Befor i buy

[bobfig]

hello guys i just want any final thoughts on this before i click the buy button.

i plan on making a pair of bass reflex book shelf speakers. the internal distentions are 13.25"H x 8"W x 7.5"D and has a total volume of 13L but with the port and some crossover it will come out to around 12L. the port is 1 7/8" in diameter, flared, 4.3" long, and tuned to 55Hz. the box is going to be made of 3/4" MDF except the front baffle will be made up of some 3/4" hard wood.

ima use a 2nd order L-R crossover at 3000Hz and have a L-Pad in the high pass and zobel in the low pass.

One question with the zobel part of the network, my calculator says i need a cap of 26.6uF but i cant find any. i was told that you can put caps in parallel to equal the uF that i need, but i read that the lower uF cap will draw more volts and im concerned. did i chose a good combination?

Parts list

2x Tweeter: DC28FS-8
2x Woofer: Peerless 830656
2x Port tube: Port Tube 1-7/8" ID
2x Binding Post: Round Speaker Terminal 2-7/8" Gold Binding Post
4x Inducer: Jantzen 0.85mH 18 AWG Air Core Inductor
Caps: 4x Dayton PMPC-3.3 3.3uF 250V Precision Audio Capacitor , 2x Dayton PMPC-6.8 6.8uF 250V Precision Audio Capacitor , 2x Dayton PMPC-20 20uF 250V Precision Audio Capacitor
2x Resister: Dayton DNR-7.5 7.5 Ohm 10W Precision Audio Grade Resistor
2x L-Pad: L-Pad 100W Mono 3/8" Shaft 8 Ohm

[infinia]

Hi

Placing the port between the midbass and tweeter is bad practice. You want the 2 drivers to simulate a point source and have better power (polar) response.
Using crossover calculators is more of a miss than hit in general, but can be a start for some folks. If you search the net or even this site you can probably get a better crossover design for this. Otherwise you might need to account for loss of bass in your Xover design because of small cabinets and far field listening ie BSC.
As far as answering your Q about zobels, I use NonPolar electrolytics in that application. Using expensive film caps are IMO wasteful for parallel connection esp using a big R in series. Just use any value in the range of 20-30 uF, it's not that key for accuracy and may even work better without one. I think the Zobel resistor s/b =Re+(5-10&#37 or closer to 6R4 ohms anyway.

[bobfig]

hay thanks for a response.

Placing the port between the midbass and tweeter is bad practice....

i liked the look of them being like that, but i guess your right since ill be using them for close range listening (less then 2 meters) the woofer and tweeter should be close together as possible. i moved the port to the bottom as a slot port. i really don't want it on the back is because im not going to have room behind them so its going to be pointless.

Using expensive film caps are IMO wasteful for parallel connection esp using a big R in series. Just use any value in the range of 20-30 uF

will do

I think the Zobel resistor s/b =Re+(5-10%) or closer to 6R4 ohms anyway.

not 100% sure what u meant there?

[infinia]

Non of the good designers use crossover calculators!
read this http://www.zaphaudio.com/ZBM4.html also crossing at 3KHz plus no zobel required!
Look at the crossover network response. he talks about BSC due to changing the value of L in the lowpass section.

Using slotted ports have a correction factor (they act like a longer tube ) tube ports right at the inside wall behave similarly

[raypalmer]

Don't use hardwood! It's far more resonant than ply or mdf and has other bad habits to boot.

Birch ply with a good hardwood veneer will always sound better.

[bobfig]

ok so no hard wood. its all going to be painted 3/4" MDF. would the bottem slot be better or should i do duel 1" flared ports down there?

[infinia]

Seems if you move everything up and make the mid-bass edge touch the tweeter flange, the original tubular port should fit fine.

[raypalmer]

Originally Posted by infinia

Seems if you move everything up and make the mid-bass edge touch the tweeter flange, the original tubular port should fit fine.

Or move everything up and maintain the gap 'tween woofer and tweeter but offset the port to one side or the other.

Another option would be to pinch the whole box so it's narrower and taller, only so much as to allow the port in.

[bobfig]

Thanks guys for the ideas. Another question, would it be better if the port is centerd in the baffel or offset? And if you offset the port would the cabnents have a serton side they have to be on? i.e. the ports be on the inside or the out side of the woofers.

[bobfig]

hay guys i found this tweeter and was wondering if i could use it.


its 15 watts nominal power and i plan on using a reciver to drive these bookshelf speakers that puts out ~100watts rms. its going to be crossed at 3k still. could these tweeters handel it?