House Jam Micro Cab

[Chienmortbb]

2 hours ago, cbd said:

Is there any benefit to putting a capacitor in series with the speaker as a crude high pass filter? Just had a go on a crossover calculator website which reckons a 220uf bipolar would give you a 6db/octave cutoff at around 90Hz - that would cost about £2.50. Or would it have to be steeper than that to avoid taking too much off the higher frequencies?

To make a decent HPF at the driver end  mean big heavy and expensive components . You need IMHO something line 18-24dB. That entails a 3rd or 4th order filter. A first or even 2nd order filter ( 6-12dB) would putter cutoff frequency too high. 
 

As @Woodwind says it is easier to achieve in ghe signal path rather after the power stages. I think the Thumpinator sets the -3dB point too low although there are lots of them about. 
 

If you have WinISD, you can model the driver and then add various filters to see the effect on the low increase by adding higher order filters. 

[Phil Starr]

On 16/12/2024 at 21:10, cbd said:

Is there any benefit to putting a capacitor in series with the speaker as a crude high pass filter? Just had a go on a crossover calculator website which reckons a 220uf bipolar would give you a 6db/octave cutoff at around 90Hz - that would cost about £2.50. Or would it have to be steeper than that to avoid taking too much off the higher frequencies?

 

You almost certainly have a tone control which will roll off the bass by 12db or more. It would be easier to just use that as a starting point, not least because it costs you nothing and you can restore the system back to normal when that has finished. I don't want to speculate too much but anyone using the cab for the first time will sense the loss of the bottom frequencies and probably boost the bass on their amp or bass if it is active. We've all played with guitarists who swear blind that they haven't turned up even when you can see it on the meters. Bassists can be just as naughty

 

The thing is that it is perfectly acceptable to use a big amp with a small speaker if you are aware of all the parameters. As the owner of everything you know the risks and will be careful accordingly. For a bassist just jamming with their mates and no knowledge of the gear involved you'll just go for it. Just swapping from a bridge pup to a neck pup could be enbough to put you in the red zone.  At open mic nights I reckon I'd match my cabs to double the amp power for 'safety' as you have no idea what fx or playing style you will come across and some people are brutal with their equipment.

Edited Wednesday at 09:46 by Phil Starr

[Phil Starr]

Another factor with a capacitor is that the whole design of this cab with the very high tuning of 87Hz was to get the flattest response possible down to below 80 Hz. As you can see with your own WINIsd plot it's hard to get a flat response low down with other tunings. All cab design is a matter of compromise and this one was done by compromising on power handling and the speaker being almost unloaded below 70Hz in part mitigted by it's intended use with a Gnome/Elf/BAM style amp which has a bit of HPF going on.

 

I'm a bit prejudiced against a simple in line capacitor. In the olden days when I built amps I found a few that really didn't lke a capacitative load. In addition the capacitor produces a phase shift. @stevie is more expert than I but I instinctively wouldn't want that happening at the port tuning frequency. Being lazy I haven't looked at any calculations though

[pete.young]

7 minutes ago, Phil Starr said:

 

 

I'm a bit prejudiced against a simple in line capacitor.

A capacitor is how Tecamp (and presumably Eich) high-pass the feed to the mid/upper driver in their combos and cabs. Greeeted with widespread derision in my repair thread about my Puma combo!

[Chienmortbb]

7 minutes ago, Phil Starr said:

I'm a bit prejudiced against a simple in line capacitor. In the olden days when I built amps I found a few that really didn't like a capacitative load.

Yes you need to be careful here. Amplifiers have limits to the size of capacitive load and you could cause your amp to shut down. This is true of Class D amps but may class A/B amps have trouble with capacitive loads.

[Chienmortbb]

2 minutes ago, pete.young said:

A capacitor is how Tecamp (and presumably Eich) high-pass the feed to the mid/upper driver in their combos and cabs

It has been a thing at the cheaper end of the market, paying lip service to the higher frequencies. Shame on Eich for saving money this way although they are not alone. It is one of the reasons that boutique makers like Greenboy, LFSys, and others exist, because the usual suspects play fast and loose with the top end. SEarch on here or on T*lkbass for Markbass combos and the  issues with their top ends. If the best you can do is a tweeter and capacitor, do not bother.

[cbd]

On 16/12/2024 at 23:41, Chienmortbb said:

If you have WinISD, you can model the driver and then add various filters to see the effect on the low increase by adding higher order filters. 

I didn't know about that feature, great idea. If I add an 80Hz 1st order high pass filter to my winISD model of the 10L house jam cab it looks like it takes out lots more around from ~120Hz than I expected.

 

5 hours ago, Phil Starr said:

As you can see with your own WINIsd plot it's hard to get a flat response low down with other tunings.

Yep - it's super interesting with that speaker actually how tuning the box lower suddenly makes all the bass disappear. Quite counter-intuitive, I'd never have expected tuning higher to increase the low end but that's what's happening here as far as I've understood WinISD!

[Phil Starr]

19 hours ago, cbd said:

Yep - it's super interesting with that speaker actually how tuning the box lower suddenly makes all the bass disappear. Quite counter-intuitive, I'd never have expected tuning higher to increase the low end but that's what's happening here as far as I've understood WinISD!

Yes it's all about tuning a whle set of frequency dependent factors, some of them characteristic of the driver and others of the box itself. Obviously you cant really change the characteristics of the driver other than by going for a different one.

 

Basically you have control of the volume of the box and in a ported enclosure the resonance of the cab. Essentially the volume of the cab affects the bass response, a large volume giving more bass with a lower roll off point but with a drooping response, a small cab raises the roll off point and can give a significant boost in output around the cut off point which is at a higher frequency. That boost can become unpleasant and you can have a cab which is too big or too small. There's a Goldilocks size for each speaker and an area within which you can fiddle around a bit and optimise the output to your design spec or just your taste.

 

With a ported cab you aim to extend the flat area of the output by getting the port tuned just below the point where the speaker's output us falling and the cone is starting to flap around outside it's safe excursion limits. At the tuning point the cab resonates on it's own (sort of) and 180deg out of phase with the cone which started the resonance. That means the air in the cab is moving the 'wrong' way and creates enough pressure on the speaker cone to stop it moving, What you hear is all coming out of the port.

 

The Goldilocks point for the cab is where it is 'maximally flat' the flattest response possible. WINIsd goes for those first (They are called things like QB3, BB4, SBB4 and C4) and they can be calculated simply just knowing two parameters Qts and Vas. The clever bit of programs like WINIsd is that you can go off piste, They can calculate exactly how far the cone can move at every frequency and work out the frequency response, power handling, excursion and so on for pretty much any design changes you make. That's brilliant because it's so quick if like me you've ever had to do the calculations by hand.

 

If you are interested I can go through the process that helped me come up with the original House Jam cab to Illustrate one approach to designing a cab and choosing the right driver to go in it.

 

 

[cbd]

10 hours ago, Phil Starr said:

If you are interested I can go through the process that helped me come up with the original House Jam cab to Illustrate one approach to designing a cab and choosing the right driver to go in it

If you don't mind then absolutely!

[RhythmJunky]

Has anybody ever used this with keyboards?  I'm thinking of building a stereo version for use as a practice/ small jazz group jam combo. Voiced mostly as an acoustic piano, but also a Rhodes and maybe some B3 style organs. 

 

I'll probably power it with a small generic stereo 25 watt class D amp, but also have a Warwick Gnome,  (I also play bass) so it could be pretty versatile. Building two seperate 1x6's would be the most flexible, but I do fancy a single box solution. If I ever wanted more power I could just get a second Gnome (btw, apparently the collective noun for a group of Gnomes is a 'donsy of gnomes'). 

 

I'd build it as one box seperated into 2 chambers. 

 

[Phil Starr]

OK, start with a design spec, what you need and what would be desirable.

 

I started wanting a simple single speaker design with a flattish extended upper response to cover up to 8kHz and a decent off axis HF. I could tolerate a peak in response at 3kHz or above but it needed to be well damped (broad and flat) rather than a sharp peak. Most important was that I was prepared to sacrifice a drop in bass response below 80Hz but I needed the 2nd harmonic octave 80-160Hz to be ruler flat, desirable was that the roll off below 80 Hz was fairly smooth.

 

Desirable also was high efficiency, My aim wa s to be able to play along with other people up to but short of a full drumkit. This was to play at home with friends but I was also looking for something that might work at an open mic. My target was 110db or better.

 

The 80-160Hz thing was absolutely crucial though. This speaker was to test a theory I'd held for a long time, that a rich rendition of the second harmonic was 90% subjectively of what we hear as 'bass'

 

Time to select a driver. I knew I probably wanted a 6" cab from instinct, anything smaller was likely to lack efficiency and an 8" driver was going to need a bigger cab but I included a search of smaller and bigger speakers. Never trust intuition

 

The first thing I'll look at is the frequency response graph. This is really going to define the sound of the speaker as it determines which harmonics we are going to hear. Particularly in the 6" size there are quite a few specialist mid-range drivers which won't handle bass and a few dedicated bass drivers with thicker heavier cones

 

What I also know is that the size of a cab, at least in the Goldilocks region is defined by two factors Qts and Vas. Qts (Q for the whole speaker) is related to how much control the speakers magnet, electrical characteristics plus the mechanical components have over the cone movement. Knowing Q also gives me some idea of the probable. bass response. Low Q means tight control of the cone movement and bass being restricted, high Q means the cone movement is less well controlled and you will get a bass boost towards the bottom end of the frequency range. For a flat response I need Q to be in the range 0.3 to 0.6 and 0.4 is the Goldilocks point.Vas is a weird concoction of parameters but is the volume of air with the same mechanical characteristics as the speaker. My eventual cab size is going to be close to Vas so anything too big or small is out, With Qts I'm halfway to knowing the frequency response and with both Q and Vas I can work out the cab size in my head.

 

So now I'm looking for a speaker that will do 80-8khz, reach 110db ideally with a modest amp and do all that in a cab of around 10l and I spend a couple of hours looking at every major brand available in the UK offerings of 6" drivers simply eliminating any that don't fit this spec. Mainly that involves looking at everything Lean Audio and Blue Aran offer. It's surprising how few drivers fit that sort of brief. The majority sacrifice efficiency for bass response or don't have the extended upper response that I wanted. I ended with a short list of around 10, none of them perfect and I then put those into Winisd to model them with a bit more accuracy and see how far I could stretch the design to make them do what I wanted. At this point I knew I'd have to compromise and the datea was going to tell me exactly what the compromises would be. Essentially that was mainly swapping efficiency for bass response only one speaker was going to be loud enough, all of the others would give more bass than the Fane but would compromise the top end response with their heavier cones and longer coils. I was going to have to sacrifice something like 3db or be fairly smart about the cab design to get the Fane to behave down to 80Hz.

 

At this point I've got the best three drivers up on screenand I'm running two models of each. One is the Winisd recommendation and the other is the one I'm trying different cab sizes and tunings with. Eventually I've just got the FAne left and the issue is the Fane's resonant frequency of 111Hz which is too high. I know I can get a bit more bass by putting it in a cab which is a bit bigger than the Winisd suggested size but if I make it too big then it will quickly cease to be flat around 80Hz I also know I can shape the response down below 111Hz by careful tuning of the cab. I ended up with a 10l cab and 87Hz tuning and acheived my design spec. The cost was a unusually big reduction in power handling between 90-200Hz  due to over-excursion. The Fane sacrifices excursion for efficiency so I was expecting that. At this point I was expecting to use the cab with a 20W amp so that was fine. the cab as designed will start distorting at about 20-30W  mainly by compressing the bass but will operate safely up to 50W or maybe a smidgin more. I use mine nowadays with a 130W Gnome but roll off the bass control by 3dB on the Gnome if I'm running it flat out. Putting it on a floor back against a rear wall more than resores that 3db of roll off. 50W is enough to give the 110db I wanted from the cab.

 

So there you go, in designing this cab I looked at maybe 100 drivers, shortlisted and modelled 10 and worked in detail on three or four before ending up with what is a simple but remarkable little cab. It sounds long winded but I've done this so many times I can pretty much hear the final cab in my head just from a set of figures, shortlisting took a couple of hours and modelling the cabs a couple of evenings. During Covid and lockdown it was good fun especially when I plugged in a proper big amp for the first time and turned it up to see just how far this thing could be pushed

[Phil Starr]

13 hours ago, RhythmJunky said:

Has anybody ever used this with keyboards?  I'm thinking of building a stereo version for use as a practice/ small jazz group jam combo. Voiced mostly as an acoustic piano, but also a Rhodes and maybe some B3 style organs. 

 

I'll probably power it with a small generic stereo 25 watt class D amp, but also have a Warwick Gnome,  (I also play bass) so it could be pretty versatile. Building two seperate 1x6's would be the most flexible, but I do fancy a single box solution. If I ever wanted more power I could just get a second Gnome (btw, apparently the collective noun for a group of Gnomes is a 'donsy of gnomes'). 

 

I'd build it as one box seperated into 2 chambers. 

 

No, I have tried it as a vocal monitor at rehearsal and it does a great job. The problem with keys is they potentially have more deep bass than a bass guitar and they will have harmonic content all the way to the top of human hearing. This thing will only do 80-8kHz. However they might be better than the little built in speakers most Keyboards use. 25W will be fine in terms of power handling and take you loud enough for your jazz combo but you might need to add a tweeter. It might be acceptable though for piano and a Rhodes sound. the only certain way is to try it. Maybe someone here has built one and lives near you. Where do you live?

[RhythmJunky]

7 hours ago, Phil Starr said:

No, I have tried it as a vocal monitor at rehearsal and it does a great job. The problem with keys is they potentially have more deep bass than a bass guitar and they will have harmonic content all the way to the top of human hearing. This thing will only do 80-8kHz. However they might be better than the little built in speakers most Keyboards use. 25W will be fine in terms of power handling and take you loud enough for your jazz combo but you might need to add a tweeter. It might be acceptable though for piano and a Rhodes sound. the only certain way is to try it. Maybe someone here has built one and lives near you. Where do you live?

 

Thanks Phil, I appreciate your response. It seems it may be prudent to factor a tweeter, and the volume needed, into the design. I'll have to look around for suitable candidates. Do you think it'll need 2x or just one for the right hand ? 

 

Unfortunately, I think it's very unlikely that anybody near me has built one as I live in an idyllic rural wilderness in the very centre of Ireland. 

 

[bremen]

Put me up for a weekend and I'll build one and deliver it 😉

[RhythmJunky]

9 minutes ago, bremen said:

Put me up for a weekend and I'll build one and deliver it 😉

 

Sounds like a deal.  We've even got Guinness here 😆 

Edited 20 hours ago by RhythmJunky

[rwillett]

15 minutes ago, bremen said:

Put me up for a weekend and I'll build one and deliver it 😉

I'll take you up on that and throw in a slap up meal at Mrs Miggins Pie Shop...

[bremen]

Forget Round Ireland With a Fridge, seems I can do Free Lodgings Round Britain With a Bass Cab.

 

It's the Experience that airbnb has yet to monetise

[Phil Starr]

4 hours ago, RhythmJunky said:

 

Thanks Phil, I appreciate your response. It seems it may be prudent to factor a tweeter, and the volume needed, into the design. I'll have to look around for suitable candidates. Do you think it'll need 2x or just one for the right hand ? 

 

Unfortunately, I think it's very unlikely that anybody near me has built one as I live in an idyllic rural wilderness in the very centre of Ireland. 

 

If you want to go ahead with this I think I would start by building just one of the House Jam cabs as it is designed. Maybe moving the mounting of the speaker from it's central position to allow for the addition of a small horn. That way you have a usable bass cab and a tiny system for lighter gigs using the Warwick Gnome. You can then try it for keys and judge whether the lack of treble is an issue or not. As designed you are only missing the final octave of human hearing from this cab, it might sound OK, it might not. If it is good then go for a second cab and you can get stereo and a useful extra 6db of sound output. With the Gnome you'll get the full 200W ouput potential through 4ohms if you use both cabs.

 

Adding a tweeter is slightly problematic, you really need a crossover. What you could do is adapt the tweeter and crossover from @stevie's lockdown 10" design. It has a crossover with just three components which we wired with a connecting block so no soldering. It won't be perfect and youd probably need to increase the value of the resistor a little to match the smaller 6" driver but this simple solution sounds great with the 10" speaker and it might work here too.

[RhythmJunky]

Thanks again Phil. I've read that thread again. I think what I'll do is build a 2x6 cabinet that will basically be two 1x6 cabinets joined together and seperated internally. I can then use this as a mono 8ohm 1x6 or a 4 ohm 2x6, with one Gnome, or a stereo unit with a small stereo class d amp. 

 

Alternatively, I could always just buy another Gnome, so if I needed a more powerful stereo combo, I'll be gnome and dry. Seems to be a bit of a gnome-brainer to be honest....sorry....quiet day in work.

 

If I'm unhappy with the treble response, I'll build a seperate, stackable, tweeter cabinet with the drivers from the 1x10 and the x-over(s) in the cab. 

[Pea Turgh]

8khz is still quite high.  A lot of people like putting keys through guitar amps, and they top out about 5khz?

Depends on the sorts of keys sounds you need, and what your tastes are, I guess.

Might try my daughter’s electric piano (Kawai somethingorother) through my micro cab this afternoon to see what it sounds like.

I love the idea of a 2x6.  Got the cab building itch again…

 

[RhythmJunky]

1 hour ago, Pea Turgh said:

8khz is still quite high.  A lot of people like putting keys through guitar amps, and they top out about 5khz?

Depends on the sorts of keys sounds you need, and what your tastes are, I guess.

Might try my daughter’s electric piano (Kawai somethingorother) through my micro cab this afternoon to see what it sounds like.

I love the idea of a 2x6.  Got the cab building itch again…

 

Thanks Pea. I'd be interested to hear what you think. 

 

I have ran my keyboard (also a Kawai somethingorother) through various bass and guitar speakers in the past and it generally sounds okay, but not very hifi. Not much top end and a bit boomy. So far I've used it on a Peavey Minx (50W bass amp), an Ashdown 4x8 bass cab and a Peavey Mace (a 160 W valve, 2x12 guitar combo).

 

The 4x8 is by far the best, but isn't stereo. I think that the 2x6 is the way to go. I did think about splitting the 4x8 into two 2x8's and run it stereo, but am reluctant to start chopping into it. It's also really heavy and far too big for what I currently need. 

 

I've always read that it's generally not a great idea to put a full 88 key piano through a guitar amp, but apparently plenty of people used to use VOX AC30s with a Rhodes back in the day. 

[rwillett]

3 hours ago, RhythmJunky said:

Thanks again Phil. I've read that thread again. I think what I'll do is build a 2x6 cabinet that will basically be two 1x6 cabinets joined together and seperated internally. I can then use this as a mono 8ohm 1x6 or a 4 ohm 2x6, with one Gnome, or a stereo unit with a small stereo class d amp. 

 

Alternatively, I could always just buy another Gnome, so if I needed a more powerful stereo combo, I'll be gnome and dry. Seems to be a bit of a gnome-brainer to be honest....sorry....quiet day in work.

 

If I'm unhappy with the treble response, I'll build a seperate, stackable, tweeter cabinet with the drivers from the 1x10 and the x-over(s) in the cab. 

 

Would love to see that build. 2 x 6" sounds interesting.

 

Rob