Speakers for my son.

Dedicated to those large boxes at one end of the room
JamesD
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#1 Speakers for my son.

Post by JamesD »

Hello All :D

Earlier this year I had to design and build a pair of speakers for my son and his wife. The speakers had to meet a definite set of criteria and had to sound as good as my Quasars but max budget was limited.

Here is a picture of the resultlt and I'll waffle away tonight about the limitations and how I attempted to meet them...

ciao

James
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Nick
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#2

Post by Nick »

HiYa James, long time, no post.

Hmm, "and had to sound as good as my Quasars but max budget was limited."

Not setting the standrd too low are you :-)

I will be very interested to find what you have come up with.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
JamesD
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#3

Post by JamesD »

Too long without posting - things have been busy but fun, I went out to New Zealand for 10 weeks to do a little job out there for TVNZ. Greatly enjoyed the trip.

The speaker design spec. was interesting. My son lives in a nice but tiny flat so size was always going to be an issue. Also it is a top floor flat in a converted house so sound isolatation, particularly at lf is an issue and meeting the Quasar sound was a real interesting challenge... and lead directly to the speaker design I used...

more later

James
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#4

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JamesD
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#5

Post by JamesD »

Hello Scott,

Its good to be back :D

Yep! FX120 it is... but keep it quiet or people will start buying them up!

I tried lots of 4" to 6" drivers and these are streets ahead of the rest and (whisper it) possibly better than the AERs on voices... (hush my mouth)

Care to guess what the cabinet alignment is :) He said knowing you won't get it (thats a hint!)

James
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#6

Post by Cressy Snr »

Hi James
Nice to see you back.
Those cabinets look extremely well built and finished.

Steve
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#7

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Dave the bass
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#8

Post by Dave the bass »

JamesD wrote:
Care to guess what the cabinet alignment is :)

James
Ooohhh, I'll have a guess.

*rubs chin* Oooo...I'd say flat against the wall and 2ft apart.

Am I right? What have I won? :)

DTB
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#9

Post by JamesD »

The requirements given to me for the speakers were as follows:

Physically fit the space available.
Match the room decor.
Full frequency response - my definition is to reproduce bottom E on a bass guitar and exceed 18KHz at the top end.
Not excite room/building resonances.
No thumping bass to upset neighbours below or beside
Capable of sounding full range at low level.
The same "quality/character" at low level as at high level.
Sound just like the Quasars.
Not cost as much as the Quasars!!!

Okay I thought easy enough :-) So we make a small version of the Quasars :D

And thats what I did - I used the Good old FE127 and a Beyma 8" bass unit and nuilt a Quasar 850mm high, 230mm wide and 370mm deep. And it worked and rocked and all was good in the world :lol:

but not quite... Ben loved them but Laura didn't 'cos they were too big and didn't fit with the telly at all - in fact they had to sit on the floor all by there own...

so back to the drawing board...

Okay so what is special about open baffles?

Umm their dispersion pattern... okay
Ummm their clean bass response that doesn't excite room resonances... Good.
Ummm... Ummm.... Ahhhh their excellent impulse response that settles down much faster than other alignments thereby minimising intermodulation and bass over-hang... Excellent, now we are getting somewhere!

So what other alignments acheive the same impulse response? Well just one other - the infinite baffle (or sealed box as Scott so inelegantly put it :D ).

So that was my next design starting point. And by this time I was getting frustrated with the 127 as well. I knew the 108EZ and old 104 and the 126 sounds close to the 127. Itried the Vifa 4", A couple of Monacor ones,The Neofane and the then decided to go for broke and get the FX120s. I knew the 120 were good having heard then before but they are relativelt expensive... Actually they are cheap for what they do - a positive bargin really. They are not as fast or clear as the AERs but they are heavenly on voices and are close to the AERs on speed.

So easy then just shove the 120s in a sealed bx and be done with it...

Well not quite. there is the little issue of getting 41Hz reproduced at the a level that it underpins the music properly (I'm not saying flat to 40Hz in this case a little leeway is required!)

If you do a conventional infinite baffle calculation for the 120s you end up wit a 6-9lite box and a response that is 3dB down at 75-80Hz and about 12-15dB down at 40Hz oh and it starts turning down at about 95-100Hz. doesn't meet the spec.

It is a little known charateristic of infinite baffle loading that as you make the box larger and in particular larger than Vas the response at below Fs actually increases and the roll off starting point increases with F3as the pivot point the slope of the roll off is getting shallower!

Now the ear/brain system does some remarkable things when presented with a shallow roll off - to some degree it ignores it! Providing the slope is well behaved = by which I mean that phase stays constant and impulse response through the region stays constant (these are related). Well with an infinite baffle they do as long as the drive unit also behaves and the little 120 does :) So the only thing to do was decide the box volume and shape.

A 30 litre box has the response only -8-9dB at 40Hz and the roll off starts at 130Hz but still onlu -3dB at 80Hz. The box shape lets them fit behind the telly and sit 3 feet apart. Ohhh Infinite baffles also throw the sound out of the box into the room so the speaker dissappears and do not excite room resonances. There is no bass overhang so no thumping bass tp upset the neighbours.

Hurrah!!! Mission acomplished!!! 8)

Testing at home was interesting, I sat the 120s infront of the Quasars and most people thought I had the big speakers on! Their attack and viseral reproduction of drums and voices fooled almost eberyone into thinking they were listening to the Quasars... Ben & Laura are very happy with the little beasties.

James.
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#10

Post by JamesD »

Hello Steve!

Thanks for the kind comments.

The cabinets were a nightmare to get right :(

I used 12mm marine grade ply with a 3mm thick ash veneer on one side. That bit was easy - expensive but easy :D

The joints are all 45 degree mitres running along the full length which was a bitch to cut straight. And the tops and bottom corners where three surfaces come together took forever to get right. It took hours of carefully shaving off a bit more of the top and bottoms to get them to fit but the result was worth it - even if I did have to cut almost every panel twice :shock:

Next time I'm not doing it that way...

I didn't use cardboard mules this time :D

I used expanded polystrene boxes with 3cm thick walls. They worked very well once I used enough duck tape around them to stop the sound pressure from forcing the boxes open!

James
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#11

Post by JamesD »

Dave,

They are not flat against the wall, there is a half inch gap :)

And they are three feet apart not two!

any excuse not to give a prize :shock:

James
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#12

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#13

Post by Dave the bass »

JamesD wrote:Dave,

They are not flat against the wall, there is a half inch gap :)

And they are three feet apart not two!

any excuse not to give a prize :shock:

James
Oh Poo!

:lol:

DTB
"The fat bourgeois and his doppelganger"
JamesD
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#14

Post by JamesD »

Scott,

Yep that's what my calcs worked out too. The best drivers for this alignment are the FX120 and the Neofanes - they sound the best too but the 120s are more lively and better on voices. The Neofanes have more bass impact.

They work well free field but they are better back against the wall. It is really surprising how they place the sound field out in the room and as its a small room you end up walking around in the sound field :D

I'm really very pleased with them as they have exceeded my expectations by quite a lot. Particularly in how they portray drums and bass guitar - rythm sections come through very strongly really underpinning the music...

No one has mentioned the chinese amp yet (or is it!)

James
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#15

Post by al newall »

I wonder if that's a Chinese amp in the photo. :roll:
Much to learn there is.
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