Nat Denkin

After 26 years looking at the same speakers, I decided it was time for a change. I thought about building a pair of Jubilees, but I really like the sound of Bob Crites CW1526C and wanted to stay with 15" drivers. I also thought the larger throat allowed a shorter horn for the same mouth and Dana Moore's design for the Jamboree 215 seemed a good choice. But, my garage is overcrowded with junk so the challenge was to build the speakers in the dining room. That meant the WAF was critical. I wanted something different and large veneered mid range horns provided the change for my wife to choose the veneer. Team building hint: let your wife choose the veneer and hardwood and she will actually like the speakers that dominate two corners of the room. You have to have a very understanding wife to allow you to totally destroy the dining room for several months (I am rather busy and this is totally hobby...no financial interests). This is still a work in progress but the speakers are a pleasure to listen to even without the Jamborees getting the cosmetic treatment.

For those of you using digital active crossovers, a simple experiment should be possible. Configuration A: setup as described in http://freerider.dyndns.org/anlage/LeCleach.htm (very easy to do if you are using a DCX2496. This setup uses 18 dB/octave Butterworth shapes and requires the -3 dB points to be spearated and the measured delays to be shifted. It's all in that link including square-wave responses. Configuration B: use the steepest slopes supported at each crossover, for example 48 dB/octave Linkwitz-Riley using the same crossover frequencies . The crossover frequencies should be within the ranges supported by the drivers and equalization and output level should be the same. Now, go to your sweet spot (the point where you want optimum performance) and listen to the same track using Configuration A and Configuration B (both should be stored in memory so each can be easily recalled). Listen for any differences in percussion and voice. If done properly, Configuration A should have the delays between drivers set to produce much less phase variation across the band than is typical. Configuration B minimizes the overlap between drivers (ok, not as sharp as extreme slope). Have someone else switching (or fakining it) and see if you can consistently tell them apart and prefer one. Are the differences (if any) the same when you move away from the sweet spot and repeat the experiment? NOTE: the results may depend on what you are listening to and whether the sound engineers who set up the microphones and did the mixing knew what they were doing! So try several tracks of different sources. Any takers? Thanks, nat

A round tractrix horn should measure very well because the driver is well loaded and there are few discontinuities. However, does the performance in a typical room benefit? While the sound from the round horn may have fewer reflections and refractions than similar cutoff rectangular horns, more energy would be reflected from the floor and ceiling of a typical room. I had thought about doing an elliptical tractrix to program the dispersion better than for a round tractrix, but with fewer discontinuities than found in a rectangular tractrix. The same possibilities would be present with other horn shapes such as exponential and LeCleach. With CNC, these should be doable...especailly with lots of hand sanding.. If you do A/B tests, you might need different equalization for round and retangular horns even when using the same drivers. nat

Al, Do you plan to make IM distortion measurements of coaxial drivers? Depending on crossover frequencies, nearly half the power would be in the same throat as the tweeter band so that I would expect IM to be higher for the tweeter band than if that band had its own horn. Thanks, nat

Nick, Let me answer your question by way of some examples. The specifications for the Crown D-75A include a single-cycle tone burst at 1 kiloHertz. At the same distortion level of 0.05%, the amplifier would deliver 30 watts at 16 ohms, 60 watts, at 8 ohms, and 120 watts at 4 ohms. The reason for this has to do with the design of the amplifier. The output voltage, Vout, is the same for loads between 4 and 16 ohms so that the output current, Iout, equals Vout/Zload where Zload would be the impedance of the driver at 1 kHz. Since the delivered power is the product of Vout and Iout, it is proportional to Vout^2/Zload. Amplifiers using negative feedback to provide a constant voltage for a given signal would behave this way and could be expected to deliver larger turn-on/turn-off transients to lower impedance loads. An amplifier designed to deliver constant current would actually deliver more power into a higher impedance. However, since woofers generally have low impedance (4 ohms is typical) and most of the signal power goes to the woofer amplifer designers would rather control the voltage rather than the current. Since vacuum tubes have very high output impedances, output transformers are used with different taps for different impedances. So a McIntosh MC275 is specified to deliver the same 75 watts into 4, 8, or 16 ohms. There are other factors to consider. A power amplifier using symetric power supplies should have smaller on/off transients than an amplifier with a single rail. If you hear a big thud or any nasty sounds when you turn on or turn off your amplifiers, you may need to protect your drivers by blocking the low frequency portion of the transients. I am in no hurry to put capacitors in front of my midrange and tweeters; however, if capacitors do not affect the sound enough for me to hear a difference, I may put some in just to be on the safe side. nat

If you are using active crossovers, within the capabilities of your drivers vary the crossover frequencies and listen to the sound. Stop when you like the results. I am tri-amping and not using either capacitors or fuses to protect my drivers, but rather, I am using Crown D-45 and D-75A amplifiers that are unlikely to fry my drivers. Here it makes a difference whether you are using 8 ohm or 16 ohm drivers because these solid state amplifiers deliver a lot less power into 16 ohms than 8 ohms. There is a slight popping sound when the amplifiers are turned off. If you do want capacitor protection, you can choose a capacitance that with the driver impedence gives a cuttoff frequency an octave or two below your selected crossover frequency. nat

While there is no free lunch, the ears are rather forgiving. Networks affect both the amplifude and phase of signals with the steeper slopes having a greater affect on both frequency and phase. While some will dispute whether you can hear the phase shifts, consider that you can sense the direction of sound not merely to your left or right, but also in front or behind and above or below. The delay of a signal getting to one ear and then the othe does not fully explain our ability to locate the source of sounds in three dimensions. The explanation of how this works has to do with reflections in the outter ear which cause a frequency dependent phase shift. For best stereo image, you need to consider phase. Keep in mind, you can recreate only the sound as it was mixed. If the engineer merely put the singer on the left feed and the piano on the right, phase is less important. But, if properly mixed, you can image each member of a small group. A function of your network is to elimate out of band power going to each of your drivers. A 6 dB slope/octave permits lots of signal getting into the woofer and squarker that they do not handle well. A higher slope is generally needed. Higher slopes require more parts and higher precision in selecting (or tuning) them, That adds to the cost, but higher slopes do reduce the overlap between the drivers. I use the Beyma CP25 and cross them at about 6kHz. They have a good response well below that so you need to consider at least 18dB/octave for them. I am driving the Beyma's directly with a Crown D-45 (triamping) with no problems. During typical music, less than 10% of the power would be going to the tweeters. Bottom line, recap your AA. I like the ALK universal which I purchased in kit form (you don't save a lot by buying parts yourself!). Others solutions get progressively expensive and your satisfaction may depend more on the music you listen too, room acoustics, and personal preferences. In one of my setups, I use the ALK universal with the Crites woofer, Atlas mid-range driving a 1" ALK trachorn and Beyma tweeter. In an ongoing project, I am triamping using a Behringer DCX2496 to provide 18dB/oct slopes as suggested by Le Cleac'h to optimize phase response. I am building Jamboree base bins to go with Greg Roberts' Lavera horns. The stereo imaging is quite good, but varies with recordings as sound engineers vary too. Good luck, nat

I've taken a few pictures...I will have to learn how to post them. They will show what it is like building bass bins in a dining room. It takes a very special kind of wife to tolerate the complete takeover of the room! nat

There are some hardcore vinyl/tube lovers that have gone the active route, but it's not something for the feint of heart. Nevertheless, I agree that some people will probably prefer sticking to the passive route... Btw, how do you control the volume right now when running the Behringers directly into your amps? The Crown's have attenuators for each channel and approximately the same change for each "click." When my wife comes in, it's about three or four clicks counter clockwise for each of the six attenuators.nat

While you are using time-alignment, have you tried the Le Cleac'h approach that minimizes phase distortion. http://freerider.dyndns.org/anlage/LeCleach.htm It is quite easy to set up if you have a DCX2496. I am crossing over at about 300Hz and 5800Hz using the Crites woofer in a clone, a 212 Hz cutoff modified tractrix built by Greg Roberts with a BMS driver and Beyma CP-25 tweeters. Since I listen to CDs, I take the SPDIF digital signal to a DEQ2496 followed by a DCX2496 converting to analog at the output stages of the DCX2496. I am using 2 Crown D-75A and a Crown D-45 with merely wire to the drivers (no capacitors--I hear the slightest pop when I power off). I need to finish my Jamborees and have the kit from Pilgham Audio to replace the output of the DCX2496 with a remotely controlled 6 channel attenuator. I really like the sound and imaging and spend so much time listening, the Jamborees are progressing too slowly. I also have ALK's Universal Filter and 1" trachorn. These provide excellent value for the money and I am keeping them in my second system when the Jamborees (with 4 more Crites 15" woofers) are completed to replace the bass bins. The 2" drivers and larger midrange horn allow me to crossover at 300Hz and I am very pleased with the results. For me they are also excellent value for the money. For those that perfer vinyl and tubes, going active presents more problems as all analog amplifiers and filters add noise, and delays are much easier to do in the digital domain. Keeping it simple may be the solution there with passive crossovers driven by a pair of amplifiers with the soft glow of the tubes displayed. Aesthetics have a place in audio too. nat

For the expert DIY, rotate the top socket 180 degrees. This places the grounds on the outside effectively shielding the natural quadrapole antenna formed by the hot and neutral leads. The modified outlet should be mounted horozontally to reduce the asymmetry when the sockets are used to power a pair of single ended amplifiers. These changes should only be attempted by qualified certifiable experts. nat

Hope I'm not hijacking this thread by focusing on the setup before the beautiful Lavera horns, but, Nat, what are you using to control volume now? Volume controls on the Crowns? Say more about a six channel volume control and new output section for the Behringer. Are you considering a tube output stage as seen here? http://forums.klipsch.com/forums/p/133949/1358083.aspx#1358083 Oops posted without seeing GotHover's post...errrr. ya....what he said... Hi Mark, To get the most out of the Lavera Horns, you want the lower crossover to be about 300Hz. The price of quality inductors and capacitors goes up as the frequency goes down. I intend to use the active crossover to determine what crossover parameters work best and also permit phase and delay adjustments. I picked up the Crown amplifiers on E-bay so the active crossover and amplifiers cost a lot less than a passive network even considering the cost of the upgrades to the Behringer. Right now, I have to adjust 6 knobs on the Crowns for gain. It's not hard since they have detents and similar gain steps, but, I am lazy and want a remote. The Lavera Horns have been easy to set up with the Behringer and get very live like you are there sound. While I do not intend to use any tubes at this time, I do have an ST-70 (with a blown output tube) so I am open to innovations. Thanks, nat

What 6 Ch volume control are you using? Goldpoint?Have you moded your behringer to remove the active output section yet? It really helps. Dave. Hi Dave, I have Jan Didden's kit that replaces the output board with a remote controlled six-channel attenuator and better quality active outputs. I should put in the modification within a few weeks. Jan also has a passive output conversion as well as some improvements in the digital sections. These horns are so efficient that very little power is needed. This is especially true with tri-amping, so eventually I may go with a passive output too. Thanks, nat

I own a pair and the sound IS AMAZING! Right now the Lavera horns are seated on top of the top hat on top of the bass bins. Yesterday, I started on my first journey to the "dark side" and am using a Behringer DCX2496 with the digital input from an Onkyo DX-7555 CD player so the signals are kept in the digital domain until the DACs after processing. Crown D-75A amplifiers are used for the woofers and midrange and a Crown D-45amplifier for the tweeters. Currently the crossovers are set at 296Hz and 5.91kHz with LR-48 filters and the relative levels were set by ear. I am building Jamborees to replace the bass bins mainly because I am tired of looking at the same bins for over 25 years. I still like the sound of the original speakers (Crites woofers/Atlas/Trachorn/Beyma/ALK Universal --and I don't think you can do better for the money) but I wanted something that looked fantastic with sound to match. I like to DIY, but it was clear to me that Greg's skills were required. I expected to see precise treatment of the midrange horn, and was not disappointed. The housing for the tweeter was beautifully done with great attention to detail that exceeded my expectations. I still need to build the Jamborees and I have the parts add a six-channel volume control and replace the output section of the Behringer. It will be a while to check out best levels, frequencies, filter shapes, filter slopes, and delays. My wife is very pleased with the Lavera Horns. nat

Al, With efficiencies about 10% that would give about 3.1 mW acoustical power in the throat. For the Beyma with a 1/4" throat, the 2nd harmonic distortion would be about 0.5% or -46 dB. With the larger throat, the Selenium numbers calculated to 0.2% or -54 dB. Thanks for making the measurements. nat

Edited as in the previous post: Looking at the Selenium datasheet we have a throat diameter of 25 mm, a cutoff near 1 kHz, and h2 about -29 dB at 5 kHz. Doing the same calculations as in my previous post, to deliver the same power as the Beyma (0.17 W acoustical) Beranek's formula estimates the h2 distortion at about 3.5%. This is in contrast to the -53 dB or 0.22% posted above. Thus, based on vendor data and Beranek's theory, both the Beyma and Selenium should have similar second harmonic levels. The Selenium sensitivity is listed as 109 dB so it would be expected to require 5 dB less drive than the Beyma, but that should have no effect on the distortion. Is anyone aware of calculations for the intermodulation products and the dependence on throat size, cuttoffs, whatever?

Edited: There are two incompatible definitions of THD and my background led me to the wrong one for audio. Thank you Al for bringing that to my attention. I have edited the posting to correctthat and I am using Al's estimate of the Beyma throat diameter. In his book Acoustics, Leo L. Beranek, derives a formula to calculate second harmonic distortion (in percent) for infinitely long exponential horns. He notes, since most of the distortion occurs near the throat, the formula is correct for finite horns. Horns with other shapes would have somewhat higher or lower values depending on whether they expand less or more rapidly than exponential. Measurements of distortion also include contributions within the driver. Beranek's formula applies to the horn portion and depends on two factors: the ratio of the frequency to the cutoff frequency and the power density in the throat. According to the Beyma CP25 datasheet, at 5kHz the output is about 104 dB and h2 is about 75 dB so that h2 is about 29 dB below the fundamental tone at 5 kHz. Converting to percent, 10^(-29/20) = 3.5%. The response drops rapidly below 1.8 kHz so that should be near the cutoff frequency. We can use Beranek's formula to estimate the power density required to have h2 = 3.5% with f/fc = 2.8 and it gives about 0.53 mW/cm^2. A drawing of the tweeter is given although the throat is not dimensioned. Al estimated the throat to be about 1/4" so the area is about 0.32 cm2 and the power in the throat about 0.17 W (acoustical). The above posted result has the 10 kHz peak about 18 dB below the 5 kHz peak or about 12.6% h2 to fundamental. In Beranek's formula, this requires about 2.2 W acoustical power. Assuming an efficiency of about 10% which would be ballpark for a driver rated 104 dB SPL, the drive power to the tweeter would be about 22 watt, very near its CW power rating of 25 watts. While this does not sound like much power, the tweeter typically receives about 10% of the program, so in use a multi-driver loudspeaker would be delivering about 22 acoustical watts and a pair would deliver 44 acoustical watts. According to Wikipedia, a jackhammer sound power level is about 1 acoustical watt. Perhaps tweeters with 10% of the program should be tested at a lower power that takes into account typical listening levels and overhead for peaks. This raises the question, what is the preferred volume forum members use for listening? Perhaps I should add...when the wife is out!

Happy and Healthy Birthday Al, and many more. nat

Happy and Healthy Birthday Al, and many more. nat

Al, What was the input power to each tweeter for this test? Thanks, nat

Al, I have been using your trachorn (Atlas driven) and unviersal crossover along with the Beyma. People are impressed with the sound and the lack of beaming (large listening sweet spot). The measurements presented at the begining of this thread suggest that the Beyma disperses the power better than the other driver/horn combinations. While the other tests appear to have been done at constant power, the conditions of the distortion test set SPL=100dB on axis at 2 feet. If the Beyma is dispersing the power better, the test would be driving it harder as it radiates a over a much greater angle. I have to wonder what the results would be if the measurement were made with 1W input measured at 1 meter and averaged over the power delivered in all directions. Are there industry standards for these tests? I recall in another thread that you used tones with differing powers for testing midrange horns. Thanks for taking the time to do independent measurements. Still, I have to wonder why providers would not publish their own test results if they had distortion measurements as low as 0.3% . nat

WIth the drivers directly connected to the transformerless amplifier output, negative feedback keeps the voltage of the amplifier output the same whether 4, 8, or 16 ohm loads are connected. Since the delivered electrical power would be V^2/R, doubling the load resistance, halves the input power. Since the maximum voltage is limited by the power supplies, amplifiers generally can deliver more power into lower impedance loads with the limit being determined by the current disspated by the output devices. In any case, I would expect drivers to be most fairly compared when generating the same acoustic power when driven by amplifers that are not challenged by the load. Apparently, Greg has done this. nat

There seem to be lots of mods for the DCX-2496 including replacing all the analog, the digital input, low-jitter clock, etc. Some of the mods cost more than the original box. Anyone with experience trying the mods? Thanks, nat

My wife is wondering why there is a stack of Baltic Birch in our livingroom...and when will it disappear! I don't know how to insert photo. nat

I just wanted to mention that 1 acoustic watt on a horn with a DI of 10dB is going to be over 117dB SPL at 1m in full space. You could see as much as 125dB SPL at 1m in a true 1/8 space environment. Cut the power back 20dB (100x less power) and you're looking at 0.061% 2nd harmonic distortion from 105dB SPL at 1m in 1/8 space. I believe Beranek's comments are also assuming that the driver is adding no distortion...yet we know that the driver tends to dominate the distortion signature (in a good horn). There's the distortion introduced by the phase plug too. Did Beranek specify the type of horn when deriving that formula? I'm guessing it's for an exponential horn, but I could be mistaken. I would expect the distortion to be less for a conical horn than for an exponential horn. Yes, it was for an "infinite" exponential. He notes that most of the distortion would occur near the throat. Any horn that expands more rapidly should have less distortion from this source. IM distortion would probably be more annoying than harmonic, anyone have a handle on that? Thanks, nat