life.
Bass box pro lite. I keep jacking up winisd. Also I have a guy on avsforum telling me sealed will play loud in a sealed box with room gain. Not saying much more than. That. Thats why I have been asking g about sealed. Than I found some other post stating this subs spe s to be off. O
I have modelled your driver. It is primarily intended to be used as a sealed driver, but gives a not very impressive performance. It requires 12db per octave boost below 50 Hz and must be high passed at 25 Hz. to avoid driver damage.

It does however perform much better in a vented alignment. It requires a slot vent, and just about skates in with a vent length that will not give an unacceptable port resonance and give a just acceptable vent air velocity at 20 meters per sec. So it will not chuff.

If you build it, this would actually be a very good sounding and performing sub.

Although this driver was clearly designed to be used sealed, it is actually a pretty poor performer, and the vented version will be better by miles. You need to add driver volume, bracing and the volume of the slot vent to the overall enclosure volume.
 

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ssmokeyy

Junior Audioholic
So i have been using winisd. I got the software to load the si sql-15. It seems like anytime i get the air speed around 20 the port length is crazy long over 50 inches. Is there a trick to keep the air speed down but also get the 22 hz port tune in a 4.8-5.5 sized box. Tried it with round ports also.
 
TLS Guy

TLS Guy

Seriously, I have no life.
So i have been using winisd. I got the software to load the si sql-15. It seems like anytime i get the air speed around 20 the port length is crazy long over 50 inches. Is there a trick to keep the air speed down but also get the 22 hz port tune in a 4.8-5.5 sized box. Tried it with round ports also.
That is a good question. Yes, that driver is aimed at sealed, but you can see it is not a good driver sealed.

So as you have found the port model as too long if you are not careful. The design uses a slot vent. See picture.



The problem is that if the vent is to long, it acts lake an open organ pipe and the port resonance becomes audible. To prevent port chuffing you like to keep port air velocity below 20 m/sec. My ported design stretches that a little and my ported model is 24 m/sec. However that is a powerful driver, and you are unlikely to get to 24 m/sec and if you did it would be so loud you would not hear it.

I am confident the ported model I did for you, would give you a really good sub you will be pleased with. The ported model flattens that nasty humped response the sealed model has.
 
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ssmokeyy

Junior Audioholic
i Looked at it again. Just want to make sure i follow your specs. First No. of Vents = 1 Vent shape = rectangle Vent ends = one flush Hv = 2.5 in Wv = 8 in Lv = 28.01 in 2.5 wide x 8 tall x 28 long Is what i see. Total box volume is 4.4 cubic before ports, driver Is there any bracing planned in those specs? So if i build the a box 10 depth x 32 wide x 32 tall I would get 4.4 cubic box before port or driver or bracing. Does it matter where i put the vent ? Looks like i could put it in the back and have it come out the side. It looks like its -6 db down around 20 hz and under. Is there still enough slam there to fill those 18hz shock waves in movies?
 
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TLS Guy

TLS Guy

Seriously, I have no life.
i Looked at it again. Just want to make sure i follow your specs. First No. of Vents = 1 Vent shape = rectangle Vent ends = one flush Hv = 2.5 in Wv = 8 in Lv = 28.01 in 2.5 wide x 8 tall x 28 long Is what i see. Total box volume is 4.4 cubic before ports, driver Is there any bracing planned in those specs? So if i build the a box 10 depth x 32 wide x 32 tall I would get 4.4 cubic box before port or driver or bracing. Does it matter where i put the vent ? Looks like i could put it in the back and have it come out the side. It looks like its -6 db down around 20 hz and under. Is there still enough slam there to fill those 18hz shock waves in movies?
I should have been clearer. The internal box air volume is 3.8 cu.ft. The program in the V total has allowed for driver and port volumes, which brings the volume up to 4.4 cu.ft, so has added just over half a cu.ft. I don't know how you will brace it, but you will have to add the volume of bracing. Pressures are high in ported cabinets so your bracing needs to be substantial.

As far a port location it is not highly critical, and ports are often placed on the rear of speakers. However a front port is optimal, but not a huge deal. The reason is that in the cabinet there is a phase inversion. The front and rear of the cone are obviously 180 degrees out of phase. However in the range where loading is active from the design, there is a 180 degree phase inversion of the rear driver radiation, so that output is emitted from the port in phase with the front cone output, so they augment each other. Having said that most of the output is from the port before the driver decouples from the box. In addition at those frequencies the outputs are omnidirectional so the phase shift due to distance has only slight significance unless the sub is very deep. Never the less, I advise front port placement as optimal. If you look at the cone displacement graph, you can see that at tuning around 20 Hz, cone displacement is reduced 4 mm, and then below 20 Hz cone displacement rapidly rises as the driver decouples from the box. That is why trying to increase output below tuning with Eq is fruitless, and does not increase bass output, but can result in driver damage as the driver looses the restoring force of the alignment.

I do think this design will be worth the effort and expense of building it. I will be surprised if you are not very pleased with it, despite the slightly high vent air velocity. I will be surprised if you hear a chuff though, unless you play it "bleeding" loud right next to you.

By the way the ported sub does just hit 109db at 19 Hz, but 118db at 40 Hz. At 19 Hz at full power cone displacement is only 8 mm. The sealed hits 103db at 19 Hz ,but will only handle 90 watts of power and is at xmax. That is a nice demonstration of the superiority of ported over sealed.
 
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ssmokeyy

Junior Audioholic
Tls do u know of any subs that have a f3 of 20hz in sealed box?
 
ryanosaur

ryanosaur

Audioholic Overlord
Tls do u know of any subs that have a f3 of 20hz in sealed box?
Personally, I haven’t seen any I can think of offhand.
From a design perspective, I’m not certain what it would take to design a Driver with such a low resonant frequency that, once put in a cabinet, would maintain higher efficiency at infrasonic frequencies. Simple physics mandates that the tuning of the system will always be higher than Driver Fs.
Where you get away from this is with Power Handling, Excursion and DSP. When you apply a Linkwitz Transform as Nick would recommend, you also need a Driver that can handle the additional Power required to force excursion to its limits, thus “allowing” the Driver to perform beyond its theoretical capabilities.
In a Sealed cabinet, this is a matter if brute force. In a ported cabinet it changes somewhat. Either requires a Motor and Suspension capable of handling the demands placed upon them.
This then gets back to what I said earlier about how the actual Driver(s) you own or buy behave against advertised spec.
How you are able to push s Driver in an extreme Subwoofer build is a dice roll against its theoretical performance capabilities. If you push too hard, it will not sound good. If you push s little further it will burn out. Possibly, you will take the Amp with it.

Like it or not, I’m just advising based on my experience with these drivers. Specifically the two I own and have tested.
There are many that seem to be quite happy with the product. Others I’ve seen are satisfied yet experienced slightly similar changes to spec as I have reported. I expect when I build and test, I will find s mixed bag.

In the end, your best option is to make certain you have a good amp, good DSP, understand how to set them up, then build and test a modeled Sub.
Then you can make changes and have some parameters to guide you.
 
TLS Guy

TLS Guy

Seriously, I have no life.
Tls do u know of any subs that have a f3 of 20hz in sealed box?
No, and you don't want one!

The fact is I have designed you a sub that meets the criteria you specified with the driver you have. Just look at the graphs in the model I did You will see there is good output to around 19 Hz. Actually, with room gain it will be pretty much flat to 20 Hz or oven enough you have to reduce output.

I have built a pretty large HT room, with an excellent response. Although in the model my speakers actually roll off around 27 Hz, in the room they don't. They go all the way to 20 Hz, and actually the room gain is such I have had to reduce power to the bass drivers, to get a flatter room response.

Lastly, stop being obsessed with sealed enclosures. They are a terrible idea and you never design and build one unless you are short of space. They will always be horrible brute force contraptions. The reason being that a loudspeaker cone has a lousy coupling to air. The physics of the idea is all against you. You need to use physics to your advantage not against you. In a sealed design you fight physics and the laws of nature all the way. Did I say a sealed sub is a terrible idea?

This rig makes physics work for it.



This is the close mic response at 1 meter, that produces the best response at the MLP.



Response at the MLP.



I pick the right battles and win. You are picking the wrong battles on the wrong hill, and will loose big time, if you don't take the advice of the experineced.
 

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