No compromises front loaded double 18” cab

[Ivan Beaver]

Re: No compromises front loaded double 18” cab

Hey Luke,

Nice work on the build.

I'm curious about the port design. Based on the link posted earlier in this thread that related aerodynamic theory and especially boundary layer friction to high power port design, your port with the different cross sections top, middle and bottom may not behave consistently. Since the boundary layer is going to affect the narrow center section of the port much more so than the top and bottom, I wonder if the ports effective tuning is going to shift upwards with power. Probably all ports exhibit a change in effective tuning at different air velocities, but this design may exaggerate that behavior.

I'm curious what your testing reveals, but a pencil sketch on napkin application of the theory indicates the best port cross section for a high power application is a circle, as it has the least surface area for a given internal area.

In either case, nice woodworking. Let us know how they perform.

Ciao
Simon

I was building my cabinet back in the 90s with triangular ports (as in this build), long before anybody else was doing it (that I was aware of).

The biggest advantages it gave me was a smaller front baffle area and greatly stiffened up the side walls of the cabinets.

I did not have any measurement gear back then-but the results I got were impressive-as compared to the cabinets that I previously built using circular ports-using the same wood (13 ply baltic) and the same drivers.

I don't know if it was the shape of the port-or the additional bracing on the side walls (most likely) or the fact I was able to get drivers closer together (not usch a big deal at those freq)-but I was happy with the results.

Take that for what it is worth.

 

[Simon Coffin]

Re: No compromises front loaded double 18” cab

I was building my cabinet back in the 90s with triangular ports (as in this build), long before anybody else was doing it (that I was aware of).

The biggest advantages it gave me was a smaller front baffle area and greatly stiffened up the side walls of the cabinets.

I did not have any measurement gear back then-but the results I got were impressive-as compared to the cabinets that I previously built using circular ports-using the same wood (13 ply baltic) and the same drivers.

I don't know if it was the shape of the port-or the additional bracing on the side walls (most likely) or the fact I was able to get drivers closer together (not usch a big deal at those freq)-but I was happy with the results.

Take that for what it is worth.

Hey Ivan,

Interesting that you had better results with a triangular port. A stiffer cabinet would certainly help, but you may have unwittingly stumbled onto something with the port design. I wonder if the effective port length, which includes a certain amount of air at the mouth that extends beyond the port, changes with output level. At higher levels more air volume is involved and shifts the port tuning up or down.

In the case of your triangular port, the boundary affect would have been more pronounced and would have narrowed the ports effective diameter. Yet, the greater air volume involved at the mouth may have compensated giving you a more stable port resonant freq.

One thing that doesn't quite add up though is that a Helmholz resonator doesn't just use a given volume of air, its shape plays a role as well. The same volume of air in a long skinny enclosure resonates differently than in a short squat one. So if the effective shape of your triangular port is changing, shouldn't the resonant freq also change?

Now that I've written all this, I'm not sure I understand the theory any better or not?!?

Ciao

Simon
Simon

 

[Timo Ulkuniemi]

Re: No compromises front loaded double 18” cab

Hello

Just to stir the soup...

If I have ONE speaker with triangle vents - division between chambers integrated - what is the difference if it is standing upright versus laying against floor, where one port gets added lenght... ???

After this headache - how am I supposed to stack 2-4-8- of them ?


Seriously - highly interesting topic - perhaps I build a pair, too ( to get rid of extra elements on shelve ) and concentrate on getting it efficient and light - 12mm birch 12-ply wood - anyways lighter than two single 18 ...

With 5&half hour of daylight there is plenty of dark time for loose wandering... - happy I do not live in the northern parts

 

[Josh Ricci]

Re: No compromises front loaded double 18” cab

I'm a little late to the party but this has been an excellent discussion.

Ports do shift their tuning as the air speeds get higher and the turbulence increases causing a breakdown in laminar air flow. I have a few measurements showing this effect both in the response shape and the impedance curve. A single, large, circular port is technically the best shape to keep the port operating in an uncompressed controlled fashion. However very large round ports often do not cleanly fit into the box in a manner that fits well with the design or proposed form factor. It is also cheaper and less labor to build a slot vent in most cases. Additionally research shows that larger vent areas support higher volumes of air before noise and compression. You will often see hard or fast rules stated such as keep vent velocity below 17m/s or 25m/s or whatever. In reality the vent shape and area needs considered as well. 30m/s of air through a skinny 1"x 10" slot vent is much different (unacceptable) than 30m/s through a 10" diameter flared pipe. If the vents have sufficient area the cross sectional shape becomes less important. The best paper that I have come across that studies the effects of port behavior was researched by JBL a number of years ago. Let me see if I can find that PDF...

I often also read comments such as you will "need" a 3 or 4kw amp to make proper use of a certain driver. What the comment means to say is in order to run the driver up to the very edge of its abilities you will need an amp with "X" amount of power rating. In my view this is the wrong way of looking at things. I prefer to use systems that over spec the drivers and perhaps under power a bit. The last 3 to 6dB out of a driver is always the most distorted and compressed. If you can run a bit under the systems limits it sounds so much better. I would much rather listen to a 18sw115 loaf on a 1200w rated amp than run a TBX100 up to its useful limits. Another factor to think about is voltage sensitivity. This is NOT efficiency. Simulations driven by TS parameters at small signals scale perfectly. The driver behavior does not change whether you input 1v or 100v. This is not how things are in the real world. Many drivers change their behavior dramatically and run out of headroom or thermal handling abruptly which throws all of that small signal stuff out the window. Most bass systems often get operated more towards the upper end of their envelope not the bottom so looking at these small signal parameters is fairly useless. The heavier more expensive drivers, with greater xmax, xmech, and larger heavier voice coils and better motor cooling are more linear devices and do not change their behavior as much when driven hard, plus their limits are higher to begin with. So while you may be looking at a simulation based on parameters pulled from tiny input signals and thinking, I've only got a 1200w rated amp and $250 driver X is a little more sensitive and seems to get louder on that much power than $500 driver V, in the real world it is likely that the less sensitive, heavier duty driver may be louder and cleaner off of the same amp due to much better behavior at those drive levels.

Definitely look for high power measurements and Klippel testing on drivers as that separates the paper tigers from the real ones. Be wary of driver companies that have specs that seem to good to be true, but do not have detailed information on things like Klippel reports, the gap height and coil wind height, shorting rings, etc...There are many from all fields.

 

[Peter Morris]

Re: No compromises front loaded double 18” cab

I'm a little late to the party but this has been an excellent discussion.

Ports do shift their tuning as the air speeds get higher and the turbulence increases causing a breakdown in laminar air flow. I have a few measurements showing this effect both in the response shape and the impedance curve. A single, large, circular port is technically the best shape to keep the port operating in an uncompressed controlled fashion. However very large round ports often do not cleanly fit into the box in a manner that fits well with the design or proposed form factor. It is also cheaper and less labor to build a slot vent in most cases. Additionally research shows that larger vent areas support higher volumes of air before noise and compression. You will often see hard or fast rules stated such as keep vent velocity below 17m/s or 25m/s or whatever. In reality the vent shape and area needs considered as well. 30m/s of air through a skinny 1"x 10" slot vent is much different (unacceptable) than 30m/s through a 10" diameter flared pipe. If the vents have sufficient area the cross sectional shape becomes less important. The best paper that I have come across that studies the effects of port behavior was researched by JBL a number of years ago. Let me see if I can find that PDF...

I often also read comments such as you will "need" a 3 or 4kw amp to make proper use of a certain driver. What the comment means to say is in order to run the driver up to the very edge of its abilities you will need an amp with "X" amount of power rating. In my view this is the wrong way of looking at things. I prefer to use systems that over spec the drivers and perhaps under power a bit. The last 3 to 6dB out of a driver is always the most distorted and compressed. If you can run a bit under the systems limits it sounds so much better. I would much rather listen to a 18sw115 loaf on a 1200w rated amp than run a TBX100 up to its useful limits. Another factor to think about is voltage sensitivity. This is NOT efficiency. Simulations driven by TS parameters at small signals scale perfectly. The driver behavior does not change whether you input 1v or 100v. This is not how things are in the real world. Many drivers change their behavior dramatically and run out of headroom or thermal handling abruptly which throws all of that small signal stuff out the window. Most bass systems often get operated more towards the upper end of their envelope not the bottom so looking at these small signal parameters is fairly useless. The heavier more expensive drivers, with greater xmax, xmech, and larger heavier voice coils and better motor cooling are more linear devices and do not change their behavior as much when driven hard, plus their limits are higher to begin with. So while you may be looking at a simulation based on parameters pulled from tiny input signals and thinking, I've only got a 1200w rated amp and $250 driver X is a little more sensitive and seems to get louder on that much power than $500 driver V, in the real world it is likely that the less sensitive, heavier duty driver may be louder and cleaner off of the same amp due to much better behavior at those drive levels.

Definitely look for high power measurements and Klippel testing on drivers as that separates the paper tigers from the real ones. Be wary of driver companies that have specs that seem to good to be true, but do not have detailed information on things like Klippel reports, the gap height and coil wind height, shorting rings, etc...There are many from all fields.

I posted a link to that paper at beginning of the thread where I was talking about one of my designs. ~~:smile:

 

[Josh Ricci]

Re: No compromises front loaded double 18” cab

I posted a link to that paper at beginning of the thread where I was talking about one of my designs. ~~:smile:

Don't know how I missed that. Thanks for the link.

 

[Jeff Bailie]

Re: No compromises front loaded double 18” cab

Hi I have a question that I think fits in this thread.

I am wondering if you guys can explain the differences between how identical drivers with a different impedance rating perform in front loaded designs. For instance, how would the performance change with 4ohm vs 8ohm SW115 drivers in the same cabinet?

With this in mind, Why do we not see more triple 18" cabinets with (3) 8ohm drivers? It would seem like amplifiers these days are ready for the duty.

 

[Ivan Beaver]

Re: No compromises front loaded double 18” cab

Hi I have a question that I think fits in this thread.

I am wondering if you guys can explain the differences between how identical drivers with a different impedance rating perform in front loaded designs. For instance, how would the performance change with 4ohm vs 8ohm SW115 drivers in the same cabinet?

With this in mind, Why do we not see more triple 18" cabinets with (3) 8ohm drivers? It would seem like amplifiers these days are ready for the duty.

The only real difference you should notice between a 4 and 8 ohm low freq driver (high freq drivers can be different-due to the weight of the wire) is the sensitivity. THe max output will not change-but the sensitivity to a particular input voltage will be higher with a lower impedance driver.

But don't assume it is 3dB for "half" the rated impedance. Often the actual driver is not 4 or 8 ohms, but rather that value is the closest "standard value".

You need to measure the impedance (not DC resistance) for one driver compared to the other to be sure of what the real differences are.

My guess on the 3x18" cabinets (there have been some in the past) is the physical size. In order to get low freq the cabinet has to have a certain internal cubic volume-and 3x18" would make for a larger cabinet that some people would not like.

Cabinet design is a compromise between performance-what the customer will accept-individual price and so forth.

Plus some people simply don't like things that are "different" than what they are used to. It takes them out of their "comfort zone" even though the end result may be better. They simply resort back to what they are "used to".

 

[Alan Sledzieski]

Re: No compromises front loaded double 18” cab

Hi I have a question that I think fits in this thread.

I am wondering if you guys can explain the differences between how identical drivers with a different impedance rating perform in front loaded designs. For instance, how would the performance change with 4ohm vs 8ohm SW115 drivers in the same cabinet?

With this in mind, Why do we not see more triple 18" cabinets with (3) 8ohm drivers? It would seem like amplifiers these days are ready for the duty.

Some people like to bridge a amp for 1 sub cabinet, most amps will not do 2.7 ohm bridged, along with being 1 big box,,,,

 

[Marjan Milosevic]

Re: No compromises front loaded double 18” cab

Martin Audio has made some 3x18 cabinets. Lots of them in use all over Europe.

 

[Luke Robinson]

Re: No compromises front loaded double 18” cab

Update! Turns out the ports performed best at 9" deep total, witch means the port piece wound up being around 8" and the baffle makes up the rest of the depth. I went back and forth with the Faital 1030, and the B&C SW100 and though both sounded great ultimately we decided that the Faital was the winner by a slim margin. It was rounder in the lower section 35-40hz. T^he B&C did perform a bit better in the upper range from about 70-85hz but in the end when played with the pa it is most often going out with (d&b Q1 array) the Faital was preferred.

We fired up the production line and are rocking on 12 subs to start. here are a few pictures of our progress.

for some reason i cannot explain it is uploading the pictures upside down :?~:-?~:???:

 

[Ivan Beaver]

Re: No compromises front loaded double 18” cab

Update! Turns out the ports performed best at 9" deep total, witch means the port piece wound up being around 8" and the baffle makes up the rest of the depth. I went back and forth with the Faital 1030, and the B&C SW100 and though both sounded great ultimately we decided that the Faital was the winner by a slim margin. It was rounder in the lower section 35-40hz. T^he B&C did perform a bit better in the upper range from about 70-85hz but in the end when played with the pa it is most often going out with (d&b Q1 array) the Faital was preferred.

We fired up the production line and are rocking on 12 subs to start. here are a few pictures of our progress.

for some reason i cannot explain it is uploading the pictures upside down :?~:-?~:???:

View attachment 11519View attachment 11520View attachment 11521View attachment 11522

How are you planning on mounting the woofers? I don't see any hole for bolts.

I also don't see any handles. That would make them easier to move around.

Are they just glued? I don't see any fastener holes in the side of the cabinet. Mechanical fasteners make the cabinets much stronger and help to "pull it together" during assembly.

 

[Luke Robinson]

Re: No compromises front loaded double 18” cab

Calm down Ivan they aren't quite done yet :razz:

In all seriousness, thanks to you and everyone for all of your help on this project, I am excited to see them finished.


to address your concerns...
I used a Narrow crown stapler with inch and a half staples along with an entire tube of liquid nails on each cabinet. The holes for the woofers get drilled after they are painted, and then I use threaded inserts and machine screws to mount the woofers.

Handle holes as well as grooves for the UHMW feet get cut on with a router jig on monday morning then a little more bracing on the inside, and we should be sanding and rounding over the corners in preparation for paint.

 

[Peter Morris]

Re: No compromises front loaded double 18” cab

Update! Turns out the ports performed best at 9" deep total, witch means the port piece wound up being around 8" and the baffle makes up the rest of the depth. I went back and forth with the Faital 1030, and the B&C SW100 and though both sounded great ultimately we decided that the Faital was the winner by a slim margin. It was rounder in the lower section 35-40hz. T^he B&C did perform a bit better in the upper range from about 70-85hz but in the end when played with the pa it is most often going out with (d&b Q1 array) the Faital was preferred.

We fired up the production line and are rocking on 12 subs to start. here are a few pictures of our progress.

for some reason i cannot explain it is uploading the pictures upside down :?~:-?~:???:

View attachment 11519View attachment 11520View attachment 11521View attachment 11522

That's looking really good so far - I think you will be really happy with your design, it's a good size and should provide excellent performance.

 

[Ivan Beaver]

Re: No compromises front loaded double 18” cab

Calm down Ivan they aren't quite done yet :razz:

In all seriousness, thanks to you and everyone for all of your help on this project, I am excited to see them finished.


to address your concerns...
I used a Narrow crown stapler with inch and a half staples along with an entire tube of liquid nails on each cabinet. The holes for the woofers get drilled after they are painted, and then I use threaded inserts and machine screws to mount the woofers.

Handle holes as well as grooves for the UHMW feet get cut on with a router jig on monday morning then a little more bracing on the inside, and we should be sanding and rounding over the corners in preparation for paint.

I have found it better to drill all holes and cut cutouts before assembly.

But maybe that is just me.

Glad you are using staples. It helps quite a bit. You need physical fasteners AND glue-either alone is asking for trouble down the road. I just could not see the "indentions" of the staples in the photos. They usually leave a good sized mark. I like to have them recessed into the wood and then fill over with bondo.

 

[Luke Robinson]

Re: No compromises front loaded double 18” cab

Update, My drivers arrived this morning! We are finishing up on sanding and should be ready for primer and bed liner by the weekend.

I filled in the indents from the staples as we were going since we were already using a putty knife to scrape away the squeeze out from the glue. I just went ahead and spread it in the staple holes. Turns out liquid nails heavy duty seems to work well for this application.

My thinking on the holes for the threaded inserts for mounting is that if i pre drill them I will wind up gunning them up with the bed liner that is eventually getting sprayed on them, and i will have to go back and re drill the holes. So i just lay the woofer in and mark the holes and drill once we are at that step. If I were getting these cut on a CNC i certainly would have had the holes drilled out in advance.

 

[Jim McKeveny]

Re: No compromises front loaded double 18” cab

I am very late to this thread, but I do have some thoughts regarding the "bowtie" port arrangement, and shared/near-shared ports in general:

By eliminating the port divider, we substantially reduce frictional/laminar losses and turbulence, no? The reduction in losses permits marginally smaller overall port size, which can be used to render either greater available volume per chamber (for a fixed cabinet size), or an overall reduction in cabinet size. Both of these are design pluses.

The concept of saving the adjacent "tuning" should one driver fail is a red herring. Modern speakers, like headlights or dual truck tires, tend to fatigue and fail closely and should be replaced as matched pairs. Both drivers are likely quite out of spec by the time one gives up the ghost. The presence of the divider simply for this end-of-driver-life scenario seems heavy handed. We can usefully stiffen the cabinet otherwise.

The divider is also a unique and substantially sized panel, so it may not be best use of time and materials.

Just a thought...

 

[Max Warasila]

Re: No compromises front loaded double 18” cab

I am very late to this thread, but I do have some thoughts regarding the "bowtie" port arrangement, and shared/near-shared ports in general:

By eliminating the port divider, we substantially reduce frictional/laminar losses and turbulence, no? The reduction in losses permits marginally smaller overall port size, which can be used to render either greater available volume per chamber (for a fixed cabinet size), or an overall reduction in cabinet size. Both of these are design pluses.

The concept of saving the adjacent "tuning" should one driver fail is a red herring. Modern speakers, like headlights or dual truck tires, tend to fatigue and fail closely and should be replaced as matched pairs. Both drivers are likely quite out of spec by the time one gives up the ghost. The presence of the divider simply for this end-of-driver-life scenario seems heavy handed. We can usefully stiffen the cabinet otherwise.

The divider is also a unique and substantially sized panel, so it may not be best use of time and materials.

Just a thought...

I'm no cabinet designer, but I have a feeling that panel is very important to the structure of the cabinet as a whole.

 

[Art Welter]

Re: No compromises front loaded double 18” cab

1)By eliminating the port divider, we substantially reduce frictional/laminar losses and turbulence, no?
2)The reduction in losses permits marginally smaller overall port size, which can be used to render either greater available volume per chamber (for a fixed cabinet size), or an overall reduction in cabinet size. Both of these are design pluses.
3)The concept of saving the adjacent "tuning" should one driver fail is a red herring. Modern speakers, like headlights or dual truck tires, tend to fatigue and fail closely and should be replaced as matched pairs. Both drivers are likely quite out of spec by the time one gives up the ghost. The presence of the divider simply for this end-of-driver-life scenario seems heavy handed. We can usefully stiffen the cabinet otherwise.
4) The divider is also a unique and substantially sized panel, so it may not be best use of time and materials.

Jim,

1) Not "substantially", but measurably, if you measure correctly.
2) Agreed, but the design pluses of separate chambers are not limited to just "failure mode".
3) I have had brand new speakers stop working from various reasons such as improper crimp connections, spade lugs falling off, wires falling out, etc.
I have measured many speakers (well) over a decade old, and the TS parameters are still nearly identical to when they were first "broken in".
I have had many an outside dual tire fail from sidewall puncture, the inner tire fortunately allowing us to "limp away" where replacement could be done with power tools. My first experience with that was over 50 years ago, and my father was not about to replace the bus tire on the one lane road we were on, but did as soon as the terrain opened up.
The dual tire is a poor analogy, they each have separate "chambers", like many designers prefer for speaker enclosures.
4) Some guys, like me, and the many other designers that have done A/B comparisons think the slight weight gain separate chambers provide are well worth the time and materials when possible. The WS 2x12" design posted at the top of this DIY Audio would be improved slightly with dual chambers, but because of the diagonal arrangement of the speakers would be difficult to implement.

Other than those 5 points (including the truck bit), we are in complete agreement ;^)

Art

 

[Ivan Beaver]

Re: No compromises front loaded double 18” cab

Jim,

1) Not "substantially", but measurably, if you measure correctly.
2) Agreed, but the design pluses of separate chambers are not limited to just "failure mode".
3) I have had brand new speakers stop working from various reasons such as improper crimp connections, spade lugs falling off, wires falling out, etc.
I have measured many speakers (well) over a decade old, and the TS parameters are still nearly identical to when they were first "broken in".
I have had many an outside dual tire fail from sidewall puncture, the inner tire fortunately allowing us to "limp away" where replacement could be done with power tools. My first experience with that was over 50 years ago, and my father was not about to replace the bus tire on the one lane road we were on, but did as soon as the terrain opened up.
The dual tire is a poor analogy, they each have separate "chambers", like many designers prefer for speaker enclosures.
4) Some guys, like me, and the many other designers that have done A/B comparisons think the slight weight gain separate chambers provide are well worth the time and materials when possible. The WS 2x12" design posted at the top of this DIY Audio would be improved slightly with dual chambers, but because of the diagonal arrangement of the speakers would be difficult to implement.

Other than those 5 points (including the truck bit), we are in complete agreement ;^)

Art

Agreed

On point 4-having a large piece of material that ties the front/back and sides all together and effectively makes the side panels "half as large" really does "tighten up" the cabinet.

This works sonically as well as physically and helps to "keep everything together".

Bracing is something many people overlook when building bass cabinets-but yet it is one of the most important parts. The more you can "tie things together" the less they are going to move-which means more energy is going out of the cabinet as compared to be absorbed by it.

But you know all that Art-just provided as information to others