The well-known and widely acclaimed Dayton 275-070 tweeter has undergone some changes recently. As most of you know, this has been my tweeter of choice for the series of high-quality, low-cost budget speakers I've designed. I was sent some "off-the-shelf" samples from Parts Express recently to have a look at them, put them through their paces, and to determine if any changes are necessary to the crossover networks used in my budget designs.

In the coming weeks, I'll be evaluating the performance of the 275-070 and posting any changes deemed necessary. While it might seem as though it's a simple matter to remeasure the tweeter, plug the data into Calsod, and come up with new component values to post, each design I publish is the result of extensive listening in conjunction with computer optimization -- the computer doesn't design the speaker, I do. Also, as you will see in this initial review, the differences between the old and new speaker from a pure 'data' perspective are quite small. From a listening perspective the new speaker has a significantly different sonic character -- and let me start off by saying it's a good one.

I. Physical Changes

The electrical changes noted in the next section are surely a result of the mechanical changes this design has undergone. First, based on testing and experimentation by a number of DIY enthusiasts, the back of the 275-070 is now cupped. While not a true rear "chamber", the new tweeter eliminates the aperiodically damped chamber that could cause an influence in the performance due to the backwave of the woofer interfering with the operation of the tweeter, especially in sealed boxes where pressure can get quite high. The addition of the cupped back should help to reduce distortion and eliminate the need to place this tweeter in a separate sub-enclosure. I never actually recommended using this tweeter in a sealed sub-enclosure, but those who performed surgery on the older model seemed to agree that adding the cup to the back end improves the distortion characteristics of the tweeter.

Rear View of the new 275-070

Also, you'll notice from this picture that the new silk dome has a foam pad on the back of the tweeters faceplate. This is very helpful for decoupling the tweeter from the enclosure and further improving overall sound quality (not to mention a nice touch). On a practical side, as a drop-in replacement for the old tweeter, your flush-mounting recessions will need to be 1/16" deeper than for the original.

275-070 -- Original Recipe

Finally, one of the major changes in the overall performance of the new version is a new doping compound used to treat the silk dome. I won't get into a discussion of what doping compounds are or what, exactly, they do. In this case all that matters is that the compound is different and appears to achieve much better overall tweeter performance. What you'll notice, visually, is that the new tweeters show what looks like a heavy, thicker, darker coating of the slightly tacky substance on the dome. I'll explain why I think it works better when we look at the numbers below.

The old version is on the left, the new is on the right

Although it's hard to see in the pictures of the domes above, the one on the right shows a darker color and a thicker, smoother coating on the dome. Although you would think that this would muddy the sound of the tweeter a little, I think that it's actually a better coating that provides a more open, airy sound and slightly improves the tweeters overall sensitivity.

II. The Numbers

I'm sure most of you are wondering what the measurements look like. I'll present them here and then in the next section my observations and recommendations.

First, here is a comparison of the old vs. the new. The newer tweeter does not measure as flat in the lower octave and has a more pronounced dip in the upper octave. Don't think this is a bad thing. Maybe the driver doesn't measure as flat, but flat measurements and good sound don't necessarily go hand-in-hand.

The new tweeter appears to be a nair more sensitive than the old version but also seems to be a little more pronounced in the peaks and dips. When we look at the impedance curves for the two tweeters, we see that the new version also has a more pronounced impedance peak.

Before you get concerned that the new driver will require a conjugate filter for impedance correction, stop. Most tweeters that use ferrofluid in the air-gap to improve power handling and lower resonance exhibit a resonance peak of this magnitude. The old driver was very atypical in this respect that it only had about a 3-4 ohm resonance peak. Further, the new peak is narrower and at a lower frequency, meaning that the crossover point for the driver has dropped slightly and the range of frequencies where the resonance will influence the performance of the driver has been decreased -- on the flip side, you should now get even better performance with reduced distortion at the same crossover frequencies being used previously (I ran a quick THD test on the new driver and it showed about a 40% decrease in 2nd and 3rd harmonic distortion. I forgot to save the result, however, and I'm reluctant to post THD measurements because they are somewhat confusing.)

Another view of the individual curves:

And the old...

III. Listening Impressions and Observations

The new tweeter, quite simply, sounds cleaner and more open than the original. In a side-by-side test in the D3's using the new tweeter as a drop-in replacement for the old, the overall sound was somewhat more dynamic although the lower treble/upper midrange region was somewhat more emphasized, probably due to the slight peaking in the 1-2khz range of the new unit. From a practical perspective, this rolloff characteristic won't be much trouble to handle when the various Dayton designs I've done are revisited and some corrections made to the highpass circuits (expect all new circuits optimized for this driver). The new doping compound appears to provide less dampening of the dome as reflected by the impedance peak magnitude at resonance and the more pronounced peaks and dips in the frequency response. While this doesn't look as good on the graphs, the truth is that it's clear from the sound that the overall performance of this unit has been significantly improved while the price has remain unchanged (not a bad deal since they added the foam pad on the back of the faceplate and the rear cup!)

Once the corrections to the circuits are made, I believe that the more dynamic nature of this tweeter will make a tweeter that was already a great bargain an even better deal.