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"Every speaker construction should start with a 15" bass driver! JBL knew this already in the mid Nineteen-forties."

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#1
That's a quote from Troels Gravesen, a super-ultra-mega-productive speaker builder from Denmark. I often check out his website and mostly every time he has come up with a new model..:)
I admire his work, not even mentioning the super advanced woodwork! That's second to none, and the number one reason I've never dared try one of his designs. Can of course hire a pro woodworker but that's like cheating..

Anyway, just wanted to show some DIY loudspeaker porn..:p

http://www.troelsgravesen.dk/

Ill-5-1-small.jpg
 

stevenswall

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#4
Depends on what you are going for. SPL? Sure. Dynamics? Maybe not... Max volume doesn't mean something is dynamic, and having a lower max volume doesn't mean something is acting like a dynamic range compressor.


I'll take a set of dual opposed 6" Devialer woofers over a 15" prioritizing SPL at all costs any day.
 
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#6
Nice to see some DIY speakers, carefully made.

My 'perfection list' for speakers is different, but I'd be interested to know if it overlaps anyone elses. day to day I listen to some Usher speakers, with 8" mid-bass, so this is thoughts: real world gets in the way!

I like the drivers as close together as possible. Ideally coaxial, like posh Tannoys.
The crossover point of 2.5kHz is quite sad, as that's the critical listening area, so IMO that should be avoided...
... as should real crossovers: the crossovers should be in a small box of suitable electronics with small components. A separate amp should drive each driver, ideally tube class A for treble and mid (if 3 drivers), and possibly a class B transistor won't be able to mess up the bass so it might be OK there.

Once that criteria is done: bass should be in a sealed box, of suitable shape, rigidity and wool stuffing. Ports are 'cool' and useful, but flapping a cone further than required gives IM distortion and the phase gets all messed up anyway.

12" bass is useful for that reason too: It doesn't have to move very far, as the surface area is a reasonable size, so dynamics are effortless.

I've actually had quite nice results with a single paper Eminence 12" Beta and a Motorola horm tweeter, not even biamped, the combination has a nice 'immediacy' to it, none of the cloying 'polite' suppressed sound of todays hi-fi shop offerings. For this reason I like the sound of whizzer cone paper speakers, with a supertweeter for the top, close by: for vocals and realism this is very nice.

Of course Alnico magnets help too: some of the well built tube table-top radios with 6" alnico speakers in them sound so spookily realistic on speech, you'd swear someone else was in the room. Think about it: Class A tube, Alnico speaker - paper (with possible whizzer) and a fully tube tuner and peramp section: we've gone forward in many ways with HiFi, but not always toward the direction of accurate sound.

To a large extent I blame the bogus THD measurement (The 2th harmonic really isn't as important as the 7th), terrible class B transistors fighting poorly understood global feedback loops: and of course the 'cable guys', who turned the persuit of sonic accuracy into a freakshow.

Which reminds me: ACF50 oil: All of the speaker connections, RCA connections etc: add a drop of ACF50, you'd be surprised how over time the metals corrode and start forming little semiconductors ;)
 
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#8
15" woofers in speakers make little sense.

If you use them for deep bass extension, you should have put them into subwoofers instead, and gone with 8-10" for better directivity.

If you use them for SPL, then the mid-range needs to be horn loaded for higher efficiency which extremely few designs have.

All the fancy cabinet work in the world doesn't make a speaker actually sound good if you have directivity mismatch between drivers.
 

Koeitje

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#9
Anything over 8" is probably overkill, you are going to need subwoofers anyway to balance it all out in a room.
 
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#11
By definition, ports reduce excursion (at and after the tuning point). You of course need a proper high pass filter.
Of course, at a particular frequency: absolutely.
But in general, a 'finger on the woofer' test for me at least, has shown sealed units have much less movement in general.
 

DSJR

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#12
How old are we all? How large are your rooms? I'd give almost anything to have large speakers again but squitty little shit-boxes are the norm now and in our rooms, subs add mess, wires and take up more space. Younger peeps use headphones I think and don't seem to know what speakers are...

You lucky people with larger rooms, loads of room to spread your stereo's out and hopefully an understanding partner and family who don't mind it all ;)
 

Jim Matthews

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#14
I'll take a set of dual opposed 6" Devialer woofers over a 15" prioritizing SPL at all costs any day.
Troels designs are built to maximize performance of his beloved Vacuum tube amps. The drivers tend to be selected for lowest distortion and broadest dynamics.

He designed an excellent 8" paper cone driver with attention paid to longterm compression effects.

More recent driver designs throw power at the problem.
 

Jim Matthews

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#15
Nice to see some DIY speakers, carefully made.

To a large extent I blame the bogus THD measurement (The 2th harmonic really isn't as important as the 7th), terrible class B transistors fighting poorly understood global feedback loops: and of course the 'cable guys', who turned the persuit of sonic accuracy into a freakshow.
You're onto something, there. My favorite tube amp has zero global feedback, and terrible bandwidth. A speaker must be built to utilize the strengths of the design. Troels has a few amps he loves, and builds speakers to suit those.

That said, my current iteration keeps the data digital until the driver and has class D amps optimized at the factory for the design.

It's *way* easier to handle without any fussiness.
 

Thomas_A

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#16
I've also looked at Troels site now and then. My take is that it boils down a compromise between actual need, space, budget and where it applies, FAF and WAF. As an example, the Ino Audio speakers from Sweden have different models depending on, among other things, SPL requirement. The larger systems consist of 4x8,5 inch woofers per channel from 80 Hz and up. Subwoofers can be configured to 4x15 inch ported variants covering 20-80 Hz or up to 16 subwoofers in sealed configuration for response down to DC in sealed rooms.

These kind of systems would however never be an option for me, not even DIY. I am more than satisfied with 5,5 inch from 80 Hz and one 8 inch per channel covering 22-80 Hz.
 

mhardy6647

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#20
Altec 515B in essentially a "620A" enclosure.
http://www.wardsweb.org/Billfort/

Started out with 604E Duplexes in there -- long story short, things changed. ;)
The woofer section of a 604E is kinda, sorta a 515B variant... so why not?

These aren't about bass extension, but they do get the dynamics very right, even with fleapower. :)
 
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