Help! Improve speakers with limited info available

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Help! Improve speakers with limited info available

Postby Rex » Sun Jan 24, 2010 10:44 am

I recently acquired a pair of speakers at a local thrift store. They're small enough, well-built enough and good-sounding enough that I want to to turn them into a truly good pair that I can use in tight spaces (for example, in a small office). The only problem is that I can find almost no information on them, so I don't know where to begin. In the hope that someone can steer me in the right direction, here's what I know and what I hope to accomplish.


THE BASICS

Acoustics Model 500;
Two-way acoustic suspension design;
Woofer: 5-1/4" woofer, marked "12P72DR-02HW" (might be a Peavey part);
Tweeter: 1" soft-dome, Japanese, marked "EAS-10KH12S";
Dimensions: approx. 11-1/2"H x 7-1/2"W x 6-1/2"D.


THE GOOD:

Sound: surprising large-speaker vibe, best with orchestral music, good low mids and upper bass (cello and viola sound sweet), tight mid-bass;
Construction: 5/8" solid oak throughout.


THE BAD:

Sound: the highs are subdued, and I'd like a little more mid-bass;
Crossover: it's just a capacitor in series with the tweeter.


ASSESSMENT:

I think many of the issues may be caused by the crossover. A decent crossover might open up the highs. But I can find no useful information on the drivers, so I don't know where to start with the crossover.


Can any of you good folk get me started on some improvements to these? Thanks!
Rex
 
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Re: Help! Improve speakers with limited info available

Postby Klaus Stock » Sun Jan 24, 2010 1:35 pm

Hi Rex,
Rex wrote:A decent crossover might open up the highs. But I can find no useful information on the drivers, so I don't know where to start with the crossover.

the driver's can be measured, utilizing a computer with a full-duplex capable sound card (today, most are), an inexpensive jig and a software like Speaker Workshop (free, available at http://www.audua.com/).

For a passive crossover, you'll need to know the driver's inductance or it's impedance curve (as the impedance varies with frequency, a passice crossover needs to be designed to the specific impedance at the crossover frequency).

Another option is an active crossover. Active crossovers do not care about the varying impedances of drivers. This requires an additional amp, though....and, of course, the active crossover. A lot people apparently like the Behringer DCX 2496, which sells for about 300 EUR. The nice thing about a digital active crossover is that one easily change crossover frequencies, slopes, levels, phase, delays and EQing. Analog active crossovers are usually cheaper, but less flexible. Not all analogue active XOs allow for a frequency change, and if they do, it may be limited to a set of a few fixed frequencies. Levels can always be adjusted at the amps directly, so it doesn't really matter if the XO doesn't allow for that. Very few analogue XOs include an EQ. I have not heard of any which included a confgurable delay (which would, I admit, be mainly of concern for pro audio application - beam steering for bass arrays and delays for speaker towers which are at some distance from the stage).

However, the option to play around with levels and crossover frequencies can be a valuable help in the crossover design process. If you can borrow a digital XO and an additional amp, you can try to find the best XO configuration and then go ahead an implement it as a passive crossover. Anoteehr way of trying out such things is to use a computer. While there is specialized software for simulation of crossovers, it is so hideously expensive that you'd be better off with a hardware solution. The "poor man's" solution might be to use some audio editor which allows to filter the signal. Open an audio file, apply a low pass filter to the left channel and a high pass filter to the right channel. Connect one speaker to your amp, with the left channel driving the mid/bass driver directly and the right channel the tweeter (careful: if you accidently supply the bass signal to the tweeter, it may break surprisingly fast when you yank up the volume). Listen to the result. Tweak your simulated crossover configuration until it doesn't get better any more. Repeat on the next day; your ears might begin to deceive you after a few hours of such hard work.

Best regards, Klaus
Klaus Stock
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Re: Help! Improve speakers with limited info available

Postby lvw » Mon Jan 25, 2010 3:27 am

Klaus' advice is excellent, and will yield good results. Just thought I'd add a couple of small things you might try immediately, to see if they help. Both are easy and reversible, since they are not sure things:

You might get a little improvement by stuffing the cabinet. (you didn't mention stuffing...) I like fibreglass for such a purpose, at about 0.5 lb per cubic foot, but try different densities. Polyester fill is less effective, but also less itchy... This might help if internal reflections are causing any problems.

IF the reduced treble is simply due to the woofer being a bit too sensitive for the tweeter (possible, since you don't mention a padding resistor in the crossover), you can reduce the woofer level slightly by adding a small weight to the woofer cone. I like oil based modeling clay, since it adheres well on most cone materials and does not leave residue if removed, in most cases. I'd try maybe three grams for a start, and see how it sounds. If it helps, you can put it on the backside of the woofer cone, maybe in three or four spots around the cone.
lvw
 
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Re: Help! Improve speakers with limited info available

Postby DVDdoug » Tue Jan 26, 2010 12:47 am

I think many of the issues may be caused by the crossover. A decent crossover might open up the highs. But I can find no useful information on the drivers, so I don't know where to start with the crossover.


If the capacitor is marked, and if you know (or can guess) the tweeter impedance, you can calculate/approximate the existing crossover frequency as follows:

f = 1/(2Pi RC)

R = tweeter impedance in ohms
C = capacitor value in Farads (It's probably marked in microfarads, so move the decimal 6 places left)
2Pi ~6.28

You could also do some experiments, such as disconnecting the tweeter and run some test-tones to see where the woofer "naturally" cuts-off. That would give you an upper-limit for your crossover design... You don't have to use the same crossover point as the existing design. (Be careful running test-ones into tweeters!!!!) Test-tones can be generated with software, in case you don't already know how to do it...

But assuming there is no resistor or pad on the tweeter, a different or "proper" crossover won't boost the high-frequency output. You'll probably have better luck with a different tweeter. I'd probably start by changing the tweeter... If that helps, I might consider upgrading to a true crossover. The problem is that you can't know in-advance if the new tweeter is any more sensitive than the existing one.

Just for reference, I'd guess the "average" tweeter has a sensitivity around 90dB @1M, 1W. If you buy one that's rated 97dB or more, the odds are very good that it will be more sensitive than the existing one. Horn tweeters can be rated around 100dB or more, but horns can have a different "sound", and are generally more directional than a dome (and a horn might not easily fit the existing cutout.)

If you end-up with a tweeter that's too sensitive, you can add a resistor or an adjustable L-Pad, etc.
DVDdoug
 
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Re: Help! Improve speakers with limited info available

Postby llung » Tue Jan 26, 2010 2:23 am

Rex,
Have you measured the frequency response of the speaker? I'd do that before making any assumptions about what it's lacking or what you may want to do to it.

-lou
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Re: Help! Improve speakers with limited info available

Postby Rex » Tue Jul 29, 2014 10:39 pm

Wow. I missed a lot of good responses. Apologies for taking over four years to respond. I though the forum would notify me (my bad), and I never received any notifications, so I never checked back.

Thank you all for a lot of good places to start investigating.
Rex
 
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