In search of that lost chord . . . or two.

I’ve been an hi-fi audio aficionado for over 40 years. During this time I’ve heard and owned some of the classics of several generations.
I’ve owned TEAC – Pioneer – Sony – JBL – Altec Lansing – Denon – Infinity- Realistic – Optimus – JVC – Panasonic – Sherwood – University Sound – EPI – HK Citation – Dynaco – Advent – AR – Polk Audio – Dual Audio – JC Penny MCS – Samsung – Yamaha and numerous custom made speakers and amplifiers.

I’ve listened to several others beyond the list above and have come to the conclusion that manufacturers all have their strength and weakness in designs. I’ve listened to various higher end products and have often found in my experience the cost of a product isn’t always going to sound better. I have recording experience with live sound as well.

Lately, due to an abrupt change in life style / income, I have purchased, repaired and sometimes modified equipment through thrift store purchase. Sometimes beyond the occasional turkey I run into a gem. One of those gems is a speaker pair that are often sold through eBay and Craigslist for shall I say, a song. The JBL 2500 and 2600 are often found at low cost and if you can find one that doesn’t need driver replacement, you can achieve a higher level of sound quality than the original design.

JBL_2500_speaker_pairThe JBL 2500 is a simple, small, two way, book shelf speaker. Covered in oak grained vinyl, no longer a popular finish, it complements a mid-century architecture home. The 2500 incorporates a 5 inch polymer treated paper woofer with .75 inch titanium tweeter with a dispersion lens crossed over at 3 Khz. The 2600 is the same design, also in a vented slightly larger cabinet and a 6 inch woofer. Neither one reaches out and grabs you when you first connect them to an audio source.

I was a little disappointed when I first tried the 2500 for a number of reasons. The first became obvious when one of the speakers would distort slightly when coaxed with a little bass. I then set about replacing the mid-bass woofer with a Goldwood magnetically shielded 5.25 inch woofer. This was a slightly larger woofer with a decent design spec but a little less efficient. I already planned to modify the crossover and thought I would adjust the tweeter to more closely match the output level of this new mid-bass woofer. I listened to them on a variety of material in combination with a subwoofer to augment the anemic bass.

After finding the problem with one of the original JBL woofers, a voice coil solder joint that had failed, I made the repair & reinstalled them into the cabinets. I also took a closer look at the construction and specifically the one thing that stood out was the short vent port. A 1.5 inch diameter port with a length of 2 inches isn’t going to augment the bass at the cutoff of a claimed 70 Hz. Speaker port calculator

I see where another individual decided to radically alter this speaker by replacing the drivers. Speaker driver replacement

JBL_2500_wooferThere’s nothing wrong with the idea but again the port is wrong no matter what driver is selected. Besides, the drivers JBL selected are better than most new speakers priced significantly higher. The titanium driver used for the tweeter is an excellent driver that is controlled without the brittle or hiss edge to high frequencies. The 5 inch woofer like all small speakers isn’t a large enough surface area to reproduce deep bass.

JBL_2500_speaker_vertical_1bAs I examined the mid-bass driver though, I realized it is well constructed with a large magnet assembly. What was really lacking was sufficient reinforcement from the back wave inside the cabinet. I found this was a product of bad port design more than anything and I set about using the speaker box calculator to assist in correcting this oversight. What I ended up with a satisfying sound with a little more bass register than I previously had for a total added cost of less than $6.00

The reason I find augmentation of the mid-bass is that is where you will hear the acoustic strumming of guitar, cello or violin. Most of the newer home theater speakers have a gap between the subwoofer and where the small speakers assume responsibility for the middle range and beyond. All too often I hear a thumping, frog burp low end and a sizzling, spitting high end. This is lousy reproduction of sound but most people have become accustomed to booms and pops without the slightest idea of what true instruments sound like.

After modifying the JBL 2500’s I have removed this dip in frequency response between subwoofer and the bookshelf speaker. speaker-2b
Click on the image for a brief sound demo of this speaker.

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