Speaker cab 'portholes'

[DGBass]

I've come across cabs over the years which appear vented but have little more than a hole cut in the baffle and no port tube or mechanism behind the hole. Sometimes its rectangular, sometimes tri-angular, but mostly a circle. I have a 1x15 cab 'on the bench' at the moment which has a basic circular hole cut in the corner of the baffle, diameter 4 inches. It's always been that way as the previous owner owned it from new and assumed it was a proper porting/venting design( from 1985 ). My question to the learned speaker cab guru's is does a simple hole in the baffle with no port tube or anything behind it other that air have any real sonic benefit where increasing speaker performance eg low end is concerned? The orignal driver is a vintage version of the modern Fane Sovereign Pro cast frame type with an enormous magnet assembly and what looks like a 3 inch voice coil. Rated 250 watts rms 8 ohms. It appears to be quite efficient but i have no specs for it. 

[Bill Fitzmaurice]

A hole is a port. A hole with a tube or extension behind it is a ducted port. Over the decades the 'ducted' part of the name has been dropped from common usage. A hole is still technically a ducted port, with the duct length being the thickness of the panel it goes through. The longer the duct the smaller the port will be and the smaller the cab may be for a given tuning frequency. The smaller the port the higher the velocity of the air vibrating within it. With sufficient velocity you can hear that air mass vibrating, so there is a point where it can be too small. Your cab may be fine, it may not, which can be determined with the exact cab dimensions and the driver specs.

[DGBass]

Thanks that does answer the question. Its a 38 year old driver so i'm never going to find specs for it nowadays. I have searched far and wide but wasn't able to find a match. The cab is reasonably large and made from 18mm mdf from what I can see so port depth is 18mm. It's sounds fine although I haven't put any serious power through it yet. I'll assume Trace Elliot knew what they were doing at the time as the cab and speaker came as a package🙂 

[stevie]

You don't actually need the specs of the driver to calculate the tuning frequency of the cab. Just the internal volume and port size.

[Bill Fitzmaurice]

3 hours ago, DGBass said:

I'll assume Trace Elliot knew what they were doing at the time as the cab and speaker came as a package🙂 

Having seen some real nightmares I never assume that anyone knew what they were doing without checking it for myself. 😉

By and large most fifteens work best with cab tuning of 45-50Hz. That can be confirmed from the cab dimensions alone.

[fleabag]

I had one of Peavey's old 1x15  Black Widow cabs, and this monster had a port hole and no duct.

 

If i remember correctly, it was 22mm  ply.  Weighed the same as Cornwall

Edited February 15, 2023 by fleabag

[Frank Blank]

I had a massive old Carlsbro cab that I kicked a hole in, tbh I was out of my Noggin at the time.

[fleabag]

I wonder what shape a hobnail boot makes. I think we can rule out round, slot, triangle.

[Frank Blank]

Just now, fleabag said:

I wonder what shape a hobnail boot makes. I think we can rule out round, slot, triangle.

And I don't think these holes are supposed to be in the speaker cone either.

[DGBass]

5 hours ago, stevie said:

You don't actually need the specs of the driver to calculate the tuning frequency of the cab. Just the internal volume and port size.

via the wonders of the internet and out of curiosity I did find something that gave an approxiamate calculation for the tuning of this box I have with the 18mm porthole.  It worked out at a cabinet tuning of approx 52-53 Hz. Sounds about right for a 15? Interestingly fitting a 3 inch depth port tube same diameter as the hole will re tune the cab to 41hz. I may experiment to see what different this makes real world.

[nekomatic]

7 hours ago, stevie said:

You don't actually need the specs of the driver to calculate the tuning frequency of the cab. Just the internal volume and port size.

Also, you can measure the specs of a driver if you have a a small amount of test gear and patience. There’s a description on Rod Elliott’s website somewhere. 

[Bill Fitzmaurice]

5 hours ago, DGBass said:

 It worked out at a cabinet tuning of approx 52-53 Hz. Sounds about right for a 15?

That's where the driver specs come in. The ideal tuning for contemporary high quality fifteens will be closer to 45 Hz, but as the saying goes they don't make them like they used to, so 53 Hz may be best for that driver. 

Quote

you can measure the specs of a driver if you have a a small amount of test gear and patience.

This and five minutes is all you need. https://www.parts-express.com/Dayton-Audio-DATS-V3-Computer-Based-Audio-Component-Test-System-390-807?quantity=1

 

Edited February 16, 2023 by Bill Fitzmaurice

[DGBass]

16 hours ago, Bill Fitzmaurice said:

you can measure the specs of a driver if you have a a small amount of test gear and patience.

Thanks BFM. The Dayton kit looks very interesting. I've messaged their UK distributor. It's often occured to me that i'd like to get more into speaker box design if only to build the ultimate small compact and lightweight 1x15 cab. Its taken years of playing many different brands of bass cab to realise mostly everything is a compromise of some sort, whether its design, weight, or cost or usually all three. I can understand why the small lightweight cab market has really taken off and why most manufacturers centre their design efforts around 10 inch and 12 inch speakers. A 12 inch driver in particular is the perfect compromise of size and performance while still being able to fit into a relatively small compact box. But I see a trend where two are really needed in real life to feel the bass. So its a great sales opportunity for these manufacturers. Being an avid user of 15 inch cabs, the notion of a lighweight compact high performance 15 inch cab is more difficult. Perhaps thats why certain lightweight cab purveyors have no such 15 cab in their offerings and perhaps its time for a BC MK IV cab, the ultimate 1x15? Or has that been done? Some specs I have in mind - 600 watt, 4 ohm, ported and able to deliver a 35Hz to 5khz range, at least 100db 1w @ 1m sensitivity. No horn or tweeter and weighing 15Kg tops. And it has to fit into a small hatchback/town car. 5 kg for a high performance neo driver, 2kg for hardware and coverings, and 8kg for an enclosure thats strong enough and small enough to to cope with the rated power without vibrating, shaking apart or compromising the drivers performance and design parameters. It also has to retail at no more than £499 😉Some folks might scoff and say 'dream on' and they might be right. It's a nice thought and if something like that could be built, I'm sure the single cab fans who just like to feel the bass and dont really care about portholes would be interested. 🙂   

[Bill Fitzmaurice]

I use a lightweight 1x12. It's not small, though. I have a lightweight 1x15 as well, also not small. I hardly use it, for outdoor gigs only. Indoors the 1x12 is plenty.

[Phil Starr]

11 hours ago, DGBass said:

Thanks BFM. The Dayton kit looks very interesting. I've messaged their UK distributor. It's often occured to me that i'd like to get more into speaker box design if only to build the ultimate small compact and lightweight 1x15 cab. Its taken years of playing many different brands of bass cab to realise mostly everything is a compromise of some sort, whether its design, weight, or cost or usually all three. I can understand why the small lightweight cab market has really taken off and why most manufacturers centre their design efforts around 10 inch and 12 inch speakers. A 12 inch driver in particular is the perfect compromise of size and performance while still being able to fit into a relatively small compact box. But I see a trend where two are really needed in real life to feel the bass. So its a great sales opportunity for these manufacturers. Being an avid user of 15 inch cabs, the notion of a lighweight compact high performance 15 inch cab is more difficult. Perhaps thats why certain lightweight cab purveyors have no such 15 cab in their offerings and perhaps its time for a BC MK IV cab, the ultimate 1x15? Or has that been done? Some specs I have in mind - 600 watt, 4 ohm, ported and able to deliver a 35Hz to 5khz range, at least 100db 1w @ 1m sensitivity. No horn or tweeter and weighing 15Kg tops. And it has to fit into a small hatchback/town car. 5 kg for a high performance neo driver, 2kg for hardware and coverings, and 8kg for an enclosure thats strong enough and small enough to to cope with the rated power without vibrating, shaking apart or compromising the drivers performance and design parameters. It also has to retail at no more than £499 😉Some folks might scoff and say 'dream on' and they might be right. It's a nice thought and if something like that could be built, I'm sure the single cab fans who just like to feel the bass and dont really care about portholes would be interested. 🙂   

 

We've toyed with the idea of a BC 1x15 cab and I have one here using an Eminence Deltalite, not quite the spec you are looking for though. I'm afraid Covid rather interrupted our plans as all our designs are tested playing live as well as being measured in the 'shed'. Limited playing opportunities and other more personal issues have meant not getting out most weeks.

 

 

There are a few technical problems with your scheme. Availability of a suitable driver being the biggest issue. If you want a single 15 for a bass cab it has to have reasonable output up to roughly 4000Hz. For a 15" driver that means it is operating under cone break up for a lot of it's range  and the cone breakup has to be well controlled. Because the high end is bound to be compromised most 15's have a bit of a peak in the kHz range which kind of compensates for the early roll off at the top end. Almost all the commercially available 15's are designed to be used in multi-way systems and to extend the bass downwards rather than the treble upwards so they have heavy cones to lower fs and make them pistonic up to the crossover point. This lowers their efficiency. If you want 600W handling then you really need a 4" voice coil so you are now in the realm of pro-audio bass drivers. The other limiting factor is excursion, a speaker might be able to handle 600W of electrical heating but if it reaches it's excursion limits at 300W then there is nothing to be gained by using a bigger amp and more expensive, heavier driver to achieve the same output levels. Similarly if you go for 4 ohms to get more power out of the amp the same physical limits on excursion mean that you gain nothing in sound output.

 

There aren't many if any drivers that meet all your design parameters. Few meet the 100db/W even on the manufacturers spec, most are dedicated bass drivers so won't have enough high end to be usable as a single bass cab. I'd probably opt for the Eminence Kappalite 15HO as the best all rounder and now priced fairly competitively in the UK. That's not news, Barefaced used them in their first cabs and BFM recommends them as do many others. It's 450W and sounds good with bass but excursion is only 5mm. You'll achieve sound levels peaks of 125db+ though which is plenty enough to destroy your hearing. The other possible candidate is the Faital HF520 a bit more expensive and heavier but with an acceptable looking top end, that is 600W but lower quoted efficiency than the Eminence. It does have better excursion but I haven't modelled the two against each other so I can't really say if you would gain much at this point. A Kappalite in a box is a good solution and would come in at around £300 as a self build. It would need a port

[fleabag]

Just in case anyone is interested, i have a Fane 15" for sale. Specs in the thread

 

 

[Bill Fitzmaurice]

4 hours ago, Phil Starr said:

 

 Few meet the 100db/W even on the manufacturers spec

None do below 100Hz.

Quote

Kappalite 15HO as the best all rounder

It's actually the Kappalite 3015. Xmax is 5.9mm, which is longer than average. It will take 450w mechanical through most of its range. The 3015LF goes lower, and will take 450w mechanical at every frequency, but lacks mids. That's OK if you use it with a midrange driver, or for a pure reggae all bottom no top tone. Otherwise it's not at all versatile. 

Quote

Some specs I have in mind - 600 watt, 4 ohm, ported and able to deliver a 35Hz to 5khz range, at least 100db 1w @ 1m sensitivity.

To get that you'd need to use two twelves.

[DGBass]

Thanks @stevie, @Phil Starr and @Bill Fitzmaurice. It's sounds like a Kappalite in a box ( with a port hole) is the real world version of the dream. I have the feeling it wouldn't be a particularly small compact box either to get the best from a Kappalite. As an example, the box 'on the bench' at present that I calculated the tuning for is not much over 3cu ft internal volume and its not exactly small. When I have the time, i'd like to look further into a self build 1x15. For now, i'm going to experiment with some cabinet tuning basics using this project box.🙂

[Bill Fitzmaurice]

The 'ideal' size for the 3015 is 3 cu ft net tuned to 50Hz. 'Ideal', because you can go larger or smaller with the box size and the tuning, depending on what your priorities are. Commercial cabs tend to go smaller, sometimes a lot smaller, as their #1 priority is sales, and the current consumer trend is for smaller and lighter. My 3015 is in a 5.6 cu ft horn loaded enclosure, as my personal priority is maximum performance. I also have a ported design for the 3015 that's 'only' 2.5 cu ft, for those who's priority is more ease of transport. Every speaker makes compromises. What experience teaches you is where you can afford to compromise and where you should not.

[DGBass]

Thought i'd just post a note to say what transpired with my porthole cab refurbishment. It's taken a while to get everything together and as always testing and making adjustments does involve time when its something non standard. Unfortunately the original 38 year old Fane Sovereign Pro 15-250 driver failed after three rehearshals after developing some voice call rub. Spending a decade in a damp garage and then a few weeks in a warm dry indoors environment seemed to have distorted the cone. However, I had a spare woofer boxed in the cupboard as all well prepared bass players have. It now has the spare 8 ohm Faital Pro driver I bought a few years ago. Some fine tuning with my internal volume calculations brought the tuning frequency as near as can be to about 50Hz which seems to be fairly standard for a mid nineteen eighties cab. Lined with 3/4 inch dacron the cab sounds well damped and the big 15 PR 400 doesn't seem to complain at all no matter what I throw at it. Everything sounds crisp and clear to me. Pick playing especially sounds good and thats not usually my bag. 

The original TE grille was re-mounted with new rubber pads, and a new speaker jack plate fitted with combi speakons. It's approx 19kg all in and lighter and smaller than my MM cab so its very likely to get a bit of use soon. It's not perfect but the cab was donated free and the spare driver was already paid for. Mostly it was just a little cosmetics cost required to get it to where it is. It's good enough to gig now and only needed a minimal amount of science to understand the cab design. For the most part it was finalized with some old fashioned listening time  🙂

 

[Phil Starr]

Well done, looks good and that Faital is a nice driver. You might be able to shed a few kilos by building a new cab the same dimensions out of lightweight ply if you get itching for more modification.