In this blog post I would like to feature a custom order completed for a customer who had requested a DIY plan set for his Altec 416-8B 15" Woofers. He consulted with me on what would be the best 2-way configuration. I recommended the ES-600 Biradial No.1978 along with the newly offered SB Audience 75CDN-T compression driver. Contingent to this recommendation was the custom rear cover.
The project scope included a passive crossover design and build. The customer already had constructed Bass Cabinet No.1838.
To summarize the project scope:
- Customer has existing Altec 416-8B woofers and Onken Cabinet No.1838
- Customer ordered
- Finished ES-600 Biradial Horns in Ash (see photos)
-
75CDN-T 1.40" compression drivers
- Drivers were ordered through us but dropped shipped by Madisound directly to customer in USA
- Rear covers No.3075
- Design and build passive crossover for speaker system (If contacting me please reference order No.3053)
- Finished ES-600 Biradial Horns in Ash (see photos)
Considerations
I took on the project because I have another customer's pair of Altec 416-8B woofers in sealed cabinets that I could use for the final tuning and adjustment of the crossover. These cabinets were featured in a previous blog here.
Crossover development
Low Frequency
I measured the response of the Altec 416-8B in-room and found the following:
- Some moderate baffle step is required to provide a rich full bass
- A steep fourth order low pass filter is required to match the response of the horn
- My customer is using the Onken cabinet No.1838 which would will provide deep and full bass. However the sealed cabinet did not provide adequate deep bass even with boundary reinforcement. This is a side-note to this project and may be of interest to the broader DIY community. Even after baffle step compensation, the sealed cabinet did not produce adequately deep bass even with the cabinet positioned close to the front wall. This comes as to no surprise given the driver's relatively low QTS of 0.23.
Below is the baffle step and low pass filter transfer function I finalized on based on subjective listening and measurement.
There is about 9dB of baffle step along with an LR4 low pass filter centered at 800Hz.
High Frequency
For the high pass filter portion of the crossover I settled on a single capacitor along with a fixed resistor L-pad. The resulting crossover slope of the HF horn + passive crossover resulted in perfect symmetry of slopes between the LF and HF.
Passive Crossover Considerations
I wanted to incorporate two adjustment points into the passive crossover that would allow the customer to tailor the sound to his personal preference. These include:
- Adjustable level for HF
- This adjustment is accommodated by swapping our Resistor R2 in the fixed resistor L-Pad.
- Adjustable Midrange presence
- This is done by adjusting C1 in the HF high pass circuit.
The customer's plan was to build his own outboard enclosure for my passive crossover. I provided the crossover board with mounted components. I left a length of wire lead on the crossover's inputs and outputs for connection to the customer's binding posts.
Terminal Strips
I decided to use screw-down terminal strips for the input and output locations, along with the adjustment points mentioned earlier.
We used open spade lugs onto the terminal strips.
CNC Laser
I used our new laser engraver to mark out directly onto the wood surface where the components are to be located.
Final Adjustment and Tuning
With a stereo pair setup in my listening room I listened to a variety of test tracks along with measurements to conclude my result.
Once the crossovers were built I then installed a second time to listen to the "as-built" version to confirm there are no issues or changes from my original testing with alligator clips.
I 3D printed little support cradles for the capacitors which get screwed to the crossover board. The capacitor is held by zip ties which loop underneath the cradle.
ES-600 Biradial Horn No.1978
The customer went with ash wood with x2 coats of Rubio 2C hard wax.
The project required the use of our custom rear covers which lowered the FS enough to use an 800Hz crossover point. A comparison blog can be found here. Technical drawings for the rear cover can be found here. You can download the 3D CAD files for the rear cover here. You can order the 3D Printed rear covers from us here.
Final Conclusions on Sound
Overall the final system offered excellent clarity especially through the critical midrange. The first order slope on the high pass filter provided the same soundstage depth that I've come to expect based on previous projects. The simplicity of the 2-way has appeal to many, and this offered a "no fuss" easy listen.
Subjective Listening Impressions
Below is a ranking for my subjective impressions on the sound quality...
Soundstage Depth --- 9/10 < Does not quite match the 2800 Speakers
Soundstage Width --- 8/10 < Slightly better than the 2800 Speakers
Smoothness --- 7/10 < directly comparing to the 2800 speakers (shown behind in the system photos) revealed slightly more refinement and smoothness from the 2800's.
Coherence between midrange and treble --- 10/10 < close driver spacing by virtue of the biradial horn paid dividends here (in contrast to a circular horn) along with a very optimized passive crossover. The system also has perfect step response (driver time alignment)
Vocal Clarity Male --- 7.5/10 < I would say there was some "chestiness" to the male vocals but I did not find it objectionable but rather added to the sense of dynamics on most recordings, either vocal or instruments such as the cello.
Vocal Clarity Female --- 10/10 < the 3" diaphragm comes into play here, providing extreme clarity. The low coloration horn is playing a part as well.
Accurate Musical Instrument timbre --- 10/10 < A simple 2-way with an appropriately sized horn offers balanced off-axis energy into the room.
Sense of Dynamic Range: --- 10/10 < Slightly more dynamic than the 2800 speakers although was not as smooth sounding across the frequency range. The speakers still sounded good on poor recordings however.
Final Thoughts
Project 3053 offered a great blend of sound characteristics including excellent dynamics, clarity, coherency, and timbre. Directly comparing to the 2800 speakers, I found the 2800 excelled in smoothness, soundstage depth, and low bass extension.
I found that I preferred the bass character of the dual 10" scanspeak woofers on the 2800 speakers since they offered a cleaner male vocal. For reference, the crossover point on the 2800 speakers is 500Hz compared to 800Hz, but I don't think this contributed to the difference I was hearing. In other words, going with a larger horn on the 3053 project would not resolve these differences. The Scanspeak offered a more damped sound across its operating range...which subjectively was cleaner and more "hifi" sounding.
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