This is a review and detailed measurements of the JBL 305P Mark ii powered studio monitor and Control 1 Pro budget passive monitor. I purchased the 305P Pro Mark ii when it first came out and it currently sells for US $147.50 from Amazon including Prime shipping. This is the price for one so you need to double that for stereo setup. The Control 1 Pro came with my
Klippel NFS speaker measurement system. It is only sold through Pro channel and costs US $164
for a pair.
The 305P Mark ii has good heft and feel to it for a budget priced monitor:
Back panel shows the connectivity and configuration:
The Control 1 Pro doesn't feel like junk but not anywhere close to 305P:
Introduction
This being the first measurement of speakers being published using this new measurement system, it will also act as a tutorial on how to read the measurements. What is presented is a small subset of what is captured but it is the most useful one. Going back to early work performed by Dr. Floyd Toole while at Canadian Research Council (NRC) (early 1980s), a collection of measurements are performed around a speaker to better characterize how it might sound in your room. This work has been refined over the years and the latest version is memorialized in standard known as CEA-2034 or CTA-2034. They are for sale publications but if you search enough, you can find online copies.
The standard and research requires that measurements be performed in an anechoic chamber, i.e. a room without any reflections. If you measure in a room, then you impart its signature on the measurements and the data is no longer valid. Anechoic chambers cost from a million dollars and up so outside of realm of all but biggest manufacturers. Fortunately we now have a Klippel NFS system which using an automated system and heavy math can extract anechoic response of a speaker that is measured in a standard room. In my case, that "room" is our three-car garage. The room has large volume and dimensions which helps a bit but still would not be good without the Klippel NFS system.
One great advantage of the Klippel system is that it measures the speaker at close distances and then computes what the measurements would be like at longer distances. CEA-2034 for example requires measurements at 2 (?) meters. That is actually a bit too close to the speaker for large tower speakers (measurements should be performed in "far field"). Not an issue for NFS system since it measures very close (inches from the speaker) and as such, can get very strong signal captured by the microphone. This makes it immune to environment noise which is a great asset as I measure speaker. NFS system generates CEA-2034 compliant curves given their guidelines and requirements so you don't need to understand these differences.
Harman called the measurements that create these results "spinorama" since the microphone was kept constant and the speaker rotated to make individual measurements. The name has stuck so you might as well be familiar with it.
If you want to understand this topic to as much depth as you like, I highly suggest purchasing Dr. Toole's book,
Sound Reproduction: The Acoustics and Psychoacoustics of Loudspeakers and Rooms:
https://www.amazon.com/Sound-Reprod...-Loudspeakers-Engineering-ebook/dp/B074CHY128
CEA-2034 "spinorama" Measurements
The classic set of measurements required for CEA-2034 is 70 as indicated (really 72 but two are duplicates):
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The Klippel NFS system doesn't work this way. It scans up close and then models what the far field response looks like. It requires more points if you have a more complex speaker or are operating in a small room. For the results you are about to see, 550 or so points were used. I will be refining these measurements more so this may vary. The scan normally takes an hour but I told the system to make multiple measurements and average them. This lengthened the time to two hours but I don't think it did much useful (lowering noise). Fortunately the whole process is automated after setup so I ate dinner and watched a movie while it was doing its thing.
Here is the overview of the system results:
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The red line shows the on-axis (direction of tweeter) if you did not use the Klippel NFS. It shows a bunch of ups and downs that get worse as you go lower in frequency. These are room reflections (shown in dashed blue) which are interfering with the direct sound. Once these are mathematically removed, we are left with the blue solid line which is now free of room variations.
The vertical dashed line delineates a different technique for getting reflections which is to cut off the measurement after certain time. If you do this right, you can capture just the direct sound. Alas, using a short window of time means that you lose low frequency information. So this technique does NOT work for low frequencies and you need another method. Here, we are letting NFS system solve that problem for us.
None of this is important with respect to understanding of the speaker measurements. So stay with me.
Overall and On-axis Response
When measuring speakers, you select a an acoustic center which is typically a line perpendicular to the tweeter. Keep that in mind and now let's look at this series of curves:
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Line 2 is what you get if you sat at the same height as the tweeter of JBL 305P and pointed the speaker directly at your ear. This is called "on-axis" response. It is short for on-axis of tweeter (if there is a tweeter). Normally you don't sit that precisely in the direction of speaker so the standard created a more relaxed region called "listening window." This is represented in green dashed line #3. It is pretty close to the on-axis line (#2) because we are not deviating much from the direct sound of the speaker.
The ideal for on-axis or listening window is a flat horizontal line. Why? Because you want the speaker to produce all the notes equally. Preference tests back this subjectively. Now, speakers are not perfect devices so don't expect to see a dead flat line as you would see in frequency response of a measurement. But flatter the better. I would say the JBL 305P is reasonably flat as speakers go.
Early Reflections Response
Unless you sit in an anechoic chamber, what you hear from a speaker is a mix of direct sound and sound from other directions reflecting from room surfaces. Depending on the speaker design, sound going in other directions than the axis of the tweeter could be similar or very different. Not all reflections are created equally though. Some have more meaning than other as shown in these two other graphs:
This the third line down in dashed blue. Research was performed by Harman [devantier] as to which early (single bounce) reflections reach the listener from a typical speaker location in a number of listening rooms. If we sum these we get an idea of the overall frequency response they represent:
View attachment 45234
As you go off-axis (i.e. not in the direction of tweeter), high frequency response tends to drop off because it is more directional than bass. As such, it is normal for the early reflection curve to slope down relative to on-axis sound. So here, we are NOT looking for flatness but we do want to see a graph that is smooth. What is smooth? A line that doesn't have a lot of variations. Here, we see a rather smooth line (again, as speakers go) but there are some peaks in there which I will address in the next section.
In addition to being smooth, the early window response sum should be similar to the direct sound. If so, then the brain doesn't think of them as unique "reflections" and "echos" and uses the information for other (positive) purposes (e.g. strengthening the volume of what you hear). If these reflections are too different, this may not happen. If you are determined to use such speakers, then you should look at absorption of these reflections (using thick, "broadband" material). That is for another topic.
Our forth line down is the dashed red and is called the sound power. This is the sum total of all the responses from the speaker in all angles:
View attachment 45233
Since low frequencies are dominant, the graph tends to tilt down even more.
Sound power by definition is highly averaged since it average all the radiation from the speaker. So it will tend to be smooth. If it is not, then there is a problem. And problem we have here: notice there are a number of peaks in the sound power. They also occur in early window (dashed blue) and direct sound. Peaks like this are commonly caused by resonances. This could be mechanical resonance, electronic or acoustic. In this case, I could easily hear the JBL 305P cabinet resonating as the measurement system ran its sweep. It would generate a buzzing sound. I lifted the speaker from its measurement stand and I could still hear it. The resonance seems to come from the back metal cabinet. A shame really since it could be fixed with a better enclosure/bracing. But hey, this is a bargain speaker so what do you want?
Despite that issue, the 305P is much superior speaker using this metric:
View attachment 45241
Bass Response
Amount and quality of bass response from a speaker is hugely important for overall fidelity. Listening tests show as much as 30% of the fidelity score coming from bass response. Alas, bass frequencies are low which means their wavelength is large (one is opposite of the other). The large wavelength winds up being closely related to dimensions of your room allowing the refection to add or subtract from each other at different places in your room and different frequencies.
Our anechoic measurements backfires on us because we are measuring something you won't see in a real room. Fortunately we do have powerful tools to deal with room modes/resonances (EQ, acoustic products, speaker/listener position). Bass response drops rapidly below a certain frequency. From what I recall the 6 dB drop point is considered a reasonable limit. Using that, the JBL 305P has a low end response down to 44 Hz:
View attachment 45232
Directivity Indices
Remembering what graph is which can give one a headache. A simple but remarkably useful couple of measurements were created to help with that. We call these directivity indices. Simply put, you two graphs and subtract them from each other and you get the "index." You see these as the bottom two lines in our spinorama graph which I am presenting here by themselves:
View attachment 45235
The more useful of the two in my opinion is the dashed blue with is the early reflection index. It is the difference between listening window and early reflection graphs. If this line is a straight line (not necessarily flat), it means that tonally the reflections are identical to direct sound from the speaker. Per earlier explanation, this is what we like to see. Again, the works is not perfect so there will be some ups and downs. More on this later.
The red line is the difference between listening window and sound power. So it is telling us how much the total sound radiating from the speaker varies from direct sound. We can allow some imperfection for sounds going behind the speaker, or bouncing around more than once in the room so its shape is not as useful. What is useful is if we see distinct peaks in it that are in sync with our other window. We clearly see that nearly 2 kHz which indicates a resonance as I mentioned before. I think the crossover frequency for the 305P is 1.7 kHz so this may have something to do with that as well as the cabinet resonances I was hearing.
Spinorama Summary
Simply put, you want a flat listening window and early reflection index that is smooth. The latter can point up if it wants. If so, the speaker is more directional. I showed you that for JBL 305P above. Here it is for JBL Control 1 Pro:
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It is clearly to see how much worse Control 1 Pro is relative to 305P. I drew an imaginary arrow in there as a reference. We see lots of variations there. We also see peaks that are not only tall but also wide.
The wider the resonance, the worse it is audibly because more notes hit it.
As we test more speakers, you will get more and more calibrated on what to expect from these graphs but these two samples should be quite demonstrative.
Predicted In Room Response (PIR)
"Oh, but how would the speaker sound in MY room?" That is the standard question asked and answer given is that nobody knows. When that is quite wrong. We do know that what we hear is a mix of the different groupings of the graphs we have seen so far. Research indicates that in "typical rooms" we can pick a formula that sums three graphs to give us the response that we are likely to hear:
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Sound power is there to represent bass. Listening window is there because that is the first sound to arrive at our ears so perceptually is important. It is not however very powerful relative to early reflections so we take more of those. The research is shown in Dr. Toole's book or the individual paper.
Since this is a combination of direct and indirect sound, we like to see a smooth, gently sloping down curve. If it is smooth but not pointing down, that is OK because we can use equalization to taste to get it there (called a "target curve"). The JBL 305P is doing well here for such a low cost speaker, courtesy of its advance waveguide. Take that away in the form of the Control 1 Pro speaker and you get this:
View attachment 45238
As noted, while you may be tempted, in general you can NOT EQ and bring up the missing midrange. The problem is that EQ sits in front of the speaker. It will impact both direct and indirect sound equally. Here, our problem is that our indirect sound has a problem so EQ in general cannot fix it. I should note that a double blind study of room EQ system did find some improvement can be made here subjectivity but it is best to avoid speaker with such dips. It is quite common when a large woofer is mated to a small tweeter with no wave guide. The woofer gets too directional before it hands off the signal to tweeter which causes off-axis response to suffer.
Miscellaneous Measurements
Story of the speaker is already told. But I know some of you want to dig deeper. More information allows us to better use a speaker. For example if slight off-axis response is better than listening window, then you may want to toe in the speaker in that direction. So here they are:
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Distortion Measurements
This measurement is work in progress for reasons noted on the graph:
View attachment 45242
I did not take the same measurement for Control 1 Pro.
Subjective Listening
The JBL 305P Mark ii is a delightful little speaker. It gives a smooth, very realistic sound impression, beating many "hi-fi" speakers. Problems are two fold: there is a tweeter hiss that you can hear in near-field applications. And it runs out of power in a large room and high volumes. Not an issue if used as studio monitors.
Review Conclusions
It is hard to believe such great performance can be had for so little money in the form of JBL 305P Mark ii. We get it because of research and measurements like I have been showing that resulted in the advanced waveguide that it has for the tweeter. So
I can definitely recommend the 305P Mark ii. Get a pair so that you can get calibrated on what good sound is like, and correlation between that and the measurements I am showing.
I have not listened to the JBL Control 1 Pro. I don't think there is a reason to purchase it. Drink less coffee and save up the money to buy the 305P instead.
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As always, questions, comments, recommendations, etc. are welcome.
This article got long. I should have proof read it but I have not. As it is, I am thinking I should get paid for the number words and graphs in there. So please dig deep in your wallet and
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