Phil's build thread, split from the big BG Ribbons thread.

[PhilDSP]

Edit by moderator This build is unique and interesting. So it didn't get lost in the shuffle posts about it were split from the massive 'BG ribbons Part 27 thread'.

That looks intriguing chasw98. I'm taking a slightly different approach. This is just a prototype without an array but it's already taken an enormous amount of time to construct.

[PhilDSP]

With the core baffles glued in place and carefully sealed I attached the outer panels using straps and clamps, sealed some obvious leaks with clear packaging tap and proceeded with some measurements. The interior of the box is entirely empty at this point. According to my estimates and simulation the unit should have had an f3 between 16 and 18 Hz. But I was very pleasantly surprised to measure 12 Hz to 45 Hz +-3dB and 14 Hz to 42 Hz +-1dB.

The problem is a very pronounced resonance in the next octave higher as all TL's will have. The trick will be to eliminate that resonance with damping material while preserving as much of the low extension as possible. I suppose an option would be to leave the box empty and cross over around 70 hz.

In music listening tests that followed at high volume at one point was a very strong full range bass note. I don't remember if it was an electric bass or was synthesized. The system handled it without problems but the lights dimmed suddenly and intensely from the power demand. That was fun :P

[JonMarsh]

Clipping causing cross conduction in your power amp between the supply rails? (some power amp designs with a lot of feedback don't have anti-latch protection in the drivers- learned how to fix that back in the 70's, but you still see it in some designs) Normal output function at full power continuous sine waves shouldn't dim the lights... :W

[PhilDSP]

Could be. I've been meaning to call an electrician though. There's likely something limiting the current in the mains. The water pump for the well also causes the lights to dim a tiny bit.

[cjd]

If you've got crap for caps in the amp and are running near capacity of your house line you could probably dim the lights also - surge on reloading a large toroid transformer sucks up the power like crazy (been playing with tiny little 600VA toroids and found this out on my stretched-near-the-limit basement circuit).

On the other hand, getting my wife to come down and laugh about the bass shaking the house (that's 4x15" Tempest-X manifold mounted and a hefty Face amp powering them) and no dimming or powerline sag at all - firing up our laser printer will trip the battery backup and I've never done that with the HT.

So yeah, I suspect something isn't right if you're dimming the lights. Take care of that before it turns into a fire.

[JonMarsh]

Older laser printers and hair driers (like my daughter's) are amazing power hogs- as you note, Chris, on startup, particularly.

Another possibility is clipping and asymmetric transformer loading on the +/- supply caps, causing the toroidal transformer to saturate and drop current straight across the primary. (yeah, I used to design pro audio gear in a past life for a living- back when 'fro's and shag carpeting were popular).

[cjd]

Another possiblity is that it IS pushing the driver to xmech and the voice coil is shorting out overloading the amp. I've had that happen in a couple systems.

[PhilDSP]

The power amp is a Rotel RB-1070 - not a shabby unit at all (for the price) from what I understand and have experienced. And yes, it does have very large toroidal transformers. Maybe this weekend I'll pop the cover and check the values of the caps and listen to the same recording again to see if it consistently occurs. I'll also check the speaker simulation to see if it predicts a heavy impedance drop below the resonance point of the driver and maybe even get around to measuring it.

The lights do also blink sometimes when the amp is powered up. I've heard others that noticed that too. So this is probably a combination of factors.

[PhilDSP]

Here she is in the buff. There are 4 10mF filter caps manufactured by BHC (the PEH200 series) in England and rebranded for Rotel. They're billed as having a 60000 hour operational life by the manufacturer, so I think they're one of the most robust caps available.

The unit is receiving a 2 phase 240V supply I presume. I'm wondering if the 63 VDC rating for the caps could eventually be a problem. It seems a bit low.

(New picture of the RB-1070 uploaded Aug. 11)

[PhilDSP]

The light dimming occured very consistently on the chorus of a song called "Wingspread" from Ritual's first album. It's a somewhat recent recording (2004) with high intensity electric bass and bass drum both containing a large amount of sub 40 Hz material. Albums from the 70's or 80's are never that demanding - production values have change in the last 10 or 15 years. The cone was definitely moving beyond the linear excursion zone and looked to be close to Xmax, though I heard no evidence of either failure or noticable distortion.

The simulation shows that without cabinet damping, the impedence drops to about a quarter of the nominal value below Fs. Since the 2 compound woofers are run in parallel the impedence must have dropped to less than an ohm. So it's no wonder that a very high power demand was created. Once the cabinet is properly damped the impedence will return to slightly above the nominal value below Fs so that problem should be resolved according to the simulation.

It's probably very fortunate to be able to probe the limits like this. I now know that the Ritual album is an excellent gauge of system performance. Both the music and audio production is first rate and exceptional. But at the same time it's very challenging for a speaker and amp. Whatever is not up to par will be exposed. Very similarly to looking through an out of focus lens, an out of focus or out of balance loudspeaker system presents a murky and incoherent picture of this recording.

P.S. I was curious about how well-known the album is and came across a couple of reviews and even a listening site. It seems the album was recorded in 1995 but remastered in 2004.

http://209.85.129.132/search?q=cache:FQrQkO55bbAJ:www.answers.com/topic/ritual-rock-album-6+ritual+%2B+wingspread&cd=7&hl=sv&ct=clnk&gl=se

http://www.musicomh.com/albums/ritual.htm

http://www.qloud.com/song/Ritual/Wingspread_--t_13619578.php

[JonMarsh]

Since the 2 compound woofers are run in parallel the impedence must have dropped to less than an ohm. So it's no wonder that a very high power demand was created. Once the cabinet is properly damped the impedence will return to slightly above the nominal value below Fs so that problem should be resolved according to the simulation.

Now THAT's an interesting situation- out of curiousity, what is the nominal value below Fs? What frequency range would it be dropping to under an ohm? If you have a box sim, I'd be curious to see it, if you're willing to share. Might be interesting to run that cut through True RTA in narrow band analysis and see where the energy is.

[PhilDSP]

I'm using George Augspurger's TLwrx software to get a rough idea of the results. I'll see if I can capture some screen prints tonight. But the package handles impedance and some other parameters in sort of an abstract way. I'm interpreting the nominal impedance to be 4 ohms (8 ohms per driver in parallel)

[PhilDSP]

Here is the simulated response of the cone and the port separately. The cone radiation is the solid line and the port radiation is the dotted line. The blue line indicates the empty box response and the red line is the response after a certain amount and type of damping material is to be used (that I selected)

Since there is a non-linear phase relationship between the cone and port output the sum needs to be taken using complex math. That is taken into account by the simulation software. The software doesn't present both undamped and damped response in the same window unfortunately. It took a bit graphic manipulation to achieve that.

[PhilDSP]

Here is the combined output. This is only a very rough estimate of the response of the prototype because TLwrx doesn't model the channel configuration that I'm using. The response I'm seeing is extended further down in frequency and has quite a different resonance pattern.

[PhilDSP]

Here is the cone excursion modeled. The interesting thing is how nicely leveled off it becomes as you go down in frequency under 40 Hz. That means it's a very stable system with no major risk for destroying a well-engineered and capable driver.

[PhilDSP]

The impedance diagram. Here too, the numbers are likely to be higher that the actual response of the prototype below 40 Hz. As you can see these are relative values. The flat base probably maps to about 3 ohms.

[ThomasW]

Just an FYI, you can put multiple attachments in a single post..

[PhilDSP]

It's taken several weeks to cut and secure all of the damping material in the woofer's channel. 8 large cans of spray contact cement will have been used at a cost of $ 120.00 for one cabinet alone.

A quick listening session of the now damped cabinet revealed very substantial differences in comparison with the same driver placed in a ported cabinet. Obvious was how much more detailed, sculpted and articulate the sound was coming from the long TL. And how tremendously more percussive it is. Electric bass glissandi just explode with life and prominence. Different pitches and octaves of any type of bass instrument are very clearly differentiated and the entire signal is so much more transparent - a large amount of cloudiness that I previously thought might be a characterization of the instrument or the recording technique or media is gone.

It may even be proper to start to talk about stereo image and spatial resolution for bass, even very low frquencies. I can very clearly hear the ambience of the room apart from the instrument itself. Similarly the image between the 2 channels emerges. I recently had a discussion with a local hifi buff who still believes the 80's misconception that the radiation point within a stereo field of a low frequency emitter can't be sensed. He is one of the people who will be present at the first public listening session for the prototype so it will be interesting to see his reaction.

[JonMarsh]

Yeah, my favorite kind of people in audio are the ones that say, "You can't hear that, it doesn't matter".... :W

[PhilDSP]

The RD75 will be placed in a heavily damped tapered TL tuned to about 200 Hz (well below the 600 Hz crossover point). The freedom from resonances, reflections and non-uniform loading should result in maintaining the RD75's superb transient response and clarity. I figure that should give the system nearly all of the advantages of a dipole open baffle configuration without the backwave interference.

The nearest baffle edge to the RD75 will have about a 6" diameter curve so diffraction will be gentle and minimal. My impression from listening is that the large 6" tall baffle helps create an enormous soundstage even without a line array of drivers in place.

[PhilDSP]

Capacitor smorgasbord ready for placement in the 4 way crossover:

Fountek NeoCD 2.0 (4Khz HP) - Clarity MR
BG RD75 (4Khz LP 600 Hz HP) - Clarity MR
SB Acoustics SB15 (600 Hz LP 150 Hz HP) - Audience Auricap
SS 25W/8567-SE (150 Hz LP) - Clarity ESA (or Auricap)

Other caps here such as Clarity PX are for evaluation purposes or to lessen the initial cash outlay and will eventually be replaced/upgraded.

[evilskillit]

Just makes me think of my amp. I have an old Parasound HCA-1000 which I am rather fond of. When you switch it on the lights dim noticably for a second during, probably due to inrush of the big torroidal transformer.

[JonMarsh]

It's taken several weeks to cut and secure all of the damping material in the woofer's channel. 8 large cans of spray contact cement will have been used at a cost of $ 120.00 for one cabinet alone.

A quick listening session of the now damped cabinet revealed very substantial differences in comparison with the same driver placed in a ported cabinet. Obvious was how much more detailed, sculpted and articulate the sound was coming from the long TL. And how tremendously more percussive it is. Electric bass glissandi just explode with life and prominence. Different pitches and octaves of any type of bass instrument are very clearly differentiated and the entire signal is so much more transparent - a large amount of cloudiness that I previously thought might be a characterization of the instrument or the recording technique or media is gone.

It may even be proper to start to talk about stereo image and spatial resolution for bass, even very low frquencies. I can very clearly hear the ambience of the room apart from the instrument itself. Similarly the image between the 2 channels emerges. I recently had a discussion with a local hifi buff who still believes the 80's misconception that the radiation point within a stereo field of a low frequency emitter can't be sensed. He is one of the people who will be present at the first public listening session for the prototype so it will be interesting to see his reaction.

Just for reference, your description reminds me of my current impressions of the bass performance of the Ardents- - which are ported, but have a hell for stout cabinet construction- certainly a contributing factor, I think. Even complex fusion jazz pieces are reproduced with a clarity in the low ranges that is well beyond other designs I've done with just dual 7" midwoofers.

Please keep us posted as you work on and refine these.

[PhilDSP]

Just for reference, your description reminds me of my current impressions of the bass performance of the Ardents- - which are ported, but have a hell for stout cabinet construction- certainly a contributing factor, I think. Even complex fusion jazz pieces are reproduced with a clarity in the low ranges that is well beyond other designs I've done with just dual 7" midwoofers.

Your Ardents are really a nod in the direction of a shorter TL though aren't they? As I remember the pipe for the port is quite short and the channel between the woofer and port is elongated and somewhat tapered with an irregular geometry. I'd certainly be interested in more perceptions and analysis of the outcome of the Ardent project.

I used to think that upper midrange with plenty of sweetening with ambience and easily detected spatial definition was where the bulk of worthwhile musical energy was centered. But now I'm more like an addict with a dependency on the high intensity flow of energy starting in the very, very low regions. The artistry involved in setting the rhythmic and tonal foundation to the music in an interesting and expressive way can be amazing and normally there is a very tight connection and communication between bass and percussion that the music can't live without.

After using up a lot of vacation time on the project and many, many nights of work until 2:00 or 3:00 in the morning I'm down to the final 12 sawcuts and last few hours of construction work before sanding and painting the prototype cabinet. Everything has been very complex and challenging and a couple of times I was nearly ready to give up out of exhaustion and frustration with things being so difficult and time consuming. Hopefully the moment of truth will make it all worth while.

[PhilDSP]

Testing the fit of the RD75 in the box before appying damping and finish.

Various stages of completion of the box. Only a few coats more of paint to go...

My favorite local Hifi shop just got in a used speaker system by a well known manufacturer. It was a top of the line model that cost in the vicinity of $ 200,000 and has been touted by reviewers of various Hifi magazines as one of, if not the best system available. It had a big sound, though not as big an image as the prototype here projects. I think the RD75 is primarily to thank for that though the solidness and authority of the bass contributes also.

The lowest bass octaves were somewhat weaker in presence in the commercial speakers than my former BR cabinets, so the high priced commercial unit would likely never hold a candle in any environment to the prototype which, as I've previously detailed, delivers exquisite resolution for both audible and sub-audible frequencies. I've done extensive measurements to certify that the prototype's (and my previous BR system) are flat in principle throughout the low end so I know that nothing is exaggerated in the prototype's bass response.

The expensive system had a light reverbiant sheen behind everything - kind of globular and indistinct. It didn't quite sound real to me as I'm used to the RD75's superb ability to separate the direct signal from room reflections and therefore portray a true picture of the spatial environment. Neither did the stereo image seem coherent - especially across the various octaves. The image also was very flat with little to no depth. Except at one moment a particular bass instrument sounded cavernously deep but after a moment when the instrument stopped playing that effect disappeared. I suspect the incoherence was mostly due to the crossover design where phases can be ill-matched between drivers. And also maybe differences in driver material producing clearly different resonant characteristics. Resonances are pretty much not a problem with the RD75 and NeoCD 2.0 assuming the enclosure doesn't create any.

At the dealer's shop I was definitely listening to a loudspeaker system, though a rather high quality one by commercial standards to be fair. The general listening experience was washy and vague compared to what I've been hearing the last few months. With the prototype you can feel the impact of every sound. The sharp transients of the bass are matched very nicely with an equivalent sharpness up into the mids and treble, once again thanks to the RD75's magical quickness I believe - not just in quickly producing a required signal but quickly removing it when it's gone from the source material. Even cymbals, for example, are vividly felt not just heard. That produces a very, very satisfying experience that nothing else can make up for.

And all of this the prototype has shown in very incomplete form, being fed by cheap electrolytic capacitors and iron core inductors (The proper crossover hasn't yet been built). And my player and amplifier is quite modest compared with the enormous class A system in the dealer's room. This is not at all to say that the commercial system was shabby. All of the other listeners were kind of oooing and aaaahing. But I know that there's more to had...

[PhilDSP]

A 10 gauge Copper Foil inductor versus a 18 gauge wire inductor of a similar value. Any idea which one will sound better?

One of the sites spoke about putting your money into copper ballast in regard to the Mundorf foil inductors. They weren't kidding! The larger one here is near the limit of how much I can lift with one hand. And I'll need 3 of them per cabinet plus one with a much larger value and others with smaller values. The foil inductors are wound *very* tightly and are extremely dense.

[Speedskater]

While they could very well sound different, after all they have different series resistance and different current capacity. It will depend on what tasks a particular crossover component has, before determining which sounds better. Sometimes the high series resistance is a positive thing. Sometimes the limitations of budget capacitors are an asset to the crossover design.

[PhilDSP]

I think you're right. The 10 gauge units are to be used for woofer and mid-woofer where most likely I'll want as much output as possible under 300 Hz. But during testing that may change if the bass starts overpowering the RD75. But I think everything is pretty nicely balanced from the start so that shouldn't be a problem.

[PhilDSP]

From the large BG Planars thread:

You'll get a cleaner response out of those RD75's with a baffle to support the lower mids; even then, my preference is about a 600 Hz crossover.

You weren't kidding Jon! During the last week or so I've been listening to each driver separately in the finished cabinet whilst I work on building the crossover. It makes a very large difference with the RD75 in the cabinet and the TL configuration for the RD75 enclosure seems to work extremely well. It produces about a 4 dB gain in volume in the enclosure compared with the pure dipole/no baffle configuration and projects a much more robust and defined sound with better stereo separation. Even the highs are sounding excellent. You do lose a bit of the wrap-around effect of being to stand anywhere around the speaker though and the image between the left and right sides is not quite as full, but IMO I'd choose the TL enclosure every day of the week.

I've also been able to compare using a non-polar electrolytic capacitor as a high pass filter versus an Auricap. Big difference there that I can hear. There is a distortion present, an uneven FR, lack of depth, a drop of about 2 dB and a loss of resolution compared with the Auricap. With the Auricap I'm surprised every time I listen at how fabulously good and faithful the sound is and am so intent on listening that I can't pull myself away for anything. With the electrolytic cap it's: "Yeah, this is not too shabby but it's time to go to sleep now."

Pictures to come soon...

[cjd]

Catching up on a slightly older post, but to answer: I believe Jon tends to tune his "ported" enclosures to what would more properly be considered a tuned pipe (quarter-wave? dunno) - at least as far as modeling responses go. For that matter, so do I.

Having compared two systems with the same mid-woofer but very different porting (my MTM vs another's) there was an open-ness in the midrange in my system (or a constrained sense in the other) - it's subtle, but very evident. And these were "budget" designs too.

I'm glad you continue to update here - not much response, but I know I'm following with interest and otherwise keeping quiet.

[PhilDSP]

Happy New Year to all! I now give to you "The Dark Menace". The cross-over needs refinement but is functioning reasonably well after some struggles to make it so. For one thing, the large low impedance foil inductors seem to require a much larger value than the simulator calculated. I'm guessing that the normal higher impedance of a standard coil adds a lot of extra damping to the response and a significantly lower Fs in comparison. The coil inductors produced 3 or 4 dB higher output than the smaller wire inductors.

On Tuesday I received a visit from some HiFi buffs who are musicians themselves who auditioned the system for several hours. Here are some of their comments (translated from Swedish):

"This morning we visited a Hifi consulting firm and listened to a $100,000 system. We're not sure exactly why it was the case, but the results were disappointing. It was simply not performing well enough to warrant the price. But your system sounds like a reference system should."

"It was well worth coming by to listen. The sound is very natural. When I start to listen to a track I'm so captivated that I don't want to interrupt it even to change to a track that I know is better."

"The front-to-rear depth is superb."

"The ceiling-to-floor image, even only with the mid-range frequencies, makes me feel as if I'm really in a concert hall."

"I'm very familiar with this cut. The vocalist's voice sounds so vivid, so real and it's such a satisfying listening experience. I've never heard that on any other system so far. So obviously I'm giving your loudspeaker high marks."

My own personal observations at this point: I was targeting a system that was lively, robust and accurate, much as a high grade studio monitor should be. I wasn't expecting a large amount of refinement but there's so much of that in conjunction with hyper detail and resolution that I'm extremely pleased. It was worth the very large effort needed.

Now I find the amount of information and the intensity of it overwhelms my poor little brain and nervous system 8O Midichlorians have become highly active in a frantic attempt to build new neural pathways and brain cells and thereby increase the information bandwidth of the soft machine :B The effect is similar to someone training in the martial arts or Kundalini yoga or Tai Chi I think. I only hope this isn't courting the dark side...

[Johnloudb]

Very nice build! The name fits it perfectly ... looks like you got some great feedback from people too! :T

Now I find the amount of information and the intensity of it overwhelms my poor little brain and nervous system

I did a build with that NeoCD3 tweeter and even though the speaker measured flat I found it that it was too bright for me. This took me awhile figure out, but I eventually dropped the tweeter down a couple dB.

We have some Nelson/Reed 804C speakers hooked up right now and they just don't have the mid-bass and bass that our broken 804B speakers had. Bass definition is excellent but just not enough, and it makes them sound really detailed but can be fatiguing on some recordings. Moving the speaker back helped.

I think the 804B had more BSC and we're trying to get those fixed up. So, I don't know if that's what you're experiencing, but just a thought.

[PhilDSP]

Very nice build! The name fits it perfectly ... looks like you got some great feedback from people too! :T


I did a build with that NeoCD3 tweeter and even though the speaker measured flat I found it that it was too bright for me. This took me awhile figure out, but I eventually dropped the tweeter down a couple dB.

Thanks for the comments. I can see how the NeoCD (2.0) could sound bright coupled with drivers that don't have a similar depth of resolution and quickness. The treble is very prominent but so are the other frequencies with this embodiment. I have everything (or will shortly have) within +- 1 dB for nearly the entire range from 20 Hz to 20KHz and wouldn't want to have anything else. A friend came over last night to listen and characterized the system as "relaxed" even as it's extremely detailed. The experience of being overwhelmed for me is very positive actually. All recordings so far have sounded much better on this system than my old one.

I feel the need to mention 5 disks that really shine on the system and that are probably unsong but are true masterpieces of both musicianship and engineering. They really exercise the system to its fullest, have many passages of superb beauty IMO and are somewhat gentle for progressive music. Except for the first all are tastefully flavored with exquisite Mellotron use. So for anyone who cares here is the list:

Ian Anderson - Divinities .................................................. ..... From Jethro Tull's flautist (no vocals here)
Illusion - Out of the Mist .................................................. ..... English music from the mid 70's
Celeste (self titled) .................................................. ............ Italian music from the mid 70's
PFM (Premiata Forneria Marconi) - Per Un Amico ("For a Friend") ... Italian music from the mid 70's
Greenslade - Time and Tide .................................................. . English music from the mid 70's

PS. I should mention that the flatness takes into account room acoustics. I'm measuring primarily from 3 meters. Fortunately a pink noise test is also very flat (pink noise results don't really correlate with room reverb - delay effects - but do respond to modes) That probably happens because of the cylindrical wave generated by the RD75 which reduces the prominence of reverb and also the extended directionality the bass produced by the long TL.

[villastrangiato]

Another possiblity is that it IS pushing the driver to xmech and the voice coil is shorting out overloading the amp. I've had that happen in a couple systems.

That would seem to be the most plausible explanation. In their published papers, Augspurger and Shultz spend a fair amount of time focusing on the benefit of transmission lines achieving critical damping with the appropriate amount of stuffing. This seems to be the most often overlooked aspect of TL bass in what you see in online discussions. Everybody seems to focus on the "enormous" 3 - to 5 db gain you get at the bottom end but in reality, it's the combined effect of reducing compression (acoustic suspension designs) and reducing the peaky resonance behavior that results in distortions induced by non linearities arising from overdriven drivers (bass reflex) by achieving near perfect damping. Acoustic suspension designs don't really mitigate the impedance peak at resonance. Ported designs seek to offset it in an arguably unstable way. But it is only the TL that has the potential of maximizing efficient use of the backwave while achieving critical damping overall. A TL without damping is like a bass reflex on steroids :righton:

The reflex designs give a narrowly define resonance to offset the driver's minimum motion point and impedance peak - but with an undamped TL - the uncontrolled third order peaks must have pulled a hell of a lot of current from your amp - your voice coils must have been glowing! :B

Based on your write up, it looks like you applied surface foam ala PMC to dampen the line - is that correct? What made you lean in that direction versus Acousta Stuff? Do you have any reservations about using it - like possibly a diminished ability to fine tune?

Very nice looking project, btw!! Those RD75 must be really sweet with that setup. :T

[villastrangiato]

I feel the need to mention 5 disks that really shine on the system and that are probably unsong but are true masterpieces of both musicianship and engineering. They really exercise the system to its fullest, have many passages of superb beauty IMO and are somewhat gentle for progressive music. Except for the first all are tastefully flavored with exquisite Mellotron use. So for anyone who cares here is the list:

Ian Anderson - Divinities .................................................. ..... From Jethro Tull's flautist (no vocals here)
Illusion - Out of the Mist .................................................. ..... English music from the mid 70's
Celeste (self titled) .................................................. ............ Italian music from the mid 70's
PFM (Premiata Forneria Marconi) - Per Un Amico ("For a Friend") ... Italian music from the mid 70's
Greenslade - Time and Tide .................................................. . English music from the mid 70's

Have you tried them out on high level close mic'd strings like some of the stuff from the late Michael Hedges (Ariel Boundaries - "Hot Type") or from Alex de Grassi? I bet the percussive sounds on those cd's would give your RD75's (and your ears) a bit of a workout.... :B

For other really cool percussive strings, I like to go back to an old cd I have that was transcribed from the Mobile Fidelity Sound Labs recording of Hiroshima. The Japanese guitar is beautfully mic'd and the effect on cuts like Kokoro is "other worldly".

[Amphiprion]

Yeah, my favorite kind of people in audio are the ones that say, "You can't hear that, it doesn't matter"...

I would like it noted that I am one of Jon's favorite people

[PhilDSP]

Acoustic suspension designs don't really mitigate the impedance peak at resonance. Ported designs seek to offset it in an arguably unstable way. But it is only the TL that has the potential of maximizing efficient use of the backwave while achieving critical damping overall. A TL without damping is like a bass reflex on steroids :righton:

Based on your write up, it looks like you applied surface foam ala PMC to dampen the line - is that correct? What made you lean in that direction versus Acousta Stuff? Do you have any reservations about using it - like possibly a diminished ability to fine tune?

Very nice looking project, btw!! Those RD75 must be really sweet with that setup. :T

Yup, everything you said was right on as far as I understand things. There no longer seems to be a problem with roasting the coils : since the damping material was added.

Actually the material you probably saw in the side where the RD75 vents is felt carpet. It looks good enough IMO to lie on the outside. Essentially all internal walls have a layer of it glued to them. On top of that I've glued at least one 1 1/2" layer of carpeted long fiber wool in most places. Legend has it that wool is a far superior material than anything else. I won't argue that myself but I'm completely satisfied with the results.

[PhilDSP]

Have you tried them out on high level close mic'd strings like some of the stuff from the late Michael Hedges (Ariel Boundaries - "Hot Type") or from Alex de Grassi? I bet the percussive sounds on those cd's would give your RD75's (and your ears) a bit of a workout.... :B

For other really cool percussive strings, I like to go back to an old cd I have that was transcribed from the Mobile Fidelity Sound Labs recording of Hiroshima. The Japanese guitar is beautfully mic'd and the effect on cuts like Kokoro is "other worldly".

A couple of weeks ago I listened to Ariel Boundaries (feels like I'm not spelling that right. Is it aerial?) before the woofers were added to the mix and it sounded spectacular - very shimmery and alive. I have to admit that it had never quite been one of my favorites but could be appreciated none-the-less. But now, yes, it's on the must listen to again and again list. Liona Boyd's classical guitar recordings are to die for now too.

I've heard of Alex de Grassi but it sounds like something to acquire soon. I'll look up the Hiroshima guitar stuff too.

[villastrangiato]

I have major ribbon envy.....lucky bastid