audio-talk

It seems that Behringer USB interface gadgets are currently pretty much unobtanium - reflected in the differential between the Amazon list and ebay seller prices - so, assuming I need the two inputs recommended by Chris, this looks like an alternative;

https://www.gear4music.com/Recording-an ... rface/25KZ

I'm going to ask a stupid question here. Well, two actually.

1/ How much experience at taking loudspeaker acoustic measurements do you have? And
2/ How far down the rabbit hole do you want to go?

I ask because if you're not too used to it, and you're not planning on rivalling Avalon in terms of fine precision of design focus and attention to detail, then I would suggest you make life easy for yourself: REW and a UMIK-1 or equivalent quality USB measurement microphone will be more than adequate for your purposes. At least to start with. It's all many very experienced and capable designers find they require, and is more straightforward (as well as being cheaper) to set up and use. Yes, condensor mics. with phantom power and other software are ultimately more capable, but the key there is 'ultimately', because to benefit from the extra capability, you're probably an advanced designer in terms of your knowledge base.

Scottmoose wrote: ↑Sat Jan 02, 2021 2:14 pm I'm going to ask a stupid question here. Well, two actually.

1/ How much experience at taking loudspeaker acoustic measurements do you have? And
2/ How far down the rabbit hole do you want to go?

I ask because if you're not too used to it, and you're not planning on rivalling Avalon in terms of fine precision of design focus and attention to detail, then I would suggest you make life easy for yourself: REW and a UMIK-1 or equivalent quality USB measurement microphone will be more than adequate for your purposes. At least to start with. It's all many very experienced and capable designers find they require, and is more straightforward (as well as being cheaper) to set up and use. Yes, condensor mics. with phantom power and other software are ultimately more capable, but the key there is 'ultimately', because to benefit from the extra capability, you're probably an advanced designer in terms of your knowledge base.

There just the same stupid questions as I'm asking myself Scott!

The answers are;

1/ Nil - but I think I probably need to learn some basics.
2/ Not far - just enough to achieve the requirement I set out a few posts back.

I've been wondering if this is getting over-complicated, especially as the cost keep going up!

Then if you want uncle Scott's advice: buy yourself a UMIK-1 (or direct equivalent) + microphone boom and download REW, or get Omnimic + microphone boom if you prefer that option (I regularly use it myself). You do not need anything more complicated when starting out. This is far from a 'poor man's solution' either, so you don't need to bat an eyelid over that: many highly experienced designers, including the late, great and much-missed Jeff Bagby regularly use USB measurement microphones & accompanying software. If it was good enough for Jeff...

I took the advice of uncle Scott and have a UMIK-1 on the way. Cost less than the other stuff too.

Now to download and install REW.

Scottmoose wrote: ↑Sat Jan 02, 2021 3:37 pm The late..Jeff Bagby regularly use USB measurement microphones & accompanying software. If it was good enough for Jeff...

Who did Jeff Bagby post as, Scott ?

Depends where, but usually Jeff B. I knew him very slightly (wish I'd known him much better).

For the purpose of reference for any future readers of the thread, since it's important to know: Jeff was first and foremost an engineer / designer. Hence all the design & development software he created or co-created. He was not, and never pretended to be an 'internet guru'; his posts were generally factual information, contributions or answers to specific questions, adjusted to the level of the debate, and when opinions came into it, he did not expect or want his to be taken as anything other than an individual preference.

So, let's assume that I've got my UMIC-1 and I've assembled/tested a bandwidth limited MoFo and I'm now ready to measure the frequency response of the amplifier/full-range driver in combination - I guess I need to assemble the driver onto a baffle of about the size I plan to eventually use - I'm thinking I need to visit B&Q and get them to cut a piece of chipboard.

Unless you're driver testing (as in assessing driver performance as a goal in itself) then yes: the measurements of most relevance are those taken of it on the intended baffle / in the intended enclosure, or something of the same size & shape.

What you'll need are gated for everything above, about, 300Hz with an MLS signal (REW can handle that if you can attach a lead from your soundcard to the preamplifier / amplifier). Depending on the size of the driver[s] in question the distance you take them at can vary a bit. 1m is the usual defalt, although that's as much down to it being a default for nominal levels as anything else. Some smaller speakers you can measure closer, and there can be some advantage in that. Larger, or greater spacing between different types of drive units (as relevant), and you'll need to move further back for accurate integration. 1m is a good starting point though since you know where you are, and you can always try different things later once you're used to the hardware / software.

Low frequencies (usually below about 300Hz or so) aren't accurately measured with a gated response; they're still corrupted by room modes. Nothing you can do about that. So generally people either take a nearfield (microphone very close to the cone) or ground-plane measurement, and splice the results together in their choice of software package. A nearfield measurement typically appears to show the levels boosted by about 6dB relative to the rest of the range due to the proximity of the mic., so you either need to adjust the levels, or simply ignore that as an artefact of the process (as John Atkinson often does for his Stereophile measurements). Personally I'd avoid ground-plane measurements -they're not all that easy to set up & get right. Alternatively -just stick with the regular 1m gated measures and ignore everything at the bass end for the time being.

If this sounds complicated, it isn't really. Setup is simple enough; and when you get your mic. it's quick enough to get up and running. See these two pages which cover the basics that will get you started:

https://www.minidsp.com/applications/ac ... p-with-rew
https://www.minidsp.com/applications/ac ... asurements

Cheers Scott and thanks for your advice and support.

It does sound complicated on an initial scan through but I'm sure that it'll fall into place when I read it carefully, along with the links you provided. I've plenty of time to assimilate this before I need to do any measurements.

Narry a problem.

It's not as bad as all that though when you get used to it, and you don't want to go OTT. A lot of what is in the first link is basic setup advice for the hardware / software; once you know how to do that (and it's essentially just a few mouse-clicks in a couple of different menus / screens), you can get on with the rest, much of which is in the second link. In essence

1/ You need to set up the hardware and software. So, mount the microphone on a boom, plug it into a USB port, open up REW, load the calibration file, and set that up also per the guides, which are lengthy because of the text and screen shots, but in practice amount to just a few mouse clicks. Job-jobbed.

2/ Assuming you want to take measurements which you can use for designing, plug a speaker into an amplifier and take an audio output from your laptop or quality external soundcard into the amp. A good external soundcard is preferable but the former should do for the time being.

3/ Position the microphone tip 1m away from the baffle, and level with the intended listening height, whether that is directly in front of the driver or not. I know that might sound odd at first glance, but think of it like this. Take the Quasar: you don't have two sets of ears, one set listening to the direct-ahead output of the AER wideband, and a second set of ears 2ft lower down listening to the direct-ahead output of the Supravox. You have one set of ears, which apart from single-driver speakers and coax / triax units will never be level with all drive units on a baffle simultaneously. Make sense? As noted, 1m isn't necessarily an 'ideal' distance, but it's a good starting point.

4/ Put some ear-plugs in and play the sweep tone. The plugs aren't strictly necessary, but multiple bursts can get a bit uncomfortable.

5/ Decide if you wish to apply some smoothing, or to gate the measurements (or both). Gated is usually preferable, so follow the procedure in the second link, and remember everything below about 300Hz becomes progressively less accurate due to room effects etc.

As I mentioned in my previous post, low frequency measurements are done differently, but we'll leave that for another day. Get confident at taking this type of measurement first, then you can look at the others if you wish.

I've just had the UMIK-1 delivered.