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Multi-Way Conventional loudspeakers with crossovers

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Old 6th August 2006, 06:51 PM   #1
mikee55 is offline mikee55  United Kingdom
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Default Where to begin.

Hi all, I recieved little info on my Acostic Research AV120's.I know they sold them here in the UK for £50,so I havn't got anything exciting.You probably think, "why bother?". I was given them for free,a good start, then the WAF come in and said, "Ah, smaller boxes,2 sixes have to equal 12 so no loss in bass and more room in the lounge! "
Well okay they have a narrow footprint compared to my Goodmans Magnum K2 with 12" cone, thing is they ain't got the bass of the Goodmans and they are reflex loaded, where as the Goodmans are sealed. The only crossover is a small cap 3.3uf on the tweeter and thats it.The 2 bass/mids are parallel wired for 4 ohms,and the wire is cheapy zip/figure8.

What can I do to improve things? The wire is first on the aggenda,crossover-don't know,was thinking of adding a coil,I've got a pair of coils but don't know the value. That would probably muck up the mid to treble area.Theres no stuffing,the whole cab is lightweight and the ports are rear firing. Speaking of which, could they be shortened or lengthened? Response is 48hz to 20khz

Then I'll add a sub and...

Thanks
Mikee55
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Old 6th August 2006, 11:52 PM   #2
mikee55 is offline mikee55  United Kingdom
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Smile Anyone

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Old 7th August 2006, 03:13 AM   #3
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What can you do to improve things - that depends on your budget. I would recommend you completely rebuild them - look at them as free cabinets, not free complete speakers.

Remove the rear panels on the cabinets - you'll have do do some sawing - then add bracing inside. Put a baffle between the woofers and the tweeter to completely separate them. Get some sound-absorbing foam and polyfill.

Replace all the drivers with higher end ones, and build or have built "true" crossover networks. Select woofers that are compatible with the cabinet volume, and remove/seal the ports since you are going to use a subwoofer. The 6" woofers should be used primarily as wide midranges, the very bottom frequencies left for the sub.

By the way, I'm not sure if you were joking or not, but two 6" woofers do not equal the surface area of a 12" - they add up to about 42 square inches, whereas a single 12" has about 83 - almost twice as much. (If I did my math right - I know it's pi X radius squared, but I don't remember pi exactly - I think it's 2.314...).
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Old 7th August 2006, 03:49 AM   #4
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Default I don't know much (grin)...

I don't know much (grin) but in my humble opinion you should scrap the idea of messing with these cabs. MDF is cheap and designs are plentiful. Honestly, the gains you'll make messing with these things are minimal.

Okay, you could add bracing, upgrade the drivers etc... But really, the cabs are designed to do what they do now. Even though they are cheap (50 quid? Really now mate...) a bunch of guys made 'em to do what they do. Believe it or not, even the cheap junk has some thought behind it. A room full of engineers making the cheapest saleable sound possible.

Think of it this way. If you applied to the company to design speakers, do you think they'd hire you? Or would they go for a guy from Birmingham Tech?

Build something yourself based on one of the many designs out there. Partsexpress.com or Madisound.com has a pile o'designs on the cheap. Something someone has thought through nicely.

The DIY community is good. They design nice stuff - on the cheap.

Lash back a few pints and choose one. You can't go wrong - cheap cabs will always sound dreck no matter what you do to them. Maybe better than they were but hardly worth the effort compared to a few sponduliks and some elbow grease.

Just my opinion but - been there, done that.

Lipstick on a pig...?

Regards,
Tom
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Old 7th August 2006, 03:54 AM   #5
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First, pi = 3.1415926535....

pi*r^2....

pi*3^2 = 28.2743 in^2

pi*6^2 = 113.0973 in^2

so (2) 6" drivers = 56.5487 in^2 compared to a 12" drivers 113.0973 in^2, so one would need almost exactly (4) 6" drivers to equal the surface area of (1) 12" driver.
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Old 7th August 2006, 10:46 AM   #6
mikee55 is offline mikee55  United Kingdom
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Thumbs up Return of the Goodmans

Hi,thanks for replying.Her indoors has had a change of mind and I can go back to the Goodmans.I was allways told 2 drivers at 6 = 12" etc. Ok, it don't matter now anyway. My Goodmans,although aged now, are still good units.They're 3 way sealed and have a sensible crossover. I stick those other boxes in the attic for one of my kids when they're older. The only gripe with them, I had to replace the tweeters and one of the mids has been repaired with PVA glue, but still put out an impressive sound.

I was worried I would have to put up with them other things because of the WAF. I'd still like a IB setup or a mass of subs where the WAF goes out the window on those ideas, so ones got to compromise. I'd tri-amp my Goodmans,but the complications of measuring the individual driver parameters to get a working active crossover is beyond the scope of my abilities at this time.I had ideas of replacing the mids for small bass/mid drivers, mounting them in they're own chamber and using a Linkwitz Transform on the 12" woofer.

Again, here I need T/S para's, and the cost of new drivers is not an option for a while. So I guess I'll just carry on as I am for now.

Cheers All

Mikee55
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Old 7th August 2006, 12:26 PM   #7
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Off-topic:

Hey Mike, long time since we last talked. Been busy, i guess When you have time, hop back onto Yahoo
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Old 7th August 2006, 05:36 PM   #8
mikee55 is offline mikee55  United Kingdom
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Thumbs up Hey Khron

Hows you?

My PC suffered a Death,had to get new mobo and cpu.Also had a lot of hassle with Yahoo, so I don't use it now. It seemed a lot of hassle and got in the way with some off my apps.

Could do with a simpler application. Any suggestions?

Cheers

Mikee55
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Old 7th August 2006, 05:54 PM   #9
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Quote:
Originally posted by LightwaveDude
First, pi = 3.1415926535....

pi*r^2....

pi*3^2 = 28.2743 in^2

pi*6^2 = 113.0973 in^2

so (2) 6" drivers = 56.5487 in^2 compared to a 12" drivers 113.0973 in^2, so one would need almost exactly (4) 6" drivers to equal the surface area of (1) 12" driver.
DOH! I KNEW I was gonna mess that up! Well anyway I got the proportional difference about right - that was the point.
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Old 7th August 2006, 10:35 PM   #10
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If I understand correctly, you got this pair of AR AV120's for free and basically you want to make them better with little amount of money. Well things all depend on how little amount of money you are really willing to spend. Personally going out and upgrading drivers is obviously costly, and if you are going to "upgrade the drivers" you may as well build an entirely new pair of speaker. One thing that speaker companies dread is building the cabinet. The cabinet can get to be quite a bit of money in labor and materials. If you are willing to get some testing equipment that would be wonderful, but at the same time, you could also spend that money towards building another pair of speakers. Anyway, if you have or buy test equipment you can measure the drivers to help you design a better enclosure and crossover. If no measuring equipment then use what you know. Measure the cabinet to find internal volume and use the port or measure port area. If you are not too worried about time, try different port sizes, try stuffing the cabinet differently, etc. to find better low end. Once you find what you like, you can rebuild the enclosures or just stick with the AV120 modified enclosures, preferably your own enclosures that are properly braced. Also, replacing the wire will make a difference, but when the XO is only a single cap for 2.5way speaker, I don't think it will make too much of a difference. Take out the cap, find the value. Also, measure the tweeter resistance to find the XO point that AR designed. Upgrade the cap and buy the appropriate inductor to have a proper first order XO at that frequency. Hopefully your work will have paid off.

Good Luck,

Josh
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