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Multi-Way Conventional loudspeakers with crossovers

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Old 3rd January 2013, 11:51 PM   #1
DRam is offline DRam  United States
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Default New person with questions.

As promised in the Introductions section a few days ago I have spent time searching for answers both here and, thanks to advice found here, on the Parts Express TechTalk Speaker forum.

Having never built a speaker I naively thought I could upgrade my present speakers by using my present speaker boxes, buying new drivers, installing them and then sit back listening. That hasn't worked quite as well as anticipated.

New woofers were installed, but the bass is really weak. So before buyingf new tweeters and mids the search for knowledge began, and I've now learned enough to realize how little I know about the subject.

My first concern is box size / bass speaker optimum size. One source strongly warned against putting the bass speaker in too large a box. The box I'm working with is 1.7 cu. feet. Putting my speaker specs into a caluclating program calls for 1.42 cu. ft. Would .3 of a cubic foot make a significant difference in speaker performance? Or should I be looking elsewhere?

There are many more questions, but for the moment this one foremost. What is undertaken next depends on the box design.

Thanks for the information found here, and any advice you can give.


Ron B.
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Old 4th January 2013, 12:08 AM   #2
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re: 'Putting my speaker specs into a caluclating program' - a good one, like Unibox or Winisd will show you the graph, so you can see the results of any changes in box size & tuning. What drivers, & do you have a link to their specs?
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Impedance varies with frequency, use impedance plots of your drivers and make crossover calculations using the actual impedance of the driver at the crossover frequency
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Old 4th January 2013, 12:23 AM   #3
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hi and welcome ,
what drivers you bought ? u need to share driver's specs here, is your current box ported or sealed ? what was your previous drivers ?, you need to redo all the crossover circuit to change speaker in a multi way system and same goes for port length or maybe diameter ,... my guess is your new driver have way higher fs maybe .
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Old 4th January 2013, 12:29 AM   #4
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Making a box smaller is far less complicated than making one bigger, but typically a small increase in size is less likely to be detrimental than the reverse. Bass extension won't improve with too small, it may with too big.

Provide some driver specs and we can go from broad seeping statements to guidence.
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Old 4th January 2013, 02:30 AM   #5
DRam is offline DRam  United States
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Thanks for the quick replies.

So far the only drivers purchased have been a pair of Dayton Audio Series II 12" woofers. Link to specs:

http://www.parts-express.com/pe/showdetl.cfm?partnumber=295-120



Previous drivers were those that Marantz installed. I have no idea what their specs are - or were, in the case of the woofers which are long gone. There are numbers that may let me find out what the tweeters and mids are and get their specs. I'll check that out tonight.

The boxes are Marantz 7 MK II. Internal dimensions: 24"h, 9 7/8"d, 13 3/16"w
They are sealed.

Thanks for heads up on programs. The one I used didn't provide any graphs. I'll take a look at those tonight.

Ron




THIELE-SMALL PARAMETERSResonant Frequency (Fs) 29.6 Hz DC Resistance (Re) 6 ohms Voice Coil Inductance (Le) 3.07 mH Mechanical Q (Qms) 10.55 Electromagnetic Q (Qes) 0.36 Total Q (Qts) 0.35 Compliance Equivalent Volume (Vas) 4.52 ft.³ Mechanical Compliance of Suspension (Cms) 0.36 mm/N BL Product (BL) 15.92 Tm Diaphragm Mass Inc. Airload (Mms) 81.33g Maximum Linear Excursion (Xmax) 8 mm Surface Area of Cone (Sd) 506.7 cm²
THIELE-SMALL PARAMETERSResonant Frequency (Fs) 29.6 Hz DC Resistance (Re) 6 ohms Voice Coil Inductance (Le) 3.07 mH Mechanical Q (Qms) 10.55 Electromagnetic Q (Qes) 0.36 Total Q (Qts) 0.35 Compliance Equivalent Volume (Vas) 4.52 ft.³ Mechanical Compliance of Suspension (Cms) 0.36 mm/N BL Product (BL) 15.92 Tm Diaphragm Mass Inc. Airload (Mms) 81.33g Maximum Linear Excursion (Xmax) 8 mm Surface Area of Cone (Sd) 506.7 cm²
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Old 4th January 2013, 06:49 AM   #6
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I've modeled that woofer a couple of times and I think it needs a fairly big box closer to 80 or 90 liters (3ft<3)
Post pix of the box and crossover if you can and provide the values of the components too if you can
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Old 4th January 2013, 07:05 AM   #7
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OK 90 liters (Plus appropriate stuffing ) is for a critical Q sealed box
50 liters should give 110dB with 100 watts and 10dB down at 32 Hz
perhaps you were looking for a peaked high "Q" bass response?
That would need a box of a cubic foot or less; give or take a liter

The site isn't accepting my attachments of I would paste in the graphs
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Old 4th January 2013, 08:53 PM   #8
DRam is offline DRam  United States
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Here are the pictures requested.

Values:
Upper left cap: 15.0 uF, 100V
Upper right cap: 4.0 uF, 100V
The two resistors: 8 0hms, 10%, 5W
Bottim cap (silver): 33 MF

Also a link to information about the Marantz speaker, which I bought new sometime in the mid-70's.

Legendary Audio Classics: Marantz Model 7MKII Speaker

As for what I expect from the speaker, it isn't necessary for the walls to rattle, I just want to hear the bass component in everything from classical to rock.
Attached Images
File Type: jpg Crossover-1.jpg (70.8 KB, 50 views)
File Type: jpg Crossover-2.jpg (50.5 KB, 49 views)
File Type: jpg Crossover-3.jpg (45.6 KB, 48 views)
File Type: jpg Crossover-4.jpg (38.6 KB, 47 views)
File Type: jpg Speaker-Box.jpg (26.1 KB, 49 views)
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Old 4th January 2013, 10:59 PM   #9
Dissi is offline Dissi  Switzerland
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Quote:
Originally Posted by DRam View Post
New woofers were installed, but the bass is really weak.
Hi Ron,

A simulation of the Dayton in your cabinet. I hope I got the crossover right, the coil value is estimated:

SimulationDRam.jpg
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Old 5th January 2013, 03:02 AM   #10
DRam is offline DRam  United States
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Thanks for the graph. It lookes like that speaker will work well with the present crossover although I'd like to it flat down to 35 or so.

Time to start studying crossover circuitry.

Just an aside, when I reinstalled the drivers after the photo session the bass came back. Any bets I wired the drivers out of phase when I installed them? Ten to one I did.

I'm still toying with the idea of modifying the box volume, but want to research what that might do to driver/crossover/box relationships. This speaker stuff is a whole lot more complex than I thought.

Before that, however, new tweeters.
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