[David Ellis]

I was intentionally vague about cabinet stuffing in my 1801 cabinet plans.  This is solely because I wanted people to experiment with this arena of cabinet building.  Experimentation with stuffing is very easy, and can be very audible.  I sincerely hoped for some of my customers to experiment and provide some feedback about what they heard.  Well, it hasn't happened.  Hence, I am formally sharing exactly how I stuff my 1801s.  

These pictures are NOT intended to be THE only method of stuffing the 1801s.  It is, nonetheless, how I stuff my 1801s.  I have experimented with this somewhat, and this my method.

There is no foam in the back of the cabinet.  The center region between the vertical braces is fully lined with foam.  The front region is lined on the deep side, top, and bottom.  Poly batting is then thumb-tacked to the first brace with overhang on the shallow side.  The "deep side" and shallow side" are created by the slight woofer offset.

These first two pictures were taken before the poly batting is placed behind the woofer.





These next two pictures were taken after the poly batting is placed behind the woofer.

[salva]

Yes ...

OK, regarding stuffing ...

It was clear to me that the center section was fully lined, and the front
section was partially lined with only top bottom and the side furthest from
the woofeer.

Now, the poly batting is directly behind the woofer.

- What was expected to achieve with that ?

- Why don't just use foam instead of poly batting ?


Salva

[David Ellis]

There are a few issues happening here. Hopefully I will make good sense of the issues with my remarks.  These remarks pertain to material directly behind the woofer only.  My remarks aren't intended to supplant the Master Handbook of Acoustics by F. Alton Everest (an excellent text).  They are intended to address the basic issues present when hanging some stuffing material behind the woofer.

The obvious objective is to kill the axial mode behind the woofer that will effectively bounce between the front and back wall of the cabinet.  The trick is to accomplish this without adding theoretical mass to the woofer and without killing the bass resonance of the cabinet.  Avoiding these latter artifacts requires judicious use of stuffing material.

Since there ins't any physical space on the back wall of the cabinet, I decided to hang some stuffing from the first brace.  Intuitively this makes the most sense.  Tis' better to kill that wave before it propagates too far.

Using a heavy stuffing material effectively kills the back wave, but also couples with the cone and kills the cabinet resonance (i.e. bass).  The former is obviously good.  The latter is bad in this application.  In other applications, adding theoretical mass to the cone  is desireable - like some subwoofers.  The degree the stuffing couples with the cone depends on the type of stuffing, the distance from the cone, and the frequencies present.  The impact of the frequencies depends on the stuffing material too.  Not all stuffing material has the same mass, or the same coefficient of absorption.  Explaining the mathematical detail in any specific setting is brutal.  Understanding the basic tenants/tendencies are fairly simple.  

Heavy stuffing kills the back wave, couples with the cone, and kills the cabinet resonance.

Light stuffing will attenuate the back wave, not couple with the cone, and have little impact on cabinet resonance.

I tried several materials behind the cone, including foam, and found about 3/4" of polyester batting the best compromise.  I accomplished frequency response measurements during my testing, and found little/no change.  I did not accomplish impedance measurements.  My decision about stuffing material was base purely on subjective impact.  I liked a light layer of poly batting the best.

This is not the only method viable for stuffing a ported cabinet.  The gent who initially inspired me to build speakers, Mike Bengfort, uses a softball size wad of acoustastuff behind the woofer in his ported cabinets.  He does a bunch of tuning by ear.  His results are excellent, and I certainly cannot fault him.  His methods work.  Hence, there are other viable methods for cabinet stuffing.

[Val]

Dave, have you tried lambswool? Old timers used it exclusively, of course there weren't the many options available now, but they knew a thing or two.

[David Ellis]

Yep,

I tried genuine Lambs wool - the heavy/coarse stuff.  I purchased it from the Wool Warehouse in Billings Montana.  This guy bought/sold wool by the ton, and gave me a box of wool.

There really wasn't any differnence between the wool and other stuffing material.  Also, after sitting in my basement for about 18 months, the box became much lighter.  It was infested with little bugs - eating the wool.  It was pretty gross, and I threw the box in the garbage.  

I suppose treated wool might be acceptable for speaker stuffing material, but this is too much hassle for little/no impact IMO/IME.

Dave

[David Ellis]

I'll try removing the stuffing in the center section, and will do the lining the walls. What's the name of that black thingy which Dave lined the wall? Egg crate? I should get some next time I go to WalMart.

I will occasionally use Black Hole 5 to Line the center section of the 1801s.  On this speaker I also used some BH5 in the deeper front section, top & bottom.

I must admit hearing a very slight improvement with BH5 in the 1801s. http://www.soniccraft.com/parts/blackhole5.htm I hear the improvment with middle register piano keys.  Almost nobody heard the improvement with BH5 in the audition 1801s.  As such, I don't recommend you spend $ on BH5 until your system electronics are very good.  

Wal-Mart egg crate mattress pad foam is just fine.  I use this stuff most often.

[Doug Kim]

I recently changed the stuffings in my 1801 kit according to Dave's suggestion.
At first, I stuffed first and second section of the cabinets with poly-fils purchased at WalMart. Bass was a problem.
Now, as can be seen from Dave's photos, I lined 4 walls of first and second section with Black Hole 5, and I put poly-fil netting behind the woofers. I did almost same with Dave.
I wanted to try listening the differences in the stuffing procedure, but I was lazy to do it. I mean, it will be a good experience if I listen the difference after lining second section, and then first section, and then netting.
Anyways, after doing the new stuffing, the bass got deeper and fuller, and the midrange became richer.

When I listened to Tchaikovsky's 1812 overture (conducted by Antal Dorati) at very high volume level, I was just amazed how fast and deep bass this 1801s can produce.

I'm going to write a full review later, but if I'll mention a little bit of comparison between 1801 and Harbeth Compact 7 ES-2 :
- imaging is better with 1801
- low level performance is better with Harbeth (I don't think this is a shorcoming of 1801. Harbeth C7 really shines at low level playing)
- Harbeth's bass is slightly faster, 1801's bass is slightly more solid.
(All IMO)

Doug

[David Ellis]

When you lined the cabinet with polyfill previously, did you fill the center of the cabinet or just line the walls?

I do apprecaite your response and sincerely hope that more folks will contribute their findings.  If they contribute to my conclusions - good.  If others find something that works better - great!

Dave

[Doug Kim]

I filled the first and second sections at first, didn't line the walls.
I think that is the way to stuff a "mass loaded transmission line speaker".

Doug

[BrunoB]

When you lined the cabinet with polyfill previously, did you fill the center of the cabinet or just line the walls?

I do apprecaite your response and sincerely hope that more folks will contribute their findings.  If they contribute to my conclusions - good.  If others find something that works better - great!

Dave

Here is my finding: go to  Wal Mart, buy a Simmons Beautyrest SmartFoam Pillow (~$19), cut the foam into 1 inch thick slices and line the wall using foam glue (3M).

Memory foam is much denser than acoustic foam. It is very soft. I think that it is a better material than acoustic foam. I am using it to line my VMPS 626 speakers. So far I liked it better than BH5.
I hope someone else would like to try as well.


Edit: I bought a second pillow at WM and found that the foam was different: color is changed (orange), more holes and faster recovery. Seems to be not as good as the first batch.


Bruno

[natemil]

Hi,

I came across something interesting in regards to this subject.  It is information on furnace insulation blanket.  

http://www.anvilfire.com/sales/ThermalCeramics/514-205.pdf

At the bottom of page 2, it has data on acoustical performance per ASTM and sound absorption coefficient.  I'm not sure what this means since I have not seen other materials' data to compare.

Would appreciate any feedback.  Thanks,  Doug

[David Ellis]

My hunch is that Wool Furnace Insulation blanket is very fire resistant.  I'm certain it's better than acoustic foam.  This is likely why these products are produced.

Owens Corning also has some Absorption numbers on their web site.  The Master Handbook of Acoustics (Everest) has some numbers for various materials too.  All of these are very tangible and usable.  

There are indeed methods to these numbers that have a VERY scientific basis.  I think it's great that manufacturers can and do objectify their products with absorption coefficients at various frequencies.  It certainly provides some basis to what is heard.

So, if you want to try some of this blanket - great!   It'll be even better when you post your findings here.  I suggest you try the 4pcf stuff and experiment with how much & where you place the wool.

I must also admit that I find very small changes with stuffing material.  Sure, Black Hole 5 is the best, but the changes are not very pronounced.  Most folks can't even hear the changes/improvments.

[BrunoB]

My hunch is that Wool Furnace Insulation blanket is very fire resistant.  I'm certain it's better than acoustic foam.  This is likely why these products are produced.

Owens Corning also has some Absorption numbers on their web site.  The Master Handbook of Acoustics (Everest) has some numbers for various materials too.  All of these are very tangible and usable.  

There are indeed methods to these numbers that have a VERY scientific basis.  I think it's great that manufacturers can and do objectify th ...

What about some activated carbon with pore size optimised for air molecules? That sounds even cooler!
No kidding, Kef is using this technology:
http://www.hometoys.com/htinews/feb04/articles/kef/ace.htm

[David Ellis]

I managed to model the W18 driver in a 7 liter enclosure with no stuffing:



This is the same driver in the same cabinet with 100% fiberglass stuffing:



Please compare these graphs to the before and after graphs on the KEF page.

I believe "a picture tells 1000 words" .  However, if you require further explanation, I can easily dispell all the marketing hype on the KEF page.  Please let me know if you require a full explanation.

While it's true that I am very irritated with much of the B.S. hype found in commercial loudspeaker manufacturing, I would rather not directly discredit their marketing with long narratives and explanations.  This is bad practice.  It also requires considerable time and effort.  Smear campaigns in loudspeaker manufacturing can certainly be on par with the very best political efforts.  However, I would rather not engage in such effort.

I'd rather focus my effort on tangible postive results.  As such, I have no problem with anyone comparing the 1801 to any 2-way offering from KEF.  I am very confident in the outcome.

Sincerely,

[MemphisJim]

Hi all,

Dave wanted me to post this information...

I just got done with a set of 1801's. I'll have a review and photo's up sometime in the near future. Short take, they are incredible.

Background on speakers: I used an extra 1/2" piece of mdf on the back of each cabinet. I also used whispermat 2 on the inside back wall and I used whispermat 1 on the side walls in the first and second chambers (from the front).

When I first completed the speakers, I left out the dacron stuffing included in the kit because I got in a hurry and I wanted to see how they sounded to make sure I didn't do anything wrong xover wise. I had the whispermat already glued in. The speakers sounded incredible and I started playing around with a lot of different cd's to see how everything sounded. I found that cd's had a wide range of quality. Mostly bad (in my collection) outside of my sacd's and dvd-a's. But I did run across a few gems such as the live cd from Natalie Merchant. This sounds incredible, but I noticed something on this cd (and a few others like the Dead's American Beauty DVD-A) that bothered me. There was a boom present in the bass. It wasn't on the first portion of the note played, the boominess was on the back end of the note, so to speak. It was bothersome. I heard the boominess on other cd's and sacd's/ dvd-a's, but I can't remember what all of them were, I just noted the sound so I could question Dave about it when I got a better feel for it. I figured it was my room and that I was going to have to put bass traps in the corners (probably not a bad idea anyways).

Well, I did question Dave and he said not to remove any of the port tube, but instead to lengthen it. I opened up my speakers and remembered the stuffing. I grabbed it from the kit, cut what he included in half and then placed each half into the cabinet right behind the woofer as outlined earlier in this thread. The response was enlightening to say the least. The boominess was GONE! At first I didn't like it as much because the feel of the bass dropped across most all cd's. Well, the word "drop" is probably not the best term. "Balanced" would be a better term.

Dave had mentioned to me that these speakers can make bad recordings unlistenable by showing all the flaws of the recording. Well, I see what he means. Before the stuffing, I have plenty of cd's of bad recordings that would be listenable. Now, they are mostly unlistenable (at least from a sweet spot point of view). Now that the bass is more balanced, wow. The good recordings sound even better, fuller, more balanced.

Jim

[David Ellis]

I really appreciate your subjective input and will offer some of the theory behind what you heard.  I believe your hearing is accurate, and there are good reasons that support what you heard.

One theory is that inserting the poly batting behind the woofer slowed the sound/air travel inside the cabinet.  The result is that the cabinet appears larger to the driver and the bass response gets leaner.  This is certainly one possibility, so I must allow that it could be happening.  However, I really don't think this is overwhelmingly valid in this case.

The second issue present, that IS valid in this case, is that the poly batting actually kills some of the cabinet resonance in the bass region.  The resonance I am referring to is the resonance setup by the port & driver inside the cabinet.  This resonance is desired.  Theoretically, the frequencies @30hz - @60hz are quite low, and the impact of the poly batting will be minor.  However, many folks use stuffing material in transmission lines to slow sound propagation.  Hence, I believe the poly stuffing does indeed have an impact and does indeed kill some of the bass resonance inside the speaker.

I this regard, I must admit, that I heard very little/no impact in the bass region when I accomplished po.  However, it certainly might be present.  I cannot argue with Jim's findings, and I haven't returned to testing this for @ ... 2 years.  The next time I complete a pair of 1801s I will take some measurements of this phenomena and post them here.

Well, I did question Dave and he said not to remove any of the port tube, but instead to lengthen it.

Yep, this follows comments elsewhere about port length.  Ports make bass tuning very easy.  The port provides a bass bump of reinforcement as the woofer rolls-off.   A shorter port will raise the frequency of this reinforcement (more boom).  A longer port will lower the frequency of bass reinforcement (deeper and leaner).  In this regard, if there is too much bass with the standard port tube, it needs to be longer.  I suggest adding length to the port tube.

Needing a longer port has never actually happened.  However, if I had to accomplish this, I'd simply duct tape a piece of 2" PVC to the end of the port tube.  This will be extremely tedious, but it will work.  Many manufacturers actually use PVC housed around a decorative rounded external flange for port material.  PVC is fine stuff for port material.

The subjective part of the midrange impact by the poly batting is very simple.  The poly batting kills some of the midrange cabinet resonance and cleans the midrange.  I didn't find a huge impact when I accomplished this.  The impact was very minor.  Nonetheless, the impact was present, so I continued to place the poly batting behind the woofer.

Hopefully I didn't confuse the matter further.  Thanks again Jim for posting your comments.

[MemphisJim]

Thanks for the reply Dave-

I probably ought to expand on things a little that I didn't put in my earlier post. I am primarily using two different amps to drive these speakers (for the time being). One amp is a new Sony ES receiver (DA4) and the other is a Parasound 2200 II mk2. The Sony amp is advertised at 100w/channel (we all know it is less than that). The Parasound is advertised at 250W/ ch into 8 ohms and almost 400W / ch into 4 ohms. I use this thing in mono mode for my sub. It puts out almost 1000W that way, he he. Anyways, the Parasound amp has a very high dampening factor and it can really control a woofer.

The boominess I described was much more noticeable using the Parasound amp than it was using the Sony amp. The bass in the Sony amp was and is weak and mushy. The midrange is ok in the Sony, but it just doesn't have the guts to push the 1801's. However, the Parasound does and then some. The 1801's just sing using this amp basswise, I'm still not so sure I like the rest of the sound from this amp though...

In closing, I just want to reiterate that the extra power on tap in the Parasound amp made the boominess much more apparent and I'm not sure whether or not it might be heard as well using an amp with a lot less power??

Jim

[David Ellis]

First, one end of this I would like to comment on is the generally accepted power ratings of HT receivers.  The informal (not enforced) industry agreed upon standard for HT receivers is 1 channel driven at the required power rating at a time.  The manufacturer will then switch to the next channel to demostrate it's ability to support XXX watts/channel.

With old 2 channel (i.e. Stereo) receievers, the enforced industry standard was 2 channels being driven simultaneously.  The obvious impact is the power supply in these amplifiers could easily support the increased power load of 2 channels.  This stands in striking contrast to darn near ALL HT receivers having VERY whimpy power supplies, and very light weight.

This is why many older stereo receivers seem to be very heavy, and push much more power than newer HT receivers.  Guys have contended for years that their Vintage Marantz 2270 really had gusto, and regret replacing it with a newer HT amp.  

Now... to the bass heavy sound... I heard this once too with the 1801s.  I don't think it has anything to do with the whopping power handing of the amplifier.  It has everything to do with the high dampening factor and required amplifier feedback circuitry for this high dampening factor.  I have just "cracked the surface" on this concept, but most tend to agree.  I submitted my concept to the "jury" at the Madisound Discussion Group, and found my thoughts right on the mark.  My explanation will be very elementary.

Amplifier feedback is ideally all negative, but some positive slips through.  The result is a bit of grunge heard in the midrange.  Another result is increased bass "snap".  I heard this as heavy bass with the 1801s. The bass was very nice, but the reduction in midrange quality really made the bass become more prominent.

In most practical listening situations, the amplifier is pushing 2-3 watts average through the 1801s.   When the 1801s are used loud there are @10 watts average being used.  The dynamic peaks are 5-10 x higher, but even at this power level, having a good stereo 100wpc is a bunch of amp for any practical (non beer party) home.  However, guys at fraternities will certainly want more juice on Friday evenings   .

Hopefully this is helpful.  Please let me know if you require further clarification.  I must admit some of this amplifier chat is at the "edge" of my knowledge.  I am a speaker guy, not an amplifier guy.