From: owner-bass-digest (Bass and DIY Loudspeakers Digest) To: bass-digest@lunch.engr.sgi.com Subject: Bass and DIY Loudspeakers Digest V2 #259 Reply-To: bass Errors-To: owner-bass-digest@lunch.engr.sgi.com Precedence: bulk Bass and DIY Loudspeakers Digest Wednesday, October 11 1995 Volume 2, Number 259 Important Addresses: Submissions to the list: bass@lunch.engr.sgi.com (or reply to this message). Adds/removes/archives: bass-digest-request@lunch.engr.sgi.com Real, live person: owner-bass@lunch.engr.sgi.com Topics: Crossover for Carver ribbons (active) ? Re: stuffing vented box enclosures Re: JBL tweeter "recall" Re: stuffing vented box enclosures Re: Bass and DIY Loudspeakers Digest V2 #258 Re: stuffing vented box enclosures Re: stuffing vented box enclosures Re: Lining a sub - lead, yes? Re: Crossover for Carver ribbons (active) ? Re: Crossover for Carver ribbons (active) ? Re: stuffing vented box enclosures Re: Lining a sub - lead, yes? Re: stuffing vented box enclosures ---------------------------------------------------------------------- Date: Mon, 9 Oct 1995 21:46:55 +0000 From: "Gary Sanford" Subject: Crossover for Carver ribbons (active) ? First off , I'm glad to say that I have found a home. This mailing-list is wonderfull! After building speakers for 25 years,it's great to find people as fanatical as I am. Anyway...just about the time I started lurking on this list my brother wanted me to build him some no-compromise speakers. What I came up with is, the Carver ribbons with 2 NHT 1259's on each side,with perhaps one or two ribbon tweeters crossed over at 8-10khz,6db per octave to fill out the extreme highs. O.K. All that stuff is ordered and on the way. My question is. Is the "Clearview" dedicated active crossover still available? If it is, whom should I contact? Also, is there any other frequency manipulation besides negating the 6khz resonance? Is this a resonance between the magnets or side to side in the frame? Any answers are very much appreciated! GS (As an aside to Mr. Hildebrand......my brother and I also keep reef tanks. It's like building speakers and having the parameters evolve :-) ) ------------------------------ Date: Mon, 9 Oct 1995 21:27:29 -0700 From: sdinfo@ix.netcom.com (John E. Johnson, Jr. ) Subject: Re: stuffing vented box enclosures Another question I would like to ask, as I can't find the info in a book: Does proper tuning of a port, whether the port is on the back, bottom, or front, always involve desiging it so that air coming out of the port is in phase (air moving out of port as driver is moving out of enclosure) with the driver, or are there exceptions? Since air is compressible and the reaction at the port is not instantaneous, the air coming out of the port must have a certain degree of phase shift with respect to the driver, depending on the frequency? John Johnson ------------------------------ Date: Mon, 9 Oct 95 09:56:07 EDT From: jar@aluxs.att.com (Joseph Reynick) Subject: Re: JBL tweeter "recall" Cory D. Wittenborn wrote: > JBL has a free replacement policy on the particular model of tweeter I have. I found that JBL often has liberal repair ploicies. Recently, I had a pair of 22 year old JBL L100's reconed due to a surround-rot problem. While they were at it, all the other drivers in the system were reconed, free of charge. Granted, these speakers had a lifetime warranty, but one of the tweeter domes had been pushed in during a paticularily good college party back in the roaring `80s, and JBL reconed it for free anyway. It turns out that the keywords to look for in your JBL warrantee are "without time limitation." BTW, JBL claims that they never repair the surround when it has rotted. They claim it is too risky, due to possible misalignment of the voice coil. So JBL always recones the speaker in the case of a damaged surround. It seems to me that the spider supplies most of the voice coil alignment, so this should be a rather simple and safe repair. I have seen several ads for surround replacement kits. Has anyone had experience with these? ====================================================================== Joseph A. Reynick email: j.reynick@att.com AT&T Bell Labs ====================================================================== ------------------------------ Date: Tue, 10 Oct 1995 17:40:42 +1000 From: c.oneill@trl.oz.au (Chris O'Neill) Subject: Re: stuffing vented box enclosures John Johnson asked: >Another question I would like to ask, as I can't find the info in a >book: Does proper tuning of a port, whether the port is on the back, >bottom, or front, always involve desiging it so that air coming out of >the port is in phase (air moving out of port as driver is moving out of >enclosure) with the driver, or are there exceptions? Since air is >compressible and the reaction at the port is not instantaneous, the air >coming out of the port must have a certain degree of phase shift with >respect to the driver, depending on the frequency? Above the box resonance, the air in the port is in phase (0 degrees) with the front of the driver (i.e. their displacements add up). Below the box resonance, the opposite occurs (180 degrees difference). Chris ------------------------------ Date: Tue, 10 Oct 1995 15:59:50 -0400 From: Peter Basel Subject: Re: Bass and DIY Loudspeakers Digest V2 #258 Asger Munk Nielsen writes: >In Denmark there has been some atempts to correct some of the inherrent > problems pressent in passive radiator designs, while >still preserving some of its bennifits, e.g. high bass output, and >no vent noise. > >The first attempts where made, by using an ordenary woofer as slave (radiator) >, and by connecting a resonance circuit to this woofer. I believe that a >simmilar technique is used in the Extrema, introduced by Sonus faber. > >Later the woofer was actually connected to the Xover, by means of a large >inductor. The "active" radiator was modified by cutting away some of the >spider (among other things this lowers Fs, and as a bonus lowers compression >), and by adding mass to the unit (again lowers Fs). These attempts have >been made by the DIY shop Dansk Audio Teknik, situated in Copenhagen, with >very nice results, e.g. they claim that it is currently the best way to >achieve a precise and controled bass responce (without active circuits, > I might add). A comercial system actually uses the techniques described >above, the danish company Primaere known for its outstanding design, uses >this in there loudspeakers (Little 16 - I believe. It employes a ceratec >ceramic dome, a 6.5" eton woofer, and a rear mounted modified 8" seas >woofer. This boutifull litle thing has won some awards in the East. > >I have read that the best results are gained by using a woofer suited >for vented designs as the main woofer, and a slightly larger woofer as >the active slave, e.g. 6.5" main and 8" slave , 8" main and 10" slave etc. >The size of the box should be aprox. the size of a vented bo, designed for >the main woofer. > > >Here comes the Question. (finally) >I have tryed to simulate this type of system in the following way, but >since I'm not an expert in this field I do not know if I am doing it right. > >I got out a text book on loudspeakers, and found a section covvering two >not identical woofers in a closed cabinet, with out the usual aproximations. >I modeled the pressence of the large inductor, by adding the value to the >inductance of the active slave. The added mass was acounted for in the >simulation by adding th>e mass to the mass of the active slave in the calculations. >I made a program capeable of showing the tranferfunction graphically. >The results seamed to indicate that the low end had a roll off between >6 and 12 dB pr. octave, wich was a bit of a surprice to me. I am pretty >shure that the program is correct, since I have made simial programs, based >on the same book, for the common box variations, all with results that are >equal to the programs you can get off the net. (yes I could have saved some >time, had I only known that these programs existed on the net, when I went >down to the libary and got out the book). >The results allso seamed to conferm the ruel of thumb about the box size. This topology where two drivers share a common enclosure was patented in the US by Nestorovic and Modafferi: LOW RANGE LOUDSPEAKER SYSTEM, #3,984,635 in 1976. The patent covers topologies with many different networks between the input and the auxiliary radiator (AR). Unfortunately the patent doesn't provide in depth technical analysis. The authors have chosen not to enforce this patent and the 2C and 3 series loudspeakers from Vandersteen employ the topology that you describe. Don Keele provides an excellent review and theory of operation in the review of the 2c(e or i) in Audio magazine. The Vandersteen 2c uses a custom Vifa poly 8" driver P21-WO-20 similar to the standard production P21-WO-12. The 10" auxiliary radiator is a stamped frame driver with 38 oz magnet and a flat spider. A masonite disk is glued to the cone to add mass. Fb is 38 Hz the series inductor to the AR is 20 mH and the cap to the 8" is 500 uF. I have thought about this quite a bit and happen to own 2c's for my reference system. I think of the analysis of ported and passive radiator systems as being nearly identical especially if the PR has very high compliance. In the limit of infinite compliance they are the same from a small signal perspective. This is why they cut the spider to get higher compliance. I would be concerned about long term reliability of drivers with cut spiders, try to find one with a suitable Vas. Adding mass simply tunes Fb as in any passive radiator system. I think of the AR system as being a 5th order system due to the series capacitor with extra drive through the inductor to the AR boosting the output at Fb. I see two advantages to driving the auxiliary radiator. First as Keele points out a smaller box can be used or more bass obtained at Fb. Second, more stuffing material can be used in the enclosure to dampen midbass resonances with the potential loss in output at Fb compensated for by driving the AR. The first disadvantage is that the motor on the AR has limited linear displacement capability reducing the maximum output to that of the AR in a sealed enclosure (remember that the main driver provides little output at Fb). Another disadvantage is that a large inductor and capacitor are needed. These components are expensive and the inductor can introduce significant distortion. I would design a normal 4th or 5th order (B5 systems have been discussed in JAES and Speaker Builder) vented system and then build it with 1/2 the box size. The AR should be large with high compliance, long throw, and high Qms. Two long throw (Xmax >= 12mm) 12" woofers come to mind the NHT and the Audio Concepts DV12. The DV12 is less expensive and is probably better suited since it has a higher Vas, I don't recall the Qms value. Stuff the box as described in my previous posting. Use 500uF * 40/Fb * 6/Rvc in series with the main woofer and 20 mH * 40/Fb * Rvc/6 in series with the AR. These are the Vandersteen values scaled by impedance and Fb. With regard to your basic question, I would use SPICE to simulate the electro-acoustical model, including the inductor and capacitor, as the easiest way to get to an answer. If I had more time I would crank out the transfer function and model it in a custom program. What book did you use and what about the series cap? I would expect the low end to reach an eventual rolloff of 30 dB/octave (5th order system) but the drive to the AR may cause a more gradual slope. I actually wrote to the supplier of CALSOD and asked them to add this type of system to their simulation program. I didn't get a response, I'm not sure if they understood the request. I have to question the merits of this system. Could an equal or better system be designed in the same volume with the 8" in a closed or Qb3 vented box and the AR in a closed box with a first order crossover? The low end would rolloff at a more gradual 12 dB/octave. Also would the AR have better performance alone as compared to when coupled to the smaller driver? The Vandersteens have excellent bass quality but the maximum output is somewhat limited. - --Pete Basel ------------------------------ Date: Tue, 10 Oct 1995 14:22:25 -0500 (EST) From: John Busenitz Subject: Re: stuffing vented box enclosures > >bottom, or front, always involve desiging it so that air coming out of > >the port is in phase (air moving out of port as driver is moving out of > >enclosure) with the driver, or are there exceptions? Since air is > >compressible and the reaction at the port is not instantaneous, the air > >coming out of the port must have a certain degree of phase shift with > >respect to the driver, depending on the frequency? > > Above the box resonance, the air in the port is in phase (0 degrees) with > the front of the driver (i.e. their displacements add up). Below the box > resonance, the opposite occurs (180 degrees difference). I keep forgetting the phase _AT_ system resonance. Can anyone remind me? However, I do know that it is somewhat irrelevant, as at resonance the majority of the output eminates from the vent; it replaces the output of the driver. John Busenitz ------------------------------ Date: Tue, 10 Oct 1995 11:41:00 -0400 From: "david (d.) dal farra" Subject: Re: stuffing vented box enclosures From: Peter Basel >A number of papers come to mind on the resistive properties of acoustical >damping materials: > >1. W. M. Leach, "Electroacoustic-Analogous Circuit Models for Filled Enclosure > JAES July/August 1989. > >2. L.J.S. Bradbury, "The Use of Fibrous Materials in Loudspeaker Enclosures," > Loudspeakers vol. 1-25, pp 404-412, Audio Engineering Society, Inc. 1980. .... >5. R. H. Small, "Closed-Box Loudspeaker Systems, Pt. I: Analysis," J. Audio E > Soc., vol. 20, (Dec. 1972). > >Articles 1,2, and 3 do not give specific recommendations for vented systems and >I pretty much agree with Dave that the research info is weak in this area. Great post! I guess the bottom line is that there is currently no way to tie in Leach's work into the Thiel/Small model with Bradbury's work on the acoustical properties of fibrous tangles. First off, Bradbury wasn't totally correct below 100 Hz. There's being work done right now that contradicts Bradbury's results, and proof of its correctness, but I can't go into detail until the author publishes. Small's analysis on the topic only showed one example where by adding box losses (using stuffing in a vented box) reduced your bass output via slower roll off but this even happens with a sealed box if you can lower the Q. My idea is to see if you can account for the losses via box size/port tuning and still get decent alignments, with the attendant benefit of mid range absorption. In the same way that Bullock adjusted Ql and accounted for it in vented alignments a few years back, work is needed to find a model where adjustments in Qa can be accounted for and predicted. This is one huge void in the state of the art I wish I (or anyone else) had the time to fill right now. Dave Dal Farra (gpz750@bnr.ca) "I was moving so fast I started Bell Northern Research using Him as a braking marker" Audio Design Group FJ1200/GPz750 ------------------------------ Date: Wed, 11 Oct 1995 10:11:39 +1000 (EST) From: Andrew Congdon Subject: Re: Lining a sub - lead, yes? > > Or do we want some "blending" of sound? Would a commercial sub (or > > speaker, for that matter) be better if it maintained the same volume > > but was made of thicker timber and lined with lead? > > Because of the low frequencies being reproduced, the thicker material > will lend considerable stiffness to the walls of the enclosure. This will > possibly improve the accuracy of the bass transients, as flexing of the > walls may reduce the fidelity of the reproduction. The lead lining will > work to reduce the structural resonant frequencies, which may not be > such a good thing in this case. > | Witold Waldman | Aeronautical & Maritime Research Lab | I build a smallish sub recently using 16mm MDF and lined it with lead. One of the major design criteria was the small size of the enclosure for my diminutive house. The enclosure was fairly well braced (IMHO) and I used the lead to increase the stiffness of the unbraced sections of the enclosure and the braces themselves. I used a roll of lead roof flashing. This was a relatively cheap method of achieving a similar effect to using a significantly thicker box material, a compromise arrived at since I had the 16mm MDF and I wanted the smallest possible enclosure for the given internal volume. I double lined the box with the lead sheets and glued and stapled them in place - much pissing around. To retrofit, you'd want to make sure the box you have is well braced and strong because the lead will add a great deal of weight! Are you sure you want to sacrifice internal volume for rigidity - might be better to line the outside of the box with 12mm MDF. - -- Andrew Congdon | Genasys II Pty Ltd | Level 13, 33 Berry St, North Sydney 2060, NSW, Australia | Phone: +61-2-954-0022 (-9930 FAX) | Internet: andrewc@genasys.com.au ------------------------------ Date: Wed, 11 Oct 95 08:09:13 EST From: "John Bailey" Subject: Re: Crossover for Carver ribbons (active) ? I'd be interested to know how well the 1259s will handle those frequencies up to around 10kHz, which it xeems to me they will be required to do in this setup? john jbailey@ccmgate.fbr.com ______________________________ Reply Separator _________________________________ Subject: Crossover for Carver ribbons (active) ? Author: bass@lunch.engr.sgi.com at Internet Date: 10/9/95 10:25 PM First off , I'm glad to say that I have found a home. This mailing-list is wonderfull! After building speakers for 25 years,it's great to find people as fanatical as I am. Anyway...just about the time I started lurking on this list my brother wanted me to build him some no-compromise speakers. What I came up with is, the Carver ribbons with 2 NHT 1259's on each side,with perhaps one or two ribbon tweeters crossed over at 8-10khz,6db per octave to fill out the extreme highs. O.K. All that stuff is ordered and on the way. My question is. Is the "Clearview" dedicated active crossover still available? If it is, whom should I contact? Also, is there any other frequency manipulation besides negating the 6khz resonance? Is this a resonance between the magnets or side to side in the frame? Any answers are very much appreciated! GS (As an aside to Mr. Hildebrand......my brother and I also keep reef tanks. It's like building speakers and having the parameters evolve :-) ) ------------------------------ Date: Wed, 11 Oct 95 8:02:55 PDT From: Don Perley Subject: Re: Crossover for Carver ribbons (active) ? > > I'd be interested to know how well the 1259s will handle those > frequencies up to around 10kHz, which it xeems to me they will be > required to do in this setup? >> What I came up with is, the Carver ribbons with 2 NHT 1259's >> on each side,with perhaps one or two ribbon tweeters crossed >> over at 8-10khz,6db per octave to fill out the extreme highs. >> O.K. All that stuff is ordered and on the way. The original query wasn't mine, but if you read carefully, the 10khz crossover is between the carver ribbons and the "ribbon tweeters" - -Don Perley ------------------------------ Date: Wed, 11 Oct 1995 08:05:28 +0100 From: edtjek@garbo.ericsson.se (Johan Ekman) Subject: Re: stuffing vented box enclosures > > > > Above the box resonance, the air in the port is in phase (0 degrees) with > > the front of the driver (i.e. their displacements add up). Below the box > > resonance, the opposite occurs (180 degrees difference). > > I keep forgetting the phase _AT_ system resonance. Can anyone remind > me? At _port_ resonance, the output from the port is in phase with the driver. It wouldn't be able to prevent the woofer from moving other- wise. Below resonance, the output slowly becomes out of phase, and at DC it's 180 degrees. That change in phase is what causes the system to have a fourth order (approx.) roloff. Above port resonance the port gets out of phase again. Johan > > However, I do know that it is somewhat irrelevant, as at resonance the > majority of the output eminates from the vent; it replaces the output > of the driver. > > John Busenitz > > ------------------------------ Date: Wed, 11 Oct 1995 13:00:20 -0400 (EDT) From: 92dyhein@wave.scar.utoronto.ca (DY HEINRICH) Subject: Re: Lining a sub - lead, yes? Unless you have time and money to spare, I would suggest not doing so. I lined a sub with glass before and it was much much more stiffer and sounds much more deader, but somehow, it sounded much worse than in a normal 3/4" particle board box (sounds like there was much more harmonic distortion or something like that at least in that there were much more upper freq. sounds coming out WITH TEST TONES) In any case, if you have time and money to spare, then go ahead and try it and report your results ... maybe it would do all of us good :) Heinrich 92dyhein@wave.scar.utoronto.ca ------------------------------ Date: Wed, 11 Oct 1995 14:21:17 -0400 (EDT) From: THM1959@delphi.com Subject: Re: stuffing vented box enclosures ------------------------------ End of Bass and DIY Loudspeakers Digest V2 #259 *********************************************** A non-digest (direct mail) version of this list is also available; to subscribe to that instead, send the command lines: unsubscribe bass-digest subscribe bass end in the body of a message to majordomo@lunch.engr.sgi.com. 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