Sanity Check on a HT bookshelf design - AVS Forum
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post #1 of 6 Old 09-03-2013, 01:34 PM - Thread Starter
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Firstly, I have spent many hours reading this forum and I have learned much as a result. I am very new to this and I would like a sanity check on the following design.

I am trying to design a L/C/R (placed vertically) for HT use using the following:

.3 ft3 bookshelf enclosure tuned to 70 Hz (2" diameter ~4.25" length)

5-1/4" Tang Band mid- I like this speaker due to it's perceived value and its frequency response. I believe it will allow me to cross the tweeter at a higher frequency.
http://www.parts-express.com/pe/pshowdetl.cfm?&Partnumber=264-850&scqty=1

1-1/8" Dayton RS28A tweeter- From my novice perspective this tweeter seemed like a good pairing to the Tang Band mid
http://www.parts-express.com/pe/pshowdetl.cfm?&Partnumber=275-130&scqty=1


X-over Design- I have no clue what I am doing here, but I have come up with this; which I believe will work as a 3rd order x-over for my 6 Ohm Mid and my 4 Ohm tweeter crossed at roughly 5KHz:

C1 = 5.3 uF
C2 = 16 uF
C3 = 7.0 uF
Inductors
L1 = 0.1 mH
L2 = 0.3 mH
L3 = 0.1 mH


I have downloaded a couple of free-ware speaker design programs. Unfortunately I appear to be too challenged to figure out how to make them work. I did find a freeware excel spreadsheet design tool that I was able to make some progress in designing the speaker; however as an novice I am definitely open to advice. Is my crossover design even close to correct? Is there a better way to accomplish this goal of a L/C/R? This set up costs approximately $172/speaker (before wood/mdf costs)

Please help smile.gif
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post #2 of 6 Old 09-03-2013, 04:08 PM
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If you're really not sure what you're doing with crossover designs, you might want to just build a proven design that has all the kinks worked out already.

As luck would have it, Bill Waslo is designing a midsized bookshelf speaker using that woofer. I was at his house last night helping with measurements.
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post #3 of 6 Old 09-03-2013, 05:40 PM
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Quote:
Originally Posted by eqpablon View Post

Firstly, I have spent many hours reading this forum and I have learned much as a result. I am very new to this and I would like a sanity check on the following design.

I am trying to design a L/C/R (placed vertically) for HT use using the following:

.3 ft3 bookshelf enclosure tuned to 70 Hz (2" diameter ~4.25" length)

5-1/4" Tang Band mid- I like this speaker due to it's perceived value and its frequency response. I believe it will allow me to cross the tweeter at a higher frequency.
http://www.parts-express.com/pe/pshowdetl.cfm?&Partnumber=264-850&scqty=1

1-1/8" Dayton RS28A tweeter- From my novice perspective this tweeter seemed like a good pairing to the Tang Band mid
http://www.parts-express.com/pe/pshowdetl.cfm?&Partnumber=275-130&scqty=1


X-over Design- I have no clue what I am doing here, but I have come up with this; which I believe will work as a 3rd order x-over for my 6 Ohm Mid and my 4 Ohm tweeter crossed at roughly 5KHz:

C1 = 5.3 uF
C2 = 16 uF
C3 = 7.0 uF
Inductors
L1 = 0.1 mH
L2 = 0.3 mH
L3 = 0.1 mH

I have downloaded a couple of free-ware speaker design programs. Unfortunately I appear to be too challenged to figure out how to make them work. I did find a freeware excel spreadsheet design tool that I was able to make some progress in designing the speaker; however as an novice I am definitely open to advice. Is my crossover design even close to correct? Is there a better way to accomplish this goal of a L/C/R? This set up costs approximately $172/speaker (before wood/mdf costs)

You are way, way, way over your head.

First problem I see is the rated sensitivity of the woofer and tweeter are the same number of dB. Given how approximate these numbers are, there is a possibility that your tweeter is actuallyless sensitive than your woofer, and will always make the system sound dull.

Second comment is that your crossover is way far under-designed. You are supposed to consider the impedance curve, not just the rated impedance of the drivers.

To scratch-design speakers you need acoustical testing equipment, ideally the same as people use for tuning their systems, meaning a measurement mic, a mic preamp/phantom power unit, a analog to digital converter or a PC with one built in, a PC and software such as Room Eq Wizard.
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post #4 of 6 Old 09-03-2013, 06:17 PM
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well, you could give it a shot and hope for the best. :-)

using the impedance from the measurement on the spec page will get you much closer than using the nominal impedance.

around 5khz, the impedance on the woofer is about 16 ohms or so.

an "L-pad" that you could use to adjust the tweeter level would make it easier to get things matched up.

you didn't mention anything about baffle step correction, so you may end up with speakers with really weak bass.

or, you could get a copy of the loudspeaker design cookbook by dickason as that would be a good start to learning about speaker building...

Listen. It's All Good.
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post #5 of 6 Old 09-04-2013, 04:50 AM
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Dig around on the Parts Express Tech-Talk board and see if you find someone that has already worked on this pairing of drivers (or with a similar, less expensive, tweeter). If no one has worked with this pairing, there may be a good reason. The RS28A is a nice tweeter and you should be able to easily find a really decent design that nails what you are looking for. You do not need to reinvent the wheel. Regarding the sanity check - you are insane to try a ground up one-off design when someone out there has already done the work for you. wink.gif
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post #6 of 6 Old 09-04-2013, 07:29 AM - Thread Starter
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Thanks to everyone for their insight!

Eric H- I will have to keep an eye on the forum for that bookshelf design, please post it here when you all have it finalized. As far as pre-built designs go, I was leaning towards the Fusion Alchemy's; but those have been shot down by my beautiful wife.

Arny/LTD02- I am in way over my head; but I love to tinker smile.gif Your test equipment suggestions along with LTD02 suggestion of the Loudspeaker Cookbook are good both ideas

Mobeer4don- The good kind of insane, right? haha
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