JBL Stage A170 loudspeaker Measurements

Sidebar 3: Measurements

I used DRA Labs' MLSSA system and a calibrated DPA 4006 microphone to measure the JBL Stage A170's frequency response in the farfield, and an Earthworks QTC-40 mike for the nearfield responses. I left off the loudspeaker's grille for the measurements.

JBL specifies the A170's sensitivity as 89dB/2.83V/m, which is both higher than average and confirmed by my measurements. Props to JBL for an honest sensitivity specification. The impedance is specified as 6 ohms; while the solid trace in fig.1 shows that the impedance does drop below 6 ohms in the lower midrange and high treble, it is higher than that over much of the audioband. The minimum magnitude is 4.5 ohms between 190Hz and 210Hz, and though the electrical phase angle (dotted trace) is occasionally greater than 40°, the magnitude at those frequencies is relatively high. The JBL is not a difficult load for the partnering amplifier to drive.

1019JBL170fig1

Fig.1 JBL Stage A170, electrical impedance (solid) and phase (dashed) (2 ohms/vertical div.).

A small discontinuity between 200Hz and 300Hz in the impedance traces suggests there is some sort of resonance in that region. When I investigated the enclosure's vibrational behavior with a plastic-tape accelerometer, I found a high-level mode at 254Hz on all the enclosure's surfaces (fig.2). However, this mode has a high Q, meaning that it takes a while to be fully excited and possibly lead to audible congestion in the midrange.

1019JBL170fig2

Fig.2 JBL Stage A170, cumulative spectral-decay plot calculated from output of accelerometer fastened to center of sidewall level with lower woofer (MLS driving voltage to speaker, 7.55V; measurement bandwidth, 2kHz).

There is another discontinuity around 150Hz in the impedance graph. When I examined the outputs of the two woofers and two ports in the nearfield, I found a small suckout in the summed output of the woofers (fig.3, green trace) and a steeper-than-usual upper-frequency rolloff in the summed output of the two ports (red trace). This behavior suggests that there is some sort of antiresonance in the ports' outputs. (Both ports open into the same interior chamber.)

1019JBL170fig3

Fig.3 JBL Stage A170, acoustic crossover on tweeter axis at 50", corrected for microphone response, with nearfield woofer (green) and port (red) responses respectively plotted below 355Hz and 1kHz.

The impedance magnitude trace has a saddle centered on 55Hz,which implies that this is the tuning frequency of the two ports. The woofers' nearfield response does have its minimum-motion notch at 55Hz. This is the frequency at which the back pressure from the port resonance holds the cone stationary and is higher than I would have expected from a tower speaker with twin woofers. JBL describes the A170 as a "2.5-way" design with crossover frequencies of 1.8kHz and 2.8kHz. I assume from this that the upper woofer extends a little higher in frequency than the lower woofer. My measurements indicated that both woofers behave identically below 1kHz. However, the green trace in fig.3 suggests that the combined farfield output of the woofers (green trace) crosses over to the tweeter (blue trace) at 1.8kHz rather than 2.8kHz. Even so, the upper-frequency rolloff of the woofers is disturbed by a slight peak between 2.5kHz and 3.5kHz, which might be due to the upper woofer extending higher in frequency than the lower woofer.

Fig.3 shows that the tweeter's output starts to rise two octaves above the crossover frequency, and this can also be seen in the JBL's farfield response, averaged across a 30° horizontal window centered on the tweeter axis (fig.4). The A170's response is otherwise flat and even between 300Hz and 6kHz. The response with the grille was similar but with slightly more energy apparent between 4kHz and 9kHz, but there was a significant suckout centered on 3kHz. The grille will therefore both make the A170 sound a little polite and emphasize the excess energy in the top octaves. The trace below 300Hz in fig.4 shows the sum of the nearfield woofer and port outputs, taking into account acoustic phase and the different distance of each radiator from a nominal farfield microphone position.

1019JBL170fig4

Fig.4 JBL Stage A170, anechoic response on tweeter axis at 50", averaged across 30° horizontal window and corrected for microphone response, with the complex sum of the nearfield woofer and port responses plotted below 300Hz.

The rise in response in the upper bass is due in part to the nearfield measurement technique but is disturbed by the ports' antiresonance I mentioned earlier. The low-frequency –6dB point, referenced to the level at 1kHz, lies at the specified 44Hz.

The JBL Stage A170's horizontal dispersion, with each trace normalized to the tweeter-axis response, is shown in fig.5. The contour lines in this graph are even in the midrange and low treble, implying stable stereo imaging, but the excess of top-octave energy in the on-axis output is maintained to the speaker's sides. In the vertical plane (fig.6), a suckout develops in the crossover region 15° above the tweeter axis, but the JBL's on-axis balance is otherwise preserved over a relatively wide window.

1019JBL170fig5

Fig.5 JBL Stage A170, lateral response family at 50", normalized to response on tweeter axis, from back to front: differences in response 90–5° off axis, reference response, differences in response 5–90° off axis.

1019JBL170fig6

Fig.6 JBL Stage A170, vertical response family at 50", normalized to response on tweeter axis, from back to front: differences in response 15–5° above axis, reference response, differences in response 5–15° below axis.

In the time domain, the A170's step response on the tweeter axis (fig.7) indicates that the tweeter and woofers are all connected in positive acoustic polarity. The decay of the tweeter's step, which arrives first at the microphone, smoothly blends with the start of the woofers' step. This suggests optimal crossover implementation. The JBL's cumulative spectral-decay plot (fig.8) is clean overall, but there is a ridge of delayed energy associated with the on-axis response peak at 16.2kHz. This frequency is a couple of kHz higher than my high-frequency cutoff, but it may well be heard as a slight whistle by younger listeners.

1019JBL170fig7

Fig.7 JBL Stage A170, step response on tweeter axis at 50" (5ms time window, 30kHz bandwidth).

1019JBL170fig8

Fig.8 JBL Stage A170, cumulative spectral-decay plot on tweeter axis at 50" (0.15ms risetime).

To sum up, JBL's Stage A170 offers excellent measured performance, especially considering its affordable price.—John Atkinson

COMPANY INFO
JBL division of Harman International Industries Inc.
8500 Balboa Blvd
Northridge, CA 91329
(800) 336-4525
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COMMENTS
mtrot's picture

Looking around online, the price seems to be $600/pair.

Bogolu Haranath's picture

May be the tariffs are the reason for the price increase? :-) ........

invaderzim's picture

In an age where everyone and their uncle is a 'reviewer', that just talks about how great each product they get sounds, this is what a real review is. I was there listening to them with you and can tell which speakers you mentioned would likely do best with which amp I'd use.

And at the same time it is reviews like this that make me want to go out and listen to more speakers, to experience them in person. I miss the days when audio stores were all over and I could stop by and check them out. I spent a couple hours picking out the first speakers I ever bought and I still have them and use them daily, thirty years later. No online purchase has ever lasted me that long.

philipjohnwright's picture

No not the speakers, Herb. He knows his stuff for sure, it's the quality of his writing that shines through though. Words crafted like a true artisan, meaning conveyed by how he writes as much as what.

Art's quite good too :-)

Phil

AaronGarrett's picture

That might be the first time Beachy Head was ever used in an audiophile review! I hope you listened to "Hot on the Heels of Love" as well.

Ortofan's picture

... might be the Studio 590 speakers, presently on sale for $1,000/pair.

https://www.jbl.com/loudspeakers/STUDIO+590.html?cgid=loudspeakers&dwvar_STUDIO%20590_color=Black-USA-Support#start=1

mtrot's picture

Yes, I saw that when checking on the A170!

Anton's picture

And beautiful!!!!

Zavato's picture

Definitely $600 a pair

tonykaz's picture

Your darn Toot'n!

Because:

1.) Loudspeakers are expensive to ship properly, wreaking havoc on their re-sale values. My Oldest Son just purchased a Mint Pair of OHM Walsh 2 Loudspeakers, at a Garage Sale, for $125. Another Son bought a nice pair of 3.3 Magnepans from a Pawn Shop where they collected dust for a few months.

2.) There are closets full of useful Electronics made available on eBay.

3.) High Quality Music Sources are now easily accessible for any Library Member.

4.) A dam nice "Audiophile" Grade Audio System is within reach of anyone that has a stable home and time to listen. ( not having to work 3 jobs )

5.) All for dirt Cheap!!!

I can recall when any decent System would have a Starting Price of $5,000.

6.) Now, an Apple Computer, Schiit Asgard 2, a $100 DAC and a Pair of Sennheiser HD600 headphones will reliably achieve $50,000 Big System Sound Quality. ( without the chest thumping bass, of course )

This is the "best time ever" , no doubt about it, especially compared to what we had to go thru from 1950 to 2010.

Now we even have reliable guidance from Stereophile's best writers & reviewers. We NEVAH had that before.

It's a Great Time to be an Audiophile!!!

Tony in Venice

Long-time listener's picture

"Now, an Apple Computer, Schiit Asgard 2, a $100 DAC and a Pair of Sennheiser HD600 headphones will reliably achieve $50,000 Big System Sound Quality."

Your points are mostly very well made. But: The Sennheiser HD600s don't have any deep bass at all (whereas a good pair of $100 in-ears will), and I disagree about the $100 DAC. I think it will be OK with headphones but in a setup with speakers it won't get you anywhere near the resolution, tone and timbre, bass, or soundstaging you'll need. Best regards, LTL

tonykaz's picture

Of course, I might have been exaggerating or even Extrapolating ( considering what Schiit are turning out, quality wise )

I own Sennheiser HD600s that can reproduce the ultra Low frequencies that Bob Katz puts into his Bombay Dub Orchestra Mastering . ( under 10hz ) But, of course, they don't deliver Chest thumping Bass, as you accurately describe.

You might be right about those $100 DACs but I rather doubt that the average Audiophile could sense or perceive much difference until a comparison is made directly with one of PS Audio Ted Smith DACs. Then, get out the American Express Card and kiss your next year's disposable income good-by, adios!!!

But:

I contend that the average Citizen is a Music Loving Audiophile with only a Sound Bar and not even knowing that they have a $100 DAC built into their Music Device or/and a Car with multiple speakers as part of a $5,000 Dash package option.

Back in 1970 we needed a Stereo Speciality Shop to buy Mac Tube Amps and Bozak Loudspeakers. Now we only need an internet connection, a few dollars and 125 VAC.

Audiophiles have Won Life's Lottery.

Tony in Venice

ps. I'll help those working on getting Health Coverage as freely accessible as Music has become.

Bogolu Haranath's picture

See the review of the Devialet Expert Pro integrated amp with the SAM (speaker active management) technology, in the recent issue of TAS ........ It can be useful with passive speakers ........ It is somewhat different from the DSP currently being used in some active and with some passive speakers :-) ........

AJ's picture

2010??
Tony, Harmans other brand Infinity was making similarly well engineered/cost effective speakers in the late 90s. These JBLs are obviously a bargain.
Btw, just fyi now that you are in Venice, the Suncooast Audio Society (tampa/st pete) is host a touring Brazilian cellist and pianist - playing on hosts home Steinway baby grand this weekend. The performance will be digitally and analog recorded in situ, then played on the hosts stereo system (Einstein/Hegel/Quad ESL63/Gradient subwoofers) afterwards.
If you are interested in that sort of thing. If not, enjoy the weather ;-).

Bogolu Haranath's picture

Sony is introducing '360 Reality Audio' and Dolby is introducing 'Dolby Atmos' audio ....... Both formats are intended for audio only .... not for video and movies ....... Both formats are intended to deliver 3-D sound ...... Both formats can also be heard through headphones/IEMs .......... See S&V website :-) .........

tonykaz's picture

Can you purchase that Sony System and do a nice review for us?

We've been hearing claims like this for the last 5 Decades, haven't we.

We should inquire with Kal who just abandoned reporting on these things.

So:

I suppose it's up to you to fill in the empty spaces, read between the lines, do an in depth investigation and write up a proper 5,000 word report/review.

I promise that I'll read each and every word and even make a few opinionated comments.

You could be our next Stereophile Reviewer. for gods sake !!

Tony in Venice

tonykaz's picture

Can you purchase that Sony System and do a nice review for us?

We've been hearing claims like this for the last 5 Decades, haven't we.

We should inquire with Kal who just abandoned reporting on these things.

So:

I suppose it's up to you to fill in the empty spaces, read between the lines, do an in depth investigation and write up a proper 5,000 word report/review.

I promise that I'll read each and every word and even make a few opinionated comments.

You could be our next Stereophile Reviewer. for gods sake !!

Tony in Venice

Bogolu Haranath's picture

Sony is having a demonstration at their store in NYC right now from Oct 16th to Oct 20th ......... I mentioned about it to Mr.Austin in another forum ........ May be some of the Stereophile reviewers could attend that demo and tell us about it :-) .........

tonykaz's picture

I'm about one hour south of these lads via I75 interstate.

Here in Florida, from now on, I'm bicycle, which confines me to an approx. 20 mile radius, or so.

Of course I still Fly, with two nearby International Airports .

Thank you for pointing out this Musical Event.

However, I'm transportation support for the Bernie Sander's Campaign and things are beginning to get busy for all of us.

Still:

I'm anxious to subscribe to Tampa's Music scene. I'm hunting for a kindred spirit here in Venice. Fingers crossed.

Thanks for taking the time to write.

Tony in Venice

AJ's picture

Just remember, here in Florida, you're not a pedestrian or bicylist. You're a target. For cel phones driving around, with human things attached.

joemariano's picture

Mr. Reichert - Great piece as usual. Really digging the structure and how you showed what was compared to what. You are 110% correct: reviews and measurements are "meaningless abstractions" until confirmed by the listener's own experience. I hope I can hear these (and everything else you review) someday! Will you get a second Schiit Aegir to play in mono style? It could make for an interesting followup!

MFK's picture

1

MFK's picture

Thank you for another entertaining and informative review. You are truly one of the very best writers on audio ever. The review confirms my contemporary experience that we are in a golden age for high value hi-fi products, particularly speakers. I remember attending a presentation in the 2000s by an elite US based speaker manufacturer (still in business). The representative was advocating spending 75% of a system's cost on speakers. I wonder if he still has the same opinion. My DAC, preamp and power amp in combination are worth more than three times the price of my speakers. After many years in the hobby I've found a system that I have no intention of changing.

smileday's picture

The port tuning frequency of this JBL is quite high compared to that of another 2.5way tall-boy (not very tall indeed) speaker reviewed by Stereophile, Spendor D7.

Lack_of_credibility's picture

Surprised that JA didn't mention the sawtooth response from 10k to 20kHz. Can't imagine that helps the speaker's tonality.

John Atkinson's picture
Lack_of_credibility wrote:
Surprised that JA didn't mention the sawtooth response from 10k to 20kHz. Can't imagine that helps the speaker's tonality.

I did write that the on-axis response peak at 16.2kHz is a couple of kHz higher than my high-frequency cutoff, but may well be heard as a slight whistle by younger listeners. The JBL's rise in response in the top octave is to high in frequency to affect tonality but will probably lead to an increased sense of air or spaciousness.

John Atkinson
Technical Editor, Stereophile

tbirdron's picture

B&h in NYC sold me a pair for $423.

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