Mintos' n00bie questions ... (Multiple threads merged)

[mintos]

For a MTM design crossing around 2500 with a second order filter, which driver would be better for base? (or sound better overall) M6N or RS150S?

[Undefinition]

For a MTM design crossing around 2500 with a second order filter, which driver would be better for base? (or sound better overall) M6N or RS150S?

Good luck getting the RS150 to cross at 2500 Hz. The M6n, I don't know. I have a pair I was going to use in a 2-way, but haven't gotten around to it.

[Paul Ebert]

Due to its cone breakup, I think doing a 2nd order at 2500 is out of the question for the RS150S. If you put a notch filter on the cone breakup for the M6N, you might be able to use it that way. But, I'd be concerned about the impedance blip that accompanies the breakup. That might indicate that a notch would be restricted in its impact.

For either driver, a 4th order would be a better choice, in my opinion. If 2nd order is important to you, look for a paper or poly cone with little cone breakup. If you can afford it, the Seas ER15RLY might work with a 2nd order at 2500.

As to relative bass output between the two, I'd model both in Unibox and see what I get.

My guess is that the RS150S would have lower distortion.

[mintos]

I've finished modeling a 2nd order crossover with 2xM6N and a Tang bang 25-1719S. Is the crossover point to low for the tweeter? Looks like crossed at 1800 with the tweeter Fs at 800.

[brianpowers27]

I've finished modeling a 2nd order crossover with 2xM6N and a Tang bang 25-1719S. Is the crossover point to low for the tweeter? Looks like crossed at 1800 with the tweeter Fs at 800.

It looks like a reasonable model. THe m6n appears to have breakup nodes similar to the RS150. It is hard to say for sure if they will sound that nasty. If you are absolutely after 2nd order, it will be tough with this woofer(judging by specs).If you are not set on 2nd order, try 3rd order.

The little hill you see on your modeled system response around 4700hz is partly due to the breakup node of the m6n. I imagine that the S sound will seem a little sharp. (Sibiliance). It is my opinion that a notich might help but the driver will still be more distorted than optimal outside of its preferred operating range.

P.S. I assume that we are both referring to 2nd order as 2nd order acoustic rolloffs, not eletrical.

[HareBrained]

If the purple line in your FR is the phase, you're missing some data. It doesn't look right.

[mintos]

what kind of missing info? Can you tell from the different PCD screen cap of driver phases? So long as the crossover does can do a reasonable job, I'll be happy. trying to keep it simple and cheap. Also, how accurately does PCD and Speaker workshop model crossovers? (As opposed to real life measurement)

[fjhuerta]

2nd order at 1,800 Hz with a small TB tweeter? That sounds like a recipe for lots of distortion.


Besides... a 2nd order would need some sort of phase alignment, mechanical or electrical. That makes it a more complex circuit than a 4th order L-R.

[mintos]

The Fs for the TB is at 800. Also the electrical crossover point for the TB is actually around 3k. I just ment the two drivers seem to cross at 1800.

[mintos]

How do I make sure the resistors I have can handle the power?

I still am not able to tell if the resistors I use can handle the right amount of power for the speakers. Rs in series lowers votages and Rs in parallel lower current. Which is the one to use?

[peter_m]

How many watts is your amplifier? How many watts are the resistors rated for?

your 2ohm resistor can be replaced by two parallel 4ohm resistors to double the watt rating... Your 8ohm resistor can be replaced by two 16ohm resistors in parallel.

Peter

[mintos]

My amp is good for around 50. Res is good for 10watts. So that means I should use 5 40 to get 8 and 5 10s to get 2? That seems a bit overboard? Doesn't the speakers themselves come into play? Say my speaker is 8ohm and can handle 30 watt. Doesn't that mean I only need my res to handle 20? (If they are in parallel). If in series, I think the Rs need to match up to the speaker, right?

[jquin]

Start with 1/4W resistors test them at full load while pinching them firmly between your thumb and index finger.
Keep increasing the wattage value of the resistor till you find a resistor that doesn't instantly set your fingers on fire. :rofl: :rofl: :rofl: :rofl:

[peter_m]

My amp is good for around 50. Res is good for 10watts.

Your math is correct but not needed. 10watt resistors are more then enough. A single 10 watt resistor is all you need. I thought you were using 1/4 watt resistors or something...

[mintos]

Newb Question: Frequency Range vs FS

Sometimes I see FR range way above FS and sometimes I see they are the same. (Ex: ND28F-6, FR 2200-20000, FS 1097) Which do I go by? Is -24db good enough at the FS? Or do I need to be safe and have it at the lower range limit?

[ThomasW]

I certainly wouldn't use a crossover anywhere near the Fs (1097Hz), and that's probably why PE specs 2.2kHz as the lowest frequency. Realistically if you want to keep the tweeter safe use 3-3.5kHz..



If you want a tweeter that's 24dB/octave safe a 1.1kHz, you need a driver with a 500Hz or lower Fs.

[mintos]

huh? Of course I wouldn't use the driver near FS...what I meant is does the specs call for -24db at FS or -24db at the lower FR usable range. As of now, I have a XO with -30 ish near 1097.

[bluewizard]

Perhaps I'm confused, but Frequency Response and Resonance Frequency are two different and unrelated things.

The speaker resonate where it resonates, that can be in the working range (woofers) or out of the working range (midrange and tweeters).

In a woofer, it is by coincidence that the speaker resonates at a frequency that is close to it working low limit. With midrange and tweeters, the resonance is frequently below the working range; again, with in a certain context, a mere coincidence.

One does not dictate or determine the other...more or less...within a certain context.

In midrange and tweeters resonance limits how low you can go only because you want to stay away from the resonance frequency, at least by one octave if not two.

So, the two specs influence each other from the point of design considerations, but one does not force or create the other.

So, one of us is confused. Though fairly, it could be both of us.

Steve/bluewizard

[mintos]

I'm probally the one confused, but I've seen some tweeters spec'ed with range starting at FS (Ex. http://www.parts-express.com/pe/show...number=264-865) Tang Band 25-1719S

[Undefinition]

Tang Band's spec sheets are mostly useless.

The general rule-of-thumb is that the lowest you should cross a tweeter is at 2x its Fs. However, that particular tweeter does not follow that rule. Its Fs is pretty low (800 Hz or so), however, if you try to cross it below 2.5-3 KHz, it sounds pretty harsh and sizzly.

To investigate further why it acted this, I took some harmonic distortion sweeps. (Keep in mind that odd-order distortion tends to sound more offensive) If you look between 2-3 KHz, the 3rd order distortion drops significantly. Once you get to 3 KHz, the thing should sound pretty good.



The Dayton ND28f, on the other hand, I was able to cross at 2 KHz, and it sounded very good. And looking at its harmonic distortion sweep, you can see that there is far less odd-order distortion down that low.



This isn't to say that harmonic distortion sweeps are the last word in driver performance. However, they can definitely give you insight into a driver's "cleanliness" in its useful range, and to what range it might be best suited.

[mintos]

Does Non-Inductive Resisters matter in LP section?

I figure even if there were some induction, it's tiny and won't affect the woffer section XO. Is that correct?

[dmalphur]

I've measured the inductance of many wirewound resistors and have never found it to be a concern, even in tweeter circuits.

PE's "non-inductive" wirewound resistors are plain wirewounds, there is nothing special about them.

-David

[mintos]

B4N or RS125

Between these two small woffers, which has better bass?

[ThomasW]

RS125



Hi-Vi's B4N measurements



PE's B4N plot

[mintos]

wow... my own named tread. Not sure if I should feel honored or insulted though :P ... but seriously, I can't decided between another pair of B4N or try something with RS125. I'll post some pics of the B4N MTM I built soon. I like the base, but the stamp frame got bent when I screwed too tightly. I want to build another small MTM, but I want something with better quality frame.

[ThomasW]

Care must be taken with any of these small drivers. The stamped frames bend, the cast metal frames will crack with too much pressure.

Besides the FR plots you want to compare the Vd (swept volume = Sd times Xmax doubled) when looking at bass output. The more air moved the greater the bass output. Factor power handling in here as well. This is where you're copy of WinISD or other sim program can be put to good use .... :T

[mintos]

Just sharing some pics of my various projects. lol the first TM is funny because I tried to make it piano black finish... but instead it turned out like some faux

[mintos]

Here, I answered my own question. Quick compare of B4M MTM vs RS125-4 in parallel (not sure if that's doable though). Top graph is the RS125.

[ThomasW]

Good job

Sure you can wire them in parallel, but make sure the amp is happy driving a 4 ohm load

[mintos]

It's more like a 2 ohm load