Understanding Zaph's Frequency Response and Power Handling Curves

[jarsoffart]

So I'm trying to gauge which of Zaph's Bargain Mini Monitor (ZBM4), Bargain MTM, or L18/27TBFCG would be best for running full-range without a subwoofer.

From the Measured Response chart, it seems like the monitors are good between 100 Hz and 20 kHz. (1) At what distance is the SPL of about 80 dB measured and (2) what is the input power?

Now I'm looking at the modeled low end response and from what I can gather, the blue curves are just the frequency responses at different input powers with the lowest blue curve being 1 W and increasing in multiples of 2. However, (3) how come this frequency response curve is different from the "Measured Response" curve. For example, now the usable range for +/- 3 dB seems to be from 60 Hz to 1 kHz. My guess is that this Frequency Response is for the woofer alone, not the 2-way ZBM4 as a whole. (4) How does one find the data on the Frequency Response for the woofer? I couldn't find a data sheet on MCM's page for this woofer.

Zaph mentions "If run full range, all it takes is about 10 watts to drive the woofer into distortion at 70 to 80hz."
(5) From what I can see, this 2-way cannot be run full range at any power level if full range is full audible range, i.e. 20 Hz to 20 kHz as per Wikipedia. I know this is unreasonable, so how else is "full range" defined? (6) How does Zaph conclude that at about 10 watts, the woofer is driven into distortion at 70 to 80 Hz. Is it because the excursion for the 16 watt red curve exceeds 3mm which is some maximum excursion? If so, where does one find the specs for a maximum excursion. On the other hand, is it because the excursion curve isn't flat enough? If the latter, how flat does it need to be in order to not distort? (7) What is excursion? I'm guessing it's the horizontal displacement of the voice coil in the woofer, but I can't find absolute verification.

From the looks of it, all of Zaph's speakers that I'm looking at can not really give me 20 Hz to 20 kHz without a subwoofer at any SPL. (8) Ballpark how much power would I need to put in a subwoofer as compared to the power into the bookshelf speakers. For example, if I were to put 10 watts into each of the ZBM4, what wattage would give me the subwoofer output to fill the low end at the same SPL. I know this depends on the efficiency of the subwoofer, but I'm just wondering, do I really need a 100 watt plate amp or can I get away with a TDA1554Q based amp.

Thanks for getting through the post and for any help you may be able to offer.

[DougL]

it seems like the monitors are good between 100 Hz and 20 kHz.

To me they look 6 db down at 50Hz. Plus or Minus 6 to 10 dB is the normal standard for speakers.

(5) From what I can see, this 2-way cannot be run full range at any power level if full range is full audible range, i.e. 20 Hz to 20 kHz as per Wikipedia.

From your questions, you are an engineering student. Real world engineering is about compromises. None of the commercial mini monitors will play full range at a reasonable volume by your definition without a subwoofer. However, unless you are into pipe organ music, the low note on an electric base is about 39 Hz.

6) How does Zaph conclude that at about 10 watts, the woofer is driven into distortion at 70 to 80 Hz. Is it because the excursion for the 16 watt red curve exceeds 3mm which is some maximum excursion?

Zaph does not necessarily include all of his measurements in his published documentation. If he says 10 watts at 70 Hz distorts, my feeling is he measured it and found it above his rule of thumb threshold, maybe 2%.

(7) What is excursion? I'm guessing it's the horizontal displacement of the voice coil in the woofer, but I can't find absolute verification.

Well said. The maximum excursion is referred to Xmax, and can be either peak to peak or just peak.

how come this frequency response curve is different from the "Measured Response" curve.

The modeling software is predicting the approximate frequency response, excursion and impedance at various power levels. It ignores the non-ideal response of the woofer to simplify the model. The phrase "The map is not the territory" comes to mind. The graph was included to illustrate just the point you saw, that frequencies below 40 Hz will lead to very large excursions and possible woofer damage.

(4) How does one find the data on the Frequency Response for the woofer? I couldn't find a data sheet on MCM's page for this woofer.

Not all drivers have published data by the manufacture. However, Zaph publishes that data on his web site for many common drivers.

HTH

Doug

[jumpfroggy]

Originally posted by jarsoffart
Now I'm looking at the modeled low end response and from what I can gather, the blue curves are just the frequency responses at different input powers with the lowest blue curve being 1 W and increasing in multiples of 2. However, (3) how come this frequency response curve is different from the "Measured Response" curve. For example, now the usable range for +/- 3 dB seems to be from 60 Hz to 1 kHz. My guess is that this Frequency Response is for the woofer alone, not the 2-way ZBM4 as a whole.

I've wondered the same thing! I've been reading and rereading his pages a lot in prep for my build, and I still don't know much yet. Can't help you there...

Zaph mentions "If run full range, all it takes is about 10 watts to drive the woofer into distortion at 70 to 80hz."
(5) From what I can see, this 2-way cannot be run full range at any power level if full range is full audible range, i.e. 20 Hz to 20 kHz as per Wikipedia. I know this is unreasonable, so how else is "full range" defined? (6) How does Zaph conclude that at about 10 watts, the woofer is driven into distortion at 70 to 80 Hz. Is it because the excursion for the 16 watt red curve exceeds 3mm which is some maximum excursion? If so, where does one find the specs for a maximum excursion. On the other hand, is it because the excursion curve isn't flat enough? If the latter, how flat does it need to be in order to not distort? (7) What is excursion? I'm guessing it's the horizontal displacement of the voice coil in the woofer, but I can't find absolute verification.

For 5), I think full-range doesn't mean "will produce all frequencies from 20hz-20khz". I think he means if you run these speakers by themselves with no external filters (ie. full range), vs. running this on a high-pass filter along with a subwoofer, in which case these are limited to higher-frequencies only. So "full range" in this case doesn't imply that the speakers can produce those frequencies, only that you are "running" them to produce everything they can. So as an example, even if you have a set of speakers that can perfectly reproduce all audible frequencies, if you're limiting them with a high pass filter (to use with a subwoofer), then you're not "running them full range". On the other hand, even if you have some speakers that can only get to 80hz, you can still "run" them full range (ie. w/o sub).

For 6), I figured the same thing. Seen here:
http://www.mcmelectronics.com/product/55-1853
Xmax (ie. maximum excursion on X axis) is 2.75mm. So in that graph, the 4th red line (8 watts) goes just above 2.5mm excursion. So John/Zaph estimates about 10 watts would reach the 2.75mm excursion limit, after which you get distortion (ie. the woofer 'bottoming out'). I'm pretty sure it's just that the red line exceeds the xmax rating of the speaker, since that would introduce physical clipping (and maybe speaker damage, maybe?), which is distortion. I don't think the flatness of the curve has anything to do with it. Also, as a note, I think that the

From the looks of it, all of Zaph's speakers that I'm looking at can not really give me 20 Hz to 20 kHz without a subwoofer at any SPL.

Probably not, but 20hz is probably asking a lot from any speaker that's not huge. I'm planning on building the ZBM4's as nearfield monitors for my computer, and I'm debating in my head whether or not I'll need a subwoofer. I imagine I probably wont since my volumes will mostly be pretty low. The lower the volume, the easier it is for these guys to produce the lower frequencies. Unfortunately, the free donation receiver I got does not have any subwoofer filtering, so I'll have to figure out either another receiver or some kind of high/low pass filters/crossover, all of which is more money. I'm trying to build the speakers for as cheap as possible, and it already looks like the budget is at least $100 for all materials, not including labor for the ZBM4's. Throw in a new receiver, subwoofer w/ amp, and things could quickly increase.

All of this could be wrong, I'm just learning and don't know much. Hopefully someone else will correct me.

[sreten]

Originally posted by jumpfroggy

.... I'm planning on building the ZBM4's as nearfield monitors for my computer ....

Hi, consider RB kit : grab it while you can ...... , /sreten.

[rco3]

20 - 20k is a great spec for an amplifier, and not hard to accomplish. For a speaker, it's VERY hard to do and generally overkill. There isn't much musical content below 40 Hz unless you're listening to huge pipe organs or Mickey Hart (yes, I'm generalizing, I know), and movie soundtracks with explosions and the like are intended for sub-equipped systems. As DougL says, speakers are all about compromise.

In fact, I'd have a hard time believing that any reasonable pair of two-way or 2.5-way speakers could do 20 Hz at any usable level. I'm sure someone will chime in with a counter-example, but I'm betting they'll be something enormous and exotic like Altec A-7 horns or something. On a bookshelf, forget it. All of this is without considering the effect of room interaction...

You want to add a sub? Cross the ZBM4's over at 80 or 100 and they'll handle a fair amount of power - 50 watts or so according to Zaph's graph. I've never measured, but I drive mine pretty hard. I use a 300W BASH amp driving an RSS265HF with my ZBM4's, and have no power shortage. Using a 44-watt chip amp might be underkill. I wouldn't go less than 100W of plate amp, bass takes power and headroom is your friend.

Me, I like the ZBM4s. They sound good, are inexpensive, and are easy to build except for the tweeter mounting. They also benefit from a sub at any listening level, IMHO. I've built 5 for myself (two in T-line cabinets based on MJK's spreadsheets), helped friends build 4 more, and have more friends lined up to build another 20 or so. Haven't heard the other two you mentioned, but I'm also in the process of a group build of Zaph's Waveguide TMMs - two pairs complete, 8 more pairs to go. They sound very nice, but much more dough and more complicated build.

Note: much of the above is opinion. Audio is like that.

[bobhowell]

I have built both ZBM4 and BAMTM. ZBM4 has little bass and low effency, so it must have a lot of power , which means it hits distortion quickly. BAMTM has High effency and can take 20 watts without distortion. So, in my 16x12 room, it plays fine without a sub. I built 33L sealed, cabs. I play with output from a HTPC running Windows XP and use Windows Media Player with Equalizer. I boost the 31HZ tab up 4-5db and it sounds great. The BAMTM has great sound. The ZBM4 sounds good, but must be crossed at 100hz active. Nowhere near the volume,(or sound stage).