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Basschat easy-build lockdown cab project


stevie

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On 09/06/2021 at 15:33, stevie said:

which is the stuff they use in duvets, pillows and sleeping bags. The original eBay felt supplier now has a minimum order of 15 metres, which is a shame.

Morrison's super-cheap pillows might be a good source for small quantities.

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That's an excellent idea, @Stub Mandrel. At £3 a pop, it's hard to go wrong. The stuffing is made from recycled plastic bottles and is used in a number of acoustic products - so eco-friendly too. The only question is whether the material is self-supporting, like sheets of BAF wadding, or whether it's loose fill, which would be difficult to fix down inside a cab. 

I'll buy one next time I pass Morrisons and report back.

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5 hours ago, stevie said:

That's an excellent idea, @Stub Mandrel. At £3 a pop, it's hard to go wrong. The stuffing is made from recycled plastic bottles and is used in a number of acoustic products - so eco-friendly too. The only question is whether the material is self-supporting, like sheets of BAF wadding, or whether it's loose fill, which would be difficult to fix down inside a cab. 

I'll buy one next time I pass Morrisons and report back.

They are quite puny, I am very fussy about pillow height, so I have three decent ones and use two Morrisons ones as height adjusters 🤣

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I use old duvets as my source of polyester wadding. I'm also currently eyeing up a memory foam mattress topper, probably not what I want but I hate wasting anything.

If you want the old fashioned felt most carpet warehouses (not some of the big sheds though) still provide it and will sell you a metre. They also will also have cardboard tubes the perfect size for speaker ports which are used to wrap carpet around.

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Just for completeness I thought I would post a picture of mine finished ... ish.  I have never actually been able to play out loud since I started learning in February and have always used headphones and my audio interface, I completed most of the build a while ago but wasn't able to try it out until my amplifier arrived a few days ago (I ordered a Warwick head unit which took 4 weeks to arrive).

thing.thumb.jpg.fe46148f2df8b21d02616a97092a4c08.jpg

 

The build quality / finish of my cabinet is not that fantastic as I am not really a 'detail' guy but its certainly sturdy, e.g. I just bought a can of black paint and went mental on it and there's a few sharp bits. Obviously I don't have any reference for comparison but for my small room it is very loud and I had to turn everything down a lot (I think I am on the lowest volume the amp will turn down to) , my left ear is still recovering from the test, lol. Its also interesting, playing through a speaker seems a lot more forgiving, I sound better out loud than I do through headphones!

Overall I am pretty happy, I don't know how it would compare with an off-the-shelf unit but I enjoyed the build process and learnt some stuff.  Thank you to the peeps in this thread who provided the design and the guidance, much appreciated.

😎

J

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Mine began to take shape today

15mm scrap ply from a friend, so I've had to tweak dims a bit to keep internal volume correct. If it's a winner, then i'll probably make a couple from 12mm

Will probably end up carpeting it and fitting an aluminium grille

About 4 hours into it so far

Minimal tools - speaker hole cut with router on an arm pinned to the centre of the circle. Will also use router to radius the edges of the cabinet before carpeting

Horn and port holes cut with a jigsaw with a normal blade. Take your time and you'll be fine!

All panels cut from the best bits of the scrap offcuts with a worx mini circular saw. Did the job a treat.

All panels and battens PVA glued (lots of) and pinned in place with a cheap silverline air powered brad nailer. They only hold the pieces in place whilst the glue dries

Easy!

Small!

Fun! 

Measure twice (or more if you fancy) and cut once. 

Have a go!

Thanks for all the shared information on here. 

Jon

 

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Edited by carnabass
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On 18/07/2021 at 15:03, Jolltax said:

Just for completeness I thought I would post a picture of mine finished ... ish.  I have never actually been able to play out loud since I started learning in February and have always used headphones and my audio interface, I completed most of the build a while ago but wasn't able to try it out until my amplifier arrived a few days ago (I ordered a Warwick head unit which took 4 weeks to arrive).

thing.thumb.jpg.fe46148f2df8b21d02616a97092a4c08.jpg

 

The build quality / finish of my cabinet is not that fantastic as I am not really a 'detail' guy but its certainly sturdy, e.g. I just bought a can of black paint and went mental on it and there's a few sharp bits. Obviously I don't have any reference for comparison but for my small room it is very loud and I had to turn everything down a lot (I think I am on the lowest volume the amp will turn down to) , my left ear is still recovering from the test, lol. Its also interesting, playing through a speaker seems a lot more forgiving, I sound better out loud than I do through headphones!

Overall I am pretty happy, I don't know how it would compare with an off-the-shelf unit but I enjoyed the build process and learnt some stuff.  Thank you to the peeps in this thread who provided the design and the guidance, much appreciated.

😎

J

Well done, it's always rewarding to see a project carried through, I hope you have many happy hours and hopefully a few gigs with your speaker.

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Me again.... You'll all be sick of me soon

I've put the necessaries into winisd for the pulse 10 in the lockdown cab

I've used 30 litres and 50hz as the tune

My question is - am I doing something wrong? I've got the port length as 23.46cm @ 100mm dia

If I put 200w into this, it appears that i'm exceeding x max 

I'm not questioning the knowledge of you guys... i'm simply wondering what i'm doing wrong

To get the port length to correlate with your findings, i'm having to tune to 55hz. Xmax is still exceeded

I'll build to your specs, but just wanted to see what I was doing wrong.

Hopefully i'll get my scrapwood challenge together this coming weekend

Cheers!

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11 hours ago, carnabass said:

Me again.... You'll all be sick of me soon

I've put the necessaries into winisd for the pulse 10 in the lockdown cab

I've used 30 litres and 50hz as the tune

My question is - am I doing something wrong? I've got the port length as 23.46cm @ 100mm dia

If I put 200w into this, it appears that i'm exceeding x max 

I'm not questioning the knowledge of you guys... i'm simply wondering what i'm doing wrong

To get the port length to correlate with your findings, i'm having to tune to 55hz. Xmax is still exceeded

I'll build to your specs, but just wanted to see what I was doing wrong.

Hopefully i'll get my scrapwood challenge together this coming weekend

Cheers!

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Sorry wrote a load of tosh so deleted.

 

Edited by Chienmortbb
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I'll add some totally unqualified pub-talk here. Don't base any design decisions on this!

My limited experience with cab building leads me to suspect that a cab of this size, with this driver and port will struggle with 200w, in the modelling realm. You'll go over the red Xmax line and the port velocity will be higher than you'd want it to be. That's the bad news, in my unqualified opinion.

Two thoughts about why you don't need to worry about it too much though:

1) In real life 200w is more than you'd be likely to feed a small cab  (not saying you won't have a 200w+ amp, but it won't be playing 200w constantly) and the good design and components used here mean that it will sound loud and very good none the less, as a compact cab. If you really want a bigger sound there are loads of bigger and two-cab options there, but I'm sure this will be a great design for its intended purpose.

2) Secondly, the modelling realm is not the real world, so although the excursion crosses the red line in the software in the 75hz ish zone, in real life once it does so the relationship between power-in and excursion changes so that it sort of self-limits excursion for several reasons. This means you don't have to worry about it as much as that graph suggests. Also, although you are beyond xmax, you are probably no where near Xlim (the limit) so there isn't much to trouble you there. The extreme excursion you see down at about 30hz is subsonic, and if it were me I'd use a thumpinator or some kind of HPF / EQ to cut that crud out of the signal.

Anyway - I'm sure someone will be along shortly to give you a proper answer, these are just based on my own experience and 'learning' from  lockdown builds.

Edited by funkydoug
typos
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15 hours ago, carnabass said:

Me again.... You'll all be sick of me soon

I've put the necessaries into winisd for the pulse 10 in the lockdown cab

I've used 30 litres and 50hz as the tune

My question is - am I doing something wrong? I've got the port length as 23.46cm @ 100mm dia

If I put 200w into this, it appears that i'm exceeding x max 

I'm not questioning the knowledge of you guys... i'm simply wondering what i'm doing wrong

To get the port length to correlate with your findings, i'm having to tune to 55hz. Xmax is still exceeded

I'll build to your specs, but just wanted to see what I was doing wrong.

Hopefully i'll get my scrapwood challenge together this coming weekend

Cheers!

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Nothing wrong with you or WinISD.

This was Stevie's design, I designed the basic 30l box for a 12" project and built the box untuned for Stevie to develop. Once the design was finalised it came back to me and i rebuilt it to the original design and added an extra brace. Before I did I ran it through WinISD and got the same result you did.

First I know Stevie checks the tuning after building the cab. In practice the computer models only get you so close. Some of the data we get from manufacturers is only approximate, is hard to measure completely accurately and subject to manufacturing spread. There are also other factors like leakage in the cab and around the speaker that change the tuning (there's something called Ql that allows for that) but not mentioned in some of the simpler explanations. I don't know what Stevie's target tuning was but I do know he would have measured it after building the cab and tweaking the port to suit. It's all in his diary somewhere.

Xmax is measured differently by manufacturers (not necessarily a fiddle) It's meant to tell you when the coil moves out of the magnetic field which extends beyond the magnet itself. Some use a distortion measurement to give Xmax as the sound measurably distorts when the coil moves too far. Others use a mathematical formula to calculate the size of the magnetic field but Celestion use the old fashioned worst case calculation of half the difference between the coil length and the magnet gap depth. They pretty much all say how they calculate Xmax so it's not a problem for us. The point is that the coil doesn't suddenly move out of the magnetic field and xmax tries to identify when it first starts to leave the magnets control. Eminence for example would say this speaker has an Xmax of around 5.5mm so we aren't too worried.

The curve you have is the same shape for all speakers in a ported cab and pretty much none of them can handle the full thermally rated power without exceeding Xmax. That's right, none of them including all those expensive boutique wonders.

So why won't this speaker blow and why aren't there thousands of broken bass speakers? The answer is that there isn't much fundamental coming out of the bass pickups, most of the energy is in the second harmonic and upwards, the pickups are well away from the centre of the strings where the fundamental is loudest. The bass is effectively rolled off by the positioning of the pickups and the position of the plucking hand. We are all familiar with the bridge pups having less bass than the neck pups.

So build with confidence

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I think Phil designed this box to be 30 litres net  - or about 34 litres gross. WINisd probably deducts the volume of the driver and port from the total - my software does this. Also, and without checking, it's quite possible that the internal diameter of the 100mm port is something like 97 or 98mm internally.

I only used modelling software to prove the concept and did the tuning on the box itself. You'll find the impedance curve showing the tuning frequency a few pages back in this thread.

As others have pointed out, you have to be very careful with xmax, as there are different ways of calculating it. I tend to use coil length and xlim as my yardsticks nowadays. The three power-limiting factors - thermal power handling, excursion and vent speed - are nicely balanced in this design, which should work well with a 200W amp.

Edited by stevie
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The thing about Celestion and Xmax would explain why every Celestion driver I’ve ever tried modelling a cabinet with has seemed to be completely useless. In contrast to me I guess the people who specify and buy them in quantity actually know what they’re doing. 

Francis Deck (off of Talkbass, and of Fdeck preamp fame) had a web page that would model speaker designs and included a ‘bass-weighted’ (as in the instrument) excursion plot, but the page seems to be down now. 

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looking good, have you braced by the horn/port/speaker on the baffle? It's a real weak spot and we had real problems taming a resonance there. The fix was a brace across between the bass driver and the port/horn and a similar one across the rear panel with a third brace connecting them front to back. I just used the same material I had for the rest of the cab so you should be able to use any offcuts for that.

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The baffle brace you've already done helps a lot but adding the back to front brace sorted the problem completely for me. I need to amend the build and drawings to include it but I tried a few options on the prototype so a photo of what's left would probably be quite confusing. 

 

Running test tones didn't show a lot of problems with vibration of the rear panel but you need something to fix the front to back strut to and a simple H shaped brace is easy to do and every little helps.

 

Looking forward to hearing how it sounds, it's a lovely moment when you plug it all in and hear your first bass sounds :)

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this was made of 15mm Phill as it was donated to the cause by a friend (so i guess that'll help a bit)

 

to be honest - i'm not proud of the build. It's not as accurate as I would normally make an cab to, but my intention was to use it as a test and then build from 12mm

 

But... as usual... the desire to get it looking nice has taken over and i've spent much longer than I had planned on it

 

I've got a cut list together for the 12mm ply. Looks like you can get three complete cabs and one spare of each panel from an 8' x 4'

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Yeah 15mm helps a lot as does denser/heavier ply. My preference is for 18mm hardwood ply. Wickes in particular used to do a really nice marine ply with good facing veneers. It's a long time since I've been to Wickes due to the plague but they still sold a nice exterior ply last time I went. For my own use I do like a really tough cab which is not going to disintegrate if it gets a bit damp. It's a tough life going between van and gig. Fortunately cabs are getting smaller and ultimate light weight is not a big concern for me, and let's face it these cabs are pretty small. This cab is 12mm poplar ply because that is what Stevie preferred. My original 'Easy Build' cab was 12mm because that was what i had enough off cuts of to build the cab. Not very scientific! 

 

What I'd really like to do is  build a series of cabs all the same internal volume and weight with different bracing systems and compare them for cab induced resonances. Is a 9mm cab with an extensive equal mass of bracing better than an 18mm cab with no bracing, or enough better to be worth the effort for the home builder. There is a lot of theory about panel resonances  and the car industry has done a lot of work to silence panel resonances. What there isn't is a simple piece of software to design the bracing for a speaker cab so a lot of it is a combination of experience and suck it and see.  A friend of mine works for Jaguar/Land Rover and one day I'm going to pump her for inside information. Most of what the auto industry do is to add mass in critical places and they use a lot of 'lossy' materials to damp resonances. My current hi-fi speakers have a lead/MDF sandwich structure with a plastic foam joining them. I'll leave the lead lined bass cab to Trace Elliott though :)

 

 

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Hello carnabass,


Some more food for thought here:-

 

Panel thickness, bracing, cross-bracing, materials, screws, construction methods etc..
https://www.audioholics.com/loudspeaker-design/loudspeaker-cabinets
https://www.diyaudioandvideo.com/Guide/BuildSpeakerBox/
https://www.linkwitzlab.com/frontiers_2.htm

 

With hi-fi they're going to the 'nth degree of nuttiness, but for the fundamentals within these pages, they are are good guide to musical instrument/bass speakers. I have my preferences and you may have yours, it all depends on what you're trying to achieve.

 

Nice job on your speaker, by the way.

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Hello Again!

 

Well.... the teeny tiny cab is together and has been tested

 

It's definitely easy build

 

I haven't applied any finish to the cab or a grille as this was a test version (although i'm falling in love already)

 

I made the crossover on a piece of thin ply. 

 

It really is a compact cab. 

 

I used araldite to glue the port extension on and then stretched some gaffa round it nice and tight for support

 

One point I would bring up (and I could be talking rubbish here).... The port ends closer to the rear wall than I would have expected to be ideal. My thoughts were that you needed at least the diameter of the port. Any thoughts on this chaps? (port length 170mm) Or does it not matter? 

 

I coupled up my BH800 and played some tunes through it via an ipod. I was very pleasantly surprised. Nicely balanced with neutral equalisation and with a good dispersion of higher frequencies.

 

My better half said "that sounds nice" - praise indeed.

 

I've played my precision through it for a few minutes and its great! Not bottom heavy, but then I didn't really expect it to be. 

 

BUT

 

It's clear, punchy and responds very well to EQ changes. 

 

Would I gig with it? Probably not unless it was a small room.... Would I gig with it plus another cab (minus the tweeter section) yes definitely!

 

Its probably a bit unfair to do a review after such a short time, but I promised myself that i'd contribute to this project as well as gain from it. I'll report back once i've done a rehearsal with it

 

Anyone can make this cab. The joy of hearing your creation come to life is soooo worth it!

 

I am v tempted to knock some 12mm versions together (although the V3 basschat design is calling me)

 

Thank you to all who are involved in this wonderful little design

 

Pics attached - drill shown for scale 😊

 

Jon

 

 

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Get a couple of coats of Tuff Coat on it and it will look the business. You've done a good job with that and I really hope you get a lot of happy hours using it.

 

I think you are right about the volume, WinISD shows a broad band output of about 118dB at 200W which is fairly typical for a 10" speaker. Adding a second would give you 123-4dB depending upon the amp which puts you well into the gigging range. It would work well with an untweetered Pulse10 in the same sized cab underneath if you wanted to save a little money. In terms of practicality I use mine as my go to for rehearsals. I like it for gigs too because I have PA support so it is just a monitor and is plenty loud enough for me to hear everything and it sounds good. The sound engineer loves it because it's not overwhelming the vocal mics and my drummer is not so keen because he likes to 'feel' the bass.

 

I don't think building it in 12mm ply would give you any advantages other than weight saving and maybe a better quality ply would be tougher and easier to finish. Have you weighed the cab? Mine came out at dead on 10kg.

 

Thanks for the review, it really helps anyone thinking of a build having an opinion from someone unconnected with the design. 

 

Well done 

 

Phil

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