Deja VU: Box Design and The JBL 2235H

[Loren42]

Originally Posted by infinia

Hi Loren
deja vu all over again. seems when I 1st met you here on this forum you had a similar problem /thread Re box tuning with a JBL driver. I forgot what you did to solve it. hard earned lessons learned makes the best teachers.

I would like to think I learned something.

My ultimate solution was two-fold. One was to replace the JBLs with Acoustic Elegance TD15Hs.

The second was to reduce internal volume of the cabinet to about 5 cubic feet and change the box tuning to about 35 Hz.

Then I mated Beyma TPL-150 ribbons to the woofers and what a difference!

Even at background levels the bass is much more pronounced and solid. The high end is amazingly clean and you can sit just about anywhere and get great audio imaging.

[infinia]

Loren thanks for the detailed reply , so the JBL's just didn't pan out as woofers capable of reasonable bass considering you went on to build a new box anyways?

[Loren42]

Originally Posted by infinia

Loren thanks for the detailed reply , so the JBL's just didn't pan out as woofers capable of reasonable bass considering you went on to build a new box anyways?

Not quite true. The JBLs are very good drivers. Mine were cosmetically challenged with crushed domes. I could have them re-coned, but... The TD15H T/S parameters were nearly identical and offer more excision and far less inductance at a cost (before the current price increases) that was not much more than the cost of reconing the 2235Hs.

The old boxes were too big for the new furniture we got. We bought two beautiful American Leather sofas for the room. We love them!

With the lack of room I gave the old speaker cabinets and the JBLs to a good friend and after much prodding from my girlfriend, began a fresh new project. The goal was a smaller footprint enclosure with similar performance. So off to the drawing board I went.

In the end the footprint was only somewhat smaller and I was discouraged to the point of just nixing the project altogether, but my girlfriend insisted I go forward. I am glad I did.

For starters, the cabinet was rectangular with the inner dimensions set to the Golden Ratio. I used two layers of 17mm baltic birch with Green Glue between the layers for a constrained layer box.

I wanted to extend the things I learned with the old cabinets and bring them to a new design.

I also wanted to try a 2-way build instead of three-way. The problem with that idea was the 15" woofer has an upper limit of about 1 kHz before directivity falls away. Even though the AE TD15Hs had a very good upper limit compared to most woofers that size, that left me with few choices for a tweeter.

A horn was the most likely candidate, but after following all the posts from Dr. Earl Geddes I felt that getting the degree of performance I wanted was probably going to be beyond my available time and my technical abilities.

Things started to fall together when I discovered the Beyma TPL-150. It was pricy. There also wasn't a lot of prior art using it available on the web. However, what comments were on the net gave it high marks for its directivity and sonic performance.

It was a gamble buying these, but the Klingon in me (It's a good day to die) ruled the day and I ordered a pair.

How did it work? Well, it exceeded my expectations. My previous mid and tweeters were Audax PR170s and Morel MDT-37s. Both are really good drivers and the Morels are nothing to sneeze at. However, the sound from the ribbons leaves the old setup in the dust. Off-axis response is so much wider that even listening at an off-axis of 60 degrees yields amazing results. They are just so clear and detailed.

I believe that reducing the cabinet volume and raising the box tuning a little compared to the old design made a significant improvement in the bass. I no longer needed the bass compensation on the preamp to get good bass. I know my room acoustics are very poor and I have a ceramic tile floor.

However, raising the woofers higher on the baffle, less internal volume, better cabinet construction, and higher box tuning all worked to enhance the bottom end quite a bit.

I will be taking more measurements in the future and then plan to dial in the crossover to see how much better things can get, but so far both of us are very pleased with the new results.