Q&A # 210 - December 12, 2000

Staff

Q Where would I go to get the Vas, Qts and Fs measured of a driver that I would like to use in a sub? I have contacted the manufacturer (Cerwin Vega) and they do not give out the specs on their drivers.

A If you're willing to plop down a couple hundred dollars, you can get the Woofer Tester" from http://www.parts-express.com.  It will generate T/S parameters, as well as calculate the inductance of coils, and do a wide-range impedance sweep.

Q I am considering a B&K Ref 7250 (200w x 5), and a B&K AV5000 II (125W x 5). I have auditioned both in my system, and I found that both are about the same in the mid and upper range. The 7250 however has better dynamics in the lower end (damping factor of 450 on the 7250 vs. 150 on the AV5000). What I was planning was to combine the AV5000 with a Velodyne 12" sub (to take care of the low end). Would this combo have better/equal overall dynamics than the 7250 by itself? I am finding it hard to justify paying double the price of the AV5000 just for low end dynamics. In fact for the $1200 that I can save with a AV5000, I can buy an excellent sub that would really be a low end kicker. Is there something else I would miss out by taking the later route? I am not worried about the power rating difference of 2 dB between the two (200W Vs. 125W). With my sensitive Infinities (90 dB/w/m) I don't think that's much of a problem. I have been worrying about this for the past two weeks. I just want to make the right decision and stick with it without having to regret it later. I hate to get into the upgrading mania that most of the audiophiles are afflicted with.

A Although the 7250 has only 2 dB more power output as you say, that is if you have it cranked to the top. The 200 watt capability comes in handy when listening at much lower volume, say about 20 watts per channel on average. Along comes a crash boom, and the 7250 can handle the transient peak better than the 5000. That is why you notice the difference in dynamics. And this will come through regardless of having a good subwoofer because the subwoofer does not decrease the need for dynamic presentation in the other speakers. If you could limit the other channels to 50 Hz and above using a high pass, that would reduce the problem, but unfortunately, most receivers only offer a high pass of about 90 Hz, which I feel is much too high. My fear is that you might buy the 5000 and a great subwoofer, but still feel something is missing. So, I would suggest getting the store to agree to letting you have the 5000 and the sub with the understanding you can bring the 5000 back for exchange with the 7250 within a reasonable time frame.

Q I have two sets of Definitive Technology BP 2000 speakers (front and rear) along with a D.T. Powerfield 18 sub. I have a Denon VRR 3801 receiver. Would  you recommend that I connect all five subs together? If so, how do I connect  them? Also, how is the Digital Optical cable to be used? Will I get a better  picture or sound? Finally, I have an awkward room layout. The TV is at an angle at the side of the room so we do not get straight front and rear sound.  The room size is 20x21 (it is part of a 20x50 room which contains kitchen,  dining, and family/TV room. Without putting the TV in the middle of the viewing area, what can I do to get a more balanced home theatre sound?

A I would suggest leaving the Def Tech subs as they are now, part of the sound coming from each speaker. The crossover frequencies might not be appropriate for using them together with the Powerfield. Secondly, there is stereo sub information that you would lose if you connected them to one output. The digital optical cable (Toslink) is for sound only, not video. You connect it between your DVD player (or CD player) and your receiver. It will reduce the problem of ground loop hum. For your TV room, you can adjust the angle of your speakers so that they vary in how they face your listening position. This can help balance the sound in odd sized or odd shaped rooms.

Q I have a Yamaha HTR-5250 running a pair of Acoustic Research AR-318PS as fronts on my computer setup. The Yamaha is giving out 100wpc, but my speakers can handle 175 rms. Will I notice a better soundstage and sound quality if I use the Audiosource Amp3 compared with the built-in amp in the Yamaha?

A Yes, you will have much better dynamics with the Amp3. This also frees up some of the power supply in the Yamaha to deliver power to the other channels.

Q I read your reviews on the B&K and Onkyo A/V receivers. I have also read reviews on these units by others. It seems that these two receivers are my final choices to buy from. I understand that the Onkyo 989 is abundant on features, while the B&K might be superior sonically in some ways (at least so was my impression). Since I would hate to have any sonic compromises, I was wondering if choosing the Onkyo over the B&K would end me up with a problem?

A The B&K and Onkyo are about neck and neck in terms of absolute sound quality if you're talking exclusively about the preamplifier section. The B&K can swing a little more voltage if you really need to overdrive an outboard amplifier, but between them, purely as a preamp, features, aside, I'd go with the Onkyo as it stands when I reviewed them.

However, while the Onkyo is DSP upgradeable, the B&K is also supposedly, and their (B&K) products in my experience have proven to be, completely upgradeable in terms of both software and hardware, so that edge may disappear, if it hasn't already.

In terms of lots of functional features, the Onkyo wins hands down, simply because the B&K really lacks them, or did when I reviewed it. Again, it's completely upgradeable.

As a stand-alone unit, performance alone, I'd go with the B&K, because while the Onkyo might make its rated power at 8 ohms with all channels driven, that's all it's got, and lower impedances might pose a problem with the most dramatic scenes. The B&K receiver isn't a match for the larger outboard amplifiers, but it's got a more robust power supply, with a decent amount of filter capacitance.

Q I am an electrical engineering student. Where can I find information on DIY amplifier projects?

A Here are some links. http://www.hifiheaven.com/electronics-diy.htm    http://www.worldaudiodesign.co.uk/taps.html    http://www.geocities.com/Tokyo/5913/    http://home.earthlink.net/~lotusblossom/.

Q Can I record cassettes and LPs on the JVC XL-R5000BK CD recorder?

A Assuming you're using a stereo preamp and/or a home theater processor, you take the tape out left and right cables into the recorder's left and right  analog inputs. If you want to do digital dubs from an external source, you connect the external source to the digital input (which looks to be Toslink only).  As for setting levels, I'm afraid you're on your own here, I don't have a manual
available to check this.

Q 1) THX certified speakers are best for Home Theater, but how about in two-channel music? Are DTS CDs (5.1) suitable for THX certified speakers? How can I get the best from both worlds?

2 ) I am using full range old DIY speakers in the rear of my Home Theater. I am thinking of adding THX certified dipole speakers to enhance the surround effect ( I love THX). But somehow I am afraid the two dipole speakers will mess up the surround effect which the movie studios have designed. 

A THX certification just means the component (speakers and amplifiers) have been designed to certain standards. THX is not a type of sound. So, it will be the fact that your new speakers are dipole, rather than THX, that would affect the way your rear channels sound. It is my opinion that, with 5.1 digital surround, the front and rear speakers should be the same type, i.e., direct, dipole, or bipole, for the best blend all around the room. Back when it was just Pro Logic, the rear was mono and had a limited frequency range. Digital 5.1 has changed all that. Lastly, your THX speakers should sound fine with two-channel stereo.

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