PlayJazzGuitar.com Forum

[randyc]

The following is a scenario that I - and many others - have experienced. Needing to replace a loudspeaker, how does one make a sensible selection when it's not possible to make a side-by-side comparison between two different speakers ?

Unhappy with the performance of the loudspeaker in his small amplifier, Tal would like to replace it. He's looked up the original speaker, which the manufacturer describes as:

"Very loud, touch sensitive and responsive with nice bell-sounding top end and a little bite."

He is thinking about a speaker recommended by a friend that has this description:

"Performance optimized for lead guitar. Also suitable for bass guitar, vocal P.A., keyboards, club music systems and stage monitors."

Unimpressed by marketingspeak, and slightly troubled by the fact that the same manufacturer actually makes BOTH speakers, our man decides that a comparison between the two should be based on measurements of the two speakers under consideration. A side-by-side comparison being impossible, he makes a brief search of the products on the internet and finds these sound pressure level (SPL) curves, one for his existing speaker and one for the new speaker being considered:



Yankee's Best Loudspeaker SPL



Empire Ruler Loudspeaker SPL

Looking at both performance curves carefully, Tal observes that "his" Yankee has higher SPL (it's louder) but less bandwidth (total frequency response) than the Empire. He makes what he believes is a reasonable assumption: that the total power the speakers can project is actually about the same. He believes the difference is in the way that the power is distributed across the frequency range.

Tal doesn't spend money carelessly and he wants to make this speaker exchange only ONCE. He feels that the speaker decision needs to be based on how he's always made decisions about music: with his ears, but how to do this ?

Technological advances in digital signal processing (the same technology represented in low cost CD players) have progressed logically toward sophisticated computer recording and editing programs. These are universally available, free or at modest cost. These programs have an incredible array of post-processing features, some of which are overlooked due to their simplicity of purpose.

Tal has downloaded a free, open source recording/editing DSP-based program called "Audacity". As his flash of intuition has suggested, he opens the program and notes that there is an "EQ effect" that he can adjust to emulate an SPL curve to any desired level of accuracy (depending upon how much time he wants to spend equalizing the SPL curve).

(Note that "Audacity" is not claimed to be superior to similar commercial programs but it is free.)

Re-examining the original "Yankee's Best" SPL curve, Tal makes some graphical modifications. He's noted that the lines depicting measured speaker SPL are not smooth, there are lots of "squiggles" in the frequency response. Most can be ignored because differences in levels of less than 2 dB or so are not distinguishable by the typical human ear.

Tal starts to draw some straight lines through the erratic responses of the SPL curves, approximating the slopes and magnitudes of the measured response. He realizes that if he WANTED to exactly replicate every nuance of the squiggly variations of the SPL curves, he could do so, but it would require a LOT of time.

(There are many ways to perform this exercise, one of the easiest is to click on the SPL curve displayed on the internet by the speaker manufacturer, "copy" the information, then "paste" it somewhere convenient, like this document that I'm typing. Then "draw" the lines with whatever drawing tools are available on your computer. Since this document was typed with Microsoft "Word", I used the tools available in "Word". Microsoft "Paint" also works well, just use whatever works and is familiar to you. If you happen to have the catalog with the SPL curve displayed, you can draw in the straight line approximations with a pencil.)

This is Tal's approximation of the SPL curve after he drew his lines on it:



Yankee's Best Loudspeaker SPL Approximation

After this exercise, Tal wants to use "Audacity" to set up an equalization curve (in the "effects" section) to duplicate his speaker SPL curve. (Each of these recording programs has it's own peculiarities and preferences, since "Audacity" is the one that I have, it must be the reference for our purposes.)

Tal needs to establish a maximum signal level and for Audacity this is 0 dB reference. (Note that the SPL curve, properly, is calibrated in a scale that is appropriate for the human ear, not for our recording purposes.) Tal decides to modify the SPL level curve by "normalizing" it to "0 dB". This is easily accomplished by subtracting the maximum SPL from the SPL of each point on the curve. The first point on the curve, 70 dB, would become (70 - 108) or -38 dB, the next point on the curve, 96 dB becomes (96 - 108) or -12 dB, the peak reading of 108 dB becomes (108 - 108) or 0 dB and so forth.

(Note that the SPL curve characteristics have NOT CHANGED, just re-referenced to a level that the recording program can use "0 dB". Attempting to input SPL of 108 dB would either not have been permitted by the program or would have resulted in unbearable, hard-limited compression.)

After Tal adjusted the Audacity equalizer, he gave it a name (the speaker name) and saved it in the program … but it looked like this:



Yankee's Best Loudspeaker EQ

He then repeats the exercise, using the SPL curves from the "Empire Ruler" speaker that he is considering.



Empire Ruler Loudspeaker SPL

After "normalizing" again (and noting that the peak SPL for this curve is 100 dB, not 108 dB) to a peak level of "0 dB", Tal adjusts the EQ curve in the effects section of Audacity and saves it. It looks like this:



Empire Ruler Loudspeaker EQ

Tal is almost done … he's created and stored the SPL curves of the two speakers, now all he need do is play some music through them and LISTEN. But he doesn't want to use pre-recorded music, if possible, because it's ALREADY EQed and adjusted. The best possible tool, since his intent is to put the speaker in a guitar amplifier, is his guitar, recorded direct into the computer, no amplification (which would "color" the sound of the instrument).

(So plug in your guitar, controls set as you normally would adjust them, and record a clean track using as many different positions on the neck possible, single notes and chords. It doesn't have to be good PLAYING, just representative of your guitar(s) sounds. Save an unmodified copy of this for other, future comparisons. Using your recording software, separate the recording into two tracks, left and right. EQ one of the tracks using the "Yankee's Best" SPL curve created a few minutes ago. EQ the other track with the "Empire Ruler" SPL curve just created.)

Now the two tracks have to be adjusted for level (remember that the two speakers have different peak SPL - they are 8 dB different). Tal sets the amplitude of the "Yankee's Best" track to a convenient level, consistent with no distortion or computer (hardware or software) problems noting that the other track has to be adjusted 8 dB LOWER in level.

In Audacity, Tal simply picks "amplify" from the effects menu, sets the level to "0 dB" and "amplifies" the "Yankee's Best" track. Then switching to "Empire Ruler" track and selecting "-8 dB" from the level effect, he "amplifies" the new track. Both tracks are now adjusted for frequency response and relative amplitude for both speakers.

Plugging a pair of flat-response headphones into his computer (sound card, that is), Tal plays back his work. Alternately slipping a headphone off an ear, listening to a single channel, then doing the same on the other ear, gives him a very good idea of the differences between the two speakers. (Playing back the two tracks through speakers may not provide an accurate comparison because of the contribution from room acoustics.)

NOTE: Whatever means is being used to evaluate the two tracks MUST have a flat frequency response - if not, the comparison is invalid due to variation in SPL curves introduced by monitor speakers or headphones.

I'm sure that many are thinking at this point that this is a LOT of work. But it's not, it takes about ten minutes to EQ a SPL curve, start to finish. Add five minutes or so to record your instrument and another ten minutes to set up your software, EQ and playback … the entire process should take way less than an hour. And once you have your source material (guitar) recorded, the comparison of other speaker SPL curves will require only the ten minutes or so required to create another EQ curve and a few moments listening time.

OK, so let's hear a sample …. I picked a CD from a musician named "Bob Culbertson", a slight acquaintance from the San Francisco Bay area. This is his composition "Bourbon Street" and he's playing a "Chapman Stick". Rather than trying to make my abused fingers functional, I used Bob's music because his Chapman Stick covers a fairly broad audio spectrum. The left track is the "Yankee's Best" speaker emulation and the right track is the "Empire Ruler" speaker emulation.

Click here to listen to 06 Bourbon Street.mp3

So what's Tal think about the listening comparison ? As he later told his friend: "That's a nice speaker, I can hear more presence in it than MY speaker BUT it's maybe a little wimpy. That volume level is on the edge, I'd be inclined to crank it up a bit and the thing would probably distort. I'll keep on looking and listening."

[randyc]

Here are two more comparisons, same process as above.

10 inch original speaker (left channel) to Jensen P10Q (right channel)



10 inch original speaker (left channel) to 12 inch speaker (right channel)



Frankly, I'm surprised at how well the original 10 inch speaker performs - even against a typical 12 inch speaker found in many amplifiers.

[Jazz Playa]

What model speaker was the 12 inch?

[randyc]

[Jazz Playa]

The 10" is definitely brighter than the 12" (that would be expected though) but the AlNiCo magnet 10" still has smoother highs than the 12" and also sounds more 3-dimensional all the way around to me than the ferrite magnet speaker. The 12" has somewhat broader upper mids and more bass but I think that's just because its a 12". Well that's what my ears hear. Too bad you don't have the capability to do the same comparison with an AlNiCo vs a Ferrite speaker of the same size.

[randyc]

You're hearing things that I can no longer detect. When I plot out the spectrum (from the Audacity software), I SEE the differences, though. The advantage of this technique is that ANY speaker can be "heard", so long as measured SL curves are available.

Almost all major manufacturers now provide this information (Weber, for some reason, does not). So toss out the names of two speakers that you'd like compared and I'll do the EQ, it only takes a few minutes. (The speakers must have a measured SPL.)

[Jazz Playa]

Cool just give me a minute to think about what two speakers.

[Jazz Playa]

A Jensen P12N compared to a Jensen C12N would be good since they're the same power in watts and both 12" speakers, just one is AlNiCo and the other is Ferrite. Also any two speakers you happen to have on hand that are the same size but just different magnet types it would also be cool to hear a clip of each to compare and contrast the sounds.

I don't know why Weber doesn't list any data on their website. The sound clips they post on their website don't do the speakers justice IMO. If they're gonna post clips they should have a clip of the speaker clean and a clip of the speaker dirty. You can't tell anything by all that chicken pickin they've got posted in the sound clips

[randyc]

Observation of the two SPL curves reveals that the Jensen loudspeakers are VERY similar. My ears are useless for these comparisons but I did perform spectral analyses on both tracks - to me, they still appear virtually identical.

Here they are, the P12N on the left track and the C12N on the right track

Click here to listen to 03 Track 3.mp3

[Generic Sobriquet]

[randyc]

Either that or perhaps the measured performance curves may not be particularly impressive. There's a lot of superstition (lacking a better word) in many musicians concerning equipment. I've brought up the Weber topic a couple of times on other forums when the conversation appeared to be lagging ... a sure way to generate discussion.

As I've pointed out before, it's difficult to hold a manufacturer's feet to the fire because his speaker did not produce the "thrilling highs" or "sledge hammer mid-range" his advertising led one to expect. It's a very different proposition when the manufacturer fails to conform to his own published measurements.

[Jazz Playa]

[Generic Sobriquet]

Randyc, yes, that's included in what I describe. It's all obfuscation, muddying waters to make them seem deep, without having to back it up. And if you don't get it, well, that's your fault.
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[sunflower]

Note there are other characteristics of a loudspeaker than the fz response

Waterfall plots , impulse response , impedance curves
off axis response etc.
also what enclosures were used for the fz plots etc

[randyc]