C1's + 13

[heeman]

I cannot live worrying about bottoming out the drivers in the C1's while crankin' tunes any longer.

I really love the way the C1's sound in my dedicated room, so what do I do?

Do I spend major bucks on C2's, C4's, C60's?

Do I have other options?

Well....................yeah!!

There is a member on here that believes in building your own speakers. So he convinced me that this is the right solution. Keep the C1's and build woofers to compliment them and the existing subs. Use an active cross-over, high pass the C1's at around 300Hz, low pass the woofers at 300Hz and run the subs from 60 or 40Hz down.

So Flint and I started to discuss the different options. I will let him discuss the technical justification on the design.

Kyle, one of my friends that I work with is a Mechanical Engineer and he detailed the design with a 3D model and drawings for each individual cabinet part.

So, let the build begin!!

I purchased the drivers, ports and terminals from Madisound as specified by Flint.

I had Home Depot cut 2 sheets of 4' x 8'; 3/4" MDF in half to make them more manageable.

An 80 tooth blade for my table saw; a circle jig, rabbeting and dado bits for the router. A bunch of clamps and glue.

 

[heeman]

 

[heeman]

 

[heeman]

 

[heeman]

 

[heeman]

 

[heeman]

Here is the model.

 

[heeman]

I finished the first "tuning/balancing" session tonight.

No more issues with obtaining desired high SPL's..............

Drivers on the C1's no longer going berserk!!!

Sounding better than the system ever has before...........................

 

[Dentman]

Congrats!!!! Well done.
I look forward to more info on exactly what changes you hear. Also, are you running a sub?

 

[Flint]

This has been an extremely fun project! I will post tomorrow about the design decisions and goals based on Heeman's listening preferences.

 

[Haywood]

Wow. That is a pretty cool project that I wish I could hear.

 

[Batman]

Outstanding job!!

 

[PaulyT]

Awesome! But but but... They're not black.

 

[Flint]

A little background - Heeman and I have been chatting about his dream sound system for years. over that time I've learned his tastes in sound and what he loves to do with his system to experience true audio bliss. He loves cranking loud rock concerts, bluray and such, at concert levels and he loves clean sound with clarity and well defined playback. He also love powerful, punchy, pounding bass like you get from the stacks of subwoofers at large venue concerts - something which is always a challenge to recreate in a small, sealed room at home.

Over time and after running through a large range of speakers, which we all poke fun at home for doing, he discovered the smooth, dynamic, clean sound of Dynaudio Confidence series, specifically the C1, met he a large portion of his desires. But he struggled with the powerful and punchy concert level bass performance he was seeking. To try to find a solution he auditioned a set of PSB speakers with big 10" drivers and horn loaded tweeters. While they had the punch, they didn't provide the clean, smooth, accurate clarity of the Dynaudio speakers. He was frustrated.

Even with two massive subwoofers in his relatively small room, the bass was lacking. His sub-bass was phenomenal, his midrange and treble was ideal, it was all about the bass - the three-octave range from about 50Hz to 400Hz. Those little 6" drivers in the Dynaudios, which are amazing speakers, just couldn't keep up with the demands he was putting on them. Those are amazing speakers, for sure, but he needed more. He could have upgraded to the C2, but that was an insanely costly proposition and one which merely doubled the amount of woofer power, which is empirically a 6dB improvement in max output in the bass range. That could help, but it would make more sense to get at least a 10dB improvement - preferably more.

As Heeman's journey progressed, about two years ago I started suggesting he consider building his own speakers, or at least a set of bass bins for his C1 speakers which could create that bass performance he was seeking. A full custom 3-way system with the best dynamic transducers and active crossovers which would blow away his C1s would cost less than a pair of C2s, and he could customize the tone and balance to get exactly what he loved. But that was a stretch for him.

When I visited his new HT in Wisconsin and helped him fine tune his speakers and subs, he had a great sounding system, but one track in particular, his Moby Dick, the bane of his existence, was an old Van Halen song where at one point Alex Van Halen slams a tom and bottomed out his C1. He feared the speaker was damaged and with help from our fearless leader Batman he got a replacement from Dynaudio - the speaker was fine. I convinced him to plug the ports in the speakers to restrict the woofers and prevent the bottoming out, but realized there was no way those little speakers were ever going to give Heeman what he desired and start aggressively promoting the idea of building woofer cabinets. I even started researching what raw loudspeakers were available which could do the job.

I started sending Heeman recommendations, drawings, and conceptual plans for various designs and he opened up to the idea of doing this himself. Then shit got serious. I debated on whether to go with two 9" woofers from Eton or one 13" woofer from Scan-Speak and after fully designing both and modeling the resulting performance (predictions), and running past Heeman many times, we settled on a large woofer cabinet with a single 13" woofer from Scan-Speak. The design was modeled to have an in-room -3dB bass response to 23Hz and an effective -10dB bass limit of about 19Hz. The bass performance from 40Hz to 400Hz would be solid and powerful, with extremely low distortion due to the woofer's design. The anechoic (free-field) max output at 60Hz of 113dB SPL (or about 118dB SPL in-room) per woofer and with two woofers and amps the combined max in-room output would be more than 124dB SPL. Heeman doesn't need those output levels, but he does want clean, tight, dynamic, and effectively limitless output in the 50Hz to 400Hz range which these speakers would provide.

Heeman signed on and we assembled a shopping list of parts, including woofers, ports, screws, wood, input terminals, speaker wire, and everything else he would need to make these speakers. As he mentioned above, he brought in a young co-worker with mechanical engineering skills to help, which made a great big difference, and ultimately built these speakers.

 

[Flint]

Some interesting aspects to speaker building were discussed while going through this process.

One of them was the speed of sound and its impact on designing a cabinet and adjusting resonate port parameters. When we design speaker cabinets we have to make assumptions about the speed of sound to predict which cabinet volume will resonate at which frequency for the woofer to work in. The whole system is one resonate chamber and tube and if the real speed of sound when installed is significantly higher or lower than the assumed speed of sound when designing and modeling the speaker, the results will not reflect the models. Well, in real life this is not a huge deal in most cases. We design speakers with the assumption of the speed of sound at sea level and a barometric pressure of 1 and in the vast majority of installations this is plenty effective.

This came up because Heeman and his engineer friend were making slight modifications to the design to accommodate their limitations on tooling and such - not to mention they managed to get the CAD drawings for the woofer to exactly calculate the displacement of the woofer in the enclosure when drawn up in the computer. Since I had calculated the ideal effective internal volume of the enclosure, the physical internal volume needs to be larger to account for bracing, the woofer displacement, the volume of the port, at any other item inside the cabinet taking up volume. They were very concerned about that and the dimensions of the enclosure were modified over and over as we made new accountings of items inside the cabinet. They wanted it to be perfect and I was growing concerned that they would even try to account for the hookup wire running from the input terminals to the woofer. At some point you have to accept that enough is enough, so I explained that with speaker design, tolerances of 5% are not a problem. They were striving for a tolerance of 0%, or perfection, but just the variable of the speed of sound alone makes that impossible. My "ideal" internal volume cannot be absolutely perfect unless I go to Heeman's house and measure the parameters which impact the speed of sound over the course of a year and average them all out and adjust all my calculations to account for that - and even then the speed of sound will change throughout the year depending on barometric pressure, temperature, and humidity - the ideal performance would only occur during those periods where the speed of sound matched our calculations. I explained that we will not hear any difference if the enclosure is off by as much as 5% - same for the tuning of the port. HOWEVER - striving for perfection would result in reducing variability given there are certain aspects beyond the speed of sound we cannot account for such as manufacturing tolerances with the speaker, the losses in the enclosure as the MDF adjusts to the environment of Heeman's home, and so on. Being accurate where we can is a good idea - but it can also go too far and stifle progress on the project.

So, once they accepted there was no more tweaking to be done, they started cutting and made the cabinets in the photos above. I was very impressed they decided to make dados for all the joints. That increases the surface area for glue to hold the cabinets together and also makes it easier to assemble with all the joints perfectly aligned and square. That was very nice work. I personally do not go to the trouble in most cases. I convinced them to assemble the cabinets with only glue holding things together as nails, brads, and screws are rarely necessary and MDF just expands and crumbles when you start firing things into it. Also, it makes life so much easier to round over edges, sand, seal, and finish the MDF if there are no metal bits to work with. I believe that if Heeman ever goes to the trouble to paint these speakers, he will appreciate that no metal brads or screws are present.

I also had Heeman apply mineral loaded dampening sheets to the larger surfaces of the cabinet, on the inside - that's the shiny metal sheets you see in the photos above. To save money he used dampening sheets designed to sound proof automobiles which has the metal on it for heat protection. This will reduce losses in the cabinet in two ways - the large areas between the cabinet braces will still vibrate, but the added mass lowers the frequency of the resonance and the compliance of the sheets absorbs mechanical energy and significantly reduces how long the vibration might occur. This makes the speaker cabinet more dead than the braces alone can address. In addition, I designed the bracing so that no two large open areas were the same dimensions - this results in any resonances which may occur never being at the exact same frequency on two panel areas. Also, since the plastic port he used was so long and large (that's what she said), I recommended he wrap it with a couple of strips of the dampening sheets to eliminate any tube vibrations that might occur. Due to the large amount of bracing and deadening sheets, I recommended Heeman not install any acoustic dampening material initially and get the full efficiency of the cabinet's resonance at the tuning frequency. He can pull out the woofer and add some raw wool, Acoustistuff®, cotton fiber, fiberglass, or other sound absorbing material a little at a time until he finds the perfect balance of control and resonance.

Ultimately, these were designed to be musical, dynamic, and powerful with extremely low distortion and completely effortless performance in Heeman's rig. The construction was top notch, and much easier than I think Heeman was expecting.

 

[Flint]

I will add, Heeman was able to purchase what is perhaps the best High-Fidelity large format woofer in general OEM manufacture today. It was very expensive, but is unlikely to be outperformed by any other woofer in this class. When you start with the best ingredients and marry them with good design, the results can be astonishingly good.

 

[Flint]

We integrated these new cabinets using the MiniDSP 2.x HD DSP speaker controller as a simple crossover. Based solely on physics and best practices, we chose a crossover point of 300Hz, which is shy of being three octaves higher than the tuning frequency of the C1 cabinets. This will filter out any bass below 300Hz from going to the C1 woofer, thus freeing it from having to reproduce bass notes while simultaneously playing subtle midrange details. This should significantly reduce distortion in the midrange and virtually eliminate Doppler distortion which can sometimes be a problem when small mid-bass drivers are pushed hard. Heeman should get MORE clarity from the midrange than before. It also eliminates all potential for bottoming out the woofer. Heeman was pushing these little woofers hard - hard enough that at concert levels the bass range was losing its dynamics and getting flat sounding rather than exciting. It is a testament to the C1 that it can take such a beating and keep on playing music as well as it does - one reason they are worth the price.

To make it easier to adjust the settings, I recommended a Linkwitz-Riley 48dB/Octave slope to virtually eliminate any interaction between the C1 and the new 13" woofers and any issues with crossover phase or overlap are reduced to a narrow spot in the spectrum. This makes adjusting levels easy for a novice. Just measure the response and turn down the gain on whichever speaker is too loud until a target response curve is met. Simple.

Heeman loves his subwoofers, so while I have been strongly encouraging him to adjust the front speaker settings on his preamp / processor to "LARGE", thus sending all the bass to the front stereo speakers with not bass redirect, he is leery of that. So, for now he is using the traditional 80Hz subwoofer crossover on his pre/pro. I will eventually convince him otherwise, but there are some room issues that need to be addressed. When I visit to perform a serious measurement and tuning session, things might change.

The MiniDSP also has processing allowing us to add a delay to the signal of each output, so we will time align the signal for the cabinets, we can also add EQ and FIR phase tuning to the signals. This is going to be killer.

 

[Randy]

Outfrickinstanding!!!
Very cool project.
Great work to all.

 

[Flint]

By the way, when designing the woofer cabinets I focused on a baffle height which would work well as a speaker stand for the C1s, a width which would work well on new upper speakers should Heeman ever decide to build a fully custom three-way system, and the depth was whatever worked for to achieve the ideal volume for the enclosure. So, height and width were effectively fixed to address specific needs both present and future and the depth was whatever it needed to be. The concept of designing around internal dimensions which prevent internal resonances was ignored since I knew the woofer would not operate any higher than 400Hz.

 

[Deleted member 133]

Heeman loves his subwoofers, so while I have been strongly encouraging him to adjust the front speaker settings on his preamp / processor to "LARGE", thus sending all the bass to the front stereo speakers with not bass redirect, he is leery of that. So, for now he is using the traditional 80Hz subwoofer crossover on his pre/pro. I will eventually convince him otherwise, but there are some room issues that need to be addressed. When I visit to perform a serious measurement and tuning session, things might change.

Thanks. I was just above to ask about the electronics / signal diagram when you posted.

But regarding the quote above, I am both with you, and Heeman. I think the 80Hz subwoofer crossover setting is way too high, but I also think that running the F L/R on large with no crossover is perhaps not the best as well. Why not a 40Hz setting? There are some equivalent-to-LFE frequencies present in the F L/R channels of some source material, material that the dedicated subs, and not the new bass bins, should be handling - IMHO.

Jeff

ps. Need at least one more woofer bin under the centre!

ps. Congrats Keith!