RM 7300 Mods

dmongrain

So I've been reading around for the past few months about either building my own speakers, and have found a lot of great info out there. I have at home now a RM7302 and pair of 7300's, as well as the smaller satellites. I ended up getting a little adventurous and took one of the speakers apart.

I realized that the top and bottom pieces were nothing more than thin plastic moulding, I was guessing that there had to be a way to make this speaker sound better. So I did a little research about modding speakers and found out about ductseal around the basket, thought that would be a good place to start. I went out and got a 5lb block and started adding it to the basket as well as the top and bottom plastic pieces. I also added some to the the plastic faceplate that the tweeter is attached to. I also added a little more stuffing from another speaker that had been sacrificed to my endeavors behind the tweeter in an open cavity.

I put the speakers back together (I modded only one of the 7300 speakers, running 4.1 and pretty happy with it right now!) and plugged them in. I have them bi-amped through my Pioneer VSX-917 (5.1 biamped instead of 7.1, uses the two extra terminals for the rear surrounds). I definitely have to say that there is a marked variance between a modded and unmodded speaker. The entire mid-range seems much less coloured. There is another level of detail added to the sound coming out of the speaker as well. It seems like the volume was much louder coming from the modded speaker, but the SPL's were equal.

I ended up proceeding to mod the second 7300.

I was pleased with most of the changes, but the sound seems to be much less dynamic now. Although the detail and clarity is there, it seems also that the sound is much 'thinner' then before.

I have now decided to order some upgrades to the crossover and internal wiring to see how the changes affect the sound of the speaker.

My question to those of you with experience with this sort of thing , is why does the speaker sound 'thinner'. My theory is that I added too much stuffing, or perhaps the plastic top and bottom were acting as a radiator for those frequencies and that was accounted for in the design of the speaker.

Attached are some pictures with some more to follow.

dmongrain

more pic's

dmongrain

Putty added to parts...

dmongrain

The black foam part in the last picture has the underside aluminum cutout from it, so I'm guessing that it was designed to filter out the higher frequencies and allow the lower frequencies to pass through.

dmongrain

Now my question is, what can I do to allow for the 'fullness' to come back a little more to the speakers. Another question that I have is what further mods can I make? I think that I will replace both the capacitors and resistors with metalized polyprop and metal oxide respectively.

I look forward to your comments....

dmongrain

So I guess nobody has any ideas.....

jay2862

I don't have any ideas... but I'm interested in the outcome of your mods as I have a pair of RM-30's.

Face

Adding too much stuffing will lower low frequency response.

Try not to block the port. Also, try to place the stuffing between the woofer and the rear wall.

Replacing the film cap with one of better quality will make an audible difference. I also wouldn't bother upgrading the internal wiring.

dmongrain

Thanks for the reply, I have the caps and new resistors as well now, I will be putting them in today (hopefully). So you don't think that replacing the wiring will make a difference? Is that from experience or theory? The reason that I'm asking is that appears to be a fairly common exercise in modding speakers...

dorokusai

Replace the caps and leave it at that. Don't over-engineer it to death.

jcaut

Agree with the above: There's only so much you can do to improve that basic design and you've about covered it.

Take the extra polyfill out and see if your "fullness" comes back.

The stuffing does a couple of things: It helps to absorb or dissipate internal reflections (which is a good thing for all speakers) and it lowers the "Q" of the enclosure (which may or may not be a good thing, depending on the design). My guess is that you don't need the extra stuffing and that having it in there is damping a peak in the upper bass frequencies which you're hearing as a loss of "fullness".

You also need to be mindful of reducing internal cabinet volume when you're adding the ductseal material, so don't get carried away.

jay2862

How did replacing the caps turn out?

dmongrain

Sorry, been a little busy with stuff.....I'll get a detailed posting tomorrow.....

dmongrain

Well here we go......

This first set of pics is the original crossover, the cross over beside the replacement parts and finally the original parts removed from the board side by side with the replacement part.

dmongrain

This is the completed board. Well, completed until I put it all together again and then tried to put the speaker in .........realized that the bottom of the speaker touched the top of the cap............(insert all curse words that you can think of here...........)

The next pic shows the caps soldered to the bottom of the board, then the clean top of the board. The final pic is installed underneath some insulation.

Sound impression:

I did something that I probably shouldn't have and removed some of the excess insulation that I added before, kind of removes the ability to defiantly hear the difference that the crossover parts made. With that said, I don't think that the insulation makes a difference to the sound, potentially it should only change colouration.

The dynamic range of the speakers must have increased, cause man, they sound a lot better!! The speakers sound MUCH more open, even my wife noticed:)

Where I also noticed a lot of difference is in the snare. It sounds a lot faster, not sure if that makes sense or not. The level of detail in the voice also has increased.

What I notice is that there is still a lot of colouration in the lower range of a mans voice. I have a suspicion that the black foam pieces (mentioned them earlier) are letting sound through and that this is the cause of colouration.

dmongrain

Overall after modifying these speakers, I am not only greatly impressed with the changes that happen, but the level of change that occurs. I found myself asking why, for a pair of list price near $1000 why they could not use these pieces of quality crossover components at the factory?? If it only cost me $50cdn for the parts for three speakers, by the time you factor the price that polk would pay (cost, not retail, and in high qty...) and the price that they already pay for the parts that they use, would you not think that it would be worth the additional $10/pair????

I know that this is an industry wide practice, but why would they not spend that extra little amount and buy quality components?

I am really glad that I undertook this project, I learned a great deal about speaker construction, how making minor changes can really improve the quality of sound, learning that it is really easy to make changes that sound bad, as well as learning to do a trial fit before I solder and glue everything together!!

Would I do it again, absolutely. What I will do next is compare a stock speaker against a modified one, really looking forward to that, just need to find a few hours that I can play around with.


I also was recently spoiled with the gift of an older Rotel receiver, man does it sound good........talk about a wideopen soundstage. Listening to music yesterday, I thought that my wife was singing background vocals behind/beside me, I thought to myself "when did she learn to sing on key?" for a few seconds until I realized that it was just the background singer in the song.

jay2862

Good to hear that the mods you made turned out so well. I think I'll have to break my RM-30's open and replace the caps to begin with, then possibly try some of the other changes you made.

What brand of caps did you use?

dmongrain

Solen fast caps and metal oxide resistors. I don't remember the exact values, but if you're interested I'm sure that I could dig that information out for you.:D