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Old 17th July 2009, 07:49 AM   #1
alspe is offline alspe  Finland
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Default Classic monitor designs?

Hi.

Post here if you have constructed or found designs on internet about classic monitor designs.

Here is couple of what I have found.

http://www.troelsgravesen.dk/3WClassic.htm

http://www.troelsgravesen.dk/CSM_KIT3.htm

I don't seek for slim floorstanders or small monitors but bit larger monitors which have bass grunt by their bigger cabinet volume and wider baffle. And yes, they can be bigger than those examples. 8-12" bass would be fine :-)

If you have seen cabinet construction with thin walled enclosures, please post here. I think some british speakers are made of thin material and they sound lively.
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Old 17th July 2009, 09:47 AM   #2
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Just of curiosity, why are you looking for thin cabinet constructions?
I am designing a 2-way floorstander ( not a monitor type speaker ), but it could be easily converted to a monitor. If you have interest I will post the final version hereq it should be ready within a month.
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Old 18th July 2009, 02:16 AM   #3
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Thin, non or poorly braced walls can resonate audibly and that's what produces that "lively" sound you're talking about.

But this is an artifact of the cabinet and is not from the original recording - it's not music - most listeners don't want this.
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Old 18th July 2009, 06:11 AM   #4
alspe is offline alspe  Finland
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Yes I know they can resonate. Have you heard Spendor classics?

If I understand right, you can not make cabinet fully rigid even with very thick material. Rigid cabinet can "ring" at high frequencies. Idea for thin walled and bitumen damped walls is that they resonate at low frequencies where ear is not very sensitive. Make any sense?

Back in topic, any ideas for classic 3-way monitor?
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Old 18th July 2009, 04:53 PM   #5
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Quote:
Originally posted by alspe
If I understand right, you can not make cabinet fully rigid even with very thick material. Rigid cabinet can "ring" at high frequencies. Idea for thin walled and bitumen damped walls is that they resonate at low frequencies where ear is not very sensitive.
True, that's the whole point of making them rigid, to push its Fs above the driver's intended pass-band, ergo it can't be excited, i.e. it's acoustically inert. It also provides the driver with a very stable work platform, maximizing its electro-acoustical-mechanical efficiency.

Obviously then, going in the other direction requires considerable mass loading (as in thick concrete) to push its Fs down far enough to be inert unless the cab alignment has a high cut-off, so for mid-bass/bass/sub alignments this style construction is best suited for damping high Q systems.

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Old 31st July 2009, 08:06 AM   #6
alspe is offline alspe  Finland
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True, that's the whole point of making them rigid, to push its Fs above the driver's intended pass-band, ergo it can't be excited, i.e. it's acoustically inert. It also provides the driver with a very stable work platform, maximizing its electro-acoustical-mechanical efficiency.
Do you mean that if Fs of box is above "driver's" area that box can not "sing" or "ring". Do you mean bass/mid driver by driver you say?
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Old 31st July 2009, 03:58 PM   #7
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If I understand your question, the cab must be rigid enough to have a Fs well above the desired pass-band regardless of whether it is a sub-woofer, woofer, etc.. For example, my cabs have a 500 Hz/2nd order, so I needed the cab's Fs to be at least a half octave higher (~707 Hz) and ideally one octave (1 kHz). Using void free 0.75" thick marine grade plywood plus bracing I had no trouble getting close to one octave.

I did not know it at the time (this was back in 1969), but it would have taken at least 1.125" thick MDF plus much more bracing than I used. Since my ~20 ft^3 cabs weigh a calculated ~245 lbs, using MDF would have meant me having to severely compromise its LF performance to keep weight down.

That said, once we move higher up in frequency, i.e. a mid driver only used above ~500 Hz, then in theory using MDF is an option since its basic Fs is in the ~250-400 Hz range depending on a number of manufacturing variables. I say in theory because MDF has enough damping factor to potentially 'suck the life' out of a wide BW driver if it does not have a high Qts. For lower pass-bands then, MDF or even lower Fs materials are best suited for higher Qts driver and/or Qtc sealed alignments.

Bottom line, for accurate reproduction the cab should not contribute to it beyond driver loading, so can not resonate in the speaker's pass-band, so use the right 'tools' (material, bracing scheme) for the job.

All that said, accurate reproduction of many recordings (particularly since the 1980s) can sound very 'dry'/'sterile' due to a variety of things and in general, we humans like 'rich' in the food we eat, what we look at and feel touch our skin and so we do with the sounds we hear. So a good argument can be made for cabs that 'sing' to add some additional harmonics to make such recordings sound more 'musical', but getting it right for some recordings often means it's not quite right for others, so finding an acceptable compromise is no trivial pursuit. Better IMO to take the cab out of the equation and use some form of adjustable EQ. For example, a SET preamp/medium-low output impedance amp with adjustable damping/HF by-pass (bass/treble) tone controls coupled to relatively high efficiency (HE) speakers with passive XOs is the traditional way.

To maximize accuracy without sacrificing (and in some ways, increasing) any 'musicality' requires compression horn loading of all the audible pass-band of the source signal, but its size plus requisite room volume means only the wealthy can afford them and why the earliest studio monitors/'HIFI' ('Salon') systems only used them in our most acute hearing BW above ~800 Hz coupled to an ultra-wide BW mid-bass sealed or reflex system since there was as yet no practical way to reproduce anything below ~75 Hz.

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Old 31st July 2009, 04:07 PM   #8
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Back on topic, if you still want to go the 'singing' cab route, then a good tutorial is the development of the BBC's LS-5 which I assume the Spendors are based on: http://www.bbc.co.uk/rd/pubs/reports/1977-03.pdf

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Old 8th December 2009, 01:15 PM   #9
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Have you seen any more DIY designs which look like big classic monitors? Like Spendor SP100, Spendor 1/2, Harbeth 40.1, Super HL-5 or Compact 7.

http://www.6moons.com/industryfeatures/bo2007/jeff1.jpg

http://www.soundmates.jp/spendor4.jpg

I like the looks of these speakers. They look like _speakers_, not those fancy slim decoration things. Speakers for men.
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Old 8th December 2009, 01:20 PM   #10
tinitus is offline tinitus  Europe
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As we "speak" I am in process of cutting wood fore this "classic monitor
Front baffle is missing in cutting plans
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