Isobaric Cabinets - Can they go low with less inches?

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ROOGROOG Frets: 416

Just wondered if anyone had experience of or understood the principles behind these types of enclosures?

I would like to build my own small ‘low profile’ bass cabinet, it is purely for home use and doesn’t need to go loud.

To make it smaller I was planning on using small drivers, say 5”and I was wondering if an ‘isobaric’ enclosure arrangement (using a second speaker in the enclosure behind the front one, “piggy back”) might help extend the bass response of the smaller diameter drive units.

I appreciate that it will be less efficient than a conventional infinite baffle or ported enclosure and that it may present a lower impedance load to the amplifier. The need to double up on drivers, increased cost and lower efficiency make this option unattractive to commercial manufacturers, but in my case the wish to keep it small ‘low profile’ and with no requirement for making it ‘loud’ makes it an interesting proposition. Provided that the ‘Isobaric’ principle does extend the bass response from small drivers?

So…..is that what ‘isobaric’ systems do?

 

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  • fretmeisterfretmeister Frets: 11412
    By the time you've got a couple of 5 inch drivers, you might as well have a modern 10 inch driver instead and you won't have to do any maths about the getting the rear cone toe right distance from the ports.

    Hello darkness my old friend.


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  • ICBMICBM Frets: 41527
    My only experience with an Isobaric cabinet (an Ampeg) was the exact opposite of what you're describing… it was incredibly efficient, sounded fantastic, but was much larger and heavier than a conventional cab - not to mention awkward - or seemed to be when I was trying to get it into my car, not least because it was very deep.

    I think they sold poorly because they were so expensive and a massive pain to move, not because they weren't efficient.

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  • ROOGROOG Frets: 416

    I can see that with most gear historically aimed at the gigging professional the need for; cost effective, robust, reliable, and loud gear is important.

    I was aware that Orange have tried an isobaric solution and have seen pictures of big clumsy 2x10" plus 1x15" isobaric enclosures, but both use sizable drivers.

    In the world of HiFi there have been a few solutions using Isobaric enclosures using smaller drivers, but these products seem few and far between.

    I really don't mind how efficient or not the cab is, to some extent the cost of the extra drivers isn't the big problem I'd just like a small cabinet that can do bass reasonably well at modest levels that "I can shove under the bed". 

    I note that the 'isobaric principle' is used in car audio solutions where space is at a premium, problems is its difficult to get much sense out of those forums.   

    Plus I quite like the idea!

     

     

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  • RockerRocker Frets: 3411
    Linn made a small isobaric speaker called Sara. Needed a powerful amp but sounded very good. Google.
    Insanity: doing the same thing over and over again and expecting different results. [Albert Einstein]

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  • ROOGROOG Frets: 416
    Rocker said:
    Linn made a small isobaric speaker called Sara. Needed a powerful amp but sounded very good. Google.


    @rocker you're right, Linn did tinker with HiFi designs like this for a while, I recall that reports at the time said that they were difficult to drive by many amplifiers of the day and of course they were expensive.

    There simply isn't a great deal of accessible stuff out there which talks about the properties of this type of cabinet design. the main one seems to be that you can put your bass driver in a smaller enclosure, very little is said of using smaller drivers to get acceptable bass.

     

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  • capo4thcapo4th Frets: 3213
    I prefer The Inspiral Carpets myself
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  • strtdvstrtdv Frets: 1526
    I think Markbass used to make a small 2x8 cab which is probably worth checking out if you can find a used one, it would fit the bill of small and good sounding
    Robot Lords of Tokyo, SMILE TASTE KITTENS!
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  • ROOGROOG Frets: 416
    I am also considering Phil Jones and tc electronic alternatives

     

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  • strtdvstrtdv Frets: 1526
    The days of lugging around huge bass amps are pretty much gone, unless you particularly want to go down that line.
    There are loads of great sounding, lightweight setups out there. My Markbass combo plus an extension 1x12 is 500 watts and the whole thing weighs under 50lbs. TC do similarly compact and also very nice sounding stuff (IMO not quite the power of the Markbass but lovely warmth/compression to the sound at medium volumes, and probably more features).
    I'd avoid Trace and Ashdown though if it's compact stuff you're looking for, and I've heard of speaker cone splitting issues with Hartke's aluminium drivers
    Robot Lords of Tokyo, SMILE TASTE KITTENS!
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  • ROOGROOG Frets: 416
    strtdv said:
    The days of lugging around huge bass amps are pretty much gone, unless you particularly want to go down that line.
    There are loads of great sounding, lightweight setups out there. My Markbass combo plus an extension 1x12 is 500 watts and the whole thing weighs under 50lbs. TC do similarly compact and also very nice sounding stuff (IMO not quite the power of the Markbass but lovely warmth/compression to the sound at medium volumes, and probably more features).
    I'd avoid Trace and Ashdown though if it's compact stuff you're looking for, and I've heard of speaker cone splitting issues with Hartke's aluminium drivers

    Thanks for the advice @strtdv im definitely not looking for big, quite the opposite.  I like the look of the small JP combos, but would like to try the tc range of tone print heads, so a super small cab to go with it would be just the job.

     

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  • strtdvstrtdv Frets: 1526
    ROOG;518185" said:

    Thanks for the advice @strtdv im definitely not looking for big, quite the opposite.  I like the look of the small JP combos, but would like to try the tc range of tone print heads, so a super small cab to go with it would be just the job.
    The tone print heads seem very versatile, not to mention incredibly compact. As far as I know the tc cabs are particularly voiced to match the tc heads so it's probably worth trying out the head with a matching cab. The cabs are very light so should fit the bill too, although I've not personally tried them
    Robot Lords of Tokyo, SMILE TASTE KITTENS!
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  • ROOGROOG Frets: 416
    Yep, like the Markbass one, tcelectronic do a 2 x 8 as well

     

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  • NomadNomad Frets: 526
    edited February 2015

    Isobarics won't change the frequency range of the drivers. What they do is double the power of the motor (a speaker is a type of electric motor) which, for a given sealed box volume, means the air inside the box can be compressed more, which means that the cab's natural damping effect (due to air compression and rarefaction within the box) is halved compared to a single driver. That means more low bass comes out. If you took one driver and stuck it in an IB enclosure of twice the volume, you'd get the same bass response as the half-volume isobaric.

    Although the air volume behind the inner speaker can be half that of a single-driver box, there is still an increase in relative terms because you need to include a 'dead' chamber that houses the inner driver and whatever airspace is between that and the outer one. The overall outer box will be a bit more than half the volume of the single-driver version.

    You also, ideally, want to make the cab deeper than it would be for the single driver version - the big, whumping movements of the drivers at low frequencies can cause the air to smack against the back of the cab and bounce straight forward again, which can bugger up the sound in various ways. So, you need to increase cab depth, ideally put something in the rear corner to send the backwards-going pressure front in a different direction (an angled or curved shape made of something solid), and more than likely, put some sort of acoustic damping inside the cab (such as foam, wadding, etc).

    Watch out for speaker impedance - if the drivers are wired in parallel, then the impedance will be half.

    Also, check out the spec of the drivers - there is usually an ideal cabinet volume which will give best bass extension, beyond which there is little more to be had (or even a range of volumes with guidelines on how much loss to expect), and good makers will provide that data. In general, for sealed boxes, the bigger the volume, the more low bass.

    Nomad
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  • ROOGROOG Frets: 416
    Thanks @Nomad I am tempted to give it a go. My current plan is to try a low profile 2 x 6" driver cab with the secondary drivers in chambers behind, making it a 4 x 6" isobaric cab. If it doesn't work out I can always use the drivers to build a conventional 4 x 6" cabinet.

     

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