Change of plans...

[WmAx]

Chris,

So If I were doing two way speakers all around, I could get by with two DCX 2496, correct?

Yes.

Consider it this way: Each DCX has 3 analog inputs and 6 analog outputs. You can configure these inputs/outputs or route them in any way you wish, and apply any crossover(s) or filter(s) to each channel as you wish. The daisy chain networking is an important feature that this unit has if you are using multiples. Also, the DCX can be connected to the computer with a very nice GUI program that makes experimentation while listening a very valuable tool for the DIYer when fine tuning the speaker(s). Imagine being able to try a different order crossover, or moving the crossover frequency, or altering a parametric band, all in real time while listening, and sitting comfortably in your listening chair. BTW, it is rarely mentioned, but the DCX has a PCMCIA slot on the front for a flash memory card so that you can store/backup your settings/programs or transfer them to remote unit easily without having to use a computer interface.

I intend to never go back to passive crossovers.

-Chris

 

[Hi Ho]

Well, it looks like I will be building a pair of speakers after all. My dad still wants me to do a senior project. With only three weeks left, I'm cutting it close.

I don't want to spend much. I need anything fancy. I have thrown together some parts at P arts E xpress:

Drivers:
DAYTON RS150S-8 6" REFERENCE SERIES # 295-362 (x2)
DAYTON DC28F-8 1-1/8" SILK DOME TWEETER # 275-070 (x2)

Crossover:
1.00mH 18 GA PERFECT LAYER INDUCTOR COIL # 266-826 (x4)
DAYTON DMPC-2.0 2.0uF-250V POLYPROPYLENE CAPACITOR # 027-414 (x8)
4 OHM 10W RESISTOR # 016-4 (x2)

Other:
GOLD HIGH POWER TERMINAL RECTANGLE # 260-309 (x2)
PORT TUBE 2-1/16" I.D. x 5" # 260-322 (x2)

TOTAL W/SHIPPING: $157.58 + MDF/veneer

The crossover parts are based on the Dayton 2500hz crossover (seen HERE, replace *** with p arts e xpress in address bar). The extra 4 OHM resistor was recommended by someone using the same tweeter to tame the highs.

Using WinISD I calculated the box to be about 13.5 x 8.5 x 11.5 inches (outer dimensions) for an internal volume of 840^in using 3/4" MDF. The port would be left at 5" for a tuning of around 50hz.

Is this a decent setup? Could I do better for the money? I will probably stick these in my room. As long as they sound decent I will be happy and I will have a completed senior project. I need to do this within three weeks.

 

[Rip Van Woofer]

Since this is a school project with a tight deadline, I suggest you proceed in that spirit and accept that the initial results will be less than optimal. In other words, approach this as a learning project for now rather than as finished speakers for your system. Even a pro cannot design a fully sorted out speaker in three weeks!

However, the quality of the drivers is a big factor in the sound too, so even if your crossover is less than ideal they'll probably be OK.

So after you've fulfilled the senior project requirements, you can experiment further with the crossover, box dimensions etc. at your leisure. You'll eventually arrive at a very good sounding DIY speaker and learn lots of stuff doing it.

And if you don't get an A, slash the teacher's tires!

 

[Hi Ho]

Thanks for the response. I don't intend to use those speakers in my main system. That system is reserved for much better ones down the road and the Advents are filling tha position at the moment.

I know it's not possible to get the best out of a speaker design in one shot (unless I'm really lucky) but as long as they sound better than the Sanyo mini system speakers in my room now I will be happy. I would think that crossing them over a bit below the woofers max and a bit above the tweeters minimum would yield a decent starting point. Is this not correct?

My main dilema now is the tweeter. I have no idea if the one I chose is any good. Are there any better ones in the same price range, maybe a little more?

EDIT: I have another question. I have found that crossover schematic I linked to above to be quite confusing. The diagram shows one of each component. However, there is a "(2)" handwritten by each capacitor on the diagram. Does this mean there are supposed to be two capacitors? Would they be in series or parallel?

 

[Hi Ho]

I ordered the components last night. I guess I will see how it turns out. I'm still wondering about the crossover schematic.

 

[Swerd]

I have found that crossover schematic I linked to above to be quite confusing. The diagram shows one of each component. However, there is a "(2)" handwritten by each capacitor on the diagram. Does this mean there are supposed to be two capacitors? Would they be in series or parallel?

Yes there should be two capacitors, 2 µF each, in parallel with each other. Look in the schematic in the lower left corner. It says, C1 and C2 are each 3.98 µF. To add two smaller capacitors and get the sum of their values, twist their leads together in parallel.

I would think that crossing them over a bit below the woofers max and a bit above the tweeters minimum would yield a decent starting point. Is this not correct?

There is a bit more to it than that. Read this to get an idea of how to go about selecting a crossover point http://www.speakerbuilder.net/web_files/Articles/xover article/xpointmain.htm . Since you have very little time, use the 2,500 Hz crossover now. Later when you have more time, take a good look at the frequency response curve of your RS180 woofer and decide if 2,500 Hz might be too high for a 2nd order filter with a 12 dB/octave roll off. Pay attention to the RS180's big breakup peaks that are above 5,000 Hz. If you hear harshness, and think it might be coming from the tweeter, it might actually be from the woofer. Remember that 5 to 10 kHz is between 2 and 3 octaves above the crossover point. It may be lower by 24 dB but considering the size of those breakup peaks, you might be hear them anyway.

That link I wrote in above seems to be dead now. I made a copy of it in Word. If you want to read it, email me and I can send it you.

My main dilema now is the tweeter. I have no idea if the one I chose is any good. Are there any better ones in the same price range, maybe a little more?

The Dayton 1" silk tweeter is one of the lowest price, decent sounding tweeters you can buy. A general rule of thumb for a crossover point for a tweeter is to triple the resonance frequency (Fs) value. For this tweeter Fs = 900 Hz. Triple is 2700 Hz, not at all far from 2500.

So the crossover may be fine for the tweeter, but may possibly be trouble for the aluminum woofer. Try it and see.

 

[Hi Ho]

Thanks for the advice. The stuff will be here on Friday (assuming UPS doesn't screw up) and I will start building. It will give me a senior project, and if I don't like the sound, I can tweak it later.

HERE is what I plan to build. It will be covered in cherry veneer with a high gloss finish. The cutout dimensions are estimates until I get the stuff in my hand. Is there any magic formula for the offset of the tweeter? Does anyone know of any free CAD programs?

 

[Swerd]

HERE is what I plan to build. It will be covered in cherry veneer with a high gloss finish. The cutout dimensions are estimates until I get the stuff in my hand. Is there any magic formula for the offset of the tweeter? Does anyone know of any free CAD programs?

Most designs I've seen that have the tweeter off-center put it 1" away from the vertical center line. I don't know any formula for tweeter offset.

Are you going to flush mount the drivers? The only way I get the flange depth correct is to make a test cutout on a scrap piece of wood and test fit the drivers. In the scrap wood, I set the depth for exactly what the flange depth is on the driver. I use foam gasketing tape (PE 260-540) or black sealing caulk (PE 269-300) when I test fit the driver and see how much extra depth is needed for the caulk or gasket tape when it is compressed by the mounting screws. It seems like a lot of extra work, but before I did that I could never get the flange depth quite right and I could always see the poor results. I like using the black sealing caulk because you can break off a length and roll it out until it is much thinner. PE usually throws in some free if you order speakers .

 

[Hi Ho]

Yes, I am flush mounting the drivers. Thanks for the advice. It looks like I guessed right in putting the tweeter one inch off.

 

[Hi Ho]

Here's an update. The components arrived yesterday and I assembled one of the crossovers last night. So far so good. With no enclosure there's not a whole lot of bass but the crossover works and, from what I can hear, the crossover point is good for this pair of drivers.

HERE are some pictures. The crossover is very ugly on the back but it does work fine. I need to clean that camera lens too...

 

[Swerd]

You asked earlier if there was a formula to use when mounting a tweeter off center. I haven't found a simple equation to use, but I did find an article that explains how to go about locating a tweeter off center.

http://www.rjbaudio.com/Audiofiles/tweeter diffraction.html