Some time ago I built a pair of Seas Mimir speakers. As it turns out they very occasionally sound a little harsh in the mid range on some recordings, especially clean amplified electric guitar sounds. Frequency analysis of the speaker with TrueRTA shows a few dB lift for an octave or so around 2khz.
What I noticed is that the tweeters (seas 27TDFC) are not flush with the baffle, in fact on the right side it is proud by about 3mm in some places and near level in others.
To be honest, these were my first attempt a building a speaker in some time. I'm thinking of cleaning up or rebuilding the cabinets anyway.
My question is: does it seem likely that this error is enough to cause a 3-4dB peak in midrange response?
Many thanks in advance for any help with this!
Dave
What I noticed is that the tweeters (seas 27TDFC) are not flush with the baffle, in fact on the right side it is proud by about 3mm in some places and near level in others.
To be honest, these were my first attempt a building a speaker in some time. I'm thinking of cleaning up or rebuilding the cabinets anyway.
My question is: does it seem likely that this error is enough to cause a 3-4dB peak in midrange response?
Many thanks in advance for any help with this!
Dave
Many thanks for the link, an hour in the garage with the router cleaning out the tweeter mountings and they seem to sound considerably better.
I've not taken any new measurements yet, but they sound much cleaner on the recordings that previously sounded a bit harsh.
I've not taken any new measurements yet, but they sound much cleaner on the recordings that previously sounded a bit harsh.
Dave,
The link from giralfino is interesting but probably not showing all the picture?! 2KHz? 3/4KHz??? What crossover?
It must be something else. After saying that what system do you have? You only mention the SEAS Prestige 27TDFC (H1189) Textile
I would say, guessing, that you are using a first order. To little info here to be objective.
The link from giralfino is interesting but probably not showing all the picture?! 2KHz? 3/4KHz??? What crossover?
It must be something else. After saying that what system do you have? You only mention the SEAS Prestige 27TDFC (H1189) Textile
I would say, guessing, that you are using a first order. To little info here to be objective.
Only in the case that the tweeter flange is round and thick, and the tweeter is not flush mounted but is surface mounted, do you get much deviation in the frequency response. Flush mounting minimizes or eliminates these effects.
Keep in mind that other boundaries influence the frequency response, most notable of these are the cabinet edges. Small (3cm radius and less) roundovers of the edge do not really do much to help because they are too small. Placing the tweeter off-center can reduce these effects quite a bit, but it takes some experimentation or planning using a diffraction modeler. A good program to check out for modeling diffraction effects is "The Edge" (Home of the Edge). Make sure to make the "circle" that represents your driver only the size of the radiating surface (not the frame of flange outer diameter!). You can get the diameter of the radiating surface from the radiating area, Sd, where r is the radius and PI*r^2 = Sd.
One way to investigate whether the flange is causing some response irregularities is to put some good quality wool felt around the tweeter flange edges. You can also apply the felt so that it has a rectangular opening and overlaps the flange a bit. Re-measure the response and see what happens to the 2kHz bump.
Thanks all, there's a lot of information here and linked sites that I'll plough through.
Sorry I did not originally include the link, the speakers are built to the Seas Mimir spec: (Mimir DIY Speaker), at the moment there are essentially no adjustments and the crossover is implemented to spec. Cabinet is built from 18mm high grade Birch plywood.
What is interesting on the Zaph audio site linked above is that there is a speaker very similar to the Mimir (ZR71); on that page in the room placement section off axis listening is recommended. Further, looking at the off axis SPL on the seas website shows a similar trend.
The sound seems a lot better since the two adjustments, but I'll give it a couple of days to see how it sounds as I get used to it. I can always make a small change to the HF crossover if needed anyway.
Sorry I did not originally include the link, the speakers are built to the Seas Mimir spec: (Mimir DIY Speaker), at the moment there are essentially no adjustments and the crossover is implemented to spec. Cabinet is built from 18mm high grade Birch plywood.
What is interesting on the Zaph audio site linked above is that there is a speaker very similar to the Mimir (ZR71); on that page in the room placement section off axis listening is recommended. Further, looking at the off axis SPL on the seas website shows a similar trend.
The sound seems a lot better since the two adjustments, but I'll give it a couple of days to see how it sounds as I get used to it. I can always make a small change to the HF crossover if needed anyway.
Ha, the link says it all.
The -3dBs crossing is giving the bump by summation. Bad implementation, drivers and crossover (to many problems to solve/sell). Probably the best Seas got @2KHz...
Tony already mentioned in the previous post.
7" SEAS CA18RNX (H1215) - https://www.madisoundspeakerstore.c...ige-ca18rnx-h1215-7-coated-paper-cone-woofer/
7" SEAS ER18RNX (H1456) - https://www.madisoundspeakerstore.c...stige-er18rnx-h1456-7-reed-paper-cone-woofer/
If you can or don't mind using a FAST, move crossover to 400Hz. I would use the SEAS Prestige ER18RNX (H1456) 7" instead of H1215-08 CA18RNX, look also at the voice coil inductance it's almost double. Build up new speakers with a small fullrange driver and shelve the tweeter for a future build, or use it then for two different projects. You will probably end with a 3-way with the new midrange, but it will make you think and DIY!
Falcon Acoustics | The Leading DIY Speaker Parts and Kit Supplier since 1972
Speaker Repair, Speaker Kits, Loudspeaker Repair, Kits and Drive Units, Subwoofer Amplifier Kit
The -3dBs crossing is giving the bump by summation. Bad implementation, drivers and crossover (to many problems to solve/sell). Probably the best Seas got @2KHz...
Tony already mentioned in the previous post.
7" SEAS CA18RNX (H1215) - https://www.madisoundspeakerstore.c...ige-ca18rnx-h1215-7-coated-paper-cone-woofer/
7" SEAS ER18RNX (H1456) - https://www.madisoundspeakerstore.c...stige-er18rnx-h1456-7-reed-paper-cone-woofer/
If you can or don't mind using a FAST, move crossover to 400Hz. I would use the SEAS Prestige ER18RNX (H1456) 7" instead of H1215-08 CA18RNX, look also at the voice coil inductance it's almost double. Build up new speakers with a small fullrange driver and shelve the tweeter for a future build, or use it then for two different projects. You will probably end with a 3-way with the new midrange, but it will make you think and DIY!
Falcon Acoustics | The Leading DIY Speaker Parts and Kit Supplier since 1972
Speaker Repair, Speaker Kits, Loudspeaker Repair, Kits and Drive Units, Subwoofer Amplifier Kit
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Many thanks inductor for this advice.
I've done another critical listening this morning and although the midrange is better than before, the problem is not fully solved. I've got a couple of long term plans that can reuse most of the components of the Mimir anyway.
I'm thinking of this design: Jenzen CA has anyone experience with this design, is it a choice for someone with reasonable wood-working skills? This would now be my third speaker build, (although I've done quite a few turntable plinths too).
My usage is about 50/50 music / home cinema. Music tends to be either vinyl from a modified Rega unit sporting a Benz Micro Ace or FLAC/CD from Cambridge audio 752BD stereo out.
I'm thinking of making the units semi-active with a single NC-400 unit in each base.
I was thinking of pairing this with CENTER-641
Does this sound like a reasonable plan?
I've done another critical listening this morning and although the midrange is better than before, the problem is not fully solved. I've got a couple of long term plans that can reuse most of the components of the Mimir anyway.
I'm thinking of this design: Jenzen CA has anyone experience with this design, is it a choice for someone with reasonable wood-working skills? This would now be my third speaker build, (although I've done quite a few turntable plinths too).
My usage is about 50/50 music / home cinema. Music tends to be either vinyl from a modified Rega unit sporting a Benz Micro Ace or FLAC/CD from Cambridge audio 752BD stereo out.
I'm thinking of making the units semi-active with a single NC-400 unit in each base.
I was thinking of pairing this with CENTER-641
Does this sound like a reasonable plan?
I took a 1.75" diameter cone tweeter and got 120 degree horizontal dispersion in the 10-20KHz octave by using a small cardboard K-coupler
I'd just like to put the concluding message on this thread.. Many thanks to all who helped out. After months of deliberation I went ahead and built the Jenzen ER from Troels Gravesen's web site. They've took the sound of my system up to a different level, so easy to listen to and so much detail. Components from the Mimir will not go to waste, they will be split into two; with the bass units going to a new centre, and the tweeters going to new surrounds.
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