center channel driver selection

[vince]

Well, I think I have decided on drivers for my new three way center channel. I wan't to use the "Peerless 830883 8" woofer" in a MTM conf. sealed I think, only require response down to 80hz for centrer and mains, don't know just yet, I will give up some bass for tight accurate sound in the mid bass. Mid will be the "Hiquphon dome tweeter OW I" three quarter inch dome. And for the mid I,m going to use the "C44-8 Ceramic 2" Midrange by Accuton". All will be elec. x-over 24db per octave. The only thing I'm not sure of yet is the x over piont. They rec. that the tweeter get crossed over at least 2.5 from the mid, but the mid to the Peerless woofer, is what I kind of don't understand. Accuton rec. the mid be crossed from the woofer at 1000hz. It has such a nice response so much lower than that so I am wondering why so high?? But fortunately the Peerless 8 inch woofers are really nice out to 1K, so maybe this would work fine. I might have to play around and measure responses, close mic and in room.
Anyway wanted to post this to see if any of you have any of these drivers in your settup to see what you think of the match up.
Thanks,
Vince

PS also for time allignment I was going to built the woofers out on the front baffle in relation to the tweet and mid to properly get voice coils right. I think Morell did something like this in one of thier MTM designs?

[Anthony]

I've been going through a similar thing with my OB 3-ways. HiVi B3N mids, Dayton Ref 8" woofs, and a Neo3PDR tweeter.

The woofs only play well up to 1k or so (nasty breakup at 1.8kHz), the tweeter CAN play down to 1.8kHz, but that's stretching its limits, so I went three way.

I recommend keeping the crossover above 3kHz if your mids can handle it. The ear is most sensitive between 1kHz and 3kHz, so any crossover anomalies stand out. However many speakers successfully cross in this region, so don't let me scare you too much.

Many times the mids need to be crossed higher than their FR would indicate due to the generation of low harmonics. Zaph explains it better, but sometimes if a mid that's only good to 200Hz tries to play 100Hz, you get undertones at pretty high levels. And you NEVER want to use harmonic distortion to extend frequency response

The same goes true for playing woofers and subs too high. Sometimes all you are hearing is the harmonics, not the fundamental. It sounds louder and measures farther up, but the sound quality is not good at that point.

Good luck and keep us posted.

[vince]

Thanks for the input. I did not consider this. I know that the proper cross point is very important, I guess one cannot base a good cross over point just by looking at the freq curves alone! unfortunatly I don't think I can measure harmonic problems with my R and D software and mic/soundcard setup Is this not something someone would have to do by ear?
Also, Peerless does not seem to make a four ohm woofer in an 8", and with using two, and being electroniclly crossed over, could one use a inline reistor or something simple without screwing up anything? I have built in 12 position rotary switches with one percent metal fim resistors on for the mid and tweeter, but would still like to get as close a match before having to use these controls. I am at position 12 now on the rotary switch because my current setup, woofer parallel setup is four ohm, and tweeter is an 8 ohm. Lucky I had this many positions on rotory switch.
Is there a way to measure the bad harmonics a speaker is generating with say an improper crossover point? Maybe a close mic test instead of the regular one meter testing that is used to generate the curves that the man. puts out?
Its allways nice to get this kind of input before spending, and feeling like your about to build somethig that may suck
Thanks,
Vince

[Anthony]

Well, the really simple way to measure (and time-consuming) is to use Room EQ Wizard and use the SPL meter function with a sine wave tone.

There are two boxes underneath the main reading for harmonics levels (2nd and 3rd).

You would have to manually sweep and write values down (and I'm not sure how well developed/tested/supported this feature is -- but it seems to work).

I use Speaker Workshop and have a jig and test stand built. I use the Behringer ECM8000 mic, an M-Audio MobilePre sound card, and an old car audio MOSFET amp powered by a 12V power converter. The amp is the weak link, but it works and at least any biases are consistent.

In SW the distortion tests are tedious, but at least automated. I usually set it up and leave for about 10 minutes while it runs test tones and measures harmonics. The low ones aren't too bad, but when it gets into the 3k+ region, it's hard to be in the room when the test is going on.

I have not idea how to do this in R+D. I think Ethan Winer uses that a lot (he's in the acoustics forum here) and Doug (one of the developers) posts here a lot, so maybe they can help.

good luck.

[vince]

Thanks, Anthony I have built one of the jigs you are reffering to, though I have'nt used it in some time. I was into Speaker Workshop a couple of years ago, that is when I biult the jig you are refering to. Maybe I need to take a second look at Speaker Workshop again. Or perhaps check out the functions of R plus D to see if this can help. I also, have the Behringer 8000 mic, but have recently purchased the B&K soundcard and mic from Doug at acoustisoft, What I do like about the B&K mic is they measure it and give you a calibrarion file on 3.5 in diskette, and the mic is labeled also.
Anyway I have not purchased anything yet, but am getting ready to, just waiting on a couple of replies from Madisound and Accutron.
Thanks,
vince

[ktaillon]

Also take a look at measuring software by ARTA, very simple works great....

http://www.fesb.hr/~mateljan/arta/

Have you run your drivers through any crossover programs yet? That is a nice set of drivers..