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jam4jaudio

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FRFR  Cabinet Project        

   

 

 

                      ©2016 SpeakerBuilderSupply.com       

What is FRFR?

     In simple terms a FRFR stands for “full range flat response”. Many different types of speakers fall into this category including PA speakers, studio monitors, home stereo, headphones, even those little earbuds that we listen to music with are all ideally FRFR. Guitar speakers on the other hand are anything but FRFR, because they’re basically nothing more than “woofers” mounted in a cabinet and thus do a pretty efficient job of reproducing tons of midrange frequencies, but very little low end or high frequency tones. This is not a bad thing. If fact this is ideal for the electric guitar. Try adding much high frequency content to your guitar tone and it’ll sound terrible. Try plugging your guitar amp directly into a FRFR cabinet and you’ll see what I mean.

Why FRFR?

Three words: Amp Modeling Technology.

    Actually, amp modeling is really nothing new -remember the Tom Scholtz rockman from the early 80’s? You just plugged your guitar into it and plugged the output into your PA or home stereo, and you got some pretty decent guitar tones. I think it even had a headphone jack.

    Truth be known, I bet we would be surprised how many great guitar recordings we done even years before that, by simply running an electric guitar direct into a mixing console. Of course, adding a bunch of effects such as an echoplex, and maybe a fuzzbox along with a ton of EQ would help. (#primitive amp modeling?)

    You have to admit that amp modeling has come a long way in the last few years, but admittedly it’s not for everybody. Some players just want to plug their guitar into a good amp and dial in their tone and maybe add a distortion/overdrive pedal and maybe a wah pedal once in a while to add some variety and that’s all they need.

    But others like the idea of having a hundred or so different preset tones dialed in and being able to recall them at a touch of a button.

Some things to consider:

    First of all you have to remember that the factory presets rarely sound perfect. These presets are more or less just examples of what the unit can do, and can be great starting points for dialing in your own presets, so it will require some tweaking to dial in your own presets.

    Most amp modelers can be used in couple of different ways. Most units can be used in “pedalboard” mode, where the device is used in front of a traditional guitar amp, to replace a rack full of pedals. Or it can be used in true modeling mode. In modeling mode the unit can be used to replace an entire amp/speaker cabinet along the all the pedalboard effects. There are advantages to both: If you really like the sound of your amp, and you want to preserve the sound of it, but just want to add some pedalboard effects, then pedalboard mode is the best option. Please note that you can use one of these units in modeling mode in front of a regular guitar amp, but say, for example you have the unit set up to model a Marshall JCM800 and you have the device plugged into a Fender Twin Reverb, the resulting tone will, more than likely, be some kind of Marshall/Fender mix (Fendall?..Marsher?). This isn’t necessarily bad or good, it’s just different. And it’s just another possibility when using a modeling device.

    But, in my opinion, where these modeling units really shine is when used in true modeling mode. Where the unit replaces a traditional pedalboard, amp, and speaker cabinet setup completely. It would even replace that pesky mic that you would normally position in front of your speaker to pipe the sound through the main PA/monitor system.

    The simplest (but probably not the best) way of doing this is to just plug your modeling unit directly into the main sound system and then monitor your sound through the PA monitors.  The disadvantage, of course is that you have to rely on the sound Technician to get your monitor mix just right. Most players will opt to have their own onstage sound setup of some type. Just a small mixer/amp through a full range speaker cabinet would work nicely. You can then split the signal from your modeling device, or use a line out to send a copy of your signal to the PA. The biggest advantage is that what you hear onstage is exactly what the audience will hear through the PA. One of the biggest struggles for guitarist is that you can spend hours dialing your tone, but then you’re never quite sure if what the audience is hearing is even remotely close to what you’re hearing onstage. Sound technicians don’t always have the greatest ear for guitar tone either!

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So anyway, where was I?

    Oh yeah, the project! The main difference between an FRFR cabinet and a regular guitar cabinet is that a typical guitar speaker cabinet is designed to give you tons of tone of one type or another. You’ve got open back cabinets, closed back cabinets, semi-open cabinets, convertible cabinets, thiele inspired cabinets designed to enhance certain low-end frequencies, plus literally hundreds of different speaker choices from the bell like chime of Alnicos to the growl of something like a vintage 30. Thousands of different combinations each designed to the player his preferred tone.

    An FRFR cabinet on the other hand is designed for no tone, no tone in that an ideal FRFR cabinet should be neutral and not color the sound in any way. What goes in comes out. Thus, an FRFR cabinet build will incorporate same design aspects of a well designed full range PA cabinet…Full Range, and Flat Response.

    For our project we decided to go with a three way speaker design, with a woofer, midrange, and hf horn/driver, along with a high quality 3 way crossover. We could have gone with a 2 way design, but since most of the meaty part of a guitars frequency falls in the midrange, we want as much of this frequency range to be covered by a traditional cone driver, as I think that this will give the guitar a more natural sound. Plus, with a 2 way design the crossover frequency would likely fall somewhere in the 2kHz to 2.5kHz, which is right smack in the middle of the guitar’s frequency range which might have the potential to sound unnatural.  

The components that we chose are as follows:

·       An Eminence Delta 12LFA for the low end: After searching through the Eminence catalog we determined that this speaker was the best compromise of price and performance. Eminence also makes this speaker in a regular 12A model, but the 12LFA offers a little boost in the low end, at the sacrifice of some midrange, but since this is a 3 way design the 500Hz crossover point is well with range of what this speaker can handle. If this were a 2 way cabinet we would have probably chosen the regular Delta 12A model or something similar.

·       Eminence Delta Pro-8A 8" for the midrange: As we said earlier, the bulk of the guitar’s tone is in the all-important midrange, so we didn’t want to scrimp here. The Delta Pro-8A will handle the low end well below the 500Hz low/mid crossover point and will extend well beyond the 4kHz mid/high crossover point. Plus, it will handle plenty of power.

·       Eminence PSD:2002S-8 1" Titanium Driver for the highs: We’ve used these drivers before and have been very pleased. They have a nice smooth frequency response and handle plenty of power, especially when crossed over at 4kHz. The 1-3/8” x 18TPI mounting format will screw right on to our Dayton horn lens.

·       Dayton Audio H6512 6-1/2" x 12" Waveguide. To be honest we chose this because we had a few NOS pieces on the shelf, but it just happened to be perfect for this application.

·       Dayton Dayton Audio XO3W-500/4K 3-Way Crossover 500/4,000 Hz: We’ve used a lot of Dayton crossovers and have always been pleased. We chose the 500/4,000 Hz unit because we wanted to keep the mid/high crossover point toward the higher end of the spectrum. Again, to let the midrange cone driver handle as much of the guitar’s frequency range as possible.

Cabinet Design:

    What we really wanted was to create an FRFR cabinet that looked more like a traditional guitar speaker cabinet, and we started drawing up some plans, but then remembered that we had a couple of unfinished bass cabinets in the warehouse, and after checking them out a little closer we found the perfect specimen. It was originally built as a 4x10 angled front British style cabinet. (British style in that the speaker baffle, was removable, and pulled out from the rear of the cabinet, and the grill cloth attached directly to the baffle). All we had to do was pull the old 4x10 baffle out and dispose of it and then cut a new baffle with the appropriate cut outs for our new components. -easy-peasy…with a couple of hitches though....

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     First, being that the cabinet was rather smallish, and that it is a angled design with a split baffle with each half being just over 11”, we discovered that the bottom portion of the baffle wasn’t going to be quite big enough to handle a full 12” speaker. We worked around this by routing into the top, angled part of the baffle enough to allow the 12” speaker rim to sit flat. See the picture:                           

    Also, since the cabinet is a 3 way cabinet we wanted to isolate the midrange speaker from the woofer so the speakers wouldn’t react with each other in an adverse way. Thus we decided to house the 8in midrange in it’s own little isolation box. So we ended up with cabinet within a cabinet, so to speak. Not too much of a problem, but remember that this is a removable baffle design, so it did take some very careful measuring and calculating to come up with something that would work.

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    We knew that the Delta 12 would really work best in a vented cabinet, so we calculated the internal volume of the finished box as closely as we could and entered the box volume into our Eminence Designer software program and determined that one of our 3” diameter by 4-1/2” long port tubes would be just about perfect.

    Since the grill cloth was going to be attached directly to the speaker baffle, the rim of the port tube as well as the rim of the Dayton waveguide were recessed into the baffle so that the surface would be nice and flat, so the grill cloth would lay nice and flat. The woofer and midrange were rear mounted so we installed 10-32 t-nuts into the front of the baffle and recessed those also.

    Notice also how we recessed the t-nuts. We then test fitted all the components to make sure there wasn’t going to be any problems. Once we were sure that everything fit correctly, we removed the speakers and then went over the front of the baffle with a sander to round off all the edges slightly to make sure the grill cloth wouldn’t snag when stretching it over the baffle. We then painted the front of the baffle with some flat black spray paint, which is always a good idea, since some types of grill cloth are quite transparent.

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    Once the baffle was all prepped we went ahead and put everything together.

    Here’s the baffle with everything installed and wired up. Note that our Eminence HF driver hadn’t arrive yet, so we temporarily used a Dayton unit that we had lying around. Note also the PTFE twisted pair wire which makes for a nice neat wiring job.

    I couldn’t wait to demo this cabinet so I went ahead and installed the baffle into the cabinet and put the back panel on and then played a bunch of recorded music through it to break in the speakers. I must say, I was very impressed with the sound. I also ran some sine wave test cd’s through this cabinet and the frequency response is indeed very flat. Most of my playing these days is with guitar backing tracks and this cabinet is exactly what I needed. I power the cabinet with a mixer/amp and plug my mp3 player and my modeling unit directly into it and it makes for a great sounding setup. This cabinet not only would make a great FRFR guitar cabinet, but it could even be used as an onstage side fill monitor cabinet.

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    The cabinet is now finished. We went with a two tone tolex job and used Black Bronco and British Cabernet Bronco tolex, along with Salt and Pepper grill cloth, with black piping and string. Also made up some black Mesa style leather corners. I think it looks pretty good.

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