What can I do without drivers in hand? (1 Viewer)

I am about to be on spring break from college and might want to occupy my time by beginning to create my speaker project. I have the drivers picked out but I won't own them until I get them this summer. Is there anything I can work on in the meantime to get a really good start? I am reading The loudspeaker design cookbook but it really seems that the information in there is something you want to take step by step along with the building of your project. I am just looking for something to get started on as I can't wait to really start this summer

Get measurement equipment and practice using it. The simplest setup (though not cheapest) seems to be a Behringer ECM8000 mic and a UB802 mixer.

Learn how to use speaker modeling software. Speaker workshop is free and also has measurement capability.

Model the drivers you want to use using whatever specs and measurements are available. If all you can find is mfg graphs you can trace them with SPLTrace from the FRD consortium to get .frd and .zma files. It won't be the same as working from your own measurements but it will get you familiar with the software and whether the drivers you are planning to use are complimentary.

whats the point of the mixer? And can't most of the measurements be taken via a volt meter? I want to keep cost as low as possible

The Behringer mic requires phantom power, which the 802 mixer provides. You can build your own mic from a Panasonic mic capsule and a jig for less money, but you will have to invest time into it.

I meant acoustic frequency response measurements.

A normal mic isn't "good enough"?

No, not really. Just like speaker drivers, microphones have their own frequency response and most of them are not anywhere close to flat, especially at the low and high ends. If your mic had a peak at 4KHz how would you know if the peak was from the speaker or from the mic? If you adjusted your crossover to get rid of that peak you would end up with a dip in your speaker's response.

Ideally, you would want a microphone that has been calibrated to a known flat system. Calibration doesn't mean that the microphone has been altered in any way, but that a calibration file has been produced that when combined with the microphone's response in your software will yield a flat response. Out of the box, the Behringer mic is fairly flat. Mics built for voice and instruments seldom are.

An alternative would be to use an analog Radioshack SPL meter and one of the many calibration files for it that are available over the web. I wouldn't recommend it, though.

whats wrong with the SPL meter?

Secondly, I think my dad can take it to his work and take measurements on it in their acoustic chambers . So using that might not be all that necessary. So I should just try to model it in a program? Should I start building the box too?

Lastly, In the Loudspeaker cookbook it says that you MUST put a filter for subsonic frequencies on vented bookshelfs is this true? If this isn't necessary is there a chance to damage the drivers? I would hate to lose drivers because I was too cheap to spen a few extra bucks to make a filter

My concern regarding the RS SPL meter is that the mfg tolerances don't allow for consistency from one meter to the next.

If your receiver has the ability to lowpass to a subwoofer then you can set your speakers to SMALL on the receiver and implement a highpass to your midwoof that way.

The idea behind a highpass filter on a vented driver is to keep it from receiving low frequency signal that might cause it to have excursion past its safe operating range. That depends on the driver, box loading, and power used.

As far as making a box goes, yes, you can start building them before you have the drivers. A couple of things to consider is whether the drivers you are using will work how you expect them to and will thus be the drivers you finally end up using. Also, are the mfg specs close enough to the measurements of the drivers you actually obtain so that the box will not have to have to undergo major changes?

What drivers are you looking at?

I am looking at using two Vifa MG18SK09-04 Along with now a seas tweeter 27TDFC/TV. Obviously I will be making a pair of these MTM bookshelfs. I was going to use a D25 double chamber until I found out there was no way to shield it and it didn't come in a shielded version unless it was single chamber. I contacted madisound to see if they have the seas in stock, if they do I will go with that other wise I will use the D25 without the dual chamber.

Last I knew Madisound didn't have them in stock though I heard Zalytron does. I don't see it on their site, though. If you want to go sheilded there is also the Morel DMS-20 to consider.

Have you found any other projects using these drivers? For your first time out it can be quite useful to have something to check against in case any problems arise.

Have you considered a Dayton RS-180/Seas 27TDFC/TV combo?

No use of this driver is pretty rare. Thanks for the tip on the tweeter. I just want something that will match up well with the Vifa driver and is not too expensive. This is a learning experience for me as I want to try and use what I have learned in my EE classes to work on these. Don't expect them to be perfect but anything is better than my current dual 4" w/tweeter mains from my HTB-505 Kenwood HTiB

My brother doesn't think I can make speakers that sound as good as the ones in stores and my dad sounds doubtful too, so I am out to prove them wrong

Why not build a proven MTM design that uses the XG18 and the 27TDFC?
http://home.new.rr.com/zaph/audio/audio-speaker16.html

Well, I can't use the XT18 because it only comes in 8 ohm versions and I want to build an 8 ohm nominal MTM speaker so that doesn't work. I could use the Seas with the MG18 as it is also a fibreglass cone.

If you plan on parallelling the midwoofers in a MTM, the way to achieve 8 ohms nominal impedance is to use midwoofers with 16 ohm nominal impedance, otherwise, you'll be stuck with a nominal impedance profile around 4 ohms if you parallel the midwoofers with 8 ohms nominal impedance.

I was going to put two 4 ohm speakers in series? Does that not work??

If it doesn't...who makes 16 ohm speakers...because I haven't seen them

By wiring the drivers in parallel you get a 6dB gain in output. By wiring in series you get no gain. ONE of the reasons people go MTM is to match output of the woofs to the more efficient tweeter so the tweeter doesn't have to be padded down.

GR Research has 16 ohm drivers as do others, though they are rare.

so if they were in series I would have to attentuate the woofers? I am not sure what you are trying to say about the tweeter. I do appreciate this information though. Give a newbie to the field a second chance . I heard that the reason for MTM's is a wider soundfield or something along those lines. Thanks for all your help I really appreciate it

Say you are going with two of the Vifa MG18s and a Seas 27TDFC/TV. In series, the two Vifas would still be 87dB combined and the tweeter would be 90dB so you would have to attenuate the tweeter 3dB. That would be if you were mounting in a large baffle such as a wall. When you add in baffle step you would have to attenuate the tweeter closer to 6dB.

An MTM is desirable for left and right channels where each driver is the same distance from the listener, but not in a center channel where only one person can be centered and thus equidistant from the drivers. In a 2-way center MTM the flanking drivers will have an uneven response for off-axis listeners, which is why many people go with an WMTW setup for center channels where the tweeter is above the midrange flanked by the two woofers. In this example the woofers don't play higher in frequency than the their spacing. That is, if the center to center distance between the woofers is 11" then the woofers would not play higher than say 1.2KHz.

ah so because they are in series I lose some of the potential volume of the woofers. Is that really bad to have to attenuate the tweeter? Or is it just because it complicates things? How come so many people build 4 ohm nominal speakers when most receivers I see are 8 ohm or about that amount? I am looking into getting a HK335 or 435 but it is still 8 ohms nominal. So most people use a seperate amp?

The problem with attenuating the tweeter that much is that the overall efficiency of your speaker goes down and it takes a lot more amplifier power to get the same volume.

Say you are putting in 3dB of baffle step in your design so that the tweeter is playing 3dB quieter than the woofs (simplistic example). In series you have the woofs at 87dB so the tweeter is padded down to 84dB. In parallel the woofers are at 93dB and the tweeter is at 90dB. That 6dB difference means that it takes 4 times the amp power to achieve the same sound levels.

A lot of the better amps can handle 4 ohm loads, especially if they aren't driven to max output. With the difference in efficiency shown above that is likely.

The HK amps are decent. I just put in an AVR635 for a friend of mine. It is in a 5.1 setup with the 2nd zone powering his patio speakers. He initially bought an AVR630 that kept tripping (we went through 3 different ones) and HK finally sent him the 635 as a replacement. The HK amps are high current and should have the reserve to drive 4 ohm speakers, though I won't swear to it until his new speakers are finished.