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[dchown_13]

Hello, I have recently completed a set of three way loudspeakers using two 8” woofers, an Italiavox 5100M8 4” Midrange, and a 1 inch poly Beyma SMC 2012 (if anyone has specs on these please send them). These were obtained at a speaker store in Toronto for extremely good discount prices, and are crossed over at 1.2 kHz and 5kHz in a sealed cabinet that is 3.02 cubic feet in volume. Information on the woofer was not known at purchase time, only the volume needed (their product number is 182TM, they are a polypropylene cone with a cast iron basket/rubber surround, 120RMS each, and Xmax just shy of 1cm by the looks of it..I do not have any real specs on it, if anyone knows what it is i would be forever grateful), as I had premade the cabinets hoping to find woofers that would fit the volume, or else add in a internal shelf to tweak the volume, as well as use acoustic stuffing and whatnot. Being my first project, I was not too worried about exact specifications and a perfect design, rather somthing to gain experience on. The sound with the current volume sounds fairly balanced and flat to me through a series of frequency tests, but I do not have any formal testing equipment. I am posting in the hope of gaining some knowledge in the area of attenuating certain drivers together and evening out resistance in different frequency ranges. I know that my mid and tweeter are 8 ohm units, and I currently have my woofers hooked up in parallel, which sounds very good, however, the likelihood of them being 16ohm is very low, proven by a multimeter reading of the entire speaker at 3.8ohms. I gather that it is not ideal to have a 8 ohm tweeter and midrange along with 8 ohm woofers in a dual woofer setup, as it is impossible to achieve the same impedance without adding resistors to the circuit. I was thinking about adding in 8 ohm resistors in each woofer loop, resulting in a new parallel impedance of 8ohms. I am running the speakers off of a 120 watt per channel HK3480, and the max wattage I see on parts express for resistors is 25 watts, however, I do not have a lot of experience in this area. Another question I had is that if it turns out that the right thing to do is add resistors to the circuit, then is it also possible to add in attenuating resistors, or possibly an Lpad. A site I found that seems to address this is http://www.mhsoft.nl/spk_calc.asp, but i dont know what you guys think of that. One other thing I was wondering is that the Beyma is rated at 12 watts each, with a 97 db sensitivity (as far as I can see), however, I have had the woofers nearly at their limits and the tweeters are still going completely fine...i know it takes a lower amount of watts to produce the same volume as frequency increases, but I didnt know it was so durastic (any explanations are appreciated), and also, if this is the case, then it is basically pointless to rate a tweeters wattage unless it is being used in extreme volume setups...I am running my speakers in a very large room and they can still make your ears bleed. Anyways, I am just trying to take my system to a higher level by tweaking the curcuitry and such to get the most I can out of my current drivers...Thanks a lot,

Dan Chown
dchown_13@hotmail.com

[ocool_15]

are the woofers already mounted in a box?
Look up L-pad for attenuation
Do you have a crossover or have you been doing this full range?
You can measure your own speakers for parameters. several books cover this. Testing Loudspeakers-Joseph D'Appolito is a good one. Bass Box Pro software allows you to do it faster.

[dchown_13]

hello,

yes I do have them hooked up in the enclosure but I have not sealed them in...they are hooked up in a 3 cubic foot cabinet, and I have the system crossed over at 1.2 and 5kHz. Is there any way I can measure sensitivity an SPL meter? Also what are your thoughts towards the relevance of tweeter RMS ratings? Thanks for that advice on measuring the TS myself, I had no idea.

Dan

[ocool_15]

you could with an spl meter if it was calibrated... you can get it from the T/S parameters which IMHO is alot easier. ... You mean 120Hz not 1.2 right?

For power ratings a manufacture makes numbers as accurate as they want to Though low frequencies are largely enclosure dependant and High frequencies(tweets) depend alot on the crossover. I have less of an understanding of tweets in that respect.

For the most part the lower a speaker is intended to play the less its efficiency. I believe no(efficency) relates to ?/fs^3.

[dchown_13]

nope, they are crossed over at 1.2kHz, quite high for a 3 way, but it seems to suit the woofers well, unless i am completely wrong, which is possible because they easily hit in the 25 Hz range...last post i meant to ask if you could get the SPL without a measuring device...simply from the previously devised TS parameters, but i am guessing you cant. Do you think it would be helpful to look at a similar woofer (cone material, RMS, Xmax, range etc.) on parts express (or any other speaker selling sites that you may know of, post them)and use those parameters, or should i just give up on specs for these woofers (there is no marking other than a 182TM serial number on the surround)? Also, as you were saying about the lower they are intended to play, the less efficient they are, this would probably mean that my woofers are substantially less efficient than my tweeter (on a random site it was said to be 12RMS and 97db, Beyma no longer has the parameters for the driver on their site anymore), but as I say, for all i know, 12RMS could be plenty for a tweeter, all i know is that they go extremely loud in a very large room. Cheers,

Dan

[ocool_15]

Other drivers may not be of much use unless you know for sure they were both set up for the same application and even then you can have alot of differences.

A typical 8" woofer will be more like 89-90dB efficient

Reference eff