Q12 12" Sub

Here is a plot of the frequency response of the bms12 in a reflex cabinet. Measurement was done outside with both the speaker and microphone placed on the floor.

edit: forgot to mention this is pre eq.



Edited by Steve_B - 20 August 2009 at 7:49pm

Tony,

It is an older version of Smaart. I got it in exchange for some work I did for an acquaintance who has moved on from his audio obsession and no longer needed it. Prior to that I used to borrow Spectralab from work. As I now consider audio to be more of a hobby than job I couldn't really justify a big spend on software for the amount of speakers I now build. I was just fortunate to know the right person at the right time.

If you are measuring outside or in an anechoic environment using a pink noise source, then you know that the reference source is flat and a RTA read out gives the same response as a transfer function. The phase measurement makes setting up crossover points easier and the coherence plot highlights where the curve is giving a false reading, but by changing the test setup and getting similar readings you can be confident that your measurements are good. Anything with a higher res than 1/12 octave should get close. In most cases if you set up the same cabinet three times you end up with three slightly different settings on the crossover eq. If the measurements are wildly different something is wrong.

One of the problems with aligning subs with mid/tops on a tripod stand is not being able to set up consistently at gigs. I usually do a few measurements putting the cabs in different positions to try an get a feel for what is happening. At pub gigs there is never a chance to do any alignment in situ.

Both myself and Steve_B deliberately wanted the peak which gives about 2db at just about the most influential bass frequency. It is a trade off between extension and size but one which seems to work very well indeed.

If you just want extension then just build a 60L box tuned to 28hz and they will go lower than most 18" ers   i.e. -3db @ 32hz.

Tony

If you stick with the 48 litre box but tune at 42Hz instead of 47Hz, you will lose the peak at 60Hz and gain another 2dBs at 40Hz - that's what I meant. I've got it plotted in BassBox but I don't know how to upload images to the forum. If you want the peak at 60Hz, fair enough.

Prediction programs are not that accurate. One parameter that I have never seen discussed here is Ql or box loss. This can only be measured after you have built the cabinet so any prediction software has to use an estimated value. Each software designer might use a different value. The graph of my original cabinet was tuned to 38Hz not 47Hz. Using the values you have given winisd predicts an even bigger peak this is what I would expect. A 47Hz tuning would give an even bigger peak.



The original image I posted was a measured response. It conforms closely with the predicted response in winisd which gives me confidence in the programs accuracy.

To show images you need to upload them to a website and then provide a link. If you don't have your own webspace there are loads of sites that host images for free. For posting on speakerplans I use tinypic.com. It will automatically resize your image to fit different formats and provides the tagged link which you just copy and paste into your message.

Anyone know where to get the BMS 12N630 in the uk?