Need help with DIY center plans and drivers!?

[runninkyle17]

Hello everyone-

I currently am looking to make a DIY MTM center channel. I have a pair of Peerless 6.5" drivers that with act as the woofers. I got the woofers off of eBay for a really good price. They came from the NHT M100 Studio Monitors. I contacted NHT and the information that I got from them was that the drivers can handle up to 250W and they have a frequency response of 55Hz - 20kHz. I am looking to match them up with the Peerless 811815 1" silk dome tweeter. The specs are on the Parts-Express website and the frequency response is quite good.

I would like the Xover point to be around 1800Hz or lower if at all possbile. However, this is my first attempt at DIY speakers and I need a little bit of advice. I unfortunately do not have any other information on the 6.5" woofers to work with other than the power handling and the frequency response. I have emailed NHT again, but I have not gotten a response back from them yet. They did tell me they still had some of the 6.5" drivers is stock so I am pretty sure they have the parameters on them somewhere.

I might even email Peerless and see if they have any info they can give me. Anyway, I am looking to make my center no more than 8" tall and 22" wide (the depth can be whatever it needs to be). If anyone has any info or advice please let me know! Thanks in advance.

-Kyle

[cjd]

Nothing you can get from a company is really going to get you where you need to be, though you can probably start to make some educated guesses.

The best option is to measure the drivers T/S parameters, design your box once you have that data, and then measure response and impedance in the final box - from there a crossover can be done well.

C

[runninkyle17]

I thought about doing that, but I really am not to savvy on how exactly to measure the T/S parameters. Is there a good book anywhere that has all that info in it and will I need to buy extra equipment to measure the parameters?

[ThomasW]

Measuring T/S parameters is not for noobs. Many experienced builders screw up these measurements.

The only real measurements a builder needs to make are frequency response plots of the drivers mounted in your baffles.

Problem is that the cost of the equipment and software for these types of measurements, is costly enough that you could just build one of Jon's proven designs for less money.

[cjd]

Thomas: my only reason for T/S was that it sure makes designing the box easier.

Of course, you can always just toss 'em in a nice big sealed box and call it done.

C

[ThomasW]

Oops my bad, I had separate windows open for 2 different noobie threads and transposed my answers.... ops:

[runninkyle17]

OK everyone. I should be getting the freq. response and other info in a week or so. The guy that I bought the 6.5" drivers from is sending another pair of them off to get them measured. I think I am going to settle on the Peerless 811815 1" tweeter. The frequency reponse on it is really good and I can even attach a PVC rear chamber to it if I really want to.

Anyway, I have another question. Would it be that much more trouble to make this center a 3-way design and add say a 4" midrange to it?

[Dennis H]

Peerless makes some good woofers but they aren't known for the quality of their tweeters. In the $30 range, it's hard to beat a Seas 27TBFC or 27TDFC.

And yes, 3-ways are much harder than 2-ways.

I know you probably don't want to hear this since you already have the woofers but I'd go with a proven design for a first project. Crossover design takes experience, time and money to buy the equipment and the software and learn how to use it all. It's not a simple matter of plugging numbers into a calculator.

[runninkyle17]

Once I get the measurements for my woofers and I decide on which tweeter to buy I should be able to find some help with a crossover network. I want to make my own crossover because I will learn more and be more confident when I do another project.

Also, does anyone have any experience with the Vifa D25AG3506 tweeter? I was looking the other day for a nice budget tweeter and came across this one on eBay. I did a search for it and got information on it, but I wanted to know if anyone had some personal experience or advice about it. I like the fact that it has a frequency response above 20kHz and the frequency graph looks acceptable for my needs.

[Brian Walter]

You know, I was going to write a response suggesting that you simply build one of the existing designs posted on various websites, otherwise you won't be satisfied with the results. But you know what, even the experts are often times not satisfied with their results, that's one of the reasons they keep building more speakers. They keep hoping to improve on one aspect or another of the previous design. So with that in mind, go for it, even a 3-way isn't a total loss, but be prepared to junk the first speaker and expect to be building another and another and another until you run out of money or your significant other (if you have one) puts their foot down.

Without measurement gear, even an experienced designer finds it really hard to do a very decent design; so as a beginer, don't expect stellar results. But have fun. No matter how it turns out you will probably not resent the fact that you tried it, and you will learn a lot.

One final comment, I am not familiar with the Peerless drivers you are trying to use, but if you are using a picture tube TV, make sure your drivers are shielded, or it will interfere with the picture. You may have already know this, but since you didn't mention anyting about shielding, I thought it best to at least point it out.

Brian Walter

[runninkyle17]

Thanks for the heads up Brian. I think they are shielded, but if they aren't, is it possible to shield them myself or is it too complicated?

[Brian Walter]

I've never tried shielding a driver, but there are some people around that have. I don't think the process is too hard, but the results may not be as good as you are hoping, and it could affect the TS parameters. So if you do try this, you should remeasure the TS parameters after you shield them.

Hopefully someone else will help you out the the shielding issue. Typically you would need a shielding magnet and a metal cup to cover the whole magnet assembly with. But I don't have any idea what size magnet you need or where you would get either the magnet or the shielding cup.

Brian Walter

[runninkyle17]

Anybody have any advice on a nice, fairly budget shielded tweeter? I would like to have it crossover at around 2000 Hz in a two way design, using the woofers I have previously mentioned. Thanks.

[cjd]

Not really sure your vision of budget, but the Seas tweeters are available shielded. I've used the 27TDFC/TV as well as the non-shielded in the same design. Good stuff to be sure.

At a lower price point, historically the Dayton DC28FS has been very well reviewed and has also been used with lower crossover points such as you'll be wanting with a horizontal MTM. ~$16. They've been through different versions of this tweeter with different response profiles (the most recent shipment being yet another) so you would want ot measure what you get for sure.

C

[runninkyle17]

Thanks for the advice. The Dayton sounds appealing, but I will have to look hard at the Seas. I have heard a lot of good things about the Seas tweeter in particular.