Beginning to upgrade an older OB build

mashaffer

Super Member
Years ago I built these Open Baffle Table Speakers using Goldwood 10" OEM woofers (https://www.parts-express.com/goldwood-gw-210-8-10-oem-woofer-8-ohm--290-325) and old Radioshack 12-1848 5" Fullranges that I had lying about.

The drivers were not very well balanced and the FRs had almost nothing below 200Hz (probably old stiff suspension) but I cobbled together a sort of bi-amp setup that made them work. The sound stage was actually quite sweet.20190120_142151-1.jpg

Having some nice Mark Audio CHR-70s that I have been experimenting with I thought that they might be made to blend well with the woofs. I added a 9mH inductor in series with the woofs and set the MAs (in small enclosures) on top and gave a listen. Promising but even the MAs were a bit more efficient than the GWs. I knocked up 9.5dB pads with a 250uF blocking cap (70-100uF would no doubt be better but 250 is what I had on hand) and the results are quite satisfying. I listened for a few hours to various genres and the balance is very good with the tone controls set flat. With the Sony V4 power meter indicating 1W average the output was comfortably loud but probably not efficient enough for a 2W SET. However once I get the MAs mounted I plan to try my KT88 SEUL.
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I expect some tweeking of the crossover may be necessary with the MAs on baffle but I am encouraged with the results so far.
 
Did a few more hours of listening. On second thought the blocking caps might be just about right as they allow the MAs to contribute a little bit to the bass. Will have to see what their excursion looks like when mounted OB. Could try something around 180-200uF.

As to the balance it still feels right. Instruments in all ranges sound natural with good presence. String bass, Tuba Tympani and the like sound just like they are supposed to. Electric bass is right up front.

Of course the chest rattling bass of organ pedal tones is not there but I have plans to patch into the subwoofer that I am using with my virtual pipe organ.
 
I got one of the FRs mounted. The holes for the older drivers are just the same as the outer diameter of the new drivers so I decided to just screw a mount board on from the rear. Besides just being the easist it also allows the acoustical center to line up more closely with that of the woofer.

In order to mitigate diffraction effects I tried to glue some felt to the inside of the hole (didn't want to hold as I worked my way around so will see if it lasts).

On the other speaker the new driver still sits in a seperate box on top so hard to make any real judgements but so far imaging and presence seems good with no harshness.

Honestly, one of the things I like about OB is they tend to be very forgiving. :D

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Got both speakers done and sounding good. I knocked up one line level passive sub filter and hooked into the organ sub and it worked fairly well. The second one I made had some problems causing distortion like a bad connection so I set that aside and decided to see how the SEUL KT88 sounded with them. Working it through its paces right now. The meter is hooked to thermal probe to monitor PT temp. In the past it got rather hot.

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It sounds a little brighter than the Sony but I have to use this old Rat Shack mic mixer as the preamp (which needs a deoxit bath) so can't draw too many conclusions.

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Just gotta get started on that preamp project with active sub crossover. :D
 
Began today's testing with Mozart's Clarinet Concerto. Two things were forcefully driven home to me...

1. As you probably know if you have experienced the Clarinet up close and personal, it is a fabulous instrument for judging tonal balance and clarity. The Clarinet has very complex tone quality that varies dramatically over its range of about three octaves. In the lower register (eapecially with a quality wooden instrument) the resonance is palpable. In the upper octave it can cut right through the orchestra but if it pierces suspect a speaker or recording problem.

2. Those Mark Audio drivers are an outstanding value in medium efficiency wide-ranges.
 
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